Joe,
Clear nights are hard to come by these days, so the next opportunity you have I recommend keeping the exposure the same but stack for far longer than 30 minutes. Nothing useful comes out of 30 minutes especially being so close to the city. There was a photo that you posted a while back from your balcony. It looks to me like you might be in the Scarsdale/Yonkers area, perhaps northern Bronx, maybe even Manhattan. At best you are at Bortle 7, worst case Bortle 8, I would imagine. Give it a try. It may come down to that you've hit a wall. You may need to look for brighter targets. Try the Whirlpool Galaxy (M51). The arms are bright. M81 is not easy getting detail out of it.
Here is a photo that I took of M51 a week ago. Compare that to the photo of M81 that I posted a few days ago on this thread. I think you'll do much better with M51. I think you'll see the arms.
Brian
First timer, focusing (?) problem
Re: First timer, focusing (?) problem
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Re: First timer, focusing (?) problem
Brian,
I really needed to hear your suggestion to go longer than 30 minutes. And yes, I am in northern New Jersey (about 10 miles north of Manhattan) with dense woods to my south, north west, and west (my only sky is to the north-east and east). I know I'm being a wimp, but my deck faces east (to the left of the Manhattan orange glow) and with night time temps in the 20's, once I align, I usually set up my laptop and iPad in my living room to stay warm. Bodes Nebula is the only galaxy in the east right now. So until the warmer weather...
I've read that as Live Stack accumulates images, it's important to keep tweaking the histogram (which I did not do). I assume that a long exposure (more than 30 minutes) with "tweaking" might help. Do you have any suggestions that apply specifically to light pollution exposure times, i.e., shorter (1.2 seconds or less) exposures but longer overall time. I would think that longer shutter times would amplify light pollution. As you can tell, I "almost" understand all this, but I'm clearly not there yet. Your suggestions have given me renewed hope to forge ahead.
Thank you,
Joe
I really needed to hear your suggestion to go longer than 30 minutes. And yes, I am in northern New Jersey (about 10 miles north of Manhattan) with dense woods to my south, north west, and west (my only sky is to the north-east and east). I know I'm being a wimp, but my deck faces east (to the left of the Manhattan orange glow) and with night time temps in the 20's, once I align, I usually set up my laptop and iPad in my living room to stay warm. Bodes Nebula is the only galaxy in the east right now. So until the warmer weather...
I've read that as Live Stack accumulates images, it's important to keep tweaking the histogram (which I did not do). I assume that a long exposure (more than 30 minutes) with "tweaking" might help. Do you have any suggestions that apply specifically to light pollution exposure times, i.e., shorter (1.2 seconds or less) exposures but longer overall time. I would think that longer shutter times would amplify light pollution. As you can tell, I "almost" understand all this, but I'm clearly not there yet. Your suggestions have given me renewed hope to forge ahead.
Thank you,
Joe
Re: First timer, focusing (?) problem
Your image this past week is amazing! Thank you for sending, it encourages me to stay the course. Question: at the lower left of your photo, is that another galaxy?
Joe
Joe
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AussieHowie
- Posts: 25
- Joined: Fri Aug 11, 2017 12:23 am
Re: First timer, focusing (?) problem
Joe, I noticed way back in your thread you asked ... "Looking at the histogram in your last post, the curve is on the left side...not sure what the histogram is showing. I guess what I'm saying is what should I be doing with the histogram and why?"
Good video in the link explains it well. https://www.youtube.com/watch?v=CIbcS6Qkel8
Couple of things ....
* He doesn't say is if the histogram is way over on the left hand side (underexposed), then the only way to move it right is to increase gain or exposure time or both. And vice versa ... if the histogram is way over on the right hand side, then the only way to move it left is to decrease gain or exp time or both.
* He says we want the hump to look like in the video stretching all the way from the left to the right in a big "lump". We struggle to get that in EAA or AP. A typical astro image the hump (or as we say the data) is usually way over on the left.
So at night with astro images (histogram way over on the left), your job is to adjust the gain and/or exposure time of the camera so that the very start of the rise up the hump has just moved away from the left vertical axis. NOTE that this is the start of the curve as it rises up the histogram which needs to start rising just off the left hand vertical axis. Not the peak ... it is the start of the rising curve needs to be off the left!
Only when that curve is away from the left, is it time to start stacking. If you start stacking before then, beginners usually struggle trying to tease out the faint nebulosity or galaxy arms or whatever. With experience you can pull details when the curve is jammed up against the left ... but as a beginner move the curve off the left hand side before stacking.
What he does not mention is what the blackpoint and whitepoint sliders are in SharpCap (and other software). You saw in that video he grouped the horizontal axis tones from left to right as Darks, then further across Shadows, then further MidTones then on the right as Highlights. If you move the blackpoint slider from Darks more right across to the Shadows ... then you are instructing the software to display the Shadow tones as Dark. So any shades of lighter than totally dark is going to now display dark ... you loose the detail in the lighter-than-dark stuff. So use it with caution. You will find a grey background between the stars will get darker as you adjust / move the blackpoint more right. But watch the faint nebulosity / galaxy arms too as they will dim and you do not want to push blackpoint too far right as it will totally get rid of that detail.
If you move the whitepoint slider from Highlights more left across to the MidTones ... then you are telling the software to display the MidTones as Highlights. So now those previously mid tones will become overblown white loosing mid details. So again, watch the image carefully as you adjust whitepoint.
Lastly a reminder .... only the exp time and or gain can move that histogram. Adjusting the blackpoint and whitepoint are only adjusting the DISPLAY of the image. NOT the image itself! IE if your first image does not show stars (to allow stacking) and you move the whitepoint slider left so this brightens up the image so you can see stars .... if you stack you will more than likely get rejected frames and stacking does not happen -you get a failure message. Because it was only the displayed image which was brightened ... while the pixels in the actual frames from the camera still had the same exp time and gain which showed zero stars or stars which were too faint to see clearly.
Good video in the link explains it well. https://www.youtube.com/watch?v=CIbcS6Qkel8
Couple of things ....
* He doesn't say is if the histogram is way over on the left hand side (underexposed), then the only way to move it right is to increase gain or exposure time or both. And vice versa ... if the histogram is way over on the right hand side, then the only way to move it left is to decrease gain or exp time or both.
* He says we want the hump to look like in the video stretching all the way from the left to the right in a big "lump". We struggle to get that in EAA or AP. A typical astro image the hump (or as we say the data) is usually way over on the left.
So at night with astro images (histogram way over on the left), your job is to adjust the gain and/or exposure time of the camera so that the very start of the rise up the hump has just moved away from the left vertical axis. NOTE that this is the start of the curve as it rises up the histogram which needs to start rising just off the left hand vertical axis. Not the peak ... it is the start of the rising curve needs to be off the left!
Only when that curve is away from the left, is it time to start stacking. If you start stacking before then, beginners usually struggle trying to tease out the faint nebulosity or galaxy arms or whatever. With experience you can pull details when the curve is jammed up against the left ... but as a beginner move the curve off the left hand side before stacking.
What he does not mention is what the blackpoint and whitepoint sliders are in SharpCap (and other software). You saw in that video he grouped the horizontal axis tones from left to right as Darks, then further across Shadows, then further MidTones then on the right as Highlights. If you move the blackpoint slider from Darks more right across to the Shadows ... then you are instructing the software to display the Shadow tones as Dark. So any shades of lighter than totally dark is going to now display dark ... you loose the detail in the lighter-than-dark stuff. So use it with caution. You will find a grey background between the stars will get darker as you adjust / move the blackpoint more right. But watch the faint nebulosity / galaxy arms too as they will dim and you do not want to push blackpoint too far right as it will totally get rid of that detail.
If you move the whitepoint slider from Highlights more left across to the MidTones ... then you are telling the software to display the MidTones as Highlights. So now those previously mid tones will become overblown white loosing mid details. So again, watch the image carefully as you adjust whitepoint.
Lastly a reminder .... only the exp time and or gain can move that histogram. Adjusting the blackpoint and whitepoint are only adjusting the DISPLAY of the image. NOT the image itself! IE if your first image does not show stars (to allow stacking) and you move the whitepoint slider left so this brightens up the image so you can see stars .... if you stack you will more than likely get rejected frames and stacking does not happen -you get a failure message. Because it was only the displayed image which was brightened ... while the pixels in the actual frames from the camera still had the same exp time and gain which showed zero stars or stars which were too faint to see clearly.
Re: First timer, focusing (?) problem
Brian,
Thank you for taking the time to help me out. I do appreciate it. You've helped me understand something that I have been TOTALLY missing! I never realized the need to establish a good histogram "before" doing a live stack. Nor did I understand that moving the histogram takes place by adjusting exposure and gain in the camera. This was a revelation to me!!! So, if I'm understanding this, once I adjust my initial histogram (in order to achieve enough alignment stars and to have the 'hump' of the histogram towards the left), then I start a Live Stack.
Here's my question. Once the stacking takes place, I"m not sure what function the "display" histogram plays. If it is only a display, it's not effecting the stacking. Is that right? Where I'm confused is, while stacking, if I want to, say, bring out more nebulosity, I can move the histogram slider to show this, but I'm not improving the actual image. Right? To effect the image, I can't imagine that I have to keep adjusting the exposure and gain. I know I'm missing something, specifically, the fact that the display histogram doesn't effect the image. Saying this differently, moving the whitepoint/darkpoint sliders accomplishes what? I know it could enhance the display image...but what about the image being stacked. I hope you can understand my confusion.
I'm pretty sure I'm missing something quite obvious. I hope you can get me through this quagmire. I do feel I'm almost there.
Again, I can't thank you enough for your help,
Joe
Thank you for taking the time to help me out. I do appreciate it. You've helped me understand something that I have been TOTALLY missing! I never realized the need to establish a good histogram "before" doing a live stack. Nor did I understand that moving the histogram takes place by adjusting exposure and gain in the camera. This was a revelation to me!!! So, if I'm understanding this, once I adjust my initial histogram (in order to achieve enough alignment stars and to have the 'hump' of the histogram towards the left), then I start a Live Stack.
Here's my question. Once the stacking takes place, I"m not sure what function the "display" histogram plays. If it is only a display, it's not effecting the stacking. Is that right? Where I'm confused is, while stacking, if I want to, say, bring out more nebulosity, I can move the histogram slider to show this, but I'm not improving the actual image. Right? To effect the image, I can't imagine that I have to keep adjusting the exposure and gain. I know I'm missing something, specifically, the fact that the display histogram doesn't effect the image. Saying this differently, moving the whitepoint/darkpoint sliders accomplishes what? I know it could enhance the display image...but what about the image being stacked. I hope you can understand my confusion.
I'm pretty sure I'm missing something quite obvious. I hope you can get me through this quagmire. I do feel I'm almost there.
Again, I can't thank you enough for your help,
Joe
Re: First timer, focusing (?) problem
Hi Joe,
You need to direct your thanks to AussieHowie. I don't use LiveStack so I am of little use. I use SharpCap for three things: Polar Alignment, Guiding Assistance, and Periodic Error Correction. I use other software for image capture. I have a very simple technique for determining exposure of a single sub frame: I find the brightest star in the field that I can't or won't crop out and then adjust the exposure so that star comes in just below saturation. Then I start capturing data. I have software that helps me determine how many sub frames I need to capture in order to achieve a desired signal-to-noise ratio. You can find the software here:
https://snrcalc.now.sh
I recommend following AussieHowie's helpful advice, mostly because I don't know how to model your Revolution camera in software. It is designed for CMOS and CCD cameras.
Brian
You need to direct your thanks to AussieHowie. I don't use LiveStack so I am of little use. I use SharpCap for three things: Polar Alignment, Guiding Assistance, and Periodic Error Correction. I use other software for image capture. I have a very simple technique for determining exposure of a single sub frame: I find the brightest star in the field that I can't or won't crop out and then adjust the exposure so that star comes in just below saturation. Then I start capturing data. I have software that helps me determine how many sub frames I need to capture in order to achieve a desired signal-to-noise ratio. You can find the software here:
https://snrcalc.now.sh
I recommend following AussieHowie's helpful advice, mostly because I don't know how to model your Revolution camera in software. It is designed for CMOS and CCD cameras.
Brian
Re: First timer, focusing (?) problem
Much to digest,
I'll do as you suggest, you've been a great help. Thank you!!!
Joe
I'll do as you suggest, you've been a great help. Thank you!!!
Joe
Re: First timer, focusing (?) problem
Joe,
That tiny sliver of light is IC 4263, a distant spiral galaxy. There are a total of six galaxies in that photo, three of which are so small that they look like tiny fuzzy stars.
Brian
That tiny sliver of light is IC 4263, a distant spiral galaxy. There are a total of six galaxies in that photo, three of which are so small that they look like tiny fuzzy stars.
Brian
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AussieHowie
- Posts: 25
- Joined: Fri Aug 11, 2017 12:23 am
Re: First timer, focusing (?) problem
Joe, I think I'll make a video for you and post the link. You've been struggling for ages and I think a video which shows a workflow to use out at your scope would make it clearer.
But ...
In your last post you said .... "once I adjust my initial histogram (in order to achieve enough alignment stars and to have the 'hump' of the histogram towards the left), then I start a Live Stack."
Absolutely did not say that you had to have the 'hump' of the histogram towards the left ... I said ... "your job is to adjust the gain and/or exposure time of the camera so that the very start of the rise up the hump has just moved away from the left vertical axis....Not the peak ... it is the start of the rising curve needs to be off the left"
You also said in your last post ... "I know I'm missing something, specifically, the fact that the display histogram doesn't effect the image. Saying this differently, moving the whitepoint/darkpoint sliders accomplishes what? I know it could enhance the display image...but what about the image being stacked."
You'll understand totally when I post a link to the video I'll make Joe
But ...
In your last post you said .... "once I adjust my initial histogram (in order to achieve enough alignment stars and to have the 'hump' of the histogram towards the left), then I start a Live Stack."
Absolutely did not say that you had to have the 'hump' of the histogram towards the left ... I said ... "your job is to adjust the gain and/or exposure time of the camera so that the very start of the rise up the hump has just moved away from the left vertical axis....Not the peak ... it is the start of the rising curve needs to be off the left"
You also said in your last post ... "I know I'm missing something, specifically, the fact that the display histogram doesn't effect the image. Saying this differently, moving the whitepoint/darkpoint sliders accomplishes what? I know it could enhance the display image...but what about the image being stacked."
You'll understand totally when I post a link to the video I'll make Joe Re: First timer, focusing (?) problem
AussieHowie,
What can I say? Your offer to make a video is so generous and, frankly, fantastic! I look forward to your help with this. I think I'm getting close...real close, to having some success. Also, I never realized that M51 is visible from my deck! I'm elated, now that I have a better object to practice on (Bodes Nebula was a bit too challenging).
A quick question. My Revolution Imager can capture in color, if I manage to save a Live Stack in PNG, will it show color?
Once again, thank you so much for taking the time to help, I sincerely appreciate it.
Joe
What can I say? Your offer to make a video is so generous and, frankly, fantastic! I look forward to your help with this. I think I'm getting close...real close, to having some success. Also, I never realized that M51 is visible from my deck! I'm elated, now that I have a better object to practice on (Bodes Nebula was a bit too challenging).
A quick question. My Revolution Imager can capture in color, if I manage to save a Live Stack in PNG, will it show color?
Once again, thank you so much for taking the time to help, I sincerely appreciate it.
Joe