AZPhotog
Keith S
[FONT="]Hi All.[/FONT]
[FONT="]My CX is having a focus issue where the central portion of a photo (~ 1/4 to 1/3 of it) is focused, but the areas surrounding, out to the edges, are badly blurred. The closer to the edge, the more the blur increases. This occurs at f-stops from 4 to 19 or so, -- which were my test limits used. Of course it is at its worst at the larger stops such as 4 or 4.5 -- my largest stops used for the 100 ASA color print film employed. [Blur would, of course, exist at all the other stops.][/FONT]
[FONT="]It was already determined that the negatives are indeed blurred, so this is not a photo printing or scan issue.[/FONT]
[FONT="]CX HISTORY: Initial photos were never taken after I got it (“D’OH!”) so it is unknown if it functioned then. After receiving it there was a very minor CLA – the focus and aperture rings were frozen at 25’ and f8. Too bad some test shots were not run through it first.[/FONT]
[FONT="]And I do have two separate lens units for this camera. One came with the camera, another off a parts junker. Both lens units are Tricor f2.7 35mm. Both lenses were CLA’d by me, and both have given badly focused photos afterwards. The lens units’ bodies and their other components do not appear to have any physical damages. Dimensions of parts and lens elements “look” to be the same.[/FONT]
[FONT="]At the body CLA, the original “depth setting” of the aluminum ring and associated brass focus ring on the shutter unit were not adjusted (and the rings were not removed and reinstalled.) See a reference below about helicoid height dimensions. The shutter unit WAS removed, but it went back into place and seated in nicely (alignment pins/holes) so all should be good there with the lens flange-to-film spacing.[/FONT]
[FONT="]RFF member Rick Oleson verified that I have indeed reassembled the lenses correctly. Rick has very kindly worked a LOT with me lately on this issue (thanks Rick!), concerning possible problems where an element may not be fully seated, tilted in its seat, or an element is in backwards. The two lens units have broken down several times and I am comfortable now that they are going together correctly, no lens tilt, elements fully seated, elements not backwards, etc.[/FONT]
[FONT="]According to a Wikipedia article on “Cooke Triplet,” the 2.7 Tricor’s match the assembly drawing of the Cooke Triplet as far as lens element orientations. Mr. Oleson stated a known good lens he has used for his photos matches known assembly orientations and also matches a drawing of my lenses that I sent to him as reference. Also, the height of my knurled lens ring (set to infinity) above the focus ring surface matches to his known good camera. So there appears to be no issue from a misadjusted helicoid being too high or too low in my camera body.[/FONT]
[FONT="]If something is being done wrong with my lens assembly technique, it is not making itself apparent. If the focus could be affected by a few thousandths of an inch of lens placement in these lens units, how would one need to deal with that?[/FONT]
[FONT="][Users of Kodak 620 Brownie Hawkeyes sometimes turn their lens around to get the same effect my camera exhibits – central focus, unfocused away from center. Some sort of ethereal effect specific folks like.][/FONT]
[FONT="]With that considered, all things point to a backwards element in both of the lens units, yet the two lens assemblies are correctly assembled, as stated above. There has even been experimentation with putting the dual-concave lens in backwards in both lens sets. That only substantially worsened my out-of-focus issue.[/FONT]
[FONT="]Earlier on, a bench test setup using my two lenses set at 3’ shows one lens ‘focuses’ at 3’ but the other lens never came close to focusing. [That lens unit has been put aside for now.] 3M Magic Tape was placed across the film gate to act as a sort of ‘ground glass screen substitute’ to test the focus after I got several bad photo print sets from both lens assemblies. However, this crude setup is limited in what can be seen as far as overall depth of focus across the entire frame. Resolution is at best barely usable, even under magnification. It could be seen that as the focus ring was turned either side of 3’ the image would go out of focus. One other thing – the camera does try to have things in focus at various distances selected for subjects. Subjects at 3’, 10’, 20’, -- those subject distances do focus at the center as one would expect.[/FONT]
[FONT="]Both lens sets[/FONT][FONT="] have now been very carefully reassembled, watching for lens tilt or unseating during assembly and reinstalling the retaining rings. The retaining ring depth measured to the body has been verified to match the ring depth on Rick’s working lens [basically the ring and body parts are flush to each other,] so interior component spacing would seem to be correct.[/FONT]
[FONT="]Rather than waste any more time and film right now, I am at a loss as to what to try next. It is doubtful that another bench or film test would be useful.[/FONT]
[FONT="]Has anyone with a Mercury II CX run across this focus problem, or have any other suggestions to try? This does seem to be a lens issue from the symptoms, yet nothing is making itself obvious. I guess what really bothers me the most about all this is that this weird issue is such an odd one and so difficult to cure. This has now become more of an amusing hobby attempt for me to “get it going again.”[/FONT]
[FONT="]I would like to solve the issue rather than buy another Mercury II CX and never know what caused the problem. It’s a fun camera to use and I like it a lot, so getting mine working would be satisfying.[/FONT]
[FONT="]Cheers and thanks in advance to all who may respond. (Humorous comments are welcome, too.)[/FONT]
[FONT="]My CX is having a focus issue where the central portion of a photo (~ 1/4 to 1/3 of it) is focused, but the areas surrounding, out to the edges, are badly blurred. The closer to the edge, the more the blur increases. This occurs at f-stops from 4 to 19 or so, -- which were my test limits used. Of course it is at its worst at the larger stops such as 4 or 4.5 -- my largest stops used for the 100 ASA color print film employed. [Blur would, of course, exist at all the other stops.][/FONT]
[FONT="]It was already determined that the negatives are indeed blurred, so this is not a photo printing or scan issue.[/FONT]
[FONT="]CX HISTORY: Initial photos were never taken after I got it (“D’OH!”) so it is unknown if it functioned then. After receiving it there was a very minor CLA – the focus and aperture rings were frozen at 25’ and f8. Too bad some test shots were not run through it first.[/FONT]
[FONT="]And I do have two separate lens units for this camera. One came with the camera, another off a parts junker. Both lens units are Tricor f2.7 35mm. Both lenses were CLA’d by me, and both have given badly focused photos afterwards. The lens units’ bodies and their other components do not appear to have any physical damages. Dimensions of parts and lens elements “look” to be the same.[/FONT]
[FONT="]At the body CLA, the original “depth setting” of the aluminum ring and associated brass focus ring on the shutter unit were not adjusted (and the rings were not removed and reinstalled.) See a reference below about helicoid height dimensions. The shutter unit WAS removed, but it went back into place and seated in nicely (alignment pins/holes) so all should be good there with the lens flange-to-film spacing.[/FONT]
[FONT="]RFF member Rick Oleson verified that I have indeed reassembled the lenses correctly. Rick has very kindly worked a LOT with me lately on this issue (thanks Rick!), concerning possible problems where an element may not be fully seated, tilted in its seat, or an element is in backwards. The two lens units have broken down several times and I am comfortable now that they are going together correctly, no lens tilt, elements fully seated, elements not backwards, etc.[/FONT]
[FONT="]According to a Wikipedia article on “Cooke Triplet,” the 2.7 Tricor’s match the assembly drawing of the Cooke Triplet as far as lens element orientations. Mr. Oleson stated a known good lens he has used for his photos matches known assembly orientations and also matches a drawing of my lenses that I sent to him as reference. Also, the height of my knurled lens ring (set to infinity) above the focus ring surface matches to his known good camera. So there appears to be no issue from a misadjusted helicoid being too high or too low in my camera body.[/FONT]
[FONT="]If something is being done wrong with my lens assembly technique, it is not making itself apparent. If the focus could be affected by a few thousandths of an inch of lens placement in these lens units, how would one need to deal with that?[/FONT]
[FONT="][Users of Kodak 620 Brownie Hawkeyes sometimes turn their lens around to get the same effect my camera exhibits – central focus, unfocused away from center. Some sort of ethereal effect specific folks like.][/FONT]
[FONT="]With that considered, all things point to a backwards element in both of the lens units, yet the two lens assemblies are correctly assembled, as stated above. There has even been experimentation with putting the dual-concave lens in backwards in both lens sets. That only substantially worsened my out-of-focus issue.[/FONT]
[FONT="]Earlier on, a bench test setup using my two lenses set at 3’ shows one lens ‘focuses’ at 3’ but the other lens never came close to focusing. [That lens unit has been put aside for now.] 3M Magic Tape was placed across the film gate to act as a sort of ‘ground glass screen substitute’ to test the focus after I got several bad photo print sets from both lens assemblies. However, this crude setup is limited in what can be seen as far as overall depth of focus across the entire frame. Resolution is at best barely usable, even under magnification. It could be seen that as the focus ring was turned either side of 3’ the image would go out of focus. One other thing – the camera does try to have things in focus at various distances selected for subjects. Subjects at 3’, 10’, 20’, -- those subject distances do focus at the center as one would expect.[/FONT]
[FONT="]Both lens sets[/FONT][FONT="] have now been very carefully reassembled, watching for lens tilt or unseating during assembly and reinstalling the retaining rings. The retaining ring depth measured to the body has been verified to match the ring depth on Rick’s working lens [basically the ring and body parts are flush to each other,] so interior component spacing would seem to be correct.[/FONT]
[FONT="]Rather than waste any more time and film right now, I am at a loss as to what to try next. It is doubtful that another bench or film test would be useful.[/FONT]
[FONT="]Has anyone with a Mercury II CX run across this focus problem, or have any other suggestions to try? This does seem to be a lens issue from the symptoms, yet nothing is making itself obvious. I guess what really bothers me the most about all this is that this weird issue is such an odd one and so difficult to cure. This has now become more of an amusing hobby attempt for me to “get it going again.”[/FONT]
[FONT="]I would like to solve the issue rather than buy another Mercury II CX and never know what caused the problem. It’s a fun camera to use and I like it a lot, so getting mine working would be satisfying.[/FONT]
[FONT="]Cheers and thanks in advance to all who may respond. (Humorous comments are welcome, too.)[/FONT]
Last edited:
Lee Rust
Member
I've never had my Mercury lens apart, but perhaps you're trying too hard to get it 'right' and are stuck on certain assumptions. Most likely one or more of the elements is in backwards, so you could systematically try all possible 'wrong' combinations. If there are only three elements it can't take too long. Designate one of your lenses for experiment and set the other aside. Write a number with Sharpie pen on one side of each element so you don't get lost. Once you figure out the proper arrangement, clean the elements off for critical final assembly. Then fix the second lens. Fear not.
AZPhotog
Keith S
"Thank You" Lee. That is an excellent idea to try.
R
rick oleson
Guest
Handy tip: Isopropyl alcohol isn't the best solvent for very many things, but it IS just the ticket for removing Sharpie ink.
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farlymac
PF McFarland
That can be a frustrating situation. When I did my rebuild, luckily the lens only needed an external cleaning.
I did a rebuild on an Agfa Karat 36, and had the same problem. The thing is I only removed the first element for cleaning. Seems someone before me had flipped the second element. Now that lens was a Tessar design, with the last two elements being a cemented pair, so the only element that could have been flipped was the second one.
Curvatures observed on double convex lens elements sometimes are hard to determine which side has less radius than the other. Sometimes manufacturers will bevel the sides of the element with a matching landing so it's hard to get it wrong, but most of them didn't bother with that, as a simple bench test could determine if it had been assembled correctly before the next assembly step.
When doing the frosted tape check, I usually cut a piece of clear plastic from something like a broken CD holder in a size that will sit between the guide rails in the film chamber, but on the film rails. Then I put the tape on the entire lens side of the plastic, and secure the assembly with a piece of tape on both ends so there is no movement. This gives you a nice solid target that is right in the film plane, no questions asked.
PF
I did a rebuild on an Agfa Karat 36, and had the same problem. The thing is I only removed the first element for cleaning. Seems someone before me had flipped the second element. Now that lens was a Tessar design, with the last two elements being a cemented pair, so the only element that could have been flipped was the second one.
Curvatures observed on double convex lens elements sometimes are hard to determine which side has less radius than the other. Sometimes manufacturers will bevel the sides of the element with a matching landing so it's hard to get it wrong, but most of them didn't bother with that, as a simple bench test could determine if it had been assembled correctly before the next assembly step.
When doing the frosted tape check, I usually cut a piece of clear plastic from something like a broken CD holder in a size that will sit between the guide rails in the film chamber, but on the film rails. Then I put the tape on the entire lens side of the plastic, and secure the assembly with a piece of tape on both ends so there is no movement. This gives you a nice solid target that is right in the film plane, no questions asked.
PF