Manual Focus Lens - Focus off? What is happening?

Nikanon · Jul 28, 2011

Hello,

I own a 50mm Nikkor f1.4 AIS. I had begun to test this lens today to see just how sharp it is at f1.4, when I came across something interesting. I was using a chart and shooting at it from an angle so as to get only one line in focus and then zoom in on the digital image and check its sharpness. When I focused on a point (I did this MANY times, tripod and not) the focused area in the image was always closer to me than where I focused ( I have better than perfect, around 20/16 vision). I am confused now, because if the lens is focusing to my vision, which in the viewfinder should be aligned with the focal plane where the sensor or film sits, should not any error be corrected when I focus? I tested my other lens the 28mm f2.8 AIS as well and found that exactly the line I focus on was the only thing in focus all the way open. I narrowed the problem down to this particular lens. What is going on?

Nikanon · Jul 28, 2011

Im actually not positive what version this lens is. Its a 50mm Nikkor f1.4. It has a silver ring in front of the aperture with only a single black dot at the selected aperture position and the focus point distance. There are smaller aperture numbers on the end of the lens closest to the camera so I can read them through my F3 viewfinder. The aperture numbers are color coded to the DOF guide scale. I cannot find an image of my lens online anywhere. It has block grips on the barrel, most of the ones I see online have two rows of these, mine has three. The lens also gets a little larger as it goes towards the front element and dips down into the front element. The serial number is 2825811.

Nikanon · Jul 28, 2011

http://www.photosynthesis.co.nz/nikon/k5014.jpg

This is the closest image to the lens that I can find anywhere. However, mine also has the smaller aperture numbers below the larger ones to be viewed in a viewfinder. The aperture ring also looks a bit different.

John Koehrer · Jul 28, 2011

It's either an AI or AIS.
If you look at the lens mount with the meter prong at the 12 o'clock position. There's a groove at ~9 o'clock. If it's an AIS it will have a small groove just above and slightly inside the groove. If there's no groove, it's an AI lens.

Does the lens focus correctly on the F3? You can check at the film plane by putting a ground glass or even frosted scotch tape on the rails and check focus there.

If they don't agree, the image at the rails is correct. There's a possibility that the set screws holding the focusing ring weren't tight enough and allowed the ring to move slightly. The fix is this: peel the rubber grip off, find the screws, loosen them set the focusing ring at the infinity stop(without moving the barrel) and snug the screws down. They're right around 1mm screws, use a small screwdriver.=)

Just saw the pic, The lens in the pic is a non-AI lens but yours is a lens that has been AI'd. Likely
from when Nikon was offering the service.

mopar_guy · Jul 28, 2011

A 28mm lens will have more depth of field than a 50mm lens, so you may in fact not be focusing the wide angle where you think you are.

Nikanon · Jul 28, 2011

Im aware of the depth of field issue. The replicate a shallow depth of field I moved very close at a steep angle on the chart, since my 28mm can focus VERY close, and the depth of field was very similar, the point of sharpest focus was dead on.

Nikanon · Jul 28, 2011

Thanks John, now how the hell do I get this rubber off? One thing I did notice about this lens was that it shifts just a tad when I shoot. That must be the conversion issue.

Rol_Lei Nut · Jul 28, 2011

Even though the 28mm seems to focus accurately, I'd still consider a camera body problem (which BTW?): misaligned mirror or badly seated focusing screen.
Try to beg, borrow or steal a longer lens, which will make testing easier.

The AI conversion shouldn't make the lens "shift", whatever you mean exactly by that. If there is any play in the lens mount (loose mount screws or worn flanges), that could also cause the problem.

BobD · Jul 28, 2011

What body are you using the 50/1.4 on?

Bob-D659 · Jul 28, 2011

You get the rubber off by sliding a thin piece of flexible plastic under it, a piece of 4x5 sheet film works perfectly. Slide it around all the way to break any glue bond and then slide the rubber sleeve off the front. That lens in a pre AI one according to the serial number, and likely has the factory conversion aperture ring on it. Check for loose screws in the lens mount.

Edit: I suspect he is using a digital body.

If you are using one and focusing manually, the viewfinders on AF type cameras are not meant for manual/visual focusing. You are looking at an aerial image, not one focused on a ground glass. If the diopter setting on the camera is off, or if your vision is not 20/20, or if you have young eyes(under 40+), your eyes can easily focus on the wrong image plane in the viewfinder, and that will make the recorded image out of focus.

eSPhotos · Jul 29, 2011

If you're shooting stopped down and this happens then its symptom is known as 'front focus' - lens problem. However if it happens while aperture wide open (f1.4) then it is likely the fault is in the camera. As mentioned, the 28mm has much wider depth of field so you may not have noticed the same issue with the 28mm.

Smudger · Jul 29, 2011

I think,if we get more info ? Focus is out? -assessed at F1.4./F2 ?/F2.8 ?
DSLR (Whoops,sorry) should be ok if it has a manual confirmation of focus mode. Use central focus spot -normally the most accurate.
Another observation - the Nikon lens mentioned does NOT have a flat focus field - a poor choice for document copying for example..

Smudger · Jul 29, 2011

I think,if we get more info ? Focus is out? -assessed at F1.4./F2 ?/F2.8 ?
DSLR (Whoops,sorry) should be ok if it has a manual confirmation of focus mode. Use central focus spot -normally the most accurate.
Another observation - the Nikon lens mentioned does NOT have a flat focus field - a poor choice for document copying for example..

George Collier · Jul 29, 2011

Something bothers me about the set screw suggestion - if the focusing ring was out of position, it would display an incorrect distance, but the problem isn't the distance displayed vs the real distance, it's that when the image is focused on the ground glass in the pentaprism, it isn't focused on the film. Moving the focus ring will change the indicated distance, but won't affect the GG / film plane problem. Am I missing something?

What model is the camera?

John Koehrer · Jul 29, 2011

George Collier said:
Something bothers me about the set screw suggestion - if the focusing ring was out of position, it would display an incorrect distance, but the problem isn't the distance displayed vs the real distance, it's that when the image is focused on the ground glass in the pentaprism, it isn't focused on the film. Moving the focus ring will change the indicated distance, but won't affect the GG / film plane problem. Am I missing something?

What model is the camera?

First camera was a dig*, second was an F3.
Thinking(?) about it you may very well be correct.

I understand the problem to be>In focus through VF, oof at film. The indicated distance isn't a problem. The test he's doing is at close distance.
I think I would verify that infinity focus is accurate first. focus at film plane, then check VF. If they DISAGREE, adjust the focusing ring.

FWIW Practical infinity is around a block away, theoretical is 500 or 1000 times the focal length. top of an antenna/water tower, high building etc.

I'm wondering if it's a problem with the error on the electric camera and shimming of some sort. I understand there are a lot of the Voigtlander and FSU lenses that need to be shimmed to focus properly on those things.

Bob-D659 · Jul 29, 2011

The focus test should compare the image, viewfinder and the autofocus confirm light. If the image agrees with the focus confirm light, then the discrepancy lies in the viewfinder and operator.

darinwc · Jul 30, 2011

If the AI conversion was aftermarket, or if you are using a poorly designed adapter, it is possible the lens is not parallel to the film/sensor plane.
Alternatively, it may also be that the lens is not assembled correctly and it is not as sharp as it appears in the virefinder. it is very hard to judge sharpness in the viewfinder.

2F/2F · Jul 30, 2011

The stock focusing screens (and all but a few optional ones) for AF cameras are cut with a pattern that is optimized to be nice and bright for slow lenses. That is great if you use slow lenses, but not if you use fast lenses. The screens will generally show you the D of F and viewfinder brightness at f/2.8 or higher, regardless of how fast your lens is. This means that when using lenses faster than f/2.8 in very critical focusing (up close wide open, for example), things can appear tack sharp in the viewfinder when they are not really tack sharp at the focusing plane. It happens all the time with my 50mm f/1.2 on my 10D. Try using your focus confirmation dot in the camera and see if it helps. I have learned through experience to use that dot whenever possible if I am using a lens that is faster than f/2.8.

Chan Tran · Jul 30, 2011

If the OP eyesight is very good (i used to have such eyesight hichic) then I think the problem is with the camera. The op didn't actually shot some film with the F3 and see if he has the same problem.

removed account4 · Jul 30, 2011

why don't you bring your camera+lens in person to a repair shop
drop it off and get a free estimate to see what is wrong with it ...
instead of having every one here make suggestions as to what *might* be wrong.
an estimate is usually free, and repair people will have the camera+lens in hand
and be able to tell you exactly what is wrong ... instead of a guess.

fstop · Jul 30, 2011

jnanian said:
why don't you bring your camera+lens in person to a repair shop
drop it off and get a free estimate to see what is wrong with it ...
instead of having every one here make suggestions as to what *might* be wrong.
an estimate is usually free, and repair people will have the camera+lens in hand
and be able to tell you exactly what is wrong ... instead of a guess.

A: its only happening with one lens apparently
B: camera repair shops are as bad as gas stations for charging for unecessary/phony work
EI: "the focus problem is the knifler pin, we can fix it for $28.00 come back tomorrow" they hit it with compressed air and wipe it off with a silicone treated cloth,whack you $28.00

:munch:

Chan Tran · Jul 30, 2011

I don't think it's possible for many people to bring a camera+lens in person to a repair shop, and get a free estimate...
I don't know of any repair shop around here. I know a number of repair shop else where that is too far to get there and they don't do free estimate. If you don't want to repair, you will have to pay them to get it back.
Camera repair isn't so much a viable business anymore. A lot of time the work is very labor intensive and customers don't pay for repair that is more than the camera is worth. Charging less the repair shop can't make a living.

fstop · Jul 30, 2011

Chan Tran said:
I don't think it's possible for many people to bring a camera+lens in person to a repair shop, and get a free estimate...
I don't know of any repair shop around here. I know a number of repair shop else where that is too far to get there and they don't do free estimate. If you don't want to repair, you will have to pay them to get it back.
Camera repair isn't so much a viable business anymore. A lot of time the work is very labor intensive and customers don't pay for repair that is more than the camera is worth. Charging less the repair shop can't make a living.

No repair shops locally here anymore, much less camera shops. they are all gone.The biggest one, I swear would use a hammer and chisel on equipement to perform repairs and THE LAST roll of B&W they did for me had F'ing purple prints!

I've seen bodies where people swear the body was at fault for focus issues. I take a lens and focus on something with a known good body, then without changing focus swap the lens the the "afflicted" body to see if it changed. Most times you need to adjust focus very slightly, but there should be no gross errors.

Diopters, bad vision, mis use of "split pea" have all been major contributors of focus issues that I have seen.Not to say there could be a problem but its rare the body is at fault.

removed account4 · Jul 30, 2011

toofuny and sad -

i have 2 repair shops close to me that give free estimates .... sorry to hear that
repair folks near you are not to be trusted ! sounds to me like it is more than a canned air issue ...

good luck with your problem!!
john

Manual Focus Lens - Focus off? What is happening?

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