First, I’m APT registrants and my native language is Traditional Chinese , so excuse my bad English express.
I have wrote an article about “https://lukes-leisure-note.blogspot.com ... -post.html”( wrote with Traditional Chinese, you can use Google translate to your native language. Note that Google translate the “light pollution” to “light damage”)
My study how to reduce the impact of light pollution on images, here is a brief description:
I found these two videos on YouTube and watched them carefully several times:
https://youtu.be/3RH93UvP358
https://youtu.be/ub1HjvlCJ5Y
Then go to https://tools.sharpcap.co.uk/ mentioned in the above video to input the various camera parameters and the light pollution level of the shooting location to calculate the Sky Background Electron Rate.
Although I know that my home is located in the white zone, I don’t know how much Bortle Number should be entered, so I use the highest 9 to calculate. Maybe 8.5 can also be used. Think about use the SharpStar 107 F6.5 + Nikon D610 before. The post-produced images exposure was 90 seconds can still be accept.
It is quite different from the calculation. If calculate it back, the place that can be exposed for 90 seconds will be Bortle Number 4.6, this is the Suburban Sky !( It may also be possible that the shooting was late at night , and the shooting target I chose at this time was all located in a higher place.)
So... is there a way to get better data on the degree of light pollution? ( In addition to purchasing SQM )
After doing some homework, from the following articles:
* https://www.quora.com/How-can-I-measure-light-pollution
* https://earthsky.org/earth/phone-app-me ... brightness
From the description of the second article , it feels that the Dark Sky Meter app may be able to get more accurate data, because it is necessary to take a dark image with the iPhone , and then aim at the zenith ( or directly above the head ) to shoot an image of the sky. After comparing the two images, the app can calculate the quality of the sky.
This give an idea that when solve plate a target, maybe APT can then take two images( one is dark, one is that area light image) and calculate the best Exposure Length.
Is it possible APT add Calculate Best Exposure
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Radcliffe1
- Posts: 192
- Joined: Sat Oct 26, 2019 11:53 am
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Welcome !!!!!
One of the many great things about this forum is that we have members from all around the globe. The default language tends to be English and those who speak it as their first language are very aware that they have it easy ! They are often those who are least able to speak another language well, myself included.
You ask an excellent question and I think I asked something similar. I remember that what I asked was not possible. Ivo or someone should be able to give a better answer in the next few days.
best regards
Brian
One of the many great things about this forum is that we have members from all around the globe. The default language tends to be English and those who speak it as their first language are very aware that they have it easy ! They are often those who are least able to speak another language well, myself included.
You ask an excellent question and I think I asked something similar. I remember that what I asked was not possible. Ivo or someone should be able to give a better answer in the next few days.
best regards
Brian
Hi lykphoto and Brian,
I agree with Brian, lykphoto, your English is fine. I learnt both French and German for 5 years each and still can't speak either.
I'm sure the answer is that it could, and it may even be on the "to do" list already. But the problem is effort available to do it. As we all know Ivo and Maria are working hard on creating a new Auto Focusing solution (Focus Craft). So something as complex as a light pollution/exposure estimator is a long way off.
In the meantime, I use the SharpCap Sensor Analysis and Smart Histogram/Brain tools to estimate my best exposure and black level/offset for any location I am imaging from.
For my equipment, at a Bortle 6 site, it tells me that using a Skytech Light Pro filter and Unity Gain (400) then when it's nautical twilight I should use 90s exposures. When it gets to full dark I should use 150s exposures. So I set up a plan for somewhere in between, generally 120s exposures.
Here is some reading matter on the SharpCap's tools:
http://docs.sharpcap.co.uk/3.2/19_SensorAnalysis.htm
http://docs.sharpcap.co.uk/3.2/15_SmartHistogram.htm
https://forums.sharpcap.co.uk/viewtopic.php?f=35&t=456
I did not know about the Dark Sky Meter app, so I googled it. It sounded very interesting, but then I discovered Apple had bought it. And, in true Apple style, they have shut down the Android version of the app.
Cheers, Jim
I agree with Brian, lykphoto, your English is fine. I learnt both French and German for 5 years each and still can't speak either.
I'm sure the answer is that it could, and it may even be on the "to do" list already. But the problem is effort available to do it. As we all know Ivo and Maria are working hard on creating a new Auto Focusing solution (Focus Craft). So something as complex as a light pollution/exposure estimator is a long way off.
In the meantime, I use the SharpCap Sensor Analysis and Smart Histogram/Brain tools to estimate my best exposure and black level/offset for any location I am imaging from.
For my equipment, at a Bortle 6 site, it tells me that using a Skytech Light Pro filter and Unity Gain (400) then when it's nautical twilight I should use 90s exposures. When it gets to full dark I should use 150s exposures. So I set up a plan for somewhere in between, generally 120s exposures.
Here is some reading matter on the SharpCap's tools:
http://docs.sharpcap.co.uk/3.2/19_SensorAnalysis.htm
http://docs.sharpcap.co.uk/3.2/15_SmartHistogram.htm
https://forums.sharpcap.co.uk/viewtopic.php?f=35&t=456
I did not know about the Dark Sky Meter app, so I googled it. It sounded very interesting, but then I discovered Apple had bought it. And, in true Apple style, they have shut down the Android version of the app.
Cheers, Jim
Hi lykphoto,
also a warm welcome also from my side. Brian and Jim already found very good words. Fully ACK
Coming to your question
Exposure calculator:
As Brian pointed out correctly we had vividly exchanged opinion on this feature a while ago. Personally I consider these assistants for calculating the optimal exposure time as quite useless, since a lot of limiting factors are not included in the calculation. To base your exposure strategy on these calculations is quite optimistic, since other factors will be much more limiting or impacting the approach (e.g. tracking and guiding accuracy, aircraft traffic, and many more).
These calculators can only give an idea of the basic exposure times. They also seduce beginners to try to achieve this calculated exposure time at any means, instead of using the appropriate strategy for the situation. E. g. instead of going for short exposures they try to achieve the long exposure calculated by the tool, because it calculated the best benefit. For my opinion you could calculate this once for your setup, location and average sky quality just to get a basic idea. But not more and definitely not for every imaging session. Also from my experience, any AP has his/her own well-known-good exposure times like 180s, 300s and 600s. You can clearly observe that when checking the exposure times on AstroBin. You will find always the same timings.
Last but not least also consider that you want to use a Dark-Library. There you have your 3 or 4 favorite exposure timings covered.
Estimating Sky Quality:
To achieve a reliable and comparable measurement you have to use a dedicated SQM like those devices from Unihedron. I had used some software based tools, but they were never precise or constant enough. You have to be able to calibrate them and use them in a constant position when measuring. I advice you to have a look on the Unihedron page, since the they participate in light pollution mapping projects.
also a warm welcome also from my side. Brian and Jim already found very good words. Fully ACK
Coming to your question
Exposure calculator:
As Brian pointed out correctly we had vividly exchanged opinion on this feature a while ago. Personally I consider these assistants for calculating the optimal exposure time as quite useless, since a lot of limiting factors are not included in the calculation. To base your exposure strategy on these calculations is quite optimistic, since other factors will be much more limiting or impacting the approach (e.g. tracking and guiding accuracy, aircraft traffic, and many more).
These calculators can only give an idea of the basic exposure times. They also seduce beginners to try to achieve this calculated exposure time at any means, instead of using the appropriate strategy for the situation. E. g. instead of going for short exposures they try to achieve the long exposure calculated by the tool, because it calculated the best benefit. For my opinion you could calculate this once for your setup, location and average sky quality just to get a basic idea. But not more and definitely not for every imaging session. Also from my experience, any AP has his/her own well-known-good exposure times like 180s, 300s and 600s. You can clearly observe that when checking the exposure times on AstroBin. You will find always the same timings.
Last but not least also consider that you want to use a Dark-Library. There you have your 3 or 4 favorite exposure timings covered.
Estimating Sky Quality:
To achieve a reliable and comparable measurement you have to use a dedicated SQM like those devices from Unihedron. I had used some software based tools, but they were never precise or constant enough. You have to be able to calibrate them and use them in a constant position when measuring. I advice you to have a look on the Unihedron page, since the they participate in light pollution mapping projects.
Clear skies,
Ruediger
Ruediger
Hi Jim,,
I am using this APP for some time. It is nice, because you have it with you almost everywhere. But I have to admit the problem is the calibration. For a relative comparison it is pk, but not for a absolute value, though definitely besser as any subjective estimation with naked eye.
Clear skies,
Ruediger
Ruediger
Thank for you all so much for your quick and detailed responses, which really flatter me.
I will continue to research in depth based on the information you provide.
As a typhoon just passed by Taiwan, the weather will be bad in the next few days, so the Dark Sky Meter app didn’t test yet.
In fact, what I mean is that the user only needs to enter the following data:
Camera’s QE
Camera’s Pixel size
read noise of shutting ISO or Gain (R)
Telescope F Ratio
with/without Filter(if with Filter then choose what kind of filter)
APT take two images to find out Sky magnitude of target area to calculate Sky Background Electron Rate(P).then calculate the BEST(Recommended) sub length.
(This is the most critical point. If the Dark Sky Meter app is feasible through actual measurement, to calculate the best exposure time, goto https://tools.sharpcap.co.uk/ figure out Sky Background Electron Rate(P), then I can use mac’s Number enter the formula:10*R^2/P to calculate the BEST(Recommended) sub length.)
I will continue to research in depth based on the information you provide.
As a typhoon just passed by Taiwan, the weather will be bad in the next few days, so the Dark Sky Meter app didn’t test yet.
In fact, what I mean is that the user only needs to enter the following data:
Camera’s QE
Camera’s Pixel size
read noise of shutting ISO or Gain (R)
Telescope F Ratio
with/without Filter(if with Filter then choose what kind of filter)
APT take two images to find out Sky magnitude of target area to calculate Sky Background Electron Rate(P).then calculate the BEST(Recommended) sub length.
(This is the most critical point. If the Dark Sky Meter app is feasible through actual measurement, to calculate the best exposure time, goto https://tools.sharpcap.co.uk/ figure out Sky Background Electron Rate(P), then I can use mac’s Number enter the formula:10*R^2/P to calculate the BEST(Recommended) sub length.)
Hi Reudiger,
Are you saying Dr Robin Glover is wrong and the SharpCap Sensor Analysis and Smart Histogram/Brain tools are of no value?
If so, that is interesting. Because, empirically I have found it quite good. Before I used it I had an idea about what exposures worked best for my equipment and sites. Sharpcap gave/confirmed the same answer. This was with using three different stages of filtering (no filter, Light Pro and Triband) and and two different sites (Home at Bortle 6 and Chillingham at Bortle 3).
Cheers Jim
Are you saying Dr Robin Glover is wrong and the SharpCap Sensor Analysis and Smart Histogram/Brain tools are of no value?
If so, that is interesting. Because, empirically I have found it quite good. Before I used it I had an idea about what exposures worked best for my equipment and sites. Sharpcap gave/confirmed the same answer. This was with using three different stages of filtering (no filter, Light Pro and Triband) and and two different sites (Home at Bortle 6 and Chillingham at Bortle 3).
Cheers Jim
Hi Jim,
You got me completely wrong. I said it is good and correct to get a qualified estimation of best exposure time, but in the end your actual exposure time is probably different, since you have to adjust exposue due to other hard limiting factors.
Example: the calculator gave me 25 min exposure time for my site, but this was not possible with the EQ8. I ended up with 10 min exposure time - 15 minutes less than best fit.
I just pointed out, that these calculators are only one component to estimate your suitable exposure time. Nothing more, nothing less.
Also please have a look on AB. Almost all AP use the standard exposure times. I have not seen too many who use other, uncommon timings.
You got me completely wrong. I said it is good and correct to get a qualified estimation of best exposure time, but in the end your actual exposure time is probably different, since you have to adjust exposue due to other hard limiting factors.
Example: the calculator gave me 25 min exposure time for my site, but this was not possible with the EQ8. I ended up with 10 min exposure time - 15 minutes less than best fit.
I just pointed out, that these calculators are only one component to estimate your suitable exposure time. Nothing more, nothing less.
Also please have a look on AB. Almost all AP use the standard exposure times. I have not seen too many who use other, uncommon timings.
Clear skies,
Ruediger
Ruediger
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Radcliffe1
- Posts: 192
- Joined: Sat Oct 26, 2019 11:53 am
- Reputation: 0
Hi Likphoto,
You will have seen that we are all good friends who enjoy a good argument. I agree with you that an exposure calculator would be very useful but I do listen to people who know more than I do. It is not the answer I want but I think it could be possible and very useful, one day. The big unknown for me is narrowband exposure times so having a system that works it all out would be terrific.
All the best
Brian
You will have seen that we are all good friends who enjoy a good argument. I agree with you that an exposure calculator would be very useful but I do listen to people who know more than I do. It is not the answer I want but I think it could be possible and very useful, one day. The big unknown for me is narrowband exposure times so having a system that works it all out would be terrific.
All the best
Brian
Hi Brian,
Yes, this is really great here. Everybody is enjoying a good argumentation.
Brian, with narrowband you can can go for almost the maximum you can mechanically handle. Broad band, and of course Lum, are the critical ones. Here is the danger of saturating stars or collecting too much air glow or light pollution and ruin your SNR. With narrowband you dim this "bad" light dramatically. Especially if using 3.5nm Ha.
So usually 10 to 20 minutes NB should be no issue. Even in light polluted areas 10 minutes should work.
But this is easily to figure out: make a test shot with 10 minutes and meassure SNR, background and star whether the are saturated. In doubt compare to more or less exposed subs. This will give you are very good hint. But I am quite convinced that tracking and planes will be the bigger problem and force reduced exposure times.
How long do you expose Ha usually?
Yes, this is really great here. Everybody is enjoying a good argumentation.
Brian, with narrowband you can can go for almost the maximum you can mechanically handle. Broad band, and of course Lum, are the critical ones. Here is the danger of saturating stars or collecting too much air glow or light pollution and ruin your SNR. With narrowband you dim this "bad" light dramatically. Especially if using 3.5nm Ha.
So usually 10 to 20 minutes NB should be no issue. Even in light polluted areas 10 minutes should work.
But this is easily to figure out: make a test shot with 10 minutes and meassure SNR, background and star whether the are saturated. In doubt compare to more or less exposed subs. This will give you are very good hint. But I am quite convinced that tracking and planes will be the bigger problem and force reduced exposure times.
How long do you expose Ha usually?
Clear skies,
Ruediger
Ruediger
Hi Brian,
I know that everyone's discussion is positive, but I suffer from my English expression skills, and I am not able to participate immediately.(Although I use Google Translate to assistant, the translation results still need to be modified, which takes a lot of time.)
Hi Jim,
Thank you for the information, I am studying the various documents you provided about SharpCap, downloaded and installed SharpCap (Free).
Now I have a preliminary concept. Before APT provides this function, I can use the Dark Sky Meter app to measure the Sky magnitude (if feasible), then calculate the BEST (Recommended) sub length, take an image, and then use Histogram provided by SharpCap to analyze and adjust the exposure time, and then make a shooting plan.
Hi Reudiger,
I have learned a lot from your reply, thank you for such a detailed explanation.
************
In fact, the key to my suggestion is based on Dark Sky Meter's method of comparing two images (I don't know what kind of algorithm is), and the results it gets should only be for reference, maybe https://www.lightpollutionmap.info/ will be more useful.
Because Dark Sky Meter is limited to iPhone, its lens is too wide, so the calculated value can only be used for reference. My idea is that if the algorithm of Dark Sky Meter is feasible, then APT take two images of "target area", it should be more accurate to calculate the BEST (Recommended) sub length with the Sky magnitude calculated in such a small area. , It may even be more accurate than SQM.
Of course, I only put forward this ideas from the user's point of view. The difficulty of this can be known. At present, I will probably estimate the exposure time according to the method provided by Jim.
Finally, thank you all again. With your responses, I can learn knowledge that Google can't search.
I know that everyone's discussion is positive, but I suffer from my English expression skills, and I am not able to participate immediately.(Although I use Google Translate to assistant, the translation results still need to be modified, which takes a lot of time.)
Hi Jim,
Thank you for the information, I am studying the various documents you provided about SharpCap, downloaded and installed SharpCap (Free).
Now I have a preliminary concept. Before APT provides this function, I can use the Dark Sky Meter app to measure the Sky magnitude (if feasible), then calculate the BEST (Recommended) sub length, take an image, and then use Histogram provided by SharpCap to analyze and adjust the exposure time, and then make a shooting plan.
Hi Reudiger,
I have learned a lot from your reply, thank you for such a detailed explanation.
************
In fact, the key to my suggestion is based on Dark Sky Meter's method of comparing two images (I don't know what kind of algorithm is), and the results it gets should only be for reference, maybe https://www.lightpollutionmap.info/ will be more useful.
Because Dark Sky Meter is limited to iPhone, its lens is too wide, so the calculated value can only be used for reference. My idea is that if the algorithm of Dark Sky Meter is feasible, then APT take two images of "target area", it should be more accurate to calculate the BEST (Recommended) sub length with the Sky magnitude calculated in such a small area. , It may even be more accurate than SQM.
Of course, I only put forward this ideas from the user's point of view. The difficulty of this can be known. At present, I will probably estimate the exposure time according to the method provided by Jim.
Finally, thank you all again. With your responses, I can learn knowledge that Google can't search.
Hi lykphoto,
you are welcome! Your English is very good. Dont worry and take your time. We appreciate any contribution here.
Yes, try it out. All other approaches are quite theoretical and often it turns out, that reality rules out theory.
you are welcome! Your English is very good. Dont worry and take your time. We appreciate any contribution here.
Yes, try it out. All other approaches are quite theoretical and often it turns out, that reality rules out theory.
Clear skies,
Ruediger
Ruediger
Hi Jim,
After studying the articles you provided, decide to follow your steps in the future.
If Calculate Best Exposure be possible , with Brain tools(https://snrcalc.now.sh/) life will go much easier.
Thank you so much.
Hi lykphoto,
My pleasure, although Dr Robin Glover has done all the hard work !
Once you have used SharpCap for a given setup and location, you'll start to get a feel for the result it is likely to give. So you need to run it less often.
As I think I mentioned above, the results I get vary quite a lot depending on the time of the evening. So during nautical twilight it can be as low as 60s. When it's in the middle of full dark it can be up to 150s. So if you are doing a 3 hour run, which should I choose? So far I have only taken a simple approach of choosing something in the middle (e.g. 120s). However, your question has made me think that perhaps I should create a Light Plan that increase the duration throughout the evening. I usually do about 100 subs per target. So I could do 30 subs at 90sec, 35 subs at 120s and 35 subs at 150s. Hmmm, interesting thought Thanks for making me give it some thought. 
Don't forget to post your images, either here on the forum or on the Facebook page:
(https://www.facebook.com/groups/1643360112557489/)
Looking forward to seeing them!
Cheers, Jim
My pleasure, although Dr Robin Glover has done all the hard work !
Once you have used SharpCap for a given setup and location, you'll start to get a feel for the result it is likely to give. So you need to run it less often.
As I think I mentioned above, the results I get vary quite a lot depending on the time of the evening. So during nautical twilight it can be as low as 60s. When it's in the middle of full dark it can be up to 150s. So if you are doing a 3 hour run, which should I choose? So far I have only taken a simple approach of choosing something in the middle (e.g. 120s). However, your question has made me think that perhaps I should create a Light Plan that increase the duration throughout the evening. I usually do about 100 subs per target. So I could do 30 subs at 90sec, 35 subs at 120s and 35 subs at 150s. Hmmm, interesting thought
Thanks for making me give it some thought. Don't forget to post your images, either here on the forum or on the Facebook page:
(https://www.facebook.com/groups/1643360112557489/)
Looking forward to seeing them!
Cheers, Jim
I don't know if this ideal can be implement in the future with APT?
Assuming that APT has added the functions I recommend and can integrate Brian Tool, the user only needs to input the data of each equipment and desired signal-to-noise ratio, APT then automatically create appropriate shooting plan（one or two even three: 30 subs at 90sec, 35 subs at 120s and 35 subs at 150s）, press Start, and you can go to sleep , wake up to get a series of images , then get the desired finished image after post-production.
Am I too lazy?
Assuming that APT has added the functions I recommend and can integrate Brian Tool, the user only needs to input the data of each equipment and desired signal-to-noise ratio, APT then automatically create appropriate shooting plan（one or two even three: 30 subs at 90sec, 35 subs at 120s and 35 subs at 150s）, press Start, and you can go to sleep , wake up to get a series of images , then get the desired finished image after post-production.
Am I too lazy?
There has to be something left for us humans to do 
I guess anything is possible. The problem.iscyhe amount of effort required and, perhaps more importantly, available to do it.
For any implementation, there are key components to be undertaken: idea, high level requirements, detail requirements, high level design, detailed design, implementation (coding in this case), testing and documentation.
When suggesting additions to Ivo and Maria, I try to at least to provide some of these phases. Perhaps as far as high level design. So I try to provide the process flow, the maths, the structure and also involve myself in the testing. If I could do provide some working example code, that Ivo and Maria can integrate, I would.
Just a thought...
Cheers, Jim
I guess anything is possible. The problem.iscyhe amount of effort required and, perhaps more importantly, available to do it.
For any implementation, there are key components to be undertaken: idea, high level requirements, detail requirements, high level design, detailed design, implementation (coding in this case), testing and documentation.
When suggesting additions to Ivo and Maria, I try to at least to provide some of these phases. Perhaps as far as high level design. So I try to provide the process flow, the maths, the structure and also involve myself in the testing. If I could do provide some working example code, that Ivo and Maria can integrate, I would.
Just a thought...
Cheers, Jim
