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Comparison Between DSLR and ASI1600mm-Cool Images

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#76 whwang

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Posted 24 September 2016 - 12:33 PM

 

IIRC, you have the KAF-16803? I don't think you can really use that as a gauge of the performance of the ASI1600.....

It is possible to use a shorter scope with a smaller sensor to achieve the same FoV, though....

 

Hi Jon,

 

I am not using 16803's performance to judge ASI1600.  I am using my experience on 16803 to understand the limitation of the LRGB composition with mono sensors.  My science training makes me very careful on what experience can be transported to different situations and what can't.  For example, a big disadvantage of 16803 (and all other Kodak CCDs) is its high read noise.  I hate it a lot, and I criticize CCDs about this all the time.  However, I know that ASI1600 has much lower readout noise.  So I will never criticize the ASI one regarding its readout noise and any issues associated with readout noise (such as sub lengths).

 

As for using a short focal length to get FoV, you loss resolution at the same time.  If one wants to maintain resolution (with proper sampling of the stellar FWHM) and get large FoV, simple math tells you that the right way to go is high pixel counts, not short focal length.  Of course, the real word is much more complicated.  We can adjust focal length and pixel size to achieve Nyquist sampling, but there are always limits.  We are forced to live with limited choices of focal lengths (if we do not want to change the main mirror) and limited choices of sensor size/pixel size combinations.  So it's never simple, but the basic idea of going to high pixel count is still valid.

 

Cheers,

Wei-Hao


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#77 Jon Rista

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Posted 24 September 2016 - 12:46 PM

 

 

IIRC, you have the KAF-16803? I don't think you can really use that as a gauge of the performance of the ASI1600.....

It is possible to use a shorter scope with a smaller sensor to achieve the same FoV, though....

 

Hi Jon,

 

I am not using 16803's performance to judge ASI1600.  I am using my experience on 16803 to understand the limitation of the LRGB composition with mono sensors.  My science training makes me very careful on what experience can be transported to different situations and what can't.  For example, a big disadvantage of 16803 (and all other Kodak CCDs) is its high read noise.  I hate it a lot, and I criticize CCDs about this all the time.  However, I know that ASI1600 has much lower readout noise.  So I will never criticize the ASI one regarding its readout noise and any issues associated with readout noise (such as sub lengths).

 

As for using a short focal length to get FoV, you loss resolution at the same time.  If one wants to maintain resolution (with proper sampling of the stellar FWHM) and get large FoV, simple math tells you that the right way to go is high pixel counts, not short focal length.  Of course, the real word is much more complicated.  We can adjust focal length and pixel size to achieve Nyquist sampling, but there are always limits.  We are forced to live with limited choices of focal lengths (if we do not want to change the main mirror) and limited choices of sensor size/pixel size combinations.  So it's never simple, but the basic idea of going to high pixel count is still valid.

 

Cheers,

Wei-Hao

 

I agree things are not just simple. I say that a lot myself. However I have used and processed data from DSLRs, CCDs (including KAI-11002 and KAF-16803) and the ASI1600. The difference with the ASI1600 is really huge. It's surprising how much the low noise matters. It matters more than I originally thought. I do think the results speak for themselves...see my previous post comparing 2400 seconds of mono-modded, cold-fingered DSLR data to 90 seconds of ASI data. 

 

I agree, there are definite limits with shorter scopes. The dawes limit of an 80mm is about 1.4", while the dawes limit of a 200mm is abut 0.6". No question you are able to get more resolution out of a larger scope. Seeing can be a normalizing factor here. If you have good seeing, then absolutely the larger scope will deliver more detail. If you have poorer seeing, then it might not matter as much. Assuming you have great seeing, the ASI1600 has pixels about 1/3 the area of a 6D's pixels...which should still give you some resolution improvement with short, fast scopes. 

 

Higher resolution, however, is usually at the cost of FoV...which is where the mosaicing comes into play. ;) I've been using a 600mm focal length f/4 scope, and have not moved to a shorter one for that very reason...because I prefer the higher resolution of my scope over a smaller one. I also prefer the larger light gathering capacity of the bigger aperture. I do have to mosaic to get the larger FoV's...but, that hasn't really been a big issue so far. I'm able to get data for 2x2 panels in a single night when only integrating about 30 minutes of data per panel (which for some of the regions I am working on, is all I seem to need)...it only takes about two and a half hours to get enough data for a full-frame field of view.


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#78 mistikato

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Posted 24 September 2016 - 02:44 PM

One thing that is advantageous in DSLRS compared to CCDs is that they are self contained. No need of a computer (which needs power). This may not be a big deal for some, but can be an added hassle for  mobile users...

 

Also, some autoguiders are pretty smart (I use an MGEN), and can control the camera (incl dithering), so with a DSLR, I don't need to worry about using a laptop in the field. I like that, one thing less to worry about...


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#79 Jon Rista

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Posted 24 September 2016 - 04:11 PM

One thing that is advantageous in DSLRS compared to CCDs is that they are self contained. No need of a computer (which needs power). This may not be a big deal for some, but can be an added hassle for  mobile users...

Also, some autoguiders are pretty smart (I use an MGEN), and can control the camera (incl dithering), so with a DSLR, I don't need to worry about using a laptop in the field. I like that, one thing less to worry about...


That's a great point. The self-contained aspect can be quite beneficial at times.  

#80 vdb

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Posted 24 September 2016 - 05:37 PM

 

Well the loss of micro lensing on paper seems a big deal in reality it is not, these cmos sensors are pretty efficient ...
The only thing modded mono camera's without an UV/IR cut filter have is that they are so sensitive they pick up any IR emitting from the electronics ...


Without the microlenses, they are actually not that efficient. Without microlenses, Q.E. can drop to 30% or less. It was the addition of the microlenses in the first place that improve their Q.E. about a decade ago...and the move to gapless microlenses improved it more...and now in recent years, the move to offset microlenses at the periphery of large sensors that has reduced vignetting caused by the angle of incidence of light, producing more normalized Q.E. across the frame. Removal of the microlenses absolutely has an impact. I'll chop up some 100% crops for comparison...there is still no contest here. ;)

 

EDIT:

 

Comparison of 100% crops...2400s 8x300s stacked from the D600 cold finger mono mod:

 

SCdnkh0.jpg

 

Vs. a single 90s sub from the ASI1600, stretched to a similar intensity:

 

wjmt4k8.jpg

 

A difference factor of 26:1 here, just going by exposure time. Even if  you figure there may be a stop worth of f-ratio difference here, this is still over a factor of 10:1. Just for reference, here is a 2250s integration of the same crop from the ASI1600:

 

dGiRb9L.jpg

 

I do indeed believe the loss in Q.E. matters. The ASI1600 is mono and still has it's microlenses...I believe that is one of the advantages of mono cmos astro cams over mono-modded DSLRs. 

 

Ouch claiming comparison is difficult and should be under same conditions ... and then compare a pushed processed image I posted ... ah well here a single sub with a very small aperture telescope. so one sub 5 minute iso 800 not very deep cooled something like 15C ...

Attached Thumbnails

  • ngc7000-7_300sec_1x1_HA_frame1_c.jpg


#81 vdb

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Posted 24 September 2016 - 05:42 PM

100% crop ...

As you can see not really good in focus ...  it drifted out during night of bumped 9 panel (hence I posted only 3 panel)

 

Attached Thumbnails

  • ngc7000-7_300sec_1x1_HA_frame1_c-crop.jpg


#82 akulapanam

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Posted 24 September 2016 - 06:45 PM

 

 

IIRC, you have the KAF-16803? I don't think you can really use that as a gauge of the performance of the ASI1600.....

It is possible to use a shorter scope with a smaller sensor to achieve the same FoV, though....

 

Hi Jon,

 

I am not using 16803's performance to judge ASI1600.  I am using my experience on 16803 to understand the limitation of the LRGB composition with mono sensors.  My science training makes me very careful on what experience can be transported to different situations and what can't.  For example, a big disadvantage of 16803 (and all other Kodak CCDs) is its high read noise.  I hate it a lot, and I criticize CCDs about this all the time.  However, I know that ASI1600 has much lower readout noise.  So I will never criticize the ASI one regarding its readout noise and any issues associated with readout noise (such as sub lengths).

 

As for using a short focal length to get FoV, you loss resolution at the same time.  If one wants to maintain resolution (with proper sampling of the stellar FWHM) and get large FoV, simple math tells you that the right way to go is high pixel counts, not short focal length.  Of course, the real word is much more complicated.  We can adjust focal length and pixel size to achieve Nyquist sampling, but there are always limits.  We are forced to live with limited choices of focal lengths (if we do not want to change the main mirror) and limited choices of sensor size/pixel size combinations.  So it's never simple, but the basic idea of going to high pixel count is still valid.

 

Cheers,

Wei-Hao

 

 

Not if you buy a fast astrograph.  A RH200, RASA, Tak 180, Knaeble Baker Schmidt, or Hyperstar are all good options that give you lots of resolution for small pixel cameras.  The larger the scope the more of a PITA it becomes and the KAF-16803 itself is a bit of a PITA to use compared to a Sony or Panasonic chip.

 

One thing that is advantageous in DSLRS compared to CCDs is that they are self contained. No need of a computer (which needs power). This may not be a big deal for some, but can be an added hassle for  mobile users...

 

Also, some autoguiders are pretty smart (I use an MGEN), and can control the camera (incl dithering), so with a DSLR, I don't need to worry about using a laptop in the field. I like that, one thing less to worry about...

I don't know if you really want to obtain great images you need the capabilities that a computer brings especially on narrow targets.   The MGEN is nice but not when you are shooting small FOV high resolution images with faint guide stars and I was never able to get my DSLR as well focused as my CCD.  A DSLR also means you need A LOT more exposure time, even over a color CMOS/CCD to account for the higher noise.  I've had both but I didn't start getting good results until I purchased the cooled CCD/CMOS.


Edited by akulapanam, 24 September 2016 - 06:45 PM.


#83 Ron359

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Posted 24 September 2016 - 08:52 PM

 

I don't know if you really want to obtain great images you need the capabilities that a computer brings especially on narrow targets.   The MGEN is nice but not when you are shooting small FOV high resolution images with faint guide stars and I was never able to get my DSLR as well focused as my CCD.  A DSLR also means you need A LOT more exposure time, even over a color CMOS/CCD to account for the higher noise.  I've had both but I didn't start getting good results until I purchased the cooled CCD/CMOS.

 

There is a reason there is a DEDICATED CCD/CMOS Imaging Forum and DSLR Imaging Forum.  If you really need to look down your tubes and debate them ad-nauseum I'm sure they'd love to have you and any evangelical converts over there and leave the rest of us unclean, noisy DSLR users to our mediocre fates.  

 

:beat:  :lalalala:



#84 Jon Rista

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Posted 24 September 2016 - 09:05 PM

I don't know if you really want to obtain great images you need the capabilities that a computer brings especially on narrow targets.   The MGEN is nice but not when you are shooting small FOV high resolution images with faint guide stars and I was never able to get my DSLR as well focused as my CCD.  A DSLR also means you need A LOT more exposure time, even over a color CMOS/CCD to account for the higher noise.  I've had both but I didn't start getting good results until I purchased the cooled CCD/CMOS.

There is a reason there is a DEDICATED CCD/CMOS Imaging Forum and DSLR Imaging Forum.  If you really need to look down your tubes and debate them ad-nauseum I'm sure they'd love to have you and any evangelical converts over there and leave the rest of us unclean, noisy DSLR users to our mediocre fates.  
 
:beat:  :lalalala:


Every once in a while I like to shake things up in this forum...just so everyone here they don't have to be stuck with noisy DSLR data forever. ;)

#85 whwang

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Posted 24 September 2016 - 10:47 PM

 

Not if you buy a fast astrograph.  A RH200, RASA, Tak 180, Knaeble Baker Schmidt, or Hyperstar are all good options that give you lots of resolution for small pixel cameras.  The larger the scope the more of a PITA it becomes and the KAF-16803 itself is a bit of a PITA to use compared to a Sony or Panasonic chip.

 

 

I do own a TAK 180, so I understand the limits of short focal length systems, unless, TAK 180 is bad.

 

I said this already, and I don't mind saying it again.  Even if all these short focal length systems can achieve their theoretical resolution limit, once you couple them with a sensor whose pixel size properly samples the stellar PSF, the FoV is determined by the total pixel count, not by the focal length.  Think about it carefully, do some math, and one day you will realize what I say here is correct.

 

Now, back to the real world, I have high doubts on the resolution of such short focal length systems.  Their images look sharp, because of their short focal lengths, not because of high angular resolution.  Just use Hyperstar as an examples.  Have anyone tried to image the same target using a C11-proper and C11-hyperstar?  Which one can resolve more details?  I bet it will be C11-proper, if the experiment is conducted correctly.  By converting it to a Hyperstar system, you gain FoV, but you loss resolution.  Same as TAK 180. It can't give you the resolution of an equally sized but F5 Newtonian. The resolution is compromised when TAK designs the corrector of 180.



#86 Jon Rista

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Posted 24 September 2016 - 11:45 PM

Now, back to the real world, I have high doubts on the resolution of such short focal length systems.  Their images look sharp, because of their short focal lengths, not because of high angular resolution.  Just use Hyperstar as an examples.  Have anyone tried to image the same target using a C11-proper and C11-hyperstar?  Which one can resolve more details?  I bet it will be C11-proper, if the experiment is conducted correctly.  By converting it to a Hyperstar system, you gain FoV, but you loss resolution.  Same as TAK 180. It can't give you the resolution of an equally sized but F5 Newtonian. The resolution is compromised when TAK designs the corrector of 180.


I agree. The images look sharp at shorter focal lengths because they are still usually undersampled. I think that may be something that confuses a lot of people: sharpness. Sharpness does not necessarily mean resolution. Ironically, the inverse is usually true. Images acquired at a high f-ratio and with a large aperture tend to appear softer...however, they are actually more detailed (their FWHMs measure smaller!) Sharpness is really more a gauge of the crispness and acutance of an image, not it's resolution. 

 

Small pixels will help you get better sampling at short focal lengths, as you could be sampling at 3"/px rather than 5"/px at 300mm. Both are still undersampled, though. So I totally agree, of you really want truly high resolution, you want a larger aperture at a higher f-ratio, where you can be oversampling.



#87 akulapanam

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Posted 25 September 2016 - 02:05 AM

 

 

Not if you buy a fast astrograph.  A RH200, RASA, Tak 180, Knaeble Baker Schmidt, or Hyperstar are all good options that give you lots of resolution for small pixel cameras.  The larger the scope the more of a PITA it becomes and the KAF-16803 itself is a bit of a PITA to use compared to a Sony or Panasonic chip.

 

 

I do own a TAK 180, so I understand the limits of short focal length systems, unless, TAK 180 is bad.

 

I said this already, and I don't mind saying it again.  Even if all these short focal length systems can achieve their theoretical resolution limit, once you couple them with a sensor whose pixel size properly samples the stellar PSF, the FoV is determined by the total pixel count, not by the focal length.  Think about it carefully, do some math, and one day you will realize what I say here is correct.

 

Now, back to the real world, I have high doubts on the resolution of such short focal length systems.  Their images look sharp, because of their short focal lengths, not because of high angular resolution.  Just use Hyperstar as an examples.  Have anyone tried to image the same target using a C11-proper and C11-hyperstar?  Which one can resolve more details?  I bet it will be C11-proper, if the experiment is conducted correctly.  By converting it to a Hyperstar system, you gain FoV, but you loss resolution.  Same as TAK 180. It can't give you the resolution of an equally sized but F5 Newtonian. The resolution is compromised when TAK designs the corrector of 180.

 

 

 

 

Now, back to the real world, I have high doubts on the resolution of such short focal length systems.  Their images look sharp, because of their short focal lengths, not because of high angular resolution.  Just use Hyperstar as an examples.  Have anyone tried to image the same target using a C11-proper and C11-hyperstar?  Which one can resolve more details?  I bet it will be C11-proper, if the experiment is conducted correctly.  By converting it to a Hyperstar system, you gain FoV, but you loss resolution.  Same as TAK 180. It can't give you the resolution of an equally sized but F5 Newtonian. The resolution is compromised when TAK designs the corrector of 180.


I agree. The images look sharp at shorter focal lengths because they are still usually undersampled. I think that may be something that confuses a lot of people: sharpness. Sharpness does not necessarily mean resolution. Ironically, the inverse is usually true. Images acquired at a high f-ratio and with a large aperture tend to appear softer...however, they are actually more detailed (their FWHMs measure smaller!) Sharpness is really more a gauge of the crispness and acutance of an image, not it's resolution. 

 

Small pixels will help you get better sampling at short focal lengths, as you could be sampling at 3"/px rather than 5"/px at 300mm. Both are still undersampled, though. So I totally agree, of you really want truly high resolution, you want a larger aperture at a higher f-ratio, where you can be oversampling.

 

The spot sizes on the RASA and RH200 are below the spot size on a C11 edge.  I suspect that if you use a IMX178 or ICX834 based camera you will result in the same if not superior image to what you can get on a C11 edge with a 11000 or 16803 based chip for the same arc sec resolution.



#88 bobzeq25

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Posted 25 September 2016 - 02:26 AM

 

Now, back to the real world, I have high doubts on the resolution of such short focal length systems.  Their images look sharp, because of their short focal lengths, not because of high angular resolution.  Just use Hyperstar as an examples.  Have anyone tried to image the same target using a C11-proper and C11-hyperstar?  Which one can resolve more details?  I bet it will be C11-proper, if the experiment is conducted correctly.  By converting it to a Hyperstar system, you gain FoV, but you loss resolution.  Same as TAK 180. It can't give you the resolution of an equally sized but F5 Newtonian. The resolution is compromised when TAK designs the corrector of 180.


I agree. The images look sharp at shorter focal lengths because they are still usually undersampled. I think that may be something that confuses a lot of people: sharpness. Sharpness does not necessarily mean resolution. Ironically, the inverse is usually true. Images acquired at a high f-ratio and with a large aperture tend to appear softer...however, they are actually more detailed (their FWHMs measure smaller!) Sharpness is really more a gauge of the crispness and acutance of an image, not it's resolution. 

 

Small pixels will help you get better sampling at short focal lengths, as you could be sampling at 3"/px rather than 5"/px at 300mm. Both are still undersampled, though. So I totally agree, of you really want truly high resolution, you want a larger aperture at a higher f-ratio, where you can be oversampling.

 

The interesting question is whether oversampled or undersampled are more pleasing.  Obviously the technician, the pixel peeper who enlarges the image and looks at stars and fine details under magnification will like oversampled.  But, in The Deep Space imaging primer, Charles Bracken likes a bit undersampled.

 

This may be related to the thread some months back where an imager  noted with dismay that technically superb images won Image of the Day less often than somewhat artistic one.



#89 Jon Rista

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Posted 25 September 2016 - 10:02 AM

Not if you buy a fast astrograph.  A RH200, RASA, Tak 180, Knaeble Baker Schmidt, or Hyperstar are all good options that give you lots of resolution for small pixel cameras.  The larger the scope the more of a PITA it becomes and the KAF-16803 itself is a bit of a PITA to use compared to a Sony or Panasonic chip.

 
I do own a TAK 180, so I understand the limits of short focal length systems, unless, TAK 180 is bad.
 
I said this already, and I don't mind saying it again.  Even if all these short focal length systems can achieve their theoretical resolution limit, once you couple them with a sensor whose pixel size properly samples the stellar PSF, the FoV is determined by the total pixel count, not by the focal length.  Think about it carefully, do some math, and one day you will realize what I say here is correct.
 
Now, back to the real world, I have high doubts on the resolution of such short focal length systems.  Their images look sharp, because of their short focal lengths, not because of high angular resolution.  Just use Hyperstar as an examples.  Have anyone tried to image the same target using a C11-proper and C11-hyperstar?  Which one can resolve more details?  I bet it will be C11-proper, if the experiment is conducted correctly.  By converting it to a Hyperstar system, you gain FoV, but you loss resolution.  Same as TAK 180. It can't give you the resolution of an equally sized but F5 Newtonian. The resolution is compromised when TAK designs the corrector of 180.

 
 

Now, back to the real world, I have high doubts on the resolution of such short focal length systems.  Their images look sharp, because of their short focal lengths, not because of high angular resolution.  Just use Hyperstar as an examples.  Have anyone tried to image the same target using a C11-proper and C11-hyperstar?  Which one can resolve more details?  I bet it will be C11-proper, if the experiment is conducted correctly.  By converting it to a Hyperstar system, you gain FoV, but you loss resolution.  Same as TAK 180. It can't give you the resolution of an equally sized but F5 Newtonian. The resolution is compromised when TAK designs the corrector of 180.


I agree. The images look sharp at shorter focal lengths because they are still usually undersampled. I think that may be something that confuses a lot of people: sharpness. Sharpness does not necessarily mean resolution. Ironically, the inverse is usually true. Images acquired at a high f-ratio and with a large aperture tend to appear softer...however, they are actually more detailed (their FWHMs measure smaller!) Sharpness is really more a gauge of the crispness and acutance of an image, not it's resolution. 
 
Small pixels will help you get better sampling at short focal lengths, as you could be sampling at 3"/px rather than 5"/px at 300mm. Both are still undersampled, though. So I totally agree, of you really want truly high resolution, you want a larger aperture at a higher f-ratio, where you can be oversampling.

The spot sizes on the RASA and RH200 are below the spot size on a C11 edge.  I suspect that if you use a IMX178 or ICX834 based camera you will result in the same if not superior image to what you can get on a C11 edge with a 11000 or 16803 based chip for the same arc sec resolution.


Image scale is only dependent on focal length and pixel size, though. Even though the spot sizes may be better, with short focal lengths, it actually doesn't matter, since the spot size will be smaller than the pixel scale. Even if you used the smallest pixel size available today for astro use, 2.4 microns, the image scale with an RH200 would actually be lager than the spot size of the scope. There is a lower limit on pixel size...once you get into sub-micron sized pixels, then they are getting to be the size of the wavelengths of light. That would ultimately end up being a brick wall you couldn't get past. I know that 900nm pixels have been planned, but I don't think they have actually been made viable yet. So as you get to shorter focal lengths than 600mm, the primary limiting factor on blur size becomes the pixel scale itself, even if you use tiny, tiny pixels.

#90 whwang

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Posted 25 September 2016 - 05:01 PM

The spot size only tells you the linear resolution on the focal plane. What you really need is the angular resolution, which is the spot size divided by the focal length.
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#91 akulapanam

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Posted 25 September 2016 - 11:30 PM

The spot size only tells you the linear resolution on the focal plane. What you really need is the angular resolution, which is the spot size divided by the focal length.

 

Fair enough.  The 2015+ RH200 has a max spot size of 8 microns across the entire field up to 20mm off axis.  That gives us 8/600 = 0.013

 

The worst the RASA gets is about 9 microns at 20mm off axis.

http://telescope.bg/...er_FINAL_LR.pdf  9/620 = 0.015

 

The Celestron Edge C11 on the other hand gets a 60 micron spot size at 20mm off axis. 60/2790 = 0.0215 

http://www.optcorp.c...DWhitePaper.pdf

 

RASA and RH200 are a winner again here.


Edited by akulapanam, 25 September 2016 - 11:30 PM.


#92 whwang

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Posted 26 September 2016 - 02:04 AM

To get fair comparison, you need to use FWHM of the spot size, not the full extent.  The full extension only affects the apparent size of brighter stars, and the micro-contrast of nebula details.  The resolving power is more closely related to the FWHM of the spot size (plus diffraction), unless the PSF has extremely weird shapes.

 

Another way to look at this is to compare the spot size with the diffraction limit.  Both 11HD and 11RASA have the same angular resolution, but the sizes of their diffraction patterns are different due to the different focal lengths.  The Airy disk diameter is about 13um for 11HD, and 3um for RASA.  Just by reading the center of the spot diagram, I got a spot diameter of about 20um for 11HD, which is 1.5x the Airy disk.  From the spot diagram of 11RASA, 5-6um of spot diameter is probably a fair assessment for the field center, which is about 1.7x to 2x the Airy disk.  This is still excellent, but nevertheless slightly worse than its long focal length cousin.

 

The rule of thumb is that for the same aperture, wide-field design can't beat the long focal length one.  I admit that the RH system has the potential to break this rule.  However, like all other wide-field short focal length designs, the actual image quality (especially in the field corners) highly depends on the collimation of the mirrors/lenses.  Being theoretically possible doesn't always translate to being routinely achievable here.

 

Cheers,

Wei-Hao


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#93 GTom

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Posted 19 November 2016 - 05:59 PM

I had a ~5 years pause in astrophotography (missed the show :D), seeking the ideal travel camera and the ASI1600mm-cool caught my eye as a cost-efficient monochrome 4/3 unit.

 

I would be interested if anyone has produced longer, 4-5min exposures under identical conditions with a higher QE monochrome camera, such as the D5100 or NEX-5 and the ASI?

 

Where does this small camera stands between the "color" modded ILC cameras (incl a7s*) and high-end, high-QE CCD's? In practical terms, if I want a certain S/N result,

what would be the difference in exposure times between these:

 

Good APSc "color" camera, like D5100 (of course ICF removed, cooled)

Sony A7s "color"

Sony A7s monochrome (no ICF, cooled)

ASI1600mm-cool

An ICX694-based CCD camera (77% QE, low noise).


Edited by GTom, 20 November 2016 - 06:00 AM.


#94 james7ca

james7ca

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Posted 22 November 2016 - 01:13 AM

...Beyond that...90 second narrow band subs. I don't know if anyone's eve done that with results like the above before the ASI1600 came along...

Jon, you've done very nice work with the ASI1600, but to suggest that the ASI1600MM was the first CMOS camera to be used for successful, short exposure narrow-band imaging is probably a bit of an overstatement. For example, below is an image of the Horsehead Nebula that I posted to CN just over one year ago that was done with an uncooled ASI174MM using two-minute-long subs from a red-zone.

 

And here is the link to where this image was originally posted:

 

http://www.cloudynig...m/#entry6889730

 

Or, how about this Ha image of the Rosette Nebula that I did with one-minute-long subs back in November 2015?

 

http://www.cloudynig...e/#entry6878922

 

I captured this image over five months prior to the official announcement of the ASI1600, so it clearly predates anything that was done with the ASI1600 camera. There are more examples, I'm sure, from other users with different cameras certainly even prior to what I've shown above.

 

In fact, over the last year I’ve posted several narrow-band images to CN that were done with both the ASI174MM (uncooled) and the ASI178MM (cooled) that used exposures in the 1 to 4 minute range. Many of these were taken before the ASI1600 was even available.

 

I think the only "first" that can be claimed by the ASI1600 is that it was perhaps the first consumer-grade, near APS-C sized format, CMOS camera that was delivered in a astrophotography-optimized package. It is, however, not a revolution, more of an incremental upgrade over what came before in 2015 (and earlier). As for how it compares to the sensors in recent DSLRs or mirrorless APS-C/full-frame I'd have to say that each category has its strengths and weaknesses. In fact, the sensor technology that is available in recent generation consumer cameras is superior in some respects to that used in the ASI1600.

Attached Thumbnails

  • Horsehead ASI174MM.jpg

Edited by james7ca, 22 November 2016 - 04:50 AM.

  • bsavoie likes this


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