astrophotography Selecting a Scope for DSLR/CCD Astrophotography

[Lrlinnell]

I could use some expert advice on purchasing my first telescope for astrophotography. I have been using my Canon 5DMIII and an Astrotrac and have decided to upgrade to a tracking EQ mount and telescope. At first to image with my Canon and later CCD. Currently I am considering three scopes:

                 Sky-Watcher ProED (100mm doublet ED APO 900mm FL (f/9)),

                 Meade Series 6000 (80mm Triplet ED APO 480mm FL (f/6)),

                 Explore Scientific (102mm Triplet ED APO 714mm FL (f/7).

Any opinions on which would be best for astrophotography of galaxies and nebula? Are there others that are better that I should consider? I have not selected a mount yet but something like the NEQ6.

 

Thanks, Lloyd Linnell

[brantuk]

The NEQ6 would be ideal, but I think either an f-5 scope (doublet or triplet) or your f-6/f-7 apo's above, with a reducer. F-9's probably a bit too slow and will give more problems than you need even if it is a nice scope for observing. The more problems you can get rid of, the better, with astro imaging. If you can get a copy, a good read is Making Every Photon Count by Steve Richards:

https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

It's kinda the astro imager's Bible this side of the pond. Hth

[Lrlinnell]

Thanks so much for the advice. I ordered "making every photon count" yesterday! It has great reviews so I can hardly wait to receive it.

Lloyd

[ecuador]

The "galaxies and nebula" is a bit contradictory, as most nebulae (except planetary) require small focal lengths, while most galaxies (except a few large ones like some Messiers) and most planetary nebulas require larger focal lengths to get any detail. So you can't get something for everything, but you should in any case start with small focal lengths, hence you are correctly looking for an APO. The 100mm f/9 is way too slow and even the SW reducer only gets it down to f/7.65. The others are more interesting choices, but remember you'll really need a field flattener (reducer or not) with either to get nice stars near the corners of your field, so see what is available for them and calculate it in the price.

The NEQ6 though is sort of a huge mount for these scopes (especially the 80mm), not to mention a bit outdated. It will be fine if you have a permanent observatory, since you can later add a heavy OTA, but if you want any sort of portability, I'd look at some other more modern mounts, like the SW AZ-EQ5 (Orion Sirius Pro) or the iOptron iEQ30 Pro.

 

[SilverAstro]

I was also thinking about the difference in size of most galaxies vs nebulae -  as well as perhaps the variation in size of the sensors ? The 5D has a full frame sensor ? What size CCD or CMOS will you then move to ?

 

[Lrlinnell]

Quote

In looking at the SW AZ-EQ5 and the iEQ30 Pro, it looked as though they both used RS-232 interfaces. Is this an issue since everything is now USB?

On the sensor size, yes the Canon 5DMIII is full frame and I'm just thinking that I would NOT have it modified so at some point I would go to a cooled CCD but have not done any research yet. Is it a fools journey to try to use my 5DMIII? Should I go straight to CCD?

 

 

[SilverAstro]

The reason I raised the sensor size issue is because it bears on what ecuador is saying about focal length and image size (scale)

 

[Lrlinnell]

Am I heading in the right direction with a Refractor, 100mm ish, f/5 ish for astrophotography? Would it be better to just go straight to CCD rather than try to use my Canon camera?

 

[wxsatuser]

You could start off by using the dslr and if you have any half decent lenses, your good to go.

Have a good read of Steve's book and play around with a FOV calculator to get an idea what targets fit
each setup.

[Lrlinnell]

If had not thought about the FOV calculator. Great advice! thanks

[dannybgoode]

I'm in almost exactly the same position as you. I have a 5D mkIII and am going to use it to start imaging. 

For mounts I've just ordered an SW EQ6 AZ EQ GT. Means I don't have to worry about what equipment I eventually get-it'll cope with it. 

Yes it's big but it can still all be packed up and moved  (that said I don't mind lugging a bit of weight, I'm a dj from the vinyl days and until you've lugged 100 records in a record box that itself weighs a good few kilos!) and the mount will be rock solid. 

I'm going to start of using my 70-200 f2.8 L mkII lens and also my SW 150P and take it from there. 

I asked a similar question re cameras on the beginning imaging thread and the consensus was nothing for any sensible money will best the 5D. Bear in mind crop factor is not the same as zoom and a an image from an FF sensor cropped to the equivalent size as a smaller sensor will look exactly the same in terms of the size of the various objects. 

[dannybgoode]

I should also add that Making Every Photon Count is simply superb. Take your time reading it-it's not the kind of book to skim through in an evening. There's an awful lot to take in buy the book is completely accessible and very comprehensive

If I do get a bespoke imaging scope btw I'd go for the SW Evostar 80mm ED Pro with field flattener.

[Owmuchonomy]

Very, very few scopes will fill your full frame sensor with a flat field. Decide what you want to image then work backwards from there to identify what kit you need.  My view is that the most important decision is the mount. In your position I would get the HEQ5 Pro as the minimum and preferably the AZ EQ 6 GT.  The book you have ordered will steer you in the right direction.

[newbie alert]

Before going a head and just buying a refractor,look into the pro's and cons...doublets,triplets,quads..what sort of glass? but first things first..look at your fov for your chosen targets..some are so big that a 100mm wont fit it in your fov unless you want to do mosaics..id look a f ratio getting down to about 5..Obviously funds are a major influence..and for my tuppence your 5d is perfectly good enough

 

[ecuador]

12 hours ago, Lrlinnell said:

In looking at the SW AZ-EQ5 and the iEQ30 Pro, it looked as though they both used RS-232 interfaces. Is this an issue since everything is now USB?

No, it is not an issue, you get a £10 RS-232 to USB cable (just make sure you get a compatible one if you have a recent 64bit version of windows). That's actually "modern" when it comes to mounts, since for example the older HEQ5/NEQ6 (Orion Sirius/Atlas) don't have a built in ability for full control via PC, so you need to get a 3rd party solution (eqmod), which involves a special cable+chip and software (but works well in the end).

[chrisshillito]

Please note that you don't need to purchase a special cable (EQDIRECT) to connect EQMOD to the SW AZ-EQ5. That particular mount has an integrated USB port that you can connect your PC directly to (and that appears as a com port to EQMOD).

Chris.

[dannybgoode]

4 hours ago, chrisshillito said:

Please note that you don't need to purchase a special cable (EQDIRECT) to connect EQMOD to the SW AZ-EQ5. That particular mount has an integrated USB port that you can connect your PC directly to (and that appears as a com port to EQMOD).

Chris.

Which is really annoying as the AZ EQ6 GT does not!

[chrisshillito]

Well in all fairness AZEQ6GT is a much older mount - hence the lack of usb interface and only one snap port (two on the AZEQ5) - its actually good that skywatcher have finally seen the light on this!