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View Full Version here: : If only imaging, why do we need a secondary?


toc
17-08-2017, 05:30 PM
Lets say I don't care about visual astronomy - What would happen if we took a newtonian design, and replaced the secondary with a camera? I guess the tube will be a bit longer...

dimithri86
17-08-2017, 05:43 PM
You can do that. An example would be hyperstar.

Check out the link below
http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3005_HyperStar-fuer-C8---f-2-FlatField-Adapter-fuer-das-Celestron-SC-Teleskop.html

glend
17-08-2017, 05:50 PM
Sure, it works on my Edge HD8, remove the secondary and attach the Hyperstar lense to the front. You camera the becomes the central obstruction, and you lose focal length. A small round camera like a ASI works well, and its the reason for tube cameras.

Camelopardalis
17-08-2017, 07:02 PM
On top of all that, Hyperstar is waaaayyy faster than a newt...I think a C8 HS is f/2.2, C11 HS f/2.0

billdan
18-08-2017, 01:20 AM
There are some disadvantages for replacing the secondary with a camera
(thinking of a newt here)

Hiding the cables to the camera,

Extra weight of a coma corrector and spacer installed would mean a stronger spider needed,

Coming up with a method for adjusting the tilt and collimation of the camera,

Coming up with a focusing method

Locked into OSC (you could swap one filter at a time with a mono, but then run the risk of dropping a filter onto the primary, in the dark)

No OAG, which means a guide scope for guiding and probable flexure issues

Personally I think you back yourself into a corner doing this method (converting a newt).

Bill

toc
18-08-2017, 02:39 PM
Well yeah, i guess that all makes sense :lol: given the size of a cam and filterwheel, it is a fairly pointless activity.

doppler
18-08-2017, 05:49 PM
The secondary only angles the image to a accessible spot so there would not be much advantage gained, on a newt anyway.