Secondary Mirror Full Frame Sensor

[baj (Brad)]

I going down the path of a 3 inch 0.85x reducer/coma corrector for a 10 inch F4 newtonian with a 3 inch focuser. My current secondary mirror is 88mm.



Any thoughts on whether the secondary will need to larger for a full frame sensor. If so what size secondary would be sufficient for a full frame sensor?


The 3 inch 0.85x corrector is expensive so I am wondering whether this is an option that just won't work. Large secondary mirrors also seem surprisingly expensive even on aliexpress



Regards,
Brad

[OzEclipse (Joe Cali)]

Nobody can answer this question without knowing ALL the dimensions of your system. Vignetting depends on focal plane height outside the tube, diameter of the OTA, length of tube in front of the focuser.

Use a ray trace program, like newt for the web, plug in all the OTA dimensions and you'll get the answer on your own.

https://stellafane.org/tm/newt-web/newt-web.html

[mura_gadi (Steve)]

I have no idea if this is possible or feasible -

At 88mm the secondary is wider than some astro cameras, rather than go to a lot of expense, could you remake the tube and place the camera where the secondary sits. Buying a 2nd hand 10" for parts is easy and cheap.

Use a fine threaded over length bolt from the spider to the camera for a lot travel play. You just have to check the weight of your optic path with all the bits attached and see if it would be manageable on the spider.

Cable management to consider, but, you might need less bits and if you change camera's it should just be a matter of adjusting the spider camera holder.

[baj (Brad)]

Well it seems to work reasonably well. There is some vignetting for a full frame sensor however I think this has more to do with the camera connection than the secondary mirror.



M48 connection is not ideal in my opinion. There is an M54 connection to the three inch corrector that would be more suitable however all dslr t rings that I am aware of are M42 or M48.


I have noticed that many full frame cameras such as the ASI6200 come with an M54 connection.

[glend (Glen)]

Leave the secondary alone. This mania concerning full frame cameras is no reason to mess up a well designed scope. Any vignetting is easily cropped out if It bothers you.

[baj (Brad)]

I agree Glen. Full frame sensors place a lot of demands on an imaging system. Not just in terms of vignetting but also correcting the field for aberrations. Cropping is the easiest solution to both in my case since the issues are only in the far edges of the image.