Hi, I'm new with a stupid question

[Stina3246]

Hello, Let me start off by saying that I've been reading tips from this site now for a few months and LOVE the info and assignments. I've been hesitant to post anything though because in my experience from other sites the ONLY responses you often get are negative and berating with nothing constructive, or heaven forbid, nice! But I've been reading your posts and you seem like a wonderful helpful group of people.

Now for the stupid question.....

I understand that if you want a narrow depth of field you open up you aperture (more light) and if you want a wider depth of field you close it down (less light) Am I correct or am I way off base? My question is...why is that so? It seems backwards to me. I would think that if you let in more light, more things would be illuminated and there for more things in focus and vise versa.

[SusanH1970]

The only stupid questions are the ones not asked. Welcome to DPS!

You are correct - a large aperture (smaller number) will give a shallow depth of field, whereas a small aperture (larger number) will give a deep depth of field, thus having more in focus. Light has nothing to do with focus and depth of field.

Take a look at the Depth of Field Calculator. It puts things into perspective. Also see this thread: Depth of Field comparison Hope this helps!

Yeah, we're a friendly bunch, aside from a few grumps and the occasional snob - but just ignore them, LOL!

[Jim Bryant]

AHHHHHHHHH, we're not that bad. I'm only grumpy from time to time.

It you want a shadow DOP you use your smallest f-stop. The larger the number, the more depth of field you'll get. Try this, set some stationary objects (bottles) in a line about a foot a part (do this outside) take a picture of each bottle (one at a time) going from the smallest to largest f-stop. Afterwards, download them on your computer and view the images. It should help you understand f-stops in relationships to depth of field.

[Stina3246]

Originally Posted by Jim Bryant

AHHHHHHHHH, we're not that bad. I'm only grumpy from time to time.

It you want a shadow DOP you use your smallest f-stop. The larger the number, the more depth of field you'll get. Try this, set some stationary objects (bottles) in a line about a foot a part (do this outside) take a picture of each bottle (one at a time) going from the smallest to largest f-stop. Afterwards, download them on your computer and view the images. It should help you understand f-stops in relationships to depth of field.

Thanks so much!! I like the idea of the bottles....I'm gonna give that a try...who knows, maybe I'll get a cool shot out of it. And see....even the "grumpy" ones give good info!

[SusanH1970]

Eh, Jim's not that much of a grump. He likes to pretend he is, but he's a teddy bear under it all.

[candidrachel]

"Those who are afraid of asking questions are ashamed of learning" - A poster at work.

Jim had a great tip in fact I did the same trick using Russian dolls. For a long time I just couldn't get this aperture thing to register to the grey matter. I kept getting it the wrong way round like large f no = large aperture.

Best advice is to just practice and try to remember what works and what doesn't.

Susan - snobs? Hmmmm I wonder who you are referring to lol!

[Nathan deGargoyle]

Stina this is a perfect example of the fact that there are no stupid questions, just stupid answers!

Hey Guys, Stina knows that a wide aperture gives a narrow DoF, she wants to know why!

Stina welcome to DPS. I apologise for my friends inability to read a post. Personally, I don't know why a large aperture gives a small DoF but maybe a tutorial from cambridge in colour will help.

[inkista]

Originally Posted by Stina3246

My question is...why is that so? It seems backwards to me. I would think that if you let in more light, more things would be illuminated and there for more things in focus and vise versa.

The amount of light actually doesn't have much to do with it being focused. Focusing basically has to do with the angles of the light coming in and the distances they travel, so that they coherently meet at a specific spot. When the aperture is opened up wider, and more light comes in, it comes in at a wider variety of angles, so more of the light is thrown at distances where they don't focus. The narrower the angle of the light coming in, the more of it will gather up at the right distances to focus.

It's an optics thang.

Your eyes work the same way. Remember how your opthamologist tells you not to drive after your pupils have dilated? That's because your DoF got a lot smaller when your irises (aperture) opened up wider.