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 Post subject: Easy Cheap DIY DSLR adapter for Leica trinocular stereos S6d
PostPosted: Fri Jan 24, 2020 1:57 am 
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NOTE: I have so far only tested with on an m-series scope. I am pretty sure it will work on an s-series as well since they use the same camera mounting hardware, but there's an outside chance the S series might not project as big of an image circle. Please don't be mad at me if it doesn't work on yours, but either way please post your results!
I figured this would be fairly relevant given how popular S series heads are on gem microscopes, both with the GIA and others. If you have a trinocular Leica head on your gemscope (a Leica S6D, an S8 Apo, an S9(?)/S Apo or even an m series or z series with a trinocular head) and have tried to mount a dslr on it, chances are might have come across this article over at Micscape: http://www.microscopy-uk.org.uk/mag/art ... photo.html
It's a nice helpful overview of the author's attempt at setting up a camera on this particular type of Leica trinocular port using official Leica parts. He did everything right, and yet this ended up being a somewhat difficult and expensive process for him and ultimately didn't get him quite where he wanted. This is pretty typical--DSLRs are kind of an afterthought in Leica's adapter lineup so you have to get a rare and expensive 1.6x adapter for aps-c (or 2.5x for full frame) on top of the required 1x adapter, yielding a tall tower of expensive metal and glass.

I recently got my hands on an m-series trinocular head, which uses the same camera mounting hardware: a hole at the top of the head with a thread which accepts a Leica 1x (part no 10445930) adapter, which in turn gives you a standard Leica 37mm mount to accept a camera adapter. The way this is laid out the tube lenses (these take the stereo images produced by the zoom body, which are focused to infinity, and focus them for the eyepieces or camera) are pushed up into the base of the eyepiece tubes, and the trinocular port has no tube lens at all, meaning it produces the image still focused at infinity. This infinity-focused image just produces a blur on a camera, so the Leica 1x adapter contains a 200mm focal length tube lens (the article mistakenly calls this adapter lensless, but it isn't). That projected image can then resized up or down by additional lenses to fit your particular camera sensor.

This is a bad setup for our purposes--it's way too expensive and elaborate since a 200mm tube lens can project an image that is perfectly sized for APS-C with no additional hardware. Either the 1x adapter crops the image some, or it's physically arranged so the camera sensor on a dslr can't get low enough to get a focused image, but either way you can't direct project onto a DSLR sensor with what they provide.

So the best solution is to throw out the Leica tube lens entirely (or rather, not buy it), and provide your own 200mm tube lens instead. Leica stereos (and modern stereos in general) don't do corrections in the eyepieces, so the tube lens only has to be a 200mm lens of decent quality. You can find good options by seeing what experts use for high end infinity objectives like the Mitutoyo M Plan Apo series. In this excellent test the Kenko #5 enlarger lens proved to have an exceptional quality-to-price ratio. There are better tube lenses but, frankly, we're not dealing with scopes that have anywhere near the resolution or aponess of a Mitutoyo, so it's unlikely the difference is going to be noticeable. Though even if you bought a top end option it would still probably cost less than the Leica solution.

Here is how I made mine. The outer threading of the trinocular head is 38x1 or something very close (37 is definitely too small), so I got a 38x1-m42 adapter to get it to a more standard thread. This adapter is very loose until it's screwed all the way on, then it gets nice and grippy. I then threaded a female-female m42 adapter onto that, because you want to present a female thread for the rest of this.

The Kenko #5 comes in a few different sizes--I got a 49mm example. This needs to be attached to the camera at infinity focus, meaning about 200mm from the camera sensor. To do this I attached a male m49 to female m42 adapter, enough empty m42 spacers to focus it to infinity (including an m42-m42 helicoid in the stack to allow fine focusing), and then an m42-canon adapter. From there you just need a female 49mm to m42 adapter to thread it onto the adapter you put on the trinocular port.

Image

It works, and I think it works well. The image is perfectly parfocal, the sizing is perfect, and image quality seems quite good from a quick test shot (single shot no stacking) of an amber bug in darkfield illumination.
(click the image for full size)
Image
The image is almost a perfect rectangular crop from the view in a standard 21mm eyepiece.
Image
I think this is a better solution for aps-C than Leica provides, and it's definitely a heck of a lot cheaper. From reading in another thread the addition of a high quality 1.6x teleconverter would probably make this suitable for full frame too, but I have not tried that.

You can do something very similar to this on the Nikon SMZ-U, but that will be another post at some point.

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