helicoid-style extension tube

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Smokedaddy
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helicoid-style extension tube

Post by Smokedaddy »

I found a like new Diagnostic Instruments PA1-12A adapter tube on eBay at a excellent price considering what they sell for on their site. I was reading a article on a website where the author attached a helicoid-style device on the PA1-12A. I tried contacting him asking where he purchased it and the response was eBay. Here is a link to the article.

https://www.gia.edu/gems-gemology/summe ... emologists

Image

The reason I'm asking is I want to use the PA1-12A on my Optiphot Biological to mount my 50D. I also purchased a Nikon CF PL 2.5X. When everything is installed the camera and view through the trinocular are not in focus at the same time. I'm not sure that matters but was wondering if the helicoid device would allow me to parfocal. Does anyone have experience with this type of adjuster and what will work?

-JW:

Ichthyophthirius
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Post by Ichthyophthirius »

Hi JW,

Use a 10x microscope objective for making the measurements. The Nikon CF PL 2.5X needs to be in the correct position in the Nikon "chimney".

If the PA1-12A is too short, all you have to do is take the camera off the adapter and lift the camera above the adapter tube until the image comes into focus. That's how long the helicoid has to be.

If the PA1-12A is too long you will never see a sharp image through the camera.

ray_parkhurst
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Post by ray_parkhurst »

I use those helicoids occasionally. They form the basis of a coin photography system I spec'd out a few years ago. It uses a helicoid rather than a bellows, and has the advantage that the helicoid is shorter than the bellows minimum extension, so miminum magnification can be lower. I've never tried using it to correct parfocality, but it should work. I use the 17-31mm version, but there is a 12-17mm as well. There are longer ones too. Not sure how much adjustment range you will need. They are pretty cheap.

Smokedaddy
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Post by Smokedaddy »

Would you happen to have a link to one that would work with in my situation?

johan
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Post by johan »

I use a helicoid for this purpose. At the moment the connection is just held together by tape, but I'm having some adapters built for me. I bought the helicoid years ago, sorry don't have link anymore. Fwiw, they're M42, cheap, perfectly reliable.

I'm not entirely sure that PA1-12A would be right for you, it might be too long. If you can, see if you can get one with an option to return if it doesn't fit. For parfocality on my Labophot I only needed a total of 8 cm of tube (that includes helicoid and camera fitting)
My extreme-macro.co.uk site, a learning site. Your comments and input there would be gratefully appreciated.

ray_parkhurst
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Post by ray_parkhurst »

Smokedaddy wrote:Would you happen to have a link to one that would work with in my situation?
I'm not sure if it will work for you, but this is the type that I use:

http://www.ebay.com/itm/M42-to-M42-42mm ... Sw1S9Wfz~M

rockycarter
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helicoid

Post by rockycarter »

smokedaddy Here is how i mount my camera. Using a helicoid that has 52mm opening on one end. The opposite end of the helicoid is m42. I slip the helicoid down over the leitz microscope tube with a relay installed. I use adapter rings. to attach the Olympus 50mm lens, to the helicoid. I am using a sony A7R mark II full frame so no crop factor. This setup works for me hope this helps.
Image
Rocky Carter

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