Scope recommendations for planetary imaging.

[Gina]

I think I'm reasonably set up for DSO AP (on fixed installation) but I'd like to do a bit of planetary AP, so I'm open for suggestions for a planetary imaging scope for some time in the future. I have already given this a fair amount of thought. I started by thinking I might get a scope to cover smaller/fainter DSOs as well as planetary but I don't think one scope would serve both types of object very well. I have an ED80 (and now a focal reducer / field flattener) and DSLR (may get astro CCD camera later) which I think will serve me for DSO AP. But this is not suitable for planetary so now I'm thinking of getting a long focal length scope for planetary AP.

In view of the above and not having a huge observatory I'm thinking of a folded light path (as I've mentioned in other threads). I'm thinking of a budget of something like £300-500. Would a 5" scope be good enough for planetary imaging or would going bigger make a big difference? eg, SW Skymax 127 OTA.

[Uplooker]

Hi Gina,

I have a SW 150P for DSO and had a hankering for a dedicated planetary scope. I decided on a Celestron C8 SCT - F/L 2000mm. I could not afford to buy new so kept a look out on the second hand market. I eventually managed to get one throught SGL Buy/Sell (when it was still active) for approx £250. I am really pleased with it!

Ian

[Chris]

Hey Gina, if you want a compact scope just for planetary I recken you'd be hard pushed to beat a big mak like you've mentioned. I had a small 90mm mak years ago and loved it, I've seen amazing results produced with the Skymax 127, I too wonder how much better the 6" Mak is? I think the contrast is better with a Mak apposed to SCT's, is this right?, smaller central obstruction, the only downside is the long cooldown which is negated as your in an obsy:)

[gary1968]

I would suggest a 8" SCT. Blinky has one, it is great for small DSO's and would make a great Planetary scope. Keep an eye on the 2nd hand market, you should pick a nice one up for well within your budget.

Gary

[Russe]

I love my 5" mak and would only consider changing to a celestron 9.25...

[htj]

For planetary imaging I'd try and optimise aperture as much as possible. This means a newton or a cassegrain, possible used. A newton will probably be more work to collimate, but things as how good the mirror cell is and how much the scope is moved around will play a bit part of this. C6/C8/Skymax Maksutows/Longish newton (5f and up) are all good possibilities IMHO.

Seeing will be the limiting factor, but good collimation and cooldown are really important too. Cooldown will be less an issue with an obsy, but can still be a factor if the temperature drops rapidly.

If it is only for AP of planets, the central obstruction size can be largely ignored, however there will always be times when you want to have a quick peek at saturn or DSO with your "lightbucket", so I'd certainly factor it in.

[ollypenrice]

Older Meade and Celestron SCT OTAs have little value on the used market and will do this job very well indeed. Worth a look out. You could pick up a 10 inch for not a lot.

Olly

[AztecastroMcJ]

for price u mention and value 4 money

i would choose either

127mm mak brand new

or C8 2nd hand

the C8 would be much better all round 4 visual and imaging planets and moon, also can be good for dso imaging too

James

[JamesF]

The one irritation I have with the 127 Mak, Gina, is that there's a small amount of mirror shift when the focuser changes direction and it's enough to take the image completely across the camera sensor when you get up to about 4x focal length. I'm not sure it's possible to fix that beyond a certain point. The mirror is carried on a bearing that fits over the outside of the baffle tube. Also attached to the bearing is a plate that extends to the focuser position. The mirror is moved by a threaded rod fixed to the plate and turned from the outside of the OTA. So the force applied to move the mirror is very much off-centre. The mirror bearing really needs to be a tighter fit on the baffle tube, but I think if it were then I think the focuser would tend to jam.

I don't know if this is just a particularly bad problem because of the age of my Mak (it's not been uncared-for though it's clearly well-used), but I think they all exhibit it to some degree. I don't know if the SCTs are all the same. I think it would be worth researching if this is going to be your only planetary imager so that you can budget for an external focuser if you wish to. I'm tempted to get one for mine, but I'm struggling to justify it at the moment.

As has already been mentioned, the central obstruction is significantly larger in the SCTs than the Mak, so if you're comparing apertures you may want to make allowance for that. The one thing I think the Celestron SCTs do have that might be a potential advantage over the Mak (though certainly a lot more expense) is the Fastar setup.

All of the planetary images I've posted so far have been captured with the 127 Mak and an SPC900 and I feel like I'm now pushing that combination to its limits. It's becoming quite tricky to get a decent size image of Saturn that's sufficiently bright to render a good image in its current apparition. More aperture really would help there I think.

Even given your obsy, considering the number of clear nights we seem to get at the moment I think i'd have in the back of my mind the idea of a second semi-portable mount for this scope. Alignment isn't so critical as for DSO imaging and it might be tempting to at least allow for the possibility of doing a bit of planetary imaging whilst collecting subs on the scope in the obsy. I'm thinking that even when I've "moved in" to my obsy, I may well have a post set into an old car tyre filled with concrete that I can put the EQ3-2 on, so a quick polar alignment and mount up the Mak to play with whilst I'm using the NEQ6 for other things.

James

[Gina]

Hi Gina,

I have a SW 150P for DSO and had a hankering for a dedicated planetary scope. I decided on a Celestron C8 SCT - F/L 2000mm. I could not afford to buy new so kept a look out on the second hand market. I eventually managed to get one throught SGL Buy/Sell (when it was still active) for approx £250. I am really pleased with it!

Ian

Thanks Ian Pity the SGL Buy/Sell isn't still running but there we are. I'll keep an eye on AB&S for second hand

[Gina]

Hey Gina, if you want a compact scope just for planetary I recken you'd be hard pushed to beat a big mak like you've mentioned. I had a small 90mm mak years ago and loved it, I've seen amazing results produced with the Skymax 127, I too wonder how much better the 6" Mak is? I think the contrast is better with a Mak apposed to SCT's, is this right?, smaller central obstruction, the only downside is the long cooldown which is negated as your in an obsy:)

Thank you for confirming my thoughts I don't know about how the contrast compares, only that the light throughput is better for a Mak than same size SCT due to the size of secondary.

[Gina]

I would suggest a 8" SCT. Blinky has one, it is great for small DSO's and would make a great Planetary scope. Keep an eye on the 2nd hand market, you should pick a nice one up for well within your budget.

Gary

Thanks Gary That should be a very nice scope

[Gina]

I love my 5" mak and would only consider changing to a celestron 9.25...

Thank you Good to know that and yes, a 9.25 would certainly be nice

[Space Cowboy]

Simply the largest aperture you can afford whether it be 8" or 10". The skymax 127 is a smashing little scope but it can't compete with the big boys.

[Gina]

For planetary imaging I'd try and optimise aperture as much as possible. This means a newton or a cassegrain, possible used. A newton will probably be more work to collimate, but things as how good the mirror cell is and how much the scope is moved around will play a bit part of this. C6/C8/Skymax Maksutows/Longish newton (5f and up) are all good possibilities IMHO.

Main problem with a long Newt is the length and obsy space, otherwise I agree.

Seeing will be the limiting factor, but good collimation and cooldown are really important too. Cooldown will be less an issue with an obsy, but can still be a factor if the temperature drops rapidly.

I think the number of times we get a sharp temperature drop is fairly small. No experience of collimation so don't really know. Some people seem to find it a problem others don't.

If it is only for AP of planets, the central obstruction size can be largely ignored, however there will always be times when you want to have a quick peek at saturn or DSO with your "lightbucket", so I'd certainly factor it in.

Ah yes - thank you

[Gina]

Older Meade and Celestron SCT OTAs have little value on the used market and will do this job very well indeed. Worth a look out. You could pick up a 10 inch for not a lot.

Olly

Thanks Olly That's very interesting

[Gina]

for price u mention and value 4 money

i would choose either

127mm mak brand new

or C8 2nd hand

the C8 would be much better all round 4 visual and imaging planets and moon, also can be good for dso imaging too

James

Thank you James - pretty much what I thought

[JamesF]

I think the number of times we get a sharp temperature drop is fairly small. No experience of collimation so don't really know.

Collimation of the 127 Mak isn't that hard to be honest, just a bit of a faff. I think both the Mak and SCT designs are supposed to hold their collimation pretty well anyhow.

James

[Gina]

The one irritation I have with the 127 Mak, Gina, is that there's a small amount of mirror shift when the focuser changes direction and it's enough to take the image completely across the camera sensor when you get up to about 4x focal length. I'm not sure it's possible to fix that beyond a certain point. The mirror is carried on a bearing that fits over the outside of the baffle tube. Also attached to the bearing is a plate that extends to the focuser position. The mirror is moved by a threaded rod fixed to the plate and turned from the outside of the OTA. So the force applied to move the mirror is very much off-centre. The mirror bearing really needs to be a tighter fit on the baffle tube, but I think if it were then I think the focuser would tend to jam.

I haven't previously heard of that particular problem, I don't think. People have mentioned "mirror flop" as the scope moves across the sky but I think this would probably be less of a problem for planetary AP.

I don't know if this is just a particularly bad problem because of the age of my Mak (it's not been uncared-for though it's clearly well-used), but I think they all exhibit it to some degree. I don't know if the SCTs are all the same. I think it would be worth researching if this is going to be your only planetary imager so that you can budget for an external focuser if you wish to. I'm tempted to get one for mine, but I'm struggling to justify it at the moment.

Yes, I had thought of adding a focuser - image movement when changing focussing direction would certainly be a problem.

As has already been mentioned, the central obstruction is significantly larger in the SCTs than the Mak, so if you're comparing apertures you may want to make allowance for that. The one thing I think the Celestron SCTs do have that might be a potential advantage over the Mak (though certainly a lot more expense) is the Fastar setup.

Yes, I've looked into Fastar - interesting but two disadvantages :- Obviously price but also not suitable for a large camera like a DSLR. So it would want either a proper astro camera or narrow webcam. And yes, I know about the larger secondary of the SCT.

All of the planetary images I've posted so far have been captured with the 127 Mak and an SPC900 and I feel like I'm now pushing that combination to its limits. It's becoming quite tricky to get a decent size image of Saturn that's sufficiently bright to render a good image in its current apparition. More aperture really would help there I think.

I see. I do have a QHY5 I could use which is more sensitive but would need a filter wheel and LRGB filter set. Mind you, I'm also considering using the QHY5 with my ED80 for DSO so I'm thinking of filters anyway.

Even given your obsy, considering the number of clear nights we seem to get at the moment I think i'd have in the back of my mind the idea of a second semi-portable mount for this scope. Alignment isn't so critical as for DSO imaging and it might be tempting to at least allow for the possibility of doing a bit of planetary imaging whilst collecting subs on the scope in the obsy. I'm thinking that even when I've "moved in" to my obsy, I may well have a post set into an old car tyre filled with concrete that I can put the EQ3-2 on, so a quick polar alignment and mount up the Mak to play with whilst I'm using the NEQ6 for other things.

James

Now that's an interesting thought I like the idea of making double use of the clear skies when we occasionally get them

Thanks for your suggestions

[Gina]

Simply the largest aperture you can afford whether it be 8" or 10". The skymax 127 is a smashing little scope but it can't compete with the big boys.

Ah yes, I thought that would be the case Thank you

[Gina]

Collimation of the 127 Mak isn't that hard to be honest, just a bit of a faff. I think both the Mak and SCT designs are supposed to hold their collimation pretty well anyhow.

James

Yes, I've heard they hold collimation well too Thanks.

[ccbmedic]

Gina,

As somebody has already said, the 127 Mak is a great little scope and it really is, but I would get a mak with a larger aperture as the 127's hand on heart are toys when comparing to the bigger maks out there and the images they produce are far superior. I've been lucky enough to have a play with both a 180mm and a 8'' STF version.

I dont think the focuser would be an issue for you unless you no longer have your homemade leccy focuser. In my experience all Maks suffer with image shift and juddering when focusing using the knob and at times can prove a nuisance to actually bring into focus depending on target and magnification used. They do require a lengthy cool down but this again wouldnt be a problem as your primary location is outdoors in your obs. I'll keep my eyes peeled and let you know if I come across any bargains.

Best Wishes,

Chris:icon_salut:

[JamesF]

Certainly agree on the electric focuser point. Makes life *so* much easier

James

[Gina]

Gina,

As somebody has already said, the 127 Mak is a great little scope and it really is, but I would get a mak with a larger aperture as the 127's hand on heart are toys when comparing to the bigger maks out there and the images they produce are far superior. I've been lucky enough to have a play with both a 180mm and a 8'' STF version.

I was afraid of that Thank you

I dont think the focuser would be an issue for you unless you no longer have your homemade leccy focuser. In my experience all Maks suffer with image shift and juddering when focusing using the knob and at times can prove a nuisance to actually bring into focus depending on target and magnification used.

Yes, I do still have the focuser motor but usually focus the ED80 with the slo-mo manual knob while watching the image on a 17" monitor through the window in the dividing wall door. I can soon attach it or similar one to a focus knob on another scope.

They do require a lengthy cool down but this again wouldnt be a problem as your primary location is outdoors in your obs. I'll keep my eyes peeled and let you know if I come across any bargains.

Best Wishes,

Chris:icon_salut:

That's good of you - thanks very much

[Gina]

Certainly agree on the electric focuser point. Makes life *so* much easier

James

Yes, I gather these scopes have a rather coarse focussing control so well worth motorising. And yes, I would do that.