August 31, 2010

photography questions & answers

Continuing with the monthly theme where I look at search engine queries,
and answer a selection of 10 questions more directly…

01)  why two flashes with rear curtain sync?

TTL flash exposure is calculated with a pre-flash signal that the flashgun emits before the main burst of light.  The main burst of light is what gives you (hopefully) correct exposure.  But the camera needs some way of determining what that correct exposure should be. In order to do that, the camera measures the amount of light returned from that pre-flash. Looking at this diagram of the sequence of events when your shutter opens and your flash fires, you will see the pre-flash there:

Now, if you set your camera to first curtain sync, then the pre-flash and main burst are so close together, that you can’t distinguish these as two discrete bursts of light.  It looks like one blitz.  Now, if you go to rear-curtain sync, and set a slower shutter speed … then there is a discrete time interval between when the pre-flash is emitted, and the main burst is emitted.  You will see this pre-flash then as distinctly separate pulse of light.

You can test this for yourself by setting your camera to any aperture (but let’s say f4), and any ISO (but let’s go to 800 ISO just for this exercise) .. and set a 1 second shutter speed.

Set your camera to first curtain sync, and fire your shutter.  You will see one burst of light. But when you now set your camera to rear curtain sync, you will see two separate blasts of light.

02)  benefits of 1/500 flash sync speed

A higher flash sync speed is a real boost when working in bright ambient light.  The higher shutter speed implies a wider aperture, and hence more range on your flash.

An alternate way to look at it, is that in bright light, you have a better chance of over-powering the sun with a higher flash sync speed.  The higher flash sync speed cuts more of the ambient light for the same aperture.

03)  how can I take photos at a slow shutter speed and not over-expose?

The problem experienced here is that the photographer asking this question, most likely did not keep an eye on his camera’s built-in meter.  Whatever shutter speed you choose, the combination of aperture / ISO / shutter speed needs to be such that you’re not over-exposing the ambient light.

04)  stopping zoom lens from changing aperture

If you’re using a variable aperture zoom, and you find the change in aperture annoying, then don’t set your flash to the maximum aperture for the widest zoom setting.  In other words, if you are using an f3.5 – f5.6 zoom, then use f5.6 as your maximum aperture.  Or use a smaller aperture.  Now if you zoom, your aperture won’t change on your.  This is of course assuming a modern camera.  On older cameras with a mechanical link between the lens and the camera, the aperture would change regardless.

05)  will my exposure settings change if I move my position?

It depends on how you are moving in relation to the light.  If you are moving towards or away from your subject, then your settings will remain the same.  If you are moving around your subject, then your exposure settings will need to change.  (This is of course assuming a single directional light source.)

06)  difference between E-TTL / TTL flash and manual flash

The essential difference of course is that with E-TTL / TTL flash, the camera is calculating your flash exposure.  With manual flash, YOU are the one calculating the flash exposure. This of course implies a whole bunch of other things, and this is where flash photography becomes confusing interesting.

07)  Canon service and repair

For any Canon repairs (in the USA), Toshio is the man!

Contact him at:  (732) 238-8806
Toshio; TF Camera Repair; 27 Brunswick Woods Dr; East Brunswick, NJ

08)  Chinese UV filters any good?

A cheap filter is never a good idea. While I seem to be the lone proponent of the idea that using a filter is sometimes a good thing, I would agree that using a cheap filter is always a bad idea.  Stick with the known name brands.  And if you’re looking at a filter that seems horribly over-priced, then you’re probably looking at the kind of filter you should be using instead.

09)  tutorial for pop-up flash photography

Here’s my complete tutorial:  I have good news for you – you’re going shopping!

the final one for today:

wedding photography with pop-up flash?

Oh dear. No. Just a no.  It’s not negotiable.  If all you have is a pop-up flash, then wedding photography isn’t in your immediate future.  If you decide it is, I believe that Judge Judy will also be in your immediate future.

Just like this person who is considering something very dangerous:

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{ 10 comments… read them below or add one }

1 Clive Bolton September 1, 2010 at 4:23 am

In your answer to “why two flashes with rear curtain sync?”, the second half of the diagram should show 2nd-curtain sequence, not HSS sequence. Regards.


2 Neil vN September 1, 2010 at 4:32 am

Clive .. I just re-used a prior diagram about HSS .. just to show the position of the pre-flash.
I have now updated the diagram to avoid confusion, and show the timing of the preflash in relation to the first curtain and rear (2nd) curtain. Thanks.

Neil vN


3 Paul Keith Dickinson September 1, 2010 at 6:10 am

Dear Neil
Just watched your lectures on the B&H website,just FANTASTIC.You make it so simple.Can’t wait for your tour of the UK..Paul


4 Stephen September 1, 2010 at 12:41 pm

Some questions/comments about these searches:

Is the person asking about the rear flash sync for two flashes asking why it’s good to use rear sync flash for two flashes? Or why it’s bad? I thought rear flash sync is bad in one particular instance you mentioned: If the pre-flash is far enough away from the regular flash, the subject may blink on the pre-flash part, which risks you getting a picture with the subject eye’s closed or partially closed.

Most Nikons have 1/250 as maximum flash sync speed. I haven’t seen a 1/500 maximum flash sync speed since the Nikon D70 and D40.

Are there any local Nikon service centers, or do you send them to Nikon’s facility in NY?


5 Neil vN September 1, 2010 at 1:40 pm

1. Stephen, I just copied the search term as it appeared on my website analytics page.

2. Don’t nit-pick the numerical value. It’s about understanding what happens at higher flash sync speeds.

3. I just use Nikon USA repair centers when I do need something repaired. Their phone answering system is a pain to deal with though. Insanely long call waiting times.

Neil vN


6 Val September 1, 2010 at 7:31 pm

What has 1/500 flash sync speed nowadays? It’s impossible w/o electronic shutters?


7 Stephen Y. September 2, 2010 at 11:35 am

About the UV filters…
I’ve been using a Hoya Super HMC 77mm UV filter on my 70-200 for quite a while. I think I paid roughly $50 for it. Well, last week I ordered a Nikon UV filter for my new 24-70 and decided to compare the 2 UV filters. I placed them both on a white sheet of paper and looked at them under a light. To my surprise the Hoya filter actually had a pretty strong yellowish tint! And it’s isn’t even a cheap Chinese filter. Long story short, be careful what you put in front of your nice glass.


8 Stephen September 2, 2010 at 3:10 pm

Stephen Y.,
Are you talking about this Nikon filter?

The product description says it is a clear filter, so it probably doesn’t reduce UV rays all that much. I have a Hoya 77mm UV(0) filter, and the product description says it reduces blue cast, so I’m wondering if by virtue of reducing one color, it shifts towards more yellow.


9 Neil vN September 4, 2010 at 2:05 am

Stephen .. the different makes and brands of lenses and filters will all give a slightly different color representation. So that comes into the mix as well.

Neil vN


10 Grant Stringer September 18, 2010 at 4:32 pm

Thank you for this informative article – very helpful.


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