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Thread: Tech cameras and IQ.

  1. #201
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    Re: Tech cameras and IQ.

    Darr,
    Your Field camera could be used as well as an MF2 for the back portion of the setup Though MF2 is probably a bit more solid.

    I forgot you had a field body. You might just need a 141 to 6x9 adapter to allow you to mount the back on the 4x5 if you do not already have one.
    Should still be good as most Arcas, well taken care of, never have 'view camera slop'. Mine doesn't after 20 years and it has been from Antarctica to Europe and all over North America.
    Rod
    Last edited by RodK; 6th July 2011 at 14:03. Reason: grammer
    US Representative, Arca-Swiss International
    R-Line Technical Cameras, Large Format View Cameras, Tripod Heads D4, D4m, P1, P0, Z1, Z2, C1 Cube.
    http://www.rodklukas.com/arca-swiss 480-755-3364
    Instagram @arcaswissusa Facebook @arcaswissusa

  2. #202
    Porpoise
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    Re: Tech cameras and IQ.

    Quote Originally Posted by jlm View Post
    to address Rod's question:
    "IF we agree that precise shimming of a Tech Camera setup within 1/100 can make a big difference
    in terms of IQ, why shouldn't we use this precision at any distance?

    more numbers, just to give this some scale, again, the 70mm lens: not sure how meaningful in reality, but by the formula:
    lens to sensor: 70.001mm = 480 meters
    lens to sensor: 70.002mm = 245 meters (here a .001mm shim makes a 240 meter difference!)
    Just a typo: 1/100mm = .01mm.

    Look at the DoF at f/8 with a CoC of .002mm (less than pixel size):
    70.01mm: 188m - infinity
    70.02mm: 136m - 1225m
    Shrink and expansion caused by temperature will have more effect.
    So for me this kind of precision is unnecessary. YMMV

    It reminds me of my flatbed scanner which has a setting for 9600 dpi. Still, a Nikon scanner which didn't go farther than 2400 dpi, gave better resolution, obviously with much smaller files. Your whole system has to support the accuracy. Just looking at one small part which happens to have more precision than the overall accuracy, is often just sales talk.

  3. #203
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    Re: Tech cameras and IQ.

    corrections made

    regarding thermal expansion, I see the lens holder and camera body (about 300mm long aluminum) for a 70mm Rodenstock changing it's length by 0.075mm per every ten degrees C.
    Last edited by jlm; 7th July 2011 at 03:15.

  4. #204
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    Re: Tech cameras and IQ.

    Quote Originally Posted by RodK View Post
    Joe, Arca-Swiss does offer handgrip extensions which work very well.
    Allowing easier handling in a carry or hand-holding situation.


    Rod
    yes, it is a good option, i even think that it shouldn't be an option !

  5. #205
    Senior Member darr's Avatar
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    Re: Tech cameras and IQ.

    Quote Originally Posted by RodK View Post
    Darr,
    Your Field camera could be used as well as an MF2 for the back portion of the setup Though MF2 is probably a bit more solid.

    I forgot you had a field body. You might just need a 141 to 6x9 adapter to allow you to mount the back on the 4x5 if you do not already have one.
    Should still be good as most Arcas, well taken care of, never have 'view camera slop'. Mine doesn't after 20 years and it has been from Antarctica to Europe and all over North America.
    Rod
    Thanks Rod. I received the photo of the setup via email and I like what I see. I will be making it to New Hampshire so I will be play-testing an R series.

    See you there,
    Darr
    Last edited by darr; 7th July 2011 at 09:37.
    "Creativity takes courage." ~ Henri Matisse
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  6. #206
    Porpoise
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    Re: Tech cameras and IQ.

    Quote Originally Posted by jlm View Post
    corrections made

    regarding thermal expansion, I see the lens holder and camera body (about 300mm long aluminum) for a 70mm Rodenstock changing it's length by 0.075mm per every ten degrees C.
    Yes, that is about the same figure I got. But to be a bit conservative I only checked the thermal expansion for the focal length of 70mm. And then 6 degrees C (11 degrees F) is all we need to get an extra .01mm. We better shim those Alpas in hot weather. And we need temperature specific conversion tables for the Arcas.

    Luckily, IQ backs with their focus masks come to the rescue.
    Last edited by Porpoise; 7th July 2011 at 11:59. Reason: A warm (long) lens has more trouble to focus at infinity.

  7. #207
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    Re: Tech cameras and IQ.

    good news is that when it is cold, you will be more sure to get to infinity, and beyond!

    but when it warms up, you may not make it. so shim in hot weather and peep your image when it gets cold.

  8. #208
    Porpoise
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    Re: Tech cameras and IQ.

    Quote Originally Posted by jlm View Post
    so shim in hot weather and peep your image when it gets cold.
    Thanks. I stand corrected. Shimming is a summer job.

  9. #209
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    Re: Tech cameras and IQ.

    Quote Originally Posted by Joe View Post
    Thierry,
    Win some major points here ....... Market a metal adapter for your beautiful rosewood handles to fit other cameras.
    Joseph
    (RL3d owner, hint, hint, wink, wink)
    Quote Originally Posted by darr View Post
    So Rod, can I give up my rail for more accurate focus stepping?
    Quote Originally Posted by wentbackward View Post
    Hi Darr ...
    "but when does it matter if you focus with the front or the back if the plane of focus is stationary?"

    The problem with Macro is that by changing the focus (therefore the distance between the lens and the film), you actually change the size of the image projected to the film. The more magnification of the subject the more you will see this effect. So stitching becomes potentially more error prone. If you use a macro rail to actually move the whole camera you'll be better off, but you are limited to how much of the subject the macro rail can accommodate.

    By focusing with the back it is less of a problem but it's still there.

    The big problem with focus stacking is the stuff that is wider than can be accommodated with your focus rail but still close enough that changing the focus changes it's size.

    With regards to tilts. I am still working through the math and until I actually get an Alpa tilt adapter, will not really know if what I am seeing is true ... basically as you tilt, you loose DoF and need smaller apertures. It seems more and more that tilt will be quite limited on the new backs.

    Paul
    Paul,
    When you tilt you actually do not lose depth of field and do not necessarily need to stop down more. When all is level and parallel, depth of field exists from a near plane to a far plane although you are only truly focused at one plane in between. However, when you tilt, the near and far planes form a wedge shaped 'V' with the hinge beneath the camera lens combination.
    As the distance increases to a subject item, the depth of field increases as well. In most situations this means you can save some apertures, or not stop down as much as required by a straight shot. The caveat is, of course, if your foreground has verticals which take up at least 25% of the vertical heighth in the foreground, you can't use tilt if you want everything sharp as the principle plane of focus would transcend the vertical object and so top or bottom would be out of focus.
    Someone above also was speaking of focus about whether it matters whether you focus with the front or rear of the camera. If you use the rear the lens to subject distance does not change and therefore the subject does not 'swell and shrink', as the lens to subject distance does not change. If you use the front to focus the size of the object will change and the image may show some of these artifacts if you are stacking. The smallest focus increments possible when using the front for focus stacking, will yield the best possible results, though perhaps not as good as using the back for focus.
    The Arca R cameras, utilized as the front standard, gives the best chance for success with front focus, as it has the finest focus increment currently available.
    This front focus issue is something many do not discuss but it is something that is there. Most front focus mechanisms such as found on DSLRs are not fine enough for best results. On the other hand it also has to do with 'GE' factor--'Good Enough'.
    Good enough for my purposes. The photographer decides...
    Rod
    US Representative, Arca-Swiss International
    R-Line Technical Cameras, Large Format View Cameras, Tripod Heads D4, D4m, P1, P0, Z1, Z2, C1 Cube.
    http://www.rodklukas.com/arca-swiss 480-755-3364
    Instagram @arcaswissusa Facebook @arcaswissusa

  10. #210
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    Re: Tech cameras and IQ.

    Quote Originally Posted by delled View Post

    The Arca R focus helix is approximately 110mm in diameter, has 172 tick marks (numbered every 5 ticks, from 0 to 34), and moves the lens in or out 2.5mm per revolution -- i.e., 2500/360 = 6.94 microns/degree, or 2500/172 = 14.53 microns/tick mark.

    Dave.
    Dave:

    Where did you get the data, specifically 2.5 mm per revolution, on R-focus ring? I ordered RM3Di recently and was doing some brain exercise while waiting. I got a copy of the look up table for RDS 35mm from Steve at CI and was doing some math, and learned so far the followings.

    First, As Steve told me A-S is indeed using the measure focal length value instead of the stated value. If 2.5 mm is an actual design number, this particular RDS 35mm has the actual focal length of 35.3 mm

    Second, A-S uses the distance from the lens plane instead of sensor plane to determine the subject distance.

    Third, If the accurate 'travel per revolution' is known, one can calibrate each lens simply by reading the scale readings of two known distance, not necessarily 'at infinity'. Clearly you will need very accurate distance measurement with Disto or similar devices.

    I am in process of writing an iOS App (iPhone) for Tech Camera and will have a beta version soon. Anyone want to beta test the App may PM me with your tech camera type, DB and the lenses you use. I will need few testers.

    Jae M

  11. #211
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    Re: Tech cameras and IQ.

    Jae M --

    The 2.5mm (12.5mm/5 revolutions) has been widely published, although I can't lay my hands on a definitive statement. I've sent you an email regarding your other observations.

    Dave.

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