Time spent shooting mono vs colour

[Andrew Singleton]

I am potentially lucky enough to be in a position soon to buy a dedicated CMOS astronomy camera and think I have my mind set on a mono camera, an electronic filter wheel, a full set of filters and an electronic focuser. Opportunities to do astrophotography are sparse.

I am addicted to watching YouTube videos and one thing that keeps making me doubt my choice is astrobackyards Trevor Jones, his one shot colour cameras, and him telling us that this type of astrophotography is much quicker than a mono setup and much better when opportunities are sparse. He is very persuasive but I cant help but think that it might be a closer call than he is making out. Here is my thinking.

 

1. The colour cameras have the Bayer layer RGGB so for red and blue you are getting 25% protons and for green you are getting 50% protons. Lets say I image for 75 minutes using a colour camera and 75 minutes using a mono camera and filters, surely I’m pretty much getting the same amount of data, surely I’m getting an even amount of data for every filter and surely if I wanted to change these percentages it in my will to do so.
2. I get that luminance is debatably needed and that I  may need to spend more time on this.
3. Trevor seem to do a lot manual work, so can imagine that when he switches from colour to colour it takes time to switch the filter and refocus. With an electronic filter wheel and electronic focuser I am imagining that this can’t take that long. Perhaps I have underestimate the work needed here. 
4. The quantum efficiency of the mono camera is more than the OSC. Perhaps this is time gained for the mono lost to my points in 2 and 3 above.
5. He has fancy duel band and even quad band filters that he uses in his videos. These do look attractive but surely my points above of RGGB vs specific filters still apply. He is essentially putting 2 filters on blocking light and then a similar percentages of protons are getting through because they have to get through the RGGB layer too.
6. In terms of processing time, let’s face it, in Manchester I am not short on processing time. I love processing, I love the idea of having the flexibility of all these different filters to play with and to see how the different results can come out.  I completely agree that RGGB would be easier and quicker to process, I do it now with my D3100, but for me this represents no progress in my hobby and less of the fun putting it all together.

 

As you can see I have thought a lot about this, but there is still that niggle, the guy is so passionate about his choice that could he be right? What are other peoples thoughts on this? Given the points I’ve made are there any glaring misunderstandings I have relayed here? Id love for someone to constructively argue against or for the points I have made. I'd love to hear about other factors that I might be missing. 

Thanks in advance and sorry if this is an over-talked about topic in these walls, I have read up on this topic over and over again but wanted to get all my thoughts in one place.

 

P.S. We live in a golden age of youtube, Trevor’s videos are fantastic (apart from the bits at the end that make me cringe, silence follow by epic music and his results!), galactic hunters videos seem really good (perhaps the cutest geeky couple there is!), I like the toned down style of Ed Ting,  Cuiv the geek is good especially getting results in the middle of the city, Dylan O’Donnell come across as the most funny/intelligent of all the regulars and perhaps the most helpful informative video was Robin Glovers lecture which progressed my understanding of this hobby in leaps and bounds.

Edited December 8, 2020 by Andrew Singleton

[pete_l]

People generally promote the equipment they have bought. So if a person has purchased (not been given free for review) a mono camera, they will tell you how great that is. If they invested in a colour camera, they will do the same. It they got it for review (i.e. advertising) purposes then it will be "glowing" no matter what it is

While there are lots of people who can give you chapter and verse on the theory of why one sort is better than another, the only real test that is worth anything is to look at images. Look at examples (e.g. on Astrobin) and see if you can tell - without looking at the description - which RGB images were taken with a colour camera and which with a mono + filters.

Then make up your own mind, based on the evidence you have seen for yourself.

Edited December 8, 2020 by pete_l

[Andrew Singleton]

Thanks, in my understanding of quality I am pretty convinced that mono is the superior. I do really like that idea about looking at peoples photos and guessing the equipment used, I'll perhaps look at that tonight. 

My primary thinking at the moment is to do with time saved in the field(garden) using that OSC and is it really that much of a time saver. 

[happy-kat]

I think the weather thing is down to if you only get 30 minutes clear and you use osc you get something to process, whereas if using mono with filter it is 30 minutes of what ever filter you had in but no more until another opportunity.

Personally I love mono b/w images

Edited December 8, 2020 by happy-kat

[geordie85]

I've used both OSC and mono versions of the qhy183. A trade ad came about that wanted a straight swap for a zwo 183 mono.

I now have 2 mono cameras. For me as I live in bortle 6 location then mono is better as I have the opportunity of pure narrowband imaging when the moon is about. Plus my filters are pretty good at reducing the effects of light pollution.

Yes Trevor does seem passionate and gets to review alot of equipment, but would his reviews be the same if he had to buy all of the equipment he reviews? Personally I don't think they would. 

There is also a good chance that suppliers know this equipment is going out for review so they ensure the equipment is perfectly functional.

I recently posted an image in the "imaging with Samyang 135" thread that was taken in less than an hour. The OSC camera could never have got the same results in the same time, from my location.

[Andrew Singleton]

@happy-kat I like the idea of getting some b/w pics as well, I think it will help with my understanding of what these objects are made off. I think the forecast would have to have at least 2 hours predicted for me to get out, If I found the filter wheel fast enough maybe I could switch every 15 mins, I dont know.

[Andrew Singleton]

@geordie85  I really like your seven sisters pic, its just the sort of example I was looking for in fact. Good to see something done in an hour and perhaps confirms my thoughts. 

I think you might be right about the reviews being different if he were buying himself. When its his livelihood at stake I wonder who is the customer, us the viewer or the person providing him with these camera's and essentially advertising, 

I spent 10 years of my life in Newcastle. When I went visiting friends recently I went out past Corbridge, the darks skies are fantastic. 

[vlaiv]

Simple fact is that mono + LRGB is faster - in terms of achieved SNR in the same amount of time.

Mind you - it is not much faster. Difference between the two comes down to:

1. Interference filters have higher QE than absorption filters used in Bayer matrix

2. Time spent on G channel with OSC will be spent on L channel with mono +LRGB

L captures more signal per unit time than G simply because it is wider band filter.

Imagine you image with OSC for one 4 hours. Each of R, G, G and B pixels of Bayer matrix get 25% of light, so we can argue that each R, G, G and B get one hour of imaging time (25% of 4 hours).

With mono + LRGB - in 4 hours, if you spend one hour per each filter R, G and B will get the same time as OSC R, G and B, while L will get the same time as remaining G from Bayer matrix. Here you have edge in L filter.

Mono has other advantages - like ability to vary filter contribution. One might decide to do half an hour in RGB and remaining 2.5h in L. Human eye/brain system is more sensitive to noise in luminance than in color information so spending more time on L makes sense.

Narrowband filters use is another advantage.

Drawback is time spent on filter change / refocusing (very small percent of time since, especially with stepper focuser as you can memorize focus shift needed when changing filters, so refocus is just moving remembered offset).

Each filter requires its own flat - additional time spent if you don't have permanent setup and shoot flats on regular basis.

OSC has one more advantage. If you get interrupted mid session - you still have complete data to work with. In order to achieve that with mono+filters, you should really "cycle" filters after each exposure, but refocusing and filter switch time would increase greatly.

 

[smr]

OSCs might have the Bayer Filter but they're getting better and better all the time. Kind of does depend on your skies though I think. If I was in Bortle 8 I don't think I would be thinking about OSC.

[Andrew Singleton]

@vlaiv Arr yes, the flats are going to need to be considered. I dont have a permanent setup but I do plan on keeping the camera connected to the telescope so hoping I can get away with shooting flats semi-regularly. Its all well and go until I have to turn the camera 90 degrees to frame the photo. I must admit, with my DSLR I take flats after every session. With mono and multiple filters would you need to take red flats, refocus, take blue flat, refocus, take green flats, etc? That would be a major pain at 3am! I guess you could just do flats before switching to another filter. 

If time was short I was thinking of doing perhaps 15 mins at a time and cycling through, another thing I'm hoping to take advantage of is live stackibng.

Thanks for your detailed responce.

[vlaiv]

1 minute ago, Andrew Singleton said:

That would be a major pain at 3am! I guess you could just do flats before switching to another filter. 

I guess most convenient way is to do it after / before filter change.

For example - you start with Luminance, then after you finish - setup flat panel, do flats, switch filter and if you have motor focuser offset dialed in - just refocus without checking on stars and do another flat for that filter. On next filter change do nothing and then do one more flat session between last filter change (this assumes 4 filters / LRGB and having motor focuser and dialed in offsets).

If you need to refocus on stars - then you need to take flats after you finish with that filter for the night.

[Andrew Singleton]

@smr Yes I'm up against it in bortle 8, I have managed to get some decent (for me!) photos though, its the colour that seems to be the most challenging in post processing. Hopfully the mono with filters will help with that. 

[geordie85]

40 minutes ago, Andrew Singleton said:

@vlaiv Arr yes, the flats are going to need to be considered. I dont have a permanent setup but I do plan on keeping the camera connected to the telescope so hoping I can get away with shooting flats semi-regularly. Its all well and go until I have to turn the camera 90 degrees to frame the photo. I must admit, with my DSLR I take flats after every session. With mono and multiple filters would you need to take red flats, refocus, take blue flat, refocus, take green flats, etc? That would be a major pain at 3am! I guess you could just do flats before switching to another filter. 

If time was short I was thinking of doing perhaps 15 mins at a time and cycling through, another thing I'm hoping to take advantage of is live stackibng.

Thanks for your detailed responce.

Personally I don't think flats are needed for every filter. I've always only taken flats through my luminance filter and I've never had and problems with them not working. I don't have a permanent setup so I have to build up and take down every session, but I do always leave the imaging train alone.

My cameras are always connected to my scopes and I move them independently of the mount.

With regards to framing, couldn't you just rotate your OTA inside the tube rings? I know it's not ideal but may be a better option than constantly taking flats and trying to remember which flats go with which lights.

[Andrew Singleton]

2 hours ago, geordie85 said:

Personally I don't think flats are needed for every filter

Another thing I have heard from by people in these forums is that for the most light polluted areas perhaps just doing RGB or HaRGB instead of LRGB. I wonder if in these projects they took flats too. 

Personally, if I go mono, I will want to make my own mind up on whether to include L or not. I'm keen on following Robin Glovers advice doing super short subs and live stacking. 

I guess once you go down the mono route the possibilities and experimentation are endless! Another reason to go mono actually in my opinion. 

[Whirlwind]

In perfect conditions mono will always be faster because of the reasons above.  However, in the UK conditions are far from perfect.  With a colour camera even if you get an imaging run of an hour you have all the data you need for a colour photo.  With mono you can find that you have the R and G but clouds affected the B so you can end up with a partial image.  As such sequencing is important in the UK so that you run L-L-L-R-G-B set of images.  However, for a lot of set ups you might find you want to refocus per filter which adds more time setting up.  

With colour cameras you also can utilise some of the very fast RASA telescopes on the market that aren't particularly suited to mono imaging.  However their large apertures/short focal length matched with an appropriate colour camera can then offset the reduced sensitivity.

However you are correct that mono does give you more flexibility but these can be worked around to some extent.  You can still use narrowband filters (or dual band filters) to get the Ha for a HaRGB.  You can still use software to extract the Luminance from a colour image etc.

Hence it largely depends on how you see your hobby progressing in the long term.

I have mono cameras because I prefer imaging nebulae over galaxies or clusters for example which was one my prime drivers for which style to go for.

 

[tooth_dr]

17 minutes ago, Whirlwind said:

With a colour camera even if you get an imaging run of an hour you have all the data you need for a colour photo

Tuesday night was an example.  I got just under an hour of data with my OSC.  At the same time I had mono cameras recording RGB, but I didnt get all the colours so couldnt make an image.

But an hour is not enough to make anything that resembles a decent image from the OSC - so I'll revisit the same area with the OSC again.  At the same time I'll have my mono cameras running, so will complete the remaining RGB data.  Both OSC and mono will then have enough data to make an image - the mono based RGB will be better resolved.

It just depends on your expectations and how much integration time you want to put into the images.  I'd like to see images from a mono CMOS such as the 571 chip, from a fast scope to see if they are significantly better than the OSC equivalent.  I suspect there wont be a lot in it.

 

Edited December 10, 2020 by tooth_dr

[Andrew Singleton]

2 hours ago, tooth_dr said:

An hour is not enough to make anything that resembles a decent image from the OSC - so I'll revisit the same area with the OSC again.  At the same time I'll have my mono cameras running, so will complete the remaining RGB data.  Both OSC and mono will then have enough data to make an image - the mono based RGB will be better resolved

This is certainly true where I am based. For andromeda I spent several (close to) perfect evenings taking pictures of it using my cheap DSLR and the colour is no where near where I want it to be.  In Bortle 4 and below I've heard this can be done in an hour, at some point I might drive out and work that out for myself. This group has been helpful for me, I think I am now more certain about going down the mono route. For the time being I don't plan on remote photography although its on a todo list to get me to a point where I cam properly do it.

 

3 hours ago, Whirlwind said:

With colour cameras you also can utilise some of the very fast RASA telescopes on the market that aren't particularly suited to mono imaging. 

A bit of a tangent this but I'm interested as to why the RASA's are so different and better with OSC? I get that they are fast, f2 I believe, but surely the percentage of photons going through that bayer layer is the same as with an f5 newtonian or even an f10 richi cassegrain. Surely the large appature and short focal length would equally improve the mono cameras ability to the colour. This astrophotography malarkey is a constant lesson to me! 😀

 

[vlaiv]

2 minutes ago, Andrew Singleton said:

A bit of a tangent this but I'm interested as to why the RASA's are so different and better with OSC? I get that they are fast, f2 I believe, but surely the percentage of photons going through that bayer layer is the same as with an f5 newtonian or even an f10 richi cassegrain. Surely the large appature and short focal length would equally improve the mono cameras ability to the colour. This astrophotography malarkey is a constant lesson to me!

RASAs only offer wider field of view. You can have the same speed with F/5 newtonian or F/8 RC - if you select appropriate pixel size.

Same aperture gathers same amount of light and then it is only the question of gathering/funneling those photons - in buckets. If you gather the same amount of photons in a bucket - you'll get same SNR, but if you gather more photons in one bucket than the other - first one will have higher SNR than second.

Pixel size is not the bucket size here, bucket size is combination of focal length and pixel size - what is called sampling rate or arc seconds per pixel. RASA has large aperture but very short focal length - which means it utilizes that aperture on very large bucket (when paired with normal sized pixels). If you want to get same size bucket with say 8" F/4 newtonian - you need to bin your pixels x2. If you want to do it with 8" F/8 RC - you need to bin them x4. Binning will not provide you with increased FOV - RASA will have the largest FOV, then 8" F/4 newtonian and last will be 8" F/8 RC.

RASA scopes are used with OSC more then mono - for practical reasons. Camera sits in front of the scope (in front of aperture) and OSC camera can have round body and fit behind the central obstruction, but Mono camera + filter wheel can't. You either need to find round filter drawer and change filters manually or just simply use OSC cameras with RASA. I suspect most people opt for second option and for this reason RASA scopes are better with OSC - not because they are magically "better" with OSC cameras

 

[Andrew Singleton]

9 minutes ago, vlaiv said:

 

Pixel size is not the bucket size here, bucket size is combination of focal length and pixel size - what is called sampling rate or arc seconds per pixel. RASA has large aperture but very short focal length - which means it utilizes that aperture on very large bucket (when paired with normal sized pixels). If you want to get same size bucket with say 8" F/4 newtonian - you need to bin your pixels x2. If you want to do it with 8" F/8 RC - you need to bin them x4. Binning will not provide you with increased FOV - RASA will have the largest FOV, then 8" F/4 newtonian and last will be 8" F/8 RC.

Gosh, I had to read that a few times but that makes sense to me now. I'd only just started thinking about pixel size and was wondering why that makes such an effect on camera choice. Linking it to aperture was something I had not considered. I had wondered why the recommended pixel size for the red cat was so small and its because of this. 

 

13 minutes ago, vlaiv said:

 

RASA scopes are used with OSC more then mono - for practical reasons. Camera sits in front of the scope (in front of aperture) and OSC camera can have round body and fit behind the central obstruction, but Mono camera + filter wheel can't. You either need to find round filter drawer and change filters manually or just simply use OSC cameras with RASA. I suspect most people opt for second option and for this reason RASA scopes are better with OSC - not because they are magically "better" with OSC cameras

Well now you put it like that, it seems obvious that you don't want a whopping electronic filter system blocking all of those photons! 

[Whirlwind]

3 hours ago, vlaiv said:

RASA scopes are used with OSC more then mono - for practical reasons. Camera sits in front of the scope (in front of aperture) and OSC camera can have round body and fit behind the central obstruction, but Mono camera + filter wheel can't. You either need to find round filter drawer and change filters manually or just simply use OSC cameras with RASA. I suspect most people opt for second option and for this reason RASA scopes are better with OSC - not because they are magically "better" with OSC cameras

There's also the short back focus (especially for the 8" which makes things tight if you want to add a filter in).  The idea of the waving around a filter drawer in the cold and dark in front of a optical glass makes me go cold!

[kirkster501]

My thoughts on this..... 

I don't think anyone questions that mono is better, 100% of course it is. With mono you dedicate the whole sensor to that channel alone so the full resolution is available for each channel.  So the results in an ideal world will always be better and you will build a better final image.  Period.

Ideal worlds, eh????  Wouldn't that be nice......  Covid all gone, conflict all gone, live to be 150 with my super-model girlfriend on my super yacht harboured off Cannes.....  Oh, and clear and reliable skies for astronomy.  Yeah, wouldn't that be nice? 

Alas, we don't live in ideal worlds folks.  Most of us on this forum live in a cloud infested country in the path of Atlantic weather systems with three major global air-masses converging directly above the UK with the jet stream snaking all over the place.   So, I'd suggest the question should be what quality pictures *CAN* you take from these cloudy shores with the minimum amount of frustration and that keeps your interest alive in this fascinating subject?  I asked my self that question many times whilst I was doing mono with my Atik460 and 8300 chip cameras (both superb btw).  And I have a mountain of unfinished data sets and a heap of frustration to go with it.  This year I have been working on M76 in LRGB - The Little Dumbell nebula - for months and only have two colours in the can due to the UK permacloud.  In the same time I have grabbed several complete images with my OSC camera, one of them below from my QHY268C on the FSQ85.  OSC is now so much better than it used to be. 

My strategic direction is now OSC. Although I will continue with mono I will be making no further investments in it.  If I lived in a sunnier, kinder climate my answer may be different.  But I don't. I live in Nottingham, UK.

Merry Christmas,

Steve

Edited December 23, 2020 by kirkster501

[carastro]

Quote

 Yes I'm up against it in bortle 8,  SE London. 

If you live in Bortle 8 (as I do), then mono is a no brainer.  I find that the best I can do from here is narrowband or HaRGB.  

Luckily I can get to a Bortle 4 campsite in normal circumstances where I can then do LRGB, but in this stay at home year, I would not have managed without a Mono camera and narrowband.

Carole    

[kirkster501]

37 minutes ago, carastro said:

If you live in Bortle 8 (as I do), then mono is a no brainer.  I find that the best I can do from here is narrowband or HaRGB.  

Luckily I can get to a Bortle 4 campsite in normal circumstances where I can then do LRGB, but in this stay at home year, I would not have managed without a Mono camera and narrowband.

Carole    

Yes, that is also an important consideration.  But with filters like the Optolong L-Extreme with its 7nm pass band in Ha and OIII you can also do NB with a OSC.

[Glennbloke]

I have owned both OSC and now my current Mono’s. I built a roll off roof observatory and I believe having a permanent set up makes a big difference to your choices. I live in Southend on sea and Bortle 6 skies. I can be imaging within 5minutes of deciding too and stopping is just as quick (no tear downs) 
This seems to afford me the ability to grab a colour image with my mono even if time is short.

On a personal level I love to spend multiple hours on whatever target I have chosen and the ability of an image grabbed in an hour or 2 does not appeal. For me its the journey and experience of working to get that image I am truly happy with. Of course thats me and not everyones cup of tea and  a permanent set up facilitates this a lot easier than for someone who has to set up every session.

[keramos]

Hi Andrew and all who have contributed to this thread.

This has been a great read especially when I have been mulling over a dedicated DSO camera and to be honest I'm more or less inclined towards getting a mono camera (been DSLR imaging over last few months).

The one question I'm mulling over is, do I need light pollution filter?

Narrowband will happily cut through light pollution. I've been quite happy with L-Extreme and for broadband IDAS light pollution filter (2") has worked well with DSLR.

I was wondering, what do folks do for LRGB and light pollution especially for Luminance, do you replace the L filter with light pollution 
filter e.g Baader Neodymium or IDAS Filter?

Or do you simply use software to remove any effect of light pollution from Luminance data?

Would appreciate feedback from Users of Mono Camera.

Thanks in advance,

Nihal.

 

ps: I'm in Bortle 5 as per Clear Outside