Scope dilemma: please help me decide

[EricB (Eric)]

Hi there!

I hope you guys will help me make a decision as to which option to go for.

I posted about this before some month ago and got some useful advice which advanced my understanding of differences between scopes. I let the matter rest for a while, but my birthday is coming up a a few weeks and I need to make a decision soon if I want to make myself a nice presy.

I am relatively new to astrophotography. I am mostly interested (and experienced) in lunar photography, although I enjoyed planetary AP. I have no experience in deep sky photography which I am considering some time down the track. Some of you may have seen some of my pics in the Solar System forum.

I currently own an 18 month old Sky Watcher 10" Fextube dobs which has been a great scope for lunar photography. However, if I want to move to more planetary and eventually to DP photography, I need a better mount.

After exploring several options and several scope possibility (including the C11), I am now set on sticking with a Newtonian. I am also now set of the AZ EQ6 which has all the qualities of the venerable EQ6 and would allow me to operate in AZ mode for quick lunar grabs.

So having decided on the mount (AZ EQ6) and the scope type (Newtonian), I need to decide on the scope itself. At this stage I am looking at several options (as discussed in my previous post).

Option 1: Keep my current flex 10" tube and adapt it to the EQ mount.

Advantage: I now the scope performs well
Disadvantage 1: I need to adapt it to fit the mount and use a long dovetail bar (eg Losmandy C14 bar) for maximum strength (Weight: about 14.5kg)

Disadvantage 2: I am stuck with the dobs base.

Option 2: Buy the Bintel BT250 10" ($749). GSO newtonian have a good reputation and I assume this scope would be equivalent in quality to the one I SW I have.

Advantage: I can sell the Dobs if need be.
Disadvantage 1: This option is the most expensive (and thus harder to sell to my other half )
Disadvantage 2: I might still have to get a long dovetail bar for strength (weight: about 16KG, which stretches it if I want to add an autoguider and other accessories)

Option 3: Buy the Bintel BT200 8" to get the weight down.

Advantage 1: cheaper than option 2
Advantage 2: about 2.5kg less weight, allowing for a light-weight autoguider
Disadvantage: less performant than the 10"

Option 4: Same as option 3 but replacing the intel BT200 with the carbon fibre version.

All BT scopes are F4 and labelled "imaging" scopes. They could be substituted with GSO-branded equivalent (which are cheaper a Andrews Comm. and come in F4 and F5 versions).

I would be very grateful for your thoughts on the merit of each option.

Sorry for the very long post...

Cheers,

Eric

[astro_nutt]

Hi Eric.
I not too sure but I read someone made/sells a tracking platform for dobs. I think they're good for about an hour's tracking. Maybe some of the other's in this forum can help?

[Shiraz (Ray)]

depends on what camera you are looking at Eric - if something with small pixels, get a short focal length, if large get a longer fl.

You don't need the high resolution of a large aperture with DSO imaging, since the atmosphere will almost always limit you to maybe 2 arc seconds - even an 8 inch GSO scope will do much better than that with ease.

The mount looks like an excellent choice and i would suggest an 8 inch f5 (Bintel or GSO are the same I think), which will match well with DSLRs, smaller pixel cooled cameras and your existing array of uncooled cameras. f5 is way easier to set up and keep aligned than f4 and the low weight of the 8 inch scope will ensure that your mount is working well within its design rating, so it should be stable and track well. Whatever Newtonian you get, you will need a coma corrector - these will work a bit better in an f5 than an f4.

regards ray

[EricB (Eric)]

Thanks Astro_Nutt. I did consider a tracking platform at some stage, but my understanding is that they may be quite difficult to get in Australia.

Thanks Ray. This looks like sound advice. If you remember from my previous post, I wanted to go for the 12". But even the 10" might be touch and go for DSO on this mount.

What is important, as everyone keep saying, is the mount. Short of the EQ8, which is too expensive for me, I have settled for the AZ EQ6. The scope is secondary. The 8" will be fine for lunar.

Now the question is should I get the standard 8" or the CF one? Is there much difference really?

Cheers,

Eric

[Poita (Peter)]

If you want to do high resolution planetary and Lunar, then the Newt is probably a bit short at f4 or f5.

I'd look at getting a 2nd hand C8 instead, easier on the mount, much longer focal length in a shorter package, my old one was fantastic for lunar and planets.

Or buy my Meade 10" ;^)

[EricB (Eric)]

Peter, re the planets with a 200mm at F4/F5, you have a point. But re the Moon, I am not sure. The lunar captures here as at least as good as mine through an 8" (F6)

As to your Mead, it look like you have people interested in it.

Ahhh! Now you're making me doubt again

Perhaps I should just get the mount for now.

Eric

[Poita (Peter)]

Depends on your seeing, but I like nice detailed lunar closeups, and Ifound anything under the focal length of the C8 was not for me. A C8 OTA can often be had for <$500.

My scope has sold, I'd keep an eye out for (or borrow) a C8 or similar. Much much much easier to handle on that mount than a newt.

I'd get the mount then trial some scopes on it before commiting to a particular scope.

[EricB (Eric)]

Thanks Peter. This sounds like a wise approach. I'll make a decision this weekend.

Cheers,

Eric

[EricB (Eric)]

Well, I have made a decision and have just bought the AZ EQ6 . After a lenghty conversation with the retailer reviewing the options below, I have decided not to buy a scope and keep my options open for now.

Thanks you for your help everyone!

Eric

[EricB (Eric)]

The AZ EQ6 GT has arrived today. No time to set it up tonight. I will have to wait for the weekend to unbox it in set it up.

In the interim, as I wait for the right scope for this mount to eventuate, I will try to mount my SW 10" flextube on it. As it might not work because of balance issues, I don't want to invest too much in the project.

The simplest and cheapest would be to use tube rings mounted on a dovetail plate. One ring would be quite far back on the tube, while the front ring would sit just above where the scope currently connects with the fork. (see my avatar picture)

My question is: would it be ok to use a Sky Watcher Vixen style dovetail (13" or 330mm): http://www.bintel.com.au/Accessories...oductview.aspx

or should I use a wider Losmandy style dovetail like this one (14"):http://www.bintel.com.au/Accessories...oductview.aspx

Or should I use a longer one? (the maximum I could use would be 420mm)

Any feedback would be hugely appreciated!

Cheers,

Eric

[rogerco (Roger)]

I tried both sizes of bar on my C8 while I was changing over mounts, the wider "D" is definitely more rigid. I am not sure how you would mount the bars to a truss dob, wouldn't a ring either side of the current pivot point give the best balance? Then just a short "D" bar would be cheaper. Its going to be interesting to see if the mount takes it. I tried my 200mm dob on a EQ5 with rings and it was a bit wobbly

[EricB (Eric)]

Thank you for your feedback Roger. Yes, it will be interesting to see how it goes. I am not very confident that, in this configuration, the scope can be balanced satisfactorily. The general advice on forums is not to bother. But I am curious about it and keen to try.

Cheers,

Eric