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Please recommend OAG under 29mm for ASI174mm-mini

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#1 Master_Shake

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Posted 26 March 2020 - 02:46 AM

I am looking for an OAG with a large prism to take advantage of the ASI174mm-mini sensor size.  I plan on using this with the Starizona .65 FF/FR once i get it and will need 57mm backspace for train.  The max length it can be is 29mm.  It is difficult to find information on prism size.  I just bought the Teleskop Service TSOAG27 to replace the ZWO OAG.  I incorrectly interpreted the length of OAG for an M48.  I thought it was 27mm but instead it is 33mm, putting me over where i need to be.   

 

I am looking for a first-hand recommendation on what i can use.  Thank you.


Edited by Master_Shake, 26 March 2020 - 02:47 AM.


#2 Kaydubbed

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Posted 26 March 2020 - 09:01 AM

It's tough. I know. I was really disappointed when I found my imx174 had that porthole effect on my ZWO OAG. You will need at least a 12mmx12mm prism to avoid vignetting and I don't think one exists that isn't the Celestron OAG, which of course is out of your specs. The Orion Thin OAG comes close, but you will still get vignetting. I haven't been able to find the size of that prism but anecdotes on CN show that the vignetting is still there with the OTOAG, but much less than the ZWO. 



#3 Master_Shake

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Posted 26 March 2020 - 08:00 PM

bummer. I was afraid to hear this.  Thanks for you input.



#4 Master_Shake

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Posted 29 April 2020 - 12:18 AM

For anyone reading this in the future i would like to provide an update.  I found an OAG which fits my needs.  It is a chinese made OAG and goes by different names.  The most common I found is the Hercules S8239 Off-Axis Guider.  It has a huge 12x12mm prism allowing me to take full advantage of the large ASI174mm-mini sensor.  It comes with many different attachments for various setups as well as a helical focuser.   I will say the helical focuser is heavy but it has a 9mm range of travel.  I replaced mine with a ZWO helical focuser i already had on hand.  Mostly to match the color scheme.  The OAG is 26mm thick.  Below are some photos of the OAG:

 

AG8BiqBl.jpg

 

2 second 1x1 image from the ASI174mm-mini.  No vignetting.  

7iXqrafl.jpg

 

huge opening for the sensor:

2Q8VdSBl.jpg

 

View with a M48 adapter and ASI1600MM-PRO sensor (there is no M42 input)

SJsC8JAl.jpg

 

it is a tight squeeze with no room for movement (not that it is needed with the ASI174mm-mini) once installed.  You will need shims to change the rotation of the OAG and EFW together.

NhQt7Xcl.jpg


Edited by Master_Shake, 29 April 2020 - 12:19 AM.



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