Wednesday, February 23, 2011

Of light pollution and aperture...when aperture is not always king

Just one of my random musing about observing and light pollution. I have been living in the gated university apartments for about 10 months now and have always been curious as to how my 10" f/5 dob would pull in the photons as opposed to my smaller grab and go scopes. The major hurdle (and it still is!) has been the two sets of stairs I have to navigate. As they say the bigger and heavier the scope, the less likely you would have the inclination to want to use the scope as often. That rings so true in the context. Therefore other than using my 10" GS dob once my my bro in law was visiting from Perth in Australia, I have never had the motivation to use the scope. Well the big scope bug hit me hard one Friday night and I decided to give the lugging a go. Would I do it again...not a chance in hell. I had to firstly carry the OTA to the top of the stairs, then go back for the dob mount that I carried all the way to the bottom of the stairs and into the playground. Then I went back for the OTA. All it all it took like almost 4 trips to get the whole scope down. If only I had a secure lockup garage that I did not have to share with some other resident ;P

And now for the acid test. was all this lugging worth the effort. My answer is a resounding NO. While views were brighter and slightly more detailed than in my C6, the improvement was just marginal. While the 10" went deeper, there was also another unfortunate side effect, its big 10" mirror also collected stray light from the numerous light fittings around the playground and from the sky glow. As a result the views were all washed out. And this coming from a scope that has been optimized by flocking with flock paper. Maybe I need to extend out the tube so the stray light does not hit the secondary mirror. Or maybe a more permanent solution is to take out all the lights in the compound with a sling shot ;) Don't you just hate light pollution.

But in all seriousness I find the 6" f/5 to be the best balance between seeing detail in DSO's and brighter solar system fare. Its light enough to be carried with one hand down two flights of stairs and gives enough in the way of detail to make observing sessions worth the effort. This scope shows abundant detail on planets and can resolve globular clusters quite readily. I have also in my arsenal several "grab and go" scopes, my 20x80's mounted on an Orion Paragon, a Celestron Firstscope 76mm and a Celestron Cometron CO60. All scopes are great on the fly, but for more serious observations, I still go to my C6. Good examples where the C6 shines includes the galaxy pairing in Ursa Major, M81 and M82. I could make out M81, but not M82 in my tripod mounted 20x80's (will have to try this again). The galaxy pairing was very obvious in the 10" f/5 but the views were less pleasing due to the grayish background. The views in the C6 were dimmer but the darker background made up for this. Details like mottling the galaxies, etc, well that will have to wait till I get to darker skies. All these observations were performed at similar magnifications.

So yes and there you have my verdict.....aperture is king...but only till some point....