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Infinity Focus is not quite right

mehguy

Member
Joined
Apr 26, 2015
Messages
577
Location
Canada
Format
35mm
Hello,
I own a Nikon FE where I believe the Infinity focus isn't quite right. Whenever I try to focus on something in the distance, like a far away building, using the focusing aid, it focuses right up a smidge right before infinity, not *at* infinity. If I were to focus at infinity, the building in the focusing aid would look slightly misaligned.

I'm just wondering if this is normal or there is some type of misalignment.
 
Is there ever a situation where normal DoF, even at the most open aperture, would not result in a crisp image at infinity (either way)?

Which "focusing aid"; the split image? And which screen? If you are using a screen with microprism I'd consider that a better thing to check than the split image.

Which lens?

On a tripod?
 
I would have to develop a roll of film to find out.

I'm using the split image on the Nikon type K screen.

I'm using a Nikon Series E 50mm 1.8 lens
 
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No, I don't think you need to use film to answer that question. A DoF table or even the DoF markings on the lens should give youy the answer.

There has been lots of writings on the internet over history that suggests that sometimes lenses "overfocus at infinity" to accomodate temperature shifts. That may be so but the difference seems to me to be either inconsquential to practical photography or the result of erroneous measurement/testing.

Check your lens on medium and close distances. That is where any measurement/focus errors will matter.

And double check that the screen in your FE is properly installed.
 
One would use an autocollimator (or distant object) and a known good body and/or known good lens to diagnose the issue.

Do you have any other Nikon bodies or lenses?


 
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In addition to the screen, I'll add that the focusing aid might be the problem. Does it have a diopter adjustment -- as many do? Does it seem out of focus without the focusing aid? Does anyone else also see it as out-of-focus?

Do you use glasses?
 
Are you assuming that the infinity marking on the lens is correct, and your focus system is wrong?
That may not be the case.
 
I have lenses that don't quite focus to infinity (very common), and lenses that focus past it (rarer, usually only long telephotos).

I have cameras where the mirror might not be precisely in place (my Pen F's mirror actually moves very slightly if you tilt the camera above the horizon line, I assume something is loose).

How much is is a smidge? 20 ft before infinity? 40 ft? This may actually be desirable. In general you never want to shoot 35mm wide open at infinity with a vintage lens. Stopping down once or twice, depth of field should cover it.
 
ic-racer said:
One would use an autocollimator (or distant object) and a known good body and/or known good lens to diagnose the issue.

Do you have any other Nikon bodies or lenses?


View attachment 419124
Click to expand...

How did Leitz check or adjust the focus of their thread mount cameras? These bodies had a solid back without a door or panel.
 
xkaes said:
In addition to the screen, I'll add that the focusing aid might be the problem. Does it have a diopter adjustment -- as many do? Does it seem out of focus without the focusing aid? Does anyone else also see it as out-of-focus?

Do you use glasses?
Click to expand...

The Nikon FE doesn't have a diopter adjustment. I also do not wear glasses.

ic-racer said:
One would use an autocollimator (or distant object) and a known good body and/or known good lens to diagnose the issue.

Do you have any other Nikon bodies or lenses?


View attachment 419124
Click to expand...

I have another 50mm lens, but it is currently 4 hours away from me right now. Nothing on hand at the moment.
 
mehguy said:
The Nikon FE doesn't have a diopter adjustment. I also do not wear glasses.
Click to expand...

People use diopter adjustments eyepiece attachment accessories for cameras that lack built in adjustments.
I would reiterate - the camera may be focused on infinity - both the viewing system and the film - and the lens markings may be wrong or may sometimes be wrong, depending on temperature.
 

So it was a conscious decision to put a bit of over-focus?
 
mehguy said:
So it was a conscious decision to put a bit of over-focus?
Click to expand...

Probably not for a 50mm Series E. That’s more likely in long telephoto and mirror lenses.

If I were you, I’d work on verifying your observation using either matte or microprism parts of the K screen. Or a collimater if you’re not convinced that the “error” is insubstantial to practical photography. TBH, that might be where the potential discrepancy is more likely.

Regarding diopter, never heard of an aftermarket adjustable diopter viewfinder attachment gizmo for a Nikon, but there were corrective diopter eyepieces. They are marked with the diopter strength.
 
BrianShaw said:
Regarding diopter, never heard of an aftermarket adjustable diopter viewfinder attachment gizmo for a Nikon, but there were corrective diopter eyepieces. They are marked with the diopter strength.
Click to expand...

A difference in plurality here, I'm afraid. I intended to refer to the set of options as covering the various options available.
When I refer to "diopter adjustments eyepiece attachment" I'm intending to refer to a set of different options, where each attachment in the set adjusts the eyepiece a set amount, and the entire set of them gives the user a choice in order to match their eyesight correctly.
Historically, people would be able to go into a store and try out the demonstration set that the store had on hand by placing and removing different ones on to their camera and looking through the viewing system. When they had the correct demonstrator for them in place, the customer would buy one with that strength, and the demonstration set would go back in the store's display/drawer.
 
mehguy said:
So it was a conscious decision to put a bit of over-focus?
Click to expand...

Or a slight misplacement, or a slightly incorrect re-assembly.
With SLRS, people go years without ever using those numbers to scale focus or even measure/estimate distance. Lens mounts can also wear.
 
Possibilities are as follows and one would need to use the usual testing to elucidate the problem:
a) Lens infinity stop is wrong
b) Lensmount to film plane distance is wrong
c) Mirror angle is wrong
d) Focus screen distance is wrong

Curiously I have about 30 Nikon bodes and about 30 Nikkor lenses. None have ever tested wrong at the 4 points listed above.

Other brands....yes to all 4.
 

actually, DOF covers nothing; true focus is only at one plane. Everything before or behind that plane is technically out of focus but may appear reasonably sharp if within DOF. For landscape photos, it is very desirable to have infinity in true focus. If one relies on DOF for infinity focus, he or she might end up with infinity at the threshold of sharpness, which looks misfocused.
 
RalphLambrecht said:
ctually, DOF covers nothing; true focus is only at one plane.
Click to expand...

True. Everything in photography is at least in slight misalignment, the question is how much it matters in any one particular application.

I initially read his post as is camera stopping before infinity, not going past it. If it goes past it, it just requires careful focus in the viewfinder. He'll need a ground glass and loupe or a film test to know if the focus really is where the camera tells him.
 
Regarding Post #1

“Whenever I try to focus on something in the distance, like a far away building, using the focusing aid, it focuses right up a smidge right before infinity, not *at* infinity.”

Are you referring to the position of the infinity mark on the focusing ring relative to the focus index line/dot on the stationary lens barrel? If so, is this what you observe when the split-image rangefinder indicates IN FOCUS?

What was the subject distance from the lens to the target?

If these happen together when focusing on a distinct edge of a building a FINITE distance away, then both the rangefinder and the lens’s focusing scale are probably working as they should.

Experiment using a Nikon FE, 50 mm f/1.4 AIS Nikkor, Nikon IR rangefinder (used in golf, archery, hunting, target shooting, etc.).

I set focus on the lens using the FE’s split-image rangefinder using the City Hall building in my town as a target. Then I used the IR rangefinder to get a distance reading of 235 meters. I could rotate the focus ring slightly to its infinity stop without altering the split in the viewfinder.

The infinity mark on the focus ring was a fraction of a millimeter in rotation—a “smidge”—from the index dot on the lens barrel. This is as expected. The calculated position of the front of the lens at 235 meters is 0.0106 mm forward of its infinity position.

Try the split-image rangefinder focusing on the edge of the moon. Its mean distance to the earth is 324,400 km. Any “smidge off” in focus should be undetectable in focus ring position relative to the focus index line, provided that both the camera and lens are working properly.

Note: At this lunar subject distance, the front of the lens is 0.0000000065 mm forward of its infinity position when focused. Of course, we have no way to set or discern such a minute difference.

I think this might be a case of “If it ain’t broke—don’t fix it.”

Note: A diopter correction lens on the viewfinder only makes it easier for a user needing that correction to clearly see the viewfinder image. It doesn’t cause a focus error (split-image rangefinder is not affected).
 

Yes. When the split-image rangefinder indicated IN FOCUS, the position of the focusing ring relative to the focus index, was a smidge off of infinity. As in, I was able to turn it further into infinity's direction, making the split image indicate out of focus.

I have tried this on subject distances around 0.1 to 0.5 km away.
 
mehguy said:
I have tried this on subject distances around 0.1 to 0.5 km away.
Click to expand...

Try something further away. One common definition of "infinity" for photographic pursposes is 1000x - 1500x the focal length of the lens.
 

Are you sure your lens works with this camera?
 
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