Focus testing with FE-2

[Daire Quinlan]

I have an FE-2 which consistently front focuses with my Nikkor 50mm f/1.4, by 6/7mm or so.

To test focus I got a split screen from an F4 and placed it snugly against the film rails at the back of the camera (not the pressure plate rails, the inner film rails). I focused using a 5x loupe on the split screen on a typical focus test target, lines, at 45 degrees to the camera etc. Both the in-camera split screen and the split screen on the back of the camera seemed to agree precisely, but a subsequent shot of the same test target focused using the split screen in the camera resulted again in 6/7mm difference. I checked it again without film and the split screen at the back and the one in the camera line up at exactly the same spot.

I have read that a split screen on an SLR only 'sees' as though the lens is stopped down a bit, so if there's any focus shift when shooting wide open (which the nikkor 50mm 1.4 apparently exhibits to some extent), then focusing using the split screen at 1.4 won't give you an accurate focus point. Is there any truth to this ?

Something I haven't done was try a plain matte glass screen on the focal plane, I should try that and see if there's a difference I guess.

 

[JRoosa]

Does the split screen show correct focus at infinity?

I have had two FAs do that, and I ended up adjusting the mirror a bit. I think over the years the mirror became slightly out of adjustment, making it seem that the lenses were focusing past infinity, when on the film they were not.

I have an even older FM that is perfect, so who knows what's going on with the FAs.

J.

 

[gone]

Right, could be the mirror, or the lens mount might be off a little? Have you shot it w/ a different lens and had the same problem? If the other lenses work OK, it's your 50 1.4 lens. Or, have you tried shooting some shots out in the real world (not a test screen, just the usual subjects like people, places, and things)?

This is not directed at you, but I see a lot of posts here lately where people seem to over think things quite a bit. If you shoot the camera w/ film and look at the pics, and if you don't see any softness on what you're focusing on, for all intents and purposes it works fine. 6mm is less than 1/8th of an inch when I do a google search. Even a close up portrait focused on the eyes should be OK.

I honestly don't think 1/8th of an inch is going to matter one way or the other on your shots unless you're shooting bugs or something w/ a macro lens, or a micro lens in Nikon Speak.

There's no reason why a SLR or any other type of camera shouldn't give correct focus at any distance just because the lens is wide open.

 

[Daire Quinlan]

This is not directed at you, but I see a lot of posts here lately where people seem to over think things quite a bit. If you shoot the camera w/ film and look at the pics, and if you don't see any softness on what you're focusing on, for all intents and purposes it works fine. 6mm is less than 1/8th of an inch when I do a google search. Even a close up portrait focused on the eyes should be OK.

Yes I've shot it 'in the real world' which led to me deciding to test the combo (fe-2 + 50mm f/1.4) for focusing accuracy. 6mm is quite a lot at close distance if you're shooting a portrait wide open, it meant in my case that the eyes would be visibly out of focus and the bridge of the nose in focus. It could potentially be the mirror, it couldn't be the lens mount because the distance to the lens mount is irrelevant so long as the focusing screen and film plane are at the same distance to it.

The question I'm asking is, shooting a lens like the 50mm f/1.4, which is prone allegedly to a certain amount of focus shift, is the split prism actually accurate when shooting it wide open and up close where any errors would be magnified. i.e. is the split prism showing the focal point at a smaller apparent aperture than f/1.4.

 

[Mark Crabtree]

Most 35mm slr's I've owned have been off a bit. I'm surprised it doesn't get more discussion. Your approach to checking seems good, though I don't know about the split image in that situation. I just use ground glass and a magnifier on the film rails. Of course it is the real world results that matter, and those have always agreed with gg at the film plane for me. Consistent real world errors are what usually lead me to check, though sometimes I do a quick check on a new camera I get. I use fast lenses in low light, so this may be more noticeable for me than people who usually stop down a little.

My Nikkors have always been collimated well for infinity, but I wouldn't rely on that for testing unless you confirm it.

Focus shift moves the plane of focus back (farther away) as you stop down, but is usually barely noticeable because of the increased depth of field. Also, the film can only bulge forward, so that too can move the plane of focus back. So slight back focus can sometimes be explained by those issues, but front focus is most likely the finder screen position. Or possibly the mirror angle. Many/all cameras have adjustments for these, but I don't know them on yours.

The lens mount should not be able to cause front or back focus with an slr since it changes the distance equally to the gg and film.

I don't know the exact answer to your question about the split image and would like to know just how accurate they are, but it seems like the most accurate, though often least convenient, method of focusing. I do notice that moving your eye can sometimes cause changes in the alignment, at least with extreme wide angle lenses. I would prefer ground glass focusing up close. In theory you could check focus stopped down, but it is probably a hassle. And, as momus indicated, any if this is only a problem if it is a problem in the pictures you take.

 

[jochen]

Hello,
I'd use a plane transparent glas, e.g. cut to size from a 5x5 cm slide cover glas. Make some lines with a black Edding on the side toward the lens. With a very strong loupe (10 x to 20 x) you can check the focus if the image of your infinity target and the black lines are sharp at the same time together.

 

[JRoosa]

The tell for my cameras was that focus near the hinge part of the mirror was good at infinity, somewhat off at the center near the split prism, and way off at the other edge of the mirror.

Infinity was fine on film.

The only way to get this would be a crooked focus screen or the mirror off angle.

Focus on the moon or a way distant power pole and move the image up and down the screen and see if focus shifts. Even if your focal plane isn't flat, it shouldn't be biased to be worse in one direction than the other.

The other issue for me is that messing with the focus screen alignment is complex, but tweaking the mirror involves just moving the adjustment screw until the split prism was good at infinity and the ground glass showed uniform focus top to bottom.

J.

 

[Nodda Duma]

Another easy way to check focus is to make a Hartmann mask and point at a bright object like the moon or a flashlight. Then you can easily see if focus is off in viewfinder and at film plane (using a developed piece of film flattened and secured in the image plane if the camera).

If focus is off then you see a double image. Very useful device for testing and simple to make.

 

[RalphLambrecht]

from experience,I can recommend the attached focus test,but I haven't seen'perfect' focus yet other than Nikonauto focus

 

[E. von Hoegh]

Hello,
I'd use a plane transparent glas, e.g. cut to size from a 5x5 cm slide cover glas. Make some lines with a black Edding on the side toward the lens. With a very strong loupe (10 x to 20 x) you can check the focus if the image of your infinity target and the black lines are sharp at the same time together.

The best way to verify focus on an aerial image is by parallax. Nikon made some screens adapted for this, clear glass with very fine lines. The parallax method is best because your eye/brain combo does it's best to make whatever you see sharp - the parallax method (with a bit of practice) is absolutely reliable.