Focus problems

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Archive 2008 · Focus problems

rnickl
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p.1 #1 · Focus problems

I posted a while back about 90 deg finders, magnifiers and alternate screens to help with focus but, I am discovering this likely is an issue with my eye.

I get perfect focus in the finder (to my eye) but images always come out a bit back focused. I have tried 2 different lenses, 2 different bodies, off tripod, with and without diopter on the front of the lens, adjusted diopter on the view finder, made sure I wasn't pushing the camera forward when hitting the shutter and all with identical results. It's so frustrating I gave a visit to the optometrist today, I found out my vision is better than 20/20 when corrected and she had no advice for my problem.

With focus being so much more critical for macro work, I was hoping someone here may have run into a similar problem or could even give any advice where to look next. Perhaps I overlooked something that could be causing the problem?

Here is a sample shot to show the problem I'm having. The tip of the razor blade looked to be in perfect focus in the view finder but the actual focal point is just behind by about 1mm.

This image is copyrighted by the owner

Rick

Nov 22, 2008 at 05:04 AM

LordV
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p.1 #2 · Focus problems

One suggestion before diagnosis - can you try a vertical flat target- eg a cereal box and rest the camera on the same table and see if you have trouble with the focus on the printing. Plus check to see if you get focus confirm by half pressing the shutter

So do you shoot with glasses/contacts on ?

My initial thoughts.

Possibly the dioptre viewfinder adjustment not being correct but I'm really not sure if this is out that you can get a sharp image in the viewfinder at all.

Similar to a problem I found I had that is more mind over matter- I found I tended to backfocus on insects and eventually realised it was because my eyes/brain were seeing more of the image in focus and therefor registering in focus. I had to train myself to take the shot when the part I was interested in only just came into focus.

I suppose it's possible the focus screen position needs adjustment but I'm not sure how this would affect AF with normal lenses.

Brian V.

Nov 22, 2008 at 06:59 AM

rnickl
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p.1 #3 · Focus problems

Good suggestions Brian. I shot some flat print and I am sure enough still back focusing. I get a sharp image in the view finder but an OOF final image. I do not get the AF confirmation light unless I back out a bit and the image looks OOF in the finder, so it appears AF is working more accurate than my eye. I also tried with my non-dominant eye and get perfect results, in focus in the finder, AF confirmation and good final image.

I have played with the diopter adjustment and it does not move my focal point, it only changes how clearly I can see the image in the finder.

Does anyone here know how to calibrate the focus problem like this

I'm not sure how I would be able to get Nikon to calibrate the focus my my particular eye, so this may be a DIY project or maybe a local shop.

Nov 22, 2008 at 06:16 PM

LordV
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p.1 #4 · Focus problems

Hmm - does seem more of an eye problem- have you tried lining up on a target- getting focus confirm and then trying to see if you can get a clear image in the viewfinder by adjusting the dioptre ?
Almost sounds like you need prescription eye piece lens or similar if that's possible.
Brian V.

Nov 22, 2008 at 06:34 PM

Dalantech
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p.1 #5 · Focus problems

Are you shooting with glasses or contacts, and does the problem happen with and without them?

Nov 22, 2008 at 07:22 PM

DQE1.0
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p.1 #6 · Focus problems

Another possibility - I must wear my eyeglasses while using my camera. I often find that I press my glasses against the camera to an excessive extent while focusing. This is almost certain to defocus my vision since the distance between my cornea and the inner surface of my glasses needs to stay at a fairly precise distance in order to see properly. I have suspected for some time that I am therefore not always focusing accurately in spite of having good vision when using my glasses. It is possible to offset this effect if it were highly reproducible from shot to shot, but of course it isn't.

I've also wondered if it would be worthwhile to obtain a custom-fit compensation lens to the camera so that I wouldn't have to wear eyeglasses while taking photos. This way, I wouldn't be at risk of disturbing the position of my eyeglasses during the pressure of macro photography. I believe Canon sells approximate corrective lens inserts for many of their cameras - this wouldn't be practical for anything but macro photography IMHO since I need to look at the scene and quickly look through the viewfinder in non-macro work.

In addition to this, I would prefer a magnifying insert for the viewfinder, about 2.5x, in order to more precisely focus. I have the Canon 90 degree unit but find that 90 degree viewing is distracting or impractical most of the time. Thus, a straight-through magnifying insert without the 90 degree feature would seemingly be helpful in obtaining precise focus in some situations.

I hope there is something in this note that is helpful to someone.

Nov 22, 2008 at 07:51 PM

rnickl
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p.1 #7 · Focus problems

I have tried with both my glasses and contacts. It does seem a touch better with contacts but, I think only because I can get closer to the view finder. I haven't tried without correction, that wouldn't do me any good as I would never be able to see the subject to shoot it

My optometrist did say it's a good possibility my eye is just over correcting for focus. She said it's fairly common for it to happen when things are close to your face and there is nothing to be done to correct it but try to relax.

I called the local repair shop this morning and we talked a bit about re-shimming the focus screen. It will not effect auto focus but will probably cause problems if someone else uses my camera with manual focus, no big deal for me. I need to give them a call on Monday when when the "hi-tech" guy is in and talk to him, he may have a trick or two up his sleeve before I start changing anything.

Hopefully this end up being the final solution. I should be able to do it myself and will only cost me the price of the new shim.

I appreciate the ideas and input from you all.

Nov 22, 2008 at 08:27 PM

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