A few questions on apeture

C

croww

Limp Gawd
Joined
May 15, 2002
Messages
134
Hey all, I have a few questions on apeture settings. They're noobish but forgive me :)

I understand that the RESULT of adjusting your apeture in your pictures is in how the final exposure looks..an apeture of 2.8 will have what is in focus sharply in focus, and what is behind what is in focus blurred. An apeture of 8 will increase it quite a bit so what is behind what is in focus by say..oh.. x amount of meters..will ALSO be in focus. My questions really relate to ..erm..how this works, and how I can put it to use. At first glance it's pretty easy..I take a picture of a kitten (Thanks Schmave! :) ) and have my apeture set to 2.8 and whats behind the kitten will be blurred out..sometimes including the fur directly behind the focused part. If I want the whole kitten in focus, I would up my apeture to..say..5.6..I'm not sure of the number but a couple steps up, which would bring more into focus. I wouldn't go as high as say 8..because I don't want everything behind the cat in focus which takes attention away from the cat in the final picture.

Is that right? That's my understanding of it, and I know it's pretty layman's-ish. I can't grasp alot of the language they use in the explanations of apeture..I need real world examples and results, I never had a mind for numbers :(

Anyway, so thats the first part/question. The second part is this. How does apeture affect pictures taken at a distance? I notice that alot of zoom lenses are fixed apetures, say around 8..the cheaper ones mind you..and I was wondering if thats because apeture doesn't have as great an effect if you're zooming in one something. Also, how should you use apeture in cases where you're focusing on infinity. If you focus on infinity, isn't EVERYTHING in focus? For that matter, how does focusing on Infinity work? Ow, my head!

I do alot of night work..shutter speeds around 1-12 seconds, focused to infinity..and I often use the apeture to further control the amount of light I get in the final image. I've heard that shutter speed and apeture work off each other in long exposures. If you, say, adjust the shutter speed and then adjust the apeture at the same time, you could theoretically come up with basically the same picture. An example..a 2 second exposure with a apecture of 8, compared to a 1 second exposure with an apeture of 5.6. Do you follow me, those aren't exact numbers of course..just trying to get my understanding across. Somehow the apeture changes when used at night from being something that brings objects behind what is focused on into focus to being a tool to allow you to finetune the amount of light coming into the image. Again, is all that right? Help me understand please!

I know alot of you guys are deeply into photography, and really know what you're doing. If you get some time and don't mind sharing I'd really appreciate it.

Thanks all

croww
 
the aperature is an opening of variable size that lets light pass through the lens onto the film. the number is inversely related to the size, so f2.8 is larger than f5.6 which is larger than f8. by increasing the aperature (lower number) you increase the amount of light going into the camera and decrease the depth of field. that's what's physically going on.... not sure if that was what you wanted, or if there was something more detailed that you were looking for
 
Once again there is not a one answer fits all here. Many of my night shots are at and apeture of 8 and above. Depending on the set-up I love the depth of field it gives me. Daylight shots are different and I tend to blur the bg's down as you mentioned. Point and shoot cameras will restrict your shutter speeds to 15 sec or shorter on the norm so you may have to open the apeture up to get a little more light. I get better results this way than running up the iso and creating noise. The following pic was taken on a 1ds and shot at an f11 and a 30 sec shutter. I really liked the focus on the trees in the forground as well as the lighthouse. When I ran it down to f5 the lighthouse stayed sharp but the trees blurred and became distracting. (to me)




Brichttp://www.therothenbergers.com/lighthouse2.jpg
 
Guys above posted some good stuff. I'll just blurp this quick splot in:


Higher f/# the smaller the aperature, less light comes in, deeper DOF creating an overall sharper image.

Lower f/# the larger the aperature, more light comes in, shallower DOF creating a very picky workable area....although having a shallow DOF can create some nice styles.

Too high of an f/ can cause vingetting (sp?) sometimes. I did long-exposures at f/22 in low light and had serious darkening of the sides of the frame all around.
 
Thanks a ton for the answers guys. Eigt, your page was especially helpful, but the math is killing me. All those numbers just get up there and swim around. I really am trying to understand it from a technical standpoint so I can take advantage of and do the math for changing the apeture and shutter speed to get the same amount of light while changing the DOF..it's just the cursed numbers. Ugh.

Oh well, sitting here with a piece of paper doodling them out. It's like its right there..I feel so close.

Thanks all :)
 
Math is an ugly bitch, but once you get the paper bag its smooth sailing!

Cheers,
 
You must log in or register to reply here.
Back
Top