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Moving to a 10" meade from a 10" dob

Started by arawson, 03/26/2005 08:15PM
Posted 03/26/2005 08:15PM Opening Post
Moved from a 3.5" refractor to a 10" dob that I love very much. Next move I'm looking at is the RX200 10" Meade. I realize that this is going to enable me to start exploring astrophotography and the goto features will be pretty cool on top of Pinos where there are so many stars it's alitttle disconcerting. But a friend told me the seeing won't be much different from my 10" dob....is that true my 10" dob is 1250mm f4.5 while the 10" SCT is 2500mm f10. Seems to be the seeing is going to be tremendously better. Would love to hear your opinions. Thanks
Andy
Posted 03/27/2005 06:32AM #1
Andy,

Your friend might have been using the term "seeing" in its strictest sense....which doesn't mean the same thing to an astronomer as it does to a real person!

To an astronomer, "seeing" is the stability of the star, or lack of twinkling of a star. To a regular person, "seeing" seems to mean how good something looks. The Astronomer divides that regular definition into "Seeing" (or stability), "transparency" (how clear the air is), "limiting magnitude" (how dark the sky is), and probably a few other factors.

Astronomical "seeing" is dependent on many factors, including weather patterns, movement of cold fronts and warm fronts, winds coming over the mountains, etc. The stability of the air is dependent on how uniform the air is between the telescope and the star. "Cells" of air are different temperatures, and are moving. So, your "seeing" is dependent on how large the cells are, how diferent their temperature from other cells, and how they move, etc.). I am told (and I don't know how much I believe it) that this first factor, how large the cell, means that seeing is also dependent on the scope aperture. The theory goes if your aperture is smaller than the cell, it will not be affected as much by unstable air. So, your friend following this theory says--ten inches is ten inches. SO your "seeing" will be the same.

Enough about all that.

Alex
Posted 03/27/2005 08:49PM #2
Thanks for all the helpful insight. I think you talked me out potentially spending a lot of money. I just have to decide how important doing photography is to me. I think I'd rather have the aperture so I'll probably start looking for the 15"-18" dobs...big but still portable...kinda smile
Thanks again for the wonderful advice
Andy