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Thread: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

  1. #21

    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    This answers a lot of my questions, I've had a very frustrating month with this problem. My Chamonix 45N arrived in May, and most of my photographs are very much out of focus. I shoot mainly landscapes, so am focusing on infinity, but am also shooting them at night, so need the faster apertures, or else I'm standing for 45 minutes to take a single photograph. I know they're in focus on the GG, this I can see quite clearly through my loop, but so far only shots at F16 are beginning to approach being in focus.

    One additional problem I've noticed is that the film plane and GG/Fresnel plane are not parallel. I have about 20 sheets, all shot with various lenses, various new film holders, and at various apertures and all of them show the image more in focus on the far right side and less in focus on the far left side. This consistency seems to indicates a problem worse than just Chamonix not compensating for the Fresnel thickness in placing the GG. Given that I seem to be the third person in a few weeks to notice this, has anyone else seen this?

    I do trust that Chamonix will help resolve this (I only emailed Hugo about this today), but folks have mentioned about sending their cameras in to be "calibrated". Who does this sort of calibration?

  2. #22

    Join Date
    Jun 2007
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    26

    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    I think you must be unlucky.
    I've been been using 4x5 cameras for decades and are now using two Chamonix cameras and I think they are the best all round 4x5 available on the market today.
    No problems with focusing, the back and screens are interchangeable between the two and the focus still spot on.

    JON.

  3. #23

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    Jun 2009
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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Mark,

    Try placing the fresnel on the external GG surface and using critical focus wide open with the same night scenes, but in daylight. Use a loupe to see if the focus plane is flat on the gg. Also check to see if your film carriers are sitting flat on all four edges when in the camera.

    What lenses have you used when having focus trouble?

    I did have a similar (uneven) problem with some images with my 90mm Rodenstock with the fresnel between lens and GG. I'm still running tests, so too soon to tell about flatness of film back.

  4. #24

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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Quote Originally Posted by Mark Jaremko View Post
    One additional problem I've noticed is that the film plane and GG/Fresnel plane are not parallel. I have about 20 sheets, all shot with various lenses, various new film holders, and at various apertures and all of them show the image more in focus on the far right side and less in focus on the far left side. This consistency seems to indicates a problem worse than just Chamonix not compensating for the Fresnel thickness in placing the GG. Given that I seem to be the third person in a few weeks to notice this, has anyone else seen this?
    I only recently acquired my first wooden field camera, a Chamonix 5x8. I've always used metal cameras, like the Toyo 45AII, but wanted to get a feel for what the wooden camera experience is all about. While the Chamonix does seem decently made (I haven't put a micrometer to it) I'm really amazed by the total lack of "0" detents. It means you have to zero every aspect of the camera via GG inspection, for each and every new shot! While I'm very much into the slow-down mantra of LF shooting, having to go through this tedium for each new set up is a bit over the top... IMHO.

  5. #25

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    May 2009
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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Quote Originally Posted by Mark Jaremko View Post
    I do trust that Chamonix will help resolve this (I only emailed Hugo about this today), but folks have mentioned about sending their cameras in to be "calibrated". Who does this sort of calibration?
    Bill Maxwell referred me to Bill Moretz of Pro Camera, Inc. The screen is going straight to him for installation.

  6. #26

    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Thanks everyone for the information, this was my first post as I’m quite new to the LF area, this being my first 4x5 camera, so I’m certainly doing a lot of learning, and the information on this forum has been extremely useful.

    The two lenses that I’ve done all my testing with are :
    Schneider Super Angulon XL 90mm f5.6
    Schneider APO-Symmar 210mm f5.6.

    Most of my tests were done with the 210. It turns out that my subject, distance cityscapes, is an ideal test subject, the distance city light make tiny pin point sources of light that are easily seen and focused on in the GG, and similarly quite easy to tell if the resulting film is in focus.

    I took the GG holder apart and broke out the digital micrometer to take some measurement. I think I might have found a potential problem, assuming my numbers are correct. Here’s what I found.

    I measured an approximate distance from edge of film holder to GG plane to be 4.745mm on the left side, and 4.815mm on the right side (based on an average of 10 measurements). Being a difference of 0.069mm, which I’m not sure is significant.

    My understanding from an earlier post is that the specification for a film holder is 0.197”, which comes out to 5.00mm. I decided to see how accurate this was by measuring one new Fidelity Elite holder. I came up with measurements of about 4.93mm after many samples. It’s difficult to measure this distance with a standard micrometer due to ease of introducing flex in the plastic holder. This was only a sample size of 1 holder and so not statistically relevant, and it’s pretty close. Let’s go with 5.00mm as the correct distance.

    If that’s the case, then my GG was held anywhere from 0.187mm to 0.255mm closer to the lens than the film plane. Then you have to compensate for the Fresnel, which is between the GG and the lens.. The Chamonix Fresnel was a bit harder to measure, after 10 or so measurements, I saw values anywhere from 1.65mm to 1.85mm at difference areas around the lens. Another post (If I understand correctly), suggested that the effective focal plane is 1/3 the thickness of the Fresnel closer to the lens due to the Fresnel acting as a lens itself. If that’s the case, and we assume the 1/3 compensation value posted previously, then we’re at 1.77mm (average thickness of my Fresnel) / 3 = 0.59mm.

    Now the difference between film plane and GG plane grows to 0.775mm and 0.845mm, which seems like it would be very significant.

    So I removed the Fresnel. Unfortunately, with a Chamonix 45N, you can not mount the Fresnel over the GG because it’s actually shorter than the GG, and sits on a recessed ledge in the holder (to allow the GG to independently sit a fixed distance with or without the Fresnel). I need to find someone who can cut me a larger Fresenel.

    I then built 0.20mm of shims to places to move the GG surface back by that amount. This turned out to be easy as sheets of clear transparency film (the kind you use in printers), was 0.100mm, and very consistent across all the measurements I took. I put the GG holder back together, and at 1am last night, headed out the door to shoot some film. I found the 90mm impossibly difficult to focus at night without a Fresnel, only the very center of the GG had near enough light to focus with, anything outside of dead center was just pure black (unless I tilted my loupe back towards center, but then I was looking at a distorted and highly out of focus image).

    Incidentally, I found one design flaw with the GG clips on the Chamonix. The screws are too long, and if you over tighten the screws when reassembling the GG clips, you’ll easily push them through to the other side of the wood GG holder. The resulting “dent” in the wood will easily add 0.1mm of error, so you have to fix this before mounting the holder back into the camera.

    I’ll process the film and see what the results are. Thanks again for the help.

  7. #27

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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Mark,

    I'm not sure why you would need to shim the GG on the Chamonix - unless it is truly uneven and the shims are just on one or two sides for balance. On my film back the frsenel sits in a recessed space. Removing the fresnel does not change the placement set of the GG. There is also enough space on the external side of the GG to place the fresnel. Though some way of clipping it needs to be devised. I'd suggest some small wire clips and nylon washers for the moment. (This is my momentary solution).

    I'd like to see Chamonix address this, hopefully with either a modification to an existing back or a redesign of the backs. (Hugo does have the url for this thread).

    With regard to the wood screws. Of course having a machine male and female would allow regular interchange of the screens. Wood with metal will eventually wear the holes with regular service. Having several backs with different screens (if needed) is a solution. Whenever working with wood, plastic, or softer metals and steel fitings it is always advised to take care in tightening to prevent damage and buckling of the softer material.

    I don't have enough understanding of the tolerances on these backs to address your other technical observations on measurement. Perhaps someone else who has this wisdom (and by chance also owns a Chamonix 45) will weigh in. I hope to run a few more tests in the next week with all 3 of my lenses. Thanks for your input.

  8. #28

    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    It seems that removing the Fresnel and adjusting the GG location with 0.100mm shims (to line up at 5.00mm) has fixed the problem. My chromes are absolutely sharp when shot wide open (f5.6). I'm glad I bought that digital micrometer last year.

  9. #29

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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    I saw mention of this thread elsewhere here and realized that I'd never done a focus check on my Chamonix 4x5. Here's a Polaroid with a 150 5.6 with the focus point right on the five-inch line. It looks good to me. Perhaps the focus issue is not widespread?



    --Darin

  10. #30

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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Quote Originally Posted by Mark Jaremko View Post
    It seems that removing the Fresnel and adjusting the GG location with 0.100mm shims (to line up at 5.00mm) has fixed the problem. My chromes are absolutely sharp when shot wide open (f5.6). I'm glad I bought that digital micrometer last year.
    I was able to get the same (sharp focus) result by just removing the fresnel. Though I am now looking to replace the entire GG with either an Ebony or a Maxwell.

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