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Focal reducer/Flattener question

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#1 McConkey

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Posted 29 March 2020 - 06:36 PM

Good evening everyone!
I hope everyone is doing well during these times and is staying safe!
I currently image with an Orion ED80T CF with the Orion x0.8 focal reducer, capturing frames with a mono ASI1600. I’m wanting to increase my FOV and start imaging wider...does anyone have any recommendations into a x0.67 or lower focal reducer/flattener that I can use with my Orion 80mm?

Eventually I’m going to be grabbing an AT60ED or WO Redcat51 however both of these are currently unavailable so I’m thinking a focal reducer is my next best option.

Any recommendations or suggestions would be greatly appreciated!

Thanks!

#2 YAOG

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Posted 30 March 2020 - 01:52 PM

Good evening everyone!
I hope everyone is doing well during these times and is staying safe!
I currently image with an Orion ED80T CF with the Orion x0.8 focal reducer, capturing frames with a mono ASI1600. I’m wanting to increase my FOV and start imaging wider...does anyone have any recommendations into a x0.67 or lower focal reducer/flattener that I can use with my Orion 80mm?

Eventually I’m going to be grabbing an AT60ED or WO Redcat51 however both of these are currently unavailable so I’m thinking a focal reducer is my next best option.

Any recommendations or suggestions would be greatly appreciated!

Thanks!

Hi McMonkey,

 

Your system is on the verge of being undersampled at 1.63"/per pixel even without the 0.8x reducer/flattener inserted. So getting a higher amount of image reduction will hurt your image quality even more unless your seeing and transparency are routinely not very good. The trade off is between objective size, resolution and FOV. You can get a wider FOV but resolution suffers unless you find a camera with much smaller pixels and the problem there is that the smaller pixel cameras are all smaller chips at the moment. You can also use an optic better suited for the camera sensor you own but that's going to get expensive because you need a larger, faster objective for the pixels to scale well. You can look for a larger sized sensor but that is going to be very expensive too. 

 

Have you used the astronomy.tools CCD suitability calculator? You need to know with fair certainty what your typical conditions are and IMO you should try to always try to build a system that will be slightly oversampled vs undersampled if you have a choice in the process. Long term this is a cheaper strategy and your results will tend to be better in times of changing conditions. Check it out.



#3 McConkey

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Posted 31 March 2020 - 07:04 PM

Thanks for the feedback and information! I hadn’t used the astronomy.tools ccd calculator but I’ve been playing around with it all day and with my camera, I’m seeing that the 80mm is really the widest FOV I can go before undersampling. I havnt measured my seeing conditions but I would argue I range from poor to ok, with maybe a rare night or two a year in the higher range.

At this stage in the game I’d rather change up my scope as I really do love the ASI1600!

I’ll have to stick with mosaics for now!

If anyone out there is using the ASI1600 with a smaller scope (around 60mm) i’d love to hear from you and hear how you find the performance of that combination!

Thanks!


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