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Stuart, you cannot compare the Sbig camera to the DMK, they are too different in their abilities. One is designed for DSO imaging and the other is designed for speed. Besides the well depths will hold differing charges, which gives differing responses in sensitivity.
Being able to acheive those rates of expose really depends on which image scale you are working to. I would say that with a 2x barlow and an extension of say nearly 100mm will allow a good size scale (like I achieved last year) and allow you to image at 1/34 of a second or 30fps. For 60fps you will need a much larger aperture or a much brighter target, like the moon or the sun (using the correct filters)
As you increase the scale (say near to 10,000mm) your ability to gain light becomes the overriding factor. With my images this year I am using near 1/23 of a second exposure at 10,000mm and the gain is nearly at max with my C9.25. On the other hand my 18" SDM gains so much light that I am at 30fps (I have a pre 60fps DMK that I bought April 2006) and with the gain down quite low and exposure at 1/34-1/60 on Jupiter.
Best of luck.
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