ZWO difference between mc and mm

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denababy
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ZWO difference between mc and mm

Post by denababy »

Hello everyone my aunt has given me some money to buy a new camera but before I do could anyone tell me what difference I will see between the colour and mono is it a major improvement? At the moment I have a colour zwo 120 and not used it much but I have read time and again that it is a mono camera that is most desirable. I want the best results therefore the best camera that I can afford. I know there are better cameras but until I am proficient it’s best I stick with the lower cost equipment.


Bruce Girrell

Re: ZWO difference between mc and mm

Post by Bruce Girrell »

It depends a good bit on what you want to do. For Hydrogen alpha capture, mono is absolutely the way to go. A color camera has a grid of red, green and blue color filters in front of the imaging chip, one color filter for each pixel on the camera's image sensor. In any given square of four pixels, there are 1 red, 1 blue, and 2 green sensors. But Hydrogen alpha is a single wavelength of light that passes only through the red filters. That means that if you use a color camera for Ha imaging, fully 3/4 of your pixels see NOTHING. I have verified this with my Nikon SLR. The green and blue channels are completely black.*

White light imaging is a different story. A color camera is just fine for white light images of the Sun. But for faint objects, astronomers still prefer a mono camera with an attached color wheel. The reason is that so much light is lost in the color filtration that it is advantageous to acquire most of your image as monochrome, to take advantage of all the sensitivity your camera has to offer, then take separate red, green, and blue images to produce the colors. The color portion of images usually has relatively low information content. So you can take a low res color image and apply its color to a high res mono image with the result of an apparent high res color image.

If you are doing Ha imaging, you should also consider a camera with a global shutter, rather than one with a rolling shutter. Cameras with rolling shutters seem to exacerbate a phenomenon, which is called Newton's rings, and are produced by interference between two closely spaced transparent surfaces. My tests indicate that the phenomenon occurs with both rolling shutters and global shutters. They are much worse for me if I use a barlow or Powermate lens. IMHO, the reason that Newton's rings get blamed on rolling shutters is that CMOS devices tend to use rolling shutters and CCD devices tend to use global shutters. CCD devices, being of a different construction, do not have the thin SiO2 layer on them that CMOS sensors have. The SiO2 layer is very thin and is on the order as wavelengths of light. It's my belief that the Newton's rings are a result of this thin transparent layer and that all CMOS devices may exhibit them to some degree. I have two cameras, one with global shutter and one with a rolling shutter. Both have CMOS sensors. Both exhibit Newton's rings.


*Interestingly, my Sony a7R Mk II shows image data in the green and blue channels. This may be because of Sony's "back side illuminated" sensor. But even though data shows up in the green and blue channels, it can't be valid data. It must be spillover from the red channel, so there's no new information there. If you're doing Ha imaging, use a mono camera.
Last edited by Bruce Girrell on Sat Jan 27, 2018 9:17 pm, edited 1 time in total.


denababy
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Re: ZWO difference between mc and mm

Post by denababy »

Thanks for that I have now ordered a zwo 120 mm.


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