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LordV



Joined: 22 Nov 2007
Posts: 1568
Location: UK

PostPosted: Sat Nov 14, 2009 2:03 am    Post subject: Just for fun.. Reply with quote

.. I tried using a 10X objective from an old lab microscope I have (Baker) by mounting the lens in an expanded polystyrene disc and hand holding it on the end of an old set of pentax fit ext tubes which I cobbled onto a canon T mount ages ago, The length of the tubes is about 75mm. Much to my suprise I seemed to get a reasonable image on a 1.6 crop camera body (just looking in the viewfinder). The image seemed to be approx 10:1. Is it worth doing a slightly more permanent fixing (probably using a pentax body cap on the end of the tubes) for the lens or am I barking up the wrong tree ?

Brian V.
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Planapo



Joined: 07 Nov 2006
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Location: Germany, in the United States of Europe

PostPosted: Sat Nov 14, 2009 4:31 am    Post subject: Reply with quote

Brian, I don't think that you're barking up the wrong tree, otherwise we would be quite a pack barking up there. Smile

I would expect that your 10x objective has an RMS thread, so in case photographs would show that it needs its matched eyepiece for better correction of distortions like CA in the final image, and you would hence want a fully corrected objective that can be used without correcting eyepiece, you could still use that pentax body cap adapter with tubes or bellows with that, given that you can position the hole in the cap adequately centered.

I have experienced that distortions are more prone to show up in later photographs than when first looking through the objective "live" by eye alone.

--Betty
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Harold Gough



Joined: 09 Mar 2008
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Location: Reading, Berkshire, England

PostPosted: Sat Nov 14, 2009 4:52 am    Post subject: Reply with quote

There may be something here:

http://www.srb-griturn.com/t-mounts-and-t-mount-accessories-331-c.asp

They made me an adapter to use my Canon 20mm macro lens, with its RMS thread on Olympus OM via a T-mount.

Harold
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LordV



Joined: 22 Nov 2007
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Location: UK

PostPosted: Sat Nov 14, 2009 5:49 am    Post subject: Reply with quote

Thanks for the comments and info Smile
As it's slightly inclement weather outside (gales and rain), I went ahead and tried a slightly more permanent fitting using the objective attached to a body cap on the end of the tubes.
Image seems not too bad- couple of test shots (with a bit of hand stacking on the pollen) of some hibiscus bits just taken resting the camera on a table.

Brian v.




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Peter M. Macdonald



Joined: 20 Jan 2009
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Location: Berwickshire, Scotland

PostPosted: Sat Nov 14, 2009 6:03 am    Post subject: Reply with quote

Brian,

Recent thread with links to a variety of RMS to T2 adaptors

http://www.photomacrography.net/forum/viewtopic.php?p=50197&highlight=#50197

Your lens looks not to be producing much CA. Would be interesting to see the edge of a small black spot on a pure white background to see if there is a colour fringe.If not, then you have discovered a much cheaper alternative objective to the Nikon CF series.

Peter
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LordV



Joined: 22 Nov 2007
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Location: UK

PostPosted: Sat Nov 14, 2009 7:36 am    Post subject: Reply with quote

Peter M. Macdonald wrote:
Brian,

Recent thread with links to a variety of RMS to T2 adaptors

http://www.photomacrography.net/forum/viewtopic.php?p=50197&highlight=#50197

Your lens looks not to be producing much CA. Would be interesting to see the edge of a small black spot on a pure white background to see if there is a colour fringe.If not, then you have discovered a much cheaper alternative objective to the Nikon CF series.

Peter


Not sure if this will do - hard to find a good full stop when you are looking for one Smile . I took a shot with my MPE-65 of the same thing (a lot easier to focus) and cropped it to the same print magnification for comparison.
Ignore any white balance diffs - that's down to me

Brian V.

MPE-65 cropped to same print mag on 5Dmk2



10X objective on 40D


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Peter M. Macdonald



Joined: 20 Jan 2009
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Location: Berwickshire, Scotland

PostPosted: Sat Nov 14, 2009 9:49 am    Post subject: Reply with quote

Brian,

Seems that there is some lateral chromatoc aberation from the Baker objective. I took it into Photoshop and examined it at 600% in order to look for any sign of colour fringing. There is a quite obvious blue fringe on the right ende of the full stop and the letter. Just to check that it was not in the printing ink, I did the same with the MPE image. It is black and white with no colour fringe.

That said, the two images which you posted of short stacks suggest that the Baker lens performs well in a more real world test than the pixel peeping which I was doing, at least when shooting a stack which is going to be used at web resolution.

Guess this just demonstrates why we are prepared to pay more than the price of a Baker of London 10x onjective for a Nikon CF 10x.

Cheers,

Peter
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LordV



Joined: 22 Nov 2007
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PostPosted: Sat Nov 14, 2009 9:56 am    Post subject: Reply with quote

Thanks for the analysis Peter. I'll probably try it properly soon if i can find a suitable subject. Been meaning to try one of the objectives for a while but only just figured out how to DIY mount it Smile

Brian v.
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AndrewC



Joined: 14 Feb 2008
Posts: 1436
Location: Belgium

PostPosted: Sat Nov 14, 2009 10:47 am    Post subject: Reply with quote

I try and standardise my non-camera lenses onto a standard T-mount backbone.

So I have a Nikon to T-mount on the camera, then T-mount extension tubes (from SRB-Griturn), and then T-mount to RMS for microscope objectives.

Andrew
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Sat Nov 14, 2009 10:57 am    Post subject: Reply with quote

LordV wrote:
Been meaning to try one of the objectives for a while but only just figured out how to DIY mount it Smile

I used an old non-CF objective for a long time, pretty happily. The visible color fringing due to CA can mostly be removed in post-processing. Even a cheap objective will give lots more resolution than traditional macro lenses, see for example the comparisons HERE, third panel.

--Rik
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DQE



Joined: 08 Jul 2008
Posts: 1653
Location: near Portland, Maine, USA

PostPosted: Sat Nov 14, 2009 4:23 pm    Post subject: Specs for mounting a microscope objective on a DSLR Reply with quote

I have somehow acquired an understanding that it is exceptionally critical to mount lenses accurately, especially for high-quality micro and macro work. That is, I thought that very high-precision optical equipment would be needed to construct a lens mount and to verify that the microscope objective is perpendicular to the sensor plane, etc, etc.

Yet I occasionally see reasonable image quality from hand-mounted lenses using DIY components, for example a body cap with a hole drilled and tapped for a microscope objective.

Should I abandon my DIY anxieties regarding lens mounts with respect to this specific forum topic and examples?

Thanks to everyone who posted T-mount adapters for microscope objectives, etc.
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lauriek
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PostPosted: Sat Nov 14, 2009 5:09 pm    Post subject: Reply with quote

I don't think it's the end of the earth if you do this in a slightly sloppy way - I mean if you end up slightly off perpendicular then you just have a slight tilt lens, which shouldn't do any harm. You need to make sure it's pretty well centered though, otherwise it quite possibly will vignette on one corner unless well extended. (Particularly as I know Brian now uses a full frame 5DII).
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rjlittlefield
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PostPosted: Sat Nov 14, 2009 5:47 pm    Post subject: Reply with quote

DQE, your concerns are too strong in this case.

Step back and think about the big picture.

If the objective is mounted parallel to the sensor but is off center, then nothing happens except that the image circle shifts on the sensor. Even if the decentering is as bad as a full mm, this is still only a small fraction of the sensor size, so the high quality central portion is still available for cropping.

It is unlikely that the sensor will be tilted with respect to the extension axis, but even if it were, all this does is to tilt the focus plane and introduce a tiny change in "tube length" across the sensor width. Neither effect is important for the sort of subjects that Brian is shooting, or for typical focus stacks.

The biggest problem is if the objective gets tilted, since this not only tilts the focus plane but also shifts the objective's optical axis by a surprisingly large amount at the sensor. Fortunately, objectives have mounting shoulders, and many body caps have flat fronts. In this case, the objective will naturally snug up perpendicular even if the threads are not perfect.

Come to think of it, I'm not sure I've ever heard anybody say "Be sure the front of the body cap is flat." But that is important. Choosing a cap that would leave one side of the objective propped up on an embossed logo would be a Really Bad Idea.

--Rik
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DQE



Joined: 08 Jul 2008
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Location: near Portland, Maine, USA

PostPosted: Sat Nov 14, 2009 9:37 pm    Post subject: Reply with quote

rjlittlefield wrote:
DQE, your concerns are too strong in this case.

Step back and think about the big picture.

If the objective is mounted parallel to the sensor but is off center, then nothing happens except that the image circle shifts on the sensor. Even if the decentering is as bad as a full mm, this is still only a small fraction of the sensor size, so the high quality central portion is still available for cropping.

It is unlikely that the sensor will be tilted with respect to the extension axis, but even if it were, all this does is to tilt the focus plane and introduce a tiny change in "tube length" across the sensor width. Neither effect is important for the sort of subjects that Brian is shooting, or for typical focus stacks.

The biggest problem is if the objective gets tilted, since this not only tilts the focus plane but also shifts the objective's optical axis by a surprisingly large amount at the sensor. Fortunately, objectives have mounting shoulders, and many body caps have flat fronts. In this case, the objective will naturally snug up perpendicular even if the threads are not perfect.

Come to think of it, I'm not sure I've ever heard anybody say "Be sure the front of the body cap is flat." But that is important. Choosing a cap that would leave one side of the objective propped up on an embossed logo would be a Really Bad Idea.

--Rik


Rik,

Thanks for the very helpful explanation.

While reflecting on the possible source(s) of my lens mounting anxieties, I recalled that I became conditioned to the need for extreme precision in making and assembling optical devices during learning the basics of making one's own reflector astronomical telescope. There, interferometric techniques were sometimes used for testing component quality (e.g., finishing and polishing the primary mirror. Also, and more to the point, I only have a limited understanding of lens design and optics - my total education in these domains consists of a two-week summer course by the legendary Rudolph Kingslake a few decades ago at the University of Rochester.
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Harold Gough



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PostPosted: Sun Nov 15, 2009 1:36 am    Post subject: Reply with quote

rjlittlefield wrote:
many body caps have flat fronts. In this case, the objective will naturally snug up perpendicular even if the threads are not perfect.

Unlikely for recent cameras I suppose but I obtained a metal body cap for a similar project I had in mind for my OM sytem. (This was for a non-RMS lens).

Harold
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