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Cheap tube lens
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morfa



Joined: 12 Oct 2009
Posts: 556
Location: Stockholm, Sweden

PostPosted: Wed Jan 19, 2011 9:28 am    Post subject: Reply with quote

Raynox DCR-150 (+4.8 diopter) working as tube lens @ 50x:


12MP: http://farm6.static.flickr.com/5247/5369811977_710ab81d3c_o.jpg

Similar misalignment here...
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morfa



Joined: 12 Oct 2009
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Location: Stockholm, Sweden

PostPosted: Wed Jan 19, 2011 9:36 am    Post subject: Reply with quote

Back to the $9 tube lens but now at the other end of the magnification spectrum.

This is with a horizontal FOV of 0.50mm on FF (just above 70X):


12MP: http://farm6.static.flickr.com/5169/5370356890_4eccec5bd0_o.jpg

Very even performance across the frame here but definition is obviously quite limited by diffraction.
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Blame



Joined: 14 May 2010
Posts: 342

PostPosted: Wed Jan 19, 2011 11:44 am    Post subject: Reply with quote

Rough maths here.

0.28 n.a -> 1um resolution
0.55 n.a -> 0.5um resolution
pixel spacing for canon 5d Mk2 -> 6um

Start of empty magnification about 2-3 pixels for unit of objective resolution = 12x-18x for mitutoyo 10x
24-36x for your 50x objective.

Conclusion: 50x Objective: best run way below rated magnification so that every bit of the image circle contibutes. 36x might be a good choice.

10x Objective: There is probably a useful "zoom" range - up to 18x, and down to 10x or hopefully rather less... We are all watching you.


Last edited by Blame on Thu Jan 20, 2011 4:45 am; edited 1 time in total
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morfa



Joined: 12 Oct 2009
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Location: Stockholm, Sweden

PostPosted: Wed Jan 19, 2011 1:52 pm    Post subject: Reply with quote

Great info Blame – thanks a lot!

Judging from your figures and from what I've seen so far and I'm guessing the $9 tubelens + 50/0.55 has a sweet spot at around 40X. Will test that hypothesis soon.

In the meantime, here is a stack at 50X with the 50/0.55+$9 tube:

6MP: http://farm6.static.flickr.com/5169/5370247583_829f4844de_o.jpg

Cross eye stereogram HERE
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Oskar O



Joined: 13 Dec 2010
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Location: Finland

PostPosted: Wed Jan 19, 2011 3:28 pm    Post subject: Reply with quote

Another evening and another set of very interesting tests, great work and thank you! 80x is a lot, I guess it really stresses your setup to the extreme. Alignment of the setup is probably tricky, many connections that can be just slightly off.

When trying to compare the Raynox and the Nikon 4T with shorter extension, I get the impression that the Raynox has a somewhat cyan color rendition and the Nikon a slightly higher contrast. Anyone agree/disagree? I think the setup shows good potential despite the diffraction.
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ChrisR
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Joined: 14 Mar 2009
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Location: Near London, UK

PostPosted: Wed Jan 19, 2011 3:31 pm    Post subject: Reply with quote

Impressive work John. Nice lighting too, it's quite rare to see shadows on those things Smile
When you say
50X with the 50/0.55+$9 tube:
did you extend the tube lens to increase the magnification , or is it (assuming the SS figure is correct) 172/200x 50 =43x ?

Going down in magnification seems to have more mileage than going up.

Another thought...
I don't think I can remember a post where someone has tried a "tube lens" which has degraded the image in terms of aberrations, as opposed to vigneting. (Maybe the close- up lenses, as they tend to be less good away from their centre. That would account for the alignment difficulty.)

I notice Surplus Shed do a number of achromats around 150 - 200mm, 35mm or so diameter ( plenty big enough to go right behind an objective,) for a few dollars.
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Wed Jan 19, 2011 7:06 pm    Post subject: Reply with quote

Thanks for the stereo. I would not have guessed about the cupped shape of the scales without it.

--Rik
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Blame



Joined: 14 May 2010
Posts: 342

PostPosted: Thu Jan 20, 2011 3:40 am    Post subject: Reply with quote

The outer diameter for you surplus shed tube lens is 39.5mm, except for the threaded bit at the top.

This gives me ideas for mounting.

You can buy pentax m42 mount extension tubes on ebay. They have 42mm threads. I would be willing to bet that they have an internal diameter of slightly greater than than 39.5mm.

It might be possible to glue a section of tubing around the tube to give it 42mm treads. Just find some wire of the right diameter to just fit in the gap between lens and tube and stick in 3 bits at ether end (evenly spaced) to center the lens, then wait for glue to dry. Job done.

So questions.

Anybody willing to measure the inside diameter of their cheap ebay extension tubes?

Are all cheap ebay extension tubes 42mm thread, or just the ones sold as m42?

What is the thread at the end of your lens, and is it towards objective or camera?
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Craig Gerard



Joined: 01 May 2010
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Location: Australia

PostPosted: Thu Jan 20, 2011 4:15 am    Post subject: Reply with quote

Blame wrote:
Anybody willing to measure the inside diameter of their cheap ebay extension tubes?

I have a set of the following item:
http://cgi.ebay.com/M42-screw-42-thread-mount-macro-extension-tube-set-/360246527130

First measurement indicates 39mm internally at 42mm male thread end = 5mm internal rim; remainder of barrel 42mm internally ending at female 42mm thread.

The longest sub-section would be the one to use, dependent on the 'height' the $9.00 lense and its outer diameter at the widest point.

Craig
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Blame



Joined: 14 May 2010
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PostPosted: Thu Jan 20, 2011 5:46 am    Post subject: Reply with quote

My thanks Craig.

I do believe this will work.

A check of morfa's setup picture shows the threaded end towards the objective - so that is the end that needs the female thread. Clearly given the quality of his results he got it the right way round.

There are lots of m42 extension tubes on Ebay. Longest section ether 28mm or 30mm. I will buy the cheapest in the hope that budget thin metal will give me the clearance at male end.

Ok. Length of lens = 29mm, so 28-30mm section is good. We need a few mm of overlap to access the female thread, so a bit short at male end, but as it is just bolting onto another section of tubing, no problem.

Barrel diameter of lens = 39.5mm. 41mm at threaded end but mercifully that will be at the female end of tube. Internal diameter of extension tube = slightly less than 42mm (or a 42mm thread couldn't be cut into it). Great.

The only problem would be male end of tube. Just 1/2mm short on internal diameter. A bit of sandpapering might sort that out. It should be a soft metal. Hold sandpaper to internal surface of tube at male end. Place tube on flat surface, and roll. Should be nice and even.

Clearances are small enough that very accurate centering should be possible.
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seta666



Joined: 19 Mar 2010
Posts: 868
Location: Castellon, Spain

PostPosted: Thu Jan 20, 2011 6:31 am    Post subject: Reply with quote

This post has been a very interenting thing to read. I ordered one of those tube lenses myself but I do not own any infinity lenses yet. I have been away from the forums for a long while so I mised the CFI 50/0.55 too, which I regret a lot as it seem to be a very good performer with a very nice balance in resolution/working distance. (how does it compare to your SLWD 40/0.40?)
Regards and thank you for sharing this valuable info
Javier
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morfa



Joined: 12 Oct 2009
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Location: Stockholm, Sweden

PostPosted: Thu Jan 20, 2011 7:53 am    Post subject: Reply with quote

ChrisR wrote:
When you say
50X with the 50/0.55+$9 tube:
did you extend the tube lens to increase the magnification , or is it (assuming the SS figure is correct) 172/200x 50 =43x ?


Yes, good question Chris: I adjusted extension so that the horizontal FOV was 0.7mm (36/0.7≈50).

Oskar O wrote:
Alignment of the setup is probably tricky, many connections that can be just slightly off.


I think I've just identified one possible source of the alignment issue I've had – the plastic adapter sitting in the dovetail mount was a bit too small and therefore slightly off center. I've fiddled with it now and hopefully things have improved.

Quote:
I get the impression that the Raynox has a somewhat cyan color rendition and the Nikon a slightly higher contrast


I wouldn't pay too much attention to things other than detail in these test stacks. To keep it fast and simple I've used auto WB. Contrast can vary a great deal with the position of the diffuser (and I've not bothered to try and keep these things consistent from one stack to another).

Blame wrote:
What is the thread at the end of your lens, and is it towards objective or camera?t


The threaded side is used away from the camera in my test stacks so far (as can be seen in the shot where it's sitting on top of the microscope frame). I've not yet tried reversing it but it's on the list. A caliper read on the thread says it's 41mm. No idea about thread pitch etc. This thread doesn't fit anything I have.

I don't have the cheap ebay tubes so I can't try that mounting option. It seems like a good idea though! The tube lens fits very nicely inside a set of Nikon "K" extension tubes.

seta666 wrote:
how does it compare to your SLWD 40/0.40?


I'm quite fond of both but if I had to pick one I'd go with the 50/0.55.
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ChrisR
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PostPosted: Thu Jan 20, 2011 2:58 pm    Post subject: Reply with quote

Blame wrote:
Are all cheap ebay extension tubes 42mm thread, or just the ones sold as m42?
A couple of us found other very cheap Chinese tubes from the same sort of vendors had 57mm threads, so no.
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Blame



Joined: 14 May 2010
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PostPosted: Fri Jan 21, 2011 4:32 am    Post subject: Reply with quote

ChrisR: My thanks. That was my last question answered.

Morfa: I think I can mount it in ether direction in m42 tubing, I am going to order all the bits just as soon as my lens order is confirmed.

Now I hope I am not insulting you by pointing out the obvious. How about your close up lens tests. Did you reverse mount them?

I was planning on getting a Raynox, but reverse mounting is no easy matter. Finding a double sided male adapter is easy because reverse mounting lenses is normal enough. The problem is that finding a double sided female adapter is tricky. There are none I can find on ebay, and I can't think why there should be a market for them. Other, that is, than what we are doing now.

That makes me wonder how many of the tests using close up lenses used them as they should be - reverse mounted.

Oh, if you have a raynox DCR-250 it should be interesting. Focal length is 125mm. A triplet, and designed for an image up to 5/3x36mm=60mm wide on the subject side when used normally. Used as a tube lens on a full frame camera it will operate at a comfortable 36mm. If any tube lens can get to that width with sharp corners, it should.
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ChrisLilley



Joined: 01 May 2010
Posts: 680
Location: Nice, France (I'm British)

PostPosted: Fri Jan 21, 2011 9:06 am    Post subject: Reply with quote

Blame wrote:

Conclusion: 50x Objective: best run way below rated magnification so that every bit of the image circle contibutes. 36x might be a good choice.


200 * 36 / 50 = 144mm focal length for the tube lens.

1000 / 144 = +6.9 diopters

Looking at the list of close up lenses, +7 is not common.

Those with deep pockets might consider the Century Achromatic diopters from Schneider; these are intended for (and priced for) the movie industry as I understand it. They do have a +7 though.

Olympus have a 3 elements in 2 groups achromatic called the "is/L A-Lifesize Macro" with +7.7 diopters in a 49mm filter thread. That is a 130mm focal length, giving 32.5x. Seems to be discontinued.

And of course most camera systems have a 135mm prime available which might do well here.
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