Hi Brian,
Yes, I do now well longer exposure than 10 sec. When, I have started I have used exclusively exposure from Smart Histogram; then realized that I cannot get pale/weak targets, no matter how many subframes are stacked. I even tried 1500 subframes!
Very long exposure is bad as well. Light pollutions flood background.
So, there are targets (mainly galaxies) that impossible (or I don't know how) to get from bortle 7.
Otherwise, globular clusters 45 sec subframe; galaxies 3 min and nebulas with narrowband filters 5-7 min.
All the best!
Ana
Picking the correct exposure for Deep Sky
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Re: Picking the correct exposure for Deep Sky
Hi Ana,
You are in luck! You can significantly decrease the total integration time with no additional expense. I used an online calculator to see if your camera is suited to your telescope:
https://astronomy.tools/calculators/ccd_suitability
Assuming that you have a vanilla f/10 Celestron 8 with no focal reducer, your ASI294MC is over-sampling, which is beneficial for the Moon and planets, but it hurts you with Deep-Sky astrophotography. I recommend telling SharpCap to operate the camera in "Bin 2 mode". I think you will be happy with the results.
(Technically, you should re-run Sensor Analysis.)
EDIT: Some additional thoughts:
1. Watch your Gain! Look here at this graph of Read Noise versus Gain: https://astronomy-imaging-camera.com/pr ... -pro-color. Set the Gain at 120 where the Read Noise suddenly drops. Avoid the temptation to set the Gain lower. A Full Well Depth (FWD) of 63.7ke- looks attractive but that's only for advanced use. You need to first develop expertise with low FWD and low Read Noise. Stay between Gain 120 and 150. Experiment later.
2. If your camera has adjustable Offset then make sure it is set correctly. We, at the forum, can help you with that if you have questions.
3. Recapture all calibration frames at Bin 2. Don't try to use the ones you've captured at Bin 1. Fortunately with a cooled camera you can capture Darks indoors on cloudy nights.
4. Don't be fooled into thinking that you only need 20-30 Darks. Ideally, you want to have as many as you have Lights. Fortunately, you can reuse Darks, so invest the time into capturing 100 Darks now and then reuse them throughout the season.
Brian
You are in luck! You can significantly decrease the total integration time with no additional expense. I used an online calculator to see if your camera is suited to your telescope:
https://astronomy.tools/calculators/ccd_suitability
Assuming that you have a vanilla f/10 Celestron 8 with no focal reducer, your ASI294MC is over-sampling, which is beneficial for the Moon and planets, but it hurts you with Deep-Sky astrophotography. I recommend telling SharpCap to operate the camera in "Bin 2 mode". I think you will be happy with the results.
(Technically, you should re-run Sensor Analysis.)
EDIT: Some additional thoughts:
1. Watch your Gain! Look here at this graph of Read Noise versus Gain: https://astronomy-imaging-camera.com/pr ... -pro-color. Set the Gain at 120 where the Read Noise suddenly drops. Avoid the temptation to set the Gain lower. A Full Well Depth (FWD) of 63.7ke- looks attractive but that's only for advanced use. You need to first develop expertise with low FWD and low Read Noise. Stay between Gain 120 and 150. Experiment later.
2. If your camera has adjustable Offset then make sure it is set correctly. We, at the forum, can help you with that if you have questions.
3. Recapture all calibration frames at Bin 2. Don't try to use the ones you've captured at Bin 1. Fortunately with a cooled camera you can capture Darks indoors on cloudy nights.
4. Don't be fooled into thinking that you only need 20-30 Darks. Ideally, you want to have as many as you have Lights. Fortunately, you can reuse Darks, so invest the time into capturing 100 Darks now and then reuse them throughout the season.
Brian
Re: Picking the correct exposure for Deep Sky
Hi Brian,
I actually use C8 with 0.63 reducer, and vixen ED103 with ASI294MC or ASI294MM camera. How do you know it?
1. I don't oversample at such configuration. This camera with large pixel size. There is only one cooling CMOS with bigger pixels.
2. Binning with CMOS cameras is useless. Use CCD will increase exposure 4-7 times. Had CCD and sold.
3. Gain is always 121 for ASI294. Please look at their graphs and you will see, it is recommended.
4. I do not use offset.
5. I have used 25, 50 and 100 darks and flats for masters. No difference. Dithering makes difference.
Overall, listed exposure time and setting are optimal for my set up. So, it is just matter how many hours of integration, and how many frames are rejected (i am very strict about it; 10-30% frames may not go into post processing).
This said, I doubt with my set up people will properly resolute some galaxies (no M catalog) or core M80 or other NGC (no M catalog) globular clusters, no matter how they try.
This is reason people get 20K+ mounts, 20K+ scopes and 10K+ cameras... and put these into New Mexico or Chile for another 1K a month.
All the best!
Armen
I actually use C8 with 0.63 reducer, and vixen ED103 with ASI294MC or ASI294MM camera. How do you know it?
1. I don't oversample at such configuration. This camera with large pixel size. There is only one cooling CMOS with bigger pixels.
2. Binning with CMOS cameras is useless. Use CCD will increase exposure 4-7 times. Had CCD and sold.
3. Gain is always 121 for ASI294. Please look at their graphs and you will see, it is recommended.
4. I do not use offset.
5. I have used 25, 50 and 100 darks and flats for masters. No difference. Dithering makes difference.
Overall, listed exposure time and setting are optimal for my set up. So, it is just matter how many hours of integration, and how many frames are rejected (i am very strict about it; 10-30% frames may not go into post processing).
This said, I doubt with my set up people will properly resolute some galaxies (no M catalog) or core M80 or other NGC (no M catalog) globular clusters, no matter how they try.
This is reason people get 20K+ mounts, 20K+ scopes and 10K+ cameras... and put these into New Mexico or Chile for another 1K a month.
All the best!
Armen
Re: Picking the correct exposure for Deep Sky
Armen,
If I am not mistaken, you never mentioned in this topic that you use a reducer. You can't expect people like myself to look through all of your previous topics for clues to what equipment you actually have. I've wasted my time. BTW, software binning DOES increase SNR but not as much as hardware binning.
Contact Menno, He has a similar kit and has worse light pollution than you.
EDIT: It is always instructive to visit the Gallery to see what others are doing. If you see similar equipment and equal or worse light pollution, then send them a private message to see if they can help you out. Some people are happy to help while others keep their secrets close to their vest.
Brian
If I am not mistaken, you never mentioned in this topic that you use a reducer. You can't expect people like myself to look through all of your previous topics for clues to what equipment you actually have. I've wasted my time. BTW, software binning DOES increase SNR but not as much as hardware binning.
Contact Menno, He has a similar kit and has worse light pollution than you.
EDIT: It is always instructive to visit the Gallery to see what others are doing. If you see similar equipment and equal or worse light pollution, then send them a private message to see if they can help you out. Some people are happy to help while others keep their secrets close to their vest.
Brian
Re: Picking the correct exposure for Deep Sky
Brian,
I have visited many galleries and have seen many people in action. People with similar to my equipment capture similar targets, with similar resolution and with similar sensitivity.
I sometimes use C8 without reducer. I will try with binning; otherwise, there is no CMOS camera to avoid oversampling. Well, there are couple on market, but they are very expensive or ASI432MM (9um/pixel) without cooling.
Take care!
All the best!
Armen
I have visited many galleries and have seen many people in action. People with similar to my equipment capture similar targets, with similar resolution and with similar sensitivity.
I sometimes use C8 without reducer. I will try with binning; otherwise, there is no CMOS camera to avoid oversampling. Well, there are couple on market, but they are very expensive or ASI432MM (9um/pixel) without cooling.
Take care!
All the best!
Armen
Re: Picking the correct exposure for Deep Sky
Armen,
Keep using the reducer and bin 1. (You can always experiment later with bin 2.)
I see you've used the Optolong L-Pro filter. Do you know what is the primary source of your light pollution? If it is gas vapor then the Optolong filter should work. However if it is LED lighting then that could be a problem.
It could be that your best solution is to pack up your kit and drive 10 miles farther away from the LP source. You can still do astrophotography from home but your choices are limited: Lunar, Planetary, and Bright DSO. SharpCap is an excellent tool for the Moon and planets.
Brian
Keep using the reducer and bin 1. (You can always experiment later with bin 2.)
I see you've used the Optolong L-Pro filter. Do you know what is the primary source of your light pollution? If it is gas vapor then the Optolong filter should work. However if it is LED lighting then that could be a problem.
It could be that your best solution is to pack up your kit and drive 10 miles farther away from the LP source. You can still do astrophotography from home but your choices are limited: Lunar, Planetary, and Bright DSO. SharpCap is an excellent tool for the Moon and planets.
Brian
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mgutierrez
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Re: Picking the correct exposure for Deep Sky
Hi Robin,
I've just registered and I take the opportunity to say hello everyone.
I've read your fantastic explanation and also watched your video. I think I understand it quite well. However, I have a doubt I cannot figure it out and it is regarding the software implementation of the algorithm to find out the optical (minimal?) exposure time that smart histogram does.
At some point, I guess (this is my doubt), the software needs to know the adc bit depth of the camera to convert adu to e- to know the rp,sky term and be able to apply the formula, is that right? If so, how does sharpcap know such data? is it provided in some way by the driver? or is this data not needed at all?
Thanks in advance.
Miguel
I've just registered and I take the opportunity to say hello everyone.
I've read your fantastic explanation and also watched your video. I think I understand it quite well. However, I have a doubt I cannot figure it out and it is regarding the software implementation of the algorithm to find out the optical (minimal?) exposure time that smart histogram does.
At some point, I guess (this is my doubt), the software needs to know the adc bit depth of the camera to convert adu to e- to know the rp,sky term and be able to apply the formula, is that right? If so, how does sharpcap know such data? is it provided in some way by the driver? or is this data not needed at all?
Thanks in advance.
Miguel
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Re: Picking the correct exposure for Deep Sky
Hi Miguel,
all the data relating the the sensor bit depth and the e/ADU values are measured by the 'Sensor Analysis' function in SharpCap. SharpCap ships with analysis data pre-measured for about 300 popular astronomy cameras, and if your camera isn't in that list then you need to have run the sensor analysis tool to be able to use the smart histogram feature.
cheers,
Robin
all the data relating the the sensor bit depth and the e/ADU values are measured by the 'Sensor Analysis' function in SharpCap. SharpCap ships with analysis data pre-measured for about 300 popular astronomy cameras, and if your camera isn't in that list then you need to have run the sensor analysis tool to be able to use the smart histogram feature.
cheers,
Robin
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mgutierrez
- Posts: 7
- Joined: Sun Sep 03, 2023 8:07 pm
Re: Picking the correct exposure for Deep Sky
Thanks for the prompt reply Robin.
Excuse my ignorance; cause I guess then my question is addressed to sensor analysis instead of smart histogram. If my camera is not listed, at some point sensor analysis and/or smart histogram need to figure out the adc depth, no? If so, how?
Excuse my ignorance; cause I guess then my question is addressed to sensor analysis instead of smart histogram. If my camera is not listed, at some point sensor analysis and/or smart histogram need to figure out the adc depth, no? If so, how?
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admin
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Re: Picking the correct exposure for Deep Sky
Hi,
yes, the analysis procedure has to work that out. It captures images at high bit depth and looks at the values in the images - if it is a 16 bit sensor then you will see all possible values, if it's 14 bit then everything will be a multiple of 4 and so on.
cheers,
Robin
yes, the analysis procedure has to work that out. It captures images at high bit depth and looks at the values in the images - if it is a 16 bit sensor then you will see all possible values, if it's 14 bit then everything will be a multiple of 4 and so on.
cheers,
Robin