The contrast issue is a bit subtle.
Diffraction causes images to be blurred. Points are spread out. The 3"
spreads points into discs with very faint rings. The 6" spreads them into
discs with brighter rings. This reduces the contrast when compared to an
unobstructed 6". But the entire pattern is 1/2 the size of the 3" pattern.
So the amount of image destruction is less in the 6".
Rich already mentioned the lack of diffraction spikes. Since the f/ratio is
so large the scope will have less comatic aberration and it will work well
with cheaper eyepieces.
I buy the 6" and spend the money saved on better eyepieces.
-Leonard
----- Original Message -----
From: "Peter Santangeli" <peter@No-Spam>
To: "The Astronomy Connection" <sf-bay-tac@No-Spam>
Sent: Sunday, March 06, 2005 9:17 AM
Subject: p: [TAC] Scope of confusion
>
> I'm confused. I just read the S&T article on Orion's 3" off axis
> reflector. I was actually interested in this, because it is clearly so
> unusual. From the article though, when compared to Orion's *cheaper* 6"
> newtonian, it has:
>
> - less light grasp (obviously)
> - the same size tube
> - (surprisingly!) less contrast
>
> What am I missing here? Apart from it being gimicky, what advantages does
> it offer the observer?
>
> Pete
Received on Sun Mar 6 10:38:18 2005