Backfocus for Imaging with Baader Zoom

[furyz]

Hi Everyone,

Quick question regarding backfocus. I am looking to do some planetary imaging while leveraging my Baader Hyperion Zoom eyepiece to do eyepiece projection.

Took a look at the Baader documentation and I just want to make sure I am understanding everything correctly prior to buying the necessary adapters and extension tubes for correct back focus.

Baader documentation (https://www.baader-planetarium.com/en/downloads/dl/file/id/444/product/3117/digiscoping_camera_adaptations_for_ afocal_photography_and_eyepiece_pro jection.pdf)



I have a Celestron C6 and a Nikon D3100 (APS-C sized sensor). I have a Celestron T-ring for Nikon cameras (#93402) which gives me 55mm of focal length from the T-ring to the sensor.

The Hyperion Zoom has a 2" SC thread so I should be able to screw it directly into my OTA. From there I will need the Hyperion M43/T-2 adapter (#2958080). Given that my camera sensor size is APS-C, Baader says I will need 30mm of focal length from the eyepiece which I can get using two of the 15mm extension tubes (#1508154).

So my final optical train should be:

Celestron C6 Rear Cell -> Baader Hyperion Zoom -> Baader M43/T2 adaptor -> Baader 15mm + 15mm extension tube -> Celestron T-ring for Nikon -> Nikon D3100

Are there any factors that I am forgetting? Will screwing the zoom straight into the rear cell cause any problems? I am assuming the native backfocus on the Celestron C6 of 5" (132mm) is not going to be a factor at all here, as the Hyperion Zoom is the final optical element in the train.

Lastly, for those of you who have dabbled in eyepiece projection for planetary imaging, I would love your input on recommendations.

[Tulloch]

I tried using the Baader zoom and my DSLR/planetary camera for eyepiece projection imaging, and yes, the extension tubes are essential so that you can achieve focus. Even then however, the performance is not good, it is significantly better to use the prime focus method (ie screw the camera straight into the back of the OTA).

For planetary imaging, the best method is prime focus and a barlow lens to get your focal ratio to be about 5x the pixel size of your camera. For the Nikon D3100 with a pixel size of 5 microns, this puts the optimal f/num at around f/25.

However, the Nikon DSLR system is not the best camera to use for planetary imaging, as it is not possible to stream raw the Live View video straight to a computer, and using the inbuilt video is highly compressed making post-processing difficult. You can read about the process here and see why Canon DSLRs are preferred (it's how I started).
https://www.astropix.com/html/i_astrop/eq_tests/canon_one_to_one_pixel_resolution.h tml

Here's some more tips on how to take high resolution planetary images.
http://planetaryimagingtutorials.com/

Hope this helps, Andrew