Major upgrade - where to?

[GlassWalker]

As I hinted at in my intro post, I'm looking to step up my imaging kit. I've been looking for rather too long and need to get unstuck if I'm going to do much!

I guess it would help to indicate what I use so far:

Astrotrac travel kit - this includes astrotrac with tripod, gear head and polar scope for alignment, ball head for camera pointing.

Imaging kit: Canon DSLRs, Astronomik CLS, H-alpha, SII, OIII narrowband filters. Assorted lenses.

Targets are deep sky objects, leaning towards those suitable for narrowband imaging and not broad spectrum objects as I'm in an urban area of quite poor light pollution. For indication of level, even on an apparently clear night, Polaris is typically visible but hard to see by naked eye.

The limits of the existing system? I find accurate-enough polar alignment a pain! I can get away with 4 minute exposures at 135mm focal length without spending forever faffing around with the alignment. I want to go much longer focal length, which I don't think I can ever get that set up easily with the astrotrac.

Getting a fixed mount in the garden to set and forget is not a practical option. My hope at the moment is, can I get a half decent budget mount (like EQ6), set as best a polar alignment as I can, and use guiding to correct for remaining alignment offsets? While I think I get the concept of guiding, I'm lost as to how best to implement it. I'm hoping field rotation isn't significant over the time scales I'm planning on using, say up to 10 minute exposures.

The other thing I hate about the current setup is I have to set the camera direction by eye, which takes a bit of trial and error to find and centre objects. This will get impractical once I upgrade optics too. So the mount would ideally have some ability to make that easier and repeatable. For indication, I'm thinking of stepping up the optics to something like a 200mm Newtonian, so the mount should be able to cope with that size and weight easily.

I should add, I'm not working to a particular budget, but whatever a EQ6 + guiding ball park costs is within range.

[Digz]

The best piece of advice I can give is get the best mount you can afford. I have an NEQ6 Pro which is a beast of mount capable of carrying a lot of weight.

Along with my NEQ6 Pro I have a 250p DS reflector which has a focal length of 1200mm. This is good for smaller objects but the larger ones like Orion and Andromeda or even Pleiades they can be larger than the frame. Im tempted to get a smaller refractor like an 80ED.

I have an Atik Titan which I guide using my finderscope but an off axis guider is on my list especially when I move into CCD imaging. The titan is probably overkill as a guidecam so you could look into a QHY variety or modded webcam - lots of information here on the latter.

Focus is crucial, Ive just been trying out a Y mask but you also have a Bhatinov mask as well.

If narrowband is what you want to move into then a mono CCD is probably going to be your best bet - this is what I plan to get soon to start narrowband imaging.

Anyway, hope that gives you some food for thought.....

[GlassWalker]

The EQ6, in one of its incarnations I haven't looked into yet, does seem to be a popular budget choice. Budget in the sense that for something much better, the costs also goes up rapidly!

I'm still somewhat lost on guiding. I think initially for me, a separate guidescope would be easier to manage than an off-axis arrangement. Actually, I'm not even sure if off-axis would be a viable option for a HyperStar I'm considering as one option anyway. Maybe I'm grossly under-estimating their capability, but the guide cams seem like glorified webcams. Just what do you get for the money? Increase sensitivity?

On focus accuracy, I'm more worried about getting the sensor plane aligned right as that is my limiting factor so far. I have already found an issue with my modified DSLR where I have a linear band of best focus suggesting sensor and mount are tilted with respect to each other. In calculations on depth of focus, an error of magnitude around ten(s) of microns is enough to cause visible defocus, and I think this is only going to get more difficult as apertures get bigger.

I am considering a mono CCD for imaging itself and take the DSLR out of the equation, but that's probably something for another thread... but thanks for reminding me I'd love a motorised focuser at some point. Far too much shake when I do things by hand.

[Earl]

I cant comment on Hyperstar from experience but i have read it can be a real tough challenge to get good results.

If you went the route of an EQ6, ST80 + QHY5 for guiding and a 80mm APO with reducer (lots and lots to choose from out there), as they say you will be cooking with gas.

Ideally this is computer controlled via EQmod, PHD guiding etc to your flavour.

As for a Mono CCD there a re plenty of Atik's which are worth considering, choosing the right one is somewhat of head scratcher

[GlassWalker]

Thanks for the short list guiding options there. Might have to get that sooner than later and use it to practice on planets while we wait for more dark skies to return.

The "80mm APO with reducer" I assume you're suggesting for imaging? I am thinking quite a bit beyond that since I've dabbled beyond that level already with photographic kit. While I haven't decided exactly what scope to go for yet, there is one thing that is definite. It wont be smaller than 200mm aperture. Beyond that is more a size and cost thing where I think a 9.25 SCT is a reasonable balance and is currently top of my consideration list.

CCD wise again I'm kinda frustrated. The expensive ones are far too small and low resolution. The ones that start getting somewhat interesting are really expensive. It's going to be tough to work out the tradeoffs here.

Anyway, all that is possibly getting a bit off topic in this mount sub-forum. The first step to me improving is upgrading the mount and setting up guiding, so I think I'll try that first and see how I feel from there. Not like I can afford all this in one go anyway!

[perfrej]

Hmm. 9.25... Look at the EdgeHD version. With a Hyperstar and an Optec Lepus reducer you have 2350, 1457 and 540 mm in one scope.

NEQ6 is the budget choice and will take you ways and ways with guiding, a change of bearings and a tune-up. If you want to go beyond that and get the last mount you will ever buy before going professional, look at the 10Micron range - I am just totally overwhelmed with my GM2000HPS!

/per

[GlassWalker]

On the scope, I'm not sure how the Edge version compares against the standard model, if both have their respective Hyperstars fitted. Like all things, I have to work out the cost/benefit for the options in detail. Only reason I picked a 9.25 is it is the minimum that has a hyperstar that supports a DSLR, if I choose to use one. Which I might as a CCD worth bothering with isn't going to be cheap!

Mount wise, only had a very quick look at 10Micron and didn't see anything in English so far. Euro prices are not in the budget realm any more, and if I ever go to that cost I already have options on the short list. But that isn't going to be any time soon!

[swag72]

I know that you have said earlier that you won't consider an 80mm refractor, but have you looked at the FOV calulators?

Field of view Calculator<script src="title2.js"></script>

For example, you say that you are looking at a 9.25 and using a DSLR. Well, a 120 refractor and an Atik 314L for example give you the same image scale, albeit with a smaller pixel count and overall image size. With that chip size you don't need a reducer, using mine without and you get a faster scope at it's native FL.

Just a thought.

[garethmob]

im just courious GW, but which model astrotrac do you have? as i have the autoguiding version, would you be considering using that (as it does hold up to 15kg's you could get the AT pier which holds 15kg, wedge, and run small scopes like a WO 70 or ST80 onto it even have auto guiding as well, would that be considerable?

[GlassWalker]

Sara, I need to work it out later, but yes there's a big interplay between scope aperture, focal length, focal ratio, sensor size and field of view. I need to balance all that. The C9.25 with hyperstar is my fast option, but not my only option.

Gaz, I also have the Astrotrac with guiding input, but as it is one axis only it isn't enough for me. I can't get "good enough" polar alignment in any sane amount of time, so always get some trailing especially with longer focal lengths or longer exposures. I'm basically hoping a 2 axis guiding system will take that out for me, and any resulting field rotation due to polar alignment will be insignificant.

[perfrej]

My 10Micron gives 10 minute unguided subs with round stars at 1540 FL...

Guiding? Phah!

/p

[GlassWalker]

I'm sure the 10Micron mount is lovely. But I do have a rather small hurdle of the 5 figure price tag it comes with. Ok, the baby model of the range is 4 figures, but unless the 1st digit is a "2" or less it's still way out of this year's budget!

[perfrej]

Yes, it is a lovely mount. I also have an NEQ6. It has new bearings and has been tuned properly and with guiding it performs extremely well. I contemplated selling it, but as there is nothing that compares to it at that cost I will keep it as a secondary system. So, 10Micron is a total blast to be able to own, but you can do just as well with an NEQ6.

/per