Optimum bellows length

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elf
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Optimum bellows length

Post by elf »

I'm in the middle of building a new bellows setup for my camera and am wondering what the best length for the bellows would be. My first prototype is about 200mm long. The $30 ebay models seem to be about 150mm. There really isn't a physical limit on how long I can make the bellows, but optically I'm sure there is.

I bought an old Nikkor-H 50mm 2.0 (circa 1968) to use on the bellows and also have several other Nikon mount lens including an 80mm tilt/shift.

The camera is an Olympus e330 with 4/3rds sensor, so I expect diffraction will play the biggest part in the length calculation.

elf
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Post by elf »

Somehow this post ended up in the Technical and Studio forum instead of the Equipment forum. I'm not sure how to move it.

lauriek
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Post by lauriek »

I think my OM bellows are about 210mm long at max extension, I'm also using an E330 on them.. I haven't yet noticed diffraction being a particular issue, it's really only related to aperture and magnification (and sensor size, as you mention), so as long as you use faster lenses when going to higher magnification you can avoid it - at least up to a point. (This obviously does lead to rapidly decreasing DOF and increasing number of stack slices).

I have a feeling that to get any benefit from a bellows much longer than that may require a substantially larger sensor, but I'm not totally sure and I hope one of the more optically knowledgeable people around here will chip in soon and correct me if I'm wrong!

I'm sure one of the admins can move the thread over for you, perhaps PM Rik?

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Post by rjlittlefield »

I moved the thread to Equipment.

Brief answer to the question about bellows length is that 200 mm should be fine.

In theory, the limit is imposed only by effective aperture and sensor size. You want the size of the Airy disk to be roughly one pixel, and the size of the Airy disk is determined only by the effective aperture. (See http://www.cambridgeincolour.com/tutori ... graphy.htm.) So you can imagine (imagine!) sticking an f/4 FL=1000mm lens on 1000 mm of bellows, getting effective f/8 at 1:1, and doing some long distance macro with it.

In practice, the affordable lenses that give good resolution when used at high magnification all have short focal lengths. You'll see things like 50mm f/2.8 and 20 mm f/2. On 200 mm of extension, these things will drop to an effective f/11 and smaller, beyond which you'll be getting empty magnification anyway.

For the very sharpest pictures, you'll want to be using microscope objectives. The ones that are best for use on bellows will be optimized for "tube length" of typically 160 or 210 mm, which really means 150 or 200 mm from the mounting threads to the sensor plane. Both of those are nicely reachable with a 200 mm bellows.

A little more potential length won't hurt, of course, but I'm having trouble imagining a situation where it would help much either.

--Rik

elf
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Post by elf »

Thanks for the quick answer.
rjlittlefield wrote:So you can imagine (imagine!) sticking an f/4 FL=1000mm lens on 1000 mm of bellows, getting effective f/8 at 1:1, and doing some long distance macro with it.
Well, I do have a Celestron C90 with a Nikon mount, so I could try this. I don't think it's f/4 though :)
In practice, the affordable lenses that give good resolution when used at high magnification all have short focal lengths. You'll see things like 50mm f/2.8 and 20 mm f/2. On 200 mm of extension, these things will drop to an effective f/11 and smaller, beyond which you'll be getting empty magnification anyway.


The Nikkor-H 50mm seems like a good compromise between obtaining high magnification and having detail at infinity focus.

Joseph S. Wisniewski
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Post by Joseph S. Wisniewski »

Laurie's feeling is dead nuts on...

The Cambridge DOF calculator (wow, someone else mentioned it before I did, for a change) says f8 is pretty much it before diffraction turns any further extension into empty magnification. For a 50mm f2, that means 200mm from lens to sensor, and when you figure in adapters and the camera's own depth, 150mm of bellows should suffice. Going a stop past the diffraction limit, 280mm from lens to sensor means about 250mm of bellows.

For a 50mm f1.4, you can actually head for 285mm, which would give you about 250mm of bellows. That's the length I'd go for, it pretty much handles any extension you're likely to want to use with any "real world" lens. One stop past the diffraction limit means you'd be at 400,, with a 360mm bellows...

200mm is a bit too close to the sensor for either of these lenses reversed, so expect some resolution loss due to uncorrected aberrations. Fortunately, the four thirds sensor is so small that it minimizes the effects of spherical aberration.

If it were mine, I'd probably go around 250mm...

elf
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Post by elf »

Joseph S. Wisniewski wrote:Laurie's feeling is dead nuts on...

The Cambridge DOF calculator (wow, someone else mentioned it before I did, for a change) says f8 is pretty much it before diffraction turns any further extension into empty magnification. For a 50mm f2, that means 200mm from lens to sensor, and when you figure in adapters and the camera's own depth, 150mm of bellows should suffice. Going a stop past the diffraction limit, 280mm from lens to sensor means about 250mm of bellows.
Thanks Joseph. Now I need to start cutting fabric for the next version :)

Here's a couple of shots of the prototype:
Image

Image

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Post by rjlittlefield »

Joseph S. Wisniewski wrote:For a 50mm f1.4
Speaking of equipment choices, this raises another issue.

I've never had the pleasure of using a 50 mm f/1.4 that gives highest resolution at anything like wide open. Even the f/1.8's I've tested -- not top of the line to be sure -- gave better images stopped down a couple of notches.

What lenses would you recommend that are capable of exploiting a full f/1.4 aperture for this kind of work?

--Rik

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Post by augusthouse »

Why has this thread gone quiet?

I've only just re-realised how interesting it is.

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mgoodm3
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Post by mgoodm3 »

There is no magical point where "empty magnification" starts. The fall-off in image quality is a continuous process as magnification rises. You will get more resolution as the magnification rises, but there are diminishing returns as the magnification increases.

Using most lenses at the maximum aperture isn't terribly useful as optical aberrations limit the image quality far more than diffraction. With an El-Nikkor 50mm at it's sharpest aperture of f5.6 we would never get beyond a mag of 0.4 if we wanted to keep a effective aperture less than f8. I think that we all know that high quality images can be had by that lens at much higher magnifications.

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Post by rjlittlefield »

augusthouse wrote:Why has this thread gone quiet?
Perhaps the main points had been covered?

I see that one of lauriek's questions remained unanswered:
I have a feeling that to get any benefit from a bellows much longer than that may require a substantially larger sensor
Perhaps a better way to look at this issue is that a substantially larger sensor will require a proportionally longer bellows to get essentially the same benefit.

The basic rules are simple. You want to fill the sensor with the subject field you care about. You also need to limit the angle of view, because lenses only deliver a sharp image within some cone that defines their coverage. Typical coverage for a good macro lens at low power might be 20 degrees; for a microscope objective it's more like 10 degrees.

Suppose you want to shoot a 10 mm subject.

Then putting the rules together, assuming 20 degrees angle of view:
- a "1.6 crop factor" sensor will require 2.3X with the lens at least 65 mm from the sensor;
- full-frame 35 mm needs 3.6X and at least 102 mm;
- 4"x5" sheet film needs 12.7X and at least 360 mm; and
- 8"x10" film needs 25.4X and at least 720 mm.

The lenses that go along with these widely different extensions are actually quite similar. They range only from 20 mm for the APS-C to 27 mm for the 8"x10".

Back in the old days, it was common to use large format film for shooting small subjects. This involved putting short lenses on long extensions. The main benefit of that approach was greatly improved gradation, compared to using available small-format films. There was not a corresponding improvement in resolution, because the small effective f-numbers in the large-format setups introduced correspondingly large amounts of diffraction blur. With the lens properly set, diffraction blur in the final image is essentially independent of sensor size.

These days, digital sensors of almost all sizes provide the smooth gradation that used to require large format film. But the digital sensors are much smaller, so the need for long bellows has dropped off accordingly.

--Rik

DaveW
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Post by DaveW »

Using the Nikon PB-6E extension bellows on the PB-6 bellows, Nikon's bellows system, originally designed for 35mm film cameras (now FX being the digital equivalent), go out to 438mm of extension. Which would seem a bit pointless a camera firm making them if such extension was unusable?

http://www.mir.com.my/rb/photography/ha ... index3.htm

DaveW

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Post by rjlittlefield »

Nobody said "unusable" besides you, Dave.

That 438 mm of extension would be great with a reversed 135mm f/4.5, giving around 2.5X magnification with a working distance of 190 mm and an effective aperture of f/16.

Completely usable, especially on full-frame film. It's just a pretty specialized application.

--Rik

DaveW
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Post by DaveW »

I did not say anybody said they were unusable Rik, but got the impression they were implying there was a lesser maximum usable bellows length than the Nikon set-up.

As to how many sets you can couple together on the old 35mm film format. I know many have Lester Lefkowitz's book "The Manual of Close-Up Photography", so see his combination of three sets of standard bellows plus extension tubes on p.86.

Note he also makes his own ultra long extension tubes from lengths of plastic drain pipe on p.88. As he claims his centre drainpipe extension tube illustration is 27" long, that makes the longest one in the same illustration over 4ft long!

DaveW

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Post by puzzledpaul »

No comments on the use of multiple bellows rigs, other than to say I tried a setup with 2 once, when I was using the old D30 - and knew even less about stuff then than I do now :)

Thing I find interesting about bellows, is that many ppl who seem to have bought them in film days to 'try macro' hardly ever used them - hence a typical ebay listing stating 'hardly/little/never used etc ... and the 'shot in the arm' their use has been given by the arrival of digital and the associated reduced (running) costs of experimentation...

... although it does make me smile when I see in such (ebay) listings, the reason for sale of said bellows is that the user has 'gone digital' ...

Still, their loss is our (bd members) gain :)

pp
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