manual flash vs. TTL flash

Manual flash vs TTL flash

For correct flash exposure, 4 things need to be controlled and balanced:
– aperture
– distance (from the flash to subject)
– power (the flash’s actual blitz of light, taking into consideration any diffusion)

Two things relate to camera settings, and two things relate to the flash itself.
To really understand flash photography, it is essential to memorize those 4 things.

If you need an acronym to remember things more easily: PAID
Power, Aperture, ISO, Distance.

There are distinct ways in which flash exposure is controlled though – Manual flash or  TTL flash. (For the purposes of the explanation here, Auto and TTL flash can be grouped together wrt D-SLRs.)

With manual flash, you have to adjust any of those settings to balance them out for correct flash exposure. You can use a light-meter, or even use the histogram to get correct flash exposure. With TTL flash, the camera and flash control the flash output (i.e., the power) as you adjust any of the other settings. That’s it in a nutshell – the differences between Manual flash, and Auto / TTL flash.

But let’s look at this more closely …

Manual flash

Firstly, flash could simply be a constant amount of light that is emitted from the flashgun.  In the case of manual flash, there is NO control by the flashgun or camera, over the intensity or duration of the pulse of light from the flash unit.

This is manual flash.  Photographers can control the output of their flashguns by adjusting the settings in fractions of the maximum possible output, eg, ¼ power, 1/16th power.   It should be obvious that the absolute value of ¼ power will vary from flashgun to flash gun, as each model and make of flashgun has a different maximum power.  Manual flash exposure is most easily measured by a handheld flashmeter.

To re-iterate: with manual flash, we have four controls for the flash exposure:
– the actual output level from the flashgun, (ie the ratio of full power),
– distance from our light source to the subject,
– aperture,
– ISO.

Any of these four things can be used to control the amount of light falling on your subject.


TTL flash

The second way to control flash exposure, is as an automatically controlled burst of light. This flash output can either be controlled by the flashgun itself (usually called Auto mode), or by the camera in conjunction with the camera’s metering system (usually called TTL flash).  When the flash is controlled by the camera, as then measured as the amount of light coming through the camera’s lens, it is called Through-The-Lens flash metering, (hence, TTL flash.)

For most purposes in understanding the basics of flash exposure with D-SLRs, there is little difference between Auto flash and TTL flash.  So, as mentioned earlier, for simplicity’s sake here, we could group Auto flash and TTL flash together.  (There are differences with pre-digital cameras and older flashguns, in how Auto flashguns interface with the cameras, and then the explanation is slightly more complex.)

Anyway, with  TTL flash, the flash output is varied and controlled by the camera’s metering system. This means that for a certain range, our chosen aperture or ISO, or distance to our subject, does not influence our TTL flash exposure.

This is such a crucial point to understand about TTL flash, that I want to mention it again for emphasis.

With TTL flash, our chosen aperture or ISO (within a certain usable range), does not affect our exposure – and in a sense becomes transparent to our exposure metering. (Our camera and flash work together in calculating what it deems to be correct flash exposure, but increasing or decreasing the output from the flash.)  What does affect our exposure, is the reflectivity of our subject, and how large our subject appears within our frame.

In other words:  Aperture (and ISO) does NOT control flash exposure when we use TTL. This is because the camera will tell the flash to emit more (or to emit less) light, as the camera deems necessary for correct exposure.

This is something that is difficult to comprehend at first, but is easily verifiable with your D-SLR.  There, at home, you can photograph any subject in your immediate surroundings using a TTL capable flashgun. Remember to bounce your flash for best results indoors.

Using TTL flash, you can change your aperture from f4 to f5.6 to f8 … and your exposures should look the same.  Similarly if you changed your ISO, your TTL flash exposures should look the same.  The reason for this is that your camera and flashgun’s TTL flash metering system takes care of the basic flash exposure … and can do this within a certain range of chosen apertures and ISO settings.  Your flashgun will emit more or less light as required for correct exposure, dependent on your settings … but your exposures should appear similar.

So, looking back at the four things which affect manual flash, you’ll notice that none of these, not distance, nor aperture, nor ISO setting, seem to have an effect on our TTL flash exposure. (Within reasonable range of course.)

And it is in this, that we see the huge difference in using (and understanding) manual flash vs TTL flash metering.


TTL flash vs manual flash

The only way to control TTL flash metering, is with flash exposure compensation. While you could could control manual flash exposure with any of the four variables mentioned earlier on, with TTL flash you would have to change your flash exposure compensation.

In these differences, the individual strengths of using manual flash, or using TTL flash, can be seen.  And this will most likely affect which of the two kinds of flash lighting we end up using.

With manual flash, since the flash is a specific level, our subject’s reflectivity or our choice of composition (ie, how we frame our subject) has absolutely no impact on our metering.

This is a hugely important aspect of manual flash.  Once we have our lights set up at a specific distance, and determined our aperture and ISO … then the subject’s reflectivity (ie, how much lighter tones or darker tones there are), have NO effect on our flash exposure.

However, with TTL flash, the subject’s reflectivity / tonality, and our choice of composition, WILL affect our flash exposure.   And hence, we often need to control our flash exposure with the flash exposure compensation.

The concepts explained in this section are so essential to our further understanding in flash photography, that I would strongly suggest re-reading this section until it makes sense.  Also check other webpages or books on this topic.  It is also important to your own understanding of flash photography, to try and figure this out with your own camera and flashgun.

In  thoroughly grasping of the differences between manual flash and TTL flash, our approach to balancing flash with available light will become so much easier.


video tutorials to help you with your photography

If you like learning by seeing best, then these video tutorials will help you with understanding flash photography techniques and concepts. While not quite hands-on, this is as close as we can get to personal instruction. Check out these and other video tutorials and online photography workshops.


related articles

67 Comments, Add Your Own

  1. 1Dan says

    Thanks to your blog and comments, I actually decided to shoot with flash for a change, and what a difference it’s made for indoor photos! I finally got mine mailed to me just in time to try it out for family photos through all the gatherings over Christmas.

    I’m not so great a reading manuals and then keeping all of that book knowledge in my head to try and apply it later, so I took the usual route of just trying everything. So far I’ve used TTL flash, but other than adjusting +/- exposure settings on the Canon 580EX, I’ve been able to do little else. I’m hoping you’ll go over the mechanics of how flash and distance throw along with dragging the shutter and angling bounces to best like the subject come into play whether with manual or TTL settings.

    Even though I haven’t had a chance to try it out, perhaps you can go over just how to lift shadows in outdoor settings? Yes, I know you’re not a fan of saying X-settings work for X-situation, but understanding how the flash works to bounce or directly light the subject would be important to me here as well. I prefer full-manual on my camera, so why not with the flash as well?

    Thanks again for your excellent instructive dialogue. Its been a big help in approaching new subject matter, and the excellent examples round out the learning. Where’s your PayPal link? Your gratis work is totally worth a bit of monetray appreciation.


  2. 2 says

    Hi Neil

    Yet another excellent post. Could you also give me an indication of situations when one would choose manual flash over TTL and why?

    Thanks in advance

  3. 3 says

    Hugh …

    As a general rule, I would use manual flash when my subject is (fairly) static in relation to my light-source. This would be the case for either when my flash is on my camera, and I am static … or when I am using off-camera flash which is mounted on a light-stand or similar.

    Then the distance from the light-source to my subject remains the same, and manual flash is the easiest way to get consistent exposures.

    But when *I* am constantly moving around (with my flash on my camera) or my subject is moving around a lot .. then TTL flash is the easiest to use. This is because the camera’s flash metering technology brings us quite close to the correct exposure. (We might have to adjust it though with flash exposure compensation.)

    I hope this helps make the decision process a little clearer.


  4. 4 says

    This is brilliant. I did not appreciate the differences between manual and TTL flash, and definitely did not understand how TTL would compensate for the changes in ISO, Aperture and Distance. But now you’ve said it, it makes so much sense.

    Thanks again for another brilliant article that helps us lessor mortals to reach a higher level of understanding flash.



  5. 5Kafka says

    Hi, Neil,

    Since you use mostly manual exposure metering mode and always adjust such settings once you step into a new environment, what you may need to change thereafter in the flashgun’s manual mode to get your expected results is still only one of the four following factors, isn’t it?

    – the actual output level from the flashgun,
    – aperture,
    – ISO,
    – distance from our light source to the subject, which can be more or less the same if you can keep the distance between you and the subject. This doesn’t matter much while the flash is used as a fill flash, and anyway you would need to adjust something if the flash is used as a main light source. Isn’t it?

    I’ve learned a lot from your blog and here I am not challenging you at all. I am just not understanding very well. On the one hand, you suggest using manual metering to achieve consistent exposure and better learning curve, while on the other hand, adjusting flash exposure compensation seems to bring back all the concerns about tonality, reflectivity and composition which we’ve just overcome with manual exposure metering.


  6. 6 says

    Hi there, thanks for quiet few things actually one was repairing my own hot shoe thanks to you!!! Bravo
    Quick question. I shoot premieres and my Canon580II Brand New, being used with a Canon 1ds is over exopsing all the time, at times by around 3 stops!!! AAhhhhhhhhhhhhh
    It does not happen with my other flash Canon580 not the II.
    Any know settings to be changed or maybe faults with the new 580II ????
    Few people said to me that it is not compatable with the 1ds!!!!!!!!!!!!!!!

  7. 8severoon says

    I’ve searched long and hard for an explanation on why M + TTL is better than Av + FEC + TTL flash. I’ve discussed it with many talented photographers whose results I wish to have for myself, and none of them has been able to crystallize an explanation as succinctly as you do here. It seems sometimes that the world is full of experts that cannot externalize the knowledge they have simply and clearly.

    Since reading your posts on using flash properly, I’ve switched to M + TTL and started to achieve much better results. The improvement in my work due to your site is as significant as when I moved from direct undiffuse flash (way back when I started photography) to bouncing and/or diffusing. Or, what I thought was bounce–I didn’t realize that the bit of direct still hitting the subject was oftentimes keeping me from achieving the result I was after. Now, when I approach a situation, I imagine where I’d put a softbox and how big and bright it would be, and aim my half-snooted flash right there.

    I was at a complete loss to move forward before, now I can move intelligently in a positive direction. Thanks!

    P.S. Have you considered writing a book? I searched the web and the bookstore both for the info on this page and came up empty.

  8. 9 says

    Severoon …

    I actually do have a book contract, and am in the process of writing one.
    Hopefully it will be out by the end of the year.
    I will most definitely announce it here on this blog when it does come out.



  9. 11Yap Tsok Sam says

    First of all thanks for sharing. I’ve just ventured into flash photography after reading your blogs. very informative and definitely a must read site for any photographers who wish to learn flash photography.
    However, i’ve tried the experiment you suggest above that with TTL flash, our chosen aperture and ISO does not affect our exposures. I shot using manual exposures and change the aperture from 4, 5.6 and 6, but every shot i got is slightly different in exposure. Doesn’t that means my exposures got affected evrytime i change the aperture? Do i need to use direct flash or bounce for this experiment? Also, when i meter an object using in-camera meter(manual exposure), do i need to keep the exposure indicator in the view finder at the center to get proper exposure? hope you can help me to clarify this, please….. thanks.

  10. 12 says

    Hi there …

    The difference in exposure that you’re seeing now is because your ambient light exposure is now changing as you vary your aperture.

    This isn’t a negative … it’s just an indication that you now have a LOT more flexibility in mixing flash with ambient light, and doing so on the fly.

    Regarding your other questions … Yes and no. It all depends. Centering the needle of your exposure meter in your viewfinder does not necessarily mean you have correct exposure. It all depends on the tonality of your scene. Zeroing the needle will give you the same results though as any of the automatic metering modes.

    Read these series of articles to see if this all makes more sense:

    Neil vN

  11. 13Chris C says

    Hi Neil.

    Ive always thought the same regarding TTL flash (iso and aperture not influencing the exposure but a few months ago i happened onto a problem which totally baffled me)

    I tried to do this. I set up the room to be totally dark meaning i shot very late at night, windows closed and no light whatsoever. I put a white pillow up with stripes for focus locking.

    i put my camera(30D) to shutter of 1/200 and Aperture of F4. I was around 6 feet away from the pillow. I shot at iso 100 and then shifted to iso 1600. The ISO 1600 was overexposed and i cannot explain why. This is shooting with the flash gun (580 EX version 1) direct with no diffusers.

    The funny thing is, if i bounce the flash, the exposure will be the same, if i pull down the diffuser, the exposure will be the same. If i remove the flash gun and use the onboard flash the exposure is very near each other.

    In this case, the ambient did not affect my expposure because i shot a iso 1600 frame to check if any ambient was contaminating my exposure and the frame came out all black.

    can you please shed some light on this, ive been trying to wrap my head around this for like 2 months now.

    I sent in the flash for checkup and canon did not find anything wrong with it.

    Thanks Neil. Hoping you can finally give me peace of mind regarding the matter.

  12. 14 says


    Your problem is that you worked outside the range of what your flashgun is capable of. Not only do flashguns have a maximum range, but they also have a minimum range, within which the circuitry just can’t switch off in time to control your flash exposure.

    At 1600 ISO, and f4, your 580EX will give you a minimum of around 3 meters .. which is approx 10 ft. Since you were about 6 ft away, you were simply too close for the flash to control your exposure.

    So I have two pieces of good news for you.
    a. There is nothing wrong with your flashgun.
    b. You’re going to spend some more time with your 580EX manual. ;)

    Neil vN

  13. 15Chris C says

    simple yet profound hehehehe…..thanks so much Neil, i know youre used to the compliments by now but it really is true. Youve made us all better photographers. Thanks so much for helping us, your time is gold and you still help those in need. KUDOS to you!

  14. 16Chris C says

    oh and PS, FYI….i did read the manual like 3x now, my brain just chose to ignore the parts that actually explained the reason hehehehe…… ;)

  15. 17Mark says

    … so the angle of the flash head and the direction at which the light bounces to light the subject does not effect the exposure in TTL mode either – at least to the degree that the angle of the bounced light and the reflectivity of the subject does not bring light back towards the camera. From the different examples in your tutorial, you are using (+,-) EV settings to balance the light from different light sources coming from different directions. Is that correct? It took me a few reads of this post to figure out that you are not compensating for the fact that the intensity of the light is being reduced when you spread it out over a larger area and are making the light travel a farther distance. This has got to be the single most import post to read in order to understand how your flash functions mechanically. Thanks so much for all the good advice. I forward you site on to friends all the time. Let me know if I’m figuring this correctly! Thanks again.

  16. 18Sam says

    Hi Neil,

    Great blog, I’ve been following you avidly. I have a query:

    I understand TTL flash calculates its output level based on subject distance, aperture and ISO.

    In a situation recently I was experimenting with my new flash, taking a self portrait and was at f/1.8 and ISO 1600 (to get a fast enough handheld shutter speed) and was using TTL flash. However, the flash was overexposing me. Is this because the flash couldn’t get a low enough level to deal with the fact that I was letting in so much light (high aperture and high ISO)? And if so, how is it best to counteract this?



  17. 19 says

    Sam, we need a bit more detail here.

    Did you bounce your flash behind you? Or did you have your flash-head in the forward bounce position?

    The reason why I ask, is that at f1.8 and 1600 ISO, you are far too close for your flashgun to be able to switch off in time and not over-expose.

    Also, without flash, was your exposure good or even under? Because (obviously), if your ambient light is already over-exposing your subject, then adding more light from your flash isn’t going to help the situation.

    Neil vN

  18. 20Sam says

    Thanks for your response, Neil.

    I was using a TTL cable and held the flash out to the side, pointing straight at me. I think the problem may have been that I was letting too much ambient light in (I was in manual mode) In further photos when I dropped the aperture to f/4.0 and the ISO to 800 and was still experiencing over-exposures. However, the shutter speed was on 1 second.

    When I dropped the ISO down to 200 and used a 1/2 second shutter speed I was getting much better exposures.

    So would I be right in saying that to get a decent flash exposure at high ISO and aperture, I would have to drop the FEC down considerably?


  19. 21 says

    Sam … Flash Exposure Compensation doesn’t have anything to do specifically with flash exposure with high ISO and wide apertures.

    FEC is a way to control your TTL flash exposure.

    However, if you are outside of what your speedlight is capable of doing, you will get over-exposure … such as if you are too close to your subject while shooting at too wide an aperture and too high an ISO. And FEC has nothing to do with that. You’re simply trying to work outside the range of what the equipment is capable of.

    Then, 1 second exposures at 800 ISO … that would mean a fair amount of available light for most situations you’d find indoors.

    Without seeing any photos from you, I do think your problem is two-fold … you’re working outside the range of what your flashgun is capable of, and your settings are such that you probably over-exposed your available light anyway.

    So you need to step back and re-think your choice of settings here.

    Neil vN

  20. 22Ray says

    Hello Neil”

    The TTl/ BL setting does a pretty good job on my Nikon D90 with an SB600. Since i am going to be doing my first wedding. I know i would need to be concentrating on my shots a lot and my creativeness and to make sure i am covering it all as best i can. The last thing i want to do is to miss shots because of mugging about too much with manual settings. I am just not that experienced as yet.
    I there for find it easier for me to stick to the TTL/B L setting and try to keep most of the ambient light to do most of the work. For example; I would up the ISO, drop down to f2.8 most the time whiles inside and keep the shutter speed to flash minimum of 60’th sec or change D. O field as needed. Use higher shutter speed after spot meetering brighter background so as not to blow them out and the Flash does the rest on the subject e.t.c
    I don’t want to do too much creative stuff and keep things more simple for me and make fore most sure that i get the shots i need. The TTL/BL seems to do a pretty good job of things and looks to be what i would have it set on.
    I read you also use the TTL automatic function. Have you got thoughts on the BL settings?
    Cheers” Ray

  21. 23Bob Essner says


    I’ve read through almost all of your articles and blogs and am very impressed with the discussion threads and am so upset with myself at my age (61) for not taking the time in my early days when I dabbled in wedding photography. I used direct flash and bounce off the ceiling flash (if the ceiling was low enough) but never even considered bouncing off the walls (that’s what the groomsmen do at receptions!).

    Anyway, in my old brain the lightbulb has lit up and now I’m anxious to do some more flash photography. I have an Olympus E-30 with 3 different Zuiko zoom lenses and I bought the FL-36R flash. I’m guessing I should have bought the FL-50R flash now and probably will (I can still use the FL-36R as part of the lighting setup if necessary since they are both wireless).

    So my question is this – would you recommend the Olympus FL-50R flash as the highest powered compatible flash from Olympus for my E-30 – OR – the Metz 58 AF-1. I don’t intend to go in to business but just take pictures as a hobby for friends and relatives – but I do want to provide the best photography my equipment is a capable of. I completely get your manual camera settings and TTL flash setting – can’t wait to see how much better my pictures are when I master this technique.

  22. 25olympus_fotograph says

    hey bob,
    take the FL-50R, the best machine for olympus.
    the metz has a small light wich gives you direct foward light.
    if the metz is cheaper and you don´t often use the “R”-function, than take the metz.
    but with the F_-50R you stay “in family”.
    peter [E-1, E-500 and a lot of optics*g*]
    if german is your language than check
    it is a good olympus forum

  23. 26Bob Essner says

    Neil & Olympus_Fotograph,

    Thanks for the feedback. My internet searches show that both the Metz and Olympus flash are lowest priced right at $400 – so basically cost is equivalent. The Metz flash is somewhat more powerful and has USB firmware update capability which intrigues me. I trust the Olympus quality and have used Olympus starting back in the 70’s with OM-1 and OM-2 – I have a whole array of those 35mm lenses. The new Olympus Pen interests me since there is an adapter that would allow me to use all of my OM lenses on a 12.3 MP body. But back to the flash – do you know if the FL-50R is the most powerful Olympus flash available for the E series (for my E-30) ? I’m still debating.

  24. 27olympus_fotograph says

    yes, FL-50R and FL-50 is the most powerfull lightmachine they have.
    no development for a more powerfull flash yet.
    FL-50R, you can swivel the head more to the right side as the old FL-50 ;-)

  25. 28Bob Essner says


    Thanks for your replies – I think I’ve settled on the Olympus FL-50R instead of the Metz.


  26. 29Marco Ricard says

    Hi Neil;

    I start by saying that TTL is now my BFFF (best flexible field friend )…

    I few months ago, I used manual flash in some weddings to take “group pictures” inside dark churches with very high ceilings. I used a bouncing flash (no bouncer attached): Manual ½ and just closing the lens aperture to f8 or even f10 , 1/100, ISO 800..The result was just amazing catching a lot of details of the 1st plan and environment too…

    The lens was Canon 24-70mm f2.8 USM with a Canon 1d Mk3 / canon 580exII…

    This technique of maintain the bounced manual flash at ½ or even 1/1 and just playing with the aperture, is very good…it worked for me…

    Marco Ricard

  27. 30Daniel says

    The church could not have been that dark with f10 1/100 ISO 800 and just using bounced flash in a large church. Either that or you were very close to a wall of some sort to bounce off, or you were using a very powerful strobe?

  28. 31Marco Ricard says

    Hi Daniel;

    I was just using a canon 580ex II…Flash in Manual mode ½ and sometimes 1/1…
    Sometimes using the walls and sometimes the ceiling… ISO between 800-1250 max…
    Aperture often at f8 and I was just surprised to see that I was catching good pictures.
    Maybe god was helping me :-)

  29. 32 says

    Neil… always amazing information you provide. Thank you.

    Question… I grasp bounced fill-in flash and times when there is enough light to use the camera’s meter to expose properly for the scene. However, what about a VERY dark reception hall or inside a night-club? Even at an ISO of 1000, and a wide open aperture, and a shutter speed around 1/100, the meter will be blinking in the -2.

    So, how do you know if the scene will be properly exposed prior to firing a bounced flash on the subject, if the meter blinks -2? Does TTL simply calculate the correct amount of Flash to use based on its preflash?

    I’m confused as to where to start with my settings when I cannot get a good in-camera metering. Can I assume, if ISO and aperture are transparent, it doesn’t matter (within logical reason) what I set my camera to, the TTL will use the proper exposure based on the scene in any situation, as long as the subject is within the TTL’s range?

    Is this the right assumption?

  30. 33 says

    Hi there Amanda ..

    How do you know if hte scene will be properly exposed with TTL flash? You don’t really. You can anticipate it from experience and from pre-judging the scene to figure out if it will need FEC and how much .. but there is no way to pre-determine exposure like you would for manual flash or ambient light.

    So what you’re experiencing there .. where your camera tells you you are very under-exposed, yet you get proper TTL flash exposure, that’s simply how it works.

    In fact, that’s the beauty of TTL flash. Within certain constraints, it will give you correct exposure, even if there isn’t enough available light.

    Your assumption there is pretty much spot on. That’s how it works.

    Neil vN

  31. 34Emily says

    hi, im not very experianced but i really want to know..
    which is better… TTL or an auto flashgun?
    i have a canon 1000d and need a flash.. i just dont no which type is best!

    please help!


  32. 35 says

    Emily, I’d say that generally a TTL flashgun is more flexible an option that an auto-only flashgun. The reason for this is that TTL flashguns are usually better integrated with your camera and will automatically follow your settings.

    And since you asked which is the best speedlight.

    Neil vN

  33. 36natalie says


    Just wondering if I use TTL flash but want to keep my camera in manual mode what settings do I use and Why. Cheers

  34. 37 says


    Which settings you use depends on how you meter for the ambient.

    If we can distill all the infinitely possible scenarios we can encounter into just three broad types:

    1. available light is sufficient, but we just need a touch of fill-flash.
    Then we determine our camera settings my exposure metering, which can be accomplished in a number of ways. And then I would add a touch of flash – usually TTL, and dialed down to around -2ev or -3ev.

    2. available light is sufficient, but very uneven.
    Now we need to use flash to clean up the image a bit. For example, dark eye sockets or deep shadows or where there is too much contrast.
    Once again we use those exposure metering techniques to get to a good combination of settings, but we use more flash. We can use either manual or TTL flash, depending on the situation. But with TTL flash, I would most likely be around 0ev or -1ev. In other words, the flash and available light are about equal.

    3. available light is of poor quality or just too low.
    Now we use flash as a dominant light source .. and this can be either manual or TTL. If it is TTL flash, then we have a wider range of possible settings we can use, since the TTL flash will usually be able to take care of the exposure by giving out enough light. With manual flash, we would choose our settings, and then use either the histogram or flashmeter to meter for our flash, and adjust either our settings or the flash power accordingly.

    So back to your question.
    What are my settings? Depends on the situation I find myself in, but usually the available light will dictate my settings .. or at least set a base where I start from.

    Why do I choose those settings? A would choose a combination of settings such that I have:
    a. enough depth-of-field
    b. a good enough ISO that noise doesn’t become an issue. (and here we might have more headroom than we think)
    c. a fast enough shutter speed to eliminate camera shake, and if you so choose, eliminate subject movement.

    But these last three sub-headings are a wide enough topic for a big fat book … or enough material for an entire website. Delve deeper. There is a lot more here.

  35. 38 says

    Hi Neil,

    This is one awesome information portal and lifts all of us from where we are. Thanks a lot for the time you spend.

    One question repeats in my head all this reads. When I use flash on ETTL mode as I understand it calculates the flash power it requires to light up the subject if we hit the flash direct on them right?

    If true, what happens if we bounce the same flash? will the image under expose because the light get waste? DO we need FEC to handle this or we need to switch to manual when bouncing?

    Please help me clear this or guide me to a place where you wrote about it. I’m not very experienced with ETTL flashes and just purchased my first. Sorry if this is a very basic question.

    Thanks again for all these valuable information.


  36. 39 says

    Chameera … in theory you should not have to adjust your FEC, since the camera and flash calculate the amount of flash needed depending on the return strength of the preflash.

    However, in practice you usually have to bump it up a notch or two. You’ll have to see for your camera and flash.

    The preflash is emitted before the shutter opens and the main burst fires:

    Neil vN

  37. 40Joe says

    I have been reading alot of your stuff looking to find what may of gone wrong on a recent out door shoot. I was using a D300 in aperture priority mode and SB600 flash and several key shots were totally blown out. I did have my aperture at 2.8 because of the bokeh I was wanting to get but I thought the flash should compensate for this. Any ideas what could of been happening? I experienced the same thing later that night in a darkened area and the flash was too low depending on my aperture.
    Love your stuff..keep up the good work and Im ordering your book from Amazon.

  38. 42Joe says

    Yeppers…that makes a lot of sense and sounds exactly like what happened. Hope to see you sometime in NY or maybe in Vegas next year.
    Thanks again

  39. 43simon says

    Thanks for all the Neil.

    Im confused about the above post though as when i use the inbuilt flash on TTL (Nikon D40) I DO get exposue changes when changing apperture and ISO. My tests have gone through the range from 1/15-1/500 and ive done the same set up/distance etc.

  40. 44 says

    Simon .. are you sure it is the TTL exposure that is varying .. .and that you’re not seeing the ambient light changing with your settings changing? Also, you might be out of the TTL flash’s range.

    Neil vN

  41. 45simon says

    neil – thanks for reply. My tests all have my subject within a few metres of the camera/flash and i’m not moving the camera so I am not sure how the ambient light would be changing. Literally, if im on 1/125 (for example) my images are darker on f32 that f11, similar if i bring my iso down from 400 to 100. Still confused?

  42. 46 says

    f32 with your pop-up flash? It’s a near-certainty then that you’re trying to use the flash outside of it’s working range.

    Try it within an aperture / ISPO range that you’d normally use.

    See if you change from f4 to f5.6 to f8 ….. and then satisfy your curiosity.

    (I don’t think I have ever used f32 btw)

    Neil vN

  43. 47 says

    Got a question for you I cant seem to find an answer to anywhere. When you use exposure compensation what is it actually adjusting? The ISO, Aperture, Shutter Speed? Or is it just a change to the sensors sensitivity?
    I don’t see these changes on screen readings so if it changes any of the trinity it has to be minor.

    Thanks and love all your stuff.

  44. 48 says

    Joe .. that depends entirely on what exposure mode you’re in:
    – aperture priority / Av …. the shutter speed will be adjusted (since aperture is fixed)
    – shutter priority / Tv … aperture will be adjusted (since shutter speed is fixed)
    – program – both aperture and shutter speed.

    And if you have Auto ISO enabled, I am sure that the ISO will also change.

    If you are referring to TTL flash, then with Flash Exposure Compensation, the actual flash output will be controlled.

    Neil vN

  45. 49Eric says

    Neil, I think your post right above may have some unintentional mistakes.

    If we adjust EC in AV mode, it is the SHUTTER speed that will be adjusted accordingly, since Aperture is fixed here in AV mode.

    Similarly, Aperture will be adjusted in Tv mode if we dial the EC.

    Thanks for the information/instruction/clarification… you’ve shared with us!

    Beijing, China

  46. 51Maurice says

    Hi Neil, happy New Year 2011. Do have a D300 and SB-800. I am starting to use Flash Manual Mode. This is what I do : I do measure the distance from subject to my camera in feet; position myself to that distance; by pressing the select bottom in my SB-800, I do match that distance and my speedlight automatically select the power to match that distance, then, I do shoot. Is this right ?
    My camera setup : 1/250 ( to match flash sync speed ), choose to start ISO 200 and then I do match my Aperture. I do expose for the subject. My question is : if I do change my ISO, do I must change the power / distance of my flash ? I do know there is a formula in the manual, but never made sense to me, can you please explain me how to use it ? I am confuse because I do know there is GN for the SB-800 at ISO 100 ( 125 feet at 35 zoom head ) but how will I use in this case ? Can you give me an example please ?

  47. 52 says

    Hi there Maurice …

    To answer your questions:

    >> I am starting to use Flash Manual Mode. This is what I do : I do measure the distance from subject to my camera in feet; position myself to that distance; by pressing the select bottom in my SB-800, I do match that distance and my speedlight automatically select the power to match that distance, then, I do shoot. Is this right ?

    That’s essentially it.
    power (which you are adjusting) … distance … aperture and ISO
    Those are the 4 things you need to control to give you correct exposure for manual flash.

    While you could do it with the guide number (distance / aperture / ISO), and looking at the preview on your camera, it is easier and simpler to use a lightmeter for the flash.

    If you have correct exposure, and you want to change your ISO, you have to change one of the other three things (distance, power, aperture), or a combination of those 3 things, to offset the change in ISO.

    But really, manual flash is easier when you use a lightmeter.


    Neil vN

  48. 53Maurice says

    Thank you so much Neil for your answer. The reason I did ask you this, is because ( I’ve been investigating and studying a lot about using flash ) there is a table in the SB-800 manual regarding the GN ( you know about this of course ) and I found it very confusing. For example :
    Using f/4 at 18 feet at ISO 400 ( 4 x 18 = 72 / 2 – ISO factor – = 36 ), so 36 is my GN on this initial setup. Then if I look at that table for the matching number 36 from this equation, I am suppose to use 1/16 at 50 mm zoom head, so my ending setup will be : f/4 at 18 feet ISO 400 1/16 power at 50 mm zoom head ( focal lenght ). I shot this sample today and it was a bit underexposed. My speed was 1/200. My question is : how about if I want to shoot at 150 mm with my Nikon 70-200 ? In that table provided by Nikon, there is nothing more than 85 mm zoom head, so what will be my calculation ?

    I do not want to be just a photographer shooting with a flash, I want to become the best doing this as you are and I know it does require a lot of practicing but also a help from those who already know exactly what to do, so please help if you can that I would be very grateful as I’ve been so far with all your help on this thread and all others.

    Beside, I shot the same picture today but instead Manual Flash, I decided to switch to TTL-BL and bounce the flash and the results were much better, following your advises, but for some portraits, sometimes you need to shoot in Manual and I would like to really know how to calculate my setup to the perfection. I do not set myself for less and thank you for your help !!

  49. 54 says

    If you’re getting under-exposure via the GN calculation, then just open up by 1/3 or 2/3 of a stop. Or however much is necessary. Obviously then Nikon’s estimation of their GN is little boastful .. or perhaps you are trying this outside where there is no white walls to reflect some of the light and boost the GN. There could be a few factors influencing this.

    Ultimately though, if the theory doesn’t match the practical results … then be guided by the practical results. There are real world limitations that come into play why the theory doesn’t match the results. We just accept it, adjust for it … and try to get killer images. That’s the end objective. To be an artist and not a technician.

    You’re best option here still, is to rely on a lightmeter. That’s the final word on this. If it is calibrated to your camera. So there’s always that to play with and adapt to.

    Just remember, the end objective is for us to get killer images.

    Neil vN

  50. 55Maurice says

    Thanks Neil. I will buy the Sekonic L-350 flash meter to make it easier for me and you are right. Practice and shooting a lot will make the difference. Thank you so much.

  51. 56Donovan says

    Hi Neil, just started my new job as a press photographer and as you know things move pretty fast at times. From what I’ve read here you would use TTL,which I currently use but my work mates suggest I switch to Manual 1/8 – 1/16 as I’m usually a few feet away from my subject. Any advice would be great.
    P.S I do use -ev on my nikon sb900 flash sometimes (when using TTL) to prevent over exposing subject.

  52. 57 says

    Donovan, good luck on the new job. That’s pretty exciting!

    TTL vs manual flash in this instance … if the photographer is working with specific aperture setting, and with specific distance to the subject … then this fixed approach of using either 1/8 or 1/16 would work well.

    However, if you move closer or further away from your subject .. or decide to use different aperture (and ISO) settings .. then the manual flash exposure will vary MORE than the TTL flash exposure would. You would have to work within a narrow range of distance / aperture / ISO settings for such a fixed manual flash approach to work properly.

    Obviously, available light changes .. which immediately imply that shutter speed / aperture / ISO combinations change for different scenarios. Which, for me, would mean that such a limited way of using manual flash, doesn’t quite make sense.

    There are 2 more ways that using only 1/8 to 1/16 manual flash will fall down:

    – when you bounce flash, the size of the room will be a huge factor in light loss. TTL flash will automatically compensate for this.

    – the difference between fill-flash (with correct ambient exposure and FEC around -3EV) .. and flash as main soure of light (with ambient being under-exposed but flash taking up the slack) … the difference in flash exposure there is 3 stops or more.

    Finally, your colleagues would have to work within a fairly narrow set of scenarios for their approach to be consistently successful.

    Neil vN

  53. 58 says


    I shot a wedding this past weekend and was disappointed with the inconsistency in exposure while in TTL mode, mainly overexposure. i’m not sure what went wrong, although i’m reading a lot about not using auto ISO with TTL and am pondering if that made a difference.

    Also, i tried to apply some bounce techniques and found a big problem was underexposure. i was dealing with a tall black ceiling so tried bouncing mainly off walls (usually about a 20′ distance away). i couldnt get enough flash power. it was odd….and frustrating.

    i hope a little more practice will help.

  54. 59 says

    i may have figured out the second problem of light falloff. i didnt have the zoom set to max and had too much of the BFT past the flash head. which still leaves the first problem unresolved.

    i shot my D7000 mainly with an omnibounce since i didnt have time to really think about the bounce problems i was having. i shot at 1/80s, 4.5 (or so) and auto ISO, all in TTL mode. i know my ambient metering wasnt far off of -2 stops for without flash i was 1/20s, f4.5, ISO 2000 and still underexposed. my flash compensation was set to +.7 mainly to make up for poor ambient light.

    could the +EV have blown out my skin tones? i thought auto ISO would have fixed that. i never had any problem on my D200 when ISO was constant & FEV was 0. maybe i should go back to my old style and start over from there.


  55. 60 says

    Andrew, 20 ft isn’t such a huge distance to bounce flash, when used at an appropriate aperture and ISO combination. The one variable here that makes things murky, is that you used Auto ISO. This means your actual ISO that you ended up with, was probably too low.

    Neil vN

  56. 61 says

    thanks for the help…..and a sense of confirmation that auto ISO is a bad thing with TTL. stands to reason tho, now that i have time to think about it. i’ll definitely go back to constant and expose my background down a couple stops making the flash dominant.

    i’ll also kick up my EV and zoom out my flash head when using the BFT half rolled back to see how that works as a starting point. i’m sure i’ll have to adjust from there.

    am i on the right track in my thinking?


  57. 62 says

    I was a second shooter at a wedding this past Saturday.
    Was I right to set my flash at full power??
    I was bouncing the flash off the back wall of the church.
    The flash failed to go off several times, I guess it overheated. It’s a Yongnuo yn-560 II.
    Guess I need to invest in a nikon flash….. I was so disappointed.
    please help!!

  58. 64 says

    This is a brilliant and refreshing explanation of the differences between manual and TTL flash.
    I wish all photography schools presented this as logically. Congrats!

  59. 65Chaz says


    Thanks, I’m starting to put it all together. Your method of getting the proper flash exposure in Manual for the relevant white tones, using the histogram is amazing. Opening up about 1.3 stops in order to have the wedding dress white instead of gray makes sense. Question. What if you are shooting TTL, does the same method of opening up 1.3 stops apply?


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