Achromatic Refractor OTA for Planetary/Lunar Imaging?

[Steve789]

I've recently felt a growing interest in planetary and lunar imaging probably due to great views of Jupiter and seeing some of the fantastic lunar shots that are out there. I've bought and modded a LifeCam Studio to upgrade from the pretty disappointing Xbox webcam that came with my skywatcher 150p when I bought it 2nd hand. I've only used the LifeCam once (on Jupiter and the moon) and immediately realised that I want more magnification/resolving power. This got me looking into long focal length refractors as I knew that they were supposed to be better for planetary. However after digging a bit deeper I'm not entirely sure if this is the case.

Before I splash out on a new scope and use up my astro budget I need to be sure I get something that will actually perform better than my 150p. As always the budget is going to be tight and I began by looking for OTAs around the £100 mark but as usual I began to stretch the budget the more I looked around.

These are the scopes that have captured my interest so far:

Bresser 90/900 http://www.astroshop.eu/bresser-telescope-teleskop-ac-90-900-messier-ota/p,21611

Bresser 102/1000  http://www.astroshop.eu/bresser-telescope-ac-102-1000-messier-ota/p,14192

Skywatcher Evostar 120 http://www.astroshop.eu/skywatcher-telescope-ac-120-1000-evostar-bd-ota/p,15567

Tal 100 RS http://www.2020optics.co.uk/refractortelescopes/tal-100rs-ota-100mm-4-f10-refractor-telescope.html

My main question is will the smaller aperture of a refractor mean a reduction in resolving power that will negate any increase in image size from having a longer focal length?

I'm also wondering if there are any issues with imaging through a scope with higher f ratio, bearing in mind it would only be used for planetary/lunar i.e. bright objects.

I'm aware of Chromatic Aberration but I'm assuming/hoping this is rectifiable in image editing.

To give an idea of what's achievable with my current equipment I've included the following images. So would any of my above choices give significant improvements on these? They were both taken using the LifeCam studio, 2x Barlow, Skywatcher 150p, HEQ5 and stacked in Registax.

I've even wondered if I should stick with the 150p and save the cash for a decent CCD camera for planetary/guiding but truthfully I really would like a second scope.

Any advice would be greatly appreciated.

Steve.

[Astro_Baby]

I know its stretching the budget even further but would a Maksutov be even better, longer focal length and no CA to worry about.

[Steve789]

I've kind of written off the idea of a Mak for now because of the budget and hearing a lot of people mention long cool down periods. The trouble is the bigger the expense the longer I'll take to make a decision and the more likely I'll find something else to spend the money on! Also I've recently taken voluntary redundancy so need to find another job before I feel like spending too much.

[nightfisher]

Please consider the 150 pro Maksutov, superb scope for planetary imaging, keep an eye out for a used one for up to £300

[Peter Drew]

I think a better camera would be more of an upgrade than your suggested telescope options. You will need a Mak or a SCT of 6"+ aperture for better resolution and manageable OTA length.    

[ronin]

I would doubt that a refractor will improve greatly. As you say you will get some CA and although processing out might remove this not all may go and why add in or include something that has to be removed.

Unfortuantely like previous I suspect that a nice Mak or SCT will be the route to go down.

What mount have you ate present ?

I couldn't see it but only took a glance at the original post.

Wonder if a 3x barlow or power mate would help, but that could end up diverting funds, while improving nothing.

It may be time to sit down and look at everything and decide which component is actually the weakest and then improve that. A new scope is not nexessarily the optimum solution. However I suspect that ultimately for planetary imaging you will have to consider a Mak or SCT.

Do you intend to stick at the luanr+planetary aspect predominently ?

Or do DSO's call for your attention?

[Astro_Baby]

Ronin  - the OP has an HEQ5 so it would easily take a Mak 150 or even a 180.  The TAL might just pull it off as it has quite well controlled CA but much as I love my TAL 100RS I cant say I would regard it as an ideal scope for imaging when you have a 150P already. The CA is still present and I would have thought foir imaging you want the image as clean as possible from the start - hence suggesting a Mak.

[ronin]

As said I looked back and didn't see the mount, called impatience, if it doesn't jump out at me I find I do not tend to examine posts word by word for that long.

Thing is all the refractors above will give some CA and I think that they will need ultimately to look to the Mak/SCT designs, they are the ones that have consistently delivered the good planetary images. If anything more concerned they may get the first Mak/SCT to come along and be disappointed. Good example of what is possible appeared here about 10 days back the person had a C9.25 and a 2x Powermate, and that is a fair difference to a Skywatcher 127 and a 2x standard barlow.

However still think that coldly looking at everything and identifing the weakest bits is useful, as much for later as for present. As Peter says perhaps a better camera may deliver immediate improvements, same for a better barlow, even less cost is the scope checked and collimated every time? Yep everything it is taken out and used. If the scope is not delivering the best image possible then no matter what comes further along the optical path is not going to compensate.

[Steve789]

Ok so I'll have to control my urge to buy a 2nd scope for now. Thanks for the advice guys looks like you could have saved me some money. Maybe I'll look into getting a better 2X Barlow than the skywatcher one I have. A guide camera is on the shopping list so I assume if I choose carefully this will be good for planetary as well, even if it is only in mono.

I'll put a Mak on the potential wish list but DSOs have always been my primary interest and I've been considering a 200pds for some time now. There's just too much choice out there!