Since we are talking about low light performance...

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DavidWright2010 Veteran Member • Posts: 3,255
Since we are talking about low light performance...

... I thought I'd resurrect my study of The Great Nebula in Orion (M-42) that I did a couple of years ago, At the time, there sere some members who were (heroically) doing deep sky photography with Foveon-sensor cameras.

M-42 is the brightest nebula visible from the northern hemisphere; most other deep sky objects (DSOs) are much, much dimmer. So being able to render M-42 in a pleasing manner should be a very low bar to entry into the world of astrophotography.

I imaged M-42 using the Sigma 150-600 mm lens (I have this lens in both Sigma and Nikon mounts), and took 30 second exposures at ISO 100 (Sigma; 800 for Nikon) and f/6.3, on a tracking mount. For 30 sec exposures one doesn't need to guide, and typically one will take many, many such exposures and average them to increase the S/N of the nebula.

The images below are each a single 30 sec exposure, and they might have been the stars in the movie 'the good, the bad, and the ugly'

Shown here in reverse order:

The left-most is the Sigma SD1M, and the obvious color blotching will make signal averaging difficult (to say the least). The middle is a run-of-the-mill 24 mp Bayer-sensor camera (Nikon D7200). Nikon reds are not particularly strong, but the random nature of the noise means that signal averaging will be possible.

The third image is a Nikon camera (D5600) modified for better red sensitively. You will appreciate why one might be willing to spend a few hundred dollars for this mod, since it  means that a good DSO image might take only a couple of hours of light collection rather than a couple dozen hours.

The mod improves the sensitivity to red so much that using just this one 30 sec exposure, a lot of detail can be brought out:

LHS-unfiltered. RHS filtered and additional detail brought out

(BTW, those streaks are geostationary satellites. Since the camera is moving to track stars, the geostationary satellites appear to be moving.)


p.s. So my definition of "low light" is "not visible to the unaided eye". You can see just the central part of M-42 with the naked eye - it's that part in the above image that is over-exposed.

 DavidWright2010's gear list:DavidWright2010's gear list
Sigma DP1 Merrill Sigma DP2 Merrill Sigma DP3 Merrill Sigma SD1 Merrill Pentax K-1 +1 more
Sigma SD1 Merrill
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