Canon Powershot: Lower Dynamic Range at ISO 80?

[anonymous]

I recently purchased a new compact camera (Canon Powershot A720 IS), the following excerpt from this website caught my attention:

"In some digital cameras, there is an extended low ISO setting which produces less noise, but also decreases dynamic range. This is because the setting in effect overexposes the image by a full f-stop, but then later truncates the highlights-- thereby increasing the light signal. An example of this is many of the Canon cameras, which have an ISO-50 speed below the ordinary ISO-100"

(from - http://www.cambridgeincolour.com/tut...amic-range.htm)

My Powershot A720 goes down to ISO 80 (which I have been using religiously, to try and keep as little noise from entering my photos as possible), but I am now concerned that by using that setting, I may be losing out on dynamic range. Can I ask how you know about the above, and if you know whether it applies to this particular model of camera or not? (Or where I might start looking for an answer if you do not know).

[McQ]

No worries, the "ISO extension" in that article pretty much just applies to SLR cameras that explicitly call it as such in their manual/menu. You would know if it were different than a normal ISO setting.

That being said, since the physical size of pixels on the A720 is quite small, it will lead to a much lower dynamic range than that of nearly any digital SLR. On the other hand, it is definitely smaller and probably more practical to use than always having to lug around a big SLR camera.

[xeliex]

McQ, I guess this is very similar to my other question in the other post, but on my point and shoot SD1000, I either shoot ISO 100 or 200 (400 when needed).

Is it safe to assume that by avoiding ISO 80 I am capturing more dynamic range regardless of the exposure setting?

[McQ]

You might eek a little more dynamic range out of the SD1000 by using ISO80 instead of 100 or 200. Usually the only times the lowest ISO setting has less dynamic range are when the camera does not enable it or use it by default.

[Graystar]

I’ve done lots of DR testing on my Canon A710 and found that ISO80 does do a better job than ISO100 with noise and DR.

The most DR I can achieve is 7 stops worth when I shoot in RAW (using CHDK,) about 6 2/3 stops with Contrast set to –2, and about 6 stops worth when MyColors is turned off. I typically keep my A710 at –2 Contrast and +2 Sharpening, which I don’t recommend for the A720 because the DIGIC III process performs more sharpening at its default setting. On really gray days I boost the contrast to 0 or +2 (depending on the day) and drop the sharpening to +1. If I think a scene is going to be difficult I turn on RAW.

I’ve also discovered that some highlight clipping occurs during the in-camera post-processing. So if you setup the camera on a tripod and meter on a bright lamp, you’ll get different amounts of highlight clipping between MyColors "Off" and "Vivid". But with MyColors set to "Neutral" you won’t get any clipping.

I believe this is why people claim that Canon’s metering tends to clip highlights. I actually feel that Canon’s metering is very accurate...what people are experiencing is the effects of the post-processing.

When conditions are right and the scene affords it, a polarizer can really help provide an apparent increase in DR. Here’s an image I had snapped as an example just to demonstrate the effect. The polarized image is on the right. Notice the sky, brighter foliage, and brighter shadow areas.