C11 scopes cheaper than C9.25. Why?

[markclaire50]

I often see secondhand C11 scopes being sold at lower prices than C9.25. Why is this? I might be forgiven for believing the C9.25 is regarded as better?? 

Anyone have any thoughts on this. Why shouldn't I spend less for an apparently bigger aperture? 

Thanks 

Mark 

[JamesF]

Just supply and demand, I guess.  The C11 is probably quite a handful for a lot of people to get on and off a mount or to move around, especially as they get older.  There is also a suggestion that perhaps the 9.25 is the largest you can go before the effects of seeing outweigh the increase in aperture on all but the most perfect of nights.

I'd still be willing to try it for myself though :)

James

[johninderby]

The C9.25 has the reputation of being the best of the Celestron SCTs which probably explains why the C9.25 is seen as more desireable. Had a C11, and while it was good, for some reason was never over impressed by it. Just had the feeling it should have been better.

Old thread here:

 

Edited April 24, 2019 by johninderby

[Stu]

Yes, the C9.25 is a slightly different optical design in that it has an f2.3 primary mirror rather than f2 for the others. This document has some good information in it.

91030-XLT_91040-XLT_91050-XLT_91060-XLT_EdgeHD_OpticalTube_Manual_English_web.pdf

[GazOC]

Isn't page 14 giving the main mirror focal ratio of the 9.25 as 2.0/ 2.1, the same the 8 and the 11?

Edited April 24, 2019 by GazOC

[Stu]

9 minutes ago, GazOC said:

Isn't page 14 giving the main mirror focal ratio of the 9.25 as 2.0/ 2.1, the same the 8 and the 11?

Hmm, not sure. Perhaps I'm misrecalling something but I was sure that the C9.25 had a longer focal length primary because the OTA is relatively longer than the others.

[GazOC]

I only checked as I remembered reading a few years ago that, optically speaking, there's no reason why the 9.25 should be better than the other members of the line up. It's the same design, it either hits a sweet spot terms of size/ aperture for a lot of people's seeing conditions or it's a bit of an urban myth that's gained traction.

All second-hand info and I can't recall the source so take it with a bucketful of salt ?

 

[johninderby]

Damian Peach’s review of the C9.25 which has comments on the differences between the C9.25 and C11.

http://www.damianpeach.com/c925review.htm

 

[GazOC]

But all the Starizona Hyperstar literature gives system as imaging at ~f2? Both can't be correct, surely?

[GazOC]

Just found a page at Rother Valley that gives the system at f2.2 or 2.3 depending on the Hyperstar version. Looks like Celestron, my info and maybe even Damien Peach are off the mark ?

[Stu]

30 minutes ago, johninderby said:

Damian Peach’s review of the C9.25 which has comments on the differences between the C9.25 and C11.

http://www.damianpeach.com/c925review.htm

 

Thanks John, I'm sure that's where I read it in the first place. I think i just assumed the whitepaper would back it up, but am beginning to doubt that a little now...

[johninderby]

From Starizona’s website.

Edited April 24, 2019 by johninderby

[Stu]

2 minutes ago, GazOC said:

Just found a page at Rother Valley that gives the system at f2.2 or 2.3 depending on the Hyperstar version. Looks like Celestron, my info and maybe even Damien Peach are off the mark ?

Seems like a fair amount of confusion all round Gaz, not least for myself ??

Hopefully someone can clarify it for us.

[GazOC]

I stand corrected, Stu ?

[ollypenrice]

I think planetary imagers looking for finest resolution will follow Damian Peach (since not following the advice of such an expert would be lunacy.) But visual observers may prefer the additional aperture of the C11. I must say that I'd advise deep sky imagers to use neither.

Olly

[JimothyC]

I think Mr Peach uses C14s exclusively. So take from that what you will. 

[Stu]

5 minutes ago, JimothyC said:

I think Mr Peach uses C14s exclusively. So take from that what you will. 

I guess ultimately resolution associated with aperture is what counts in planetary imaging, so given the kinds of skies Damian will seek out, the C14 would always outperform a smaller aperture, all other things being equal (excepting the small difference in focal ratio of the primary in the C925 of course)

[johninderby]

Damian has used the C9.25, C11 exttensively as well as the C14. 

[JimothyC]

10 minutes ago, johninderby said:

Damian has used the C9.25, C11 exttensively as well as the C14. 

Ah ok, went on a course with him a couple of months ago and he spoke about his 2 C14s and the trials of travelling with them. He now has one in the UK and one in Barbados to save the hassle of carting them about. I'm not at all jealous, honest. He didn't mention any other scopes at the time, so I assumed he only used those. 

[JamesF]

It must be tough when you're forced to buy a second C14 to keep in Barbados because it's so much hassle transporting the one from home.  I swear I almost feel sorry for him :D

James

[johninderby]

I think he now mostly uses the C14.

http://www.damianpeach.com/c925review.htm