Meade versus Celestron?

mykc wrote: The main weaknesses of SCTs are the difficulty of obtaining precise focus and the related problem of mirror shift. Those problems can be solved by replacing the stock focuser with a microfocuser (though that does not eliminate image shift), or by adding a Crayford style or helical focuser. I chose a helical focuser, which gave a significant improvement in ease of use, and this is an upgrade that is definitely worth the extra cost, in my view. It is worth bearing in mind that the cost of accessories, such as a focal reducer, a microfocuser, a 2" diagonal for use with longer focal length eyepieces, and various adapters to connect all the bits together, can be very substantial. You may well find that you spend as much again (over a period of time) on eyepieces and accessories as you did on the scope.

And even those solutions may not be enough depending on what you buy. For example my (second hand as it happens!) Celestron CPC 9.25 has no way to lock the mirror in place. There are DIY solutions to this which involve basically drilling holes into the tube and adding screws to keep the mirror in place, but not what you want to do with a new scope!

I haven't gone down that route (yet anyway!), my astrophotography isn't yet at the level where that's the lowest source of error! But I do find my helical focuser great, especially for photograph, you just can't get that accuracy of focus from the regular SCT focus knobs.

You can image with a fork provided you have a decent wedge as Dave says. Mind you a decent wedge is another €500.

Secondhand SCT's come up reasonably regularly here. Check back over the for sale section, or try posting in the wanted section.

You might be interested in this solution Albert.

www.maison-astronomie.com/bagues-et-acce...celestron-8-925.html
www.sciencecenter.net/hutech/misc/focuslk/


Mike

mykc wrote: You might be interested in this solution Albert.

www.maison-astronomie.com/bagues-et-acce...celestron-8-925.html
www.sciencecenter.net/hutech/misc/focuslk/

Thanks. The trouble with those types of solutions is that they don't actually lock the mirror, they really just secure the focuser. That gives an improvement but doesn't eliminate the problem from what I've read. I was thinking more of this www.marsastro.org/presentations/MARS_Mirror-Lock.pdf or look at adding screws to lock the mirror like the 'transport screws' the C14 has.

I see that the newer meade sct's come with a mirror lock to stop mirror flop, mine is an older model with no lock, but it did come with a shipping bolt so I can use a modified version of this bolt to lock down the mirror, I had found that without this, the weight of the 12" mirror+cell shifts the fov when it crosses the meridian. I got the peterson focuser mod and it worked a treat to make the focuser a little smoother. The scope also came with the a microfocuser so you can lock the mirror with the bolt and further refine the focus, its not thee best mircofocuser out there, but it does works ok for me.

Keep in mind that ACF and HD optics will not work with a standard f6.3 SCT focal reducer, the meade ACF scopes can be either F10 or F8. The HD scopes are F10 but capable of been hyperstarred, meaning they can be set to f3~ for imaging, a big plus for widefield imaging.

Interesting work around there Pheonix, buying from their clearance depo from the US shop, thanks for that !.

albertw wrote: ...or look at adding screws to lock the mirror like the 'transport screws' the C14 has.

I'm not sure if Andy is still making his locking mechanism - but there is an email address for him...

www.intint.com/andy/build.html

I bought his older version (without the indicator at the time) a few years back and can attest to the fact they lock down the mirror enough that mirror flop is not a huge problem all the time. Of course, you only need to do this for astrophotography - but you then have to attach a motorised focuser that can move your camera to achieve focus (since the mirror can no longer move). It can get very expensive...

Overall, I think any debate about Meade/Celestron is like any other debate about competing similar products (VW v Ford v Renault v Opel ...). Decide what you want to do and pick the product that covers as many of the bases you need - or all of them if you're lucky.

Of course, you could just buy one of these: www.rcopticalsystems.com/mounts/hispeed.html

Dave

Thanks Paul, Dave, Kieran, Mike & Albert. These are some great insider tips and it'll digest them all as I think about my next move.

As I said it's early days yet as I'm only getting to know my way around the sky using the 8inch Dob.

Once I get more confident I'm sure I'll begin to focus on one or other combination of a scope and mount.

Dominic