Exposure length and ISO invariance

[Mark1489]

Hi,

After a lot of reading I think I understand the iso invariance of some cameras, that being using a lower iso and boosting the exposure in post processing will not increase the image noise, and a greater dynamic range is produced (please correct me if I’m wrong).

How do I apply this in a practical sense? I have a Nikon D5300 and the data points towards ISO 200 as the sweet spot. Now obviously if I expose for my usual sub frame length (1 minute) my histogram is going to be up against the left, I guess what I’m trying to ask is how do I know if I’m clipping data at this point? I’ve always used the histogram clear of the left edge technique to properly expose my images, but it seems this wouldn’t work if I’m using a lower ISO. Anyone have any ideas how I should go ahead with this? 
 

Thanks

Mark

[Alien 13]

I have similar issues with my Canon camera that also has a suggested ISO setting of 200 for AP due to its ISO invariance, I do suggest that you stick to a range of ISO between 200-400 and basically ignore what the histogram is telling you. The camera wont catch any more photons from stars by increasing the ISO anyway....

Alan

[JamesF]

32 minutes ago, KevS said:

This makes interesting reading.

https://dslr-astrophotography.com/long-exposures-multiple-shorter-exposures/

K

I think that's very much consistent with what Robin (author of SharpCap) presented in his talk earlier this year, in that the payback for longer exposures is much more significant under dark skies than light-polluted ones.

James

[Mark1489]

4 hours ago, Alien 13 said:

I have similar issues with my Canon camera that also has a suggested ISO setting of 200 for AP due to its ISO invariance, I do suggest that you stick to a range of ISO between 200-400 and basically ignore what the histogram is telling you. The camera wont catch any more photons from stars by increasing the ISO anyway....

Alan

Definitely going to do a test next time and take some exposures just changing the iso and nothing else, while equalising all the exposures in processing! 
 

2 hours ago, KevS said:

This makes interesting reading.

https://dslr-astrophotography.com/long-exposures-multiple-shorter-exposures/

K

Yes very interesting read! The only reason I bumped the iso higher was to gain clear separation from the left, I image under 21.2 or 21.7 skies mostly so there’s some light pollution but not a lot. My next target is the Orion Nebula so a perfect example to test the extended dynamic range of a lower iso 😊

[bottletopburly]

Recently changed to  a Nikon D5300 I too read the above article and so have been using iso 200 results here on Orion and The Pleiades 

 roughly both images have approx 8 hrs data .

 

[Mark1489]

Had a quick window of opportunity last night on M42, the moon was out so not ideal but I was bored of waiting 😂 I used Iso 400 and 30 sec sub frames, stacked 12 and got this! 

[wxsatuser]

That's quite nice considering the short exposures.