Frustrating center blur/overexposure problem.

Frisius · Apr 16, 2020

Hi!
For quite a while now, I seem to have a weird problem and I'm unable to find the cause.
In about 15-25% of my pictures taken with a specific lens, there's is a center blur that is often accompanied by local overexposure.

There are some facts:
- I use a Nikon F5 with a 50mm AF-D f1.4 lens
- I scan my negatives with an Epson Perfection v700.
- It happens more often (or is way more visible) in color photographs than in black and whites.
- I often buy film in Eastern Europe and sometimes I have to buy whatever I can get.
- Developing is done by the nearest professional lab wherever I am.
- My camera's internal wiring isn't perfect anymore. I notice this only in the selector dial.

There are some suspicions (some include Hybrid workflow):
- Maybe my lens is broken, either decentered or it gives a focus pull in the split second that I click (because of wiring).
- Maybe my film is of bad quality and doesn't stay flat inside the camera. But it also happens sometimes with high quality film.
- Or, same but it doesn't stay flat in the scanner. (Used two different scanners, same outcome, so it's not a broken scanner.)

Otherwise I don't know and it's driving me mad. I can't afford to replace ALL of my equipment so I would like to find out the culprit!
Please have a look at the examples. I hope someone recognises the problem!
Many thanks in advance!

MattKing · Apr 16, 2020

Welcome to Photrio.
I am assuming that you scan your film in strips.
By chance are the problem images always occurring at the same location in the negative holder? If so, that would mean a problem in the scanner.
Can you see evidence of the problem on the ((magnified) negatives themselves when you look at them away from the scanner?

Frisius · Apr 16, 2020

@MattKing
Thanks!
No, the problem seems to occur at random, but it is clustered around the use of this lens. It took me a while to figure that out, since I exchange lenses regularly.
I have found evidence of the problem in negatives when I held them up against the light and viewed them with a magnifying glass. But it is not always so clear. And for example the picture of the girl could at first glance be just a focus mishap by me.
I should have made it clearer maybe but I am quite sure that the problem is caused by either my lens or the camera in combination with the lens.
Thanks for the effort though!

jtk · Apr 16, 2020

Forget your initial diagnosis (even tho it may be correct) and consider possibility that the problem is with the pressure plate. Might be a film chip.

Huss · Apr 16, 2020

Have you tried another lens? It looks like something is wrong with/at the rear elements.

shutterfinger · Apr 16, 2020

Place any suspect negative flat on a light box and examine with a good loupe. Pay close attention to the sharpness of fine detail.
Check the suspect lens for a loose element at the front or rear by feel, internal by gentle shaking. Check for play in the focusing, and verify the aperture is operating smoothly. Verify that the lens mount is secure and not visibly worn.
If the body will operate on B with the lens removed load a scrap roll of film, lock the shutter open on B and check that the film is flat and secure at the film plane.

Frisius · Apr 16, 2020

@jtk and @shutterfinger If it is the pressure plate, then why does it only occur with the 50mm lens? I will check in B as shutterfinger recommends. I checked negatives with a loupe, and even though it's not always clear, sometimes it is. For example, on the negative of the picture with the balcony (nr4) I can't say for sure that I see the problem, however on the first negative (girl) it is obvious...
I will check my lens tomorrow (bedtime here). But I can already say that I ask a lot of my equipment: it's always hanging around my shoulder and I have used it in self defense on multiple occations. It's leading a rougher life than me, so maybe this lens is just done for.
Will report tomorrow.
Thanks people!!

Frisius · Apr 16, 2020

And @Huss What makes you say that? Why specifically the rear? (Have tried other lenses and then the problem does NOT occur.) Thanks!

Patrick Robert James · Apr 16, 2020

It looks to me like there is an issue with an element, or maybe a group. Perhaps someone took it apart and didn't put it back correctly. That is definitely your lens though. No chance something like that could happen in the camera.

shutterfinger · Apr 16, 2020

There is a factory service manual for a 50mm f1.4D lens at http://arcticwolfs.net/
This is the lens diagram:

Elements G1, G2, G3, G6, G7 are air spaced; elements G4 and G5 are a cemented pair.

John Koehrer · Apr 16, 2020

I've run into a lens or two with a loose element as shutterfinger mentioned.
There will be a barely noticeable sound from the aperture blades but a loose element rattles
relatively loudly.

mohmad khatab · Apr 17, 2020

Frisius said:
Hi!
For quite a while now, I seem to have a weird problem and I'm unable to find the cause.
In about 15-25% of my pictures taken with a specific lens, there's is a center blur that is often accompanied by local overexposure.

There are some facts:
- I use a Nikon F5 with a 50mm AF-D f1.4 lens
- I scan my negatives with an Epson Perfection v700.
- It happens more often (or is way more visible) in color photographs than in black and whites.
- I often buy film in Eastern Europe and sometimes I have to buy whatever I can get.
- Developing is done by the nearest professional lab wherever I am.
- My camera's internal wiring isn't perfect anymore. I notice this only in the selector dial.

There are some suspicions (some include Hybrid workflow):
- Maybe my lens is broken, either decentered or it gives a focus pull in the split second that I click (because of wiring).
- Maybe my film is of bad quality and doesn't stay flat inside the camera. But it also happens sometimes with high quality film.
- Or, same but it doesn't stay flat in the scanner. (Used two different scanners, same outcome, so it's not a broken scanner.)

Otherwise I don't know and it's driving me mad. I can't afford to replace ALL of my equipment so I would like to find out the culprit!
Please have a look at the examples. I hope someone recognises the problem!
Many thanks in advance!
View attachment 244067 View attachment 244068 View attachment 244069 View attachment 244070 View attachment 244071

You are from the beautiful Vienna ...
You can go to Mr. / Rudi - at his home if the quarantine procedures allow you to do that, maybe he lives on the back street of your street - search for it and go to him with the camera and negatives and inevitably he will search this problem in a wonderful scientific way and will tell you the real reason.
- Do not forget to offer him condolences and sympathy as his father passed away - that great man, the professor at the College of Agriculture, for nearly a week.

grain elevator · Apr 17, 2020

To me it doesn't seem plausible that the lens could cause something so local. De-centering should be visible most strongly in at least one corner, not near the center, and an element moving back and forth I can't imagine to cause something only locally, either. A chip in, or dirt on, the rear element, possibly, although you would have seen that and even that I'd expect to have more of an effect on the whole image.
Even though they also seem unlikely, your suspicion that the AF mechanism moves around during exposure seems more plausible to me, but I don't know much about AF. Otherwise I think the possibility that the correlation with the lens is incidental is still more likely than an optical defect in the lens. Do you by any chance only use wide angles otherwise, where DOF might mask the issue? It could be a pressure plate or even film transport problem that leads to a bulge, or indeed an issue with film flatness during scanning, but you have ruled that out by examining the negatives.
Don't withhold the stories how you "used it in self defense on multiple occasions" form us!

Frisius · Apr 17, 2020

@mohmad khatab I live in Vienna but I'm currently in isolation in the Netherlands and not able to travel back since Austria, Bavaria and Czechia are locked. But thanks for the tip and I will definitely keep mr. Rudi in mind.

@John Koehrer All AF lenses rattle a little bit and if I hold the plastic I hear almost no rattle other than what I suspect to be the aperture blades.

Frisius · Apr 17, 2020

@grain elevator My other lens is a Nikon AF-S 24-85mm f3.5 that I use mainly in the 24 to 50 mm range. So you could be right about the DOF masking the problem, however, I also use it often in 50mm because I don't use my 50/1.4 anymore, and I've never had any issue with it.
I also researched the pressure plate with a film in B with the lens off and it seemed super flat.

This is not really the place for a long story I'm afraid but in the 20+ years that I've travelled and photographed I have at some occasions used my camera to punch robbers, swing it at rabid dogs and I fought a policeman at the Moldovan border to get it back. Maybe some day I'll share them.

Frisius · Apr 17, 2020

Okay so I borrowed someone's digital camera (I am an absolute rookie if it comes to digital photography) and fit the 50mm f1.4 lens and I got the same results. On the two examples you can see 1: this weird blue shine around overexposed parts (that you see for example in the original last 3 pictures) and 2: weird focus behaviour.
It gets more and more obvious to me that the lens is the culprit. I still don't know what it is, but maybe I should just buy a new one and move on.

grain elevator · Apr 17, 2020

I don't see an unsharp area like in the pictures in post #1 in these digital ones. The blue shine is bad though.

Frisius · Apr 17, 2020

@grain elevator In the second digital pic, wouldn't you say that the (overexposed) shrub outside is more in forcus than the wooden box with papers? All while the heating pipes are also in focus. Similar to- for example- post#1 pic 2 where there is focus in the foreground and in the background but not in between.

grain elevator · Apr 17, 2020

Possibly, but not positively like in the pictures in post #1. It's very hard to tell because of the overexposure and as the foreground objects aren't in one plane.
Can you take a picture in which we can clearly see the shape of the focal "plane"? Something like a checkerboard, newspaper, textured floor... but not straight on, but at an angle, so that if the focal plane is flat, the area in focus will form a horizontal (or vertical if you prefer) line.

cowanw · Apr 17, 2020

I agree, I think you need to get systematic. I would suggest three metre sticks set left, right , and centre at an angle of 30 degrees or so. Or any constantly lit (no mixed indoor and outdoor lighting) and repetitive pattern ( looking at apples and apples) against a uniformly lit background (to address local overexposure) subject.
You see picture one as being the most definitive, but I see a focus at the front of shoulder (which is equivalent to ear distance) which may well just be a depth of field/fstop issue.
Time to get scientific here!

shutterfinger · Apr 17, 2020

So you have eliminated the camera body and confirmed its that lens. With the caps removed sit the lens front down on a flat surface and measure from the table/lens front to the lens mount, is it the same distance at any point around the lens? Do this with the focus at each extreme.
Is the mount tight to the lens body? Is the mount heavily worn? Is there any oil on the internal lens elements or is the lens crystal clear?

Frisius · Apr 17, 2020

@grain elevator and @cowanw
Yes time to get scientific. But, it also takes a lot of time and I'm close to giving it up and just buying a new lens. I'll try to do a test tomorrow, when the sun shines.

I feel the blur occurs mainly (but again- not always) when there's high contrast in the picture. I haven't been able to reproduce a center blur in taking 50 pictures of a tiled floor. The blue shine is there and sometimes creates the sense of a blur, mainly when there's an overexposed rim.
I did find another analogue picture where the center blur is well, I would say, irrefutable.
Sorry for all these bad pictures btw! I'm usually quite artistic

Frisius · Apr 17, 2020

shutterfinger said:
So you have eliminated the camera body and confirmed its that lens. With the caps removed sit the lens front down on a flat surface and measure from the table/lens front to the lens mount, is it the same distance at any point around the lens? Do this with the focus at each extreme.
Is the mount tight to the lens body? Is the mount heavily worn? Is there any oil on the internal lens elements or is the lens crystal clear?

Lens measures the same all around at both extremes (42-50mm). Mount is tight, lens seems absolutely clear and there's no wear on the mount that concerns me.

cowanw · Apr 17, 2020

Yes that looks very bad. You are not shooting at f1.4 are you?

Frisius · Apr 17, 2020

@cowanw I am often yes, in that example most probably, why?

Frustrating center blur/overexposure problem.

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