Newbie question of AV mode on G9

[fayewolf]

I'm a super newbie here. New as in, I didn't know what aperture, shutter speed means yesterday. (now i have a better grasp!)

Okay, I know that point and shoot camera's are not good for shallow depth of field picture, but getting a SRL will be way over my head and I'll just ended up being very frustrated with it.

I am trying to take some photo with shallow depth of field but it doesn't seem like it's working. In AV mode, I'm suppose to be able to get the AF to F2.8, but sometimes, it will not let me go further and stop at 4. Why is that?

Also, sometimes I would specify the ISO to 200 instead of letting it to it automatically, but on my display, it will say ISO 800 , I don't want alot of noise, so I'm trying to make the ISO lower, but it won't let me.. I'm so confused.

Here are a few samples that i uploaded to flickr:

http://farm3.static.flickr.com/2298/3544698206_b606fabd53_o.jpg

I think this one has a little bit of the effect, can anyone tell me if I'm doing something wrong? Thanks!

http://farm3.static.flickr.com/2161/3544698942_ccef425aa8_o.jpg

[MarKap77]

A little bit about max aperture on a zoom lens:

If you read the specifications on the lens for your G9, it will you that the lens is 7.4 to 44.4mm f/2.8-f/4.8. This means, that as you zoom from wide angle to telephoto, the maximum aperture the lens is capable of making gets to be smaller as a percentage of the focal length. Remember, the maximum aperture of a lens is actually listed as an arithmetical expression, focal length of the lens (f) divided by X (the number listed on the lens) = the actual size of the opening in mm. So, taking the widest angle setting on the G9, that would be f/2.8, or 7.4/2.8, which equals 2.68mm. But when you zoom to full telephoto, the arithmetic becomes 44.4/4.8, which equals 9.25mm. This is standard on a lot of zoom lenses.

Concerning the ISO, if you have the mode selector set to AUTO (not the ISO selector, the mode selector), then you don't have control of the ISO. Moving the ISO selector when the mode selector is in AUTO does nothing. Set the mode selector to something else.

Read the manual all the way through while you have the camera in your hand. Change things on the camera and see if you can understand what the manual is telling you. That will go a long way toward helping you understand your camera and its many capabilities.

[denncald]

As was mentioned above, as you zoom out with the G9, the max f-stop range (widest opening) decreases - at the widest angle you can get f/2.8, at full telephoto zoom you will only get f/4.8. Here' is an article from Gordon Buck with a table of ranges on the topic;

http://lightdescription.blogspot.com/search/label/f-stop

Also, to try to get the shallow DOF, you will have to work around the limitations of the small sensor of the G9. I've found the best results by using the Macro mode. Here's more from Gordon Buck on the topic;

http://lightdescription.blogspot.com/search/label/macro

He also has a good article on DOF;

http://lightdescription.blogspot.com/search/label/depth%20of%20field

I've used his blog, because it is G9 specific, and he's "been there and done that".

Here's a shot I took using macro. I stood off about as far as you can get in macro, and zoomed in, but had plenty of light from the sun. There was some distance from the objects behind the plant, but the DOF was shallow enough that they were blurred out. Just take lots of trial and error shots to learn how. I also cropped to show just the center 10% to 15%.

http://farm4.static.flickr.com/3169/3279503083_ae360ab800_o.jpg

Dennis

[fayewolf]

As was mentioned above, as you zoom out with the G9, the max f-stop range (widest opening) decreases - at the widest angle you can get f/2.8, at full telephoto zoom you will only get f/4.8. Here' is an article from Gordon Buck with a table of ranges on the topic;

http://lightdescription.blogspot.com/search/label/f-stop

Also, to try to get the shallow DOF, you will have to work around the limitations of the small sensor of the G9. I've found the best results by using the Macro mode. Here's more from Gordon Buck on the topic;

http://lightdescription.blogspot.com/search/label/macro

He also has a good article on DOF;

http://lightdescription.blogspot.com/search/label/depth%20of%20field

I've used his blog, because it is G9 specific, and he's "been there and done that".

Here's a shot I took using macro. I stood off about as far as you can get in macro, and zoomed in, but had plenty of light from the sun. There was some distance from the objects behind the plant, but the DOF was shallow enough that they were blurred out. Just take lots of trial and error shots to learn how. I also cropped to show just the center 10% to 15%.

http://farm4.static.flickr.com/3169/3279503083_ae360ab800_o.jpg

Dennis

Dennis, this is very helpful, and beautiful picture!!! I will experiment and start reading the manual!! :)

[Cathan]

those with canon g9. a question about max dof, in av mode.

do you use normal f8, or stop down 7.1 or 6.3? (have you found differences in sharpness from corner to corner?)

[tmwag]

Also, sometimes I would specify the ISO to 200 instead of letting it to it automatically, but on my display, it will say ISO 800 , I don't want alot of noise, so I'm trying to make the ISO lower, but it won't let me.. I'm so confused.



In the shooting mode menu check "Auto ISO Shift." If it's "on" it will automatically "shift" the ISO to a higher value depending on the light

[weezerfan84]

The G10 is magnificent for macro work. The lens does a great job, but it can't get the shallow DOF without using macro. Even with the wide end at 2.8. The more I use mine the more I enjoy it. It has its faults, but for a point and shoot, it's very nice.

[MarKap77]

those with canon g9. a question about max dof, in av mode.

do you use normal f8, or stop down 7.1 or 6.3? (have you found differences in sharpness from corner to corner?)

First off, going from f/8 to f/7.1 or f/6.3 is not "stopping down". You are actually making the aperture larger and shortening the depth of field.

Second, Av mode is not what alters depth of field, it is aperture. To get a wider depth of field, you need a smaller aperture. To get a narrower depth of field, a larger aperture. In Av mode you are directly controlling the aperture, but then you are also controlling it in manual mode. And you can control it indirectly in Tv mode my limiting your choice of shutter speed to keep the aperture within a certain range. But if you are thinking of doing something to adjust the depth of field, you need to be thinking about adjusting the aperture, whatever mode you are using.

As to sharpness from corner to corner, that is only related to depth of field in that it is affected by aperture. Corner sharpness is a result of the physics of light and lenses. Some lenses do better than others. On the G9, specifically, I have not found any difference in corner to corner sharpness between any apertures or zoom settings. With such a small sensor and lens, it doesn't seem to be an issue. For me at least.