56 replies to this topic

[imtl]

You collected data for 9 hours. How you divide it is not the point.

[UP4014Fan]

Say I take a photo with a dslr, set shutter time to 4 seconds, and the photo is of a blue surface. It's going to be a four second exposure even though only 1/4 of the pixels are doing much and even if the source is a narrow spectrum. I see your idea that exposure time would be as part of the full spectrum/all three bands - but what is a full spectrum to begin with, not every photo necessarily contains all three r, g, b at all, all this is needless convolution of the fact that duration of the exposure was four seconds.

So, JWolf_21, I'm with your buddies on this one

I was once learned, a long time ago, that a good color image should fundamentally be a good monochrome image if desaturated, something I’ve started to re-learn here. So maybe we should be talking luminance?

[JWolf_21]

Focal ratio is intrinsic to integration time. If you just ignore it on the basis that it is another parameter that remains invariant the I just don't understand the whole argument. What about target brightness? Is that also just another parameter that should remain invariant? Pixel size too? Other sensor parameters such as full wheel depth? This is my point. There are so many variables that it sort of becomes futile IMHO.

The question is quite simple. I give you my equipment, whatever it is. You shoot an object (you choose it) on 3 channels and then stack them to get a final image.

 

You ask me to replicate your picture with the same equipment, and you tell me the total stacking time was X hours.

 

How am I going to get the same result if I only know that you were working for X hours?

 

And don't tell me that between your session and mine the Moon has moved so the object is not the same any more

[JWolf_21]

You collected data for 9 hours. How you divide it is not the point.

So, it's 8 hours of R, 30 min of G and 30 min of B the same as 30 min of R, 4 h of G and 4 h of B? Genuine question... I would say no, it's not the same, but I'm not as experienced, maybe the final picture is the same...

[Zambiadarkskies]

Integration hours is something people can fairly easily relate to and compare. Total photons per filter per hour per sqm per focal ratio per sensor specs is way too much for me. Then comes the fairly acknowledged component of an image which is processing skills being between 50 to 80 percent of an image.... How to measure that or compare oneself to that? It all starts to make the simple measure of integration time look more and more attractive to my simple needs. Flawed but relatable.

[UP4014Fan]

Integration hours is something people can fairly easily relate to and compare. Total photons per filter per hour per sqm per focal ratio per sensor specs is way too much for me. Then comes the fairly acknowledged component of an image which is processing skills being between 50 to 80 percent of an image.... How to measure that or compare oneself to that? It all starts to make the simple measure of integration time look more and more attractive to my simple needs. Flawed but relatable.

Agreed - this is all starting to feel like “How many angels can dance on the head of a pin?”

[acrh2]

Hi!

 

After reading around for a while, I think I have found the answer to my noob question but not 100% sure.

 

I'm used to hear to some of my astrophotography friends, and many internet posts, say "the exposure time of this image was 9 hours.... 3 hours of Ha, 3 hours of OIII and 3 hours of NII" or whatever filters they are using, RGB, whatever...

 

From my point of view, the exposure time of the full picture should be 3 hours, not 9, since you are collecting data of different, not-overlapping, parts of the spectrum. The procedure took you 9 hours, of course (plus probably 3 more hours of mounting-unmounting the telescope that you're not counting), but you collected photons only for 3 hours in each band, so the exposure time of what you're showing to me is 3 hours.

 

It's like if I do regular photography with a DSLR of a beach landscape, I shoot for 1 second, and I say that the exposure time is 3 seconds because RGB...

 

I have tried to discuss this topic several times with them and I learnt to shut up

 

Any light on this? (pum well-intented)

 

I have a solution for you.

Are you familiar with a saying in physics "shut up and calculate?" Well, shut up and integrate!

[JWolf_21]

Integration hours is something people can fairly easily relate to and compare. Total photons per filter per hour per sqm per focal ratio per sensor specs is way too much for me. Then comes the fairly acknowledged component of an image which is processing skills being between 50 to 80 percent of an image.... How to measure that or compare oneself to that? It all starts to make the simple measure of integration time look more and more attractive to my simple needs. Flawed but relatable.

I never said "Total photons per filter per hour per sqm per focal ratio per sensor specs". You said it. I just said to keep the time per channel, what everybody already reports. And that I don't understand the usage of total integration time as a measure to compare anything. Because your 9 hours picture and my 9 hours picture, will be very different (I think), with the same equipment, if we shoot different times per channel.

 

If you think this parameter is useful to you somehow, great, but I doubt you could replicate my picture with my equipment if you only know the total integration time.

[JWolf_21]

I have a solution for you.

Are you familiar with a saying in physics "shut up and calculate?" Well, shut up and integrate!

Precisely because I calculated, I don't see how hours on different wavelengths can be integrated as if they would be the same photons

[Zambiadarkskies]

I never said "Total photons per filter per hour per sqm per focal ratio per sensor specs". You said it. I just said to keep the time per channel, what everybody already reports. And that I don't understand the usage of total integration time as a measure to compare anything. Because your 9 hours picture and my 9 hours picture, will be very different (I think), with the same equipment, if we shoot different times per channel.

If you think this parameter is useful to you somehow, great, but I doubt you could replicate my picture with my equipment if you only know the total integration time.

Go take a look at the "process my data" thread. Literally no one comes up with replicated images from the exact same data.

[imtl]

So, it's 8 hours of R, 30 min of G and 30 min of B the same as 30 min of R, 4 h of G and 4 h of B? Genuine question... I would say no, it's not the same, but I'm not as experienced, maybe the final picture is the same...

No one claim the divisions are the same. That's not the point. The point is that when someone says their image is 9 hours exposure then it's 9 hours exposure. How they divide that time and whether you or anyone else like the image or not is a personal preference.

[JWolf_21]

Go take a look at the "process my data" thread. Literally no one comes up with replicated images from the exact same data.

So instead of focusing on the simple original question, involving only a sensor and light, to know if exposure of different wavelengths should be summed up or not, you keep adding unrelated parameters like FL, processing flow, etc... And yes, if we print our pictures, I'm sure the printer calibration will show different results It was a nice debate though. Thanks for your suggestions.

[JWolf_21]

No one claim the divisions are the same. That's not the point. The point is that when someone says their image is 9 hours exposure then it's 9 hours exposure. How they divide that time and whether you or anyone else like the image or not is a personal preference.

This is the whole point of the topic... because when one tells me that a picture is 9 hours... I assume is 9 hours per channel!! I assume he collected 9 hours of photons in whatever wavelength he chose! Not 3+3+3, 7+1+1 or so...

[Alex McConahay]

>>>>>>>>>>>>How am I going to get the same result if I only know that you were working for X hours?

 

It is kinda pointless to try to "get the same result" by just shooting for the same time per filter. There are so many other things to think about. And, besides, you should not be replicating somebody else's work. 

 

 

>>>>>>>>>>>>>>because when one tells me that a picture is 9 hours... I assume is 9 hours per channel!!

 

 

You mean you are still assuming that after most of the last 38 posts have been telling you that is NOT what it means?

 

It does not sound like it is a problem that any one else can cure. 

 

Alex

[UP4014Fan]

Go take a look at the "process my data" thread. Literally no one comes up with replicated images from the exact same data.

Heck - I found 8 different ways to process my master of the Orion Nebula before I was happy!

[JWolf_21]

Ok, in general I see that the point of my question is lost. For sure it's my fault, maybe I didn't express myself correctly. Thanks to all for your suggestions and help on this topic. Clear skies!

[AstroFromHome]

The monochrome sensor can gather the same spectrum at all pixels. OSC just on 1 or 2 pixels per array of 4 pixels.

If you shoot narrowband for instance. The OSC with a Ha and O3 DNB filter. You image for 4 hours.

At the same time you image with a monochrome 2h with Ha and 2h of O3 filter.

Both cameras ran for 4 hours. So four hours of integration time.

 

To be frank the OSC turned just 1/4 of the photons into digital signal. You could say just 1h off what could have been possible. As O3 is partially in the blue, partially in green you may end up with about 2h of what has been possible to convert into digital signal.

 

The monochrome camera captured 2h Ha signal and 2h of O3 signal on its full sensor.

 

As each channel can have different integration times the full time spend capturing photos counts into the overall integration time.

No one would ever come to the conclusion that spending 4h with an OSC under the stars to just say it has been about 3h because of the Bayer Matrix.

 

Everyone spend the same time under the stars collecting photons. You will see in the images that the 2h monochrome in the example above are better than the 4h with the OSC. Especially if you would split the time per channel.

[rgsalinger]

Yes, but I was speaking in very rough terms, disregarding the spectral distribution of the target, the human eye's higher sensitivity to green, the red blocking filter on land cameras, and the spectral absorption characteristics of the bayer filter dyes.

 

Based on the published spectral characteristics, I have actually calculated the integration of the total photon capture of a few common OSC astro sensors compared to the mono equivalent across the spectrum assuming a flat spectral target and you do capture only about 1/3 the amount of light, but some OSC cameras have enough overlap in the absorption of the various R,G, B channels that it can as high as 50%.   But that is a 2x reduction at best, much more than just a 30% reduction.  Certainly OSC cameras cut more than 30% of the photons reaching the sensor compared to a mono version of the same sensor.

 

"1/3" was the simple answer, but just like anything, the perfect answer is infinitely more complex than the simple answer.  

I think I see. You are comparing the number of photons captured by a pixel using a luminance filter - wide band pass - to those captured by same pixel with (say) a green filter. Is that correct? If so, then I get it, because of the bandpass difference plus the effect of the dye in the "cheap plastic" sloppy Bayer matrix. 

 

So far so good. Unfortunately, you will now end up with a monochrome image. If you want a color image using your mono camera, don't you now need to shoot more subs with RGB filters? So, if that's the case then the total flux difference between using a mono camera with filters and an OSC camera in the same period of time gets much smaller.  

 

What did I get wrong here? I really don't want to sell my OSC cameras as they are so easy to use. There does have to be some resolution loss unless you can get it back with drizzling, but I don't see that you will end of with 1/3 of the total flux after (say) 6 hours of imaging using mono with filters. 

Edited by rgsalinger, 19 April 2025 - 06:42 PM.

[imtl]

This is the whole point of the topic... because when one tells me that a picture is 9 hours... I assume is 9 hours per channel!! I assume he collected 9 hours of photons in whatever wavelength he chose! Not 3+3+3, 7+1+1 or so...

Well, there is what you assume and there is what everyone else have been using as terminology forever. When someone says 9 hours they mean 9 hours total. I always add the divisions that I use. But I'm also very much aware what is the common terminology used in this hobby. So, it's your choice to go with it or try and change it. I think the latter might be very challenging for you to do.

[JWolf_21]

Well, there is what you assume and there is what everyone else have been using as terminology forever. When someone says 9 hours they mean 9 hours total. I always add the divisions that I use. But I'm also very much aware what is the common terminology used in this hobby. So, it's your choice to go with it or try and change it. I think the latter might be very challenging for you to do.

I don't want to change anything, everybody is free to talk with whatever level of accuracy they desire. My question was if somehow I was wrong by understanding that 3+3+3 hours on different channels is not 9 hours in total, and now my question is answered. So I'll continue to shut up when people around use that parameter, which is easier than trying to get accurate info

[Alex McConahay]

I don't want to change anything, everybody is free to talk with whatever level of accuracy they desire. My question was if somehow I was wrong by understanding that 3+3+3 hours on different channels is not 9 hours in total, and now my question is answered. So I'll continue to shut up when people around use that parameter, which is easier than trying to get accurate info

No need to shut up.......If you need to know more, just ask: "How much time in each filter?" 

 

And "Did you bin it?"

 

And "What was the focal ratio of the scope?

 

And whatever else  you need to know to reproduce the shot. 

 

But realize that you do not need to do what they did. You need to do what you need to do considering your configuration, your equipment, your sky conditions, your level of ability, and all that. 

 

You made sense all the way along in your question. People acknowledged that there was a lot left unknown when you lump all the exposure into one "Total Exposure Time." They got what you were talking about. They saw your point (even if they did not agree it meant changing the meaning of the expression "total exposure time." 

 

The only difficulty respondents in this thread had was telling you that "Total exposure Time" meant how much time was on the target, regardless of which filter or whatever......

 

Alex

[smiller]

I don't want to change anything, everybody is free to talk with whatever level of accuracy they desire. My question was if somehow I was wrong by understanding that 3+3+3 hours on different channels is not 9 hours in total, and now my question is answered. So I'll continue to shut up when people around use that parameter, which is easier than trying to get accurate info

I think the question to ask yourself when you are thinking "trying to get accurate info" is defining the measurement that you want to increase the accuracy of.  If you can define that, I expect there is a process to deliver it.

 

Can you define what the measurement is that you want more "accurately"?  

 

For example:     Is it the total amount of light collected (total photons) per square unit of sky? (ex: Total photons per square arcsecond of sky?)

 

I think that is where people are stuck in your followups.  It appears you are referring to some aspect of imaging "productivity" or  equivalent "effectiveness" between two situations.  It you can define what that metric exactly is that you are trying to equate, then there is hope.

 

 

An equivalency I often try to do is this:

 

1) How long will it take for me to capture an image as good as one I've found on Astrobin?

 

To do this, there are several factors I look at:

 

1) The total photon collecting power of the scope on the target area (scope aperture, also scope F-ratio and camera sensor size if FOV factors are important)

2) The amount of sky background noise they had:  Mainly Sky Bortle Number, target altitude if that's material (it may be high for them but low for me at my 46 degree latitude)  and known, and moon phase if that's material and known.

3) How much did they attenuate the noise from the sky background:  Narrowness of the narrowband filters (for narrowband captures of emission nebula)

4) How many hours of integration time did they utilize

 

With these four factors, I can roughly translate into my shooting situation: My scope, camera, filters, Sky Bortle.   To make it more accurate, I try to find examples on Astrobin that most closely match my situation (Bortle, scope aperture, filter bandpass, etc...) and hit the threshold of quality I'm trying to achieve.

 

It actually works reasonably well.  My images are usually "in the ballpark" with respect to visual appeal, SNR and the visibility of the dimmest features relative to the benchmark compares after I've adjusted for the differences listed.

 

Perhaps this is what you are striving for?

Edited by smiller, 20 April 2025 - 09:26 AM.

[gsaramet]

 

I don't see any complication, if you report that your image had X hours per channel. If there's a complication, if any, it would be to sum those hours to give an additional value that is meaningless (except for the usage count of your sensor).

It's a bit like this. If you check images on astrobin, you'll often find the time per filter. You can find that information, or you can ask for it. Same here - if it's not posted, ask the poster. 

 

And now I will make it a bit advanced. And my opinion can be disagreed with, of course.

 

Astrophotography is not science. It's mostly art. Done with science stuff, that's true, but still an art. So, asking the integration time per filter in order to duplicate the image is not unlike asking how much of each pigment bleemin' Picasso used to paint bleemin' Guernica. 

 

An experienced person will add integration time until they get the result they want. That includes both signal and signal-to-noise-ratio. It's not the same from night to night or season to season. You get moon, different altitudes, different seeing, etcaetera. You add time until you get what you want - or get bored.

 

You can image Andromeda for a few hours and get a perfectly good image, especially in good skies. Or you can image it for a thousand of hours and get this:

 

https://www.astrobin.com/ymtvkr/F/

 

It's quite fun to select a faint target and image it for a long time. And I speak from the point of view of Bortle 9 backyard shooter. 

 

Now, looking at other people's images and trying to image the same object is a good education. I know that 100h duo-band imaging from my backyard will yield worse results than 20h of mono imaging from a good sky. How do I know? I tried Here's a 100h of garlic. You can easily find better garlics with less integration times in better skies on astrobin. 

 

https://www.astrobin.com/usgnu6/0/

 

When I am looking at a narrowband image details, the one that interest me the most is total integration time. Then I'll look at Oiii time, because that's where my OSC rig limits me most. If the image is broadband and in good skies, I loose my interest quickly, because of the huge light pollution I shoot in. 

 

The other details are a bit less interesting to me. I don't expect somebody who puts 50h towards a target to shoot it very low, or against the moon or with clouds on the sky or with an f/20 scope, or... you get my meaning

 

Now, to end my slightly_more_experienced_imager rant: total integration time is the parameter which describes best the effort needed for an image. There are other parameters, and they are generally available. However, one should focus on getting what one wants, not what other people wanted.

[AstroFromHome]

Yeah! No need to shut up! Everyone is free to speak up, ask question or to respond. 

 

Sure with each filter on the monochrome camera you end up with a black and white image that represents the specific spectrum of light.

It is the same an OSC camera does. It processes three individual images internally.

 

Imaging 3h RGB with an OSC is about equal to 1h red, 1h green and 1h blue with a monochrome camera. 

 

Both users talk about 3h of integration time what is absolutely correct as both spent this time imaging.

 

Whereas 1h of Luminance is worth as much as 1h R, 1h G and 1h B in terms of signal with a monochrome camera as no wavelengthsare blocked.

 

To sell off your OSC nobody asked for.  I also have two OSC cameras next to two monochrome cameras. All of them I like a lot. Each camera has its use-case in my portfolio.

 

Everyone takes his decision and has his reasons why he is choosing one of the technologies and a certain sensor size.

 

Total integration time is used the way like often in general usage. Just the easy way and to make things comparable. Not more and not less the total time of images taken and integrated.

 

No rocket science and no one of us should make this amazing hobby to it. OK, it is somewhat rocket science already.

[Marcus1]

After reading the thread it seems to me that the rendition is essentially an artistic endeavor, so asking about integration times on different filters is akin to asking Leonardo to detail how many tubes of different paint were used on the Mona Lisa.