May 6, 2009

With D-SLRs having ever higher resolving power, and lenses just getting better in terms of optical quality .. and digital photography giving us the possibility of looking at images at 100% resolution, we are becoming ever more aware of slight discrepancies in focusing and sharpness. Especially so with lenses that have very wide apertures.

Quite often a camera will be within spec, and a lens be within spec in terms of their individual tolerances, but combined, they might be outside of tolerance. Or perhaps a lens wasn’t quite within spec .. but for whatever reason, we might end up with a camera and lens combination which juuuuust isn’t quite as sharp as it could be.

For example, with the one lens I recently bought, the Nikon 200mm f2 VR, I frequently felt that I could touch up the focus manually a little better than the camera had focused.  And checking on the camera’s LCD screen, I could see that.  From the most recent shoot where I used this lens, (which I’ve shown in earlier postings), here is an image where the lens back-focused.  And it appeared to do this consistently.


[ click on the image to see a larger version ]

Now at normal web-size and even small print enlargements, you wouldn’t be able to discern that the image isn’t quite focused accurately on her nearest eye.  But as soon as you go to 100%, you can see the focusing error …


[ click on the image to see a larger version ]

… and this simply isn’t good enough.  I like sharp.  I really like images to be crisp. 
Any softness in the image should be a deliberate choice on my part.

Now there are a few ways to address this small focusing error.  You can either send your equipment in for calibration, but that means you are without your equipment for what is a small, yet seriously niggling problem.   Or, you can adjust the camera yourself if you are fortunate enough to own one of the more recent models of D-SLRs that boast a feature where you can micro-adjust the auto-focus.

The Canon 50D, 5D mk2, 1D mk3, 1Ds mk3; or Nikon  D300, D700, D3, D3x; and even the most recent Sony A900, and Pentax K20 have this feature. 

You can either create a make-shift device, or you can take a convenient shortcut like I did, and get the LensAlign Pro kit, which allows you to do the AF micro-adjustment on your camera with confidence.   They also have a smaller kit available that you can assemble yourself.

Some of the make-shift methods I’ve seen on the forums, rely on you to photograph a ruler on an incline, focusing on a certain spot.  The problem here is that if your camera’s focusing sensor isn’t exactly placed where it is marked in the viewfinder, you might think you have a camera that back-focuses, when in fact it doesn’t.  This will then send you off on a wild-goose chase trying to figure out where the problem actually lies.

The LensAlign system side-steps that problem by a simple yet ingenious way that you position your camera at the exact perpendicular angle to the target.  This is described in detail on the LensAlign site, as well as the thorough review on the Luminous Landscape site, so I won’t go into the particular method.  (There are video clips as well on how to set this up.)

You then focus on, and photograph the vertical target.  The incline ruler then gives a clear visual indication of whether your camera is in fact focusing where you think it is.  Here are the results I got with setting up my 200mm f2 lens.

With the AF fine-tune set to the zero default, here is what I saw:
(clicking on the image will bring up a larger version)

.. and looking at the image at 100% you can clearly see that the lens does indeed back-focus.

Then through a series of images taken at various settings of the AF Fine-Tune on the Nikon D3, I was able to get the lens to focus such that I thought it looked sharpest at the exact plane of focus.  To judge the sharpness, I used the magnified view on the LCD; as well as the Live-View feature on the camera; but the most accurate way of judging the sharpness was on the computer screen.   

And here is the result with the AF Fine Tune set to -10 with that specific body.  (My other D3 body needed a setting of -12)

This now gives me the confidence that my lens will work as it should during a shoot, focusing with accuracy. 

That is something that is hugely important to me … that I have confidence in how my gear performs.  The LensAlign Pro kit helped me considerably with this, and I would highly recommend it to any serious photographer who demands the best from their equipment.

 

{ 37 comments… read them below or add one }

1 Jason Smith May 7, 2009 at 4:47 am

Thanks Neil
I have often seen threads on this issue however fixing the issue looked very technical and tedious. This seems an inexpensive and efficient way to fix this.

Just so I am clear. You mentioned lens being out of spec so are Are you adjusting the micro focus each time you change lens.

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2 Neil May 7, 2009 at 4:54 am

Hi there Jason ..

Nope, each of the D3 bodies will remember 20 lenses. So if you have different lenses (even of the same model), the camera will remember that specific lens’ micro AF adjustment settings, and apply that AF fine-tune setting.

I assume it would work in a similar manner for the other makes and models.

Neil vN

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3 Rory Mole May 7, 2009 at 8:32 am

Hi there Neil,

Do you know if the Canon 40D has this feature of being able to make this adjustment. I am going to be taking delivery of my 40D tomorrow and this could be a good thing at the start.

Also, I have encountered another problem which I thought perhaps you could post an article up about how to avoid this. Maybe you already have addressed this in the past, but I haven’t seen it on your site.

I have found that when I have focussed on a person’s nearest eye and then recomposed the shot, I have come up with slightly out of focus images. Some of them are just a little bit off and others are a bit more. Do you perhaps have some tips as to how we should go about first focussing and then recomposing. I found this to happen when shooting with large apertures around F1.8 to about F2.8. I also use the center AF point to focus with. Is this wrong? Should I use another focus point to make recomposing easier?

Obviously the dof is much smaller at those apertures and the margins are too. Just the recomposition of a shot once I’ve focussed will give me “softer images” I was quite confused when this was happening until I worked it out myself.

Any thoughts on this….?
Thanks a ton once again for a great site….

Regards,

Rory

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4 David May 7, 2009 at 8:38 am

If I may answer Rory above –
No, the Canon 40D does not have the micro adjustment feature.

As for focusing-then-recomposing — at very wide apertures, even the slightest movement can result in a soft image, that’s why I avoid focus-the-recompose. Instead, I use a different focus point and place it directly on the spot I want. If it’s not composed perfectly this way, you can always pull back wider and crop later.

-Dave

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5 Harry Simpson May 7, 2009 at 10:37 am

Neil,

I’ve been meaning to do this with my lenses. the stuff I’ve read usually says the test must be made with an LCD monitor but they are doing the moire test pattern. I’ve done the 45 degree angle test before but always relied on getting the camera at a 45 degree angle on the tripod. Much easier to turn the the target like this kit provides. Thanks for sharing this.

Harry

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6 Z May 7, 2009 at 10:57 am

To Add to what Dave has said, and responding to Rory:

do you remember studying right triangles way back in trig class? (and you thought all that math wasn’t going to be useful in real life) you have a ‘film’ plane which is 2 dimensional, thus the focal plane (or where your DOF is) is also going to be a plane. now say we are shooting a portrait really shallow F1.2 the DOF will be extremely thin (just like we want it) and since we want to have that focal plane go from our models eye all the way down to her toe, we set the camera up so that the film plane is exactly perpendicular to that line. now when we tilt the camera up so that the center focus point is on the models face we change the distance from film plane to model, so that when ‘recomposed’ the focus plane is inches behind where we want it!

and after all that I thought I’d do a google search, here is the first one that came up… and there are pics.
http://visual-vacations.com/Photography/focus-recompose_sucks.htm
http://lmgtfy.com/?q=focus+and+recompose

Thanks,
~Z

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7 Aric May 7, 2009 at 11:12 am

Dang, I have this problem with my 10D and the 50mm 1.8.

Unfortunately I know there’s the problem and there is nothing I can do about it since I don’t have money to upgrade anytime soon. Grrr…..

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8 Stephen May 7, 2009 at 12:00 pm

I will have to look into this product as I have been suspecting my Nikon D300 and lenses are not accurately focusing on target. Thanks for the review.

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9 Ulysses May 7, 2009 at 1:00 pm

Very good and very practical review, Neil. I’d written up a mini-review of the LensAlign myself, and after extensive usage and testing with it I came to the exact same conclusion.

Of course, there are a number of DIY options available, and many of them work fairly well. Just as you said, it’s all about having confidence in the reliability and predictability of your gear. If a tool like LensAlign helps you to achieve that, it’s well worth it to a serious professional who makes a living through photography, and who wants an easily repeatable way to maintain his own gear. I recommend it to others, as well.

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10 Jack May 7, 2009 at 6:08 pm

Hi Neil, really like your blog, great info. I’ve got a Nikon D300 and have several lenses that I’m concerned with including zoom lenses. My 70-200 2.8 and my 17-55 2.8. I’ve never read anything about zoom lenses, can you do this at one focal length (say 70mm) and have it work thoughout the entire focal length zoom?

Thanks in advance,
Jack

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11 Neil May 7, 2009 at 7:09 pm

Jack, from what I can glean from other sources, it would seem that with zoom lenses you might find that its focus behavior changes as you zoom. So if you used a setup like the LensAlign kit, you might have to find a compromise zoom setting, or alternately, your favorite focal length, and adjust it for that focal length as your best choice.

But, as I said, this isn’t something I’ve experimented with, and my comments there are second-hand info.

best

Neil vN

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12 James Tosch May 7, 2009 at 8:12 pm

Hey Neil,

Interesting post as I just got done recalibrating my 1d mk3 after it was sent back from canon for a focus check. I had never had a problem with my original 5d and it produces much sharper focus than the mark 3 did. I just got done with a shoot using the mark 3 in which I manual focused and it was superb, huge differnece between what auto was giving me.

So I setup a ruler paralel to the camera and shot every lens I own tinkering with the focus at both center and left/right outer edges. Eventually it produced focus in the proper portions in relation to the focus points. Most of my 100mm or larger lenses are calibrated +15 or a little more and the lower than 100mm one have between +4 and +8. I then confirmed by focusing manually on something using the live view focusing mode, switched to autofocus and made sure the focus ring didn’t move from where I had manually focus it. A good solution for those tight on cash.

Before this camera I had never had focusing issues but I also had a 40d that produced soft results so the micro adjustment is a tremendous feature although it takes some time to get totally dialed in

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13 Steven Seelig May 7, 2009 at 8:47 pm

I have not used the LensAlign system, but when I have used a homemade version, I have never relied on the LCD image. Instead, I take a series of -16 through +16 or something like that and then bring them up on my computer screen at 100% to decide which adjust is best. Nonetheless, there is something appealing about the design of this device.

Neil, is there any functional difference between the full system and the Lite version, other than one requires a bit of assembly?

Thanks for your great blog. I check it frequently! Steven

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14 Neil May 7, 2009 at 10:51 pm

Steven, I only have the Pro kit. So check the LensAlign website for a description of the differences between the Pro and Lite kits.

Neil vN

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15 Skedonk May 8, 2009 at 12:46 pm

Hi Neil,

One thing that still leaves me curious is that the AF mechanism will always pick the highest contrast region to focus on. In your first example it seems to be the highlights on the iris (which is a good case for using constant lights over strobes). To me it is more often the case that the focus will lock on the eye lashes instead. Do you find that there are more keepers after the adjustment?

Thanks.

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16 Neil May 8, 2009 at 1:23 pm

Skedonk, I am definitely seeing an improvement in focusing accuracy now with that lens.

Neil vN

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17 Craig Herold May 8, 2009 at 1:30 pm

Hi,

You may also find this article of interest.

Focus Shift, by Lloyd L. Chambers
Some photographers think their lens is soft when it’s not; here’s how to fix it.

This article is in the May/June issue of Photo Techniques starting on page 35. Lens align starts out with the lens set wide open which may not be the best point. In fact it may be the worst and if you calibrate for the worst it may cause misalignment in the sweet area.

Also on the auto focus/recompose issue there ought to be some rough guide line. For instance if the original focus point is more then x percentage from the center of the view finder then that method shouldn’t be used.
Don’t ask me for numbers I don’t know.

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18 Neil May 8, 2009 at 5:56 pm

Craig, I can see how that might be true.

The Canon 50mm f1.2 is famous for exhibiting focus shift as you stop down. Wider than f2.8 it is sharp enough, but then for a certain aperture range smaller than f2.8 there is pronounced focus shift .. and then at smaller apertures again, the depth-of-field covers the focus error.

With this lens that I set up, I intend pretty much only using it at f2.o .. so I should be okay there.

Neil vN

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19 Rory Mole May 9, 2009 at 1:20 am

Hi there Dave and Z,

Thanks guys for answering for Neil. I have already moved away from the focus and recompose techniques I have used before and have moved on to using another focus point and this is working just fine. Thanks Z for the link… I’ve already visited the first site and read up on it all.

Once again, many thanks guys..

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20 Steven Seelig May 9, 2009 at 9:22 am

Perhaps I missed it, but what is the issue with auto focus/recompose. Not sure I understand why one would not get a sharp picture if distance between subject an camera does not change.

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21 Mark F May 10, 2009 at 5:56 pm

Hi Neil,

There has been some discussion on other sites that calibrating for one focus distance might not be accurate for another distance. For example, calibrating a lens at its closest focusing distance would not be accurate for infinity and vice versa. Is there truth in this?

Thanks.

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22 Neil May 12, 2009 at 2:59 am

Mark, that is another thing I wouldn’t have any knowledge of.

But I can entirely see how optical design and optical behavior isn’t clear-cut and simple, but might very well exhibit such behavior … focusing with different accuracy at the extreme ends of the range of the lens.

So this is another topic I would have to leave to the experts. :)

Since I would be using the 200mm f2.o primarily for portraits (close-up and half-length), I’d be staying in a certain range, so I am hoping that the fine-tuning with the LensAlign kit will at least optimize it for my usual working range.

But I would have to specifically test still how the lens now behaves at further distances.

best

Neil vN

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23 Mark F May 12, 2009 at 9:50 am

Thanks for your reply.

I’ve noticed that my two wide-angle lenses (16-35mm 2.8LII and 28-70 2.8L) have slightly different auto focus results when compared to live view. Both tested at infinity or near infinity. So I guess it’s time for Lens Align :-(

By the way, I find it interesting that many people are using a 200mm for portraits these days. Time was when “the” portrait lens was a 105mm. Much shorter than that was thought to distort facial features while much longer (even a 135mm) was thought to flatten out facial features. I guess that every time has its own style.

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24 Neil May 12, 2009 at 1:25 pm

Mark, I think the choice of this focal length has more to do with how the background is rendered, rather than an ideal about what would be the most flattering focal length for portraits. And shooting at f2 with the 200mm lens does give a certain look to it. : )

Neil vN

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25 Max Surikov May 12, 2009 at 6:52 pm

I have been skeptical of this product, but I am going to check it out.

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26 Stephen May 13, 2009 at 10:28 am

I read that focus shift article, and I don’t think what it says precludes the use of the Lens Align product. In the article, the author also uses a ruler target (looks like Jeffrey Friedl’s autofocus test sheet) to test lens shift. This target could just as well be the Lens Align product.

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27 Rod Edwards May 26, 2009 at 2:36 am

Do you find that AF micro adjustment settings change with subject distance ?

I’ve run stringent tests with Lens Align Pro and found that this is true with my Canon 1Ds 3 and my 5D 2. The AF Micro adjustment settings required at close focus distance are different to the settings required as i move further away from my subject.

My equipment has been factory calibrated by Canon Pro in the UK three times, but I still find the af system is inaccurate / varies at close focus distances.

Any personal thoughts would be appreciated as this seems to be an inherent problem with fast lenses and Canon cameras !!!

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28 Neil May 27, 2009 at 3:51 am

Ron, though I haven’t specifically made any tests to see if there are variations with distance – I fear you might be correct – that the focus error differs with the distance that you’re using the lens at. It’s something I have to still investigate.

In adjusting this lens, I am happy that it is now correct for what would be the majority range that I work in when photographing portraits.

I’ve seen recommendations that ideally the lens alignment should be done at 50x the focal length. But then I can’t discern the detail necessary to make the adjustments. Even at 25x it’s a bit of a push.

best

Neil vN

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29 Tim Schooler June 3, 2009 at 3:01 am

Hi Neil, have you tried testing any of your zooms? I have found a focusing error on my 70-200 when used on my D3x, but the 70-200 is perfect on my D3. I used Lens Align Pro and found the 70-200 was front focusing but only at 135 and 150mm focal lengths. At 200mm and all other focal lengths it is perfect. I don’t see any way to micro fine tune for different focal lengths on the same lens. Just curious as to whether you have found the same thing in testing zooms, or whether you have tried it?

Regards,

Tim

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30 Neil June 3, 2009 at 3:54 am

Tim, I haven’t done such a thorough test on my 70-200 .. but I am very happy with that lens.

But you’re right, there isn’t a way for a user to adjust or finesse a lens’ focusing performance like that. Perhaps it needs a trip to Nikon Service Center.

Neil vN

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31 Tim Schooler June 3, 2009 at 1:30 pm

Hey Neil, thanks so much for the reply. I am thinking about sending it in, but the 70-200 is flawless on my D3 so I hate to have them adjust it for the D3x since I suspect that may affect its performance on the D3.

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32 Ed Wilson June 17, 2009 at 5:37 pm

Neil!

Thanks for this… My D-300 is so bad that I’ve abandoned all my AF lenses for the moment. The last three shoots I’ve done with vintage
Manual focus lenses. I’ve thought about using the adjustment utility but the one time I tried, I quickly realized without an objective measuring device, I’d just be guessing at which way to go. Hopping over to the LensAlign site to further enrich them… Thnx

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33 Neil June 26, 2009 at 4:17 am

Just an update.

I’ve used this Nikon 200mm f2 a lot again at a few shoots recently, and I am really happy with how sharp it is now. No issues with back-focusing. But I did work within a close range for these tight portraits, and not anywhere near infinity.

Neil vN

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34 Curtis Copeland July 15, 2009 at 3:03 pm

Great information. I was just noticing some focusing issues with my 5D MKII. Thanks for the insight!

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35 Ed Wilson August 14, 2009 at 1:26 pm

Neil… I am taking the plunge on the LenAlign… I have had nothing but
grief from my zoom lenses ( sigma and nikon ). The problem is so bad that
I have been using my legacy primes dating back to 1974 in order to get satisfactory
sharpness. Trouble is my eyes are old too. Still, I’m getting far better results with old AI glass… not supposed to happen. OTOH I am very happy with the sharpness of my 60mm Micro Nikkor and a 24-60 2.8 Sigma… everything else is mush.. The lens align will either solve the problem, or lead to determining if I need a new lensmount on the camera body.. or just a new camera..

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36 Carlos Espinoza January 4, 2010 at 12:37 pm

Neil:

Thanks for your informative article. There is one thing in it that wasn’t explained though. The AF fine tuning settings you choose will only be good for a particular distance/aperture combination. If you typically shoot at fairly the same distances and apertures, your adjustment will work fine and will render sharp pictures. However, if you are a generalist, (i.e., the type of guy who photographs under different subjects/distances/apertures situations), you must be aware that one single setting will not be good to cover all these situations. For example, if your take a picture at 10 feet with a 300mm F/4 and you came up with a AF fine tuning setting of +12, you will not get you sharp pics if you photograph a subject located at 30 feet using the same AF Fine Tuning setting.

In summary and based on my tests, I believe now that one should use AF Fine Tuning only when there is an abnormal (excessive) front or back focus situation.

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37 Carlos Espinoza January 4, 2010 at 1:26 pm

One clarification to my previous post:

As you increase your camera/subject distance, the DOF area recedes. So, if your lens suffers from a slight front focusing problem at 10 feet for example, instead of messing around with AF Fine tuning you better stop down so, when you shoot beyond 10 feet, the DOF will fall where it belongs.

On the contrary, if your lens has even a slight back focusing problem, you better adjust the AF fine tuning setting. That is because as you increase the camera/subject distance your DOF will move even further away from you and you will end up with worthless pictures.

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