From: Milton Aupperle <milton@outcastsoft.com>

Date: February 25, 2008 9:04:18 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: More New Images!


Hi Antonio;


On 25-Feb-08, at 1:43 AM, aa27100 wrote:

Hi Jim,

nice shot: perfect collimation really seems to be the most important issue with reflecting 

scopes!

Indeed, it was hard for me to believe that you guys imaging at 200 mm (or more) aperture 

have only a slight edge on my 102-mm apo refractor. Compare your (and Milton's) 

recently posted Saturn and Mars images with my last efforts (seeing 4/5, other details 

with pictures):


Mars:

http://tech.ph.groups.yahoo.com/group/Astro_IIDC/photos/view/cf01?b=1&o=2


Saturn:

http://tech.ph.groups.yahoo.com/group/Astro_IIDC/photos/view/cf01?b=2&o=2


Seeing is the major issue here. I get a 4/5 seeing night maybe 1 or twice a year in Calgary.


After many years spent on deep-sky astrophotography, I am starting to enjoy also solar 

system imaging and I am considering a dedicated equipment: something in the range 

180-210 mm (compatible with a GM8 mount and reasonably portable). Mewlons are on 

top of the list, but just for starting I might want to play with some friend's C8, to make 

practice with alignment issues. I know larger apertures are better, but the occurrence of 

excellent seeing here does not justify the investment. What is your opinion?


I'd agree. Unless you have either commonly exceptional seeing or lots of time to go out each clear night and try imaging to catch those rare 4/5 night, it may not be worth buying a large aperture / long focal length scope.


From my current location in Calgary which has the Jet Stream directly over me, frequent inversions where the air 50 meters above me may be 10 or even 20 degrees centigrade hotter than the surface is and turbulence from roiling air columns generated by apartment blocks and building, a longer focal lengths scope would have been a waste of money for me. I believe Jim is in a similar situation from Toronto with respect to turbulence too, even though we are separated by around 4,000 kilometers.


The only thing about larger scopes is they collect more light than a smaller scope.  This means you can run at shorter exposure times and at faster frame rates which is supposed to help reduce turbulence. However many nights I have shot the moon with exposures as lows as 3 milliseconds and that made very little difference.


Milton J. Aupperle