F stop confusion

cwphotos

Ok here goes. I didnt know where else to ask this so im sorry if it seems off topic. I know F stop is the light let into the camera, so the high the number the less light. I also know f stop determines what is in focus and what becomes bokeh. So If I was somewhere and wanted everything in focus and had a f/2.8 lens what would I do? I mean if couldnt set it to f/22 (not enough light)....or could I ?

I hope im making sense.

Pindy

Perhaps you should get to know your depth-of-field preview button, which most DSLRs have now. This will tell you what's in focus and what's not, once you get over the darkened viewfinder.

controld

cwphotos wrote:

Ok here goes. I didnt know where else to ask this so im sorry if it seems off topic. I know F stop is the light let into the camera, so the high the number the less light. I also know f stop determines what is in focus and what becomes bokeh. So If I was somewhere and wanted everything in focus and had a f/2.8 lens what would I do? I mean if couldnt set it to f/22 (not enough light)....or could I ?

I hope im making sense.

The short answer is to remember the inverse relationship between f-stop and shutter speed. Hence - if you need f/22 to manage your depth of focus and you know that at f/2.8 you would use a shutter speed of 1/500 you are looking at a shutter speed 36 times slower (6 full stops - 6^2), or approx 1/15. This likely means a tripod.

Too complicate - you can double the ISO to save one stop, so if you crank your ISO from 100 to 800 you only have too slow shutter speed a factor of 9X, or approx 1/60th.

See http://www.ncc.sdccd.cc.ca.us/resource/qtvr/qtvrlm2/lm2p4.html for more info.

- Mike

sirsloop

Also keep in mind, most lenses sweet spot is between f/5.6 and f/11. Once you get over like f/14 the image quality degrades slightly. Not to say you cant successfully shoot a f/22 photo, just letting you know.

Other than closing the aperture, you can also adjust your distance to the subject, and adjust the distance of the subject compared to the background.
Example: If you are shooting with your 35mm f/2.0 lens at f/2.0.


If you are 3ft from your subject, and behing your subject is a 100 yard field, you'll end up with a photo of the subject and a completely green background.

If you are 3ft from your subject and the subject is leaning up against a brick wall, then most everything will be in focus

If you are 100 yards away from your subject, and there's a 100 yard field behind the sugject, most of the shot will be in focus.

DoctorIt

cwphotos wrote:

I mean if couldnt set it to f/22 (not enough light)....or could I?

I hope im making sense.

Useful info in the posts above, but don't know if anyone has answered your actual question - lemme see if I understand, and if not, I deduce you are not making sense.

Unless your lens or camera is broken, why on earth wouldn't you be able to set the lens, any lens, to f/22 (I don't know of any consumer lens that doesn't close down that far)? Answer that before we go further...

you seem to know what changing the aperture does to your photo, but mechanically, confirm that you know what is happening in the lens.

DJ-S1

Aperture(f-stop as you say), shutter speed, and ISO (film speed) all work together to set the exposure. Sure you can set f/22, but you have to compensate with one or both of the other 2.

Less light into the sensor (f/22) means EITHER slower shutter speed (allows more time for light to "accumulate"), OR higher ISO (makes sensor more sensitive to the light), OR BOTH.

In practice, I have rarely used anything near f/22 for the reasons stated.

sirsloop

easiest way to get a first hand understanding is to set the lens to f/22, press the DOF preview, and look at the front of the lens. You will see the aperture physically closed. If you let go of the button, the aperture opens (also called wide open). When you shoot a photo with the lens set at its largest aperture, the aperture blades do not move. That is the physical maximum amount of light that lens can capture.

Duckys54

Take multiple exposures with the same ISO, Aperture, and Shutter Speed and change the focus from the first object that was in focus to the first out of focus object and repeat.

wxwax

You want everything in focus. That means a small aperture. But there isn't enough light. To solve that, raise your ISO as much as necessary. Slow your shutter speed down. Both maximize the light that's available.

Not enough light? Things blurry because they're moving?

Your only choice now, is to add artificial light: a flash.

erich6

wxwax wrote:

You want everything in focus. That means a small aperture. But there isn't enough light. To solve that, raise your ISO as much as necessary. Slow your shutter speed down. Both maximize the light that's available.

Not enough light? Things blurry because they're moving?

Your only choice now, is to add artificial light: a flash.

Dont' forget the tripod!

wxwax

erich6 wrote:

Dont' forget the tripod!

Good one.

Glenn NK

Just joined last night - seems like a good site.

To the OP's question, I went online and typed in "understanding exposure", as that's what first came to mind. Many photographers recommend a book by this name by Bryan Peterson, although I'm not familiar with it.

What I did find was a another site that might be more suited to a beginner, rather than the OP:

http://www.photonhead.com/simcam/shutteraperture.php

For other members just starting out in photography, this little tool seems to illustrate the relationship between shutter speed, aperture and depth of field (which affects so-called bokeh).

ziggy53

Glenn NK wrote:

Just joined last night - seems like a good site.

To the OP's question, I went online and typed in "understanding exposure", as that's what first came to mind. Many photographers recommend a book by this name by Bryan Peterson, although I'm not familiar with it.

What I did find was a another site that might be more suited to a beginner, rather than the OP:

http://www.photonhead.com/simcam/shutteraperture.php

For other members just starting out in photography, this little tool seems to illustrate the relationship between shutter speed, aperture and depth of field (which affects so-called bokeh).

Welcome to the Digital Grin (DGrin). Nice find!

ziggy53

Glenn NK

ziggy53 wrote:

Welcome to the Digital Grin (DGrin). Nice find!

ziggy53

Thanks for the welcome.

I've seen downloadable and online DOF calculators, but never something like this.

The little tool in the link is really useful (I think) to get the basic concepts of photography across; oddly I've never seen it mentioned anywhere before.

Briggie

just sharing a little anecdote...

my photog teacher had a really simple way to explain aperture. imagine the aperture setting is a faucet, and the film/camera is a glass. if you open your tap wide open (f2.0 lets say), your glass (film) will fill up with water (light) very quickly, and you don't need to keep the tap open very long. if you let the water (light) dribble into the glass (film), it takes a longer time to fill up, and you might need to rest the glass (camera) on something, like a tripod for example...

i thought it was a fun way to explain the abc's of apertures...

b

Glenn NK

Briggie wrote:

just sharing a little anecdote...

my photog teacher had a really simple way to explain aperture. imagine the aperture setting is a faucet, and the film/camera is a glass. if you open your tap wide open (f2.0 lets say), your glass (film) will fill up with water (light) very quickly, and you don't need to keep the tap open very long. if you let the water (light) dribble into the glass (film), it takes a longer time to fill up, and you might need to rest the glass (camera) on something, like a tripod for example...

i thought it was a fun way to explain the abc's of apertures...

b

Another good analogy or parallel is even closer to us - the human eye. When it's darker your "f/stop" automatically opens up - just as you would open up the aperture.