11 replies to this topic

[GoBlue]

Concensus seems to be histogram kept to left third is good. Can only get there with very short subs, 30 secs or less. Iso doesn’t seem to make much difference. Any tips to share for you guys doing 3 min and up exposures? Using a cls, the red is almost always all the way left, and green/blue way right. Unfiltered most of my subs are middle right. Thank you.

[GoBlue]

Forgot to ask if the histogram on the camera is different from the display on backyardeos. Doesn’t seem like it would be but references I researched here all mention the camera display and not eos. Thanks again and if there’s a search option here please point it out, dont want to waste anyones time with already asked questions.

[bmhjr]

I use BYEOS histogram and never turn on the camera display.  What camera/scope are you using and what are your sky conditions?

Edited by bmhjr, 06 April 2018 - 01:21 PM.

[GoBlue]

ES80ed - 480mm / f6 / limiting magnitude 12 / resolution 1.45 arcsec.

Canon t3i excellent condition.

 

Sky conditions:

SQM 20.10 mag./arc sec2
Brightness 0.987 mcd/m2
Artif. bright. 815 μcd/m2
Ratio 4.77

Bortle class 5

 

Thanks

[GoFish]

ISO?

[bmhjr]

Interesting. I image in skies 21.2 with same camera at f6 ISO 1600 and get 5 minute exposures to move the histogram 1/3 over from left. No idea why you can only do 30 seconds.

[calypsob]

Concensus seems to be histogram kept to left third is good. Can only get there with very short subs, 30 secs or less. Iso doesn’t seem to make much difference. Any tips to share for you guys doing 3 min and up exposures? Using a cls, the red is almost always all the way left, and green/blue way right. Unfiltered most of my subs are middle right. Thank you.

Dont look at the rgb histogram, its likely not white balanced at all form your explanation.  Only look at the luminance curve.

 

This will give you a better idea of how long to expose. 

[bobzeq25]

Two things are extremely surprising. So much so there has to be something else going on.

You say ISO doesn't matter. That doesn't make any sense at all. A one stop difference in ISO (say, going from 1600 to 800) should double the exposure.

You say you can only image for 30 sec in pretty dark skies. Don't see why that should be the case unless you're using very high ISO.

[gilbertgrape87]

Yeah, you must be using an extreme high ISO. I can pull about 1.5-2 minutes with f/5.6 and mid 18 skies. ISO is the only piece of the puzzle that's left.

[17.5Dob]

I'm baffled as well.

From my mid 18 SQM backyard, I could get 90-120" subs @ f4 and keep it at 1/3 histo, ISO 400.

 

 

 

From my darksite, I can't even get to 1/16 histo in 6 minutes @ f6.5, ISO 200

 

Ramp up to ISO 400, f6.5 and even at 7 minutes, my histo is still barely 1/8

 

I generally "NEVER" shoot at ISO 1600, but after setting up one night , the winds started gusting 25-35 so I tried to salvage the night by using ISO 1600 and shooting "short" 90 sec subs. My histo is still only 1/16 to 1/8 over @ f6.5




Any chance that somehow the camera is stuck on auto ISO ??

Edited by 17.5Dob, 08 April 2018 - 07:18 PM.

[Samir Kharusi]

Please note that there is a HUGE difference between the Back of Camera Histogram and any histogram output from software that generates a Linear image. All references to 1/3rd refer to the BoC Histogram or equivalent. Equivalent are histograms of a frame that has been processed in any software as a normal, daytime photo, i.e. including a gamma-stretch. To digest what is going on please convert any Raw photo using Linear and Normal (nonLinear). These are both available in Canon Digital Photo Pro that comes packaged with Canon DSLRs.

 

The vertical axis displays the numbers after a gamma-stretch, the horizontal are after Linear conversion from Raw. One third Histogram (BoC !)  is roughly 20,000 on the Y-axis (90% Stacking Efficiency) = roughly 2% in a Linear Histogram. Huge difference...

[GoBlue]

Had better luck this weekend. Short answer is it’s all about sky quality. Thanks to all.