Zoom Tube Lens for Numismatic Photography

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ray_parkhurst
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Zoom Tube Lens for Numismatic Photography

Post by ray_parkhurst »

I'm thinking that an alternative to the bellows I've been using for coin photography may be a zoom tube lens, but to make an improvement in functionality over the bellows I'd need the following characteristics in the lens:

- Fixed overall length vs focal length
- At least 3x zoom ratio
- Prefer something like 25-75 or as close as possible
- Prefer to have a tripod mount
- EOS preferred but Nikon OK. FD maybe.

I'm looking for a final magnification range of approx 0.33...1.0, and would like to use a 75mm lens. I could tolerate up to 105mm lens but don't want to go further, so min focal length of 35mm would be the outside limit.

I think the key to this is the fixed overall length so that I can set the lens-coin distance and adjust zoom for framing.

What problems am I asking for? Will I have a serious vignetting issue at lower mags? I'm actually fine with some vignetting since coins are round, but it can't crop beyond the vertical height of the frame.

Can anyone suggest a solution?

Thanks in advance...

Ray

Edited to add that the "push pull" zooms won't do the job since the mechanisms are pretty easy to move, thus won't hold their position when in vertical orientation. I have a 100-300 Vivitar zoom that is a model of what I want, with no change in physical length and a 3x range, but it's focal length is too long...

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Post by rjlittlefield »

I usually see the words "tube lens" used in conjunction with infinity objectives, but I have the feeling that you're using it in some different way.

Can you clarify for me what you have in mind?

--Rik

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Post by ray_parkhurst »

rjlittlefield wrote:I usually see the words "tube lens" used in conjunction with infinity objectives, but I have the feeling that you're using it in some different way.

Can you clarify for me what you have in mind?

--Rik
I view "stacked lenses" similarly to infinity optics. I'd like to use a 75mm lens as the objective, then a 25-75 zoom lens focused at infinity for a 0.33-1.0x variable magnification stacked lens setup.

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Post by rjlittlefield »

I assume this is for APS-C. With 28 mm diagonal on the sensor, a 25 mm focused on infinity gives a diagonal angle of view around 58 degrees.

So, outright vignetting aside, your 75 mm in front also needs to tolerate being looked through at 29 degrees off axis, from wherever that 25's entrance pupil happens to be. Yes, this is sounding challenging. What did you have in mind for the front 75?

If you don't mind, I'd like to back off and ask about functional requirements for your whole setup. Reading between the lines of your current question, I'm guessing that you want to optimize workflow by separating framing and focus into two completely separate issues, instead of having them mixed together as with bellows systems. Are there other goals? What's driving the constraint for 75-100 mm on front, versus say 150 or 200?

--Rik

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Post by ray_parkhurst »

rjlittlefield wrote:I assume this is for APS-C. With 28 mm diagonal on the sensor, a 25 mm focused on infinity gives a diagonal angle of view around 58 degrees.

So, outright vignetting aside, your 75 mm in front also needs to tolerate being looked through at 29 degrees off axis, from wherever that 25's entrance pupil happens to be. Yes, this is sounding challenging. What did you have in mind for the front 75?

If you don't mind, I'd like to back off and ask about functional requirements for your whole setup. Reading between the lines of your current question, I'm guessing that you want to optimize workflow by separating framing and focus into two completely separate issues, instead of having them mixed together as with bellows systems. Are there other goals? What's driving the constraint for 75-100 mm on front, versus say 150 or 200?

--Rik
When I take pictures for folks at coin club meetings or shows, I am having to change magnifications quite often and the bellows is a bit slower than I'd like. So to improve on this, I was thinking of a stacked lens setup that would allow variable-magnification with constant working distance and possibly parfocality.

The magnification range I'm looking for is 0.33:1 for coins a bit larger than a Dollar to 1.0:1 for coins a bit smaller than a Dime. To keep the physical setup to a reasonable size, a shorter focal length objective would be nice, and I was hoping to use my 75ARD1 or perhaps an enlarger lens up to 105mm for this purpose. The longer the lens, the larger the setup due to increased working distance. That may not be a horrible thing, but going with something like a 70-210 would require a 210mm objective, which is going to be too long for a compact setup.

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Post by rjlittlefield »

Got it. That all sounds very reasonable. I still don't know lenses to do it, though.

--Rik

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Post by Chris S. »

Ray,

In my mind’s eye, I see the Nikkor 24-70 f/2.8 reversed on the 75 ARD1 working—at least by the numbers—for this. But as we know, combinations are hit or miss. While I have these optics, my gut feel is that the result would be a disaster; it’s hard for me to muster enthusiasm for going through the mechanical rigging needed to test this combination.

For the 1/3x to 1x regime, I usually use a standard (and so-called) “macro” or (Nikon speak) "micro" lens. Why not simply do this, putting the camera on a vertical stand with easy adjustability so that parfocality isn’t important? Since I have a very sharp Nikkor 105mm f/2.8 AF-D “micro,” I’d probably use that (though it lacks a lens collar). Or I’d use the Nikkor 200mm f/4 IF-ED AF-D "micro", which has a collar. My experience with this lens is also very positive, but its focal length would require you to mount it fairly high—though this would not be a problem if you built a stand appropriate for it. And though I have no experience with it, the well-regarded—and collared—Sigma 150mm macro would seem a very good choice. And Canon surely has excellent "macro" lenses, though I’m unfamiliar with them. (Using quotation marks around "macro" because at this forum, we'd generally consider this range "close-up.")

The 1/3x to 1x regime seems to have very good—and widely used—lenses available. Is there something unworkable with such a straightforward approach for coins?

--Chris

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Post by Pau »

I fully agree with Cris S. recommendation. For this magnification range there is a wide offer of excellent optics from most camera makers. For coins I would sugest one of the micro Nikkor 105 or one of the Canon EF 100mm f2.8 (both have internal focusing), but even cheaper lenses like a micro Nikkor 50, a Canon Compact macro EF 50 f 2.5 with a 25mm extension tube or a Sigma will do the job with high quality.
The need of more exotic optics beguins over 1X magnification.

But of course with all of them you will need to refocus to change magnification. May be your goal is to change magnification without refocusing like in good zoom stereomicroscopes?
Pau

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Post by ChrisR »

You could look at at the Schneider Betavaron. Iirc it's a zoom enlarger lens, with (approximate ?) parfocality over a range. I doubt it goes to 1:1 though.

I believe I tried it on tubes, which probably lost the parfocality, but wouldn't rely on my memory.

-----

You can certainly do what you want, in terms of field width, and parfocality, with a zoom with a close-up lens. You can even use a Compact - then it all fits in a jacket pocket.

To avoid vignetting in the CU lens you'd want the longer end of a zoom. You need a 3:1 range to be usable. With a "6x" compact you can get about a 20 - 60mm field of view on the zoom, with a Raynox 250 (125mm FL). For other widths, you can switch to a different Raynox. All fits in your pocket.
You get a slew of aberrations and distortion of course.
A wide-range tele zoom on a DSLR with a Raynox, I haven't tried.
A Canon 55-250 might be interesting.

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Post by ray_parkhurst »

Chris S. wrote:Ray,

In my mind’s eye, I see the Nikkor 24-70 f/2.8 reversed on the 75 ARD1 working—at least by the numbers—for this. But as we know, combinations are hit or miss. While I have these optics, my gut feel is that the result would be a disaster; it’s hard for me to muster enthusiasm for going through the mechanical rigging needed to test this combination.

For the 1/3x to 1x regime, I usually use a standard (and so-called) “macro” or (Nikon speak) "micro" lens. Why not simply do this, putting the camera on a vertical stand with easy adjustability so that parfocality isn’t important? Since I have a very sharp Nikkor 105mm f/2.8 AF-D “micro,” I’d probably use that (though it lacks a lens collar). Or I’d use the Nikkor 200mm f/4 IF-ED AF-D "micro", which has a collar. My experience with this lens is also very positive, but its focal length would require you to mount it fairly high—though this would not be a problem if you built a stand appropriate for it. And though I have no experience with it, the well-regarded—and collared—Sigma 150mm macro would seem a very good choice. And Canon surely has excellent "macro" lenses, though I’m unfamiliar with them. (Using quotation marks around "macro" because at this forum, we'd generally consider this range "close-up.")

The 1/3x to 1x regime seems to have very good—and widely used—lenses available. Is there something unworkable with such a straightforward approach for coins?

--Chris
Does the Nikon 24-70 keep a fixed overall length when zooming? If so that might be an excellent option.

Most coin photographers seem to use the Sigma 150. It's an excellent lens and gives good results, as good as such a long lens can give. But their setups end up quite large, requiring gigantic copy stands to accommodate larger coins.

One added factor I did not mention was that folks often want higher mag details of their coins to show die varieties. This ends up being problematic if a 4-5x magnification is needed and suddenly I need to be at 20mm WD rather than 400mm. This is why a compact setup is desirable.
Pau wrote:I fully agree with Cris S. recommendation. For this magnification range there is a wide offer of excellent optics from most camera makers. For coins I would sugest one of the micro Nikkor 105 or one of the Canon EF 100mm f2.8 (both have internal focusing), but even cheaper lenses like a micro Nikkor 50, a Canon Compact macro EF 50 f 2.5 with a 25mm extension tube or a Sigma will do the job with high quality.
The need of more exotic optics beguins over 1X magnification.

But of course with all of them you will need to refocus to change magnification. May be your goal is to change magnification without refocusing like in good zoom stereomicroscopes?
A problem with the shorter dedicated Macro lenses is their relatively large physical diameter, which blocks light from reaching the coin at a high angle. Same issue as with microscope objectives but at a larger scale. In addition, most dedicated Macros significantly shorten their focal length at higher magnifications, which reduces the workign distance and makes the problem even worse. I have a Nikkor 105VR but at 1:1 it shortens its focal length to something like 60mm, and is so large in diameter that I can't get lights any higher than about 45-deg, which is highly undesirable. This is why a lot of folks go with 150mm Sigma, ie to get enough working distance for lighting flexibility. But for larger coins the focal length is longer, so working distance increases more than it would from a fixed FL lens.

I believe with a stacked/tube/infinite type setup, with tube lens focused at infinity, the WD doesn't move as the tube lens focal length is varied once the subject is in focus, correct? That sounds like an ideal setup for coins if the tube lens can be made to work.

Actually, examples of this already exist in the machine vision world. My B&L Monozoom7 has a 7:1 zoom range with exactly this characteristic. But its variable-mag infinite tube lens is a pretty long in focal length and this results in a very long working distance. Going to a lower mag objective makes the WD unworkable. Plus, the NA on the MZ7 is not that great.
ChrisR wrote:You could look at at the Schneider Betavaron. Iirc it's a zoom enlarger lens, with (approximate ?) parfocality over a range. I doubt it goes to 1:1 though.

I believe I tried it on tubes, which probably lost the parfocality, but wouldn't rely on my memory.

-----

You can certainly do what you want, in terms of field width, and parfocality, with a zoom with a close-up lens. You can even use a Compact - then it all fits in a jacket pocket.

To avoid vignetting in the CU lens you'd want the longer end of a zoom. You need a 3:1 range to be usable. With a "6x" compact you can get about a 20 - 60mm field of view on the zoom, with a Raynox 250 (125mm FL). For other widths, you can switch to a different Raynox. All fits in your pocket.
You get a slew of aberrations and distortion of course.
A wide-range tele zoom on a DSLR with a Raynox, I haven't tried.
A Canon 55-250 might be interesting.
I have not tried a Betavaron but I don't think it's mag range is what I'm looking for. I think it is 3:1 min / 1:3 max depending on orientation.

I had not considered a Raynox 250 or other FL add-ons instead of macro objectives. I will think about that. But in any case it still comes down to having a zoom that will work without physical length changes vs FL and can work with good stability while vertical.

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Post by rjlittlefield »

Raynox 250 = 125 mm. The viewing through it is not good at wide angles. At 1:3 on my Canon 18-55, the edges are obviously soft, with lateral CA.

--Rik

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Post by Chris S. »

ray_parkhurst wrote:Does the Nikon 24-70 keep a fixed overall length when zooming?
No. It has its shortest physical length (approx 135mm) at about the 50mm focal length setting. It lengthens by about 5mm when zooming to 70mm FL. From the 50mm FL setting, it lengthens by about 20mm when zooming to 24mm FL.

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Post by ChrisR »

Yes, the Raynoxes seem to be better with less wide-angle prime lenses, not so bad with the long end of the standard zoom, or maybe a 55-250 as suggested. And yes the Raynox 250 is 125mm.
I can't see you not compromising on IQ for this "parfocal" project.

You might think about a "Leitz macro stand style" support Ray. Then the camera can move up and down, wth your support, and whatever "front" lens and coin staying put.
I have two variations, the more useful of which mounts to the filter ring of a normal lens with 4 legs. Easier for your application perhaps than dangling off a tripod.
This version (the original probably, the clones vary) has lens-specific rings which go into a camera, but shows the legs - one's hidden!
I have a third, diy version which uses lengths of studding for the legs, which screw right through the supporting plate.
Image
Last edited by ChrisR on Tue Mar 26, 2013 2:57 pm, edited 1 time in total.

mgoodm3
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Post by mgoodm3 »

I haven't found zoom lenses to work well when stacked. USing an internal focus lens as you tube lens will work since they change their focal length with the focus ring. My 200/4 micro goes from about 200 to 100 mm from near to far focus and will give about a 2:1 magnification range.

Anything shorter than about 100mm tends to have a lot of vignetting when used as the "tube lens" in this scenario.

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Post by mgoodm3 »

I have also had no luck with much of anything under 2:1 mag with stacked lenses - vignetting also.

edit:

Why don't you just reverse a standard zoom lens? As long as you use an FD lens with an aperture ring, it will give you a magnification range in the area that you are looking.

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