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Mono vs. OSC - trying to decide

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#1 The_8_Bit_Zombie

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Posted 12 July 2019 - 04:46 AM

I'm in the market for a cooled astronomy camera and I'm trying to figure out if I should go OSC or not. Problem is I have very limited access to dark sites; in general I get around 3-5 hours of imaging time per month. And based on what I've heard, and also what I've seen from Astrobin images, it seems like mono cameras require more integration time than OSCs. (Possibly a lot more time? Not sure.)

 

I'm looking at the ASI183mm-Pro for mono, and the ASI294MC-Pro for OSC. (I ruled out the ASI1600mm-Pro because of its microlensing diffraction.) I would use the camera with a Stellarvue SV70T telescope, which is 420mm FL and f/6 without a reducer, and 336mm FL and f/4.8 with a reducer.

 

My reasons against picking a monochrome camera:

  • I image from areas with very low light pollution, so I wouldn't benefit from the monochrome camera reducing the effects of LP. (I image at a bortle 3 site and a Bortle 1.5 site)
  • I have very limited time at dark sites, around 3-5 hours of imaging time a month.
  • I'm not interested in narrowband so if I had a monochrome camera I'd just image in LRGB anyway.
  • OSC is much less complex than mono, which would most likely lead to more integration time. (More time imaging and less time switching filters, refocusing, etc.)

 

My reasons for picking a monochrome camera:

  • I could image in HaRGB, which would be nice
  • I could gather Ha data from my backyard (Bortle 8)
  • I most likely wouldn't want to upgrade cameras for a long time, as it seems that mono cameras give you a lot of room to grow

 

What do you all think? Also if I got anything wrong please let me know, I'm still very much a newbie when it comes to dedicated astronomy cameras.

 

Thank you for your time!



#2 apophisOAS

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Posted 12 July 2019 - 05:13 AM

I can only speak for the asi183mm as i stepped up from DSLR to this about a year ago and processing notwithstanding , i found it very easy to use at first and got almost instant results, heres my astrobin gallery for you to see examples,

http://www.astrobin.com/users/apophis/

HTH 

Roger


Edited by apophisOAS, 12 July 2019 - 05:14 AM.


#3 terry59

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Posted 12 July 2019 - 06:42 AM

Ha would add much to your data and increase your potential target list. For this reason alone the mono camera would be far more versatile. Also, with the control software available, switching filters and refocusing (which should be done regardless of OSC or mono) can be automated. My experiences with OSC and NB filters left me unimpressed



#4 descott12

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Posted 12 July 2019 - 07:54 AM

I don't do AP at all but I read alot on CN and I know many people have mentioned the microlens problem with the 1600 but I think the rebuttal is always that it only happens with a very short list of the very brightest stars. So that may or may not be an issue for you. Also, in just playing around a little, I have seen some microlensing with my 294 PRO. I think it may have been Sirius but I can't quite remember.



#5 WadeH237

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Posted 12 July 2019 - 08:07 AM

I'm confused.

First you say:
 

Problem is I have very limited access to dark sites

And then you say:
 

I image from areas with very low light pollution

Which is it?

And regarding this:
 

it seems like mono cameras require more integration time than OSCs.

Mono cameras do not require more integration time than OSC. In practice, they often require less. There are numerous threads discussing this if you do a search.


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#6 2ghouls

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Posted 12 July 2019 - 09:14 AM

It seems like mono cameras require more integration time than OSCs. (Possibly a lot more time? Not sure.)

No, they don't. A 2 hour integration with a mono camera and RGB filters will typically have a higher SNR (signal to noise ratio) than a 2 hour integration with OSC. However, to get to the point where gathering 2 hours of mono data takes roughly the same amount of time as gathering 2 hours of OSC data depends on how much money are you willing to throw at it, and how quickly you learn the software. If you don't have a motorized, automated focuser (and can therefore set filter offsets) you will likely have to focus between every filter change. To minimize the number of times you are focusing this means you will probably shoot lots of red frames, then the green frames, then the blue frames. The problem with this is it leaves a lot up to chance. Let's say clouds come in before you can shoot the blue frames. The next time you shoot, the conditions (seeing, transparency) are completely different and now your blue frames are bloated compared to your red and green. So you re-shoot everything. Not trying to dissuade you from mono, I love it, just explaining why it can take more time to shoot this way in practice. If you do already have (or are planning to get) an automated focuser (and the software to run it), then you should be good to go with mono, and I recommend it. (edit: see Jon Rista's longer post below for more detail on some of these points).

 

 

I'm not interested in narrowband so if I had a monochrome camera I'd just image in LRGB anyway.

 

 

I could image in HaRGB, which would be nice

I could gather Ha data from my backyard (Bortle 8)

?? The latter statements are true, and should not be taken lightly. Taken at face value they seem to contradict your statement that if you had a mono camera you would just image in LRGB. I gather tons of Ha from Bortle 8/9 zones, and I think you will find that pretty addictive. Ha is narrowband, so maybe you mean you're not interested in pure narrowband imaging.  Keep in mind narrowband does not have to equal crazy colors. I do a lot of narrowband imaging where I keep the Ha red, and the OIII blue, and complement the narrowband channels by shooting RGB for good star color.


Edited by 2ghouls, 12 July 2019 - 12:35 PM.

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#7 Jon Rista

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Posted 12 July 2019 - 11:41 AM

I'm in the market for a cooled astronomy camera and I'm trying to figure out if I should go OSC or not. Problem is I have very limited access to dark sites; in general I get around 3-5 hours of imaging time per month. And based on what I've heard, and also what I've seen from Astrobin images, it seems like mono cameras require more integration time than OSCs. (Possibly a lot more time? Not sure.)

 

I'm looking at the ASI183mm-Pro for mono, and the ASI294MC-Pro for OSC. (I ruled out the ASI1600mm-Pro because of its microlensing diffraction.) I would use the camera with a Stellarvue SV70T telescope, which is 420mm FL and f/6 without a reducer, and 336mm FL and f/4.8 with a reducer.

 

My reasons against picking a monochrome camera:

  • I image from areas with very low light pollution, so I wouldn't benefit from the monochrome camera reducing the effects of LP. (I image at a bortle 3 site and a Bortle 1.5 site)
  • I have very limited time at dark sites, around 3-5 hours of imaging time a month.
  • I'm not interested in narrowband so if I had a monochrome camera I'd just image in LRGB anyway.
  • OSC is much less complex than mono, which would most likely lead to more integration time. (More time imaging and less time switching filters, refocusing, etc.)

 

My reasons for picking a monochrome camera:

  • I could image in HaRGB, which would be nice
  • I could gather Ha data from my backyard (Bortle 8)
  • I most likely wouldn't want to upgrade cameras for a long time, as it seems that mono cameras give you a lot of room to grow

 

What do you all think? Also if I got anything wrong please let me know, I'm still very much a newbie when it comes to dedicated astronomy cameras.

 

Thank you for your time!

While OSC is fine if you image at dark sites, I once again feel the need to dispute that OSC is "much" less complex than mono. It is less complex, but the difficulties of imaging with a mono camera and a filter wheel are frequently overwrought. Lets just get down to the base case: OSC vs. Mono+RGB (EXcluding L). Three filters. Here are the additional complexities:

 

1) Buy and set up a filter wheel.

2) Operate the filter wheel.

3) Focus with each filter.

4) Integrate three images instead of one.

 

Ok, first off, #1 is super easy, and a once-and-done sort of thing. You buy it, you put the filters in, you attach it to your camera. You don't really have to do that again...not, at least, on a regular basis or anything like that. Maybe if you choose to add or change filters (which is an option, an added bonus, with mono...a choice you do not really have with OSC!)

 

Regarding #2. Unless you hope to image without a computer of any kind...which might be possible with a DSLR, but is not really an option for most AP OSC...then you need software to run your imaging sequences. You need to configure this software, you need to focus with OSC anyway, etc. Adding the operation of a filter wheel is, again, a once-and-done sort of thing. You install the drivers, you configure your imaging program. The only recurring factor here is acquiring data in three separate channels, than one sequence of OSC data. This is not hard, and minimally more complex than operating OSC with the same software.

 

Regarding #3. This is the one area that might indeed be more complex. You need to focus more often...which is actually pretty easy but wastes time. OR...you spend time, again mostly as a once-and-done sort of thing, upfront to configure your filters properly, including filter offsets. Most filter wheels, filter wheel drivers and imaging programs these days support some kind of "filter offset" focusing feature. This means determining how each filter differs in terms of focus (most scopes are not well corrected enough to focus all light at exactly the same point, so depending on the filter you have to adjust focus a little; this is, in fact, a BENEFIT of mono, in that you CAN control this...you have no control with OSC, since you acquire all channels all at once). There are some well defined procedures that can help you determine these offsets and configure them. Once configured, you can then focus once, periodically, with a particular filter (say G), then let the software/driver handle adjusting for the other filters via offset config. This then allows much easier operation, as you only need to focus about as often as you would with OSC, and it allows channel interleaving during acquisition. Rather than acquire all data on one filter, then another, you cycle through each filter and acquire all three channels simultaneously. More on this in a moment.

 

Regarding #4. If you can integrate one channel, you can integrate any number of channels. Pre-processing Mono data is actually a simpler process overall than it is for OSC. With OSC, you need at least one extra step, possibly two, in order to get the best results: deconvolution and bayer drizzling. This is on top of the core pre-processing steps: calibrate, register, integrate. Deconvolution is necessary to ensure proper registration of OSC data, bayer drizzing is highly recommended to get the best resolution and overall quality from OSC data (assuming you have enough frames...) Pre-processing mono data is actually pretty simple: Calibrate, Register, Integrate. Calibration can usually be done with a shared master dark, but different flats. There are programs (or scripts for PI) that simplify this process and can automatically match darks and flats to each channel for you. Registration can, and should, usually be done in bulk for all frames at once, to a single common reference frame. Integration is then done three times, one for each channel. In my experience...mono pre-processing actually goes faster than OSC pre-processing. OSC data, once demosaiced, tends to be significantly larger in terms of data and memory footprint, more data must be moved around at once per frame, which can slow things down. I've always been amazed at how quickly I can rip through pre-processing a ton of 20mp mono frames for three or four (or more) channels...vs. pre-processing 22mp OSC frames from my 5D III. The latter usually requires significantly more time to pre-process, and there is also the added step of drizzling to get the best resolution (something simply not necessary with IMX183 data, which is already well sampled most of the time and already at more optimal resolution.)

 

Processing mono RGB data only really requires one additional step: Combine the separate RGB channels into a single RGB image. Once you have the RGB image? You can process the same way you would process OSC...or, quite possibly, process with even fewer steps. Mono data is very clean, usually more detailed, doesn't suffer from the same kind of color noise issues that OSC cameras often do, and may not need the kind of extra sharpening or detail enhancement steps that may be required to pull out details with OSC data. With dark skies, these differences may be less than with more light polluted skies, but the differences still generally remain.

 

So the main complexity increase here is filters and a filter wheel, focusing, and acquisition with multiple filters. Most of the filter wheel stuff, as mentioned above, is a once-and-done sort of thing. The ongoing additional complexity is acquiring the data and focusing. For this, I highly recommend interleaving your acquisition across all filters simultaneously, rather than acquiring one filter at a time. This can be done with many acquisition programs these days, including SGP which is what I currently use, and what a lot of imagers use. Nina, Voyager, TSX and others should also support this. With interleaving, you acquire red, then green, then blue, or maybe a couple of each. THEN dither once. THEN periodically, say every 1C temp change, or every 30 minutes, focus. Then acquire all three channels again. This does a few things. One it limits overhead time. If you acquire one frame at a time then dither, then focus, you can easily waste 30-50% of each night. Not recommended. With filter offsets, you do not have to focus between each filter. When acquiring different filters one after the other, there is no need to dither between each...you can dither after each set of filters. This can greatly reduce the amount of time you spend dithering. Instead of say dithering every 2 minutes, you might dither every 6 minutes. Or if you intend to stack a lot of frames (hours of integration), you might even dither every 2 exposures per channel, meaning you could dither once ever 12 minutes (assuming 2m exposures)! If you focus every 30 minutes, then on a per-hour basis, you have 5 dithers and 2 focus routines. Dithers should not be longer than 10 seconds, so that is less than 1 minute total. Focus might take a couple of minutes each time. So you have overhead of about 5 minutes every 60...not bad at all!

 

There are then the general benefits of mono. Aside from the 100% fill factor, you actually have the ability to tune focus for each channel. Unlike OSC, where you simply have to focus as best as possible for all three channels concurrently, which could well means that one of the channels scatters more, with mono you can optimize focus for each channel, getting the smallest stars and the least scattering/dispersion possible. This improves IQ. You acquire all channels at every pixel on the sensor all the time. While you can use bayer drizzling to offset the spatial cost of a CFA, you have to actually do bayer drizzling. This is an additional pre-processing step that can be fairly time consuming, and is on top of the other additional pre-processing costs for OSC data. Drizzling cannot help with the focus limitations of OSC, though. With mono, you don't have to drizzle if you are already well sampled (and with tiny 2.4 micron pixels, it doesn't take much focal length to get very well sampled data), and you can focus optimally for every channel. Further, with mono, you have the option of doing Ha imaging, and doing it properly, benefiting from the full fill factor that a mono sensor offers. You can also add OIII, SII, NII, and even other channels if you so desire (if you are a planetary nebula imager, multiple narrow band channels including more exotic bands could be useful). Transmission with LRGB filter sets is also usually very high, well over 90% and in some cases over 97%. CFA filters in bayer sensors are often not as high, sometimes much lower. So there could potentially be a transmission cost to OSC as well.

 

Mono "sounds" scary and overly complex. But a lot of the complexities are things you only really have to endure once, then you can forget about them. I set up a filter wheel once a year ago...and imaged with it over and over and over. I only re-configured it once just a couple of days ago. I could easily use the current configuration for years, across multiple scopes and scope configurations. Previously, I had my filter wheel set up for about another year. It is a very infrequent operation to fiddle with a filter wheel. Some people configure them, put em on scopes in remote observatories, and don't touch them for years on end.

 

The hardest thing is focus and determining and configuring focus offsets. First, for focus, you should be using motorized focus that supports ASCOM or INDI and can be automated. For determining offsets, there are reliable procedures that can assist, and as long as you test offsets when the scope has reached equilibrium with the ambient temperature, the results are usually pretty repeatable. Pick a filter, say green. Focus (preferably with a reliable autofocus routine, but accurate focus with some kind of focus assist mask will also do.) Log the focus position and filter. Switch to your alternate filter, say red or blue (just one at a time). Focus. Log the focus position and filter. Switch to green, focus again, log. Switch to red, focus again, log. Do this about a dozen times. Average the green and red focus positions, and perhaps discard any obvious outliers. Calculate the difference between the two using green as the reference point (offset may be positive or negative!!) Repeat the process with blue. Set your filter offsets in your filter wheel driver or acquisition software. As long as you use this scope, camera, filter and filter wheels...your offsets should apply. So you don't have to repeat this process. You can now interleave exposures across channels as much as you want, and minimize your overhead, and focus as infrequently as necessary. Focus frequency here should be about the same as with OSC, in fact.

 

I'll also offer this. I've been imaging with mono for years now. Once you get automation set up...imaging with mono is no more complex and requires no more time than imaging with OSC. It's all automated. You pick a target, slew, center, configure a sequence...and go. From that point on, even though more moving parts are involved, mono doesn't require my attention any more than OSC does. Both are hands off. I can go to bed, and get up in the morning with a pile of data either way (barring weather). The key difference with mono vs. OSC, and this goes for both cooled AP OSC as well as DSLR, is that mono has consistently delivered better quality for me than OSC. I have dark site OSC data, and I really like a lot of the images I've acquired with OSC from dark sites. But I have no question that under the same conditions, the mono camera would have delivered higher resolution data, with lower noise, particularly lower color noise, more and sharper detail, and generally better contrast.


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#8 OldManSky

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Posted 12 July 2019 - 12:06 PM

zombie, I think I mentioned this in your other thread, but it bears repeating (and reinforces what Jon said above):

 

*Capture* is less complex with OSC.  No filter wheel, no focus offsets for filters, etc.  Hook up your camera, focus, and go.

*Processing* is at least as complex (it not more so) with OSC.

 

So IMHO, you give up a little front-end complexity, and in return you get more back-end complexity.  

All in all, I think it's a wash as far as "complexity" goes.

 

In the long run, just about everybody who gets "serious" about imaging winds up with a mono camera.  For the very simple reason that the final result can be better.  

That's not to say that OSC isn't a bad way to start, or that there aren't some amazingly wonderful OSC images being done.

But it's still the case.


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#9 dmdouglass

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Posted 12 July 2019 - 12:13 PM

There is a clear answer to your situation.

And this is a serious suggestion.

 

Get two cameras.  A OSC for general use.

A Mono camera for special use.

 

Problem solved !


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#10 DSO_Viewer

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Posted 12 July 2019 - 01:06 PM

I'm in the market for a cooled astronomy camera and I'm trying to figure out if I should go OSC or not. Problem is I have very limited access to dark sites; in general I get around 3-5 hours of imaging time per month. And based on what I've heard, and also what I've seen from Astrobin images, it seems like mono cameras require more integration time than OSCs. (Possibly a lot more time? Not sure.)

 

I'm looking at the ASI183mm-Pro for mono, and the ASI294MC-Pro for OSC. (I ruled out the ASI1600mm-Pro because of its microlensing diffraction.) I would use the camera with a Stellarvue SV70T telescope, which is 420mm FL and f/6 without a reducer, and 336mm FL and f/4.8 with a reducer.

 

My reasons against picking a monochrome camera:

  • I image from areas with very low light pollution, so I wouldn't benefit from the monochrome camera reducing the effects of LP. (I image at a bortle 3 site and a Bortle 1.5 site)
  • I have very limited time at dark sites, around 3-5 hours of imaging time a month.
  • I'm not interested in narrowband so if I had a monochrome camera I'd just image in LRGB anyway.
  • OSC is much less complex than mono, which would most likely lead to more integration time. (More time imaging and less time switching filters, refocusing, etc.)

 

My reasons for picking a monochrome camera:

  • I could image in HaRGB, which would be nice
  • I could gather Ha data from my backyard (Bortle 8)
  • I most likely wouldn't want to upgrade cameras for a long time, as it seems that mono cameras give you a lot of room to grow

 

What do you all think? Also if I got anything wrong please let me know, I'm still very much a newbie when it comes to dedicated astronomy cameras.

 

Thank you for your time!

You said that your are not interested in narrowband imaging , however, you mention doing HaRGB and Ha IS narrowband??

 

Steve



#11 stargzr66207

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Posted 12 July 2019 - 01:21 PM

Zombie,
In my humble opinion, OSC is the way to go.
Reasons:
More time exposing light, less time changing filters, re-focusing,
etc.
Although the final result with OSC might not be as eye-catching
as LRGB, for a lot of folks, me included, the extra time to image
new targets during an evening makes up for it.
I image from a Bortle 3 zone, but do not get out under the stars
as much as I'd like. Therefore, when I do, I like to have as much to
show for it as possible. It's nice to build a beautiful, eye-catching
image with one hour each of LRG and B, but I like to have more to
show for each night than just one image. I guess I'm too impatient.
Oh well, that's just me, but thought I'd add my 2-cents worth.
Ron Abbott

#12 bobzeq25

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Posted 12 July 2019 - 04:18 PM

Zombie,
In my humble opinion, OSC is the way to go.
Reasons:
More time exposing light, less time changing filters, re-focusing,
etc.
Although the final result with OSC might not be as eye-catching
as LRGB, for a lot of folks, me included, the extra time to image
new targets during an evening makes up for it.
I image from a Bortle 3 zone, but do not get out under the stars
as much as I'd like. Therefore, when I do, I like to have as much to
show for it as possible. It's nice to build a beautiful, eye-catching
image with one hour each of LRG and B, but I like to have more to
show for each night than just one image. I guess I'm too impatient.
Oh well, that's just me, but thought I'd add my 2-cents worth.
Ron Abbott

If you want to make the best use of your imaging time.

 

One hour of L, 20 minutes each of R,G,B, binned 2X2.  You're gathering photons a _lot_ faster.

 

There's nothing wrong with OSC, and it's way cheaper than mono, but the idea that it saves imaging time is just wrong.  The Bayer filter approach works fine for terrestrial, where light is abundant.  For low light astro, it's inefficient.  Using methods like the above, it's not close.


Edited by bobzeq25, 12 July 2019 - 04:27 PM.

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#13 Akwilliams

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Posted 13 July 2019 - 04:10 PM

If you had asked me 2 months ago, i would say mono all the time, everytime.    I have had an OSC in the past.. a good one at that, but i never got good results, whereas i have had some very good success with mono - both LRGB and NB.

 

I really wanted to try OSC again.. and eventually went for the ZWO ASI071 (my mono is the 1600 pro - so i have confidence with ZWO)  I wasn't expecting anything great from past experience, but boy was i wrong!

 

The 071 has performed far beyond by expectations.    The decider for me if i had to make a choice would be against the targets you want to image?

 

OSC as a (and i do say this a bit flippantly) grab and go with a good match between the camera and scope

Mono for flexibility and ability to image anything with the right filters.

 

It will also depend alot on your skies.   I am about Bortle 5-6 so certainly not great.. But i get good results from both.



#14 jgraham

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Posted 14 July 2019 - 11:50 AM

" There is a clear answer to your situation.
And this is a serious suggestion.

Get two cameras.  A OSC for general use.
A Mono camera for special use.

Problem solved !"

 

Actually, this isn't a bad idea at all! For many years I always bought my cameras in pairs; one color the other monochrome. I even had pairs of matched telescopes so that I could take monochrome and color data at the same time. This was one of many variation that I have used over the years making the best use of my limited imaging time from my Bortle 8 backyard. However, over the years I have seen a steady improvement in color cameras while monochrome cameras have stayed pretty much the same; maybe a few changes in size, cooling, and cost, but they have always been very capable and have stayed that way. Meanwhile, color cameras have gotten so good that the lines have blurred between them to the point where I do almost all of my imaging with my color cameras; even my narrowband imaging using the new multi-band narrowband filters. My monochrome cameras have seen a steady decline in use and are now largely used for specialty tasks like solar imaging where color isn't needed.

 

I am glad that I have the options to go one way or the other, but modern color cameras are very capable and very easy to use.

 

Food for thought.


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#15 WadeH237

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Posted 14 July 2019 - 07:23 PM

Get two cameras.  A OSC for general use.
A Mono camera for special use.

I've considered this.

 

I have a mount more or less always set up and available for imaging.  Right now, I use a single OTA and swap it out when I want to significantly change my field of view.  I've thought about going side-by-side with a long focal length scope and a OSC camera, next to a short focal length scope and my mono camera.

 

I supposed that ideally, I could use the ST10 that I already have for the long focal length work.  It's got a much higher QE than just about any OSC camera available.  But part of me wants a OSC camera, just because.



#16 nimitz69

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Posted 15 July 2019 - 09:12 AM

OnWhile OSC is fine if you image at dark sites, I once again feel the need to dispute that OSC is "much" less complex than mono. It is less complex, but the difficulties of imaging with a mono camera and a filter wheel are frequently overwrought. Lets just get down to the base case: OSC vs. Mono+RGB (EXcluding L). Three filters. Here are the additional complexities:

 

1) Buy and set up a filter wheel.

2) Operate the filter wheel.

3) Focus with each filter.

4) Integrate three images instead of one.

 

Ok, first off, #1 is super easy, and a once-and-done sort of thing. You buy it, you put the filters in, you attach it to your camera. You don't really have to do that again...not, at least, on a regular basis or anything like that. Maybe if you choose to add or change filters (which is an option, an added bonus, with mono...a choice you do not really have with OSC!)

 

Regarding #2. Unless you hope to image without a computer of any kind...which might be possible with a DSLR, but is not really an option for most AP OSC...then you need software to run your imaging sequences. You need to configure this software, you need to focus with OSC anyway, etc. Adding the operation of a filter wheel is, again, a once-and-done sort of thing. You install the drivers, you configure your imaging program. The only recurring factor here is acquiring data in three separate channels, than one sequence of OSC data. This is not hard, and minimally more complex than operating OSC with the same software.

 

Regarding #3. This is the one area that might indeed be more complex. You need to focus more often...which is actually pretty easy but wastes time. OR...you spend time, again mostly as a once-and-done sort of thing, upfront to configure your filters properly, including filter offsets. Most filter wheels, filter wheel drivers and imaging programs these days support some kind of "filter offset" focusing feature. This means determining how each filter differs in terms of focus (most scopes are not well corrected enough to focus all light at exactly the same point, so depending on the filter you have to adjust focus a little; this is, in fact, a BENEFIT of mono, in that you CAN control this...you have no control with OSC, since you acquire all channels all at once). There are some well defined procedures that can help you determine these offsets and configure them. Once configured, you can then focus once, periodically, with a particular filter (say G), then let the software/driver handle adjusting for the other filters via offset config. This then allows much easier operation, as you only need to focus about as often as you would with OSC, and it allows channel interleaving during acquisition. Rather than acquire all data on one filter, then another, you cycle through each filter and acquire all three channels simultaneously. More on this in a moment.

 

Regarding #4. If you can integrate one channel, you can integrate any number of channels. Pre-processing Mono data is actually a simpler process overall than it is for OSC. With OSC, you need at least one extra step, possibly two, in order to get the best results: deconvolution and bayer drizzling. This is on top of the core pre-processing steps: calibrate, register, integrate. Deconvolution is necessary to ensure proper registration of OSC data, bayer drizzing is highly recommended to get the best resolution and overall quality from OSC data (assuming you have enough frames...) Pre-processing mono data is actually pretty simple: Calibrate, Register, Integrate. Calibration can usually be done with a shared master dark, but different flats. There are programs (or scripts for PI) that simplify this process and can automatically match darks and flats to each channel for you. Registration can, and should, usually be done in bulk for all frames at once, to a single common reference frame. Integration is then done three times, one for each channel. In my experience...mono pre-processing actually goes faster than OSC pre-processing. OSC data, once demosaiced, tends to be significantly larger in terms of data and memory footprint, more data must be moved around at once per frame, which can slow things down. I've always been amazed at how quickly I can rip through pre-processing a ton of 20mp mono frames for three or four (or more) channels...vs. pre-processing 22mp OSC frames from my 5D III. The latter usually requires significantly more time to pre-process, and there is also the added step of drizzling to get the best resolution (something simply not necessary with IMX183 data, which is already well sampled most of the time and already at more optimal resolution.)

 

Processing mono RGB data only really requires one additional step: Combine the separate RGB channels into a single RGB image. Once you have the RGB image? You can process the same way you would process OSC...or, quite possibly, process with even fewer steps. Mono data is very clean, usually more detailed, doesn't suffer from the same kind of color noise issues that OSC cameras often do, and may not need the kind of extra sharpening or detail enhancement steps that may be required to pull out details with OSC data. With dark skies, these differences may be less than with more light polluted skies, but the differences still generally remain.

 

So the main complexity increase here is filters and a filter wheel, focusing, and acquisition with multiple filters. Most of the filter wheel stuff, as mentioned above, is a once-and-done sort of thing. The ongoing additional complexity is acquiring the data and focusing. For this, I highly recommend interleaving your acquisition across all filters simultaneously, rather than acquiring one filter at a time. This can be done with many acquisition programs these days, including SGP which is what I currently use, and what a lot of imagers use. Nina, Voyager, TSX and others should also support this. With interleaving, you acquire red, then green, then blue, or maybe a couple of each. THEN dither once. THEN periodically, say every 1C temp change, or every 30 minutes, focus. Then acquire all three channels again. This does a few things. One it limits overhead time. If you acquire one frame at a time then dither, then focus, you can easily waste 30-50% of each night. Not recommended. With filter offsets, you do not have to focus between each filter. When acquiring different filters one after the other, there is no need to dither between each...you can dither after each set of filters. This can greatly reduce the amount of time you spend dithering. Instead of say dithering every 2 minutes, you might dither every 6 minutes. Or if you intend to stack a lot of frames (hours of integration), you might even dither every 2 exposures per channel, meaning you could dither once ever 12 minutes (assuming 2m exposures)! If you focus every 30 minutes, then on a per-hour basis, you have 5 dithers and 2 focus routines. Dithers should not be longer than 10 seconds, so that is less than 1 minute total. Focus might take a couple of minutes each time. So you have overhead of about 5 minutes every 60...not bad at all!

 

There are then the general benefits of mono. Aside from the 100% fill factor, you actually have the ability to tune focus for each channel. Unlike OSC, where you simply have to focus as best as possible for all three channels concurrently, which could well means that one of the channels scatters more, with mono you can optimize focus for each channel, getting the smallest stars and the least scattering/dispersion possible. This improves IQ. You acquire all channels at every pixel on the sensor all the time. While you can use bayer drizzling to offset the spatial cost of a CFA, you have to actually do bayer drizzling. This is an additional pre-processing step that can be fairly time consuming, and is on top of the other additional pre-processing costs for OSC data. Drizzling cannot help with the focus limitations of OSC, though. With mono, you don't have to drizzle if you are already well sampled (and with tiny 2.4 micron pixels, it doesn't take much focal length to get very well sampled data), and you can focus optimally for every channel. Further, with mono, you have the option of doing Ha imaging, and doing it properly, benefiting from the full fill factor that a mono sensor offers. You can also add OIII, SII, NII, and even other channels if you so desire (if you are a planetary nebula imager, multiple narrow band channels including more exotic bands could be useful). Transmission with LRGB filter sets is also usually very high, well over 90% and in some cases over 97%. CFA filters in bayer sensors are often not as high, sometimes much lower. So there could potentially be a transmission cost to OSC as well.

 

Mono "sounds" scary and overly complex. But a lot of the complexities are things you only really have to endure once, then you can forget about them. I set up a filter wheel once a year ago...and imaged with it over and over and over. I only re-configured it once just a couple of days ago. I could easily use the current configuration for years, across multiple scopes and scope configurations. Previously, I had my filter wheel set up for about another year. It is a very infrequent operation to fiddle with a filter wheel. Some people configure them, put em on scopes in remote observatories, and don't touch them for years on end.

 

The hardest thing is focus and determining and configuring focus offsets. First, for focus, you should be using motorized focus that supports ASCOM or INDI and can be automated. For determining offsets, there are reliable procedures that can assist, and as long as you test offsets when the scope has reached equilibrium with the ambient temperature, the results are usually pretty repeatable. Pick a filter, say green. Focus (preferably with a reliable autofocus routine, but accurate focus with some kind of focus assist mask will also do.) Log the focus position and filter. Switch to your alternate filter, say red or blue (just one at a time). Focus. Log the focus position and filter. Switch to green, focus again, log. Switch to red, focus again, log. Do this about a dozen times. Average the green and red focus positions, and perhaps discard any obvious outliers. Calculate the difference between the two using green as the reference point (offset may be positive or negative!!) Repeat the process with blue. Set your filter offsets in your filter wheel driver or acquisition software. As long as you use this scope, camera, filter and filter wheels...your offsets should apply. So you don't have to repeat this process. You can now interleave exposures across channels as much as you want, and minimize your overhead, and focus as infrequently as necessary. Focus frequency here should be about the same as with OSC, in fact.

 

I'll also offer this. I've been imaging with mono for years now. Once you get automation set up...imaging with mono is no more complex and requires no more time than imaging with OSC. It's all automated. You pick a target, slew, center, configure a sequence...and go. From that point on, even though more moving parts are involved, mono doesn't require my attention any more than OSC does. Both are hands off. I can go to bed, and get up in the morning with a pile of data either way (barring weather). The key difference with mono vs. OSC, and this goes for both cooled AP OSC as well as DSLR, is that mono has consistently delivered better quality for me than OSC. I have dark site OSC data, and I really like a lot of the images I've acquired with OSC from dark sites. But I have no question that under the same conditions, the mono camera would have delivered higher resolution data, with lower noise, particularly lower color noise, more and sharper detail, and generally better contrast.

Anyone want to buy  my lightly used 294 MC Pro?  dalek12.gif

On second thought ... maybe I should finish building my observatory first ....


Edited by nimitz69, 15 July 2019 - 09:14 AM.



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