Astrophotography with a 10" dob

[Furious_D]

Hi there,

I'm having a bit of trouble focusing with my new setup, hoping someone can help! After finally getting myself a Canon 700D, a T-adapter and T-ring, I hooked up my 10" dob, pointed it at Jupiter, and took a few beautiful photos of my primary mirror.

After a quick look on youtube, I saw a video where someone with the same problem had bought a 2x barlow lens and sorted their problem out. I spent $60 for a saxon 2x barlow, stuck it in, pointed my gear at Jupiter again, and achieved the same results.

So, is there anything I can do to avoid buying a 2" barlow lens and T-adapter? Has anyone else found a solution to this?

If it's of any interest, my scope has a focal length of 1200mm.

Thanks!

[Nikolas]

Unfortunately dobs and dslr's don't mix cleanly, what you need to do is to use a t adapter and eyepiece projection.
http://www.astronomysource.com/2011/10/13/eyepiece-projection/

and also https://www.youtube.com/watch?v=ckfdaSeSoCI

The other option is to move the mirror forward but that is a bit of a project

[janoskiss]

Mike's howto should cover most of what you need to know. http://www.iceinspace.com.au/63-201-0-0-1-0.html

[raymo]

Firstly, what make of dob do you have? Most Newtonians do not permit
direct attachment of a DSLR for prime focus photography. They don't have sufficient back focus. Skywatcher Newts however do permit it. Ones that
don't permit it can be modified by moving the primary mirror further up
the tube. If a scope is not suitable, using a 2X barlow only partially
solves the problem, because a f/5 scope then becomes an f/10, which
means that without tracking, only the very brightest of objects can be imaged.
If you're scope is a Skywatcher[Saxon, same thing] do you understand
the rather odd set up for attaching a DSLR, maybe you are doing something wrong in that department.
raymo

[mswhin63]

I have had good success in imaging from a DOB. mine is a 12" 1500mm FL. The DOB are mostly used for viaual observing so the focal point is deeper than a camera. To solve this I screw the primary lens closer to the secondary and then collimated.

The focus travel was then within range. To get good close ups I then made an equatorial platform for motion control as free hand worked but not well.

My favourite image from the DOB was M42 (https://goo.gl/photos/hqvtpRSMsWeSNn73A)
and best planetary from the DOB is Jupiter (https://goo.gl/photos/tgH39ANq8LrXzsuJ6)
and lunar done with a webcam https://goo.gl/photos/qPz9FGanWvNtPdB77

[Furious_D]

Thanks for all the info!


Raymo - I have a Saxon 10" dob, focal distance 1200mm. My setup is telescope-2xbarlow-t-adapter-t-ring-camera.

I'm a little nervous about adjusting the mirror. Would that also affect viewing with an eyepiece? Is it easy enough to do?

I'm leaning towards eyepiece projection, but I'd really like to take prime focus photos first if possible.

[janoskiss]

Get lower profile focusser with 10:1 fine focus. You won't need to reposition the mirror then. The Saxon 10" comes with a big old Crayford that is a blessing in disguise: your primary mirror is already closer to the secondary than on other comparable Dobs in order for regular EPs to reach focus with that bulky focusser.

Even if you give up on imaging with a push-to Dob (you probably will), a low-profile focusser would still be a worthwhile investment because it will make your telescope more versatile: it allows use of wider variety of EPs, barlows etc., and it makes it easier to reach focus with binoviewers. On a tight budget even just a GSO 10:1 Crayford will yield considerable improvement. (You can always add an extension tube to a low-profile focusser to regain your earlier high-profile setup if needed. But you cannot so easily go the other way.)

[raymo]

You don't need to do anything to your scope. If it has the standard focuser
all you do is undo the two screws/knobs on the side of the focuser[ at the
outer end of the focuser tube] and remove the bevelled plate with the tube
that the 1.25" eyepieces slide into still attached to it.
Unscrew the tube from the plate, and screw your camera's T-ring onto
the male thread that is exposed when the tube is removed.
Attach the T-ring and tube assembly to your camera.
Put the the plate with camera attached back into the open end of the focuser,
and nip up the two screws/knobs that you loosened in the first place.
It will come to prime focus with the focuser racked out about 12mm.
This assumes that you have the standard Skywatcher/Saxon focuser.Sounds complicated, but takes a few seconds after you've done it once.
raymo

[Furious_D]

Thanks again for the info Raymo. The T-ring does fix onto the attachment, which is great! It's a bit wet outside tonight but I'm looking forward to giving it a shot soon. I'm not sure what you mean about the bevelled plate though - do you mean over the focussing knobs? This is a photo of the same focusser that I have - do you mean the part at the bottom of the photo?:

http://www.saxon.com.au/media/catalog/product/cache/1/small_image/313x/9df78eab33525d08d6e5fb8d27136e95/1/_/1.25_reflector_focuser_with_2_adapt er_for_large_telescopes.jpg

What would be the significance of removing the plate? Sorry for all the newbie questions - I'm still trying to wrap my head around how the whole machine works :confused2:

Thanks,
Graham

[raymo]

Yours has what looks to be the same focuser that Synta made Newts have,
but the eyepiece/ camera fittings are different.What exactly does your T-ring
screw onto? Is whatever it screws onto there in the picture? Maybe you can post a pic with the camera attached to whatever it is it screws onto.
raymo

[janoskiss]

Funny post Raymo. You say "don't have to do anything to your scope", then you follow up with lengthy instructions on what the OP should do to their scope.

@OP The basic 1x Synta Crayford leaves a lot to be desired. If you can afford to get something better it's well worth it - you'll never look back. If you cannot then it sounds like Raymo may have a workable solution figured out for you. I do vaguely recalll camera adapter threads on my original Saxon 10" focusser.

[raymo]

I was meaning that you don't have to do any modification[s], as are
required with scopes that don't have sufficient back focus to allow the attachment of a DSLR, [most Newtonians]. You just have to use the existing parts and a T-ring. As I said, the focuser shown in his pic seems to have different eyepiece attachment fittings, but as it is otherwise still the same basic scope, I'm pretty sure his problem can be sorted.
The description I gave is how a DSLR is attached to almost all Synta
[Skywatcher/ Saxon newts. You are not really DOING anything to the
scope, that's how the manufacturer intends it to be attached.
raymo

[janoskiss]

I know what you meant, Raymo. Was just stirring for a laugh. It's just the way your post reads that's funny. I remember that focusser and there was indeed a T-ring adapter on it once you removed the EP holder bit (though I'd never used it).

The focusser was also the weakest bit of an otherwise great scope: despite being a Crayford it still had considerable wobble (equivalent of rack & pinion backlash). Maybe I got a bad one but I don't think so; it looked like a design flaw. But hopefully Synta made improvements to it since I got mine around 10 years ago.

[raymo]

As others have said, I think the Saxon versions are made a little cheaper.
I have owned or used a number of the Skywatcher versions, and although
the focusers are cheap Crayford style ones, they do an o.k. job.
cheers raymo

[astro_nutt]

Don't forget to make your own Bathinov mask to fine tune focusing with your DSLR.
Cheers!

[Furious_D]

I had a chance to try out the existing adapter tonight - worked like a charm! Thanks Raymo, you saved me a small fortune :lol:

[raymo]

Glad to help,
raymo