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Old 13-03-2013, 07:58 PM
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Scope options for lunar & planetary imaging

Hi there,

I have now been imaging for over a year and having a absolute ball! I have mostly imaged the Moon (tons of it), Jupiter, and will hopefully image Saturn soon. So far, my main interest has really been lunar AP. I just can't get enough of the Moon.

I am very happy with my current scope (a 10" Sky-Watcher GO-TO Dobs). As a beginners scope, it's been great. However, it's really a visual scope, and I have started to think about getting another scope in say a couple of years (I need to save up) that is more suited to AP. Given my interest in lunar and planetary photography, I wonder what would constitute a good scope for me that would be a good step up from the 10" dob.

I am quite attracted by the idea of getting a SCT such as a C9.25 or a C11. I quite like the convenience of the Alt Az mount which can be set up in a couple of minutes, so a fork mount would be easy for me and (I assume) wouldn't be a problem for lunar and planetary AP. But, as I want to eventually dab into DSO AP, an EQ6 may be preferable. This said, I am not set on a SCT.

The astro bug has bitten hard enough for me to want to continue this hobby for years to come, so I want to get a good scope that will last, and that is prominently good at lunar and planetary photography, but could also do some DSO occasionally.

I would be very grateful for any suggestion, comment and advice.

Cheers,

Eric

PS I use DMKs and ASI120 cameras
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Old 14-03-2013, 04:41 PM
gbeal
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Stick with the 10" then. It is what I always return to, especially for lunar, nothing beats aperture, well seeing does, but apart from that. Many use SCT's, and the C11 is a great scope, C14 better still, but factor in a decent beefy mount once you get to the C14.
Continue with the 10" is my suggestion.
Gary
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Old 14-03-2013, 06:35 PM
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Quote:
Originally Posted by gbeal View Post
Stick with the 10" then. It is what I always return to, especially for lunar, nothing beats aperture, well seeing does, but apart from that. Many use SCT's, and the C11 is a great scope, C14 better still, but factor in a decent beefy mount once you get to the C14.
Continue with the 10" is my suggestion.
Gary
Thanks for your advice Gary. I am not excluding keeping the dobs. I think that optically it's adequate, specially for lunar AP. But I would really like a better mount in order to give DSO AP a go. The C14 is out of my reach financially, so I wouldn't consider it.

Cheers,

Eric
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Old 14-03-2013, 07:39 PM
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Hi Eric. I would have said that your Dob was better than adequate, based on the images you post. To take Gary's suggestion further, maybe keep the Dob and get a smallish refractor for DSO. If you get an EQ6, you could consider using it for both planetary with the 10inch in tube rings (or even a bolted on mounting plate) and DSO with the refractor. If you want AZ as well, the EQ6 comes in EQ/AZ form. regards ray

Last edited by Shiraz; 14-03-2013 at 08:51 PM.
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Old 15-03-2013, 12:19 PM
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Hi Eric. I would have said that your Dob was better than adequate, based on the images you post. To take Gary's suggestion further, maybe keep the Dob and get a smallish refractor for DSO. If you get an EQ6, you could consider using it for both planetary with the 10inch in tube rings (or even a bolted on mounting plate) and DSO with the refractor. If you want AZ as well, the EQ6 comes in EQ/AZ form. regards ray
Thanks Ray for your feedback. Yes, you are right, the SW is more than "adequate" (wrong choice of word). Prhaps keeping the 10" is a good solution if I can mount it on an EQ6 or on an EQ/AZ mount. But given that my scope in a truss/collapsible one, I don't know if it can be easily monted on a EQ mount. Can it be done without major modifications? If it is, the combination ofan EQ mount, and 80mm ED refractor + the 10" would work out cheaper than a C9.25, I think.

Eric
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Old 15-03-2013, 05:00 PM
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Originally Posted by EricB View Post
Thanks Ray for your feedback. Yes, you are right, the SW is more than "adequate" (wrong choice of word). Prhaps keeping the 10" is a good solution if I can mount it on an EQ6 or on an EQ/AZ mount. But given that my scope in a truss/collapsible one, I don't know if it can be easily monted on a EQ mount. Can it be done without major modifications? If it is, the combination ofan EQ mount, and 80mm ED refractor + the 10" would work out cheaper than a C9.25, I think.

Eric
not seen it done Eric, but the primary tube extends on both sides of the CofG, so in principle it should be possible to fit tube rings without any mods at all. Not sure of the stability of the truss - have you had any problems with collimation drift while imaging with it in az mode? There is clearly a risk that it would not work out, but it would not cost you much to try it - you will need something like an EQ6 in any case, so the additional cost would be that of the tube rings and bar. If it isn't stable enough, sell the Dob and the tube rings and go to plan B? It's a possibility anyway. regards Ray

Last edited by Shiraz; 15-03-2013 at 05:14 PM.
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Old 15-03-2013, 07:09 PM
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not seen it done Eric, but the primary tube extends on both sides of the CofG, so in principle it should be possible to fit tube rings without any mods at all. Not sure of the stability of the truss - have you had any problems with collimation drift while imaging with it in az mode? There is clearly a risk that it would not work out, but it would not cost you much to try it - you will need something like an EQ6 in any case, so the additional cost would be that of the tube rings and bar. If it isn't stable enough, sell the Dob and the tube rings and go to plan B? It's a possibility anyway. regards Ray
Thanks Ray. I have to do a bit more research and see what others have done. I remember having read about someone doing it on a 12" truss dobs (I can't remember where I read about it). A quick search has pointed me to the following thread:

http://www.iceinspace.com.au/forum/a...p/t-23213.html and http://www.iceinspace.com.au/forum/a...p/t-54464.html.

Doesn't look too promising.

Eric

Last edited by EricB; 15-03-2013 at 07:23 PM.
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Old 15-03-2013, 07:40 PM
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don't be put off too much by those discussions.

The EQ6 holds my 300mm GSO ex-Dob Newt just fine for planetary imaging http://www.iceinspace.com.au/forum/s...ad.php?t=85990 - those posts were talking in terms of DSO imaging - I wouldn't even think about trying that.

One of the posts was worried about crushing the struts - if you put the rings on the main tube, no probs. Another was worried about the weight of the main mirror section unbalancing everything - the Dob already has that under control since the El axis passes through the CogG - again not a problem. The real problem is simply one of getting enough stiffness in the coupling between the primary mirror section and the top bit - I have no feel for how strong the truss is. sounds like a really interesting challenge to me, but you would need to be interested in messing with equipment. regards ray

Last edited by Shiraz; 15-03-2013 at 08:46 PM.
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Old 16-03-2013, 09:24 AM
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Hi Ray. Again, thank you very much for your comments. The truss look pretty strong to me. The scope holds collimation pretty well, to the point that I don't need to recollimate at the start of each session (but I often check). As long as there is not much modification to the equipment to be made, and as long as I can find some rings, I could give it a shot. As you say, if it doesn't work out, it won't have cost me a fortune. I wouldn't want to wreck the scope by doing mods that are beyond my skills (which are virtually nil, given that I am not mechanically-minded).

Thanks for the link. Your work on the scope is impressive and the Saturn picture is great!

Cheers,

Eric
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Old 16-03-2013, 09:48 AM
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Andrews have 303mm GSO rings (measure to make sure these fit) for $49 a pair and a 330mm Skywatcher dovetail bar for $39. Other suppliers should have similar
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Old 16-03-2013, 12:52 PM
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Hi Ray. Thanks. In fact, the rings are 303mm (not 330mm). The diameter of my scope is 280mm, so unless the rings can be adjusted (?), I don't think these rings would fit. My Astroshop sell S-W 285mm rings for $79. These would probably be ok.

I was hoping I could mount the rings either side of the main tube's bearing brackets attaching the tube to the mount, but there is not enough room between the bracket and the end of the tube to allow a ring (see picture). I suppose that this means that the brackets would have to go.

Also because of the truss attachments that protrude by 60mm along the upper part of the main tube, I would have to fit the rings below the truss attachments, which would mean I couldn't fit the rings equally around the C of G axis, but below it. That would be a problem, wouldn't it?

Cheers,

Eric
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Old 16-03-2013, 01:47 PM
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Can you shoot another picture of where the alt bearing are please, from a bit further back, I am sure something can be done.
Gary
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Old 16-03-2013, 02:55 PM
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Can you shoot another picture of where the alt bearing are please, from a bit further back, I am sure something can be done.
Gary
Hi Gary! Here are several pictures of the scope.

Cheers,

Eric
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Old 18-03-2013, 09:21 AM
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Eric,
I assume or hope the OTA is easily separated from the base?
If not we are stuck. If so, a set of tube rings either side of the alt bearings.
Gary
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Old 18-03-2013, 09:35 AM
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The big plastic 'bearings' bolted to the tube come off easy enough.
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Old 18-03-2013, 05:58 PM
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Thanks Greg and John.

Yes I can lift the OTA from the base. However, I think I will need to take off the ALT bearings to fit the rings.

My first step is going to be to get an EQ6. Then I will try to fit the SW OTA on it.

It this doesn't work. I will either get a SCT or a Newtonian OTA. Btw, out of curiosity, can a 12" Newt be mounted the EQ6 for AP? Or is it pushing the mount to its limits?

Thanks again for your advice.

Cheers,

Eric
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Old 18-03-2013, 06:10 PM
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What is the total weight of the OTA assembly, Eric? It's limit is 14-16 KG. I'm swinging a 14" SW collapsible (heavily modded obviously!!) & it's weight is 14.5KG. The EQ6 will JUST do it..
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Old 18-03-2013, 06:29 PM
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Thanks Greg and John.

Btw, out of curiosity, can a 12" Newt be mounted the EQ6 for AP? Or is it pushing the mount to its limits?

Eric
thats what I have on mine - see earlier link. Fine for solar system - wouldn't attempt DSO with it.
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Old 18-03-2013, 08:41 PM
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Thanks John and Ray. The OTA weighs 15 kg. with a barlow and camera, plus view finder possibly 16kg.

Ray, what's the weight of your 12"?

Cheers,

Eric
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Old 18-03-2013, 09:22 PM
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all up it is well over 20kg - haven't weighed it lately, but it seems to be getting slightly heavier each time I lift it onto the mount. the key to getting it fairly stable at this weight was to make strong rings - early versions that I made were not stiff enough and the scope wobbled at the slightest disturbance. the mount itself does the job without complaint - really impressive bit of kit.

on a philosophical note: as I see it, the advantage in modifying your existing Dob is that you can quickly turn it back into a Dob if you need/wish to - two scopes for the price of one. When you have finished with it, it will still be a valuable item to sell as a goto Dob. However, if you intend to permanently transform it (ie you don't want to use it as Dob again) maybe you could also consider the possibility of selling the current goto one and getting a much cheaper bare bones one to mod?

Last edited by Shiraz; 18-03-2013 at 09:50 PM.
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