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Old 23-01-2013, 09:09 AM
originaltrilogy (Petr)
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Colour vs Mono CCD?

I am a mono imager but looking for a new camera.

I was put off by colour versions of same mono camera only being half as sensitive QE for each colour.

But then I'm thinking I have to take image for twice as long with colour camera to get same sensitivity as mono camera with filter.

But for mono I have to take 4 images L, R, G, B. So if I take 1hr per filter I have to image for 4 hours with mono, or 2 hours with colour camera to get equivalent image.

So colour camera is really twice as sensitive for same target. Plus save lot of processing time.

Also colour data on OSC camera comes from exact same time period and sky position and seeing conditions, so data should be more accurate and less detail lose to aligning images taken at different times.

Is my thinking correct?
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Old 23-01-2013, 05:37 PM
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Originally Posted by originaltrilogy View Post
So colour camera is really twice as sensitive for same target. Plus save lot of processing time.
LRGB imaging with a mono camera is generally always going to get you data quicker than with an OSC camera (assuming a sensor of similar performance). Here's why: a filter works by blocking photons. With an OSC camera every pixel has a filter and the sensor only sees a proportion of the photons falling on it. This is true of a mono camera with RGB filters as well, but the magic happens when you collect Luminance. In this case you are using a clear filter and the sensor sees all of the photons, at least all those corresponding to visible light (the clear filter may be IR blocking). The L part of LRGB is more efficient than an OSC can ever be and the RGB part is effectively the same. Hence the LRGB combination is overall more efficient.

The disadvantage of a mono camera comes when your imaging run is curtailed by weather or whatever. If you get only 60 minutes of OSC data you might be able to get an image, albeit not a great one. If you get 45 minutes of Luminance and 15 minutes of Red then you don't get anything...

BTW, I don't think that processing OSC data is necessarily any easier. To do it well you generally need to process the Luminance and colours separately anyway.

Cheers,
Rick.
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Old 24-01-2013, 08:22 AM
Poita (Peter)
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I reckon processing from a OSC camera is a bit easier. For one thing each colour channel is already aligned in each sub, and the seeing for each channel is identical for each sub.

Looking at the data for most cameras it would appear that Petr is right, for RGB you get the same depth of data in half the time on an OSC compared to a mono camera.

So you can get your RGB in 9 hours instead of 18.
That leaves the Luminance channel, which is twice as quick on a mono as on an OSC (I could be wrong here, does anyone actually collect Luma separately with an OSC camera?).

I think most people just make a psuedo luma channel from the RGB data when using an OSC camera? You could also use a mono camera just to collect the luma data if you have one.

Either way, you could either get the same/similar data in near half the timewith an OSC vs with a mono camera, or go nearly twice as deep with an OSC in the same amount of time.

Last edited by Poita; 24-01-2013 at 09:02 AM.
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Old 24-01-2013, 09:58 AM
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But then I'm thinking I have to take image for twice as long with colour camera to get same sensitivity as mono camera with filter.

But for mono I have to take 4 images L, R, G, B. So if I take 1hr per filter I have to image for 4 hours with mono, or 2 hours with colour camera to get equivalent image.

So colour camera is really twice as sensitive for same target. Plus save lot of processing time.

Also colour data on OSC camera comes from exact same time period and sky position and seeing conditions, so data should be more accurate and less detail lose to aligning images taken at different times.

Is my thinking correct?[/QUOTE]

No that isn't correct. Mono chips are typically nearly twice as sensitive to light as colour is. So the statement 2 hours to get an equivalent image is not correct. It will be in no way equivalent. The mono image will be way less noise, stronger signal, richer and deeper colours and more detail.

You can get great results with one shot colour CCDs. But they require more exposure for the not quite the same result. Typically the problem with one shot colour is noise in the dim areas.

Greg.
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Old 24-01-2013, 10:39 AM
Poita (Peter)
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Has anyone got any shots taken with mono vs OSC with the same total exposure and the same sensor?

Quote:
Originally Posted by gregbradley View Post
But then I'm thinking I have to take image for twice as long with colour camera to get same sensitivity as mono camera with filter.

But for mono I have to take 4 images L, R, G, B. So if I take 1hr per filter I have to image for 4 hours with mono, or 2 hours with colour camera to get equivalent image.

So colour camera is really twice as sensitive for same target. Plus save lot of processing time.

Also colour data on OSC camera comes from exact same time period and sky position and seeing conditions, so data should be more accurate and less detail lose to aligning images taken at different times.

Is my thinking correct?
No that isn't correct. Mono chips are typically nearly twice as sensitive to light as colour is. So the statement 2 hours to get an equivalent image is not correct. It will be in no way equivalent. The mono image will be way less noise, stronger signal, richer and deeper colours and more detail.

You can get great results with one shot colour CCDs. But they require more exposure for the not quite the same result. Typically the problem with one shot colour is noise in the dim areas.

Greg.[/QUOTE]
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Old 24-01-2013, 11:08 AM
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Has anyone got any shots taken with mono vs OSC with the same total exposure and the same sensor?
I don't but I have used both and definitely prefer mono for the quality and speed of the results.

An OSC is really just a mono camera with filters you can't remove. A mono camera with filters can do everything that an OSC can do and it can also take Luminance and do narrowband.
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Old 24-01-2013, 07:52 PM
Ken
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I have used both and had good results with both including imaging with ha filters on OSC cameras. I think if the scope has a focal length over 1200mm and the OSC has fairly small 10 or 12 mp aps size sensor you could bin 2x2 for a luminance channel to speed things up. Of course you can do this with mono as well but normally this is done with the rgb channels. I sold my QHY8 a few years back but would like to try one of the latest cameras as I seem to produce a lot more images per month with the OSC. Another advantage is the cost filter wheel and good filters, also you can have a aps size chip instead of the 8300 size for the same money.
If you wish for full narrowband imaging then osc is the go.
Clear skies Ken.
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Old 24-01-2013, 08:24 PM
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Quote:
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If you wish for full narrowband imaging then osc is the go.
Clear skies Ken.
My thoughts were going to be the exact opposite to this, if only for the flexibility to do narrowband imaging I would go a mono camera. If you strap your HA filter to an OSC camera then you are only going to use 1 out of 4 pixels in the array. I am using a mono camera at the moment If I dropped my image scale to the same as an 8300c with a HA filter ( If I bin my camera it should be the same) I gain even more signal than the standard sensor.
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Old 24-01-2013, 08:39 PM
Ken
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Sorry I must have Brain drain I meant to say mono camera for narrowband imaging.
Clear skies Ken.
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Old 28-01-2013, 07:30 PM
Ken
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Another potential problem with mono and filter wheel is the extra focus travel needed for some setups. Newtonians have limited focus with coma correctors,oag or ao units in use the filter wheel may be the final straw.
Wide field imaging using camera lens can be another problem with filter wheel in place.
Good strong colour in the image is a little harder to achieve in osc but with a fast optical system giving good colour saturation a great image will result.
Clear skies Ken.
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Old 30-01-2013, 06:17 PM
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Another thing to consider is your optics. If your using a RC or Newtonian with only mirrors in the path either camera is fine. However a refractor (low or medium quality) or say a cass with a corrector plate then chromic errors at different wavelengths can focus different colours at different places, so you better off with a mono camera as you can find best focus on each colour and they may be different (mine is).
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Old 31-01-2013, 08:22 AM
Poita (Peter)
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This is the scope I was trying to find, it is f1.44!
A Houghton-Terebizh telescope.

http://www.baader-planetarium.de/tec...300mm_7deg.pdf
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Old 31-01-2013, 05:20 PM
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Quote:
Originally Posted by RickS View Post
...
The disadvantage of a mono camera comes when your imaging run is curtailed by weather or whatever. If you get only 60 minutes of OSC data you might be able to get an image, albeit not a great one. If you get 45 minutes of Luminance and 15 minutes of Red then you don't get anything...
It does not have to be that way

Program your iimage acquisistion and then you can do, say, 10 mins L (not many use subs londer than that) and then 5 mins each of RGB binned 2x2. If you think it will be cloudy do LRGBLRGB etc rather than LLLRRRGGGBBB and you will have useable data after one 25 minute cycle. This assumes you have a parfocal system (reflector and filters) OR you have automated focus. Personally I fond mono with manual focus and FW to be a pita. You can get more sophisticated of course - eg collect yout B and L data with your objective is highest (close to transit) to maximise resolution (minimise seeing effects).

Mono is really the only choice for NB imaging and photometry.

Regards

John
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Old 31-01-2013, 05:33 PM
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It does not have to be that way

Program your iimage acquisistion and then you can do, say, 10 mins L (not many use subs londer than that) and then 5 mins each of RGB binned 2x2. If you think it will be cloudy do LRGBLRGB etc rather than LLLRRRGGGBBB and you will have useable data after one 25 minute cycle. This assumes you have a parfocal system (reflector and filters) OR you have automated focus. Personally I fond mono with manual focus and FW to be a pita. You can get more sophisticated of course - eg collect yout B and L data with your objective is highest (close to transit) to maximise resolution (minimise seeing effects).
That's what I actually do most of the time, apart from a tweak to favour L and B subs when my target is highest. I use preprogrammed filter offsets to adjust focus because my parfocal filters aren't parfocal at f/5
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Old 31-01-2013, 07:19 PM
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Quote:
Originally Posted by originaltrilogy View Post
....
So colour camera is really twice as sensitive for same target. Plus save lot of processing time.

...

Is my thinking correct?
Nope.

BW camera is (in theory) up to 3x as sensitive as colour camera.
There were threads on this earlier, try to do a search, something must pop out.
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Old 01-02-2013, 02:10 PM
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Meru (Michael)
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Another food for thought - do you have a good DSLR Petr? If you do then why not got for a DSLR/Mono CCD combo. Granted it'll never match a cooled CCD but depending on what you're after, it may be 'good enough'

Once in a while you'll see peltier-cooled Canons coming on here for sale, or even through other forums. They might be a good investment
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