Mono vs color

[Nova2000]

Hi 

My question is that what is the difference between a color and mono(sensitivity I know one requires filters) 

What gives better color? 

Which gives less noise? 

What are the advantages? 

[swag72]

Here's my thoughts on the difference between mono and OSC. This is based on nothing more than my experience of using both types

Mono can be used throughout the month regardless of the moon (with NB filters Ha is best) and I have surprised myself last month with how, with planning to try to image away from the moon, you can actually get data that can be made to look OK. A OSC however I found utterly useless when the moon was around at all. To that end it was useless for almost 2 weeks in a month for me. Added to that, you can be your bottom dollar that the clear will be when the moon is about.

Processing of both..... I find the mono much easier to process. The OSC was akin to processing with the devil, I found it hard to control and get it to do what I wanted.

People say that with a mono you can end up with unfinished images..... If you get your run to collect data as L,R,G,B,L,R,G,B then you have a decent change pf getting all the necessary channels in a run. 

Mono for me is just more versatile all round..... Narrowband for example is going to get you much better results with a mono camera. 

Just my thoughts..... When I borrowed my friends colour camera I was all for getting a dual system up and running with a mono on one scope and a OSC on the other....... Suffice to say that after the OSC experience I went for another mono

People will say that they have their place - Sure they do and people get some great pictures from them, but they are not for me. Hopefully you can get a balanced view from both camps. I'd like to say something positive about the OSC that I used and honestly I can't........ There was nothing positive about the experience except showing me that OSC wasn't for me  

[brrttpaul]

I have a OSC (never owned a mono) but saving up for one (the zwo), have to agree the learning curve with the OSC to say its been steep is an understatement (in my view anyway)

[RayD]

This post has some good arguments for both camps, so worth a read.  Suffice to say, the "real" imagers on the forum generally tend to use mono.

[Racey]

And don't forget, as per your question about sensitivity, a similar sized mono is far more sensitive than a OSC as every pixel is registering all photons hitting it. With the Bayer Matrix in a OSC each pixel is assigned to registering a particular "colour" thereby reducing overall sensitivity...

[ronin]

5 minutes ago, Racey said:

And don't forget, as per your question about sensitivity, a similar sized mono is far more sensthan a OSC as every pixel is registering all photons hitting it. With the Bayer Matrix in a OSC each pixel is assigned to registering a particular "colour" thereby reducing overall sensitivity...

Don't think this can be true. The idea of mono is to select the wavelength by applying suitable filters. So if you apply an Ha filter then the sensor cannot receive say the OIII line, so not all photons are getting to the sensor, so not all photons, only those allowed through. This could be a small amount only as even with Ha the other red wavelengths are blocked. It is no use having a green photon registering as a red one.

On an OSC you have a Bayer Matrix so assuming the pixels are evenly split, they are not, only 1/3 registers Red, 1/3 registers Green. 1/3 registers Blue. So in mono all pixels are used but the registered wavelength is dependant of the filters applied. One hint is the name "narrow band". So not lots of photons just a narrow band of them.

The advantage of the OSC is time. You head out and get say 30 exposures, head home and start processing. With mono you are likely to want to get say 20 at red, 20 at green and 20 at blue. With the changing of filters, the extra equipment and a possible change in focus. But with mono you can expect a more detailed final result.

At advanced an object may need 10 hours of exposures, that means multiple nights usually. Some people have taken half the exposure one year then completed the next.

So a consideration is the time available to you. If you sort of manage once a month and not a chance of much more then you likely want to grab what you can when you can. If you are in town then narrow band is better for the overall light pollution, or if you have the time for mono then you should get a better final result.

 

[Nova2000]

Hi. I stay in a city with orange skies. Does this mean if I use a mono camera with a h alpha filter the light pollution won't affect me? Or do I have to use a lp filter also? Mono seems interesting to me. 

56 minutes ago, swag72 said:

Here's my thoughts on the difference between mono and OSC. This is based on nothing more than my experience of using both types

Mono can be used throughout the month regardless of the moon (with NB filters Ha is best) and I have surprised myself last month with how, with planning to try to image away from the moon, you can actually get data that can be made to look OK. A OSC however I found utterly useless when the moon was around at all. To that end it was useless for almost 2 weeks in a month for me. Added to that, you can be your bottom dollar that the clear will be when the moon is about.

Processing of both..... I find the mono much easier to process. The OSC was akin to processing with the devil, I found it hard to control and get it to do what I wanted.

People say that with a mono you can end up with unfinished images..... If you get your run to collect data as L,R,G,B,L,R,G,B then you have a decent change pf getting all the necessary channels in a run. 

Mono for me is just more versatile all round..... Narrowband for example is going to get you much better results with a mono camera. 

Just my thoughts..... When I borrowed my friends colour camera I was all for getting a dual system up and running with a mono on one scope and a OSC on the other....... Suffice to say that after the OSC experience I went for another mono

People will say that they have their place - Sure they do and people get some great pictures from them, but they are not for me. Hopefully you can get a balanced view from both camps. I'd like to say something positive about the OSC that I used and honestly I can't........ There was nothing positive about the experience except showing me that OSC wasn't for me  

 

13 minutes ago, ronin said:

Don't think this can be true. The idea of mono is to select the wavelength by applying suitable filters. So if you apply an Ha filter then the sensor cannot receive say the OIII line, so not all photons are getting to the sensor, so not all photons, only those allowed through. This could be a small amount only as even with Ha the other red wavelengths are blocked. It is no use having a green photon registering as a red one.

On an OSC you have a Bayer Matrix so assuming the pixels are evenly split, they are not, only 1/3 registers Red, 1/3 registers Green. 1/3 registers Blue. So in mono all pixels are used but the registered wavelength is dependant of the filters applied. One hint is the name "narrow band". So not lots of photons just a narrow band of them.

The advantage of the OSC is time. You head out and get say 30 exposures, head home and start processing. With mono you are likely to want to get say 20 at red, 20 at green and 20 at blue. With the changing of filters, the extra equipment and a possible change in focus. But with mono you can expect a more detailed final result.

At advanced an object may need 10 hours of exposures, that means multiple nights usually. Some people have taken half the exposure one year then completed the next.

So a consideration is the time available to you. If you sort of manage once a month and not a chance of much more then you likely want to grab what you can when you can. If you are in town then narrow band is better for the overall light pollution, or if you have the time for mono then you should get a better final result.

 

OK so the basic filters are luminous, green, red, blue, H2 and o3? Any more? 

[ollypenrice]

53 minutes ago, ronin said:

Don't think this can be true.

 

It is true - during the luminance part of the shoot. That is precisely why mono is faster. An OSC can only take colour so none of its pixels can ever record more than a third of the available light. (Nova2000, all CCD cameras use filters. In an OSC they are just fixed in place over each pixel in a Bayer Matrix of RGGB in a repeating pattern.) So in a 4 hour shoot an OSC captures 4x1/3 of the light so let's call that '4 units of light.' In an LRGB shoot with a mono you get 3x1/3 in the three hours of colour collection and then 3x1/3 in the luminance hour. (A luminance filter passes all three colours at once but can't distinguish between them.) This totals '6 units of light' so the light grasp of the mono camera is better by 6 to 4. Now suppose you make that a 5 hour shoot and do an hour per colour and two hours luminance in the mono. Then the ratio goes to 5 units of light for the OSC and 9 units of light for the mono. That is a massive increase in camera light grasp. It is the main reason why mono is so much faster.

OSC has another shortcoming because the Bayer matrix has twice as many green filters as red or blue. In the daytime, capturing reflected daylight, the green makes an effective luminance layer. But in astronomy more green is the last thing you want! It does not make an effective luminance layer because targets tend to be dominated by either red emission or blue reflection. At least two astro image processing tools are designed to get rid of unwanted green!

And then, as Sara says, you can use an Ha filter effectively in the moon. An Ha filter can only be 25% efficient in an OSC camera bacause only the red filters pass the light.

The loss of resolution with OSC is minimal though. The software which debayers the data is very good at interpolating missing real information.

Olly

[Racey]

1 hour ago, ollypenrice said:

It is true - during the luminance part of the shoot. That is precisely why mono is faster. An OSC can only take colour so none of its pixels can ever record more than a third of the available light. (Nova2000, all CCD cameras use filters. In an OSC they are just fixed in place over each pixel in a Bayer Matrix of RGGB in a repeating pattern.) So in a 4 hour shoot an OSC captures 4x1/3 of the light so let's call that '4 units of light.' In an LRGB shoot with a mono you get 3x1/3 in the three hours of colour collection and then 3x1/3 in the luminance hour. (A luminance filter passes all three colours at once but can't distinguish between them.) This totals '6 units of light' so the light grasp of the mono camera is better by 6 to 4. Now suppose you make that a 5 hour shoot and do an hour per colour and two hours luminance in the mono. Then the ratio goes to 5 units of light for the OSC and 9 units of light for the mono. That is a massive increase in camera light grasp. It is the main reason why mono is so much faster.

OSC has another shortcoming because the Bayer matrix has twice as many green filters as red or blue. In the daytime, capturing reflected daylight, the green makes an effective luminance layer. But in astronomy more green is the last thing you want! It does not make an effective luminance layer because targets tend to be dominated by either red emission or blue reflection. At least two astro image processing tools are designed to get rid of unwanted green!

And then, as Sara says, you can use an Ha filter effectively in the moon. An Ha filter can only be 25% efficient in an OSC camera bacause only the red filters pass the light.

The loss of resolution with OSC is minimal though. The software which debayers the data is very good at interpolating missing real information.

Olly

Thanks for confirmation Olly. OP asked about sensitivity in part of his question. Had done a tremendous amount of reading before electing which route to go with guide and imaging cameras. Every article said mono is more sensitive and consequently, despite the need to expose via RGB and maybe L, imaging times end up similar...  Glad to know on only post 15 I didn't commit a "schoolboy" !! :-)

[ollypenrice]

3 minutes ago, Racey said:

Thanks for confirmation Olly. OP asked about sensitivity in part of his question. Had done a tremendous amount of reading before electing which route to go with guide and imaging cameras. Every article said mono is more sensitive and consequently, despite the need to expose via RGB and maybe L, imaging times end up similar...  Glad to know on only post 15 I didn't commit a "schoolboy" !! :-)

You didn't. Remember than an OSC camera is imaging in RGB as well. The real difference is that a mono can shoot without the RGB filters and an OSC can't. In an effort to demonstrate the speed of mono camera imaging I posted this two hour Heart Nebula in HaRGB a while ago. Two hours at F5, no fancy processing.

Olly

 

[Racey]

1 minute ago, ollypenrice said:

You didn't. Remember than an OSC camera is imaging in RGB as well. The real difference is that a mono can shoot without the RGB filters and an OSC can't. In an effort to demonstrate the speed of mono camera imaging I posted this two hour Heart Nebula in HaRGB a while ago. Two hours at F5, no fancy processing.

Olly

 

I remember seeing that and the associated discussion / comparison...

However one thing i may take issue with (diplomatically of course) is to highlight that one man's "no fancy processing" is something another might one day aspire to having had a crack at your Cave nebula project recently !! ;-) 

[ollypenrice]

4 minutes ago, Racey said:

I remember seeing that and the associated discussion / comparison...

However one thing i may take issue with (diplomatically of course) is to highlight that one man's "no fancy processing" is something another might one day aspire to having had a crack at your Cave nebula project recently !! ;-) 

Sure, but the Cave did require fancy processing, as anything dusty always will. It was a difficult target. In the image above I just used a Curves stretch for the Ha, a log stretch for the RGB and added the Ha to red in blend mode lighten. I did the whole thing in an hour or so. I wanted to keep to the spirit of the demonstration which was aimed at the relative beginner.

Olly

[Nova2000]

3 minutes ago, ollypenrice said:

Sure, but the Cave did require fancy processing, as anything dusty always will. It was a difficult target. In the image above I just used a Curves stretch for the Ha, a log stretch for the RGB and added the Ha to red in blend mode lighten. I did the whole thing in an hour or so. I wanted to keep to the spirit of the demonstration which was aimed at the relative beginner.

Olly

What kind of filters are needed for dusty nebula and reflection nebula? 

[ollypenrice]

Just now, Nova2000 said:

What kind of filters are needed for dusty nebula and reflection nebula? 

LRGB. The key problem with dust is that it's dark, so it doesn't easily record any signal strong enough to rise above the noise floor. It isn't particularly colourful, though, which is a help because it means you can shoot a lot of luminance relative the amount of colour you shoot. It is easier to process an image if you shoot equal amounts of LRGB but for the faint stuff there is a lot to be said for exploiting the L filter for longer. You then have to be careful not to stretch it too hard in the brighter parts or the colour will become very washed out or overly diluted-looking. The trick is to use a stretch in luminance which pulls out the dust at the darker end of the scale while not overdoing the middle and higher brightnesses. You can find out about this by experimenting with different curves designed to optimize different parts of the image. It isn't difficult once you have some data to play with.

You can also add strong L to weaker colour in partial iterations. Between each iteration you slightly increase the saturation and gently noise reduce the resulting image before adding a little more L to it each time. In the final iteration you don't do the noise reduction so you restore all the original lum sharpness. It soon becomes second nature.

Olly

[geordie85]

28 minutes ago, ollypenrice said:

LRGB. The key problem with dust is that it's dark, so it doesn't easily record any signal strong enough to rise above the noise floor. It isn't particularly colourful, though, which is a help because it means you can shoot a lot of luminance relative the amount of colour you shoot. It is easier to process an image if you shoot equal amounts of LRGB but for the faint stuff there is a lot to be said for exploiting the L filter for longer. You then have to be careful not to stretch it too hard in the brighter parts or the colour will become very washed out or overly diluted-looking. The trick is to use a stretch in luminance which pulls out the dust at the darker end of the scale while not overdoing the middle and higher brightnesses. You can find out about this by experimenting with different curves designed to optimize different parts of the image. It isn't difficult once you have some data to play with.

You can also add strong L to weaker colour in partial iterations. Between each iteration you slightly increase the saturation and gently noise reduce the resulting image before adding a little more L to it each time. In the final iteration you don't do the noise reduction so you restore all the original lum sharpness. It soon becomes second nature.

Olly

Have you ever thought about doing a tutorial video on advanced Photoshop processing?

Or maybe know of some good (easy to understand) tutorials that you can point me in the direction of?

[Nova2000]

Olly , will a lp filter work as a luminance filter? 

[swag72]

2 minutes ago, Nova2000 said:

Olly , will a lp filter work as a luminance filter? 

Sure will - I use a Hutech IDAS LP filter as my luminance......

.... sorry I jumped in there and I'm not Olly  But I was reading at the time so answered  

[Nova2000]

5 minutes ago, swag72 said:

Sure will - I use a Hutech IDAS LP filter as my luminance......

.... sorry I jumped in there and I'm not Olly  But I was reading at the time so answered  

[Nova2000]

Haha no problem Swag72. 

[ollypenrice]

31 minutes ago, swag72 said:

Sure will - I use a Hutech IDAS LP filter as my luminance......

.... sorry I jumped in there and I'm not Olly  But I was reading at the time so answered  

Go ahead, Sara because, for one thing, you knew the answer and I didn't! I've heard of this light pollution stuff but I can't say I like the sound of it...  (Well, OK, we sometimes get a bit of infra-red from the sheep on the distant hillside...)

45 minutes ago, geordie85 said:

Have you ever thought about doing a tutorial video on advanced Photoshop processing?

Or maybe know of some good (easy to understand) tutorials that you can point me in the direction of?

I haven't done any but there are excellent tutorials available. You won't go wrong if you follow anything by Adam Block or Warren Keller, for instance. Warren has courses for PS and PI.  I do lots of one-to-one tutorials here though. I try to keep my processing as simple as possible. If there's one key skill in processing I believe it's learning to look critically at a developing picture to see where it's going right and where it's going wrong. That's the number one thing, to look at the picture. It may sound obvious but it's true. (It's like the secret of passing exams. The secret is to answer the question. What the examiners say, year after year, is that the candidates answered slightly different questions to the ones they were asked...)

Olly

[swag72]

2 minutes ago, ollypenrice said:

...........I've heard of this light pollution stuff but I can't say I like the sound of it...  (Well, OK, we sometimes get a bit of infra-red from the sheep on the distant hillside...)

Oh you poor thing  How do you cope?  

[cjdawson]

Just want to weigh in with a slightly different thought....

For a colour image, you capture all the colours at the same time.  However, this means that you have to focus all colours at the same time.  As most scopes have some chromatic aboration, to a greater or lesser extent, it does mean that you have to find an average focal point for all colours in the bayer matrix.

When shooting in mono, you capture only one colour at a time, this means that you can focus the scope for blue colours, which are all similar wavelengths. So you will have the ability to get a sharper focus .

[RayD]

10 minutes ago, cjdawson said:

Just want to weigh in with a slightly different thought....

For a colour image, you capture all the colours at the same time.  However, this means that you have to focus all colours at the same time.  As most scopes have some chromatic aboration, to a greater or lesser extent, it does mean that you have to find an average focal point for all colours in the bayer matrix.

When shooting in mono, you capture only one colour at a time, this means that you can focus the scope for blue colours, which are all similar wavelengths. So you will have the ability to get a sharper focus .

I would have thought the "filters" used on the Bayer matrix would be par focal? I don't know this but assume that would make sense.  I know my Baader LRGB say they are so there is no need to refocus between filters, and the only time I really need to refocus is if I start on NB, or due to temperature change. 

[Nova2000]

In ccd camera. Lower the temperature less the noise? 

[cjdawson]

2 hours ago, RayD said:

I would have thought the "filters" used on the Bayer matrix would be par focal? I don't know this but assume that would make sense.  I know my Baader LRGB say they are so there is no need to refocus between filters, and the only time I really need to refocus is if I start on NB, or due to temperature change. 

The filters on the bayer matrix are par focal.  However, depending on the scope that the camera is attached to, you can get issues with the focal plane being in different places for different colours.  It can be mitigated by using Aprochromatic optics, which will mitigate the issue, but it won't completely resolve it for all wavelengths of light.

Using a mono camera and applying a filter for just the colour that you are imaging, means that you can focus the telescope for the specific wavelengths that you are interested it, so the mitigation that Aprochromatic scopes do isn't required.  This means that the optics of the telescope can be simpler, cheaper to produce and at the same time by having fewer surfaces means that you will have fewer reflection opportunities without the optical path.   All of this happens before hitting the colour filter, or bayer matrix.