645 DOF problem

Discussion in 'Medium Format' started by Karim Ghantous, Jan 5, 2021.

  1. I haven't done a product shoot in ages. But, as an exercise, I decided to pullout the Pentax 645 (which I bought on a whim some years ago and have used only once!) to see if the DOF would let me do a particular task. The task is to basically photograph a brick, at a 45 degree angle, close to the camera, with a 75mm lens.

    The brick represents a typical small object that I've had to shoot now and then. Usually I'd be shooting chandeliers or tables or lamps. But here and there I've had to shoot statuettes, some of which were long rather than tall. The problem is that I don't think that the 645 can do it.

    I've attached a photo of the 645's viewfinder so you can see what I'm getting at. The front edge of the brick is at minimum focusing distance, which is 60cm. The rear edge is at about 75cm. Even stopped down to f/22, the DOF wouldn't cover it. So... what would you do?

    brick_through_VF.jpeg

    DOF_scale_75mm.jpeg

    I do have two other lenses, a 45mm and an 80-160. The brick can easily be covered by the 45mm, even at f/16. But I don't want to shoot with this focal length. The zoom doesn't have a useful DOF scale at all, although it does stop down to f/32. This kind of situation is a piece of cake with 35mm, of course.

    This is not by any means a big problem. Partly because I imagine that I'll be using a digital camera if I get more commercial jobs (not likely but you never know). But, I do want to actually use this gear for something. I don't want to waste it by just shooting road signs and flowers. I actually want to give this thing some work, including casual wildlife subject matter. Yeah, I'm looking at the 300mm...

    I think I've found a lab that offers the ideal balance of cost, turnaround and scan quality. I don't need to shoot medium format, but I'd certainly like to. It's terrific stuff.
     
  2. I'd take out my Rolleiflex SL66 or SL66E (oops, both are long gone) and use their build-in tiltable bellows to stretch DOF to cover that brick front to back. Too bad the Pentax 645 is a film camera - otherwise you could focus stack.
     
  3. IMO, wrong tool for the job. MF is large enough to have a serious lack of DOF even at small apertures, but it's not LF where you can easily apply swings and tilts. Oddly, I've run into this problem where 35mm or FF digital couldn't help me, but an old tiny sensor bridge camera saved the day. Not everything can be focus stacked, but that's the other way out.
     
    bobbudding likes this.
  4. SCL

    SCL

    Couldn't you move the camera body further away from the brick to secure focus of the entire brick and then crop the image?
     
  5. You look to have focused on the very nearest corner of the brick. The usual advice is to focus one third of the way into the distance range you want to try and get sharp. Or half way, at short distances.
     
  6. Focus stacking would be ideal. But even with a digital camera, unless it has the feature internally it's a PITA. This is one reason why I like Olympus.

    Good points. And there are ways to maximise image quality from smaller sensors, if you really need to use them.

    Well, yes. ;-) But then I may as well shoot 35mm.

    Perhaps my language wasn't clear. Here's the problem in a nutshell: I have a subject which I want acceptably sharp, from the front to the back. The approximate total distance is 15cm. 60cm is the closest point, 75cm is the furthest point. Both points are significantly outside what can be covered by f/22, as you can see via the DOF scale.

    I think Conrad is right: 645 is not the right tool for this job. I could use a low ISO emulsion in 35mm for those objects that can't be photographed with 645. That would not be such a bad compromise. If I used modern lenses I might get a result that comes a little bit closer to 645.
     
  7. The problem doesn't go away when switching to 35 mm. You either need a camera that allows swinging the plane of focus, or employ focus stacking.
     
  8. Dustin McAmera

    Dustin McAmera Yorkshire, mostly on film.

    I think only Bronica offered a lens with tilt for 6x45, for the ETR series. Rare and expensive.
    If I needed to do this and insisted on roll film, I'd try my Century Graphic, with 6x7 or 6x9 back. It has entry-level tilt.
     
  9. Get a Nikon PB-4 bellows. It has the ability to swing the lens. Or spend big-time on a Tilt-shift lens or adapter.

    Alternatively, a digital compact with a tiny sensor might have sufficient DoF without resorting to lens or back movements.

    Going up in format size is definitely the wrong direction, unless you move up to a camera that offers lens or back swing.
     
  10. I can in fact do this with 35mm. A 50mm lens can just work at f/16, but preferably at f/22. Although diffraction might affect the image too much.

    I think some Rollei and Fuji cameras had integrated bellows, too.

    True. But you wouldn't have to go that small. 35mm can do it, although only just. APS-C and Micro 4/3 can easily handle it, and that's without focus stacking. At this time, a 1" sensor is the smallest I would accept as 'professional grade'. I suppose that every camera system has its weak point, and we just have to live with that.
     
  11. This is the diffraction you get at small apertures.
    Crops of halftone dots -
    F5-6_1.jpg

    F16_1.jpg
    F22_1.jpg
    And it gets worse with smaller sensor size!

    F/11 will look pretty fuzzy on a 1" (not really, actually 9x12mm) sensor.

    So you're trading off an out-of-focus blur for a diffraction blur. Whatever; you still end up with blur. Except the diffraction blur affects the 'sharp' parts of the image as well.

    This is the effect of sensor size on depth-of-field - all taken at the same aperture.
    D800.jpg
    24mmx36mm (Full Frame)

    D7200.jpg
    APS-C

    Coolpix-P6000.jpg
    Compact - 6mm x 8mm

    So even going to a very tiny sensor doesn't really get you full front-to back focus.

    Do the job properly and use a solution that allows the lens axis to be angled WRT the image plane!
     
  12. In case anyone needs convincing that tilt/swing camera movements are more effective than simply stopping down.

    I trotted out the spice containers once again and fitted a 100mm Componon lens to my PB-4 swing/shift bellows. All attached to the full-frame D800.

    The lens square-on at f/8:
    f8_100mm_Componon.jpg
    Quite fuzzy at each end of the row.

    Now stopped down to f/22:
    f22_100mm_Componon.jpg
    Still not passing the pixel-peeping test.

    Back to f/8, but this time with lens swing:
    f8_swung_100mm_Componon.jpg
    All in focus at last!

    Here are 100% crops of the left and right spice labels - at f/22 straight (top) and with lens-swing at f/8 (bottom):
    f22-vs-swung-f8.jpg
    With a bit more care and time in setup the left label could probably have been made even sharper.

    Oh, yes; another disadvantage of simply stopping down was that the flash had to be wound up to full output, as well as the ISO speed being raised.
     
    Last edited: Jan 9, 2021
  13. Thank you for sharing that demo - I think it proves the point that focus stacking or lens movements are superior to smaller apertures. Regarding the half tone dots, I'd say f/16 is acceptable, but f/22 is out of the question. On Micro 4/3, f/8 is the smallest I'd go.
     
  14. I just looked at the price of a PB-4 bellows on *Bay. Wowser! The price has shot up recently, except from Japanese sellers for some reason.

    A PB-4 and a 100 - 105mm enlarging lens is still cheaper than any Tilt/Shift lens though.

    Maybe there's a market for an affordable ball-and-socket lens mount that'll take a decent lens, rather than a lensbaby bottle-bottom?
     

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