Gaoersi 617 infinity focus probs

Discussion in 'Panoramic Cameras and Accessories' started by rvarland, Jun 2, 2009.

  1. rvarland

    rvarland Member

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    Kind of a rookie with pano and large format lenses. Just bought a older Gaoersi body, installed my Fuji 90/8, and then discovered it won't focus at infinity. The focus mechanism is all the way in and it is beyond me how anything could be adjusted to get it closer. Hence, am I correct in that it has something to do with flange distance? The camera measures up at 102mm and I'm afraid my Fuji needs shorter than that. Any advice, including which lenses might work, would be greatly appreciated. (Seller wasn't sure what lens used to be on the camera, thought maybe a Super Angulon) Roger in Michigan
     
  2. Ian Grant

    Ian Grant Subscriber

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    Welcome to APUG.

    The Gaoersi like other 617's with interchangeable lenses uses different lens cones for each focal length. So firts you need to make sure you have the correct cone. I have a first series Gaoersi and a cone set up for a 90mm Grandagon so can measure that for you. When I bought my camera they asked what lenses I was going to use and then set my cone specifically for them.

    I will go get the cone, finding a ruler may be more difficult :D

    Ian
     
  3. Ian Grant

    Ian Grant Subscriber

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    Easier than I thought, the overall distance of the cone on its own when at Infinity is 6.5cm, and when fitted to the camera approx 10.3cm, so it sounds quite similar.

    You should be able to find data sheets for the Fuji and Super Angulons and they will tell you the flange distance needed at Infinity, Gaoersi themselves can tell you how to adjust the cone if necessary I've always found them very helpful.

    Ian
     
    Last edited by a moderator: Jun 3, 2009
  4. Lachlan 617

    Lachlan 617 Member

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    Does it seem far off infinity when you get to the lock point?

    In other words, is the furtherest point of focus far from the camera? Given the majority of shooting with this camera is with f16 and above (seeing you have the f8, not the f5.6 lens, I'm assuming that you're not after speed for hand held sooting), you may have a focus distance clode to the hyperfocal distance. If so, forget about infinity and shoot away!!

    While you're looking for the data page that Ian suggested, also look for the page with hyperfocal distances for your lens as well. Even if you fix your issue, this information will be vital for any future shooting with this lens/camera combo. I have all of my lenses' HF and DOF data on a simple spreadsheet on my iPhone. I can't stress the importance of using HF over infinity!

    Lachlan.
     
  5. rvarland

    rvarland Member

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    Thanks for your comments so far. I am learning more about the importance of flange distance with fixed mounts, something my 4x5 never insisted upon. Anyway, via a test roll, it appears that acceptable sharpness arrives at f32; workable, but not convenient. The DoF charts along with using HF are things I'm familiar with, but I'd like to be a little closer to the ball park. At this point, I think the solution is a different lens as opposed to a new adapter for the camera. (easier to sell a lens than an adapter) I'll try to post again when things are working, or I hit another dead end. Thanks again!
     
  6. Lachlan 617

    Lachlan 617 Member

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    Two last thing (although I doubt either will be the case):

    1) Check that the shutter is touching the helical mount (i.e. not sitting out a mm or two). There isn't a second retaining ring on the thread? You haven't cross-threaded the ring? It seems that you are very close with this lens (given the closer to infinity you focus, the less movement is required).

    2) Have you got the right hole size for your shutter? Again, if the hole is too small, the lens cound be sitting off the mount.

    Both seem too trivial to be right, but it's hard to tell without seeing the actual item.

    Lachlan.
     
  7. Lachlan 617

    Lachlan 617 Member

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  8. fotoman

    fotoman Member

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    102mm camera FFD

    The camera's 102mm set up is appropriate for three different Schneider Super Angulons... the SA 5.6, SA 6.8 Classic, and SA 5.6 XL... all big and heavy lenses. All the other 90's, by an maker, have shorter FFD's, and will not achieve infinity focus.

    Shooting @f32 will bring more into (better) focus, but the lens is probably diffraction limited at f16 (maybe f22)... so you are paying a big price in image quality.
     
  9. fotoman

    fotoman Member

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  10. Ian Grant

    Ian Grant Subscriber

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    Large format lenses are normally designed and optimised for use at f22, they are not diffraction limited to f16, and are still very usable at f32 and in many cases f45. You only need to read data from Zeiss, Schneider & Rodenstock etc and use lenses at these apertures and make large prints to see this statement isn't true.

    This goes back to the Tessar design where edges and corners aren't sharp until f22, which is the recommended aperture given by Carl Zeiss & later Doctor Optic. Lenses like the late production f5.6 150mm Xenar stop down to f64 annd are excellent at f32. Sometimes the effects of diffraction are over-hyped and the very small decrease in image sharpness in the centre has to be traded off against an increase at the edges and also far greater DOF. In most cases it's the last marked aperture that begins to suffer diffraction, and you'd have difficulty seeing any drop in quality in a print, but of course it can be measured on an optical bench, or by examining negatives of test charts with a microscope.

    Ian
     
  11. rvarland

    rvarland Member

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    The saga continues . . .

    Based on some e-mail exchanges with someone at Gaoersi, I went out and purchased a Fuji 90/5.6 . Unfortunately, the diameter of the rear lens group is too large to move far enough forward to thread into the shutter, let alone move forward during focusing. I appreciate the insight about the Schneiders and may have to try that next, although I'm going to be broke before long. At the moment, I'm second guessing myself and wishing I would have bought a complete camera. Again, I appreciate the comments and am learning plenty about the intricacies of lenses and fixed mounts.
     
  12. Dave Wooten

    Dave Wooten Subscriber

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    Fugi F/8 should fit and covers the format
     
  13. rvarland

    rvarland Member

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    Dave -
    What started this whole conundrum is the lens adapter is too long for Fuji 90/8, hence no infinity focus. I didn't know about flange distance when I bought the camera, so now I'm on the quest to find a lens that will focus AND fit inside the camera.
    Roger
     
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  15. Ian Grant

    Ian Grant Subscriber

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    There are a lot of APUG members in Michigan maybe someone could help you out and let you try fitting a lens 90mm Schneider or Rodenstock and check the Infinity focus before you buy a lens. Do you have the focus screen with the camera ?

    Ian
     
  16. Dave Wooten

    Dave Wooten Subscriber

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    Got it, I use the fugi 8 on da yi/ focus set up and works fine, see photo of set up posted in tech gallery...I was thinking your set up was similar..
     
  17. rvarland

    rvarland Member

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    more interesting details from China

    The latest quirk in this mystery is Super Angulon 90/5.6 won't work either. While it will thread together, it will not close focus due to lack of clearance inside the cone. The people at Gaoersi, when confronted with this and accompanying photos, claim the lens cone is not theirs, but was made by someone else. So the next question for anyone still reading this ongoing comedy, what company might make a lens cone that would fit on a Gaoersi? Are some pano lens cones interchangeable? Thanks to all once again.
     
  18. ic-racer

    ic-racer Member

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    You can't 'design' a lens to have any specific diffraction characteristic. It a physical function of aperture size. Its simple, the smaller the aperture, the more the diffraction (or the larger the bullseyes). Its physics of light, not design of the lens.
     
  19. stevew

    stevew Member

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    On the Gaoersi, you can adjust the overall lens mount distance by backing out set screws on the mount and setting infinity focus (I focus at about 1/3 of frame width instead of center). Granted there are different cone lenghts as Paul has mentioned, bu there is quite an adjustment range on the mount.
     
  20. rvarland

    rvarland Member

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    wrong adapter?

    I think I understand the procedure as described in the last post, but I'm also beginning to believe that what I purchased is not 100% Gaoersi. The body has the name in several places, so I'm good there. The next piece, rectangular, about 1" thick, mounts up to the body with 4 thumb screws and must also be Gaoersi.(?) However, the next two pieces (lens cone? and focusing ring) could be another brand? These last two connect to the first via a threaded 85mm hole. Is this hole common to other cameras? If so, could a previous owner have swapped components? Again, I am unsure how much interchangeability there is among these fixed mount cameras. Maybe I need to figure out where to post some pictures and give better clues. Thanks again for the collective insight.
     
  21. rvarland

    rvarland Member

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    Problem Solved (sort of)

    Today I finally discovered that the reason I hadn't been able to put two and two together is that the front end of the camera had been rebuilt by SK Grimes, a high-end camera machine shop. The custom work had been designed specifically for a SA 90/5.6 XL. Though I tried a SA 90/5.6 MC that did not work, the slightly different shape of the cone on the rear lens allows the XL to operate. Though I'm happy to have the problem solved, what I originally thought was as simple as mounting up my trusty Fuji 90/8, has now turned into a punt or provide some stimulus money to someone via a purchase of a 90 XL at somewhere around 1000+. Anyways, thanks again to all for your input. I know a lot more than I did previously.
     
  22. Ian Grant

    Ian Grant Subscriber

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    As aperture is relative to focal length it goes without saying that an LF lens at f22 is quite different to a an equivalent 35mm or 120 lens of the same field of view at the same aperture. Diffraction is more apparent with lenses of smaller formats and manufacturers of LF lenses take this into account when designing their lenses, it's not a co-incidence that virtually all of them state the optimum aperture is f22 for their LF lenses.

    As you say it's simple but the diameter of an aperture of f22 on a 35mm camera is more likely to be equivalent of f45 or even f64 with an LF lens, and f90 or f128 with ULF lenses, hence the reason f22 is used for best overall balance with 5x4 lenses.

    Ian
     
  23. fotoman

    fotoman Member

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    I have heard and read this reference, many times. However...

    having studied their websites, and all of the hard copy documentation I have from Rodenstock, Schneider and Nikon... I can't seem to find any statements (or data) indicating that f22 should be used for best overall balance with 5x4 lenses.

    Schneider and Rodenstock do publish MTF data for their lenses, which clearly shows that f22 may in fact NOT be the best performing aperture for many of their lenses. Additionally, resolution testing of LF lenses (multiple samples) by Chris Perez and Kerry Thallman would also bare this out... see http://www.hevanet.com/cperez/testing.html.

    I wonder where this bit of photolore originated?
     
  24. Ian Grant

    Ian Grant Subscriber

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    Try looking at the Doctor Optic website for the LF Tessar's, you will have to use the Internet archives, (my saved copy is in the UK), f22 is Zeiss/Doctor Optics recommended aperture for optimal performance. I originally found the link to the Doctor Optics site via Perez/Thalman a few yeras ago. Other manufacturers (Schneider/Rodenstok) give much of their data on coverage etc at f22, this is f-stop they general chose for measuring movements.

    One problem is that lens tests like Chris Perez/Kerry Thalman are very subjective and made from images of test charts and while very useful they are based on small samples of each lens - usually just one, although there are exceptions ie 90mm Angulons etc. Few LF lenses are flat field lenses so shouldn't necessarily give high resolution results of a test chart at all apertures, but you would expect process lenses like G-Claron's or Artar's to possibly perform better under these circumstances.

    Another issue not covered by Perez/Thalman or MFT testing is the actual use of a lens in real life situations, particularly when Depth of Field and/or use of movements may be critical. The general rule of thumb with most lenses from top manufacturers has always been that the smallest marked aperture is weak, but that one or two stops up will give excellent performance. But like all rules some lenses will break them. One thing the Perez/Thalman chart highlights is that most lenses perform well at f16/f22 some are actually far better at f22, others may have better overall sharpness at f22 but better central sharpness at f16 or even f11.

    In reality we are both nit-picking because it's how well a lens performs in actual use, as I said earlier I've never noticed or been able to spot any drop in performance of my LF lenses at f22 or even f32 and f45 with some of them. My Tessars & Xenar very definitely only become sharp across the full field at f22, and this as I said before is exactly what Zeiss have always said, and Chris Perez confirms.

    I really don't know where the f22 figure comes from for other manufacturers/lenses but it's common across them all for 5x4 format lenses, and in general use by photographers around the world.

    Interestingly someone once did a breakdown of the Apertures used by John Sexton, and no-one can doubt the quality of his images, the figures were:

    For example, I looked at the technical data for the 49 photographs in John Sexton's Listen to the trees, done with a 4x5. The breakdown was as follows:

    f16 5%
    f22 30%
    f32 50%
    f45 20%
    f64 5%


    Those figures can't be quite right as they add up to 110% but they do give a fair indication that f32 is the most common aperture he's using followed by f22 and f45. I'd also guess that they aren't far off other peoples use as well.

    Ian
     
  25. BlairWare

    BlairWare Member

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    Sorry to open up this thread again, but I am seeking some insight.

    I have been trying to mount a Super Angulon 90mm f/5.6 on gen. 1 Gaoersi 617. I can't get enough distance to get infinity and a reasonable close focus distance at the same time. I even taken to putting a small spacer (3mm) between the flange and helecoid to give me a little more distance.

    Unfortunately, the rear element of the SA bumps into the inside of the helicoid as it is extended, further reducing the close focus distance. Even with the spacer, the close focus distance is about 2.5m.

    To top it off, the helicoid focusing mount only has about a half-turn of thread connecting it to the adaptor. While Gaoersi claims compatability with the f/5.6 SA, do I need a consider getting a smaller lens with a shorter flange to film distance?

    Any suggestions will be appreciated.

    Cheers, Blair
     
  26. Ian Grant

    Ian Grant Subscriber

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    Send Gaoersi an email, they are very helpful.

    I used my f6.8 Grandagon on my Gaoersi with no problems, I have an f5.6 90mm SA but never tried it and when I bought the cones the company set them up for my specific lenses, which might be your problem.

    Ian