fstops - what does it do

maxalmon

maxalmon

Active Member
I just copied this from the web and it's a pretty basic description of what the fstop does, I'll post a series of photo that have been shot bracket style, meaning that I'll use the same stationary image and go up 1 fstop with each image and then you'll see what the fstop setting does.
Quote
f/stops are a bit more confusing because the numbers appear so arbitrary. This is the standard sequence of f/stops from f/1.4 to f/22. Although it doesn't seem intuitive at first, in this sequence the f/1.4 setting lets in the most light while the f/22 setting lets in the least. Also, each of these f/stops has precisely the same halving/doubling relationship as the shutter speed sequence.
1.4 2.0 2.8 4 5.6 8 11 16 22
On the face of it, going from f/4 to f/5.6 doesn't sound like halving the amount of light. What's more, 5.6 is a larger number and sounds like it ought to be more light, not less
 
bpophoto79

bpophoto79

Member
Think of f/stops as a fraction of the light entering the lens. 1/5.6 is definitely less than 1/4. The f/stop controls the amount of light entering the lens and controls the depth of field (how much of the photo is in focus from front to back). The smaller the f/stop the greater the depth of field. Hope this helps.
 
maxalmon

maxalmon

Active Member
Ok, here is a series of 18 photo's of the same Acan, no adjustment were made to the camera other than increasing the fstop by 1 setting, this will give you an idea of how the fstop helps with depth of field, but also cause color shifts and darkness as you increase the fstop the max of 29 which is the smallest opening for light to pass thru.
The focal point of this image is almost dead center, a little down and a little to the right
1/50 sec - F/4
Exposure Comp.: -0.7 EV

1/40 sec - F/4.5
Exposure Comp.: -0.7 EV

1/40 sec - F/5
Exposure Comp.: -0.7 EV

1/30 sec - F/5.6
Exposure Comp.: -0.7 EV

1/25 sec - F/6.3
Exposure Comp.: -0.7 EV
 
maxalmon

maxalmon

Active Member
continued
1/20 sec - F/7.1
Exposure Comp.: -0.7 EV

1/15 sec - F/8
Exposure Comp.: -0.7 EV

1/13 sec - F/9
Exposure Comp.: -0.7 EV

1/10 sec - F/10
Exposure Comp.: -0.7 EV

1/8 sec - F/11
Exposure Comp.: -0.7 EV
 
maxalmon

maxalmon

Active Member
continued
1/6 sec - F/13
Exposure Comp.: -0.7 EV

1/5 sec - F/14
Exposure Comp.: -0.7 EV

1/4 sec - F/16
Exposure Comp.: -0.7 EV

1/3 sec - F/18
Exposure Comp.: -0.7 EV

1/2.5 sec - F/20
Exposure Comp.: -0.7 EV
 
maxalmon

maxalmon

Active Member
And the final pics
1/2 sec - F/22
Exposure Comp.: -0.7 EV

1/1.6 sec - F/25
Exposure Comp.: -0.7 EV

1/1.3 sec - F/29
Exposure Comp.: -0.7 EV
 
maxalmon

maxalmon

Active Member
LOL...thanks...
Point is, if you look at image #1, you see that the almost dead center of the image is in focus and the outer fields are blurry, image is bright as well, scroll down a few images and you start to see that some areas are now in focus and image is becoming a little darker.
Use the very center, bottom of the image and focus on it, then scroll down and you start to see what I'm getting at
I had a buddy (thanks Rob!) come over who showed me this system for seeing how the fstop works, explained and showed me the same way as I presented the above pics............this was the learning/turning point where I kinda got an idea of "Oh, now I get it" from there I started playing around with manual focus, shutter speed etc....This thread was in ways an attempt to explain how fstops work, but more of a visual to show other reefers who just got cameras how the fstop affects images, from there you branch out and figure out the other settings...hope this in someway helps other
 
rhagemann

rhagemann

Member
Very cool sequence of photos and well explained Jim. I wished I would have had something like this to show you a few months ago. Now others can learn and see the effects of the changes....
Well done!!
Rob
 
maxalmon

maxalmon

Active Member
Hey Rob, ever since you came over and explained/showed me what the fstop settings will do to an image, it's been all uphill since.....I'm just about ready to adventure into the scarry "manual" zone...LOL.....Oh yeah, I got the evil eye and "why is there another tank in the garage" yesterday.....Thanks
 
bronco300

bronco300

Active Member
we have a canon rebel xt at work here but i have yet to figure out how to work it...especially this fstop thing...i have a number on the led readout that goes from 5-32...any clue? MAX
 
05xrunner

05xrunner

Active Member
there is more to them then just DOF. the more you stop down your lens. Close it. the sharper the images are. BUT there is usually a sweet spot and thats different from lens to lens. Most of the time f8 is usually where the lens is the sharpest. most of the time not counting prime lens. A lens at its largets fstop..lowest # tend to be softer then when its stopped down.
Most lens usually go to f32 and some go to f42.
lens with a large aperture will also be able to focus more accurately. I dont know about nikon but on the Canon XTi,30D,20D if you have a lens with a f2.8 as its largest fstop then it will activate a cross hair AF sensor in the center point to be much more precise on contrast and give you better focus. on the 40D they now added even more to the center point on lens 2.8 and faster, and now the surrounding AF points have the cross hair sensor at f5.6 and faster.
thats Why when you see those lens that have a constant f2.8 they cost SOO much, you are able to have a very fast lens at all zoom ranges and also helps the camera with its focus accuracy. Plus they use much higher grade of glass as well.
 
ladylinn

ladylinn

Member

Originally Posted by 05xrunner
there is more to them then just DOF. the more you stop down your lens. Close it. the sharper the images are. BUT there is usually a sweet spot and thats different from lens to lens. Most of the time f8 is usually where the lens is the sharpest. most of the time not counting prime lens. A lens at its largets fstop..lowest # tend to be softer then when its stopped down.
Most lens usually go to f32 and some go to f42.
lens with a large aperture will also be able to focus more accurately. I dont know about nikon but on the Canon XTi,30D,20D if you have a lens with a f2.8 as its largest fstop then it will activate a cross hair AF sensor in the center point to be much more precise on contrast and give you better focus. on the 40D they now added even more to the center point on lens 2.8 and faster, and now the surrounding AF points have the cross hair sensor at f5.6 and faster.
thats Why when you see those lens that have a constant f2.8 they cost SOO much, you are able to have a very fast lens at all zoom ranges and also helps the camera with its focus accuracy. Plus they use much higher grade of glass as well.
Can you please tell me anything on the sony cybershot dsc h-5. I know it has potential for awesome pix, but cant quite get that crisp. Has anyone taken a look /shrimpi's thread" just got new camara", pictures are amazing
 
05xrunner

05xrunner

Active Member
sorry..I dont really use point and shoots so i dont know much about it. the same can be applied to it though. Get as fast a shutter speed as you can to stop action. I wouldnt advise going over ISO 400 on a P&S unless you want a snowy looking pic. Adjust the fstop to as low as it goes. Since a point and shoot sensor is MUCH smaller then a DSLR they do not have the same depth of fields. a Point and shoot a f2.8 would look like a DSLR at like f7.1
 
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