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Extreme extension tube.

 
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All Ex



Joined: 20 Jul 2015
Posts: 221
Location: Greece Thessaloniki

PostPosted: Fri Jul 28, 2017 4:25 am    Post subject: Extreme extension tube. Reply with quote

Recently I `ve got a rather crazy idea, I`ve found an extended carton roll and I shaped It, with the proper adaptors to an extension tube. I wonder what 1f, instead of f=200, as my objectives require, make my distance from the sensor, with my tube together (inserting in that number my flange focal distance) 755 mm.
I know that the first problem that I`ll face is the illumination, I`m planning to use 3 flashes in full power. The first thing to do is to measure the magnification with my objectives especially with my recently obtained Mitutoyo 5X 0.14 M Plan Apo.
What do you thi0ng about my experiment?
(For the time being, I`m preparing my rig, If my experiment succeeds I `ll post the results.)
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Last edited by All Ex on Fri Jul 28, 2017 5:51 am; edited 2 times in total
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lonepal



Joined: 28 Jan 2017
Posts: 154
Location: Turkey

PostPosted: Fri Jul 28, 2017 5:24 am    Post subject: Reply with quote

I think you will get a very bad IQ image if you can get Smile
You will need a lot of light.

I am very impatient to see the result.
Good luck!
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Omer
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ChrisR
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Joined: 14 Mar 2009
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PostPosted: Fri Jul 28, 2017 5:56 am    Post subject: Reply with quote

So, are you using a Mitutoyo (infnite) objective without a "tube" lens, and focusing it at 755mm?

Your Objectives should be focused at infinity, not 200mm.
200mm is just the FL of the "tube" lens you need to get the stated magnification.

a 5x mitty is about 40mm FL, so on that extension you'll get magnification about 19x and effective aperture f/333
If my maths is right that's an Airy disc about 0.35mm across. I may be wrong there - it'll be BAD anyway!
But, you never know all that happens until you try, maybe.Smile
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All Ex



Joined: 20 Jul 2015
Posts: 221
Location: Greece Thessaloniki

PostPosted: Fri Jul 28, 2017 6:39 am    Post subject: Reply with quote

The effective aperture f/333 is something I`ll have to consider very much, in fact, my lighting is not enough.
For starting I intend to place the objective in front of a Nikon Ai 200mm MF focused in the infinity, to see how it compares.
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rjlittlefield
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PostPosted: Fri Jul 28, 2017 8:52 am    Post subject: Reply with quote

With the rear lens focused at infinity, distance between the objective and the tube lens does not affect magnification or effective f-number.

Greatly extending that distance would serve only to add severe vignetting.

If you add the extension behind the tube lens, then you'll get more magnification and a bigger effective f-number. In that case, the effect of the added extension varies depending on separation between objective and tube lens. Larger separation between objective and tube lens reduces the effect of adding extension behind the tube lens.

--Rik
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All Ex



Joined: 20 Jul 2015
Posts: 221
Location: Greece Thessaloniki

PostPosted: Fri Jul 28, 2017 10:13 am    Post subject: Reply with quote

I`ll work on it, Rik, tomorrow when I`ll have time. It finally seems that I'll need more than I expected.

Thanks for your lights.

Wink
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All Ex



Joined: 20 Jul 2015
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PostPosted: Sat Jul 29, 2017 10:52 am    Post subject: Reply with quote

Eventually, after rearranging my rig to its maximum extension, I`ll have to shorten my carton tube in order to place my Nikon 200mm, as a tube lens
After I` ll test my Mitutoyo 5X I`ll do the same with my Nikon 20X ELWD.
I`ll post the results in that thread.
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All Ex



Joined: 20 Jul 2015
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PostPosted: Thu Nov 30, 2017 12:46 am    Post subject: Reply with quote

In the end, my carton "extension tube" broke under its weight.
It has been a long time now that I`m preparing some self-made extension tubes, I hope I`ll post a thread describing my experiences on them (building & results).
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