[35mmfilmfan]

Just acquired a set of M42 bellows, with a PK adapter (tightly) attached at the body end. Using on K20d body - what prime focal length(s) would be recommended for macro work, please?

[Lux Legere]

You can use an enlarger-lens very well (50 or 80 mm). Therefor you need an adapter for M39 (i think so). Good enlarger-lenses are not so expensive (except some of those rodenstock or schneider).

[Kobayashi.K]

Butkus has manuals for the Bellows II and Auto Bellows A on its web site.
They contain useful info how to use them with tables and formulas.
Pentax camera instruction manuals, Pentax professional instruction manuals

[stevebrot]

Much depends on clearance at the rear standard* and back of bellows rail for the camera body; that and the length of the camera rails. The basic rules run something like this:

• Magnification is a function of extension with 1:1 (1x) attained at double the lens focal length
• Working distance** for a given magnification varies by focal length with longer lenses providing greater working distance. Specialized macro lenses (no focus helicoid) are usually 100mm. Less than 50mm may be unworkable due to bellows + standards thickness issues.
• Enlarger lenses are often suggested because they are optimized for flat-field to flat-field reproduction and perform well for flat art, coins, and stamps
• Focus with a bellows is not done by increasing/decreasing extension. Instead, it is done by using a focus rail or equivalent to move the camera, bellows, and lens as a unit.

Note too that at 1:1 magnification, the f/2 becomes f/2.8 f/2 becomes an effective f/4, only without an increase in depth of field.


Steve

* The rear standard is the frame that provides attachment to the camera. The lens mounts to the front standard.

** Measured from the front element to the subject.

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Last edited by stevebrot; 02-24-2020 at 09:51 AM.

[pacerr]

As always, focal length depends on what you're trying to accomplish. In general, any quality lens between 35 -135mm will serve as a start. The longer the FL, the narrower the field of view and the greater the working distance from the subject.

Bellows/macro photography is normally a very deliberate process and depth of field is minimal (fractions of an inch) so a fast lens isn't necessary. A classic, economical Pentax SMC f 1.8/50 or 55mm lens would be a fine start. The learning curve is steep and a solid mount/tripod and good lighting are crucial.

Many on-line resources are available for reference:

Macro by any means necessary club

The MaQro Qlub!

[35mmfilmfan]

Thank you all very much for this info - they are totally non-auto, unidentified bellows, except for a sticker saying 'Made in GDR'; the camera will mount very close to the rear standard (thanks for the technical terms), and, although there are centimetre marks along the LH rail, there is no indication of function or use ! The rails are fixed to the rear standard, and the front one moves by undoing a knob and sliding by hand - as I said, extremely basic ! As with anything, patience, experimentation, trial and error and keeping notes will be essential. I have a ring flash which will attach to the filter thread on whichever lens I get, and a focusing rail to move the entire setup back and forth. Am I right in assuming the lens should be focussed at infinity, or can I use the lens helicoid focus for fine adjustment ?

I do realise that more modern, hi-tech bellows are available, but these had one great advantage - they were free !

Thank you too for the links - much appreciated.

[fwwidall]

You might want to check out the very informative Extreme Macro Photography by fellow pentaxian Johan J Ingles-Le Nobel. A great resource for all things macro.

As for lenses its all down to how much magnification you want to achieve. An 50mm will get you to around 4X, a 28mm around 8X. I'm using microscope objectives (as opposed to camera lenses) to get to around 13X.

If you're interesting in really extreme macro then the forums at www.photomacrography.net offer a wealth of knowledge and experience.

Have fun,

Fred.

[photoptimist]

lthough there are centimetre marks along the LH rail, there is no indication of function or use !

Those marks should tell you the distance from the rear mount (the camera) to the front mount (the lens). If so, you can use them to quickly set front standard to a particular mark to get an approximate magnification. A 50 mm (5 cm) lens needs 5 cm of extension for every unit of magnification. Thus, 3X needs 15 cm of extension. Similarly, a 28mm (2.8 cm) lens needs 2.8 cm of extension for every unit of magnification. If you know the focal length and desired magnification, a wee bit of math beats trial & error on getting what you want.

Am I right in assuming the lens should be focussed at infinity, or can I use the lens helicoid focus for fine adjustment ?.

Yes, you can use the lens helicoid focus for fine adjustment. You might find that adjustment more useful if you turn the focus to the middle of the range (not infinity) so you have some adjustment in both direction.

I do realise that more modern, hi-tech bellows are available, but these had one great advantage - they were free !.

That's even a bargain at twice the price!

what prime focal length(s) would be recommended for macro work, please?

Shorter focal lengths get much higher magnification for a given about of extension but much tighter working distances. In some cases, at high magnification with a wide-angle lens, the point of focus might be touching the front element or perhaps even inside the lens.

Longer focal lengths don't provide as much magnification but do give better working distances which enables more even lighting.

Note: the rule of thumb about wide angle lenses having deeper depth-of-field does not work in macro.

[Thagomizer]

The "right" focal length depends on the size of the object you're shooting, how much of it you're wanting to show, and at what size you want it to be. I often go to greater than 1:1 for full body shots of small insects or portrait shots of larger ones. At higher magnification, depth of field gets shallower and shallower, so the orientation of your subject with regards to the thin plane of focus becomes an important consideration.

You can also reverse the lens you're using on the bellows with an M42 reverse adapter ring. Most non-macro lenses 50mm and shorter perform better for macro work when they are reversed. References linked above have information on lens reversal. You're already going without automatic diaphragm with the bellows, so reversing the lens on the front standard isn't really costing you anything. With shorter focal length lenses reversed on extension, you never face the problem, noted above by photoptimist, of your focus point ending up inside the lens when they're mounted normally on extension. Your working distance will be the flange focal distance of the reversed lens you're using. With Pentax lenses for 35mm film or DSLR, that distance is about 45mm. Because you're mounting it via the filter threads rather than the lens mount, you can use any brand lens, as long as you've got the right combination of reverse adapter and stepping rings to fit.

Here's one of my go to links for macro ideas:

CHEAP MACRO -- Buying or exploiting a lens for ultraclose work - PentaxForums.com

Have fun, and if you feel so inclined, share your results.

[35mmfilmfan]

Again, my grateful thanks. I shall visit my local friendly dealer (yes, they still exist !) and see what he has in the way of M42 W/A lenses. I had wondered about the reversing rings too - had one yonks ago when I had an old Praktica. And, of course, with a reversing ring, I wouldn't need to worry about the lens mount, as a reversed PK lens - and I have a selection of those - would fit with an M42 reversing ring.

When I get some results (any results !) I shall endeavour to share them. After all, others can hopefully learn by my mistakes.

[From1980]

Note too that at 1:1 magnification, the f/2 becomes f/2.8, only without an increase in depth of field.

Lots of good info here for someone who is new to bellows extension and macro in general. Just a gentle correction needed for the above quote though. Determining effective aperture (EA) depends on a factor of (m + 1) squared. "m" is magnification of image size on the film or sensor relative to actual subject size. So that exposure factor at 1:1 is (m + 1)(m +1). 2 X 2 = 4. A factor of 4X is two stops so that f/2 on the lens is effectively f/4. As mentioned, depth of field barely increases at higher magnifications but EA is important to know for exposure and understanding limitations due to diffraction. Very tiny EAs can be reached with short lenses and even moderate magnification so that sharpness of details in an image are easily muddied. As above, best results will probably come from using enlarger lenses or reversed camera lenses. Keep demands moderate with camera lenses on a bellows along with quite cheap adapters and enjoy.

[Wheatfield]

I have a selection of enlarger lenses that I use. My bellows of choice is a screw mount unit because it is so easy to adapt enlarger lenses to it.
Also, if you can find a bellows 100/4 lens, it is an excellent choice.

[35mmfilmfan]

Just put in a bid on a couple of cheap enlarger lenses - Schneider and Nikon. If I win, got a link to an 39-42 adapter as well, also 49mm filter to M42 rev ring. Don't think this'll ever be a major part of my photography, but as I get older and more decrepit, may give me something to do while I wait for other bits of me to stop working or fall off !

[stevebrot]

So that exposure factor at 1:1 is (m + 1)(m +1). 2 X 2 = 4. A factor of 4X is two stops so that f/2 on the lens is effectively f/4.

You are correct...my bad

The key word here is "effective". Thank you for the correction.


Steve

[stevebrot]

In general, any quality lens between 35 -135mm will serve as a start

That is a good general range, although things might get a little tight if wanting to shoot at less than 1:1 with 35mm focal length. The combination of thickness for front and rear standards and fully compressed accordion bellows on my Pentax Bellows Unit K only allows for a minimum 32mm extension, though things might be better with other bellows. As always, YMMV.


Steve