Chamonix 451N focus problem

Discussion in 'Large Format Cameras and Accessories' started by Andrew Moxom, Oct 16, 2009.

  1. Andrew Moxom

    Andrew Moxom Subscriber

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    On LF forum, there are a few threads around some issues with the way Chamonix has installed their fresnel and GG's. Apparently, there is a focus shift after focusing with the factory installed fresnel, which is installed in front of the GG, and then inserting the film holder. The focus plane shifts to make noticeable lack of sharpness on some images. Especially when shooting at larger apertures. Apparently, by moving the fresnel screen to the back, the problem should be mitigated. I am not fond of the vitriolic nature of LFF so I am asking my question here. I was wondering if the more friendly Chamonix users on APUG have seen this problem on their Chamonix cameras?
     
  2. keithwms

    keithwms Member

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    I'm not a chamonix user, nor do I use fresnels, but... I think, generally, a fresnel in front (lens side) of the GG will necessarily shift the focus... roughly in proportion to the thickness of the fresnel. It's a lens, of course it will shift the focus. That's nothing new. I guess the solution is to (1) use a thinner fresnel, or (2) figure out the offset for a particular focusing distance and correct for it, or (3) put the fresnel on the back, or (4) my favourite option, don't use a fresnel at all when focus is extremely critical. Obviously for infinity focus it's not going to be as big an issue as for those ultrashallow DOF portraits that some people do.

    Maybe I'm wrong but I think any fresnel is going to shift the focus somewhat. It's all a matter of what's acceptable.
     
  3. keithwms

    keithwms Member

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    P.S. Ah, here is a useful old thread, the last comment is very good one, the best solution seems to be a partial fresnel GG. Pricey, but if you really want to do it right...

    http://photo.net/large-format-photography-forum/00HaVS

    So with the sinar screen you'd do general composition via the fresnel portion and then do critical focus via the non-lensing portion.

    Anywya I don't care for fresnels, they annoy my eyeballs!
     
  4. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    There have been some backs, like Graphic backs, where the fresnel is designed to fit in front of the groundglass and is calibrated to function that way with the groundglass surface still at the film plane, but I'd be very surprised if this were true of the Chamonix. I don't recall precisely, but the Linhof Tech III may have had the fresnel on the lens side of the groundglass.

    You could always measure and compare the depth of the back to the groundglass surface to the depth of a filmholder with film in it.

    It does make some sense to put the fresnel in front, since it's usually plastic and easily scratched, unlike the groundglass, but it makes calibration much more complicated, and you can't easily swap out the fresnel for another one, say if you want one optimized for wide lenses, so this is rarely done on any LF camera anymore. I can't think of any contemporary LF camera with the fresnel on the inside.

    SLRs, though, often have the fresnel on the inside, or have a combination screen with the fresnel portion on the bottom.
     
  5. ic-racer

    ic-racer Member

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    Horseman FA field camera has the fresnel on inside.
     
  6. Toffle

    Toffle Member

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    Hey Andrew,
    I'm not a Chamonix user, but I am sure you have seen the announcement on their website. The "fix" they describe seems like a stop-gap until they solve the underlying issues. The problems are serious enough that you would think a more substantial remedy should be a priority. Their apology and promise of a fix in the next model is small comfort for owners who have to make alterations to their cameras or shooting techniques in order to achieve acceptable sharpness.

    Cheers... hope you are doing well. :smile: Hope to see you next June in Michigan.
     
  7. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    Thanks. Forgot about that one.
     
  8. Steve Hamley

    Steve Hamley Member

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    Keith, I'm not sure this is true or at least a comparable situation. I'm reasonably certain that Sinar did not put a clear spot on the fresnel because they mis-spaced the image-forming surface! I am assuming that the Sinar fresnel does not have a frosted side that faces the lens. If this assumption is true, you can easily see that the Sinar screen will also produce a mis-placed image forming surface by considering the "absurd" case of a 1-foot thick clear screen with the image forming surface behind it.

    Andrew, there's good news and bad news. The bad news is there isn't going to be any "fix" for already manufactured cameras to use the existing fresnel in front of the GG. You can put it behind, and it will get scuffed up sooner or later, likely sooner. You could "calibrate" the focusing knob to re-position the film holder after critical focusing, but that's non a good solution (although workable) IMO.

    The good news is that there are several perfectly workable solutions, and the Chamonix frame is apparently made to the same design specs (haven't measured one though) as an Ebony and most every other view camera for a century or more. Chamonix just put a clear fresnel in front of the frosted GG where it was not designed be according to the way the frame was actually manufactured. I'd much rather fix the fresnel or GG than the frame. I'd actually be more concerned if they "fix" the frame where a different fresnel or a standard GG would be mis-space the image forming surface rather than the current situation.

    The Ebony fresnel is frosted on one side which faces the lens, and a clear cover glass goes behind it to protect the fresnel. A Maxwell can be made either way, or a Steve Hopf GG (sells on eBay as "photofixation" I believe, and has GG store) would be nice if you don't care for fresnels.

    The important thing to remember is that the image-forming surface HAS to be against the GG frame in the Chamonix case, otherwise it's mis-spaced, and that mis-spacing may or may not show effects in a given situation given the many variables.

    Cheers, Steve
     
  9. wildbill

    wildbill Member

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    Sounds like a recall is in order but I highly doubt they'll do it. "We can't fix it", that's not a very good announcement!
    I did the ruler test (photographing a ruler on a slant) with my 90mm 4.5 nikkor and my 210mm fujinon and couldn't see any issues. I also did a test with a fujinon focus chart and found that it was sharp with both lenses. Both those tests were with instant film, however. Maybe I should shoot some sheets with and w/o to be sure. My negs from normal shooting seem to be sharp when enlarged though.
    Update- I just tried the fujinon back focus chart test again. I set up the chart on the wall about 4 ft from the film plane. This time just with a 8x loupe, no film. The 210mm checked out fine with and w/o the fresnel installed. The 90mm nikkor 4.5 requires an additional millemeter (aprox.) of bellows to focus w/o the factory fresnel installed.
     
    Last edited by a moderator: Oct 18, 2009
  10. Andrew Moxom

    Andrew Moxom Subscriber

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    Vinny, I am wondering if I just remove the fresnel, put the GG back, and cut down one of those cheap map reading fresnels from Staples to fit the correct size on the Chamonix? I do know the GG is larger than the fresnel itself so reusing the stock one is not really an option as it keeps falling off! So if I cut down the map reading one, I could make it the right size, and so it is held down by the stock mounting screws/washers.
     
  11. Barry S

    Barry S Subscriber

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    Andrew--did you test your 45N-1 to confirm an issue with the focus? I haven't experienced any focus issues with my 45N-1, but I haven't done any specific testing.
     
  12. Jon Butler

    Jon Butler Subscriber

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    Andrew,
    I've seen your images their fine. My two Chamonix cameras are fine and I will not be doing any tests.
    If you test any LF camera you will find something wrong. I use my cameras in the same way including close ups and
    get the same sharp results as when I use my Ebony.
    I think some people prefer to test and fiddle about rather then taking pictures.
    JON.
     
  13. John Bond

    John Bond Member

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    I have not noticed any problems with my Chamonix. I suppose this might be a problem with close ups or with large apertures. However, when focusing on distant objects at a calculated hyperfocal distance for a given f stop, the thickness of the fresnel will actually make the farther distances sharper while pushing the nearest point of acceptable sharpness a little farther away, probably not enough to be a problem.
     
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  15. Andrew Moxom

    Andrew Moxom Subscriber

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    I have noticed some issues shooting close up with a 203mm Ektar lens... It's very noticable softness. Also with my 90mm SA f8 on infinity shots... Seems soft compared to my shots done with a Canham DLC. Not done side by side shots though. Also, some of my petzval wide open shots, I have noticed some softness issues on the negs afterwards when I was certain nothing moved in the center where the sharpest area of the petzval lens signature resides. I was careful to focus, and the negs are not 100% what I would expect.
     
  16. Barry S

    Barry S Subscriber

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    It sounds like you definitely have an issue. I'm getting one of those full page fresnels for my 8x10 camera, so I'd do exactly what you suggest. Remove the Chamonix fresnel and cut down the Staples fresnel to fit behind the ground glass.
     
  17. wildbill

    wildbill Member

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    well, viewing images online isn't an accurate method of gauging sharpness. Stopping a lens down isn't an acceptable solution in my book. If there is something wrong, fix it.
    since the cameras in question are made by hand out of wood, their could be variances from camera to camera. If your camera works fine, that doesn't mean mine will. Your "acceptable sharpness" may not meet andrew's standards.
    Andrew, I've use the staples brand magnifiers on my old shen hao and my 8x10 as well. They're great with short focal lengths. I've now removed the fresnel from my chamonix and will be installing the staples version. I'd recommend you do a test just for peace of mind. Test the depth of the film plane to the gg while you're at it.
     
  18. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member

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    A fresnel isn't really a necessity. Accurate focus is.
     
  19. wildbill

    wildbill Member

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  20. keithwms

    keithwms Member

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    My sentiments exactly.
     
  21. Andrew Moxom

    Andrew Moxom Subscriber

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    Vinny, I might try that...... Or see how much it would cost to get the thing modified to work as it should!! I see Chamonix doing absolutely nothing about this. Unless they give people spare fresnels as they get scratched from being on the back in harms way!!! The fact is, they have a turd and want us to polish it! I hate to think what this will do for their resale value!!
     
  22. Toffle

    Toffle Member

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    Indeed... the whole issue gets a big WTF??? from me. I'm not even a Chamonix customer and this has me ticked off. This should be fixed... and pronto. The cost of fixing a problem like this should be seen as an investment in customer relations and future sales.
     
  23. wildbill

    wildbill Member

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    I almost installed mine on the outside this afternoon then I realized (as you did) that it'll get scratched to hell. I'll stick with the staples version for $8.

    This situation is similar to the problem with Chamonix's bubble levels. They have said to have new ones which are better (don't leak out) and actually accurate but they aren't recalling the bad ones. I've replaced mine twice and asked for the new ones but no luck yet. It's impossible to line all three levels up on my camera back.

    As for the turd polish, if word gets out that that turd polish will fix this issue, the price is going to go up!
     
  24. Mike1234

    Mike1234 Inactive

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  25. keithwms

    keithwms Member

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    This reminds me of one of the Fundamental Laws of Sh*t: "you can't polish sh*t... unless it's really old."

    The other Fundamental Laws that I recall are: sh*t rolls down hill; and, you can't throw sh*t without getting some on yourself.

    I think there are seven more but alas I do not recall them.
     
  26. Steve Hamley

    Steve Hamley Member

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    Geez,

    And you guys think the LF forum is vitriolic. O.K. maybe curmudgeon Dan gets cranked up...

    I posted this over on LF and thought it mght be appropriate here.

    Keith, look me up when you're down CNMS way.

    Cheers, Steve

    "I think I understand the technical issues now. The confusion in the thread seems to exist because people are talking about several different things at once, technical and economic (support) issues.

    The solutions seem to be:

    What can the user do?

    1) Remove the fresnel. The GG is in the proper place.

    Drawbacks: the image is now quite a bit darker.

    2) Remove the Chamonix GG and Chamonix fresnel, and install an aftermarket fresnel IN PLACE OF THE GG (not the Chamonix fresnel) that has a "frosted" side facing the lens, so that the image-forming surface is in the same place as the Chamonix GG. Then install a cover glass to protect the fresnel. The fresnel is now effectively BEHIND the GG and the image-forming surface is in the same (correct) place. This is the "Ebony" or "Maxwell" option referenced on the Chamonix website.

    Drawbacks: You pay unless Chamonix does.

    3) Have someone re-mill the GG frame to work with the existing fresnel.

    Drawback #1: Shipping and wait if you have Chamonix, Ritter, etc do it, cost if Chamonix doesn't do it gratus.

    Drawback #2: If the back is re-milled to relocate the GG, it will no longer work with a plain GG or with the Ebony/Maxwell option mentioned above, and may not work with any other fresnel of a different power.

    Note: Personally I would not modify the back to be non-standard and to work only with a fresnel of unknown characteristics.

    So you just have to pick which one you want.

    Unless Chamonix picks up the tab, you're going to get darker on the screen or lighter in the wallet if you want accurate focus under all conditions.

    I'm not sure what Chamonix does at this point. They're sort of, well, screwed, but they did it to themselves. I'd probably offer what Mike suggested, send us the frame/camera and we'll fix it and pay shipping. I don't think they can send out "fix it" kits since many of the cameras have been re-sold so they wouldn't know who really has one, or for that matter, if all the cameras have the same problem given the QA/QC. As a business entity, Chamonix clearly needs to make the quality assurance/quality control a little more balanced with the apparently superb craftsmanship they exhibit.

    Cheers, Steve"