EOS R5 ISO issue

[iomrr]

good morning / evening 

this is omar al jassim canon R5 user 

i have great camera i i like it so much but when i shot at night i find it not too good "noise''

i tried many things to avoid this but without any succeed . 

iso 6400 15 sec 15-35 2.8

[jrhoffman75]

Higher ISOs will have noise. There are many good software programs that can address noise without adversely impacting your image. 

[rs-eos]

Or, slow the shutter.  A 2 minute exposure would have allowed for ISO to be 800.

[jrhoffman75]

He is doing astro photography. Looking to get “point stars”. Short shutter speeds are necessary to avoid star trails. A high pixel sensor like the R5 needs to follow roughly the ‘300 rule” - shutter speed X focal length 300 or less, so 15 seconds SS is appropriate. 

[rs-eos]

Ah, excellent point; thanks, John.

[jrhoffman75]

One problem with astro photography is the wide dynamic range. Getting any sort of detail in the darker areas typically leads to blowing out the stars - they become pure white rather than capturing the colors of the stars.

For this image I would want to have the foreground a little darker - maybe shoot at ISO 3200.

For some newer cameras, the R5 being one of them, the sensors are ISO invariant. This means that shooting at two or three stops underexposed and then boosting exposure in post doesn't produce any more noise than shooting at correct exposure.

 

In astro work that means shoot at lower ISO so the stars aren't blown out and increase the shadows in post to bring up detail in the darker areas. There will still be the ISO noise to deal with, but it is less than if the image was shot underexposed with a non-ISO invariant sensor.

I ran test with my 1D X Mark III (ISO invariant) and a Rebel T6s/760D (not ISO invariant). I shot an image at correct exposure and then a second images several stops underexposed. In post I boosted the underexposed images to obtain equivalent images.

You can see that the ISO invariant images have basically the same noise, where as the Rebel is much worse when boosted.

This technique is useful for any scenario where there is a large dynamic range, highlights want to be preserved, and there is a significant amount of dark area - could be astro, maybe concerts, maybe night cityscapes where the skyline is bright but a small portion of the image.