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Old 23-04-2010, 05:50 PM
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Mono v Colour Image Processing Question

Hi All

I have been pondering the purchase of a CCD for some time now. I only have one last issue to resolve - mono or osc. On this, I have a question that I was hoping to get answered here.

I have been using my EOS400 for deepsky objects and my dmk21 and QHY5 for planetary. I am comfortable with taking sequences in L,R,G, then B then combining for my planetary shots.

My question is, how much different is combining the four channels for a deepsky object from doing the combining for a planetary? Is the process essentially the same? Is it much more difficult to get the alignment right? If I can do it okay on a planetary, does that suggest I should have no trouble for a DSO?

I am leaning towards a mono.

Thanks
Darrell
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Old 23-04-2010, 05:56 PM
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multiweb (Marc)
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It's not much different but are you ready to spend 4h to take 1h of Lum, 1h of red, 1h of blue and 1h of green or would you rather take 1h with an OSC? Or even have 4h with an OSC in the same time?
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Old 23-04-2010, 06:04 PM
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Quote:
Originally Posted by multiweb View Post
It's not much different but are you ready to spend 4h to take 1h of Lum, 1h of red, 1h of blue and 1h of green or would you rather take 1h with an OSC? Or even have 4h with an OSC in the same time?
Marc please it is not like that and maybe you know it.

You can take 1 hour of luminance and say 20 minutes each on 2x binning for the RGB pic and get a very nice result.
The rgb is only there to get the color in the picture and can be made noise free with blurring etc.

Darrel it is the same as for the qhy5 so go ahead and get a mono ccd
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Old 23-04-2010, 06:07 PM
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mswhin63 (Malcolm)
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I must admit I have no practical experience on this only theoretical experience and sort of confirmed why they still make mono cameras in the first place.

I suspect with colour cameras the preciseness of the colour pixels in the camera would vary based on the filtering of RGB for each pixel where with mono each pixel of exposure is identical for each colour with only variation being the filter which can be easily resolved with software.

Each pixel filter in colour cameras would need to be exactly same throughout and manfacturing process's may not be that tight.

I believe there may be some cameras that use 4 seperate sensors to resolve this and maybe used in space scopes.
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Old 23-04-2010, 09:26 PM
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Yes Marc, its not that simple and you know it.

You get a far better result even for the same total exposure time (binning colour), and more res, and more QE and more.....

Darrel, combining seperate filtered images is easier than you think and becomes second nature after a while. Astro software does it in a few mouse clicks, and in PS its also a no brainer.

In the end you will end up with a mono cam anyway, its a given, so might as well start now and avoid wareing out the training wheels.
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Old 23-04-2010, 09:33 PM
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Guys

Thanks for the comments. Mono it is. I have also got myself a copy of "Photoshop Astronomy" (Scott Ireland). I figure this is where I now need to start learning.

Darrell
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Old 23-04-2010, 09:47 PM
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Yes Marc, its not that simple and you know it.
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Marc please it is not like that and maybe you know it.
Sorry guys. Don't misunderstand me. I'm not bagging mono. Mono's fine if you have the patience to do each channels separately. OSC is way easier from a practical point of view especially if you have a mobile set-up.
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Old 23-04-2010, 10:07 PM
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It is true that OSC would be easier, it really depends to what degree you images will end up. I kinda think OSC CCD element design is improving so it may be in a practical sense negligable. I was hoping someone might know on a practicle level the difference as technical techies can be a bit over the top
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Old 23-04-2010, 10:19 PM
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Originally Posted by mswhin63 View Post
It is true that OSC would be easier, it really depends to what degree you images will end up. I kinda think OSC CCD element design is improving so it may be in a practical sense negligable. I was hoping someone might know on a practicle level the difference as technical techies can be a bit over the top
Well I was looking purely from a practical level. Darrel has experience in planetary RGB which is different. He also used a DSLR which is OSC. For DSO you do need to put in the time in subs to get the data. If he has a semi permanent set-up then yeah go mono all the way. As Fred and others pointed out, better QE & resolution (no doubt, there's no bayer matrix). Now I use a QHY8 and I did dabble a bit in narrowband. For me and I stress for me it is a real pain. I don't use a filter wheel and I'm always on the go. That's why I can't see myself having the time or patience to use a mono. I wouldn't complete anything. May be when I retire and get and Obs
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Old 23-04-2010, 11:07 PM
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Marc if you use the autosave routines MaximDL mono requires very little patience. Get it all set and go and have a beer.

Mark
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Old 23-04-2010, 11:14 PM
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Marc if you use the autosave routines MaximDL mono requires very little patience. Get it all set and go and have a beer.

Mark
I know Maxim is smart and will detect Lum, R, G & B in your subs and does a very good job at organising all this but as far as acquisition goes I don't use a filter wheel. I should rephrase and replace "patience" by "time". I spend litterally days processing but only hours capturing data. I like to keep it simple. I have my little routine all set now. Mono's not for me. Sorry. Not yet.
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Old 23-04-2010, 11:45 PM
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. I spend litterally days processing but only hours capturing data. I like to keep it simple. I have my little routine all set now. Mono's not for me. Sorry. Not yet.
No need to apologise, I am the exact opposite . I use my time to image and can't be bothered spending more then 15 minutes processing. When I had my QHY8 and DSLR I found I had to take more shots to get the results I wanted where the mono gets that detail very quickly so less work at the mount. The mono is also easier to process as the shots are smoother to start with. Calibrating and stacking the subs only takes a couple of minutes so that gives me 13 minutes to do the rest . By the way that link you posted for the green removal tool for PS was great. My last 5 pics got the treatment and it only took a minute to do.

Mark
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Old 24-04-2010, 02:54 AM
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darrellx (Darrell)
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Marc

You mention "if I have a semi permanent set-up, then yeh go mono". I do actualy have two piers setup - one in the front yard on the Gold Coast and one at my dark sky site near Warwick. I suppose you are meaning that it will save time in setting up etc. Therefore have more time to do the imaging - nothing else.

I am also a bit curious about your dabble in narrowband. Some time in the future, this is where I would like to head. What was your main reason for not continuing? Time?

Thanks
Darrell
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Old 24-04-2010, 02:01 PM
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I suppose you are meaning that it will save time in setting up etc.
If you're shooting different channels with mono you ideally will need a filter wheel. You also might not have the time to shoot all the channels in one night. so if you have a pier and leave the scope on it, it will greatly help because you can match your subs back to where you left them. These are things to be aware of.

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I am also a bit curious about your dabble in narrowband. Some time in the future, this is where I would like to head. What was your main reason for not continuing? Time?
Oh no, I'm still doing it. What I meant is that this alone gave me a taste of what mono feels like because I have to use filters, so I will shoot Ha one night, then Oiii another night, then Sii (eventually) and it's all very time consuming and 'touch n' go' with the weather of late. So I find it really refreshing when I go on a dark site and plonk the camera and shoot RGB all night not having to worry about channels and complete everything righ there on the spot.

That's all. That's where I'm coming from. Mono's not for me. I don't want to put you off. Just a few facts.
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Old 24-04-2010, 04:00 PM
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Another point is if you ever want to do anything other than take pretty pics with your camera.
A mono camera is much more sensitive and can be used for photometry/SN searches etc compared to a OSC camera.
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Old 24-04-2010, 04:18 PM
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For me I would probably lean towards the OSC CCD. Currently, I'm quite happy with my set up (not that it's brilliant, but it will do ). I have a mobile rig and just love throwing the gear out into the back yard, cabling up and pressing go. The only thing that is bugging me with imaging at the moment is the temp of the sensor on the DSLR, summer time was a nightmare and winter really isn't all that much better. If I could swap the 350D out for a cooled CCD I'd be quite happy

Darrell, I say if you are leaning towards a mono CCD then go for it Like what some of the others are recommending, we will all end up doing LRGB with mono chips eventually, so if you are keen you may as well start now
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Old 24-04-2010, 04:26 PM
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Quote:
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If you're shooting different channels with mono you ideally will need a filter wheel. You also might not have the time to shoot all the channels in one night. so if you have a pier and leave the scope on it, it will greatly help because you can match your subs back to where you left them. These are things to be aware of.
If you are like me, you will only shoot one or two objects a night.
With programs like maxdl etc,your filter wheel will first shoot one L then a R then G and then B and so it goes on, this means that ALL channels will be shot.
The only thing with blue is that it is not as sensitive so i just make the blue exposure a bit longer than the R and G. (simple ).

When i moved from DSLR to a mono QHY9 it was an eye-opener for me because of the added detail in the pictures especially in the L channel and HA, as i have said before, the color channel can be and has to be made as noise free as possible and it can even look a bit blurred and because of the L channel (that provides the resolution and sharpness) the picture looks good.
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Old 24-04-2010, 06:57 PM
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I always try to catch red, Ha and green while the object is lower then blue before the pier flip and Lum after the flip. I set Maxim to complete all subs (usually about 6 x 10min) in one channel before moving to the next. This way I get a complete set each night. If I want more data I just repeat the exercise the following night.

Mark
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Old 25-04-2010, 07:23 AM
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There is a lot of hype about the difference between OSC and Mono CCD's but from my experience a lot of it is purely hype. If you choose to go down the OSC road you wont be dissappointed. When you look at the time differences in imaging with one against the other, processing one compared to the other and the overall end results with all being equal there is not an awfull lot in it.
Dietmar Hager did a comparison and has posted it on his website and here on IIS which gives some insights into these supposed differences. Well worth the read.
http://www.iceinspace.com.au/63-460-0-0-1-0.html
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Old 25-04-2010, 08:51 AM
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Dietmar Hager did a comparison and has posted it on his website and here on IIS which gives some insights into these supposed differences. Well worth the read.
http://www.iceinspace.com.au/63-460-0-0-1-0.html
Go Douggie! Yeah I completely forgot about this article. Great read.

Although it is true that if your camera has "big pixels" like the QHY8 (7.8um) debayering will have an impact on your resolution but I can live with it. As Terry pointed out I'm happy with doing "pretty pictures" (or trying to anyway). That's all I'm doing. The spot healing brush is my best friend and there is absolutely no scientific value in pictures I try to present.

There is not doubt that a mono QHY9 Lum will look better than a QHY8 debayer to grayscale so Martin has a very valid point and I do believe coming from a DSLR it must have been a revelation when he saw his first Lum. Here's an example of one sub 1:1 with a bayer matrix then the red channel only, then the two greens combined, then the blue. The bayer matrix is as follow:

RG
GB

So the two greens get combined and the resulting green shows better details than the 1x red or the 1x blue that are interpolated back to the full resolution of the sensor (3000x2100), which is why they appear slightly blurry. Also at this image scale (close to 3asp) you can clearly see the red, green and blue light deviate and don't end-up in the same pixels. Not an issue at higher sampling (as Dietmar mentioned).

Having said that the picture is zoomed 200% so the pixels shown in the bayer matrix appears x2 magnified on your screen. Apply a slight deconv, reduce the original from 3000px x 2100px down to let's say 1280px or even 1500px wide pic for presentation and you'd have a nice shot and be hard pressed to see a major difference IMO. So it does the job basically at a fraction of the time.
Attached Thumbnails
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Last edited by multiweb; 25-04-2010 at 10:18 AM. Reason: spelling - clarification
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