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The idea that colour sensors reduce imaging time is not correct. They generally speaking have lower QE so they take total exposure time to get to the same level as filtered imaging with mono sensors. CCD cameras are typically around 60% QE for mono and about 28% or less for one shot colour (at least half as sensitive). I think the reality is more like 1/3rd as sensitive when all factors are considered.
But you can get caught out with an incomplete set of filtered data when using a mono sensor, so that is true. But then the colour data from the same time period from a colour sensor will be noisy so whilst you may get an image it may not be that pretty either.
I have used both and colour has its advantages but where you see its weaknesses most are in dust areas, dim areas of deep sky objects. Those will be noisy and are hard to get clean compared to filtered mono imaging.
So a 2nd hand QSI 683 WSG8 with filters is about the best setup I have seen in recent years. Many award winning images, the autoguiding function seems to work well and the smaller filters it takes allows using the better narrowband filters as the cost is kept done.
You would easily get one in your budget range. I see them on Astromart or CNN for about US$3000 - $3500 with filters.
Are these ASI type colour cameras much better than a modded DSLR? Especially say a full frame modded 6D (US$1000 or less 2nd hand)?
Full frame trumps these little ASI sensors. They are tiny.
Greg.
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