new Planetary Imaging scope...yes, another thread

[Robert_T]

Hi All, I'd really value your comments, opinions, 2cents worth on this. If you've followed DP's thread, this is in much the same theme... basically I'm wondering where the next step - next 6-12months - should be in incrementally improving my planetary imaging scope setup.

I have a big observatory equatorial mounting (with huge 16inch drive wheels etc) collecting dust under the house so I was thinking perhaps of bolting this to the slab outside (covering it with a tarp) and using it to go the Newtonian path. I also have an old 12.5inch mirror that I figured to F6.7 (yep, it be big), but which needs recoating at the least and practically also a regrind/refigure to something more manageable in size (say between F5 and 5.6).

To get the mirror refigured etc to a good standard I'm looking at ~$1250au then mirror mounting bits, tube, etc etc to get it all setup. Hmmm unlikely to walk away under $2000 and probably more. Makes me wonder about getting a GSO dob 12inch at F5 (?) for half that and simply using teh OTA from that on my eq mount with all the bits I need included and money to spare for cooling mods electric focussor etc.

My questions surround thoughts on the relative optical quality of the custom version versus GSO optics in the 12in range, for planetary imaging, given diff in focal ratio of say 5.6 with the former and 5 with the latter. General thoughts on potential of a 12inch newt setup compared with the C9.25 also welcome - Asi I wonder why you don't use your 12.5inch parks scope for imaging more?

cheers guys,

[Lester]

Hi Robert,

the question regarding Asi, is that the drive on his EQ mount isn't adequate. Its a massive well machined Asi design which is smoother on both axis than my Goliath EQ mount. He probabley just needs the right person to come and fix the drive.

[asimov]

I actually need to microstep the stepper motor. It steps too coursely to take high magnification photographs. It was just a slap together radial arm drive made of bits & pieces, the whole thing coming in at under 20 bucks.

Fairy high magnification planet viewing visually, you can't notice the drive stepping.

[asimov]

In regard to GSO optical quality, I can't comment on that. In regard to a 12.5" F5 Parks thrown up against the C9.25 certainly. The Parks will win, no question. I'd love to be able to compare my 12.5" to a 12" GSO one day.

[[1ponders]]

Watching with interest ;)

[iceman]

Paul Mayo uses a 12" GSO ontop of an EQ mount for (amazing) deep-space astrophotography. There's absolutely no reason the same setup couldn't be used for planetary imaging.

The GSO optics are great for the price. I haven't seen and can't comment personally on how they compare to premium optics, but I guess it will come down to what you're prepared to pay for maybe an extra 2-5% better image.

I can only go by the images that DP and I get with out 10" GSO's.

You also have to weigh up whether a bigger scope is going to deliver a better image than a better camera would..

In my opinion, I'd be looking at getting a better camera before upgrading to a bigger scope. The 925 is more than adequate to get spectacular images. You just need a better camera.

If you've got $2k-$3k to spend, i'd look at getting a monochrome camera with motorised filter wheel and RGB filters, and use that with your 925. The Pt Grey Research cameras are better than the DMK's, and the Lumenera 075 is also better than the DMK. It just depends how much you want to spend.

But to answer your original question, a 12" GSO newt on an EQ mount would work great. My next scope will probably be a 14 or 16" newt driven by servocat for imaging.

Also remember though, the bigger the mirror, the more issues with cooldown etc.

[[1ponders]]

and seeing.

[ving]

why not keep it at f6.7? if your mount and drive can handle it then you'd get better image scale wouldnt you?

[Starkler]

What happened to Birds old scope?
Did he sell it or could he be convinced to part with it ;)

[Robert_T]

Thanks Guys,

Mike - good point on the camera, though I'm not sure I've hit the ceiling with the 900nc yet. I've also got an aversion to the filter wheel thingy of monochrome... though I may change my mind when I see the great images from you newly equipped mono guys rolling in. :D The 12inch GSO does look tempting and I'd have a Dob for fun;)

Ving - I considered just leaving at F6.7 it would be great for planetary, but the thing looks like it needs regrinding to remove pits onthe edge that would detract from contrast, so though I would make it more manageabl a size at the same time - more for storage and handling (mount copes with it).

Starkler - I had asked Bird about his ol'd 10in a while back but he wasn't inclined to part with it just yet. Really want a couple more inches to get above the 9.25 sufficiently to warrant.

Keep the suggestions rolling in.

cheers,

[ving]

okies robert, thanks fer replying :)

[Robert_T]

This is one thing (the drive) I still need to sort out to get my old EQ working. It was smooth enough - stepper has brass worm feeding a brass worm wheel which turns a big stainless worm which turns the BIG brass worm wheel so lots of reduction. Unfortunately the drive motors (old Hard disk drives) don't work no more and/or the handset needs work - long ago lost track of the guy who built it and my electronics knowledge has withered and all but died over the years so could be a challenge:D

cheers,

[davidpretorius]

At the end of the day I aim to have a c14 or c9.25 and a large reflector and an ed80.

I can't see how one scope can be all things to all people.

The aluminium tube I am wanting to build will be large so it can take that bigger mirror. Whether it gets to take a 16" mirror, I am unsure.

Maybe a c9.25 and a 12" or 14" reflector and an ed80.

I am sure the next few years will sort out the mirror cooling issues for sct's and reflectors, so it will come down to what is he best mirror configuration for what job.

[davidpretorius]

by the way Rob, i still have a few steppers left over if needed by your good self

[Robert_T]

Thanks DP - I'll let you know how I go:)

Actually had a dig around the old scope last night - mirror is filthy. The entire thing is ultra home-made down to mirror cells and secondary spiders made from hacksaw blades etc (I forgot how handy I once was) - made me all nostalgic. The tube is compressed cardboard used for concrete pillar manufacture painted. There's a dent where 15 years of sitting on a sharp box has intruded :doh: but otherwise I might just get the mount working and drag it out to see and give it a wash and a try just to see if I'm inspired to go further.

cheers,

[davidpretorius]

photos please, that sounds like a beauty. Ken's mount is an absolute beauty and I would love to see your handiwork!

[Robert_T]

will get the digital camera on to it tonight:D

[davidpretorius]

you beauty!

[gbeal]

Robert,
a couple of points.
I have used a M180, and it was a fantastic scope, much like the MN76, similar, but slightly different.
Both were eclipsed slightly by the 10" f5 newt I own. It is a Sky Instruments primary, and secondary, now sitting in a carbon fibre tube. It has turned into a do anything scope. I use it on the AP600E mount with imaging in mind, both webcam, and DSLR, but it is also quite at home in a homebrew dob base. Point here is that the 10" gives better results than the 7"'s ever did, simple physics. AND it's cost was significantly less.
If I didn't have the 10", and knew what I know now (I can just hear Ponders about now???) I would be looking to go to a 12". But the 10" in a one piece tube is about as big as most normal cars will allow, so it is the sweet spot for other reasons as well.
Gut feeling is try the old girl(s) but if the mount isn't up to snuff, then it is going to revitalise a BIG hole in your wallet.

[Robert_T]

Thanks Gary,

I value your thoughts and experience on this... it's getting down to that issue that in the end aperture wins out by virtue of the greater resolution it delivers. The mount should be fine for these size scopes (it was designed for a 20in newtonian) it's just a matter of getting the motors/handset operational. Usability in a big thing for me though. I don't need to move the thing around, but either I should be able to drag it outside and setup within 5-10minutes or drag a cover off a fixed scope - more effort than that and it's all over for me:D

cheers,

[asimov]

Thats half the reason why my parks sees very little starlight. No observatory, & I wouldn't dare leave it setup with a canvas or something over it. The OTA weighs 80 lbs...So I made like a glorified wheelbarrow to move the OTA. Still gotta lift it in, get it to the mount & lift it into the cradle.

[Robert_T]

something I should clarify re the $ figure I've mentioned below is that this would be for a full regrind from scratch (only necessary if I want to reduce the F ratio), figure and polish and recoat minus the cost of the blank. A simple refigure (to same F ratio) and recoat would be about half this amount ...