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What can you expect on Mars....

Started by Ron777, 07/26/2003 01:52PM
Posted 07/26/2003 01:52PM Opening Post
OK, here is an image of Mars, with alot of detail, I super imposed a grid. Mars is sized with the grid to represent it at opposition, about 25 arc seconds. The grids are 1 arc second square. I looked up telescope resolutions, they are as follows..
90mm= 1.3 arcS
4 inch= 1.1 arcS
10inch= .45 arcS

So in theory and perfect atmosphere, a 4 inch could discern details the size of each square a 10 inch could discern details to about 1/2 the size of each square.
Of course this also depends on the contrast of the features and scope also. This at least should give us all an idea of what we could see. After doing this I can see that the atmosphere is really a major limiting factor for most of us. I also can see why people with 4 and 5 inch apos are seeing Mars so well, as most of the time a large scope is not even getting close to it's max capabilities so the apo's crips views and high contrast are beating the veiws of the larger instruments higher resolving power that is not able to be taken advantage of.

I got started on this after all those threads about aperture and seeing, then I read Ed Tings review of the Portaball 12.5 inch, even though it had 1/27th wave optics AND more aperture, he said the two apos that were there that night still beat it on the planets, I infered from him that the ability to see lower contrast outweighed the resoving power of the portaball that night.

So I think atmosphere really is our number one enemy, not our scopes!

Take care!

Attached Image:

Ron777's attachment for post 7911
Posted 07/26/2003 02:10PM #1
Ok, I thought of something AFTER I posted this last one, heres a better idea. Not counting atmosphere, what we could see at two different resolutions. I divided mars into pixels then resized to represent two apertures.
25x25 pixels, then resized for a 4 inch scope and,
50x50 pixels, then resized for a 9-10 inch scope.

Now I can see that with good atmosphere, even an 80mm refractor with good optics could show A LOT!!!

Thanks for looking!

Attached Image:

Ron777's attachment for post 69543
Posted 07/26/2003 02:17PM #2
Cool...excellent analysis. And yes, there are nights(most nights) when my Starmaster 12.5 ELT cannot stretch its legs for the reasons you describe. The apo's contrast is a given.
Posted 07/26/2003 05:02PM #3
Hi Ron,

I agree with you 100%. I took your image and applied a gausian blur to match the pixel count on my monitor for a 10-inch and a 4-inch scope in arc seconds and then reduced them to kind of match my Six Scopes post and the images are remarkably similar to the Aberrator images.

Seeing is the thing, no doubt. And most of the time in most places the 4" scopes will give a good image on the average. It is only in those small moments that come every 1 or 2 minutes where the bigger scopes can pull ahead.

Take Care,

Jose Suro
Tierra Verde, Florida

Attached Image:

jsuro's attachment for post 69551