I have a nikkor-m 300/9 that takes pictures that are sharp in the middle and soft/foggy around the edges. If I take it off the lens board and inspect it, it looks clear and sharp all around.
What is the method I should use to visually inspect a lens to see what could be causing this issue in my shots?
I've encountered this in lenses that have been disassembled and improperly reassembled. It can also be due to misalignment of either the camera or the lens on the lens board.
Which format are you shooting with it? At what apertures?
Also make sure the rear element is not being prevented from screwing in all the way when the lens is mounted on the board (lensboard too thick, retaining ring hitting rear element, etc.).
You might try unscrewing both elements and checking for cross-threading, obstructions, etc. Also inspect the lens to look for signs of being dropped, such as bent rings, barrels, etc.
If nothing else works, send it to a competent repair person.
I'm assuming you're using this for 4x5. If you are shooting 8x10 (or larger), this may simply be the well-known characteristic of Tessar-type lenses of being soft at the edges. Stop down more and see if that helps.
Best,
Doremus
I have used one for many years and have never seen any problems. If the lens doesn't exhibit the problems outlined by Doremus, it should cover 8x10. . If after checking the items it is still soft at the edges, it needs to be seen by a lens expert.
I had this problem on one of my lenses. I found that one of the smaller lens elements had been inserted backwards in the rear lens grouping. Of course, could be a reversed element in the front grouping too.
Regarding the question of format and aperture, I'm shooting 4x5 and the apertures are anywhere between 16 and 32. I took several shots, burned a few sheets intentionally, just in case the results came out usable in spite of the ground glass, and a few of them did due to subject matter. Plus I wanted to have samples to show of the effect if I had to send them along with the lens to an expert. Or here.
If it is one of these, how would I notice and would it be possible to fix it myself?Originally Posted by djdister
This is merely a suggestion, using an example which will not necessarily look like your lens design. The attached image shows a lens with a front and rear lens grouping. Consider the vertical line in the middle as where the shutter lies. If you remove the rear lens grouping in this example, the smallest lens element that was closest to the shutter happens to be removable via a very thin retaining ring. In this example, the removable lens element looks like it would be the same regardless of how it is facing in the lens grouping, but that is not the case. One way it works as it should, turned the wrong way around, it gives you a small spot in focus and the rest of the image very out of focus. I found that the removable inner lens element of my Fujinon-W lens was facing the wrong way, and after turning it around and putting the rear lens group back together, I was able to get a normal plane of focus across the image area. Also in my case, the removable inner lens element had one edge more beveled than the other, which matched up with the corresponding bevel of the inner retaining ring. After I turned it around the matching bevels confirmed that this was now the right way for the lens element to be facing. This is a lot of supposition on my part, so this may or may not be the fix in your case, but I think it is worth checking it out.
Here's an example shot from before I turned the inner lens element around. Not much in focus, but it should have been...
And a shot with the same lens after I fixed the orientation of that inner lens element:
That's kind of what it looked like, though yours shows what looks like actual distortion, whereas mine is just blurry. I unscrewed both halves, took a look, saw nothing, put it back together, and suddenly it got sharper. I don't know why, this is the fourth or fifth time I've done so just to visually inspect it. I don't have a very good test setup, so I'll have to try it outside tomorrow to make sure. I know for a fact that the top and middle were both in focus at the same time, though, and crystal clear along those edges. The bottom not so much, but since the problem now seems to be a linear one instead of a circular one, it seems obvious to me that this is a tilt-focusing issue, which is always a pain when the front standard isn't locked in place parallel to the rear, as is the case with this 300 on my shen-hao.
Thanks for the help so far.
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