What is this Iso magic?

Started Nov 1, 2012 | Discussions thread
Robsphoto Senior Member • Posts: 1,219
Sony statement confirms that increasing the pixel count increases noise

Dennis wrote:

Robsphoto wrote:

Anyway, I think that, whenever the number of megapixels on an APS-C sensor is increased (with a consequent reduction in pixel size), it's no practical use saying, for example, that, if you downscale a 24mp image to 16mp, the high ISO images THEN look about the same. The 24mp image needs to stand on its own and a 40 inch print from a high ISO 24mp image needs to look just as good as a 33 inch print from an equivalent 16mp high ISO image.

I think that's totally unrealistic and I don't believe that it's the expectation of most people.

I think that when most cautious people are investigating whether or not to purchase a new camera that has a higher pixel count than the one they currently use, they want to ensure that the high ISO performance of the new camera is at least as good as that of the lower megapixel camera they are currently using. I don't think this is being unrealistic!

Sony is very sensitive to the fact that many photographers appreciate the fact that increasing the pixel count increases noise and that they want reassurance that the new higher megapixel sensors have adequately dealt with this problem. Consider, for example, this statement from Sony about the high pixel count of the new Sony RX100:

Question to Sony:

Why did you want a 20.2-megapixel sensor? I heard that this incredibly high pixel count would negatively impact noise levels, thereby decreasing image quality at high ISO settings.

Answer from Sony:

Ueda (Image Quality Design)

It’s true that increasing pixel count increases noise. But since we manufacture our own sensors, we can easily tweak sensor specs to suit specific needs. This allowed us to craft a totally new sensor that delivers superbly detailed images with low noise. For high-sensitivity shooting we managed to reduce noise levels below those of existing Cyber-shots by combining technologies from Cyber-shot and α Series. As a result, we can shoot at up to ISO 6400 for normal photos and up to ISO 25600 when using Multi Frame NR.


However, from what has been written about the high ISO performance of the 24mp Sony A77, there seems to be more dissatisfaction with the A77 high ISO performance than there is with that of the 16mp A55 or A57.

Although I think the bright light low ISO performance of the A77 seems to be excellent, I respect the opinions of some A77 owners who have expressed their reservations about the high ISO performance of the A77, such as in this posting:

"In my opinion, moderate (and higher) isos and heavy crops are the Achilles heel of this sensor. One of the reasons you want to have a high pixel sensor, is so that you can crop heavily when needed.  Otherwise, you might just as well get the 16MP sensor to begin with if you constantly have to resample to a lower res to control the noise. That'll work with the A77 so long as the ISO is below 400 IMHO.  It's manageable at 400 with some work and 800 with a lot of work.  Personally, when birding, I've been ETTR with an EV of +.7 and then performing as much highlight recovery as possible in RAW to control the shadow and background noise. However, ETTR leaves you with longer exposures at a given ISO which is bad for birding.

There are a lot of reasons to buy the A77 and enjoy using it, but this scenario is not one of them. Now if the AF performance and speed of the camera is better than the 16MP alternatives, then down-sizing is a reasonable compromise but not one I expected to have to use with this camera."


I think it's very difficult for any camera manufacturer to produce one camera that meets all the needs of an enthusiastic photographer! The A77 is great for low ISO bright light work and has great reach. However, if you want top notch low light images, then a full frame camera such as the A99 might be the best way to go! For example, the pixel pitch of the A99 is about 6.0 compared with about 3.9 for the A77 as explained here:


Consider the fact that the pixel pitch of the A99 is about 52% greater than that of the A77, and also that the sensor size of the A99 is 35.8mm x 23.8mm compared with 23.5mm x 15.6mm for the A77. IMHO, these two factors obviously make the A99 a much better choice for high ISO work than the A77.



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