# Focusing problems on SLRs



## David R (May 4, 2009)

This is a fairly lengthy intro to my question, please bare with me. (I'm also new to these forums)

I have a total of 5 Nikon bodies.  The two that I learned to shoot with, a Nikkormat FT, and a N2000.  These two were for a long time fine for my kind photography.  Recently I had the opportunity to pickup a couple of more bodies, a FE, a FE2 and N6006.  Never use N6006, it was really cheap so doesn't matter.  The FE2 became my favourite, love the metering.

Anyways started to notice some focus issues.  Images just didn't seem as shape as I thought they should be.  Eventually isolated down to the FE and the FE2, problem seems to be around infinity focusing.  Usually when I'm out Kayaking I just set the lens at infinity as most objects of interest are further than 50 feet, good enough for wide-angle lens.  Well it turns out that on these bodies infinity comes early, depending on the focal length of the lens.  By comparison the FT, N2000 and for that matter then N6006, hit infinity where the lens are marked as infinity.  For those note familar with these bodies, the FEs have interchangable focusing screens, while the FT, N2000, and N6006 are factory fixed focusing screens.

So after a lot of focus experiments I have something that doesn't really add up for me.  I would expect that a check of the focal plane focus verses the view finder focus would agree.  Well this is where I get confused.

I've tried several techniques, a piece of frosted mylar as a focusing screen on the film plane, with x8 loop, a focusing screen from another camera refashioned to fit on the film plane with a x8 loop, a crude collminator setup using another camera with matching lens.

The FE and FE2 both agree for view finder matching film plane focus, even though the focusing scale on the lens are off.  The FT, N2000, and N6006 don't agree for film plane verse view finder, they're just slightly off with the film plane hitting focus before the view finder.  The view finder agrees with the scale on the lens.  While normally I use the split screen center for focusing, I also watched the matte part of the screens to be sure my eyes weren't the issue.

So I'm a little lost as to what the problem is, or where to go from here.  Is there something wrong with the FEs. Am I doing something wrong in my testing.  I have tried using film tests, but it wasn't really conclusive as I was using slide film, then scanning, and my scanner isn't up to that level.  I haven't tried specific tests with neg film and enlarging, which I could do.  Its just a little time consuming and to costly right now.

Any insights would be greatly appreciated.

David R


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## Battou (May 4, 2009)

Well, I'd first look at the mount on the body. 

Is there visable ware on the mount?

If that is not the case I would check the mirror angle.

Does the image in your view finder match up with the frame on the film?

If the mirror is off it's going to effect the focusing screen by changing the distance of the mirror to the screen making the image in the screen closer or farther from the focusing aid than it would be to the film plain. Mirror angle is critical with any SLR, an exact 45 degrees is required, so much as half a degree can really tamper with things. This is more likely than mount ware but much harder to visually confirm. Slight mirror angle flaws are almost impossible to see, even under the most controlled testing, sadly I am not aware of many ways to detect it, muchless efficient ones.


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## compur (May 4, 2009)

David R said:


> Usually when I'm out Kayaking I just set the lens at infinity as most objects of interest are further than 50 feet, good enough for wide-angle lens.



If you want a "focus free" setting for your lenses _do not_ focus them at infinity.
What you want to do is set them to their hyper-focal distance.  This is done
by first deciding on an aperture, let's say it's f/11

The lens below is set for its hyper focal distance for f/11







Notice the lens aperture is set at f/11 and that it's _not focused at
infinity_.

Instead, the infinity mark on the focus scale is set for the upper limit of
acceptable focus for f/11.

This will produce acceptable focus for everything from about 5.5 feet to
infinity.  This gives the maximum range of acceptable focus at that aperture.

Also, it's not unusual for lenses to focus a little past infinity.  Many good
quality lenses do.  This is to allow for physical changes to the lens due
to temperature, wear, etc.


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## David R (May 4, 2009)

- battou, I have played with mirror settings on both of the FEs, but there isn't enough movement on the mirror stop, also there is no adjustment for the hinge point on the mirror. The only thing that resulted was being able to adjust the top to bottom focus in the view finder.

- compur, I get what your saying about hyperfocal length, and I do frequently use the technique. As you say hyperfocal length is based on acceptable image softness. For me the problem I'm having is the peek sharpness isn't where it should be, where I'm focusing. Hope I made sense.

Problem still remains, why do the FEs focus at infinity earlier than the other bodies. Why do the factory set bodies actually over focus, the film plane focus is past critical and going out of focus.

I have been suspecting the mounts, but they don't have any significant ware showing. Only thing I can think of is that they have been modified, for which I have no comparison.

I'm going to try to measure the mount to film plane distance o each of the cameras.

David R


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## David R (May 4, 2009)

- Compur, I reread my post and I don't think I said what I wanted to.

Using your pictured lens scale. A range of acceptable focus for f11 is shown, ending at infinity. The problem I'm incountering is that the limit doesn't fall where the scale says it falls.

I would think idealy that a very fast lens, say F1.2 or better, wide open, would still have to be able to focus at infinity when then scale says infinity.

Did that make sense?

David R


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## Dwig (May 4, 2009)

I suggest you review your testing procedure. Be careful that your film plane focusing "screen" is in the right position. It must seat on the inner two polished film rails, not on the body casting and not on the outer two rails. It also must remain flat when you press on the lupe.

If your tests were done correctly and the film plane and VF focus match the mirror, mirror box, focusing screen and film rails are properly align relative to each other. If infinity doesn't line up correctly then either the lens' focusing ring is mis-set or the body mount is in the wrong position. I good shop can confirm which.

If the film plane and VF don't match, it points to either a testing error or a misaligned VF system (mirror, whole mirror box, or focusing screen).


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## David R (May 4, 2009)

- Dwig, thanks for responding.  I was very careful about my pressure points when working on the film plane.  Fortunately my loop matches the inner rail for film suport.  I don't think that's the issue.  There could be a testing error as it is all make-shift materials.  Still working on the measurements.

I have contacted a few repair shops/people and they all advise just getting different bodies as their charges will be about the same.  Which basically is why I'm doing all this myself.

David R


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## compur (May 4, 2009)

David R said:


> - Compur, I reread my post and I don't think I said what I wanted to.
> 
> Using your pictured lens scale. A range of acceptable focus for f11 is shown, ending at infinity. The problem I'm incountering is that the limit doesn't fall where the scale says it falls.
> 
> ...



If you mean that the distance scale on your lens is not accurate, then
how far off is it?  Can you post a photo illustrating the difference?


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## David R (May 4, 2009)

- Compur, I'll try to get some shots tomorrow (better light and its late), showing the lens scale errors.

I made some measurements this evening.  These are the averages of four individual readings from each body. Using a digital caliper that can read depth (0.02 mm accuracy, 0.01 reaptability and resolution).  I measured from the front of the center of lens mount (bridged) to the moment of contact with the film pressure plate.  Interesting the FT had the greatest scatter, suggesting the springs for the pressure plate are weak.  The N2000 faired the best with 3 of 4 readings being the same.

FT  46.665 mm
N2000  46.635 mm
N6006  46.725 mm
FE  46.663 mm
FE2  46.665 mm

David R


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## David R (May 5, 2009)

OK here we go some pictures (no art awards here). They sure do make this a convoluted process. The target for these shots was the upper trunk of a tall tree several backyards away, 400ft give or take 50ft. An easy target to focus on because it was backlit at the same time. I have samples for the other bodies but these two should suffice. As you can see the shorter the focal length the worse the problem becomes.

N2000 50mm


 
FE2 50mm 


 
N2000 28mm


 
FE2 28mm


 
N2000 20mm


 
FE2 20mm


 
David R​


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## compur (May 5, 2009)

I see there is a difference.  Is this a problem?


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## David R (May 5, 2009)

Well...

I guess if I put black tape over the focusing scale on the lens and do everything by eye then no.

But, coming back to depth of field and hyperfocal length a problem arises. The last sample is the FE2 with a 20mm lens. The scale says that the tree is 5 feet away, when I know its more like 400 feet (the 28mm ~10ft, 50mm ~22ft). Where would I set my far point focus on the lens scale.

And still there is the question, for me anyway, why is the scale so far off, the mount to film plane isn't significantly different from the other bodies. The focus in the view finder matches the focus on the film plane. So why the scale error

I know this is a circular discussion, but its weird and it bugs me. Keeps me from being comfortable using FEs.

David R


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## compur (May 5, 2009)

Lens focus distance scales are not linear. A tiny fraction of an inch to the
left of "5" on your 20mm lens is hundreds of feet away.  It's just not possible
to paint numbers on such a compressed non-linear scale with the kind of
accuracy that you seem to require.  Manual focus SLRs were built with
eye-focus as the primary intended method.  The scale painted on the lens is
only meant to be an approximation.


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## stsinner (May 5, 2009)

Asphynchter says what??  Holy God!!!  If I pay $1000 for a DSLR, I expect it to focus accurately......  That gibberish was science-class fodder....  Just let me take pictures..


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## Sjixxxy (May 7, 2009)

Perhaps the focussing screen isn't sitting in it's proper place? With the lens off there should be a little tab you can flick from the front that will drop down a little door down that holds the focussing screen. Pull it out, resituate it, and snap it back up. Changing Focusing Screens in the Nikon FM/FE/FA

Worse case is that that easy access door for the screen is wore out and doesn't lock up all the way. This would let the Screen sit lower then it should, which I can imagine would affect the focusing precision.


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## Judge Sharpe (May 7, 2009)

In reading the various post, I have become confused as to the problem. Is it: 
1. That the focusing screen and the film plane do not match up so that when you have an indication of focus in the view finder, the film is out of focus? 

2. That the view finder and the film are both in focus but the distance indication at Infinity is off for use on a particular body? 

If the view finder and film are not both in focus at the same time, the first thing I would check is the doppler adjustment. Is it adjusted for your particular eyesight? +1, 0 or -1. If that is OK then I would find a focus target and shoot a roll of BW film, fine grain. Set the target at a known measured distance from the film plan ( this is usually indicated on the camera body.) and record the settings as you shoot through the distance indicators. If one distance is off, the others should be off by a proportionate amount. You should get softness at five feet and at infinity, providing the lens does not have an internal problem. 

If the problem is that focus is good on the view screen and the film, but the problem is the distance indicator, carefully calibrate the lens for the body you are using by making reference marks on the lens. 

The film plane should be the same for all cameras that interchangeably use the same lenses. I do not think that the use of a digital caliper will accurately measure a potential difference. The way to compare is with a calibration target to establish differing points of sharpest focus. 

Having a shop preform these checks should not be costly, a repain might be. 

Judge Sharpe


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## David R (May 7, 2009)

Sjixxxy - I have checked to make sure it isn't the focusing screens. I have had them out several times, swapped them and tried a third screen.  There are two bodies that have this odd behavour, FE2 and FE.

Judge Sharpe - I guess I muddied the waters with an observation about the differences of the different bodies.  The factory fix bodies, N2000, FT and N6006 don't agree with their view finders.  Their view finders critically focus on a far target a little after the film plane is critically focused.  Were as the FEs are in sync.  (could be the nature of my test setup, but still a difference)

My primary issue is that the focus scale is way off, for the FEs compared to the factory fixed models.  Check the (worst case) N2000 with 20mm verses FE2 with 20mm.  The FE2 focus does appear to be fine, just not were it should.  If I were to measure off targets for 5, 10, infinity the camera setup would be out of focus.

You may be correct about caliper measurements, as they did measure pretty much the same.

Alternate scales afixed to the lens maybe the answer.

Shops up here charge way to much, $125 was the quote to look at the camera.

David R


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