Infinity Focus is not quite right

[mehguy]

Are you sure your lens works with this camera?

Well it's an Nikon F mount AI lens on a nikon FE, which is what it officially supports.

 

[wiltw]

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

Have you checked that the screen is properly seated in the frame that holds the focus screen in position, and have you checked to see that the frame itself is properly latched fully upward (toward the pentaprism)?

 

[Alan Edward Klein]

Here's Gemini AI answer that might help:

Infinity focus issues on a Nikon FE are usually caused by one of three things: the lens, the mirror/screen alignment, or the "infinity stop" on the lens itself. Before you start taking things apart, we need to isolate the culprit.

1. The "Is it the Lens?" Test​

Check if the lens can achieve infinity on a different body (or a digital Nikon).

• If it fails on all cameras: The lens element has likely shifted, or a previous owner "repaired" it and didn't calibrate the infinity stop correctly.
• If it only fails on the FE: The issue is the camera's internal alignment.

---

2. Common Culprit: The Focus Screen​

On a Nikon FE, the focus screen is user-interchangeable. If it isn't seated perfectly flush, your eyes will tell you the image is out of focus even when the film will see it perfectly.

• The Fix: Open the camera back, use a pair of tweezers to release the small silver catch at the top of the mirror box. The screen will drop down. Gently push it back up until it "clicks" firmly. Even a fraction of a millimeter of tilt will ruin infinity focus.

3. The Mirror Stop Adjustment​

Over decades, the little rubber or plastic "stop" that the mirror rests on when it’s down can degrade or compress. If the mirror sits too low or too high, the distance the light travels to the viewfinder won't match the distance to the film.

• The Fix: There is a small eccentric screw inside the mirror box (usually on the side) that governs where the mirror rests.
• Warning: Only touch this if you have a "ground glass" (or Scotch tape) placed over the film rails to verify that the image is actually out of focus at the film plane. If the film is sharp but the viewfinder isn't, adjust the mirror.

4. Calibrating the Lens (The DIY Fix)​

If the lens is the problem, many Nikon AI lenses allow for a "hard stop" adjustment:

1. Peel back the rubber grip on the focus ring.
2. Look for three tiny set screws.
3. Loosen them slightly (don't remove them!).
4. Set your camera to a tripod, point it at a star or a very distant power line, and manually turn the inner focus barrel until the image is tack sharp.
5. Slide the outer focus ring to the $\infty$ mark and retighten the screws.

---

How to verify the "True" Focus​

To see if your film will actually be blurry, try the Scotch Tape Method:

1. Open the camera back (no film).
2. Set the shutter to Bulb (B) and hold it open with a cable release.
3. Place a piece of translucent matte tape (Magic Tape) across the inner film rails.
4. Look at the tape with a magnifying glass. If the image on the tape is sharp at infinity, your camera's mirror or screen is the problem, not the lens or the film alignment.

Note: If you find the mirror is hitting the "foam" at the top and staying slightly tilted, you may just need a Light Seal Replacement kit (the foam bumper is likely sticky and rotted).

 

[MattKing]

Again - the fact that the markings on the lens don't match up to your expectation says nothing about whether the system is focusing properly.
Film will tell you that.

 

[mehguy]

I just realized that my Nikon 28-80mm AF lens is compatible with my FE. I will give it a try tomorrow when there is light out.

 

[Craig]

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.

If you photograph the subject is it in focus? That's all that really matters.

 

[mehguy]

If you photograph the subject is it in focus? That's all that really matters.

According to the focusing aid, yes.

But again, far in the distance objects focus right up before infinity, but not at it.

 

[Craig]

As long as the film is in focus, I wouldn't concern myself with what the mark on the focusing ring says.

 

[wiltw]

As long as the film is in focus, I wouldn't concern myself with what the mark on the focusing ring says.

...when the subject is far away. But the error could well happen at closer distances, where DOF is less masking of focus deviation between in-viewfinder vs on-film.

 

[MattKing]

As long as the film is in focus, I wouldn't concern myself with what the mark on the focusing ring says.

Yes.
The camera may very well be focusing perfectly.
The numbers on the focusing ring are a guide, not a setting.
For some purposes, you are much better if they are accurate.
But with SLRs, they rarely matter much at all.
The important issue is whether the focus indicated by the viewing/focusing system and the focus on the film match.

 

[Brad Deputy]

My experience with infinity focus; I had a similar issue with a just-acquired-from-ebay 35/2 Zuiko --

I have 8 other lenses (<150mm) and infinity stop gives an acceptable (if not exact) sharpness wide open with objects in the distance (mountains, trees).

But this 35/2 would not focus on the infinity at all; I tested with film to confirm. I could stop it to F8 then it's fine, but dangit I want my F2 sharp since I often shoot fast film at night.

I had it repaired by Glazers in SEA; The tech said it may have been dropped at some point and just needed to be re-assembled and infinity stop reset. Now it focuses like my others.

I do have a 100/200 Zuiko as well as a Vivitar Series 1 70/210mm, and those will overshoot infinity just a smidge, which I hear is expected (as mentioned above) I can always back off a little to sharpen it up, no biggie.

 

[Ian C]

The information of Post #23 makes the problem clear.

“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.”

If this happens at 0.1 km (100 meters), the behavior described is expected. The subject distance is close enough that we can see that the infinity mark on the rotating focus ring is not at the index dot on the lens when the split-image rangefinder indicates best focus.

In my experiment with a 50 mm Nikkor, I found that there was a nearly imperceptible difference between the infinity mark and the index dot when the split-image rangefinder indicated best focus at a measured subject distance of 235 meters.

But at 0.5 km (500 meters) and farther, the difference is undetectably small (though it still exists). Something is wrong.

But what? If this was my equipment, I’d immediately mount another Nikon lens of the same focal length, or a zoom lens that can be set to that focal length and retest.

If the problem persists, the problem is in the camera. If the problem disappears, then the focus of the lens is not properly indexed and the lens needs adjustment.

The suspect lens could also be mounted on another Nikon body to see if the problem persists. If it does, then the lens is the cause of the problem.

 

[mehguy]

The information of Post #23 makes the problem clear.

“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.”

If this happens at 0.1 km (100 meters), the behavior described is expected. The subject distance is close enough that we can see that the infinity mark on the rotating focus ring is not at the index dot on the lens when the split-image rangefinder indicates best focus.

In my experiment with a 50 mm Nikkor, I found that there was a nearly imperceptible difference between the infinity mark and the index dot when the split-image rangefinder indicated best focus at a measured subject distance of 235 meters.

But at 0.5 km (500 meters) and farther, the difference is undetectably small (though it still exists). Something is wrong.

But what? If this was my equipment, I’d immediately mount another Nikon lens of the same focal length, or a zoom lens that can be set to that focal length and retest.

If the problem persists, the problem is in the camera. If the problem disappears, then the focus of the lens is not properly indexed and the lens needs adjustment.

The suspect lens could also be mounted on another Nikon body to see if the problem persists. If it does, then the lens is the cause of the problem.

I just mounted my 28-80 on the body, and the problem still persists.

What are the implications of this?

 

[ic-racer]

I just mounted my 28-80 on the body, and the problem still persists.

What are the implications of this?

If your lenses have no signs of tamper and the camera's front and lensmount has never been removed (with risk of losing or misplacing shims) it may be the mirror-stop that has drifted.

On a typical Nikon film camera, the lens-mount-to-film distance is adjustable, the focus screen distance is adjustable, the mirror angle is adjustable and each manual focus lens has an adjustable infinity stop.

So, one needs some known standard which is fixed and the other adjustments made to suit.

Sometimes a camera tech does not have the time or patience to adjust things to the critical needs of the astute film photographer, thus, there is a market for amateur and home-made autocollimators.

 

[250swb]

I just mounted my 28-80 on the body, and the problem still persists.

What are the implications of this?

There are no implications, it doesn't matter. The only thing that does matter is if the camera focuses accurately at closer distances. Infinity is a long way away, between you and infinity atmospheric haze is going to have more of an impact on whether things look sharp or not than being a couple of feet out in focusuing.

 

[mehguy]

There are no implications, it doesn't matter. The only thing that does matter is if the camera focuses accurately at closer distances. Infinity is a long way away, between you and infinity atmospheric haze is going to have more of an impact on whether things look sharp or not than being a couple of feet out in focusuing.

The comments here seem to suggest that this is a problem for it.

 

[BrianShaw]

The comments here seem to suggest that this is a problem for it.

Some comments...

Other comments suggest other things to consider.

 

[MattKing]

If your photos are not in focus when the viewing screen indicated focus, then your camera and lens has important problems.
If your photos are in focus when the viewing screen indicated focus, then your camera is fine and the lens is slightly less convenient to use if you have the unusual need to focus without using the viewing screen - i.e. you have need to scale focus.

 

[wiltw]

I just mounted my 28-80 on the body, and the problem still persists.

What are the implications of this?

...means that the problem you are having is not within any lens, but the issue of focus 'mismatch' (between the viewfinder and the focal plane) is due to the optical path to the focus screen not being as designed (i.e., optical path length to focus screen does not equal optical path length to the focal plane) The issue is likely

• focus screen not seated properly in its seat
• the frame holding the focus screen is not properly latched into place
• the reflex mirror angle is a bit off from its expected 45 degree angle and needing adjustment screw tweaking

The reason why someone has already suggested inspecting the film (with lens set to infinity mark) is to verify things are truly 'in focus' in the path to the film at indicated Infinity....while any indication that the same distance setting results in 'out of focus' in the viewfinder clearly points to the optical path length to the focus screen not matching focal plane distance!

 

[gorbas]

market for amateur and home-made autocollimators.

Any links or suggestions please?

 

[BrianShaw]

Repair: Infinity Focus Calibration

Adjusting a lens’ focus is important. If it couldn’t focus properly to infinity it won’t be useful at all and the distance and depth-of-field scales do not mean anything. I will s…

richardhaw.com

 

[ic-racer]

Any links or suggestions please?

Reveni Labs Autocollimator — Reveni Labs

In stock and ready to ship. More Information Here User Manual The Reveni Labs Autocollimator is designed to help you check lenses and cameras for accurate infinity focus, as well as and estimation of lens sharpness. It is designed to be affordable, compact, and easy to use.

www.reveni-labs.com

 

[gorbas]

Reveni Labs Autocollimator — Reveni Labs

In stock and ready to ship. More Information Here User Manual The Reveni Labs Autocollimator is designed to help you check lenses and cameras for accurate infinity focus, as well as and estimation of lens sharpness. It is designed to be affordable, compact, and easy to use.

www.reveni-labs.com

Thank you very much IC-Racer! Very tempting!

 

[4season]

On a typical Nikon film camera, the lens-mount-to-film distance is adjustable, the focus screen distance is adjustable, the mirror angle is adjustable

In the case of Nikon F or Nikkormat, how would you do this? Mirror angle adjustment is straightforward, but I don't recall seeing any shims used where lens mount meets mirror box casting, or where mirror box bolts onto main body casting. And those mirror box castings are pretty stout, and do not seem designed for bend-to-adjust alignments.

 

[RalphLambrecht]

Are you sure your lens works with this camera?

that would be 50m in his case and with building at 200+m ,he ia already far beyond that.