Full Well, ADU, and Exposure Length

[Mac]

Like this?

This is a 60 second exposure at a gain of 104 and offset of 70. Median ADU is 544.

A 30 second image at the same settings has a median ADU of 470.

A 120 second image with the same settings has a median ADU of 696.

Not sure what all of this means, but with the near full moon, it is amazing that the ADU is so much lower tonight than a few nights ago when I used a gain of 300 and the IDAS LPS D-1 filter and a median ADU of 14000!

I am going to shoot some light frames at 60 seconds and stack them up tomorrow (only because I have the darks).

Very interesting! I will post back tomorrow.

Thanks all!

Looks pretty good for a 60 second capture under a full Moon, eh?

Compare that to your IDAS filter and you'll see a big difference.

[Juno16]

Looks pretty good for a 60 second capture under a full Moon, eh?

Compare that to your IDAS filter and you'll see a big difference.

Yes it does!

I will use the IDAS filter for broadband targets, but the L-Enhance with the ASI 533 is a great combo for emission nebula.

This image is definitely nothing to write home about, but for only 22 minutes integration with no calibration frames, no sharpening or denoise with a 97% moon, to me it’s amazing.

It is almost as good as my 3 1/2 hours with the dslr and the IDAS filter a month or so ago. And, it was a slam, bam process.

Pretty cool stuff!

I see that you did 180 second subs for n your East Veil and I am still trying to understand exposure. Do you shoot for a specific ADU?

I will post later to this thread if I get time in case someone has time to look at the subs.

Thanks Steve!

[umasscrew39]

Jim- I saw your L-enhance 533 image on the other thread- excellent. Like I said, I got and used the 533 when it first came out and took a lot of images with it. A gain of 100 and offset of 50 with exposures between 90s -120s give amazing images with either the L-enhance for emission nebulae or the L-Pro for galaxies if you are in a LP area like me- Bortle 6 but you can try it with no filter or a UV/IR filter. What impressed me the most was that the read noise is so low that the images look great even before you calibrate with darks, flats, and dark flats. You will have a blast with this camera. It makes AP a lot of fun with minimal aggravation :-).

Another tool to help assess exposure is SharpCap. It has a Smart Histogram tool which determines the best exposure for your camera under your skies with your setup.

Bruce

[Juno16]

Jim- I saw your L-enhance 533 image on the other thread- excellent. Like I said, I got and used the 533 when it first came out and took a lot of images with it. A gain of 100 and offset of 50 with exposures between 90s -120s give amazing images with either the L-enhance for emission nebulae or the L-Pro for galaxies if you are in a LP area like me- Bortle 6 but you can try it with no filter or a UV/IR filter. What impressed me the most was that the read noise is so low that the images look great even before you calibrate with darks, flats, and dark flats. You will have a blast with this camera. It makes AP a lot of fun with minimal aggravation :-).

Another tool to help assess exposure is SharpCap. It has a Smart Histogram tool which determines the best exposure for your camera under your skies with your setup.

Bruce

For 22 minutes!

Thanks Bruce!

I agree. This camera will be lots of fun.

I looked at Sharpcap last night outside and ran into an issue and moved on. I will do some reading and give it another shot.

I figure that I I was close with to good at 60 seconds last night under Bortle 7-8 skies with the big moon. I need to come up with a plan though.

Thanks for the help Bruce!

[bobharmony]

Looks pretty good for a 60 second capture under a full Moon, eh?

Compare that to your IDAS filter and you'll see a big difference.

Yes it does!

I will use the IDAS filter for broadband targets, but the L-Enhance with the ASI 533 is a great combo for emission nebula.

This image is definitely nothing to write home about, but for only 22 minutes integration with no calibration frames, no sharpening or denoise with a 97% moon, to me it’s amazing.




It is almost as good as my 3 1/2 hours with the dslr and the IDAS filter a month or so ago. And, it was a slam, bam process.

Pretty cool stuff!

I see that you did 180 second subs for n your East Veil and I am still trying to understand exposure. Do you shoot for a specific ADU?

I will post later to this thread if I get time in case someone has time to look at the subs.

Thanks Steve!

Look at you, Jim. You're a natural! Nice job for a "quick test"

Bob

[STEVE333]

Hi Jim - You have received a lot of help on this one.

One clarification for the Pixel Aid tool in APT. When you click on the Whole Image choice it considers whatever is inside the widow of the Pixel Aid tool to be "Whole Image". So it isn't really the full image that is being analyzed but only that portion of the image that falls within the Pixel Aid window. It took me a while to figure this out!!!

If I want to know what the average value of the whole image is I load the image into PixInsight and use the Statistics process to find the mean value. If you have the tool set to 16-bit then you will have to divide the mean value by 4 to get to your 14-bit ADU value (and then, of course, subtract your offset).

Good luck - Steve

[Juno16]

Look at you, Jim. You're a natural! Nice job for a "quick test"

Bob

No natural here! I am just chipping away at this!

These cameras are very different than dslr's in many ways, but it is a lot of fun learning

Thanks Bob!

Hi Jim - You have received a lot of help on this one.

One clarification for the Pixel Aid tool in APT. When you click on the Whole Image choice it considers whatever is inside the widow of the Pixel Aid tool to be "Whole Image". So it isn't really the full image that is being analyzed but only that portion of the image that falls within the Pixel Aid window. It took me a while to figure this out!!!

If I want to know what the average value of the whole image is I load the image into PixInsight and use the Statistics process to find the mean value. If you have the tool set to 16-bit then you will have to divide the mean value by 4 to get to your 14-bit ADU value (and then, of course, subtract your offset).

Good luck - Steve

I surely have received a lot of very valuable help.

Thanks for the tip about the Pixel Aid Tool. I don't have Pixinsight (yet), but I used the AP Lab to generate the median ADU values. If I get time later today, I would like to upload the three subs with different exposures just in case someone wants to take a look.

I really appreciate everyone's help. I am still trying to get my head around exposure time though and how to decide on a median image ADU value for a given target.

I do have Sharpcap and need to read up on the SmartHistogram to see how it works and how it may help.

I have a outdoor project going on right now (not anywhere near as much fun as astro!) that is keeping me pretty busy (and tired). Hopefully in a few days I can get out and work with the equipment again..

Thanks Steve!

[Mac]

I see that you did 180 second subs for n your East Veil and I am still trying to understand exposure. Do you shoot for a specific ADU?

I will post later to this thread if I get time in case someone has time to look at the subs.

Thanks Steve!

Glad to see that combo is working for you Jim, I knew that it would.

I don't get so technical or pedantic about the exposure lengths. 300 seconds is a pretty standard exposure time for me now unless it's something like M31 or M42. I've even done 400 and 600 seconds on some targets.

I've been experimenting with shorter exposures without any filters and have tried various combinations with the L-Pro and L-enhance.

[Graeme1858]

Great Thread Jim!

Just a quick one, when you use Smart cap, how do you cool the camera?

Regards

Graeme

[Juno16]

Glad to see that combo is working for you Jim, I knew that it would.

I don't get so technical or pedantic about the exposure lengths. 300 seconds is a pretty standard exposure time for me now unless it's something like M31 or M42. I've even done 400 and 600 seconds on some targets.

I've been experimenting with shorter exposures without any filters and have tried various combinations with the L-Pro and L-enhance.

You are/were right! The camera and filter are very powerful tools for sure!

This is 60 one minute Cocoon image without calibration files that I shot after the short East Veil image. Definitely a much more challenging target than the much brighter Veil. Needs way more time and less than a 97% moon, but just another "test" image.

Nothing close to Kathy's [mention]KathyNS[/mention] fine Cocoon image or your really nice Cocoon, but just getting my feet wet.

This target probably would do much better with a longer exposure than 60 seconds (and lots of them).

Interesting about your exposure experience. Good to know. I am sure that the target and sky brightness (both lp and moon) can influence the exposure time somewhat.

[Juno16]

I am just going to post these links in case anyone wants to take a look

Two light frames from a few nights ago. Image stats are from AP Lab.

East Veil light frame. 60 second exposure at a gain of 104 and offset of 70. 97% moon.

Cocoon Nebula light frame. 60 second exposure at a gain of 104 and offset of 70. 97% moon.

Thanks for all of the help!

[bobharmony]

Hi Jim. The Google links are asking me to request access. Can you make them public so they will just sow up?

Bob

[Juno16]

Great Thread Jim!

Just a quick one, when you use Smart cap, how do you cool the camera?

Regards

Graeme

Hi Graeme,

Sorry, I don't know, but I would expect since this is ascom, the camera could be connected in APT also and cooling could be done there?

[Juno16]

Hi Jim. The Google links are asking me to request access. Can you make them public so they will just sow up?

Bob

Sorry Bob. In a rush to get back to the project outside. They should work now.

Thanks for pointing that out!

[Graeme1858]

Great Thread Jim!

Just a quick one, when you use Smart cap, how do you cool the camera?

Regards

Graeme

Hi Graeme,

Sorry, I don't know, but I would expect since this is ascom, the camera could be connected in APT also and cooling could be done there?

Yes, I pondered the idea of cooling the camera with ASI Studio and Capturing images with Sharpcap.

Regards

Graeme

[STEVE333]

I am just going to post these links in case anyone wants to take a look

Two light frames from a few nights ago. Image stats are from AP Lab.

East Veil light frame. 60 second exposure at a gain of 104 and offset of 70. 97% moon.



Thanks for all of the help!

Hi Jim - If my thinking is correct, and your mean e- value is for one channel (R or G or B), your Veil data shows [(615.4/4) - 70] = 84 e- as the mean value collected across the image. Because the dark current is so low it is not a factor. Thus you would be achieving

sqrt[84/(84 + 1.5 * 1.5)] = 0.987

which means you would be achieving 98.7% of the best Signal-to-Noise possible with your 60 sec exposures. Thus, from a S/N perspective 60 sec exposures are long enough. The other factor to consider is your dithering "dead time", i.e., the time from the end of one image till the start of the next image. My system vearie between 20 - 40 sec "dead time" which isn't too bad. With short image exposures like 60 sec, the dithering time starts to significantly reduce the amount of actual imaging time, so, longer exposures will lead to improved S/N in the stacked image. Of course, longer exposures will also cause more stars to be saturated. ALWAYS A TRADEOFF!!

I'm still unclear if the mean value of 615.4 e- is for one color channel or the sum of all of them or an average of the three. Can you help me with this.

If you are interested I would be glad to model your sensor to show the S/N performance (higher S/N means a better image) as a function of the Exposure Time and the Dither "dead time". Just FYI.

Cheers - Steve

[Juno16]

I am just going to post these links in case anyone wants to take a look

Two light frames from a few nights ago. Image stats are from AP Lab.

East Veil light frame. 60 second exposure at a gain of 104 and offset of 70. 97% moon.



Thanks for all of the help!

Hi Jim - If my thinking is correct, and your mean e- value is for one channel (R or G or B), your Veil data shows [(615.4/4) - 70] = 84 e- as the mean value collected across the image. Because the dark current is so low it is not a factor. Thus you would be achieving

sqrt[84/(84 + 1.5 * 1.5)] = 0.987

which means you would be achieving 98.7% of the best Signal-to-Noise possible with your 60 sec exposures. Thus, from a S/N perspective 60 sec exposures are long enough. The other factor to consider is your dithering "dead time", i.e., the time from the end of one image till the start of the next image. My system vearie between 20 - 40 sec "dead time" which isn't too bad. With short image exposures like 60 sec, the dithering time starts to significantly reduce the amount of actual imaging time, so, longer exposures will lead to improved S/N in the stacked image. Of course, longer exposures will also cause more stars to be saturated. ALWAYS A TRADEOFF!!

I'm still unclear if the mean value of 615.4 e- is for one color channel or the sum of all of them or an average of the three. Can you help me with this.

If you are interested I would be glad to model your sensor to show the S/N performance (higher S/N means a better image) as a function of the Exposure Time and the Dither "dead time". Just FYI.

Cheers - Steve

Hi Steve,

Yes, in AP Lab, it defaults to the Green channel (default).

I get the values that I posted.

If I select the Red channel, I get different values.

Using the Pixel Aid in APT set to Whole Image, I get different values (maybe average of RGB?).

pixel aid.JPG (24.41 KiB) Viewed 3649 times

When I shot the image, I was exposing for 60 seconds and dithering every 3rd image. Dithering "dead time" is about one minute.

Definitely I am interested in modeling the sensor if you have the time. NOTE: I was using the L Enhance filter if that makes any difference.

Thanks Steve!

[Juno16]

Hey Steve [mention]STEVE333[/mention] ,

In post 31 above, there are download links to the light frames if you have a better way to extract the image statistics.

[JayTee]

Hi Jim,

I just downloaded one of your light frames from above and decided to use Avis FV 2.0 (freeware) to view it. This is the first time I've used this .fits viewer. It seems that where ever you place your mouse the program gives you an ADU reading. Just another piece of software that might help.
http://www.msbsoftware.it/avis/

Cheers,
JT

[Juno16]

Hi Jim,

I just downloaded one of your light frames from above and decided to use Avis FV 2.0 (freeware) to view it. This is the first time I've used this .fits viewer. It seems that where ever you place your mouse the program gives you an ADU reading. Just another piece of software that might help.
http://www.msbsoftware.it/avis/

Cheers,
JT

Cool! Thanks JT!

I n ed to look at ASI Studio too