SX50 - Struggling between absurdities

Started Nov 4, 2012 | Discussions thread
PhilM oz
Senior MemberPosts: 1,196
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Re: SX50 - Struggling between absurdities
In reply to Augustin Man, Nov 5, 2012

I agree with you that it is a dumb limitation.

From experiments I've done on my SX40 I suspect it has to do with hot pixels on the CMOS sensor.

On these small CMOS sensors Canon is using (made by Sony I believe), you get a lot of hot pixels at long exposures and high ISO.

CHDK allows the ISO to be overridden at any shutter speed and I can tell you on the SX40 the hot pixels become quite noticeable if you crank up the ISO on a long exposure. Even at ISO 100 if you try and do a really long exposure there is a huge amount of hot pixel noise.

The second part of the problem comes from the built in long exposure noise reduction algorithm. At ISO 100 it does a good job; but at higher ISO's it's awful.

So the limit is most likely to prevent lots of complaints from the unwashed masses; at the expense of limiting what you can do if you know what you are doing.

Here's some 100% crops of images taken with the lens cap on to show what I mean:

´╗┐ISO 100, 15 sec exposure, noise reduction off.

ISO 100, 15 sec exposure, noise reduction on.

ISO 3200, 15 sec exposure, noise reduction off.

ISO 3200, 15 sec exposure, noise reduction on.

ISO 100, 512 sec exposure, noise reduction off.

Thankfully the G1X does not have this restriction or the hot pixel issue - I've taken a 17 minute exposure at ISO 100 and it is very clean.

Phil.

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