Refractor options for the moon

[rogerg]

I don't really have a good scope for the Moon. It's been bugging me a bit, and I'm wondering how cheaply I can get something which would give reasonable results.

Using my 6D I currently have:
My Megrez 90 has Fl ~620mm resulting in ~890 pixel diameter
My Megrez 90 with 2x doubler results in ~ 1764 pixel diameter

Options I see:
My Megrez 90 with 2x doubler + 1.4x extender results in ~ 2470 pixel diameter
My Megrez 90 with 2x doubler + 2x doubler results in ~ 3528 pixel diameter which only just fits in the frame.

I own a 2x but would have to buy the quite expensive 1.4x.

I wonder what the result would be like with all these doublers? People use 5x powermates and stack doublers for planetary work, I wonder what the loss of quality would be like?

Other options I see is a new cheap-ish longer focal length refractor:
Skywatcher 100ED with 2x doubler results in ~2561 pixel diameter

Refractors rarely go above 900mm focal length these days it seems.

Is there any other suggestions? I don't have much budget to play with, and it is only the Moon so not sure it justifies enormous expense.

Maybe I should be looking at something other than a refractor to bump up the focal length, but I can see that would probably get prohibitively expensive.

Regards,
Roger.

[Poita]

Are you wanting to do some really close-up crater type work?

[rogerg]

Good point to clarify.

I am only wanting full disk, but to maximise full disk (within reason).

[Poita]

I'd be inclined to get the 2" 4x powermate and use it with your existing 90, but I'm not sure that will work with your camera. There is also the t-adapter for it:
http://www.optcorp.com/te-ptr-4201-4x-powermate-t-ring-adapter-2inch.html

Atmospherics tend to be a problem more than anything, I think the resolution you will get out of the 90mm will be very good anyway and it is a capable scope. I used a powermate with my 105mm triplet and was very happy with the results.

If I was going to buy a new scope though, I'd go for a 120mm rather than the 100, seeing that you already have the 90.

The other option of course is to use a camera with a smaller chip and capture video to stack. Something like the ASI cameras do a great job if you aren't wanting to print the end result.

[Wavytone]

Fuggedabout the doublers and use eyepiece projection instead, if you used a good quality eyepiece the resulting image quality will be much better.

Even better, with eyepiece projection you can vary the magnification by changing the eyepiece focal length and/or moving the eyepiece and/or camera to produce an image scale that suits you.

[rogerg]

Thanks, I didn't realise there was a 4x powermate. A tempting option, and cheaper than the Canon 1.4x.



Interesting, I have to admit I gave up on eyepiece projection years ago when I had dodgy quality results. I still have the fittings to do it. Worth a try but I'm suspicious of the results :question:

[MortonH]

How about a 150mm f/12 Maksutov-Cassegrain? Focal length is 1800 so image scale might be about right. My Skywatcher Black Diamond is very good for visual on the Moon. Haven't tried it for photography yet.

[DavidU]

Hi Roger, I may get rubbished for this but I had great success with my 150mm,f/8 Achro, with a little fiddling with minimizing spherical aberration I got some great results with my $500 (second hand scope).
http://www.iceinspace.com.au/forum/showthread.php?t=76890&highlight=LUNA

[rogerg]

The focal length is about right. I wonder how the flatness of field fairs. Worth consideration.



Yes I wouldn't be surprised if a relatively cheap Achro would do the job. 150mm is quite a beast! Probably too big for me. I'd be interested in seeing your shot at 100% and an image before processing.

[brian nordstrom]

:) Peter just continuning on from what David said ( nice shot as well David ) here is a raw shot with my 127mm f8 Istar achro taken with a x2 2inch Powermate giving 2000mm , zero work using my Sony A200 DSLR .
Achros can give great results for little money .
Brian.

[DavidU]

Ok well, here is a moon with my ED100, nice and light scope. Same single shot with a 30D.
http://www.astrobin.com/full/1149/0/?real=&mod=

[Wavytone]

Ha ! Even I can play this game... 102mm f/7 refactor with eyepiece, coupled to my little lx3 camera...

http://www.dpreview.com/galleries/7398429248/photos/166999/moon

Using my 180mm f/15 Mak I was able to shoot mars and Saturn as well.

[MattT]

Rubbish…no way! A great lunar scope with Bino's and some kind of CA filter like Badder semi-apo or Fringe Killer.
I'd get a cheap WO binoviewer for the moon and use your existing scope.
Matt

[brian nordstrom]

:thumbsup:Spot on Matt , you want to see the moon thru my 127mm Istar frak , WO bino viewers and 20mm eyepieces ,, just awesome .
Brian.

[rogerg]

Hi all,

Thanks for your continuing replies.

Reminder that I'm after photographic only, not visual. Bino viewers won't do me much good.

Also if making a suggestion or sharing an image I really need to know the focal length of the system or image scale to know if it's suitable. Of course I can take a photograph of the moon that looks just fine at the size it is, but I'm wanting to fill more of the frame.

I measured an actual image of the moon taken through my Megrez 90 with 2x and it's actual size is quite different to the theoretical. Actual is 2845 pixels, which puts the focal length at 2000mm or prime focal length of the Megrez 90 at 1000m which is a bit strange. Perhaps my calculations are off.

A friend has offered for loan his 1970's 8" Celestron SCT which he says fits the moon perfectly in a full frame camera. Will be interesting to see how that turns out.

I am hoping to try the 8" tonight, as well as eyepiece projection. I have to admit the 4x Powermate is my preferred solution at this stage but will test results to delay unnecessary expenditure.

[brian nordstrom]

Ok , Roger these two are raw shots straight out of my Sony A200 into my computer and posted here .
Both with my Istar 127mm f8 doublet refractor and one taken with the same gear with my Tak M210 .
#1 is native at 1000mm .
#2 is using my TV 2x Powermate at 2000mm .
#3 is using my Tak Mewlon 210 at 2410mm.
Hope this gives you an idea of image scale .
And your friend is right , 2000mm using 2.5 inch focuser and 2 inch Powermate are a perfect frame of the moon in my set up , as seen here and 2410 from the M210 is a little much .
Brian.

[killswitch]

I had some pretty good results with the SW 100ED. Link here (http://www.flickr.com/photos/flipfire/9098600371/) (view at original res)

I did try a televue 2x but it looked a bit soft in comparison.

[Irish stargazer]

My 8" SCT at 2000mm works a treat. A Mak-Cass or SCT is the way to go

http://farm4.staticflickr.com/3761/10502304214_6e62f26263_o.jpg

[rogerg]

I tried my friend's orange tube C8 last night with disappointingly very soft results. The FOV was perfect though.

He's left me with his 5x powermate and 3x televue barlow to try on my Megrez 90.

[MortonH]

I guess reflectors will always be softer than a good refractor due to the central obstruction. Then there's always the possibility that collimaton isn't perfect. And larger apertures are more susceptible to seeing conditions due to their greater resolution.

[rogerg]

Yes, I wasn't meaning to dish the idea of a reflector full stop, it's just the 8" orange tube didn't work. I think it's a combination of age (attributing to the focuser being tricky to use and collimation being less smoothly adjustable) and it's collimation at the time and being more susceptible to viewing conditions.

[miki63au]

Hi Roger,
I have what you want.... and you have what I need ..... LOL
I'm after a full frame DSLR , but at this stage can't afford it :(

I have a C14HD SCT with a 0.6 deg flat(!!) FOV ...
with a dedicated 0.7x reducer the Lunar pic should be awesome in a full frame DSLR.... old Orange SCT has Coma and field curvature

You want a Celestron Edge SCT ... and you can have a sharp to the edge full frame Moon shot :)

my 2c.... Cheers,
Mick

[rogerg]

An 8" Edge would certainly be nice :) Seems like the best option.

Given I won't be spending that much money on the exercise just now, I have been fiddling with a 3x Televue Barlow and 5x Televue Powermate borrowed from my friend.

I have one image using the 3x Televue Barlow published which is acceptable but processing has let down the quality (have another thread regarding that):
http://astrophotography.com.au/the-moon/

I'm yet to process the 5x Powermate shots, but initial looks at the raw data suggest the 5x shots are flatter and have better edge clarity than the 3x Barlow, but will require stitching a mosaic as two frames are required to fit the Moon rather than one frame with the 3x Barlow.

The project is somewhat pending trying processing on higher spec'd PC, as my laptop seems incapable of processing the large files in Registax :(