Decided it was time to mod the 8" f6 dob so that I could achieve prime focus with the DSLR. So, removed the mirror cell from the tube, checked the thread size of the adjustment bolts (6mm for a GSO/Bintel dob), and after a quick trip to bunnings I had some new 50mm long screws and new compression springs. 10 minutes or so to fit, 5-10 minutes to do a quick recollimate using the laser collimator thingy, and i'm in business!
Confirmed this evening that i still have (when using a 35mm extension tube) a workable scope for visual use. And the clincher - yes i have the correct Bahtinov diffraction pattern with the DSLR at prime focus (this time without the extension tube). So thought I'd bust out a couple of prime focus shots of the moon.
This is a 1/4000s single uncalibrated exposure at ISO400 with the modded 400D and MPCC, on the dob mount. No tracking - just a fixed shot, together with a crop of the same shot to illustrate the detail a bit better.
The OWL Diagonal Calculator indicates an illumination of ~93% at the edge of the DSLR sensor, with 100% illumination out to about 0.4" field radius - so will be some minor vignetting, but that's what flats are for right!. Anyway - can't wait to set up with the NEQ6 and try this baby out on a couple of my previous targets - M83, NGC6744 and M20.
