52mm Tubes, and other adapters.

Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

Lou Jost
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Post by Lou Jost »

I think we need to know the length of the big tube before we can figure out the number of sets of small tubes needed to get to 208. But the cool thing is that NO MATTER HOW BIG the big tube is, as long as it's less than 208 minus 40, we can reach 208 exactly. May take as little as one set. Could take as many as eight sets in the worst case.

Edit--If you are willing to accept a slightly bigger gap and make it up with filter rings, and if you don't want to buy lots of sets, then Rik's solution is a better one.
Last edited by Lou Jost on Wed Mar 08, 2017 9:54 am, edited 2 times in total.

Lou Jost
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Post by Lou Jost »

By the way, I agree with you that focusing helicoids are great if they are well-made. I've had poor luck with 52mm versions. Today I got a nice one for MFT and 42mm lens, made by PIXCO. It is much less wobbly than Fotodiox 52mm helicoids.

rjlittlefield
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Post by rjlittlefield »

ChrisR wrote:Cheap simple and good are unfamiliar bedfellows but the Long Screw wouldn't be too bad. It also allows rotation setting, if you aren't too fussy about length. The skinny ring locks it. I don't see why the threads shouldn't be say 15mm long. On 2 inch" pipe threads they're 3-4 inches, but they're 11 tpi, not 0.75mm.

Image
Several years ago I built a 42mm version of this, by combining an ordinary tube for the outer section with a modified tube for the inner section. The modification was to cut off the normal thread and install a long threaded cylinder to replace it.

In my case the goal was to have essentially a fine pitch helicoid, capable of 10 mm range with usable resolution below 10 microns. It worked great on the few occasions that I needed it.

I went with a plastic inner screw, which I machined to a backlash-free fit.

But for the purposes discussed in this thread, the locking ring and looser threads would be a better solution.

I think this thing could sell. "Adjustable extension tube -- make exactly the length you need."

--Rik

Lou Jost
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Post by Lou Jost »

I'd buy it!

mjkzz
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Post by mjkzz »

here is mine ... and I use thread sealing tape to make it "stay" if necessary. It allows you to extend out between 20mm to 30mm if 5mm margin is required on each side.

Image

Lou Jost
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Post by Lou Jost »

What is the thread size? The diameter? Looks good!

ChrisR
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Post by ChrisR »

I have something which looks like that 39mm, - it came on an enlarger lens which was used in a print-lab auto printer. The focus was adjusted with that.
(It also had a lens attached, FL measured at 2000mm! :smt104 )
Chris R

mjkzz
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Post by mjkzz »

It has M42x1 threads, one female, one male and length is 20mm when fully screwed in, so if you need 5mm on each ends, you can adjust length from 20mm to 30mm. I use thread sealing tape to increase friction if I need it. The inner ring has 36mm inner diameter, it is best used right after the Raynox.

I have separated my blog site and commercial site,so here is a full write-up on my blog

ChrisR
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Post by ChrisR »

Image

Yellow is fitting ring for ringflash,
or lens hood, etc

Can also be M42 and 52mm

or 58mm and 67mm for MP-E.
Chris R

mawyatt
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Post by mawyatt »

If one doesn't need precise magnification or focus, then it's not necessary to get the "exact" tube to sensor length correct...right?

When using something like the Raynox tube lenses and various objectives (Mitutoyo for example) for stacking, isn't just getting close enough OK since you'll be stacking anyway? I don't think the IQ just quickly falls off when your a few mm off.

Aren't folks using sensor to tube lengths far from "extact" to get different effective magnifications while stacking?

Mike

Lou Jost
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Post by Lou Jost »

Yes, that's true Mike, but the sensitivity to variation depends on the NA. For high-NA lenses it could be important.

mawyatt
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Post by mawyatt »

Lou,

Thanks, I was beginning to think I was missing something!!

Best,

Mike

ChrisR
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Post by ChrisR »

If one doesn't need precise magnification or focus, then it's not necessary to get the "exact" tube to sensor length correct...right?

When using something like the Raynox tube lenses and various objectives (Mitutoyo for example) for stacking, isn't just getting close enough OK since you'll be stacking anyway? I don't think the IQ just quickly falls off when your a few mm off.

Aren't folks using sensor to tube lengths far from "extact" to get different effective magnifications while stacking?
Nobody to my knowledge has quantified things, though there are guides to relative sensitivities. This one is often quoted but remains somewhat mysterious
http://www.science-info.net/docs/etc/Tube-Length-na.gif

At low NA you can get away with "wrong" tube lengths and focus from infinity.
It tightens up considerably with NA.


Changing tube length on a finite system isn't the same as changing the extension from the sensor on a tube lens. Considering the ray diagrams, you're asking the infinite objective to focus each side of infinity.

I feel - having tried with an infinite NA 0.8, that tube lens distance from sensor, isn't critical to one millimetre. But 1mm is an arbitrary step, not worth praising as significant.

You may be OK to change focus by defocusing your tube lens a llittle, but
don't try altering the magnification of a high NA infinite by that route!
Chris R

mawyatt
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Post by mawyatt »

ChrisR wrote:
If one doesn't need precise magnification or focus, then it's not necessary to get the "exact" tube to sensor length correct...right?

When using something like the Raynox tube lenses and various objectives (Mitutoyo for example) for stacking, isn't just getting close enough OK since you'll be stacking anyway? I don't think the IQ just quickly falls off when your a few mm off.

Aren't folks using sensor to tube lengths far from "extact" to get different effective magnifications while stacking?
Nobody to my knowledge has quantified things, though there are guides to relative sensitivities. This one is often quoted but remains somewhat mysterious
http://www.science-info.net/docs/etc/Tube-Length-na.gif

At low NA you can get away with "wrong" tube lengths and focus from infinity.
It tightens up considerably with NA.


Changing tube length on a finite system isn't the same as changing the extension from the sensor on a tube lens. Considering the ray diagrams, you're asking the infinite objective to focus each side of infinity.

I feel - having tried with an infinite NA 0.8, that tube lens distance from sensor, isn't critical to one millimetre. But 1mm is an arbitrary step, not worth praising as significant.

You may be OK to change focus by defocusing your tube lens a llittle, but
don't try altering the magnification of a high NA infinite by that route!
Chris,

Thanks for the reply and reference.

From the ref it seems that if I use a Mitty 10X with NA of 0.28, then I have a 200mm range in tube to sensor spacing latitude around the nominal 200mm spacing? Assume this is before the IQ degrades, but what is considered acceptable degradation criteria? However, if I use a Mitty 20X NA of 0.42 then a range of 25mm.

If I use say a Raynox 250 (125mm) instead of the design target of 200mm for the Mittys, does this graph scale (125/200) or remain the same? Or is this 125mm considered as part of the latitude above. If so, this which would mean forget about using the Raynox 250 on any Mitty above 10X.

Sorry for all the questions, but trying to get a "feel" for how all this plays together.

Best,

Mike

Pau
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Post by Pau »

This one is often quoted but remains somewhat mysterious
http://www.science-info.net/docs/etc/Tube-Length-na.gif
For me it's also mysterious: I don't really understand what is represented.
It seems that you can change the TL of a 0.2 objective about 0.7 meter.... :smt017

This other document (second one into the pdf)
www.science-info.net/docs/leitz/Leitz-160mm-Memo.pdf

has also confused me for some time because what it says is against the theory:

Image

Now I'm convinced that it's just wrong. Leitz 170 objectives work well in a 160 scope, the only problem to be expected with low magnification ones is less parfocality*, but in practice it is not problematic and sits more or less in between the range of microscopes of that era.

* and it is when comparing a pair of 4/0.16 objectives of both standards, much less with higher magnification ones
Pau

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