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Back Focus and OAG placement

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#1 BWDenver

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Posted 01 December 2022 - 06:47 PM

It seems like my life is controlled by A) Back Focus and B) the lack of available items in various supply chains.  Like a lot of us…

 

I recently picked up a QHY286C cooled color camera.  The intent is to use it with my C11 EdgeHD OTA with Feather Touch Crayford focuser. 

 

The C11 EdgeHD has a 146.5mm overall Back Focus requirement.  The included plates in the QHY268C were of course almost there, but around 7 mm short.  I managed to locate and buy one of the last “M54 all in one” adapter kits in the US.  That arrived today and I inserted the remaining 7mm of spacers into the stack. 

 

OABF stack of 146.95 or 1/2 mm short, but I think I can live with that as when I add a filter into the mix it increases BF requirements by 1mm.… 

 

Or will 1/2 mm cause an issue?  The kit does have a .5mm shim.

 

But that leads me to my next question.  With the OAG in the stack, does it make any difference where it's place in the imaging path?  Presently it’s right up against the “center tilt switch” for the camera. 

 

Stack:  QHY268C + "center tilt switch" + OAG + 12mm spacers + Filter drawer + 2” nose piece.  So it’s as close to the imaging chip as possible.  Can it be farther away from the imaging chip, or will that lead to vignetting issues?

 

The "center tilt switch" is the unit that locks onto the camera via 3 screws and allows for camera rotation independent of the rest of the stack.  Everything else screws into it, I have no idea why they call it a "center tilt switch"...

 

Thanks in advance!

 

Bryan



#2 scadvice

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Posted 01 December 2022 - 07:10 PM

You want the OAG in front of the filter wheel or drawer and the imaging camera mounted behind the filter drawer . This is to give you the brightest star field as the filters will dim the field. Also, this gives you a longer guider focus path going up the OAG from the prism to guide camera. One of the biggest problems is not having enough focus distance for the guide camera.  Keeping the filter as close as possible to the imaging sensor helps to prevent the rim of the filter from clipping the image sensor.


Edited by scadvice, 01 December 2022 - 07:45 PM.

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#3 BWDenver

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Posted 01 December 2022 - 07:35 PM

Thanks for the info!  While I've used DSLR cameras before this is my first venture into a dedicated system.



#4 scadvice

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Posted 01 December 2022 - 07:44 PM

Thanks for the info!  While I've used DSLR cameras before this is my first venture into a dedicated system.

This fellow has some good you tube vids using the C11 and Edge

 

https://m.youtube.co...h?v=mmg57CSSLrY

 

https://m.youtube.co...h?v=i1uccN3BxMg


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#5 BWDenver

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Posted 01 December 2022 - 07:59 PM

Looks like ZWO and QHY definitely do not play well together. 

 

The tapped holes in the ZWO filter holder are 2.5mm.  The screws for the QHY kit are 3mm.

 

Taps on order....

 

If it was easy everyone would be doing it...



#6 BWDenver

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Posted 01 December 2022 - 08:00 PM

This fellow has some good you tube vids using the C11 and Edge

 

https://m.youtube.co...h?v=mmg57CSSLrY

 

https://m.youtube.co...h?v=i1uccN3BxMg

I've watched those, they are great bits of info!




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