Should I Buy a C8?

[Steve789]

I've been thinking about upgrading my SW 127 Mak for a long time now and have been looking into going for a used Celestron C8 recently.

My main interest is in imaging DSOs for which I use a SW 150pds with an Atik 314L+ on a HEQ5 mount. However all too often the only clear nights are during full (or nearly full) moons and on these occasions I like to image the moon or the planets. This is why I bought the 127 mak to try and improve on what the 150pds gives me when imaging lunar/planetary. I use my guide camera a ZWO ASI120mm to capture video for this type of imaging.

On a few evenings I've compared both my scopes for lunar and planetary and while the mak gives better results on Jupiter there's very little in it when it comes to lunar imaging. On the Mak I can't use a barlow for lunar as it gives a ghost image (like the mysterons circle) but the 150pds performs quite well barlowed when lunar imaging. In essence the difference between the two scopes isn't enough to warrant owning the 127mak.

So my question is will there be a significant improvement if I upgrade from a SW 127 mak to a C8 for lunar and planetary imaging?

I know I'll gain about 35% in focal length and I'm hoping I'll be able to use a barlow to increase that. I'm also hoping the extra aperture will make a big difference. There's also the added bonus of using the C8 with a reducer to image the smaller DSOs like M57 if I ever get my guiding good enough.

I guess I'd just like some confirmation that a C8 is the right scope before I take the plunge.

[Peter Drew]

The C8 should have a better performance for lunar and planetary imaging but a general question mark regarding DSO's. A 9.25 would be even better for the former.

[Steve789]

Thanks for the reply Peter.

A 9.25 would be nice but I need to keep an eye on the budget. After all we are talking about a scope that I won't use all that often, my primary interest is DSOs which I still intend to use the 150pds for.

I agree the C8 alone would be hopeless on DSOs but I thought if you add a reducer such as the Celestron f6.3 reducer it could be good for smaller DSOs or am I missing something?

 

[Peter Drew]

I certainly wouldn't say that a C8 would be hopeless for DSO's, just that for imaging them there are better options. I have a C8 and views of DSO's are as good as almost any other 8".

[cardconvict]

Have a look at an RC8 telescope perfect for imaging.

[ollypenrice]

4 minutes ago, cardconvict said:

Have a look at an RC8 telescope perfect for imaging.

Sorry, but I think this post is very optimistic. The RC8s can be cajoled into taking great images and you might be lucky and get one that did so from the box. But having spent several days and nights armed with Howie Glatter collimator, artificial stars and the tilt adjuster while trying to help an owner get his sorted I have to say that 'perfect imaging' remained a long way away from us! My own view of the GSO based RC8s is that they are half baked as offered to the public. We know how good they can be (see JohnRT's images) but this is always a dangerous way to set about spending money. If you look only at the best images you'll conclude that all telescopes are fine. I know people who have made them work and people who haven't. So fat I consider myself a 'haven't!!!'

A note on reducers: for small objects that will fit on the chip unreduced, the reducer has no advantage provided that you can expose for long enough to beat the read noise without it. This is the F ratio myth. For DSO I would consider a C8 Edge but not a normal C8.

Olly

 

[Stu]

10 minutes ago, ollypenrice said:

So fat I consider myself a 'haven't!!!'

 

I thought you were looking rather trim Olly, don't be so hard on yourself. ?

Apologies, back on topic.....

[ollypenrice]

Just now, Stu said:

I thought you were looking rather trim Olly, don't be so hard on yourself. ?

Apologies, back on topic.....

Heheh, a Freudian typo there because, I kid you not, trim I ain't! I used to be, but I used to be a lot of things....

Olly

[Steve789]

Thanks for the further comments.

I think I see what you're saying about reducers Olly, I probably need to read up a bit about the "f-ratio myth". I imagine a reducer might help if you're struggling with guiding just by increasing the field of view. DSOs aren't really part of the equation for now anyway as I'm only just getting to grips with guiding with the 150pds. I've fitted a belt drive to my HEQ5 which has improved things but my phd graph seems to go a bit whacky every 9 minutes or so.

A C8 edge, like a C9.25, would be nice but again budget. Also part of the appeal of the C8 is used ones come up for sale quite often. Is it worth holding out/paying a bit more for one with XLT coatings rather than just the Starbright coatings - thinking purely about planetary and lunar, forget about DSOs.

[cardconvict]

2 hours ago, ollypenrice said:

Sorry, but I think this post is very optimistic. The RC8s can be cajoled into taking great images and you might be lucky and get one that did so from the box. But having spent several days and nights armed with Howie Glatter collimator, artificial stars and the tilt adjuster while trying to help an owner get his sorted I have to say that 'perfect imaging' remained a long way away from us! My own view of the GSO based RC8s is that they are half baked as offered to the public. We know how good they can be (see JohnRT's images) but this is always a dangerous way to set about spending money. If you look only at the best images you'll conclude that all telescopes are fine. I know people who have made them work and people who haven't. So fat I consider myself a 'haven't!!!'

A note on reducers: for small objects that will fit on the chip unreduced, the reducer has no advantage provided that you can expose for long enough to beat the read noise without it. This is the F ratio myth. For DSO I would consider a C8 Edge but not a normal C8.

Olly

 

I did look around at what others had been doing with these scopes and took inspiration from John's images and after speaking with him i concluded that it would make a great scope, I'm young and have lots of time on my hands so for me I love a challenge, if the RC gives me problems which it has not yet.

 

[johnrt]

My RC came out of the box unfit for purpose and unable to image subs for more than 2/3 minutes. It took me months to work out why, in the end I tracked it down to the fact that both the primary and secondary mirrors were loose in their cells. The entire scope had to be dismantled for them to be tightened up, not nearly as frightening as you might think, but not how a new item should be delivered.

The results after the mirror issues were fixed speak for themselves, but these aren't scopes for people who aren't prepared for the possibility of having to do some work to get them going. Oh and the focuser, I'm not sure where that ended up, maybe on the roof I threw it so hard A feathertouch isn't a cheap upgrade!