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View Full Version : Native ISO speed for Canon G9?



cbope
04-19-2010, 23:35
Couple of questions:

1. Does anyone know the native ISO speed of the sensor in the G9? I believe it's 80 but I have not been able to confirm.

2. What ISO setting should I use in general for underwater photography with this camera? Should I stick to native ISO or use a bit higher to help prevent movement blurring? My G9 does have IS (optical image stabilization) and I keep that on always. IS gives 2-3 stops more "speed" so shooting at a slower shutter speed does not incur a movement penalty. Above water, I can handhold at relatively slow shutter speeds quite reliably.

I'm just getting started in underwater photography, but I have been a long-time advanced amateur photographer (close to 30 years). I just ordered an Ikelite housing for my G9, next on my shopping list is an Ike strobe and then a short port and wide-angle lens (either Inon or Ike). I rented a cheap no-name digital camera in a housing while diving in Thailand about 1.5 years ago, that's the limit of my underwater photography so far. No external strobe and lots of photoshop needed afterwards, the white balance was WAY off and lot of color correction was required.

LeeParrish
04-20-2010, 06:38
You will get the best quality image at the lower ISO settings. It's a balance in the end, but if you go look at many of the review sites and check the test images you'll see the difference when you get into the higher ISO settings you tend to lose detail and increase noise.

DevilDiver
04-20-2010, 07:43
The Canon G9 ISO option range is Auto, Hi Auto, 80 ,100, 200, 400, 800, 1600. The sensor size is 1/1.7 " (0.43 cm²), as with all point & shoot cameras (small sensor) the issue with ISO vs the pixel density of the smaller sensor is the digital noise that becomes apparent at higher settings and/or low light conditions. Digital cameras have an ISO rating indicating the level of sensitivity of their sensor to light just like using different speeds of film.

ISO 100 is the "normal" setting for most cameras, although some go as low as ISO 50. The sensitivities can be increased to 200, 400, 800, or even 3,200 on high-end digital SLRs. When increasing the sensitivity, the output of the sensor is amplified, so less light is needed. Unfortunately that also amplifies the undesired noise. Incidentally, this creates more grainy pictures, just like in conventional photography, but because of different reasons. It is similar to turning up the volume of a radio with poor reception. Doing so will not only amplify the (desired) music but also the (undesired) hiss and crackle or "noise". Improvements in sensor technology are reducing the noise levels at higher ISOs, especially on higher-end cameras. And unlike conventional film cameras which require a change of film roll or the use of multiple bodies, digital cameras allow you to instantly and conveniently change the sensitivity depending on the circumstances.

The two problems that you face as an underwater photographer and a compact camera user is that the conditions that you shoot in are automatically "low light" plus colors are filtered out of the remaining available light as soon as you descend below the surface and these issues increase and change from there with depth and conditions.

The best suggestion for your ISO setting with the G9 or any P&S camera really is probably going to be to set at 100 or 200 and leave it. Depending on how well your camera handles low light, review a few test shots you should be able to see the difference and decide on what is acceptable to you.
(Never leave it to "Auto", cameras are designed to use above water. The camera will choose for you and it will almost always be wrong)

The point is you will want to use the highest acceptable ISO for your camera and leave it there for almost all situations. Like I said above I believe that this will be 100 or 200. With the G9 I believe you should be able to use 200....

If you get some test shots post them for others to get an idea of the difference and what you found was the best setting. :smiley20:

mitsuguy
04-20-2010, 08:09
With the Canon S90, which is a higher end P&S, similar to the G9 (really, just a slightly newer version in a smaller body), I shoot everything between ISO 80 and 200 with a strobe... Exposure times vary from 1/60 to 1/250th, and F-stop between F5.6 and F8 usually...

The problems you will run into is having a good enough depth of field by using the higher range of F-stops whilst getting enough light in the camera... Most likely, underwater, you will want to turn IS off, and set your shutter speed to never go slower than 1/60th... Once you take a couple pics at your desired F-stop, and no go slower than 1/60th, you can vary your ISO underwater to approximate a proper exposure... Unfortunately, there comes a point in which you don't want to go any higher in ISO (the G9 looks pretty good even at 400, but I'd stay no more than 200), and you will have to lower the f-stop to let more light in... Then, of course, shutter speed is always a variable as well if there is too much light...

Practice practice practice... Once you get a little practice, shoot everything in RAW and in manual, and make sure to take a few white balance card shots in the same lighting conditions as your photo so that you can adjust white balance later...

CompuDude
04-20-2010, 14:53
Yup. In general, use the lowest ISO you can to get the best quality. If light is low and you need to, I wouldn't worry about going up to ISO 200. Higher than that and you're going to start losing detail and getting noticable grain.

SLRs do better in this regard that P&S cameras, even good ones like the G9.

The latest crop of better P&S cameras (like the S90 and G11) can give usable shots at ISO 400. They can go a lot higher, too, but I'd be hesitant about depending on ISO 800 on a P&S without a lot of testing.

LeeParrish
04-20-2010, 15:37
Some test shots I did with my G11 were pretty decent up to around 400, after that you could begin to see a loss of detail and the noise started to increase. I'm hoping to play around and do some more low light tests to make sure I know what I feel comfortable with before relying on it though.

What I did was do some macro shots since it's easier to see loss of detail and did them later in the evening with a tripod out on my back porch. This way I could rule out my own movement and what I shot was a pattern on a piece of lawn furniture that allowed me to see colors (this has a set of stripes in light blues and browns) as well as the fabric detail of the macro shot. I'll have to do it over again since I deleted the first images, but doing something like this is probably worth the effort with any camera to better understand the limits.

DevilDiver
04-20-2010, 18:02
Lee,

Please post a couple of the test photos when you get a chance. I would be interested to see what results you get.

cbope
04-21-2010, 09:32
Not sure I understand your reason for turning IS off. It gives you about 2-3 stops more speed than without it, and I'm not aware of any negative side effects of keeping IS on. Above water I shoot a lot of ambient light photos (flash off) and can fairly reliably shoot sharp images at 1/10 - 1/15 shutter speeds handheld at the wide-end of the zoom with IS on. Even 1/8 - 1/6 is doable, although at lower success rates. Turning off IS and I lose at least a full stop or more which may preclude getting a sharp image without pushing the ISO into noise-city. I typically leave the ISO on 80 or 100 on my G9. I got quite used to this in my film days when I used Fuji Velvia (ISO 40 slide film), although there was no IS then.
If there's a valid reason to turning off IS, please enlighten me. :smilie40:




With the Canon S90, which is a higher end P&S, similar to the G9 (really, just a slightly newer version in a smaller body), I shoot everything between ISO 80 and 200 with a strobe... Exposure times vary from 1/60 to 1/250th, and F-stop between F5.6 and F8 usually...

The problems you will run into is having a good enough depth of field by using the higher range of F-stops whilst getting enough light in the camera... Most likely, underwater, you will want to turn IS off, and set your shutter speed to never go slower than 1/60th... Once you take a couple pics at your desired F-stop, and no go slower than 1/60th, you can vary your ISO underwater to approximate a proper exposure... Unfortunately, there comes a point in which you don't want to go any higher in ISO (the G9 looks pretty good even at 400, but I'd stay no more than 200), and you will have to lower the f-stop to let more light in... Then, of course, shutter speed is always a variable as well if there is too much light...

Practice practice practice... Once you get a little practice, shoot everything in RAW and in manual, and make sure to take a few white balance card shots in the same lighting conditions as your photo so that you can adjust white balance later...