Balancing ISO & Exposure for Best Results

Started May 26, 2015 | Discussions thread
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RustierOne
RustierOne Veteran Member • Posts: 4,400
Balancing ISO & Exposure for Best Results

Since my imaging rig seems to be performing well at 15-20 minute subs with 1400 -2000 mm focal length, I have been exploring lower ISOs on my Sony cameras. For quite some time I just stuck to ISO 1600 on the Sony NEX-5N for no good reason - just noise seemed to be OK. Lately I've been using the NEX-7 at ISO 800 with decent results.

But I was wondering if these was a way to choose a good ISO/exposure combination to best utilize a camera's capabilities. Specifically - can one use measured camera performance (read noise, full-well saturation, dynamic range) to make a analytic choice of best ISO? Then using that ISO adjust exposure to get the histogram peak out of the noise floor for decent signal/noise ratio.

So I am soliciting advise, comments, words of wisdom, etc. in this regard. Perhaps using the measurements given below as an example, what would be the best ISO for general astrophotography? Here is a chart which shows some measurements of my cameras' sensors by Sensorgen.info:

Sensor Data from Sensorgen.info

Highlights in green show where one camera sensor is better at that ISO. Yellow highlights show where the cameras are equal. It looks like at base ISO the NEX-7 has 1/2 stop better dynamic range. Then the cameras are close up through ISO 400. Then the NEX-5N pulls ahead in dynamic range up through ISO 3200.

My gut feeling is that ISO 200-400 with either camera would be good. And maybe ISO 800 would be better used on the NEX-5N.

So what do you think is a good ISO given the above example measurements?

Another question comes to mind - given that both cameras out-resolve the image details in astrophotos, is there any benefit to binning (2X2) giving 4 MP with the NEX-5N and 6MP with the NEX-7?

Comments would be much appreciated.

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Best Regards,
Russ

 RustierOne's gear list:RustierOne's gear list
Sony Alpha NEX-5N Sony Alpha NEX-7 Sigma 19mm F2.8 EX DN Samyang 8mm F2.8 UMC Fisheye Sony E 35mm F1.8 OSS +4 more
Sony Alpha NEX-5N Sony Alpha NEX-7
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