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astro_dt

Advice needed on connecting cameras to a PST

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H all

Just working on a PST set up and the best way to connect a webcam, DSLR or a CCD. It will be a shared resource in our Astro Society so we need to cover as many cameras as possible.

Anyone out there with a PST that can share their experiences and what they have used?

Thanks

Danny

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Most webcam just need a 2x Barlow nosepiece screwed to the bottom end of the webcam.

Bill

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An extract from the "Modifying a PST" write-up ( copy available if you send me your email address)

Focusing a PST

The final focus position in the original PST is constrained by the 200mm focal length lens behind the etalon and the limits of the penta-prism movements. This can sometimes cause problems getting the PST to focus on the camera CCD chip. (The initial PST design concept, I believe was as a purely visual instrument, hence the issues with cameras.)

A few solutions have been used.

  • Use a short nosepiece adaptor (with no retaining shoulder) on the camera, this may be just sufficient to get the CCD to the focus.
  • Remove to bottom half of the eyepiece holder and re-assemble with the BF5 top part only. This gives approx 25mm of additional space.
  • Add a small Barlow lens into the eyepiece holder to give more back focus. This is mandatory if you want to use a DSLR.

http://sweiller.free.fr/ATM/PST-EOS.html

Hope this helps,

Ken

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Ken - I sent you a PM

Thanks to both you and Bill for the quick advice

Danny

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I've fitted a short nose-piece to my DMK and it works a treat!

Helen

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This is mandatory if you want to use a DSLR.

Well - you could try afocal imaging - I couldn't get it to work but some people get reasonable results that way.

A positive transfer lens (i.e. "eyepiece projection") is another way of making the focal plane accessible, and (unlike a barlow lens) need not have a magnifying effect on the focal length.

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Thanks Helen, Brian - I think there are some good options and I need to experiment.

Danny

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I've had reasonable success with PST/DSLR imaging by afocally connecting a zoom eyepiece to the filter ring of a Canon 400D.

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