Hello,
Recently I acquired a Tak Extender x1.6 which converts the Mewlon 180 F12 to an F19.2 ‘scope with an efl of 3450mm and last night I gave it a run using the Canon 40D.
A few test exposures soon revealed that the 40D is no ST7 in terms of sensitivity, so I slewed to 47 Tuc low in the S and took a test exposure of 60 secs. Well, heaps of noise and a few dim stars but what was very surprising, is that the stars appeared round! So I upped the exposure to 5 minutes (ISO 800) and was overjoyed that the stars remained round. I was auto guiding through a WO 66 Petzval using an (old model) Orion Deep Space Star Shooter controlled by PHD Guiding.
I managed to squeeze off 6x5 minute exposures before I had to pack up and was astonished that I had round(ish) stars at this crazy focal length. I just don’t know what I have done differently, as previously I had struggled at focal lengths of over 1700mm! I sure hope it sticks!
The attached image is the full frame (3888x2592) re-sampled down to 1600x1062. The FOV is approx 22x15 arcmins. Only the core is shown, as the outlying regions would require much longer exposures with the 40D operating at F19.2, not to mention dark skies and more sub frames!
WARNING: 1600x1062 file at 164Kb
Cheers
Dennis
