Telescope Reviews: Post a picture of the scope you made

Dave,
You ask a hard question, that has a grey answer. I did lots of analysis on my 12", and published it here: http://www.xmission.com/~alanne/DS3Baffling.html.

Since I made my 16" (and frankly, I don't have as much experience with it), I have modified my opinions a bit. Currently, I believe the following:

* What was stated in the Sky and Tel article April 2001 is a great start, but is incomplete.

* Light that reflects off of something, not into your eyepiece, is irrelevant. An example is side light on your clean primary mirror. Light that scatters off of something, and can get to your eyepiece, is relevant. An example is the ground behind your secondary in a light polluted location.

* What you want is for the lens of the eyepiece to see no stray light at all. This is at the eyepiece lense - which is a point INSIDE the focuser tube. We can partially approximate this by looking in the focuser tube with our eyes. When you do this, if you see anything that isn't black or sky, you have work/fixing to do.

* Baffling or shrouds behind the secondary is the most important addition that you can make. I use a large baffle that is foam core poster board that is bent. I then use some flat black felt paper (I forget where I got it - AstroSystems?). I believe that shrouds are then irrelevant. See the picture of Deep Space 4 - my baby - a few posts above here.

* Having a medium or longer focuser tube, and a non reflective inside to this focuser tube, is the next most important thing to stop reflections. I have been amazed at how dark the sky looks using my FeatherTouch focuser. They actually machined ridges inside of it that act like numerous baffles.

* I put black electrician's tape over the trusses, and blackened the secondary edges and holder. Not sure if it helped at all, but it made me feel better.

* I made the top of the mirror box a fairly dark stain. Once again, I don't think it helps much, but it makes me feel better.

That's about it. I find this scope gives as dark of backgrounds as any, unless there is a moon out or streetlight near - AND - I am placing the secondary where I am getting lots of reflection off of the back felt.

By the way, the advantage of only having a removeable baffle is that about half of the time, the baffle stays in the car. That way, the wind just blows through the scope without creating any vibrations. New Mexico can get windy some times!

Alan Scott