"Szaki" wrote in message
news:eU4Yb.333687$na.490998@attbi_s04...
There is some price difference , between the two scopes, also.

Julius


Not to mention availability considerations.

rdc



"Richard Crisp" wrote in message
om...
I used the same 3nm FWHM Cust Sci filter for both images.

The C14/Dream Machine (IMG10124S) camera was exposed for 20 minutes x 3
exposures.

the AP155/ST10XME was exposed for 15 minutes x 6 exposures.

Unfortunately I blew it: I should have exposed the AP155/ST10XME at 1x1
binning, but used 2x2 binning instead.

If I had done the 1x1 binning, then the plate scales would have been
pretty
close: C14/DM: 1.12 arc-sec/pixel versus AP155/ST10: 1.29 arc-sec/pixel.

But using the 2x2 binning on the AP155/ST10XME gave me 2.59
arc-sec/pixel
instead :-(

The AP155 system was operating at f/7 while the C14 was operating at
f/12.46

From an exposure perspective, the 2x2 binning used for the ST10 gave me
a
4x
speedup, so equivalent exposures at 1x1 binning would have been one hour
sub-exposures for the same exposure depth.

Here's the comparison, flawed as it is:

http://www.rdcrisp.darkhorizons.org/...55edf_page.htm

I will check, I may have some other data better for comparing. Still I
think
the comparison is interesting. One thing that surprised me is that the
stars
are a bit tighter with the C14. Although the larger aperture favors
tighter
stars, I think the figuring of the optics for the C14 is not up to the
same
level as the AP155. Still both did credible jobs.

Richard