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(first) microscope objective for above 10x - suggestions

 
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PaulFurman



Joined: 24 Oct 2009
Posts: 595
Location: SF, CA, USA

PostPosted: Tue May 11, 2010 7:14 am    Post subject: (first) microscope objective for above 10x - suggestions Reply with quote

I'm working on a full frame 12MP Nikon D700 and can get some great stuff from an Oly 20/2 macro lens on bellows up to 10x, then it starts to fall apart. I have never tried Microscope Objectives so my eyes glaze over reading those threads... but I try... and I'm beginning to get a feel for the lingo...

There was mention of the new Nikon objectives from Edmund, specifically the 5x & 10x, but not the 20x. Is there a reason to get a 10x rather than 20x? My guess is maybe if I could extend the bellows long enough, I might be better off with a 10x because that enlarges the sharp central part to fill my large, fairly low res sensor. Another thought is perhaps the aperture goes downhill when trying that trick so I'm better off staying as close as possible to the labeled range? As long as I'm at or above the specified tube length.

For the 10x approach, I've got a PB4 bellows which goes to about 200+ and another bellows I could attach somehow perhaps. Or get a cheap microscope with a good focus block - mounting the bellows above that sounds like a smart way to go although perhaps quite awkward. It seems examples I've seen all have the camera & bellows on a separate stand above the microscope such that I might as well get rid of the microscope & put the focus block on an enlarger stand.

Or just get a 20x for use on a single bellows? Which 20x? It seems maybe those are not as rare as 5x & 10x objectives?
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5805
Location: Issaquah, WA USA

PostPosted: Tue May 11, 2010 8:22 am    Post subject: Reply with quote

Paul,

So far my favorite 20X is the Nikon CF M Plan 20/0.40 ELWD. It has a 10.5mm working distance and the 0.40 numerical aperture. The big question would be using it on a full frame sensor. I've never even tried it on my full frame Canon body, so I don't know what the image quality is beyond the 28mm diagonal of my D300 and 50D.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20494
Location: Richland, Washington State, USA

PostPosted: Tue May 11, 2010 8:52 am    Post subject: Reply with quote

Quote:
There was mention of the new Nikon objectives from Edmund, specifically the 5x & 10x, but not the 20x. Is there a reason to get a 10x rather than 20x?

I've written about the "10X Nikon Achromatic Finite Conjugate Objective", Edmund part number NT59-935, $95 new HERE. I'm confident that lens would do a good job for you at 15X on 240 mm extension, and it fits standard RMS adapters such as the ones that been recently linked. As far as I can see, that lens represents a no-waiting, no-thrashing solution.

At the moment, I don't see a 20X objective offered in that same series. In general, the problem with most 20X objectives is working distance. A non-LWD 20X objective will have typically around 3 mm working distance -- pretty difficult to get light around. LWD/ELWD/SLWD objectives are available, but they are relatively expensive. In any case, to cover your full-frame sensor, you might have to run them at more like 30X, which I think is taking them outside your range of interests.

If you have a 300 mm telephoto, or say a 200 mm and a 1.4X teleconverter, than I'll go out on a limb and suggest that you pick up a Nikon 10X infinity objective such as eBay 160432208297, "Nikon CFI Plan Achromat Objective 10x/0.25 WD 10.5". On a good day, those go real cheap, like $25-30 for a one or two bid auction. (On not-so-good days, they're more like $200 at Buy-It-Now). These lenses give rated magnification and an eyepiece-sized image circle when used with a 200mm tube lens, so at 300 mm they'll give 15X and should cover full frame or close to it.

This approach has the advantage that the camera ends up talking to an ordinary camera lens, which in some cases makes the metering work better. Since you're already successfully using your D700 on bellows, this is probably not an issue for you.

It has the disadvantage of probably requiring some custom mechanical adapters. The general strategy as shown HERE by RogelioMoreno is to just hold the objective in front of the telephoto at some distance that works well. Rogelio shows a distance of several inches using a series of adapters. I am currently starting to test a much shorter setup that I expect to finalize using a screw-in lens cap. Be aware that most infinity objectives do not use RMS threads so those adapters won't work.

This route using infinity objectives with a telephoto as tube lens is not nearly so well traveled as finite objectives on bellows. I have written elsewhere that there are at least theoretical reasons to be concerned about image quality, especially in the corners. However we have now seen several reports of success using various telephotos, and no reports of serious problems. The setup that I am just starting to test uses the entry-level 55-200 mm zoom lens that came in my Canon Digital Rebel kit several years ago. This is about the least-likely-to-succeed combination that I could think of, but the first results look very promising.

--Rik
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PaulFurman



Joined: 24 Oct 2009
Posts: 595
Location: SF, CA, USA

PostPosted: Tue May 11, 2010 9:25 am    Post subject: Reply with quote

Ah, OK, it jumps to 40x with a working distance of 0.6mm.

I guess the 10x version would be a smart step into these waters as I could use it on my current rig and manage 2.5mm steps pretty easily. Stability would probably become a challenge though. I don't know, perhaps 40x would be fun too...

Thanks Charles & Rik!
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mgoodm3



Joined: 08 Sep 2008
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Location: Southern OR

PostPosted: Tue May 11, 2010 9:32 am    Post subject: Reply with quote

I have an Nikon E-plan 10/0.25 160/0 LWD that works very well on a bellows. about 10 mm working distance. Got it on EBay fo all of $55. The one problem you may have is the big detector on the D700
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Tue May 11, 2010 9:54 am    Post subject: Reply with quote

PaulFurman wrote:
... as I could use it on my current rig and manage 2.5mm steps pretty easily.

I forget what your setup is, but I'm sure "2.5mm" is a typo. 2.5 micron, perhaps, using a microscope focus block? That's more than fine enough for a 10X objective used at 15X.

--Rik
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Bob^3



Joined: 17 Jan 2010
Posts: 287
Location: Orange County, California

PostPosted: Tue May 11, 2010 10:11 am    Post subject: Reply with quote

PaulFurman wrote:
My guess is maybe if I could extend the bellows long enough, I might be better off with a 10x because that enlarges the sharp central part to fill my large, fairly low res sensor. Another thought is perhaps the aperture goes downhill when trying that trick so I'm better off staying as close as possible to the labeled range? As long as I'm at or above the specified tube length.

Hi Paul,

I also have the D700. That was the same question I had prior to purchasing a 10x M Plan 0.25 NA 210TL and 10x CF N Plan 0.30 NA 160TL. Haven’t done much testing of the M Plan 0.25 on the D700, but, IMO the CF N 0.30 does not provide acceptable quality at the edges or corners on the D700 sensor at 10x (altough it's still be OK for subjects with little detail of interest outside the 28mm image circle). I find that the edges start to improve at about 12x-13x, with very good results requiring 14x-15x. However, at this magnification I start to see some slight overall softening, likely due to diffraction. I’ve decided the D200 is a better match for this objective from about 10x to 13x, then I switch to the D700 for 14x to about 18x---don’t own a 20x objective, yet.

Regards,
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PaulFurman



Joined: 24 Oct 2009
Posts: 595
Location: SF, CA, USA

PostPosted: Tue May 11, 2010 10:36 am    Post subject: Reply with quote

rjlittlefield wrote:
PaulFurman wrote:
... as I could use it on my current rig and manage 2.5mm steps pretty easily.

I forget what your setup is, but I'm sure "2.5mm" is a typo. 2.5 micron, perhaps, using a microscope focus block? That's more than fine enough for a 10X objective used at 15X.


Right, 2.5 microns. I'm using a little micrometer to nudge my bellows front standard and it has 5 micron ticks.
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