Histogram stretch on flame & hh nebula

[AstroNebulee]

Hi

I am trying to process an image of the flame and hh nebula using photoshop cs4 as that is all I have.  I'm following a tutorial by Backyard Astro using the stretch in curves and checking the levels.  When I took the image I'm not sure if the histogram on the dslr was far enough over to the right but saying that is this why my histogram is starting to fragment, see attached  screenshot  from ps.  I'm being gentle on the curves and not going hell for leather on it.  I am very green on processing my images but want to get the basics right when I do it.  I have widefield orion images to process yet and hopefully the histograms from the dslr are better on those. Which  may not cause this fragmentation.

Edited February 13, 2021 by LeeHore7
addition

[dark knight]

Im not great at the processing side of things but it looks like your only processing the red channel? Maybe change to RGB and see what the histogram looks like.

[AstroNebulee]

1 hour ago, dark knight said:

Im not great at the processing side of things but it looks like your only processing the red channel? Maybe change to RGB and see what the histogram looks like.

Oh sorry that was just a screenshot I took as when I process my images I do each channel separately r, g and b. I'm just wondering wether the histogram from my dslr was over far enough when I took the data. 

[dark knight]

My knowledge is fairly limited but im sure some more knowledgeable folks will soon be able to help. I too use a dslr and my histogram never seems to venture too far from the left side although it is normally a little bit more than your histogram shows, does what iso we use change this, ive been using iso 400 last time out, maybe i should go back to iso 800.

[dark knight]

Sorry forgot to mention i always process as RGB and not individual channels, maybe im doing it wrong, i will follow your thread as i think i will learn a lot from it too!

[AstroNebulee]

After taking my first test image with my canon 450d unmodded dslr I check the histogram and try to get it as far away from the left as I can, I believe that as long as your at least a third of the way away from the left hand edge your ok as it doesn't clip any data. I think that you need to play around with iso and aperture to move the histogram around, the higher the iso the more noisy an image gets. But I could be wrong as I'm very green on this still.  The histogram on my ps screenshot doesn't seem to replicate what i saw on my dslr as this was stretched in processing. Here is a single sub from the said Orion image.

 

Edited February 14, 2021 by LeeHore7
addded image

[dark knight]

There is a thread somewhere on the optimal iso to use for specific dslr cameras, I'll see if i can find it

[dark knight]

http://dslr-astrophotography.com/iso-values-canon-cameras/

[AstroNebulee]

4 minutes ago, dark knight said:

http://dslr-astrophotography.com/iso-values-canon-cameras/

Thanks Carl that makes good reading, clear skies

 

[david_taurus83]

23 minutes ago, LeeHore7 said:

After taking my first test image with my canon 450d unmodded dslr I check the histogram and try to get it as far away from the left as I can, I believe that as long as your at least a third of the way away from the left hand edge your ok as it doesn't clip any data. I think that you need to play around with iso and aperture to move the histogram around, the higher the iso the more noisy an image gets. But I could be wrong as I'm very green on this still.  The histogram on my ps screenshot doesn't seem to replicate what i saw on my dslr as this was stretched in processing. Here is a single sub from the said Orion image.

 

Is that a png file? You should be working with raw cr2 files for preprocessing and then a stacked tiff file after stacking. Also, the camera histogram uses a scaled down jpeg for display purposes so the actual histogram in the raw file will be much lower. 

[AstroNebulee]

5 minutes ago, david_taurus83 said:

Is that a png file? You should be working with raw cr2 files for preprocessing and then a stacked tiff file after stacking. Also, the camera histogram uses a scaled down jpeg for display purposes so the actual histogram in the raw file will be much lower. 

Hi David.

The .png file is just to upload on here.  I always shoot in raw mode .cr2.  Then stack in dss.  Regarding the histogram on my dslr, am I right in thinking that it uses a scaled down jpeg and I'm not seeing the true raw histogram?  So saying if it shows the peak 1 third along then the raw version will be further to the left Sorry if I'm being silly here 

[david_taurus83]

1 minute ago, LeeHore7 said:

Hi David.

The .png file is just to upload on here.  I always shoot in raw mode .cr2.  Then stack in dss.  Regarding the histogram on my dslr, am I right in thinking that it uses a scaled down jpeg and I'm not seeing the true raw histogram?  So saying if it shows the peak 1 third along then the raw version will be further to the left Sorry if I'm being silly here 

Yes.

[AstroNebulee]

5 minutes ago, david_taurus83 said:

Yes.

Thank you David, so I need to really get the histogram on my dslr nearer to halfway than 1 third then?

[david_taurus83]

I don't use the DSLR histogram as I usually use a PC for imaging but if I aim for a third to halfway on the PC histogram (based on actual ADU values) then the DSLR histogram is touching the right hand side. 

It entirely depends on what target you are shooting and how bad your LP is. For Orion the short exposures are OK but lots of them. It's low down and probably more affected by LP etc. For M81 say, it's up higher and not as bright so you could get away with going longer.

[AstroNebulee]

Thanks David, I've never really got the hang of using my dslr with an imaging program, I only have APT.  I use my laptop when using my zwo planetary camera though. I'm in bortle 3 skies so very little LP.  I will try to get the dslr histogram near the halfway and see how I get on.  I have a star adventurer on order with flo and hoping to arrive sometime in mid-late march so will make things much easier for me.  Clear skies

[Andy Webster]

One thing you need to know is that high ISO does not bring high noise. The lack of light brings the noise. With high ISO you are merely asking for a lot of light, not really getting it. The effect looks like more noise because there are pixels that don’t get enough light in the time that you ask for. You can either go with more integration frames to fill in those pixels or you use a lower ISO  number. With the lower ISO number you must do a longer exposure to reach your goal. Bottom line is that if you are using short times because of star trailing you need to use higher ISO. If you are guiding, you can use the low ISO and fill in those pixels with light instead of getting digital noise. Of course, if you have light pollution creeping in, as do many of us, you will be overexposed with any long exposure not using narrowband filter.

[AstroNebulee]

Thank you for your advice Andy, it's good to learn those things, I always thought higher iso was creating the noise. It's all about getting the right balance between iso and aperture then. I shall try more subs definitely (it was blooming freezing when I took these last week). Wgern my star adventurer arrives I can go longer subs at a lower iso 800 maybe 400 and 2.8-4.0f maybe. Clear skies