I received my ASI290MC directly from ZWO last Friday (after ordering it Tuesday night, a mere 66 hours before delivery...thanks Sam!). After a few days of clouds and poor conditions, I had a chance to get first light this week. I decided to do a little shootout with my current planetary imaging cam, the ASI178MM I've been using with RGB filters for the last 5 months or so. Scope used was my CFF 160mm Apo Refractor and while the seeing was pretty good (~8/10 for this aperture) I'm not sure it would have supported the larger aperture of my C11 Edge. In any case, the C11 wasn't cooled down and the refractor was ready to go. 'Nuff said.
OK, I know you guys and gals would probably rather see a comparison between 224MC and 290MC or between 178MM and 290MM, but I don't have those other cameras to compare to . While my testing certainly wasn't controlled enough to be a rigorous comparison between a mono and color cam, the results are interesting nonetheless.
Factors in favor of ASI178MM:
+ Color seems more pleasing at least after initial combination of RGB. Color out of the color cam looks a little washed out in comparison and the saturation really needs to be cranked up to look similar, but it's still not identical possible due to the wider bandpasses in the color cam which gives less precise color reproduction?
+ Ability to get best focus for each color. This can have benefits for refractors depending on which one we're talking about, but probably less so for SCT and pure reflectors shouldn't matter. In my case with the CFF 160 I get best results by using the Baader T-size prism before the barlow lens & camera since it brings the main visual wavelengths to closer focus.
Factors in favor of ASI290MC:
+ This is not a scientific comparison, but the 290 seemed noticeably more sensitive than the 178. We have larger pixels in the 290 and I used the same imaging train for both cameras, f/20, so the ASI178 is at a disadvantage in terms of light collected per pixel (tradeoff for smaller pixels and larger image scale). I could have reduced the difference by matching image scale by using different barlows, but even then I think the 290 would appear more sensitive. Another contributing factor for this could be that in the color cam, the green bandpass is wider than a green filter from an RGB setup. In any case, I used exposure times of 4-8 ms for the 290MC while 8-15 ms is what I've typically been using for the 178MM.
+ Ability to capture time-specific events like moon/shadow transits, etc. without having to do photoshop work to match up the R/G/B from a mono cam.
+ Simplicity of operation and processing. Compared to switching filters and refocusing (which admittedly could be automated) and then the additional processing workload, operating the color cam is practically point and shoot. Stacking a single 60s sequence gives nice results, although of course taking multiple sequences and derotating them reduces noise and allows for more aggressive wavelets or stacking a smaller % of frames just as it does for a mono cam.
Note that I'm not viewing the pixel size as a positive or negative for either camera. I can vary image scale by using different barlows, so I don't see the 2.4 um vs 2.9 um pixels as being a big differentiator.
Anyway, I'm pleased to see that ZWO seems to have another winner with the ASI290MC and I think it stands up very well to a recent mono cam, the ASI178MM. It will be interesting to see future comparisons using other scopes and with the 290MM, which based on some early work from Darryl, appears to be a killer cam in the right hands !
I processed the two images below similarly but not identically. Sharpening was probably a little more agressive on the 290MC from the looks of it, and I adjusted saturation and color balance to get a close match between the two. The ASI178 image was reduced to 83% of original size to match the ASI290MC image scale. Comments and observations welcome!