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I have a Celestron 2x Barlow and 2.5 Powermate. The Powermate does not shift the focus point outward as the Barlow does and it has much better colour rendition. But I think the TV Barlow’s have good colour correction as well. The Powermate accepts a T-Ring and you can buy a camera bayonet Mount for it. The parts are sold separately but it is easy to mount a DSLR to a power mate and there are no backfocus issues. This was my main reason to get one. However, on my f/5 Newton the exposures required went up to something crazy like 15min. for the pinwheel galaxy as the system becomes f/12.5.
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