Colour or Mono-Chrome

[Nath2099]

Hi all, wondering your thoughts on colour or monochrome cameras? The benefits of each? I assume the monochrome would need 3 times the data? And is it a filter or something you sit in front of it to get the frequency you want to image?

Sorry for the noob questions, don't want to waste money!

[julianh72]

It depends on what you're planning to do.

One-shot colour cameras are great for beginners who are just starting out, especially if you're doing mainly planetary work, or bright star clusters and nebulae, because you can be capturing colour video and / or multiple colour still frames in your first night out under the stars, and can generate quite pleasing results with minimal processing.

However, I think most of the really good shots are taken on mono cameras with filters, and therefore require multiple sequences of frames to be taken to capture each of the colour channels - so you need to be prepared to dedicate more time to just capture the raw data, and then you need to learn the techniques of combining the multiple colour images into a composite colour image.

If you're just starting out, I'd probably suggest a reasonable one-shot colour camera that you can buy for just a couple of hundred dollars (or less) is more likely to give satisfying results early on, but if you get serious, you'll soon be buying more expensive cameras, modding a Canon DSLR, filter wheels, guiding scopes, ...

I wouldn't be too worried about wasting your money on your first colour camera - you can buy some very cheap astro webcams on eBay, or spend a bit more for a ZWO or similar, and if you upgrade, you'll be able to re-sell your first camera for very little loss while you save for your next bit of high-end kit.

You'll notice that a lot of astro cameras are available in both Colour and Mono variants - they actually use the same sensors, with the same number of pixels, but the Colour variants have a "Bayer Matrix" in front of the sensor, which means 2 out of each 2x2 block of pixels are filtered to capture only Green light, and one each capture Blue and Red filtered light. The camera driver interpolates a Red and Blue value for each Green pixel (and likewise, interpolates Green and Red for each Blue, and Green and Blue for each Red), to produce a full-colour RGB value for every pixel, so each full-colour frame has the same pixel-count as the mono sensor, even though only half the pixels are Green, and only 1/4 are Blue and Red. The colour cameras are less sensitive overall, as each pixel only registers some of the light which falls on it, and the RGB colour values are partially interpolated, but they have the advantage in ease and convenience of capturing full colour images over their Mono counterparts.

[Nath2099]

Cool, cheers. What's the difference between taking video and long exposure stills? The stills would be way more resolution wouldn't they? But I guess less fudge factor than video?

[ZeroID]

Hi Nathan (?)
As a 'noob' I would be starting with colour and probably a DSLR rather than a dedicated mono astro-camera.

Colour, or OSC, One Shot Colour in astro terms means you take a series of images, stack them to accumulate the photons and process to create the final image. Pro's are easiest method, minimises complex processing. Cons are a reduced image quality due to the nature of the sensor with it's colour pixel structure (RGGB), 4 pixels to capture effectively one pixel on the image.

Mono removes the coloured lens filter over the sensor and uses each pixel individually increasing resolution but requires you take 3 imaging runs for a target with a different filter for each colour (RGB). They are combined at the processing level, more complexity obviously. There is also other things to contend with, eg each colour will have it's own number of images required to achieve saturation and repeated alignment is a must.

The biggest one is getting the clouds to cooperate to collect enough of each photons over possibly several nights, maybe months apart to build the image. Some images on here have been collected over a year or more before finally completed. Skyviking (Rolf) has images consisting of 120 hours of exposure.:eyepop:

If you are just starting to think about astroimaging one of the cheaper models of Canon DSLR's is the best starting point. Good software and hardware support, lots of experienced people to call on for help and if it's not for you then you still have a good camera.

I'm still happy with my 1200D and 450D IR hardware and only just looking at moving up to a dedicated Astro camera after about 5 years.
And the technology has moved on as well, better gear is now available at better prices. :thumbsup:

Hope this helps a bit :D

EDIT: Damn, beaten to the 'punch' LOL

[julianh72]

I currently use a ZWO ASI120MC one-shot colour camera, controlled by the free FireCapture program (highly recommended! Get it from here: http://www.firecapture.de/ ).

Using FireCapture, I can control the exposure from a few milliseconds (which is all I need for shooting the Moon, Jupiter, etc) up to many seconds (twenty minutes, if I recall correctly) - well beyond the tracking capability of my telescope's mount.

Sequences of frames can be saved as either a series of BMP still images, or as an AVI video (which runs as a time-lapse if you play it back). The resolution is identical in either format; AVI is more convenient for processing, as you only need to manipulate a single file, but a series of BMP images allows you a bit more control over selecting and tweaking individual frames before you start the stacking and processing.

[julianh72]

Just to clarify - with my set-up using a ZWO ASI120MC (and I think this is typical of most colour astro cameras), I get full-colour images at the same native 1280 x 960 resolution as its Mono cousin, the ASI120MM (which uses the same sensor, without a Bayer matrix).

While each physical pixel is filtered to only register Red, Green or Blue light, the camera firmware / software interpolates the other two colour values for each pixel from the adjacent pixels, and outputs a full 1280 x 960 RGB image.

For my beginner skill levels, the one-shot colour arrangement works perfectly, particularly for bright / distributed targets. However, if you imagine a very faint Blue star happens to land on a Red pixel, the colour camera will get almost no signal, whereas the Mono sensor will register Blue (or Red, or Green) light on EVERY pixel. Similarly, when trying to shoot faint nebulae which are emitting in the H-alpha (Red) range), only 1/4 of the pixels on the Colour sensor can actually register any useful signal, so the colour camera has roughly 1/4 the total Red sensitivity as it's Mono cousin.

Even on bright targets, you can theoretically get more accurate colour rendition using the Mono version, and taking three filtered Mono images, as you will get true R, G & B values for every pixel, rather than interpolated RGB, but this comes at the cost of more time required for capture, and more processing time to combine the multiple images.

As a beginner, I'm still very happy with my one-shot colour camera.