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Just a follow-up....
Being disappointed in the 300 l/mm results, I tried some exposures with the 200 l/mm (28mm aperture) mounted on the 85mm Prime and Modded Canon 1000D.
Similar results, the 30sec started to show excessive background and the 60 sec even worse.
Good result was the faint IR stars recorded in the image (some 12 IR stars > 10mag around Musca/ Crux.
I'll try a few things...
1. Change to the "grating in the converging beam" on the ED80 to allow lo-res spectra recording of nominated objects.
2. Put the 20 deg objective prism back on an ED80 for comparison trials.
3. Do some 30 to 60 sec exposures with just the 85mm Prime to see the possible worth as a "Nova search" set-up.
Onwards and Upwards.
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