Telescope Reviews: Sky Window

Grant,

i have used a skywindow for about four or five months. back problems prompted me to buy one, and the relative light weight and compactness (compared to a parallel mount) make it easy to carry in one hand. i use the skywindow on a table top and sometimes on my car (after it has cooled down!).

while the position of looking down is very comfortable, there are some tradeoffs, a couple of which were mentioned above. you get a reversed image, and although amateur astronomers are used to seeing this in telescopes, most scopes have a relatively small FOV so you are not used to looking at a 5-8* reversed image of the night sky. viewing my favorite star clusters and asterisms in reverse took some getting use to, and i still prefer the correct orientation.

the angle also makes locating objects a challenge since you can't directly line up the bin with the object you're looking for. As Masatoshi mentions above, a green laser pointer overcomes this problem. however, i live too close to an airport to use one, so i have to search through a reversed sky, but you can get used to that too.

the one problem i have not been able to overcome is the astigmatism that my skywindow adds to the images. just like a reflector telescope, you need to cool down the skywindow before viewing with your binoculars to prevent astigmatism in your views. you should also cool down your bins (or warm them up outside in the summer if you have air conditioning in the room where you store your optics). however, if the temps are continually dropping or rising, it's hard to avoid the astigmatism. in fact, in my unit, even after cooling down for an hour in fairly stable temps, i notice that the mirror still adds a bit of astigmatism to the views. and the higher the power bin i use, the more i notice this. i also notice more astigmatism at extreme angles of the mirror. whether my unit is not on par with others, i'm not sure. a fellow club member has a skywindow and has also noticed the astigmatism. we plan to compare our two units to see if there is a significant variation. if so, we'll post a note to the vendors' page.

having said all that, i find that even mounting 8X bins to the skywindow allows me to see more detail due to the steady images, and it also reduces back pain. so like bins, using a skywindow is a matter of personal preferences. if you can live with reversed images, afford a green laser pointer (which costs almost as much as the skywindow), don't mind cooling down the mirror in advance, and can tolerate a bit of astigmatism in your views, you can't beat the skywindow for convenience and comfort.

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Oscar Zoroaster Diggs
"O.Z."

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