This thread is born of my frustration at trying to image at f8 with my RC08. Last night I was out in the Obs all night testing the RC08, which is finally approaching collimation (yes it still needs work as you can see from the image of Sculptor A below). I selected a couple of reasonably bright targets (Sculptor and M42), and one dim one (The Horsehead), as I have good library images of these from my 10" f5 Newt (and Mak-Newt MN190 f5.3). Mount is the same NEQ6 Pro for all the scopes, as is the guide camera, and other gear. Camera was my Canon 450D Full Spectrum/Cold Finger modded. Reduced sized single sub jpg images below are from the RC (Sculptor A) and from the Newt (Sculptor B). I realise both single subs have star shape problems, but it's what I have at this point for comparison purposes.
I probably shot the RC subs without enough exposure time (at 260"), but I wanted to try and eliminate any mount, guiding, influences if possible, and the sub times were greater than the F5 times (194"). I realise that f8 will always require more exposure time, which is why I included M42 which is so bright it can burn out the Trap on even short subs.
This morning stacking my subs in DSS, all failed due to poor star detection, even when I bumped it up significantly, the stack still failed. Maybe this was unrelated to the RC08 performance but the same stacking settings worked fine for the other scopes. When I examined the individual subs in Photoshop some appeared fine to me (like the M42 ones), but the Sculptor was dim and lacked detail compared to the f5 scopes. The Horsehead was barely visible.
I realise the long focal length imaging at f8 does require more time, but honestly the focal length of the RC08 (at around 1600mm) is only 20% longer than my 10" f5 newt (@ 1250mm). The 190mm Mak-newt does have an advantage at f5.3 and 1000mm fl.
When I consider the problems that I have with focuser sag on the RC08 under the weight of my cooled DSLR (which is not an issue on the Newt or Mak-Newt), I have to wonder why I am continuing to pursue refining this setup.
Perhaps I just lack the patience, skills, and time required to make this RC work well with my DSLR setup, or is there some secret RC handshake that I don't know about yet?
