Who can explain some photo stuff to me?

[MudSurfer]

I'm feeling really dumb as I can't understand the f stops and their relationship to taking pics...Is f2.8 a larger aperture than f22? And if so, with less light, do I need a lower number (2.8/4.5) to let more light in, as well as changing the shutter speed?

I am gradually learning how to use my digital camera but with varied results, and I'm way too impatient to go on a course, and would really like to get my head around the basic principles of what all these things mean, in simple terms that I can understand, so any help in what f stop is good for what kind of shot etc would be greatley appreciated.

TIA

[Apache]

Smaller number = bigger aperture = potential to use higher shutter speed

bigger aperture = smaller depth of field

[Albannach]

f/1, f/1.4, f/2, f2.8, f/4, f/5.6, f/8, f/11, f16, f/22

f/1 has the largest opening, f/22 the smallest. They are a ratio, f/1 = 1:1 f/22 = 1:22 Each one is one full Stop smaller as you move from left to right. Each stop smaller lets roughly half as much light through.

[Albannach]

I like f/8, it's a good all rounder.

[Apache]

I like f/1 because its reassuringly expensive - and uses carbon fibre and big engines

[MudSurfer]

Right - so if I'm shooting something ≈ 10m away, and use f4.5 for example, I should still get some of the background in as well, and more light, as the aperture is larger - but if I took the same shot at f8, the aperture is smaller, less light comes in and I get less of the background in focus?

The reason I want to understand this is I'm buying some manual focus lenses to use at dog agility competitions, set the focus on a piece of equipment, set the camera up manually, then when the dogs go through/over the equipment, I get high speed shots (usually 1/320 or 1/500 ISO400) that should be blur free, but light enough, but also not have too much background - I'm going for manual focus lenses on the D-SLR as I can't be bothered with the faff of having the AF constantly range finding as the dog moves and slowing down the shot and I know I can set the AF lense manually, but not that well, and the MF lenses are a fraction of the cost for telephoto ones on AF D-SLRs...

[gwh200]

geeks

[Apache]

Right - so if I'm shooting something ≈ 10m away, and use f4.5 for example, I should still get some of the background in as well, and more light, as the aperture is larger - but if I took the same shot at f8, the aperture is smaller, less light comes in and I get less of the background in focus?
..

No, smaller aperture, more of background in focus

[MudSurfer]

geeks

yank

[gwh200]

yank

[adpsimpson]

As Albannach said - the f number is the ratio of the focal length of the lens divided by the aperture diameter - hence no units. So a 50mm lens normally has a maximum aperture of f/2.8 ish, or about 18mm diameter. That's why zooming in raises your f number - the aperture stays the same but the focal length increases.

Your pupil can get to about 5mm diameter, and an eye ball is about 3 cm across (ie focal length is around 30mm) - about f/6. Make a small hole (about 0.5mm) in a bit of paper and hold it close to your eye, and you'll find everything is in focus - you're nearer f/60 now. In the same way with your camera, larger aperture=lower F number=more light but less stuff in focus. The extreme of this is a pinhole camera, which has no lens at all, just a tiny aperture.

For high speed photography, esp in low light, you need the largest aperture possible, eg f/1.8. For dogs etc the background will be very blurred - probably what you want.

The amount of light let through is proportional to the square of the aperture diameter - remember pi r squared? So in Albannach's list, f/11 lets in twice as much light as f/16 as 11^2 is roughly twice 16^2, etc.

gwh200, who you callin' a geek?? Here's something I actually know about (unlike surfs!!)

[gwh200]

As Albannach said - the f number is the ratio of the focal length of the lens divided by the aperture diameter - hence no units. So a 50mm lens normally has a maximum aperture of f/2.8 ish, or about 18mm diameter. That's why zooming in raises your f number - the aperture stays the same but the focal length increases.

Your pupil can get to about 5mm diameter, and an eye ball is about 3 cm across (ie focal length is around 30mm) - about f/6. Make a small hole (about 0.5mm) in a bit of paper and hold it close to your eye, and you'll find everything is in focus - you're nearer f/60 now. In the same way with your camera, larger aperture=lower F number=more light but less stuff in focus. The extreme of this is a pinhole camera, which has no lens at all, just a tiny aperture.

For high speed photography, esp in low light, you need the largest aperture possible, eg f/1.8. For dogs etc the background will be very blurred - probably what you want.

The amount of light let through is proportional to the square of the aperture diameter - remember pi r squared? So in Albannach's list, f/11 lets in twice as much light as f/16 as 11^2 is roughly twice 16^2, etc.

gwh200, who you callin' a geek?? Here's something I actually know about (unlike surfs!!)

terribly sorry old chap i said "geek" when i meant to say

"informed and illustrative" ....keep getting me words muddled

[MudSurfer]

Cheers all, and Andrew - that is making sense a little more now, thanks - I guess I'll keep practising and see how I get on...

[Albannach]

Cheers all, and Andrew - that is making sense a little more now, thanks - I guess I'll keep practising and see how I get on...

Get a camera, a tripod, a pen and a bit of paper, go somewhere like a wood at around midday (so the light doesn't change much) with something in the foreground, mid ground and distance.

Set the camera up on the tripod. If you can, leave the shutter on auto but put the aperture on manual. Take the same picture several times using a different aperture each time, you'll soon see the difference changing aperture makes. Like you say, practice makes perfect.

And if you ever get into photography seriously, you'll love the price of really bright long focus lenses!

[sv1000spilot]

I'm going for manual focus lenses on the D-SLR as I can't be bothered with the faff of having the AF constantly range finding as the dog moves and slowing down the shot and I know I can set the AF lense manually, but not that well, and the MF lenses are a fraction of the cost for telephoto ones on AF D-SLRs...

Be carefull though when going down this route. Make sure you try the lens on the camera. There can be compatability probs using older lenses on new bodies the same as new lenses on older bodies.

I found out the hard way that not all Canon lenses are compatable with all Canon bodies.