NGC891 First Light Image with new Scope

[joelshort]

I am extremely pleased to report that a plan I put in place 1 year ago, to have a dual scope/camera imaging rig, has finally come together and I am very, very pleased with the initial results.  It all began last November as I was looking for a longer focal length scope in order to image more galaxies and smaller objects, and given my sky conditions and mount capacity I felt that a 10" RC was best suited for my needs.  I settled on a CFF250RC, which I finally received several weeks ago.
 
Shortly after ordering the CFF last December I began to see the benefits of CMOS cameras that thrive on many short exposures, specifically as it relates to dual scope imaging.  Dual scope imaging carries with it several inherent problems, one of the largest being differential flexure between the scopes.  This is particularly true when using two of the exact same scopes that both need to be pointed at exactly the same position in the sky.  This leads to another large problem with dual scopes, needing to align those two scopes precisely.
 
So I began to think about a dual scope/camera rig that does not use the same scopes.  Long story short, I paired my SV80ST with a QHY163M and the CFF with a 16200 camera.  Since the SV80ST/QHY163M has about twice the FOV and image scale, I don't have to worry too much about exactly aligning the scopes to the same position in the sky.  I just clamped the SV80ST on top of the CFF and hoped alignment was good enough.  I did need to shim one scope ring to move the focuser end of the SV80ST up a little, and I also needed to shift the dovetail plate slightly laterally in one direction, but the star alignment between the scopes is "good enough" and I didn't have to bother with some kind of X/Y positioning plate.
 
Also, since the QHY163M is taking short exposures it avoids differential flexure or polar misalignment problems that would lead to star rotation etc that would happen with longer exposures.  
 
So while the CFF/16200 is taking 10min LUM subs, the SV80ST/QHY163 is taking 3min RGB subs.  So on average I get an RGB image for every LUM image. 
 
I really don't have the knowledge to professionally plan all this out.  In fact, a few people kindly advised me to reconsider, or at least warned me about what I was in for.  grin.gif  But really, with the CMOS camera it was easy.  I just bolted everything together and hoped for the best, and I'm pretty pleased with things so far.
 
As a first test, I had the CFF scope at f/8 (in normal practice I will probably keep it at f/6).  I chose NGC891.  When I began this I wasn't really expecting an image to come out of it as I was just testing things out, but the tests went well so I kept getting data.  The really cool thing....I got most of the 17.5hrs of data in ONE NIGHT.  Getting 10hrs of LUM data really helps smooth things out and I didn't do ANY noise reduction on the LUM data.  The RGB was of course more noisy and I was somewhat aggressive with noise reduction in the RGB, but that's the beauty of LRGB imaging.  
 
Below is a pic of my imaging rig.
 
And here is NGC891

[URL=http://buckeyestargazer.net/Pages/Galaxies/NGC891.php][/URL]

[wimvb]

NICE!

What resolutions do you get with the two scopes? (Arcsecs/pixel)

[joelshort]

8 hours ago, wimvb said:

NICE!

What resolutions do you get with the two scopes? (Arcsecs/pixel)

For this image the CFF/16200 was 0.61 arcs/px and the SV80ST/QHY163 was 1.62 arcs/px.  Once I get the system all tuned up I plan to use the CFF at f/6, which will give me an image scale of 0.81"/px.

[tomato]

Hi Joel,

I plan to be looking for a RC next year and am starting to assess the choice between a 10” CFF or going for a bigger aperture GSO (and still keep a bundle of money). I have followed your initial optics issue with the CFF scope on CN, so pleased it all worked out in the end. I would certainly go with a CFF, they are fantastic scopes. The images you have on your website with this setup are just superb,  at the moment I am inclined to fight aperture fever and go for the (much) more expensive but superior engineered option.

[ollypenrice]

I'd be interested to see a comparison between the real resolution actually achieved by both scopes. By how much is the RC at 0.61 beating the refractor at 1.62?

Olly

[joelshort]

23 hours ago, tomato said:

Hi Joel,

I plan to be looking for a RC next year and am starting to assess the choice between a 10” CFF or going for a bigger aperture GSO (and still keep a bundle of money). I have followed your initial optics issue with the CFF scope on CN, so pleased it all worked out in the end. I would certainly go with a CFF, they are fantastic scopes. The images you have on your website with this setup are just superb,  at the moment I am inclined to fight aperture fever and go for the (much) more expensive but superior engineered option.

Tomato, one thing to also consider is what are your skies like?  Will you benefit from larger aperture or are you limited by sky glow?  If you have some amount of light pollution I'm not sure that going with a big scope will be as beneficial as from a dark sky.

Without any doubt at all, were I making the choice again I would go with the much more robust CFF over a GSO.  And that's saying something because I am incredibly cheap.  Normally I look for the least expensive thing to get the job done.  In this case, the best optics in the world won't work unless they can be carefully tuned mechanically and maintain that careful alignment.  This is the difference.  The GSO mirrors are fine by all accounts, bu the CFF scope is just so tight and smooth and will keep things in alignment.  Once I got the replacement mirrors it literally took me 15min to collimate the scope under the stars.  

 

23 hours ago, ollypenrice said:

I'd be interested to see a comparison between the real resolution actually achieved by both scopes. By how much is the RC at 0.61 beating the refractor at 1.62?

Olly

What would you like to see?  Equal LUM data from both scopes?

[ollypenrice]

1 hour ago, joelshort said:

Tomato, one thing to also consider is what are your skies like?  Will you benefit from larger aperture or are you limited by sky glow?  If you have some amount of light pollution I'm not sure that going with a big scope will be as beneficial as from a dark sky.

Without any doubt at all, were I making the choice again I would go with the much more robust CFF over a GSO.  And that's saying something because I am incredibly cheap.  Normally I look for the least expensive thing to get the job done.  In this case, the best optics in the world won't work unless they can be carefully tuned mechanically and maintain that careful alignment.  This is the difference.  The GSO mirrors are fine by all accounts, bu the CFF scope is just so tight and smooth and will keep things in alignment.  Once I got the replacement mirrors it literally took me 15min to collimate the scope under the stars.  

 

What would you like to see?  Equal LUM data from both scopes?

Sure. Whatever you have. It's just that this is a much debated topic and hard comparative data is not often available.

Olly

[tomato]

I plan to move to a (at least) semi rural location when I retire, and if the scope travels well it will regularly get to a dark site in the UK. (I currently regard the Mesu 200 as a portable mount, maybe not in 15 years time).

Olly, I will watch with great interest the on-going discussions on if a well engineered RC has the edge over a larger aperture, longer FL quality refractor for imaging small galaxies, which are my preferred targets.  Especially as either option won't come cheap, and I will only be able to make this decision once.