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Celestron C8 or C9.25

Viv

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Viv

Viv

Posted
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Guys,

Other than the obvious, how much difference is there between a C8 or C9.25

Both will be within the useable weight of a HEQ5, as well.

It's for planetary imaging & DSO's.

Any advice / info is muchly apprediated.

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peteftm

peteftm

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I've had both mounted on a HEQ5 in the past.The C9.25 is a beast compared to the C8.If it's long exposure AP your wanting to do then the nine n quarter might be pushing it on the HEQ5 with all the extra weight of guide scopes etc

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ollypenrice

ollypenrice

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For DS imaging at long focal length you cannot be undermounted. The C9.25 is better visually and for planetary imaging but for DS you will need to think not only of the weight but of the autoguiding demands of a long focal length. Tim recently presented a very long FL image taken on an EQ6 but I'd call that heroic.

SCTs are quite demanding DS imaging tools. There are easier options... (You'd need the flattener reducer as well, remember.)

Olly

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nightfisher

nightfisher

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for planetary i think you would get away with the 9.25 (on a calm night) but being under mounted is just a pain, i have the 180 pro on EQ5 for lunar, thats on its limit, so much so that i have considered changing the 180 for a 150, i think i would be tempted to go for the c8

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nightfisher

nightfisher

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i looked up the weight of both tubes, they are light compared to a maksutov, the 9.25 is 9.07 kg and the c8 is 5.67 kg still think c8, my mak is 7. some thing and its at the limit

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JamesF

JamesF

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If you really get into it then you might end up thinking about an external focuser too, which would push the weight up again. Much as I hate being a slave to practicality, there are times...

What were you considering as regards cameras?

James

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x6gas

x6gas

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I would go for the 9.25 personally. And - again personally - I'd probably go for the standard version rather than the HD.

The mount is more forgiving on high frame rate planetary imaging than is the case for long exposure DSO AP.

Just my 2p worth but there are reasons why the 9.25" is considered the jewel of the Celestron SCT range (and this from an 11" HD owner...)

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Viv

Viv

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Thank you James :)

I had exactly the same problem, with my ED80 & 7D

I think it's ADM, they have a weighted bar system, but I wanted a modded camera, so just bought the 1000D instead - which made it balance.

What were you considering as regards cameras?

I was just going to use my SPC900 & modded 1000d for now.

Practicality is a terrible thing sometimes ......... :)

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Viv

Viv

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thanks gas .........

It's still a possibility, I may even invest in a second mount (NEQ6 maybe), as I still want a permanent fixture in the garden & just use it here.

Arrrghhhh - so many options :) :) :)

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JamesF

JamesF

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The problem is not that there are so many options, but that there is insufficient money :)

I can't wait to get my SPC900 into my C9.25. Once I get the obsy built (hopefully before Jupiter returns to the night sky). Sadly for the sake of domestic harmony it's packed away at the moment whilst I get a few other projects completed before I'm allowed to build the obsy...

James

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David JM

David JM

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I'm about to get [when there are some in the country] a 9.25. The 8 may be hyperstar compatable as well, the 9.25 isn't, and the .63 corrector is around £200.

If you haven't seen the specs:

8 [9.25 in brackets like this]: Rayleigh .68 [.59], Dawes .57 [.49], light gathering 843 [1127] weight of 9.25 appears to be about 4 kg heavier, they only give weights of the assembly in the 'book'

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Viv

Viv

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The problem is not that there are so many options, but that there is insufficient money :)

True !!

Hope you get that ok to start soon - would be nice before the season kicks of again.

Cheers David - am sure Flo have one ! Would be nice to see, if you get one before transit camp (shame it's not in the next few days).

Thanks for the details - that's a fair difference in light gathering !!

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x6gas

x6gas

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I thought I'd read the following somewhere and managed to dig it up from http://www.backyardvoyager.com/Celestron%209.25-2.html

WRT the 9.25": 'This time Celestron tried something a little different. They made an f/2.3 primary, which would put less strain on the secondary, this time figured at f/4.3, creating wider collimation tolerances and, most importantly, producing a flatter field with less coma, at least in film and CCD images. It also resulted in a slight physical difference. A C9.25 has a proportionately longer optical tube than other SCTs. It is, for example, nearly the length of the C11.'

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x6gas

x6gas

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Indeed. Though hyperstaring kind of baffles me.

OK so you get a superfast f/2 Schmidt camera but I don't see how you avoid an asymetric spike on bright stars from the cables.

I can't justify the new camera in addition to the hyperstar itself... and I presume you can only use a OSC camera as there is no room for a filter wheel and changing the filters manually...

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JamesF

JamesF

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Indeed. Though hyperstaring kind of baffles me.

OK so you get a superfast f/2 Schmidt camera but I don't see how you avoid an asymetric spike on bright stars from the cables.

I can't justify the new camera in addition to the hyperstar itself... and I presume you can only use a OSC camera as there is no room for a filter wheel and changing the filters manually...

I think you have to try to route the cables in such a way that the diffraction spike isn't so visible. It's always struck me as a less-than-ideal solution though.

Not to mention that for the price of the hyperstar you can get a fairly reasonable small aperture 'frac. You just have to wait a bit longer to get your subs done.

James

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