The Devils Mask

[rmuhlack (Richard)]

Originally Posted by alpal

Greg,



Yes I know,
if you are imaging a small galaxy then with a lower f ratio that galaxy will appear smaller but be brighter given the same time -
so it's a trade off.
I look at it as concentrating the photons into a smaller area.
You also get a wider field of view.

Plenty of thoughts here:
https://www.cloudynights.com/topic/4...-f-ratio-myth/


cheers
Allan

this old thread from Shiraz (Ray) is probably relevant to the discussion here

[gregbradley]

To be honest Allan, what you said is what I have experienced using both types of scopes - CDK 17 and RHA F3.8. Both image fast with these new 91QE cmos cameras. The main difference is the magnification of the image.
That's why I started taking my RHA to my dark site. It gets a fast wide image at dark skies.

Mike's image highlights the flexibility of a 12 inch F3.8 system with accurate optics.

Greg.

[strongmanmike (Michael)]

As Greg says, if one can only have one telescope the 12" F3.8 is very versatile, not to mention affordable, compared to a 16"/17" CDK/RC and 0.84"/pix image scale is certainly adequate for many applications, but about half that would be great to take better advantage of the more consistently good seeing up here and increase the sampling for traditional deconvolution to work its magic. To have optics free of astigmatism would help too ..probably lift the resolution a similar order of magnitude again that the improved seeing has

Mike

[alpal]

Originally Posted by strongmanmike

As Greg says, if one can only have one telescope the 12" F3.8 is very versatile, not to mention affordable, compared to a 16"/17" CDK/RC and 0.84"/pix image scale is certainly adequate for many applications, but about half that would be great to take better advantage of the more consistently good seeing up here and increase the sampling for traditional deconvolution to work its magic. To have optics free of astigmatism would help too ..probably lift the resolution a similar order of magnitude again that the improved seeing has

Mike

Hi Mike,
there's nothing wrong with Newts - they give impressive results.
I was always scared of RCs and other designs because of the
collimation problems people seem to have.
The big advantage of RCs etc to me is the back focus which would allow
for adaptive optics to take it to the next level.
No matter how good your mount is those stars will still dance around
and the adaptive optics takes care of that.
Also the spot sizes off axis are better - I think - for RCs
so you could use a full frame camera for a wide FOV.
Unfortunately: a high end scope, adaptive optics and the
latest high QE full frame cameras represent an enormous price tag.


cheers
Allan

[alpal]

Originally Posted by gregbradley

To be honest Allan, what you said is what I have experienced using both types of scopes - CDK 17 and RHA F3.8. Both image fast with these new 91QE cmos cameras. The main difference is the magnification of the image.
That's why I started taking my RHA to my dark site. It gets a fast wide image at dark skies.

Mike's image highlights the flexibility of a 12 inch F3.8 system with accurate optics.

Greg.

Hi Greg,
you've been spoilt with premium scopes.


cheers
Allan

[alpal]

Originally Posted by rmuhlack

this old thread from Shiraz (Ray) is probably relevant to the discussion here

yes - it's very relevant - thank you.


cheers
Allan

[strongmanmike (Michael)]

Originally Posted by alpal

yes - it's very relevant - thank you.


cheers
Allan

It's a good synopsis huh?

Mike

[alpal]

Originally Posted by strongmanmike

It's a good synopsis huh?

Mike

From what I've read it's very good although
I haven't read every post there.
I still think my calculations are a good guide.

cheers
Allan