Sampling when imaging

[Dawson]

I am trying to work out which camera would be better to image a faint tail with, such as a comet’s tail or in particular Mercury’s illusive sodium tail.

Using a narrow band filter which only transmits 589nm (sodium), the logic would follow to use my mono (ZWO 174MM) camera. But my colour camera (ZWO 585MC) has smaller pixels and more of them and deeper wells.

The sampling rates of the two with my fast short tube refractor are: 3.5″/px and 1.73″/px respectively.

Three of the four pixels (green, green and red) in the Bayer group on the 585MC have a QE of 60% at 589nm compared with all pixels on the 174MM having a QE of 65% at 589nm. Both are 12 bit ADC, 0.8e read noise, but 174MM has well depth of 37.8k and the 585MC well depth of 47k.

So my question, which camera will be a) most sensitive to the faint tail, b) show the most detail, c) have the best dynamic range / contrast? Anything else I should consider?

Thanks for any help.

James

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[David Arditti]

I think they will be very similar. The QE doesn’t seem that relevant as you will be imaging against a bright sky I suppose. Pixel size doesn’t seem important either when imaging such a nebulous thing. The larger well depth of the colour camera may give a slight advantage in pulling out a fine discrimination of brightness levels.

This sounds like a rather similar problem to the twilight imaging of the dark side of Venus, where the results are critically sensitive to altitude and sky darkness. Martin Lewis did a lot of work in quantifying the effect of noise in those observations. He gave a talk on it to a BAA meeting a few years back, which is in the YouTube archive.

• This reply was modified 12 hours, 20 minutes ago by David Arditti.

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