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

  1. #1

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

    Hi, I recently bought a Chamonix 45N-1 and have to say it really is a lovely camera.. At the same time, I have bought a Schneider Xenotar 135mm 3.5 and plan to shoot portraits with this lens wide open. At some point I will buy a 150mm 2.8 ( although I have found focusing trickier enough with this lens ). After doing some tests with this camera I noticed that the focusing was way out and was pulling a foot or so in front of what was focused on the groundglass ( after receiving film back ). I borrowed my friends Linhof to test with the same lens and sure enough, on getting the film back, what I focused on was in focus. I contacted Hugo who in turn contacted the Chamonix factory and they told me that this was the first in the factories history to have this problem and that the the problem was related to the fact that I was using a lens like the Xenotar wide open and that the groundglass that comes installed as a default on the Chamonix is a fresnel and this is apparently known for having issues with fine focusing. So I sent my back off to China and they have sent me two groundglasses back, the original fresnel and a non fresnel ( to be used with these faster lenses wide open ). Has anyone ever come across such a problem or able to shed some light on it? I haven't had a chance to test this yet but I hope the problem is fixed by the new groundglass.. Any information anyone could provide would be fantastic. Thanks. Best regards Stefan

    P.S Have used my friends account as I don't have one yet.

  2. #2

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

    Some fine focusing difficulty is inherent in any Fresnel lens. One of the reasons people pay $250 and up for Maxwell screens is that they're the easiest Fresnels to focus, at least the easiest I've used and I've used most of them. That's also one of the reasons some people prefer a plain ground glass. However, it isn't normal to be a foot off. Is this your first LF camera or your first with a Fresnel screen? If so, my guess is you just weren't used to the Fresnel and so weren't focusing it properly (what kind of screen does your friend's Linhof have?). But it's hard to say much more until you've tested your new viewing screens. It's conceivable that you got a Fresnel lens that wasn't properly matched to the focal length of the lens you were using (e.g. they inadvertantly put a wide angle Fresnel on your camera and you weren't using a wide angle lens) but this doesn't seem too likely. You were using a loupe and a dark cloth, right? FWIW, the screen on my Chamonix was fine.

    As an aside, you probably know that the widest aperture on many LF lenses is there mainly to assist in focusing. It isn't generally expected that it will be used to make photographs so you likely aren't going to get the best quality images using a 3.5 or 2.8 LF lens wide open.
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

  3. #3
    mandoman7's Avatar
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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    The main concern is that the position of the film in the holder replicates the position of the ground glass surface when inserted, so the film is in the exact position of the surface that's used for focussing. This is something that should be checked with any newly acquired lf camera (micrometer). I've regretted shooting a lot of film and founding out afterwards about a discrepancy.

    In my experience, fresnels often get weird out towards the edges with wide angles, but the center is usually pretty usable for focussing. I've never heard of a fresnel focussing differently with certain lenses. In this case, having more than one lens would help with diagnosis, as well as broadening the learning curve.
    John Youngblood
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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Hi, Thanks for the responses, much appreciated! I will write back more when I have done some actual tests with the new groundglass but that won't be till early next week. Brian in response to your answer, I used to have a Linhof Technika 5 but I never used it with this lens. With the original fresnel groundglass on the Chamonix, I did a couple of tests. One comparison was to shoot with the Xenotar @ 3.5 and a Rodenstock Sironar - N I have @ 5.6. Both images came back with focus falling ahead of what I had originally focused on. Both images appear sharp on the ground glass and it is only when I got the film back that you can see the results. To be honest, I don't think it was that my focusing was out. When I compared it with my friends Linhof
    ( which I think is a non fresnel screen ) the object was spot on in focus when the film came back.

    So as I said, will post some more when I have tested out the non fresnel variety with the Chamonix. Will be interesting......

    As for shooting wide open, the look I am after is to have an extremely sharp drop of focus for portraits and this is the only way to achieve this.... How much of a degradation of quality are we talking here? I mean it is still 5 x 4 inch film right, so the quality has to be somewhat decent I would have thought?

    As for the Maxwell screen, I have heard this recommended by a few people. Is this something that I would have to find to adjust or would I have to send him my camera for him to do. At this stage I am a little sick of sending my camera all over the world...

    To Mandoman7, I am definitely aware of how important a ground glass screen is to be spot on with the film plane of your double dark slide, what is the best way to test this? I am not particularly technical.....

    Ok, thanks again so much for your responses... Will post some more early next week. Best regards Stefan

  5. #5

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

    So after receiving a new back to my Chamonix 45N-1 with a non fresnel screen ( which I thought was fantastic customer service by the way - Thanks Hugo ) I have done some more tests with my Xenotar 135mm @ 3.5 and they have come back in focus with the non fresnel and out of focus with the fresnel type. Is this really just a case of me not being able to use the fresnel type properly? I mean, I intend to use this for portraits, so focus has to be spot on.. Any thoughts? Thanks to everyone who answered before. Cheers Stefan

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

    I would try a fresnel lens on top of your GG.
    In that way you would keep the acuracy of focusing that you have now.
    I have the same set-up with my Sinar P2 and it works good.

    Peter

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

    Quote Originally Posted by mandoman7 View Post
    The main concern is that the position of the film in the holder replicates the position of the ground glass surface when inserted, so the film is in the exact position of the surface that's used for focussing. This is something that should be checked with any newly acquired lf camera (micrometer). I've regretted shooting a lot of film and founding out afterwards about a discrepancy.
    Howdy folks!

    I have a new Chamonix 45 as well, and am having similar problems with focus @90mm.

    The lens is a very good condition Rodenstock Gradagon-N MC 90mm F6.8
    When focusing I'm using a dark cloth, a Rodenstock 4x Loupe placed in the center of the glass. The area appears sharp when focusing, but I'm finding the true focal point on film does not reflect that of the ground glass - it usually is at a point cloer to the camera than the point I have set focus. I've shot from f11 - f45. The smaller apertures fair better, but I need the option of being able to shoot wide open.

    Hugo told me some people had some problems with the Fresnels @ 90mm. He suggested I remove it and just go with the GG. I haven't tried it yet. I have two other lenses: a Fujinon A 240mm F9 MC , and a late model Rodenstock APO-Sironar-S 135mm/5.6. Before I do anymore comprehensive tests with all lenses, I'm looking for more information to proceed.

    Images with the 135mm seems to be a bit more on track with focus.

    Since all my gear is new to me (except some old film holders), how does one "check" or calibrate a new LF field camera?

    I would like to use a fresnel on this camera with all lenses. Will a different fresnel lens allow this?

    I have some past experience with 4x5 & 8x10 rail cameras for portraits with studio lighting, but it's been half a dozen years and am a bit rusty.

    TIA!

  8. #8
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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Since this problem seems to be unique to the 90 Grandagon, un-screw the front element of the lens. There should be a thin shim washer between the lens element and the shutter.

    If the shim is missing, it may be the cause of the problem.

    I doubt that the Fresnel could be throwing the image out of focus if it has been mounted properly. That defect would show up no matter which lens you used.

    A mis-match between the position of the ground glass and the position of the film in the film holder is a manufacturing problem. There are several ways to check for this. However, since the camera is new, it should be corrected under warranty.

  9. #9
    Robert A. Zeichner's Avatar
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    Re: Focusing problems with the fresnel groundglass on the Chamonix 45N-1?

    Ground glass/film plane coincidence is one of the most critical issues in getting sharp negatives. Theoretically, the frosted surface of the ground glass needs to be in precisely the same plane as the film would be when the holder is inserted into the back. Fresnels are sometimes used to brighten the image on the ground glass, but one must remember that a Fresnel is in itself, a lens. It will shift focus rearward by an amount roughly equivalent to 1/3 of its thickness. That said, if you want to use a Fresnel between the taking lens and the gg, you need to design that shift into the camera to make certain what you see on the gg is what gets onto the film. Many photographers who have grappled with adding a fresnel to a camera not designed for one, have simply placed it behind the gg, between the gg and your eyes. This solves the problem. The focal length of the lens can have a varying effect on perceived gg/film plane errors. Longer lenses projecting rays of light more closely parallel with one another may appear to withstand a bit more alignment error at the film plane than short lenses. Still, any gg/film plane error can be noticeable, even at small apertures, when compared to the same shooting set up in which that error as been corrected. I have gotten rid of Fresnels long ago and have been using finely ground home-made focusing screens with more consistent success. They are not as bright, but that just means I wait a little longer for my eyes to adjust under the dark cloth.

  10. #10

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

    Thanks for the responses guys.
    Placing the fresnel in front of the GG (or going without) has helped with the focus.

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