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Octopi tilt and backfocus adjustments (kudos to @poynting)

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#1 Bennich


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Posted 30 September 2023 - 03:37 AM

I have recently acquired an Octopi from Keith (@bugbit) - THANK YOU for excellent service and an extremely well made product!!


Setting everything up was easy, using the "documentation" (which I obviously didn't go through carefully enough) tongue2.gif  and drawings on the site - https://www.octopi.s...anical-drawings.


Last night, I set up to finally solve my tilt and backfocus issues on my Samyang 135mm F/2 lens. 
What I at least failed to realise immediately, was how the connection is between the pull and adjustment screws. 

So I spent a few hours, not really getting anywhere...I know I know  - noob wink.gif wink.gif


After looking around here, on astrobin and youtube, I found @poynting that shared he had been able to easily fix his issues. After reaching out to him in a PM asking for a bit of help he sent me the following awesome message, that I will share here as well - if anyone else need a bit of help. 


*********************FROM: @poynting****************

First would be to determine your backspacing requirements. The unit has 3mm backspacing when attached to the filter wheel (base is 3mm thick). For me, I removed the tilt plate from my QHY268M which is 5mm thick, and I have my camera bottom (sensor end) flush with the bottom of the Octopi clamp ring. So to get the backfocus about where it was I have the skinny pull screws protrude 2mm from the bottom of the clamp ring to offset it 2mm from the base when everything is put together.

Next to adjust the tilt, loosen the skinny pull screws and adjust the fat push screws, then snug the skinny pull screws to set everything. I would take a 1s image of a star field, load into ASTAP, and do tilt analysis with four corners (press f4). Eventually I figured out what screws I needed to adjust in what direction to make the tilt get better each iteration.

To adjust backfocus, loosen all of the skinny pull screws, and move all of the fat push screws the same amount in the same direction, then snug all of the skinny pull screws. I did this after fixing the tilt and could move the backfocus without disturbing the tilt adjustment.

If you want to adjust the centering of the sensor in the light cone, leave the fat push screws alone and loosen the skinny pull screws. Center the camera with the lateral adjusting screws then snug the skinny pull screws.



I am looking forward to clear skies again, to try solving my issues again - now armed with above!


Feel free to share your own tips and tricks for using and setting up the Octopi - and help spread the word about this well thougt out solution to a common problem. 

Edited by Bennich, 30 September 2023 - 03:46 AM.

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