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Denk Starsweeper

Started by JamesMiller, 05/08/2006 12:44PM
Posted 05/08/2006 12:44PM Opening Post
I've noticed that when I used my Denk Starsweeper .5X
(the 2" model) that I get MUCH better images, even when I
get nearly the same magnification. (For instance, stars
are more pinpoint and planets clearer with the 15mm set
and Starsweeper than with the 25mm set - not identical mags
I know, but the difference is striking)

I also notice that the focus spot in my SCT is very much

Is it the case, then, that my accessories (WO crayford and
Denk bino) move the focus far enough back that SA is softening
my images, but the Starsweeper is "adjusting" my focus point
back closer to the SCT's sweet spot?

I hope I'm making this question clear enough. Essentially, I'm
thinking it might be better to get rid of my 20mm eyepiece pairs,
and replace them with a 10mm set with the Starsweeper. And so on.


"Don't drop the banana!"
"Why not?"
"Good source of potassium!"
Posted 05/08/2006 01:18PM #1
Hi Jim,

If you are speaking of image quality on film or CCD then yes you could get a better image when using a StarSweeper( a focal reducer). The reason the image could improve is that the shutter speed will be reduced for the same image brightness. This in turn will reduce the effect of any tracking error.

Visually, everything we know about optics says the image will degrade slightly under the conditions that you describe. By using a focal reducer you create a faster light cone that magnifies any imperfections in your mirror.

Maybe you just happen to hit the sweet spot for magnification on the particular night you were observing. Try the same experiment over 3 or 4 nights with different EP sets and see if you can reliably duplicate your experience.