Astrophotography Lab - A Limited Overview

[UlteriorModem]

Just stumbled into this. Looks very interesting.

Since I am stuck with at least a week or two of overcast skies I will have to give this a try. It will be interesting to compare actual real world results to manufacturers claims.

As to the saturated image, no problem I have a few frames with Altinak in them

Anyhow thanks for doiing this.

[Juno16]

This is amazing stuff if I am interpreting it correctly.

I remember all of the discussion in the past few months about flats. I thought I was getting pretty decent results using mid histogram flats with my dslr.

I just turned down the brightness on my ipad, t-shirted the scope and started shooting flats at different exposure times.

At 0.4 seconds (1/2.5) my mean ADU was 7617. At 0.5 seconds (1/2), my mean ADU was 9448

Selecting just the white of Alnitak in a light frame, I saw an ADU of 16383. I guess that I should start shooting flats at about 0.4 seconds given the same brightness level. Huge difference from the 1/40 - 1/80 sec I was shooting before!

I know that a bunch of you went through all of this before. Sorry for coming late to the party!

Jim

[JayTee]

Jim,

I'm very curious why you think you need to use the saturated star's ADU value and not the sensor max linear full well capacity ADU value?

JT

[UlteriorModem]

Ugh, of course I have to be the one with problems.

When I first went to execute the program Windows defender intercepted. I chose 'run anyways' and well..

error 1 by Tom Whit, on Flickr

Error 2 by Tom Whit, on Flickr

Log File:

https://1drv.ms/t/s!AlZYjAen8Osp-ACywBo ... u?e=yqCcJo

[STEVE333]

Ugh, of course I have to be the one with problems.

Sorry you are having problems. Hope they get resolved soon.

Hello,
Perhaps a stupid question: how to take a saturated sample?

François

HI Francois - I use a light tablet pressed up against the front of my telescope/camera combination and took about a 5 sec exposure with the light up medium bright. I checked the level of the pixel signals using PixInsight, and, for this exposure almost all the pixels were saturated. You may need some processing program to make sure at least something in your image is saturated.

This is amazing stuff if I am interpreting it correctly.

I remember all of the discussion in the past few months about flats. I thought I was getting pretty decent results using mid histogram flats with my dslr.

I just turned down the brightness on my ipad, t-shirted the scope and started shooting flats at different exposure times.

At 0.4 seconds (1/2.5) my mean ADU was 7617. At 0.5 seconds (1/2), my mean ADU was 9448

Selecting just the white of Alnitak in a light frame, I saw an ADU of 16383. I guess that I should start shooting flats at about 0.4 seconds given the same brightness level. Huge difference from the 1/40 - 1/80 sec I was shooting before!

I know that a bunch of you went through all of this before. Sorry for coming late to the party!

Jim

Your reasoning makes sense to me Jim.

Jim,

I'm very curious why you think you need to use the saturated star's ADU value and not the sensor max linear full well capacity ADU value?

JT

Hi JT - If you look at my second picture in the original post, in the lower left box it shows White level 15310 ADU. The full well capacity ADU would be 16384. At least for my sensor (Canon DSLR) apparently full well only produces 15310 ADU even though the advertised value would be 16384. Not a big difference, but, the program simply measures the max ADU rather than assuming a value. I think that is why the program requests a Saturated frame.


Thanks all for the comments/questions.

Steve

[JayTee]

Hi JT - If you look at my second picture in the original post, in the lower-left box it shows White level 15310 ADU. The full well capacity ADU would be 16384. At least for my sensor (Canon DSLR) apparently full well only produces 15310 ADU even though the advertised value would be 16384. Not a big difference, but, the program simply measures the max ADU rather than assuming a value. I think that is why the program requests a Saturated frame.

Thank you Steve, I really appreciate your explanation. What it really tells me is that there can't help but be some confusion when we don't know if you are talking in 12, 14, or 16-bit depth and added on top of that that every sensor type/family/manufacturer will have a different Max ADU value. So we (myself included) need to be very careful that we are comparing apples to apples.

So now here's a blurb right out of the AP Lab QSG regarding the saturated frame and, to me, it throws a real "monkey in the wrench."
One saturated frame: Image something, and make sure some part of the image contains completely saturated pixels. Ordinary light frames will usually have saturated pixels. The saturated frame is only used to determine the white level.

If the saturated frame is only used to determine the "white level" where does it get the Max ADU value from? Or is the term white level synonymous with Max ADU? Also, this means that the entire frame does not need to be totally overexposed, just a portion of it. But once again this is only used to determine the white value.

Now I'm really confused,
JT

[Juno16]

Hi JT - If you look at my second picture in the original post, in the lower-left box it shows White level 15310 ADU. The full well capacity ADU would be 16384. At least for my sensor (Canon DSLR) apparently full well only produces 15310 ADU even though the advertised value would be 16384. Not a big difference, but, the program simply measures the max ADU rather than assuming a value. I think that is why the program requests a Saturated frame.

Thank you Steve, I really appreciate your explanation. What it really tells me is that there can't help but be some confusion when we don't know if you are talking in 12, 14, or 16-bit depth and added on top of that that every sensor type/family/manufacturer will have a different Max ADU value. So we (myself included) need to be very careful that we are comparing apples to apples.

So now here's a blurb right out of the AP Lab QSG regarding the saturated frame and, to me, it throws a real "monkey in the wrench."
One saturated frame: Image something, and make sure some part of the image contains completely saturated pixels. Ordinary light frames will usually have saturated pixels. The saturated frame is only used to determine the white level.

If the saturated frame is only used to determine the "white level" where does it get the Max ADU value from? Or is the term white level synonymous with Max ADU? Also, this means that the entire frame does not need to be totally overexposed, just a portion of it. But once again this is only used to determine the white value.

Now I'm really confused,
JT

Ahhhhh, I just read your post JT. Ok, that is how the white level is determined. So, if you have a saturated star in the light frame or the saturated frame, the software knows the camera specs and calculated the full well adu of that camera sensor. The sensor white level is the camera sensor full well capacity ADU.

Thanks,
Jim

[Juno16]

This is amazing stuff if I am interpreting it correctly.

I remember all of the discussion in the past few months about flats. I thought I was getting pretty decent results using mid histogram flats with my dslr.

I just turned down the brightness on my ipad, t-shirted the scope and started shooting flats at different exposure times.

At 0.4 seconds (1/2.5) my mean ADU was 7617. At 0.5 seconds (1/2), my mean ADU was 9448

Selecting just the white of Alnitak in a light frame, I saw an ADU of 16383. I guess that I should start shooting flats at about 0.4 seconds given the same brightness level. Huge difference from the 1/40 - 1/80 sec I was shooting before!

I know that a bunch of you went through all of this before. Sorry for coming late to the party!

Jim

Your reasoning makes sense to me Jim.

Thanks a bunch Steve!!!

The White Level in the Sensor box is my camera full well ADU! I am a bit slow to pick this up, but hopefully things are coming together.

Thanks,
Jim

[STEVE333]

Hi All - Because there has been so much discussion about Flats and exposures for Flats in the responses, I wanted to make sure that the use of Astrophotography Lab that I have presented is only for determining the proper exposure for Light frames, NOT Flats or Bias or Darks!!! Just wanted to make sure we are all "on the same page".

Thanks to all for the comments, suggestions, questions.

Steve

[SKEtrip]

Steve & all - thank you for the info!

Curiosity on my part - is this what SharpCap is doing with the Smart Histogram feature?
I did a sensor analysis for the cameras, SC stored the data & when I start a session I point at a darker area of the sky & it will give me the "best exposure time"
It will not plot a curve to give the number of exposures to take - # of exposures is calculated by user input of total time on the target.

[Juno16]

Hi All - Because there has been so much discussion about Flats and exposures for Flats in the responses, I wanted to make sure that the use of Astrophotography Lab that I have presented is only for determining the proper exposure for Light frames, NOT Flats or Bias or Darks!!! Just wanted to make sure we are all "on the same page".

Thanks to all for the comments, suggestions, questions.

Steve

Sorry Steve, I am a big contributor to the flats discussion. Yes, proper exposure for light frames is the goal. Thanks for all of your contributions to this thread.

Jim

[STEVE333]

Steve & all - thank you for the info!

Curiosity on my part - is this what SharpCap is doing with the Smart Histogram feature?
I did a sensor analysis for the cameras, SC stored the data & when I start a session I point at a darker area of the sky & it will give me the "best exposure time"
It will not plot a curve to give the number of exposures to take - # of exposures is calculated by user input of total time on the target.

I haven't used SharpCap, so, can't help you there.

There really isn't a "best # of exposures to take" unless you want to accept the answer of MORE. More is always better.

The analysis I presented works for one location, i.e., one LP condition. I always shoot from my driveway, so, my LP is always the same. If one goes to a dark site, then, an image taken from the dark site would be required as the "Light" frame to determine the proper graph for that location. Since the Dark site has lower LP noise the knee of the curve would move toward longer sub exposure times.

Steve

[SKEtrip]

Steve & all - thank you for the info!

Curiosity on my part - is this what SharpCap is doing with the Smart Histogram feature?
I did a sensor analysis for the cameras, SC stored the data & when I start a session I point at a darker area of the sky & it will give me the "best exposure time"
It will not plot a curve to give the number of exposures to take - # of exposures is calculated by user input of total time on the target.

I haven't used SharpCap, so, can't help you there.

There really isn't a "best # of exposures to take" unless you want to accept the answer of MORE. More is always better.

The analysis I presented works for one location, i.e., one LP condition. I always shoot from my driveway, so, my LP is always the same. If one goes to a dark site, then, an image taken from the dark site would be required as the "Light" frame to determine the proper graph for that location. Since the Dark site has lower LP noise the knee of the curve would move toward longer sub exposure times.

Steve

The SC program requires a sensor analysis - also done in SC then develops best exposure times based on the sky that night. Link:
https://www.sharpcap.co.uk/sharpcap/fea ... -histogram
Downside is it only comes with the SC pro license - you found free!
And I'm with ya, more is always better

[STEVE333]

The SC program requires a sensor analysis - also done in SC then develops best exposure times based on the sky that night. Link:
https://www.sharpcap.co.uk/sharpcap/fea ... -histogram
Downside is it only comes with the SC pro license - you found free!
And I'm with ya, more is always better

From your description it sounds like that is exactly what they are doing.

One thing the analysis I presented doesn't take into account is the "lost time" between images. My system takes about 1 min to download the image and perform dithering, complete with settling time, before starting the next image. When I take longer exposures there will be fewer of them, so, less "lost time" in between images.

FYI, longer exposures never hurt, so, any exposure time up in the flat portion of the curve will yield equivalent results. When in doubt, go to the longer exposure.

Glad this may be of use to you.

Cheers,

Steve

[yobbo89]

This is as far as i got, it didn't work.. :sigh:

[STEVE333]

This is as far as i got, it didn't work.. :sigh:

Sorry you are having problems. I sometimes find the program a little "touchy", but, the results are worth it.

A couple questions:
1) What camera are you using (mono, color, etc.)?
2) Did you try following the full tutorial I posted? viewtopic.php?f=22&t=6323

If following my tutorial doesn't help your problem, you can contact the programs author at: ap_lab@outlook.com

Feel free to ask any other questions (I am retired), and, please let me know if it works for you.

By the way, your telescope looks like a beauty. 12" f/4, wow. Congratulations.

Steve

[yobbo89]

The camera i have is not on the list, i had to enter the specs in , using a mono asi1600-mm-c, i followed your description in the first post. i'm using astro lab version 0.4.2 instead of the 0.4.1 as seen in your tutorial.

[yobbo89]

This is as far as i got, it didn't work.. :sigh:

By the way, your telescope looks like a beauty. 12" f/4, wow. Congratulations.

Steve

yes, she's expensive to move/track and expensive to correct coma

[UlteriorModem]

[/quote]

Sorry you are having problems. I sometimes find the program a little "touchy", but, the results are worth it.

If following my tutorial doesn't help your problem, you can contact the programs author at: ap_lab@outlook.com

Feel free to ask any other questions (I am retired), and, please let me know if it works for you.

Steve
[/quote]

Oh! somehow I was under the impression that you were the author. My mistake. I frankly was a little taken back at your response of "Hope you get our problem sorted out". My mistake.

The ONLY way to contact him is by email?

No one else has run into a false positive with the install?

[yobbo89]

ok, i have it working, the sky glow in my area is 19.07, i guess the info shows 21.9 because of the lp blocking of ha filter.

yes you get to a point where the final image does not improve much from excessive exposure lengths because of the background/lp, doing longer subs gives you the benefit of not having to deal with 100+ frames to stack..