Re: Focus Issue around edges
A couple of possible issues: One, if the camera's focussing screen is not original - it may have been replaced incorrectly... with a front-mounted separate fresnel lens without a proper re-positioning of the actual ground glass. There is a formula for this and when I purchased a separate fresnel from Bill Maxwell for my 5x7 he shared this formula with me so I could make my own adjustment. At any rate...this possibility, combined with a possible field curvature of your Nikkor lens (many lenses have very slightly (or more pronounced) curved fields), might conspire to give you the result you show...where the now incorrect focus plane would still allow a small area of "focus" when the lens is stopped down...due to its field curvature. Then again...the wide open result looks too similar to be fully explained by this. Hmmm...perhaps your lens' elements are out of proper position? I once was given a "defective" enlarging lens to mess with...and discovered that one of its elements had been installed
backwards! Probably a DIY repair gone wrong or accompanied by mind-altering substances.
Or...maybe you have a combination fresnel/groundglass which is plastic, and you are putting enough pressure on this with your focussing loupe and this is deforming the screen slightly? This actually happened to me when I briefly owned a Linhof Technikardan - which has (IMHO) a lethal design flaw in that the supplied plastic fresnel/screen is (or was, if Linhof has since corrected this) supported by four relatively small plates, and not by the proper recessed shelf which would support the entire perimeter. (why, oh why, did LINHOF do this?) At any rate...I found that only sight pressure with my focus loop was deflecting the screen!
Or...perhaps one of your lens cells has gotten a bit loose?
Re: Focus Issue around edges
A Nikkor W should not have appreciable curvature of field. Nor should it be fuzzy around the outside of the image, especially when you are using no movements that really move the sides of the image out of the image circle that much. If I were you, I'd check to make sure all my lens elements were in tightly and that everything is screwed tight to the shutter. Test by shooting a planar surface (sheet of newsprint is good) with the camera zeroed and the the back parallel to the subject plane. Shoot at a wide aperture to minimize depth of field and see if you still have out-of-focus edges. If so, I'd suspect a problem with the lens.
Best,
Doremus
Re: Focus Issue around edges
Check that the shutter is properly mounted to the lens board, the lens board is seated in its frame, and the front standard is parallel to the film plane. However, f/45 should have reduced that problem. Doremus' suggested test, or shooting a textured wall, is a good idea.
2 Attachment(s)
Re: Focus Issue around edges
Thank you guys, I will develop a couple more test shots today. Here are two photos of what it looks like in the ground glass, with the aperture wide open at f/5.6.
John Layton, you are correct when you suspected that I have a plastic fresnel/ground glass combo. I've removed it, flipped it around, upside down, even pressed on it a bit, etc, but still get the same results, so I suspect that it's a lens issue.
I have one shot dead on with everything zeroed, and one shot with front rise. As you can see in the latter, the focus is no longer at dead center when rise is applied, but at above dead center. I hope this helps.
Attachment 163065Attachment 163066
Re: Focus Issue around edges
Quote:
Originally Posted by
John Layton
A couple of possible issues: One, if the camera's focussing screen is not original - it may have been replaced incorrectly... with a front-mounted separate fresnel lens without a proper re-positioning of the actual ground glass. There is a formula for this and when I purchased a separate fresnel from Bill Maxwell for my 5x7 he shared this formula with me so I could make my own adjustment. At any rate...this possibility, combined with a possible field curvature of your Nikkor lens (many lenses have very slightly (or more pronounced) curved fields), might conspire to give you the result you show...where the now incorrect focus plane would still allow a small area of "focus" when the lens is stopped down...due to its field curvature. Then again...the wide open result looks too similar to be fully explained by this. Hmmm...perhaps your lens' elements are out of proper position? I once was given a "defective" enlarging lens to mess with...and discovered that one of its elements had been installed
backwards! Probably a DIY repair gone wrong or accompanied by mind-altering substances.
Or...maybe you have a combination fresnel/groundglass which is plastic, and you are putting enough pressure on this with your focussing loupe and this is deforming the screen slightly? This actually happened to me when I briefly owned a Linhof Technikardan - which has (IMHO) a lethal design flaw in that the supplied plastic fresnel/screen is (or was, if Linhof has since corrected this) supported by four relatively small plates, and not by the proper recessed shelf which would support the entire perimeter. (why, oh why, did LINHOF do this?) At any rate...I found that only sight pressure with my focus loop was deflecting the screen!
Or...perhaps one of your lens cells has gotten a bit loose?
Linhof never supplied a plastic Focusing screen on new cameras. All Linhof cameras ever made came with a glass groundglass.
You probably purchased a used camera that had the original ground glass replaced by someone with a Linhof Super Screen. These were never sold or used by the factory and was an optional add on that was only available in the USA and Canada and was sold under that name only because Linhof gave permission to use that name. The screen, and other similar ones like the Beattie, were manufactured in Rochester, NY by Fresnel Optics, the parent company of Beattie.
Since the screen developed the possibility of sagging Fresnel Optics kept changing the composition of the screen but they were never able to totally eliminate in so it was discontinued. It would not sag if a long shim like a matchstick was placed under the Super Screen on either long side of the screen. If one had added the Grid Overlay, which was made from float glass, to the top of the Super Screen then the pressure of the loupe could not make it sag.
Re: Focus Issue around edges
Alex,
There appears to be something wrong with your lens. Do you have other lenses? If so, mount one and see if you have a similar problem.
About your lens: Is it new to you? Have you shot with it successfully without this problem? Has it been damaged (e.g., dropped) recently? Have you had the lens repaired/disassembled recently (maybe incorrectly reassembled)?
I can't really imagine how this could be a camera problem.
Doremus
Re: Focus Issue around edges
Wista used their own combo screen fresnel and ground side it's plastic on my 45DX and excellent, very bright ad accurate..
Have you used the same lens on your monorail camera and is it OK, if not try it and if it's OK that eliminates it being a lens issue and should be the first thing you test. It's also possible someone's fitted the wrong screen to your Wista.
With the first image I'd question why you focussed at Infinity, that's not good practice.
Ian
Re: Focus Issue around edges
Quote:
Originally Posted by
Doremus Scudder
Alex,
There appears to be something wrong with your lens. Do you have other lenses? If so, mount one and see if you have a similar problem.
About your lens: Is it new to you? Have you shot with it successfully without this problem? Has it been damaged (e.g., dropped) recently? Have you had the lens repaired/disassembled recently (maybe incorrectly reassembled)?
I can't really imagine how this could be a camera problem.
Doremus
+1
Do you check if the lens originally has some washers between cell/shutter, and maybe missed?. Or the opposite scenario?
Is the shutter(aperture diaphragm) working properly? I mean during exposure?
Is it assembled on the correct shutter?
Scanned photos still may corrected before downloading.
Good luck Alex.
Re: Focus Issue around edges
Your lens is diffraction limited at f22. Have you tested it at 22?
Re: Focus Issue around edges
The only time I have seen something like that is when I took the whole rear cell off the back of my 360mm tele-xenar. It looks like a major lens issue. Like others have said it could be there is a washer/spacer missing, maybe someone has combined cells from two different lenses for some reason. It really needs to be in the hands of someone skilled in lens repair or you need to compare it to another example of the same lens, unless of course it is simply badly assembled in some obvious way.
Re: Focus Issue around edges
Are you sure you remembered to stop down or the aperture mechanism is not working. Posting a picture of the negative is always helpful.
Re: Focus Issue around edges
Quote:
Originally Posted by
Thalmees
+1
Do you check if the lens originally has some washers between cell/shutter, and maybe missed?. Or the opposite scenario?
Is the shutter(aperture diaphragm) working properly? I mean during exposure?
Is it assembled on the correct shutter?
Scanned photos still may corrected before downloading.
Good luck Alex.
Thanks Doremus and Thalmees. I have shot good images with this lens only when stopped all the way to f/64 and with movements. It's fine for still life because I can take long exposures to work with the small aperture, but I've never been able to get it it completely sharp across the whole image.
The lens I purchased used ($800 for the camera, lens, and 2 holders, seemed like a great deal). Iris looks and behaves fine, and the shutter speeds seem to be pretty spot on. Nothing on the lens feels like it's loose. There are some scratches/dings on the backside, possibly from the rear element housing getting continuously bumped when removing the lens.
It's more than likely the problem is stemming from either being banged by the previous owner or an incorrect reassembly. I don't feel comfortable taking it apart myself, so I will just have to send it in somewhere to get repaired.
Re: Focus Issue around edges
Quote:
Originally Posted by
Alex DiBacco
... I don't feel comfortable taking it apart myself, so I will just have to send it in somewhere to get repaired.
Hello Alex,
I do not think so, at least at this time. Sorry for this expression.
When you would like to swap lens boards, you should take lens cells from shutter or at least the rear cell, to access the flange ring. It's just counterclockwise disassemble.
But, please watch any spacers, they could be located:
1. Between, the rear element of the front cell, and shutter. Or.
2. Between, the front element of the rear cell, and shutter.
3. One or more spacers.
Repairing shutter is different story, though some LF photographers can repair minor things.
