Practice Makes Better, Misc. Questions, Etc.

[mooker]

Hi all,

Newbie photographer here and newbie to this site! I have been doing some reading in the forums and really appreciated the friendliness of the community as well as the accumulated knowledge of everyone, so I thought I'd sign myself up .

I made a post a few days ago on another photography site, but didn't really get any responses to to the lack of traffic to it. So I'm posting an edited version here for your reading pleasure.

I have tried to do some more reading about the theory behind picture-taking (aperture, exposure, ISO, etc.) Thanks to the help of various websites, I have been provided with some good advice (focus on one setting at a time, and taking pictures is the best way to learn), so I ventured out at lunchtime on Monday to the park and snapped some pics on my PowerShot A95. I'd love a nice SLR like a Digital Rebel of some sort, but I have the feeling that this camera will be more than enough for me for awhile.

Anyways, I decided to take some pictures of some wildflowers (they look great, and they don't really move unless a breeze picks up).

Today, I wanted to play with aperture settings, to make the object in the foreground to appear sharp, while the background is faded. Pretty basic stuff, I know. Here's my favorite one that I took:

Neat flowers

I put my aperture the lowest setting possible (2.8 for that one).

During my shots, I ran into a couple of puzzling issues, and I was hoping someone could help me with them.

1. Why is it that when I use the optical zoom (I have digital zoom disabled) that I have less aperture settings to choose from? For example, if I zoom in slightly, the aperture number automatically increases, and it will not let me lower them past a given amount.

2. On another picture, I tried to mess with the ISO setting while changing the aperture. I had the fstop at 2.8 and turned the ISO up to 200 (I think I had it on auto or 100, can't remember). When I did and took the picture, the auto-exposure on my camera showed "1/1000" in red. According to my camera manual, this means that the image is underexposed or overexposed. However, when I took the picture anyway, it appeared okay. Probably just my n00b inability to recognize over/underexposure.

So anyways, I guess that's a long enough post. If anyone could give me some advice, I would greatly appreciate it.

Thanks all!

Mooker

 

[ksmattfish]

1. Why is it that when I use the optical zoom (I have digital zoom disabled) that I have less aperture settings to choose from? For example, if I zoom in slightly, the aperture number automatically increases, and it will not let me lower them past a given amount.

2. On another picture, I tried to mess with the ISO setting while changing the aperture. I had the fstop at 2.8 and turned the ISO up to 200 (I think I had it on auto or 100, can't remember). When I did and took the picture, the auto-exposure on my camera showed "1/1000" in red. According to my camera manual, this means that the image is underexposed or overexposed. However, when I took the picture anyway, it appeared okay. Probably just my n00b inability to recognize over/underexposure.

1) f/# = focal length divided by aperture size. It's cheaper to build a lens where the actual aperture size remains constant as you zoom in and out, and so the math changes. In order to maintain the same f/# the aperture size would have to change as you zoom in and out. This is available in some more expensive SLR/DSLR zooms.

2) I'd guess that since 1/1000 was flashing it means this is your camera's maximum shutter speed, and that it was warning you it was going to over expose unless you blocked more light somehow (increase shutter speed or decrease aperture size (which is increasing the f/#)). It may have only been a slight overexposure, or you might have been metering a scene that fooled the meter into thinking it was overexposing, but really you needed the extra exposure anyway.

 

[mooker]

WOW. That was a faster response time than what I'd expected!!

f/# = focal length divided by aperture size. It's cheaper to build a lens where the actual aperture size remains constant as you zoom in and out, and so the math changes. In order to maintain the same f/# the aperture size would have to change as you zoom in and out.

<Scratches head> okay, I think that makes sense. I know my camera isn't considered a high-end camera, so it's expected that it will automatically change the aperture size because of the quality of the lens.

I'd guess that since 1/1000 was flashing it means this is your camera's maximum shutter speed, and that it was warning you it was going to over expose unless you blocked more light somehow (increase shutter speed or decrease aperture size (which is increasing the f/#)). It may have only been a slight overexposure, or you might have been metering a scene that fooled the meter into thinking it was overexposing, but really you needed the extra exposure anyway.

According to the manual, the fastest shutter speed that my camera will support is 1/2000. Why it chooses 1/1000 as the error is anyone's guess. Since the picture seemed okay, it must have been as you said, that the camera thought it was overexposing, but it actually wasn't.

I think I'll mess around with aperture more, and then once I have a better handle on knowing which setting to use (f2.8 - f8.0 is my camera's range), I'll move onto shutter speed.

Thanks!

Mooker

 

[ksmattfish]

<Scratches head> okay, I think that makes sense. I know my camera isn't considered a high-end camera, so it's expected that it will automatically change the aperture size because of the quality of the lens.

Say you have a zoom lens set at 50mm and f/2. 50mm/2=25mm. So the actual hole in the lens is 25mm wide. If you changed the focal length to 100mm, but the hole in the lens remains 25mm, then you have 100mm/25mm=f/4. If you are using a high end zoom lens where the f/# stays the same, as you change the focal length from 50mm to 100mm, the hole in the lens changes size too. To maintain f/2 it enlarges to 50mm wide. 100mm/50mm=f/2.

By the way, this math is absolutely unneccessary for taking photographs. It just explains why the f/# increases as focal length does in cheaper zoom lenses.

 

[mooker]

Say you have a zoom lens set at 50mm and f/2. 50mm/2=25mm. So the actual hole in the lens is 25mm wide. If you changed the focal length to 100mm, but the hole in the lens remains 25mm, then you have 100mm/25mm=f/4. If you are using a high end zoom lens where the f/# stays the same, as you change the focal length from 50mm to 100mm, the hole in the lens changes size too. To maintain f/2 it enlarges to 50mm wide. 100mm/50mm=f/2.

OHHHH okay, I get it now!! Thanks for the explanation . This would also explain why when I use the zoom, the minimum focal length changes too (if I try to set it manually, it will only allow me to lower it to a given amount, depending on how much I've zoomed).