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RogelioMoreno
Joined: 20 Nov 2009
Posts: 1507
Location: Panama
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 Posted: Sun May 16, 2010 9:09 pm Post subject: |
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| mgoodm3 wrote: |
have you tried this stepdown ring? I ask the question because there are two 42mm mounts out there. M42 and T-mount.
M42 (42mm x 1mm)
T-mount (42mm x 0.75mm)
Most lens threads are 0.75mm thread pitch. I can work an adapter with either though and ordered this ring. I had looked previously for a 42mm stepdown ring in the past and hadn't seen any. |
Yes, I have one of this step down ring, the 52mm side has the standard lens filter thread and the 42mm side has M42 thread.
Rogelio |
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lothman
Joined: 14 Feb 2009
Posts: 134
Location: Stuttgart/Germany
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| Posted: Sun May 16, 2010 9:12 pm Post subject: |
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Hi Rik,
do you think a 135mm lens also would work? Or dou you need the 200mm focal length. I'm asking because these 135mm lenses are cheap to get as a used MF lens and usually they show good perfomance.
Regards
Lothman |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 12558
Location: Richland, Washington State, USA
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| Posted: Sun May 16, 2010 11:34 pm Post subject: |
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| lothman wrote: | | do you think a 135mm lens also would work? Or dou you need the 200mm focal length. I'm asking because these 135mm lenses are cheap to get as a used MF lens and usually they show good perfomance. |
Well, putting it on a 135 mm turns this CFI 10X objective into a roughly 7X that on my T1i has to span a field that is 3.8 mm diagonal. That's asking quite a bit in terms of coverage.
Nonetheless, I thought it would be informative to give this a try. So, from my stash of never-to-be-used-again lenses, I retrieved a Vivitar 135 mm f/2.8 from around 1968. Onto the front of that, I taped the adapter shown earlier with the CFI 10X screwed into it. Heh, heh, this should be amusing!
But to my surprise and amazement, it worked fine! 
Here is the upper left corner, at 50% of actual pixels. The lower right portion of this image is near center of the full frame.
Being now somewhat frustrated but intrigued at my failure to determine the limits of this lens, I stuck it on a 55 mm. 
I am happy to say that the CFI 10X did not survive that stress test -- not only does it get dark in the corners, but the image quality out there is complete junk. Ahh, finally!
Nonetheless, the image quality at top and bottom center of frame seems quite good, as of course do all points in between.
Here is a single frame, actual pixels (of 4752x3168), levels adjust but no sharpening:
I measure frame height in this last case as just over 5 mm, so I guess that's the maximum diagonal coverage for the objective. Certainly much more than I would have guessed!
--Rik |
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Cyclops
Joined: 05 Aug 2006
Posts: 2718
Location: North East of England
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| Posted: Sun May 16, 2010 11:41 pm Post subject: |
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Forgive me if this sounds silly but if an infinity objective forms a focused image just in front of the tube lens (the zoom lens you're using) then how does one work on a microscope where it must focus its rays at the conventional distance of 160mm for example (the tube length)?
_________________
Canon 30D | EOS Rebel 2000-film(aka EOS 300) | Panasonic FZ-7 EB | Vivitar/Cosina 100mm f3.5 macro lens | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Vivitar Series 1 19-35 f3.5-4.5 | Slik 88 Tripod. | My new blog:
http://mybackyardsafari.blogspot.com/ |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 12558
Location: Richland, Washington State, USA
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| Posted: Sun May 16, 2010 11:55 pm Post subject: |
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| Cyclops wrote: | | Forgive me if this sounds silly but if an infinity objective forms a focused image just in front of the tube lens (the zoom lens you're using) then how does one work on a microscope where it must focus its rays at the conventional distance of 160mm for example (the tube length)? |
It's not a silly question, you're just missing some background. See http://www.microscopyu.com/articles/optics/cfintro.html, Figure 2, and the accompanying discussion.
--Rik |
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ChrisR
Joined: 14 Mar 2009
Posts: 3035
Location: Near London, UK
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| Posted: Mon May 17, 2010 12:00 am Post subject: |
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| Quote: | | if an infinity objective forms a focused image just in front of the tube lens |
It doesn't do that. It could be configured that way, but it's not designed to be used like that.
A ray diagram, would show the rays parallel as they go between the objective and the tube lens. They do that so other optical gizmos can be put in the light path and only have to deal with parallel rays comng from infinity.
So these relatively cheap telephotos are getting rays "from infinity". They're quite good at dealing with those of course.
(Edit - answered at same time as Rik - I didn't think he'd be out of bed yet!) |
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Cyclops
Joined: 05 Aug 2006
Posts: 2718
Location: North East of England
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| Posted: Mon May 17, 2010 12:03 am Post subject: |
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Thaanks Chris but now I'm more confused!
_________________
Canon 30D | EOS Rebel 2000-film(aka EOS 300) | Panasonic FZ-7 EB | Vivitar/Cosina 100mm f3.5 macro lens | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Vivitar Series 1 19-35 f3.5-4.5 | Slik 88 Tripod. | My new blog:
http://mybackyardsafari.blogspot.com/ |
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Blame
Joined: 14 May 2010
Posts: 212
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| Posted: Tue May 18, 2010 1:17 am Post subject: |
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This is amazing.
You are getting good results right out to 54mm effective field of view. That means that taped onto a 100mm lens your objective would be a 5X 0.25 with usable quality right out to the corners of a cropped sensor camera! |
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ChrisLilley
Joined: 01 May 2010
Posts: 680
Location: Nice, France (I'm British)
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| Posted: Tue May 18, 2010 4:50 am Post subject: Re: Infinity objective on low-end zoom telephoto works fine |
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| rjlittlefield wrote: |
The telephoto lens in this case is one that I expected would not work very well. It is the entry-level 55-200 mm f/4.5-5.6 zoom lens that came with my Canon Digital Rebel kit back in 2004. |
Quick clarifying questions:
* 200mm is special because it happens to cover the sensor, or results in 10x on the sensor, or for some other reason?
* the tube lens is set to infinity focus?
* the tube lens is used wide open, or at its sharpest aperture?
| rjlittlefield wrote: |
Anyway, I now wonder if part of the contrast loss could be due to light bouncing between the objective and the very nearby front surface of the lens. If so, that could be an argument in favor of keeping the two apart as far as possible without vignetting.
--Rik |
Or using a 200mm lens with a curved rather than planar front element? Or one with good multicoating?
Also, would blackening the shiny metal inside the adaptor here help? If light is bouncing off the front element of the tube lens and then off the metal and back to the sensor. Maybe even a circle of black absorbing material like flocking ....
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Blame
Joined: 14 May 2010
Posts: 212
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| Posted: Tue May 18, 2010 5:34 am Post subject: |
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With regards to cheap telephoto lenses.
slrgear.com is a good review site. It has a lot of lens tested for blur in a very detailed way. It shows why cheap lenses work better than expected.
A 10X 0.25 objective will result in about f/20 on a 200mm lens. At that aparture there is not a lot of variation between the lenses.
Working on the theory that ALL the added blur between f11 and f22 is due to difraction I would estimate that a Canon EF 55-200mm, used at f22 and 200mm is adding only about 1 blur unit to 2 for difraction.
However it is worth noting that a lot of cheap zooms work better in mid-range. For the EF 55-200mm it looks like only 1/2 unit of non-difraction blur at 135mm. Difraction blur will be less too as the aparture would be f/13.5. |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 12558
Location: Richland, Washington State, USA
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| Posted: Tue May 18, 2010 12:58 pm Post subject: |
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Answers to recent questions:
| Quote: | * 200mm is special because it happens to cover the sensor, or results in 10x on the sensor, or for some other reason?
* the tube lens is set to infinity focus?
* the tube lens is used wide open, or at its sharpest aperture?
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200 mm is special because that gives rated magnification. With infinity scopes, magnification is the ratio of focal lengths. Using a shorter tube lens gives less magnification. With this particular telephoto, there are also coverage issues as described below.
Infinity focus, yes.
The aperture of the tube lens is set to wide open. The combo then becomes stopped down to effectively f/20 due to the aperture stop of NA 0.25 in the objective.
| Quote: | | Also, would blackening the shiny metal inside the adaptor here help? If light is bouncing off the front element of the tube lens and then off the metal and back to the sensor. Maybe even a circle of black absorbing material like flocking .... |
Yes, I expect that it would. As I replied to g4lab (with high amusement), I simply overlooked this aspect in my rush to test resolution.
| Quote: | | However it is worth noting that a lot of cheap zooms work better in mid-range. For the EF 55-200mm it looks like only 1/2 unit of non-difraction blur at 135mm. Difraction blur will be less too as the aparture would be f/13.5. |
Unfortunately the EF 55-200 has a small entrance pupil, located far back. When set much below 200 mm in this application, the corners go dark due to vignetting. Even to get full coverage at 200 mm, it's necessary to place the objective very close to the telephoto.
--Rik |
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Joaquim F.
Joined: 28 Apr 2010
Posts: 172
Location: Tarragona, Spain
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| Posted: Tue May 18, 2010 2:37 pm Post subject: |
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This combo works really well! ... Nikon and Canon working together! 
This microscope objective is from the very last serie and that price is a bargain, a great discovery! Looking at Photozone test the Canon lens is an excellent candidate, full frame objective, rear elements optimized to work with digital sensors, very good performace in resolution, distortion and chromatic aberration , just the "all plastic" construction seems a problem, this has given you no stability or vibration problems? Have you used any system to hold the assembly in any way?
The scale detail is excellent, responds equally well at CA level with contrasted subjects and at the image margins? In my setup with CF PLAN 10X NA 0.30 get a good quality in about 20mm image circle, between 20mm and 25mm the quality down and over 25mm not work well, quite blurred and some strong CAs.
Displaying your results one wonders if it's worth buying the Nikon tube lens, EO give me a total cost of 215€ shipping to Europe included...
Another good candidate, probably in the bag of many of the forum participants, is the Raynox DCR-150 macro conversion lens, a 210mm (+4.8 diopters) achromatic triplet with about 35mm lens diameter. It closely resembles (if only for the shape and brightness) to the Nikon tube lens and in my tests works even a little better that the Nikkor 200/4 AI. Reverse mounted in the PB-6 52mm front bracket back screw using an Chinese aluminium adapter and adjusted in the bellows pressure clamp is a very rigid setup!
I mount in frontal bayonet the microscope objective with the beljan RMS and a T2-Nikon bayonet adapters. I have yet to properly mount the micrometer stage for stacks but I have some picture:
Gnat wing with CF PLAN 5X/0,13 and Raynox DCR-150, 30 images in ZS:
Bigger 50% central crop:
http://farm4.static.flickr.com/3217/4554155549_414e7b0494_o.jpg
After I upload a photo of the setup, not sure if my English (automatic translated) means too well! 
Cheers
Joaquim
_________________
http://www.flickr.com/photos/45863071@N03/
Last edited by Joaquim F. on Tue May 18, 2010 4:13 pm; edited 1 time in total |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 12558
Location: Richland, Washington State, USA
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| Posted: Tue May 18, 2010 3:39 pm Post subject: |
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| Joaquim F. wrote: | | just the "all plastic" construction seems a problem, this has given you no stability or vibration problems? Have you used any system to hold the assembly in any way? |
I have not used extra holding, just the objective hanging off the end of the lens.
But I would not expect stability or vibration problems. I am running with Canon T1i in LiveView mode, which uses electronic first shutter curtain, and my working area is very quiet.
| Quote: | | The scale detail is excellent, responds equally well at CA level with contrasted subjects and at the image margins? |
With the CFI, I see only a little CA as shown in the pictures. (The pictures were shot as JPEGs and have not had CA removed.) In earlier tests with my CF N Plan 10X NA 0.30, I got results similar to yours: OK to the corners of an APS-C sensor at rated extension, but the corners quickly went bad if I tried using less extension.
| Quote: | | Displaying your results one wonders if it's worth buying the Nikon tube lens |
I agree. At the moment I do not see enough potential for added value to make it worth running the test.
| Quote: | | Another good candidate, probably in the bag of many of the forum participants, is the Raynox DCR-150 macro conversion lens, a 210mm (+4.8 diopters) achromatic triplet with about 35mm lens diameter. It closely resembles (if only for the shape and brightness) to the Nikon tube lens and in my tests works even a little better that the Nikkor 200/4 AI. Reverse mounted in the PB-6 52mm front bracket back screw using an Chinese aluminium adapter and adjusted in the bellows pressure clamp is a very rigid setup! |
This sounds very promising.
| Quote: | | not sure if my English (automatic translated) means too well! |
I think it works fine. It makes perfect sense to me, anyway.
--Rik |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 12558
Location: Richland, Washington State, USA
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| Posted: Tue May 18, 2010 6:42 pm Post subject: |
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| Joaquim F. wrote: | | Looking at Photozone test the Canon lens is an excellent candidate, full frame objective |
Thanks for mentioning this. I had not noticed that the 55-200 has full frame coverage. The other kit lens is EF-S, and I had just assumed they were both limited to the smaller sensor.
This may have some small significance for the tests. Because the lens is designed for 36 x 24 mm coverage, and I am using it only for 22.3 x 14.9 mm, the concerns raised HERE about using the edges of the glass probably don't apply.
--Rik |
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dmillard
Joined: 24 Oct 2006
Posts: 454
Location: Austin, Texas
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