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04-09-2011, 01:55 AM   #1
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Pentax Bellows

Hi,

I have just purchased a set of Pentax K Bellows.
Can anyone tell me what settings I should use with aPentax 500mm f2 with my K20D or should I use a different combination?
I have a Tamron 90mm f2.5 that I could use.

Regards,
Gordon.

04-09-2011, 05:01 AM   #2
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You'll probably be happy with one of your 50mm lenses (whichever has manual aperture control). If you need more clearance between the lens and subject the 90mm lens would help (but the maximum magnification will be less.)

Use the green button to determine settings.
04-09-2011, 08:30 AM   #3
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Settings? Unless you are doing scientific work and need to know the exact reproduction ratio, the scales are pretty useless and other than aligning to the scales, there really are no settings.

I also own the Bellow K and appreciate the compact and light package. The Bellows K can sort of be viewed as bellows "light" in that while it has both a extension and focus rails (top and bottom), only the front standard of the extension rail is geared. This fact has usage implications that I will address below.

So...here is a short primer on bellows. Much also applies to extension tubes too.

Regarding focal length:
  • Shorter gives higher magnification for a given extension
  • Longer gives greater working distance for a given magnification
  • Longer requires greater extension for a given magnification
  • Using bellows with a lens longer than about 100mm is an exercise in frustration
  • 50mm is a good compromise in terms of size, ease of use, and magnification

Regarding magnification:
  • The greater the extension, the greater the magnification
  • There are formulas to calculate, but I have never found them useful in practice

Usage (non-intuitive, but correct none-the-less):
  1. Mount bellows to tripod
  2. Adjust front/rear standards for your desired initial extension providing space front and rear for later adjustment.
  3. Center the the lower rail
  4. Mount camera mount adapter to camera body
  5. Mount lens and camera to bellows
  6. Point the whole thing at your subject (duh!)
  7. Extend the bellows for the desired magnification. This is most conveniently done using the gear drive for the front standard. The viewfinder is helpful at this point (duh, again!)
  8. Focus using the lower (focus) rail. This in the part that does not make sense. At higher magnifications the focus mechanism on the lens has little affect. Moving the front standard can bring the image into focus, but only with a change in magnification. The general rule is that you focus by moving the camera rather than by extending the lens. This is not particularly easy with the Bellows K (no gearing for the focus rail), but do-able by loosening the small knob and nudging the rail forward/back with your fingers. (Note: High end bellows are frequently designed for extension only and assume the use of a separate, high precision x-y focus/positioning rail.)
  9. Adjust to the taking aperture and make your exposure
By the time you get to the focus step, you will likely have noticed that the viewfinder is pretty dim. Extension is the same as increasing the focal length so the amount of light available for focus and exposure drops off dramatically. You can (an probably should) add flash as your main light source for exposure. Unfortunately flash does little to help with focusing.

Well, that is all I have time to contribute on this topic today. Good luck!


Steve
04-09-2011, 10:45 PM   #4
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An old-time back-woods banjo player was asked if he could read musical notation.

"Notes? Hell sonny, there AIN'T no notes on a banjar -- you just PLAY!"

Settings for bellows? As stevebrot mentioned, except for precise technical shooting, don't worry about settings. Just get into position and shoot!

I do have a quibble with his otherwise-excellent analysis. I don't find that using longer lenses on extension (tubes and/or bellows) to be very frustrating, just different. And I may have different goals. So, what are the reasons for using extension, especially bellows?

1) closeup / macro work
2) flexible use of non-focusing lenses
3) ability to exploit almost any optical material

True, lenses longer than 100mm require LOTS of extension in order to get LOTS of magnification. So, adjust usage accordingly. Use lenses shorter than 50mm for LOTS of magnification and fairly close work. Use lenses longer than 100mm for less magnification and more working distance. Use 50-100mm lenses for in-between stuff. My extreme story: a Spiratone 400mm lens with a 2x TC and 400mm of tubes on a 150mm bellows, all shoulder-stock mounted -- for shooting closeups of live rattlesnakes in the wild from a safe distance, like 3-4m. In bright sunlight, of course. Extension eats light.

I have PK and M42 bellows that extend to 140mm, and a smaller M42 that goes to 110mm. For work where edge-to-edge flatfield sharpness is needed, I use enlarger lenses (EL's). For macro work (magnification of 1:1+), those are mostly in the 35-75mm range. For less magnification, I prefer the 60-130mm range. For further work with a close-focus option, it's the 100-200mm range. And if I want 'character' (ie aberrations) I'll use various scavenged MF and other lenses longer than 85mm, about the shortest FL that will reach infinity focus on my bellows.

Longer focal lengths may require tubes as well as bellows. An advantage of using camera lenses on bellows is that some extension is already built into the lens. So if i know that some close field shooting will be within a certain range, I'll use a camera lens; if I think I'll need less magnification, but the ability to focus from infinity to very close, I'll use an EL. Or a few EL's -- they're small, easy to throw a few into a pocket. Or for a small light package for 1:1 work, it's hard to beat an Industar-50/3.5 on 50mm of tubes.

As I suggested, bellows aren't limited to 'good' lenses. For interesting (ie lousy) effects, mount an eyeglass lens, or a magnifier, or a fresnel sheet, or a tail-light cover, any optical material you can shove into the bellows mount. For a 'period' effect, I'll mount the bellows with M42-PK adapter as needed; 42-43mm step ring; Raynox DCR-250 (+8 dioptre); and a 49mm +2 dioptre close-up lens. That total of +10 dioptres makes a 100/3.5 lens without lotsa modern corrections. Hmmm, I should get a 42-49 step ring, skip the Raynox (which is fairly corrected) and just use sets of closeup lenses. +12 dioptres would make about an 85/2.2 super-meniscus. Good for soft headshots. Cheap, too!

04-10-2011, 02:34 PM   #5
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QuoteOriginally posted by gordon_l34 Quote
Hi,

I have just purchased a set of Pentax K Bellows.
Can anyone tell me what settings I should use with aPentax 500mm f2 with my K20D or should I use a different combination?
I have a Tamron 90mm f2.5 that I could use.

Regards,
Gordon.
I don't think you should use that lens with your bellows - too heavy!
04-10-2011, 09:36 PM   #6
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QuoteOriginally posted by Tom S. Quote
QuoteOriginally posted by gordon_l34:
Can anyone tell me what settings I should use with aPentax 500mm f2 with my K20D or should I use a different combination?
I don't think you should use that lens with your bellows - too heavy!
Nice catch! Does a Pentax 500/2 even exist? I didn't see any in the database.
For that matter, does ANY 500/2 exist, except maybe in a spy satellite?
04-11-2011, 06:07 AM   #7
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QuoteOriginally posted by RioRico Quote
Nice catch! Does a Pentax 500/2 even exist? I didn't see any in the database.
For that matter, does ANY 500/2 exist, except maybe in a spy satellite?
For me, it wouldn't matter if it existed or not. Even if I mortgaged my house I wouldn't have enough money!

There are some F2.8's out there though. Here's an interesting 200-500 F2.8 from Sigma for Canon: Sigma

Last edited by Tom S.; 04-11-2011 at 06:13 AM.
04-12-2011, 09:31 PM   #8
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Original Poster
Hi All,

I have a typographical error in that it should be 50mm not 500mm.
Sorry for the confusion and thanks for the welcome advise.

Regards,
Gordon.

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