Tuesday, April 5, 2011

M95 & M96

One step forward, two back...as mentioned before, there were no usable reference frames for this, and most of the subs in this set were tossed out anyway.

On the right is M95, and you can just make out that it is a barred spiral. M96 is on the left, with its outer arms just out of reach. A lot of "not quite" in this set.

The shapes of the stars near the edges show a typical fault with Newtonian scopes, called coma.  Not much can be done about it, provided that the distortion is axial-meaning that it points to the middle of the field of view. Well, there IS one solution, invented by Bernhard Schmidt in 1930-it's called a Schmidt telescope, which is essentially a Newtonian with a corrector plate, or eyeglasses. These days, Schmidt-Newtonians are very rare, since Newts still have this great huge tube, where the reflector is at the back end, and the focus (and eyepiece) is at the top. More often now, the light path is bounced of yet another mirror back through a hole in the primary, so that the eyepiece is at the back of the scope, where one would expect. This halves the length of the tube, also. That is referred to as the Cassegrain focus, named for Laurent Cassegrain, who published its design in 1672. (Today, it's pronounced Kass-a-grain, which of course is nothing at all like poor Laurent would have said it. At least Schmidt's name sounds more-or-less as it should.) Combine one of these scopes with a corrector plate, and you get a Schmidt-Cassegrain, which is really a much better instrument for deep-sky photography, but they cost several times what a Newt of equal light-gathering ability does.

All of this information is to detract from the fact that there just isn't much to say about the photo here.

2 comments:

  1. Ha ha! Well a non descript photo is better than no photo. I was going to setup last night but couldn't get my butt in gear.

    Will try tonight with Mr. Schmidt's addition to the Cassegrain innovation. I too have punted on Orion and will start aiming at something in the Virgo funhouse.

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  2. You didn't miss much-Saturn was even twinkling at times.

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