Variable field curvature in a macro lens?

Discussion in 'Nature' started by ilkka_nissila, Jun 23, 2008.

  1. I was just photographing some flower close-ups, when I recalled that Minolta had made a lens which had adjustable
    field curvature. I did a google search and found this:
    <p>
    http://www.rokkorfiles.com/24mm%20VFC.htm
    <p>
    Would it not be interesting if a macro lens could be made so that it had adjustable field curvature? I would
    think it would be interesting for flower shots.
     
  2. I don't know about the "adjustable field curvature" you refer to (and thanks for the link), but the effect of controlling where the sharp focus is, is achieved in tilt lenses such as those offered by several companies. At least a few of these, while not true macro lenses, have some close focus capability.
     
  3. OK, Ilkka, today y'r blooms are concave to the film plane and roughly spherical, but with different radii; tomorrow, convex to the film plane and roughly paraboloidal, again at different, um, scales; and the day after, saddle-shaped, with, again, different radii. I don't think that what you want is feasible.

    BTW, decentering (shift, vertical/horizontal) and rotating (tilt/swing) the lens won't help in any of these situations.

    There's a trade-off between sharpness in the plane of best focus and depth of field. The higher magnification is, the harder it is go get enough of both. I approach the problem by reasoning from the largest print I expect to make and stopping down a bit less than the smallest possible. And then, que sera, sera.

    Also, I'm well aware that closeup stopping down can reduce, not increase depth of field. For more on this point, buy a copy of H. Lou Gibson's Close-Up Photography and Photomacrography. 1970. Publication N-16. Eastman Kodak Co. Rochester, NY. 98+95+6 pp. The two sections were published separately as Kodak Publications N-12A and N-12B respectively. Far and away the most terrifying book on photographic technique I've ever read.

    Cheers,

    Dan
     
  4. I suppose you're correct, here is an example with different curvature in different parts of the flower.
    <p>
    http://www.flickr.com/photos/ilkka_nissila/2606821999/sizes/o/
    <p>
    I think I will investigate software which merge several images taken at different focusing distances. My Micro-Nikkor changes framing when I adjust focus, so I would have to compensate for this by moving the camera in the depth direction. Tricky, I think. I will try find a macro lens which is unit focusing to make this easier. Taking several images like this is made more complicated by the fact that the light doesn't stay constant, and also the flower can sway due to wind.
    <p>
    I hope for some liquid lens solution to the problem :)
     
  5. I have two of Minolta's VFC lenses (24mm and 35mm shift-ca) but they never made a micro/macro lens with VFC. I
    suspect almost all micro/macro lenses were deliberately designed with flat focus fields for copy work, and I suspect they
    still are, but others have more knowledge and experience with non-Minolta lenses.

    I'm not sure why other companies didn't use the technology when Minolta introduced and produced these lenses. Their real
    value is at the edges of the lenses (outer 1/3 radius), where the subject (eg. building) begins to fall outside the depth of
    field. I tend to use the lenses almost exclusively in flat field position and adjust as needed.
     
  6. Illka, the way to adjust focus when shooting closeup is to move the camera/lens assembly as a unit. Turning the focusing ring on the lens changes extension and magnification; this is rarely what's wanted.

    The techniques are out of my range, but I understand that some of the digital boys have found fairly effective ways of, in effect, scanning in depth and then stitching to get composite images with good depth.

    For curiousity, why do you think your MikroNikkor isn't unit focusing?
     
  7. Scott, it was good to see you join this post. I was wondering: Do you happen to have Minolta's Compact Bellows? I would think that it and either of your VFC lenses would make a great combination for Ilkka. If you happen to have the Compact Bellows, try it out real quick and let us know how they perform. I agree with Ilkka: for a well behaved shape flower (center farther away than the edge of the petals, but very regular), it would seem that a VFC lens would do quite well. The question is whether the image quality suffers at such close focusing distances. And for macro work, you don't need to worry about losing infinity focus for most adapters to modern cameras. Anyway, that was just a thought.
     
  8. Minolta's compact bellow's minimum length would be too long for a 24mm lens. The focal plane may be even inside
    the lens with it. I would try less then 10mm of extension.
     
  9. Larry, how may I count the ways of being curved? Or the shapes of flowers?

    I ask in all seriousness because the last two flowers I shot were a Grass Pink and an Asclepias tuberosa. Neither is, um, bowl shaped. Thinking of which, how may I count the shapes of bowls?

    Ilkka has a real problem that I share; deep subjects and tiny depth of field when shooting closeup. Short of scanning, I don't think we can get what we want.

    Incidentally, Illka, I've realised that the 200 MicroNikkors aren't unit focusing. Silly of me to forget, especially since I have and sometimes even use one. But even with them when shooting closeup one picks a magnification and then focuses by moving camera and lens. At distance, one turns the focusing ring.
     
  10. Dan, I am sure you know a lot more about both flowers and macro photography than I do. I do not deny that. I never said that the VFC feature would help for all or even most (even bowl-shaped) flowers. I was just following up on Scott's discussion of the two Minolta VFC lenses. I just thought they may possibly warrant a try with the Compact Bellows, but by no means guaranteeing success. I also tend to agree with Tommy that even the short extension on the Compact Bellows may be too much for those two lenses. The working distance would also be murder. But my comments to Scott were based on the old adage that there's no harm in trying.
     
  11. Larry, you're right, there's no harm trying. I really wish the problem could be solved that easily.

    Interesting that you mentioned the Compact Bellows. Lovely little piece of kit that I bought after seeing one at a neighbor has. He'd replaced rear mount with a C/Y bayonet and had an adapter for attaching his 100/6.3 Luminar to the front, used it on a Contax Aria. Since I use Nikons, I've acquired two stacks of Novoflex adapters -- one stack for each end -- to let me attach mine to a Nikon and a variety of things to the front.

    Nikon really missed the boat on that one. Nikon and Minolta bought panorama adapters from the same little machine shop. I'm not sure Minolta actually made the Compact Bellows, buying in seems more likely, and what Minolta bought Nikon should have too..
     
  12. Helicon Focus has a demo version of software to stack multiple images at different planes of focus. I've played around a little with it and it works fine with JPEGs at least. Ability to process NEF's (Nikon RAW) is questionable.
     
  13. I have the compact bellows which I've used in the field with the early 60's TC 135mm f4 macro lens on a Auto Bellows
    IV focsing rail. It's the shortest focal length to get infinity focus with the compact bellows. The macro version of this lens
    has no focusing and makes a great compact macro setup for hiking.

    I haven't tried the 24mm lens but it's a hmmm... (now I have to do something), but have with Minolta's MD 50mm and
    100mm bellows (no focusing) lenses which I've also used with the compact bellows. I suspect the compact bellows can't
    compress enough with the 24mm lens where extension tubes may do a better job (which I also have).

    Ding. Sorry gotta go. The hotdogs are ready. Oh, the lens results. I'll get back to ya'.
     
  14. This is probably too late and beside the point of enjoying the use of beautifully crafted optics, but software may once again take the magic out of an optical puzzle here. In microscopy image processing, so-called "Extended Depth of Field" functions have become quite common, and are now turning up in prosumer image editors as well (see e.g. here for examples).
    The idea is that the software picks out the different focused areas from multiple shots at different focus of the exact same subject, and combines them into a single seamless image with much greater DOF than any of the source images. A bit like stitching in depth from a single POV instead of across multiple adjacent POVs.
    Doing this routinely for macro flower shots would soon become a bit tedious, but I remember reading a "camera of the near future" feature in Popular Mechanics a year or two ago, where they fantasized about a camera with a compound-eye-like lens composed of 18 facets and capable of capturing 18 focal planes with one click to produce a single EDF image from the result.
     

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