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New mono astro camera? filters?

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#1 RadOD

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Posted 18 April 2019 - 10:10 PM

I am considering making the leap from DSLR to mono camera and I'm a little overwhelmed trying to read about everything.

 

I am thinking about something along the lines of the ASI183MM Pro or ASI1600MM Pro although I'm not tied to anything.  In addition to mono, I want cooling -- but pixel size vs quantum efficiency vs sensor size vs read noise... How do I decide? I want to image large nebulae as well as small DSO's.  Short of multiple cameras on multiple scopes are mosaics a viable option?

 

My current scope for photography is an ES 102ED 714mm f/7.  I sometimes use a 0.75X flattener/reducer. 

I most often image from my backyard at Bortle 5 because it is easy. But I have easy access to Bortle 3.

CCD suitability calculator seems to say the 183 is a better fit.

 

Filters: what size?  31mm? I also have a 18" f/4.2 dob for visual - I never use that for photography but would it make sense if I wanted to do planetary or anything else? They would have to be very short exposures without real guiding.  Do you even use filters for planetary? Does it make sense to go with 36mm in case of a new scope sometime?

 

Starting with LRGB and adding others later seems a good idea.  I'm unclear what L adds - is it to collect more light faster at the expense of less color information -- making the assumption that some color is enough color?

 

For a filter wheel, I need unmounted filters?  



#2 Lead_Weight

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Posted 19 April 2019 - 12:09 AM

I have that scope, the FCD100 version. I used it with a .8x reducer and the ASI1600MM-C camera. It gives a decent FOV, not wide enough to capture super large nebula, but much wider than you would get with the 183, which is a smaller chip. I have 31mm unmounted filters in the ZWO 8 position filter wheel. You will get halos on bright stars with the ZWO filters, but they are still an inexpensive set to start with. I eventually upgraded to Astrodon filters. You can see lots of my images at my site or Astrobin.

 

Filters can be used with planetary, and of course you have to with a mono camera, but in addition some people image in UV and other filters to try to bring out extra planetary detail. I ended up with an ASI224MC color camera for planetary and forgoe the filters.

 

L is luminance, so it's capturing the true brightness of the object since it's not filtering out any color. When you add this to your color data, it really brings out the detail. You need about 3:2 ratio of luminance to RGB. I usually image 5 frames luminance, 3 RGB (each), and repeat indefinitely all night long or however long I want to image something.

 

The ZWO 5 and 8 position filter wheel use standard 1.25 mounted filters or 31mm unmounted filters. You would want 36mm filters if you move up to an APSC sized sensor, but it's not required for the 1600.



#3 bobzeq25

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Posted 19 April 2019 - 01:39 AM

I am considering making the leap from DSLR to mono camera and I'm a little overwhelmed trying to read about everything.

 

I am thinking about something along the lines of the ASI183MM Pro or ASI1600MM Pro although I'm not tied to anything.  In addition to mono, I want cooling -- but pixel size vs quantum efficiency vs sensor size vs read noise... How do I decide? I want to image large nebulae as well as small DSO's.  Short of multiple cameras on multiple scopes are mosaics a viable option?

 

My current scope for photography is an ES 102ED 714mm f/7.  I sometimes use a 0.75X flattener/reducer. 

I most often image from my backyard at Bortle 5 because it is easy. But I have easy access to Bortle 3.

CCD suitability calculator seems to say the 183 is a better fit.

 

Filters: what size?  31mm? I also have a 18" f/4.2 dob for visual - I never use that for photography but would it make sense if I wanted to do planetary or anything else? They would have to be very short exposures without real guiding.  Do you even use filters for planetary? Does it make sense to go with 36mm in case of a new scope sometime?

 

Starting with LRGB and adding others later seems a good idea.  I'm unclear what L adds - is it to collect more light faster at the expense of less color information -- making the assumption that some color is enough color?

 

For a filter wheel, I need unmounted filters?  

This is a personal decision.  But here are things to consider.  There are some simplifications involved, I believe they're useful for someone in your situation.

 

For most people sensor size is the big deal.  Quantum efficiencies cover a small range among your likely candidates.  Ditto read noise, which can be dealt with pretty well by changing the subexposure.

 

Pixel size cuts a number of ways.  Smaller pixels could theoretically give better resolution, but other things like tracking and seeing have to cooperate.   Larger pixels are easier, more "forgiving".

 

I have a 183C, like it, but can see that the small pixels are demanding.  I bought it in anticipation of a Celstron 8 RASA, 400mm, F2.  The speed and focal length are well tailored to a 183.

 

A virtue of a 1600 is that so many people own one, your user support base is large.

 

Mosaics can work well, but are not trivial to do.  Some people do them, most don't.

 

Bottom line.  2 good choices, either could work.  People here will have their recommendation.  Mine is the 1600, but, as I said, personal choice.

 

Minor points.  Filters need to be compatible with your filter wheel.

 

LRGB is a nice trick.  The L filter gathers a lot of data fast.  Your eye see detail in the L.  You can get away with less RGB data, you basically use it to paint the L.  A strategy to save even more time is to bin the RGB 2X2, that goes in and out of fashion.

 

The very best color comes from straight RGB, but that carries a big penalty because it requires a lot more total imaging time.  I've used it on bright targets, like the Ring Nebula and star clusters.  Personally wouldn't dream of using it on a dim nebula or galaxy.  The darker your skies, the less total imaging time you need, the more RGB becomes viable.

 

The 1600 is a competent planetary camera, the 183 can do planetary.  If you want color planets with a mono camera, you need to use filters.

 

Additional point.  Consider getting an Ha filter.  Black and white Ha can be very nice.  Combining Ha and RGB can also be good, the processing is not trivial.   (understatement)


Edited by bobzeq25, 19 April 2019 - 08:23 AM.


#4 RadOD

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Posted 21 April 2019 - 07:29 AM

Thanks for the detailed answers!  That gives me a much better framework of understanding to go on!

 

Wouldn't the effects of seeing/tracking on small pixels effectively be like emulating large pixels?  Ah - but then you have a smaller sensor...

 

Reading about the Astrodon filters, their site says "The I-Series filters compensate for the lower red response of these Interline detectors affecting the design of the Green and Red filters.  The Luminance and Blue filters are the same as those in our E-Series.  This means that your RGB color combine weights will be approximately 1:1:1 within perhaps 10% for equal length exposures.  This can never be perfect, but it does allow you to take one exposure time for all of your RGB data and therefore, only just one corresponding dark exposure time."  So this raises the question: do you take a full set of dark, flat, bias calibration images separately for each filter?

 

I've seen some comments on - I think - the ZWO filters not being parfocal. With SGP and a motorized focuser, focusing only takes a couple minutes. Wouldn't you want to refocus every time you change fileters?

 

I want to read some more, but I'm thinking about the ASI1600MM with a ZWO EFW 8 and Chroma 36mm unmounted LRGB filters (I know I probably only need 31mm - but the $130 premium is insurance I don't have to buy them again).  One thing about the Chroma - while they do seem to get a lot of respect as high quality, the narrowband filters are 7 to 8mm while the astrodon's are 5mm or 3mm. I could but the HaLRGB set but I might hold off on the Ha until I understand that better.

 

Sure does add up quickly!



#5 bobzeq25

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Posted 21 April 2019 - 08:10 AM

Thanks for the detailed answers!  That gives me a much better framework of understanding to go on!

 

Wouldn't the effects of seeing/tracking on small pixels effectively be like emulating large pixels?  Ah - but then you have a smaller sensor...

 

Reading about the Astrodon filters, their site says "The I-Series filters compensate for the lower red response of these Interline detectors affecting the design of the Green and Red filters.  The Luminance and Blue filters are the same as those in our E-Series.  This means that your RGB color combine weights will be approximately 1:1:1 within perhaps 10% for equal length exposures.  This can never be perfect, but it does allow you to take one exposure time for all of your RGB data and therefore, only just one corresponding dark exposure time."  So this raises the question: do you take a full set of dark, flat, bias calibration images separately for each filter?

 

I've seen some comments on - I think - the ZWO filters not being parfocal. With SGP and a motorized focuser, focusing only takes a couple minutes. Wouldn't you want to refocus every time you change fileters?

 

I want to read some more, but I'm thinking about the ASI1600MM with a ZWO EFW 8 and Chroma 36mm unmounted LRGB filters (I know I probably only need 31mm - but the $130 premium is insurance I don't have to buy them again).  One thing about the Chroma - while they do seem to get a lot of respect as high quality, the narrowband filters are 7 to 8mm while the astrodon's are 5mm or 3mm. I could but the HaLRGB set but I might hold off on the Ha until I understand that better.

 

Sure does add up quickly!

Money is the main drawback to going mono plus filters.

 

Small pixels accumulate data more slowly, because they cover less sky.  The way it's usually described is by image scale.  Take the focal length of your scope, divide by 200.  Divide the pixel size of your camera (real or theoretical camera) by that.  The result is the image scale in arc sec squared per pixel.  The usual range is about 1 to 2.  1 can theoretically provide more resolution, if other things cooperate.  2 has better signal to noise ratio, is more "forgiving".

 

I have a few different scopes and cameras, image anywhere from 1.0 to 2.7.  This is not unusual.  1.0 is generally only useful on above average nights, my location has chronically bad seeing.  There's little point to using it if you can't get the resolution.  Images on astrobin usually list the image scale, mine almost always do.

 

Since the lens is covered, bias and darks are filter independent (unless you change the exposure for the lights, then you either take separate darks or (less desirable) scale them).  You do take flats for each filter.  You calibrate and stack each filter separately, combine them later in processing.  Perhaps do some processing on each stack before combination, that varies with the imager.  For example, people differ on whether to do gradient reduction separately, or combined.  I generally do combined.

 

Refocusing varies.   I tend to do all the exposures with one filter at once.  Refocusing between filters also covers some temperature changes.  Others may shoot LRGB, LRGB,...  There are intermediate schemes.

 

I'm old, my sessions are not terribly long.  Often do the RGB one night, the other filters another.  3 nights is not unheard of.  Again, not unusual practice.

 

I use Astronmik filters, use a 6nm Ha.  Both decisions are the right cost/performance tradeoff for me.  Narrower Ha is generally better, costs more.


Edited by bobzeq25, 21 April 2019 - 08:18 AM.



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