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nitr0uzv
07-01-2005, 01:53 PM
I would like to know more about aperture I dont really understand it

i know at night when I dont want to overexpose stationary lights I should use a lower aperture

I wanna know when i should use a higher aperture F2.7
And when I should use a lower Aperture F8

a graph would be nice

I also know that Higher aperture and lower shutter speeds mix well
And lower aperture and higher shutter speeds mix well

JTL
07-01-2005, 02:33 PM
I would like to know more about aperture I dont really understand it

i know at night when I dont want to overexpose stationary lights I should use a lower aperture

I wanna know when i should use a higher aperture F2.7
And when I should use a lower Aperture F8

a graph would be nice

I also know that Higher aperture and lower shutter speeds mix well
And lower aperture and higher shutter speeds mix wellThe aperture determines how much light enters the camera.
A few practical applications to think about:
Larger aperture=lower ISO
Larger aperture plus faster shutter speed to freeze action
Larger aperture at longer focal length=shallow depth of field/zone of focus
Smaller aperture=greater depth of field/wider zone of focus
Small aperture plus slower shutter speed to show motion

Here is a link to as easy (yet in-depth) an explantion as you can get...
http://www.photoxels.com/tutorial_aperture.html

nitr0uzv
07-01-2005, 03:23 PM
Alright alright so let me get this straight

Larger aperture
Blurs background
can use faster shutter speed
less DOF

Small aperture
doesnt blur background
Slower shutter speed
more DOF

thanks! wasnt aware of the DOF thingy till now

TheObiJuan
07-01-2005, 03:26 PM
You can creatively use your aperture ranges to capture very different looking pictures.
F/1.2 will provide a lot of background seperation and very smooth bokeh (background blur). F/2.8 is what most expensive zoom lenses max out at. This provides for great low light use and still excellent background blur. Longer lenses, like the 200mm f/2.8, the background blur is even greater though. The 135 f/2, although not as long, is at f/2, so it has very nice bokeh, some say one of canon's best bokeh lenses. The 85 f/1.8 and 200 f/1.8 are better though.

F/8 provides a sharper picture, (most often), and includes a sharper, less diffused background.
For portraits it is good to use larger apertures to isolate the subject. For landscapes I would recommend shooting at f/8 or smaller.

With Digital SLRs, it is often necessary to use f/16-f/22 to get the widest depth of field. F/22 is similar to f/8 on most point and shoots.

JTL
07-01-2005, 03:26 PM
Alright alright so let me get this straight

Larger aperture
Blurs background
can use faster shutter speed
less DOF

Small aperture
doesnt blur background
Slower shutter speed
more DOF

thanks! wasnt aware of the DOP thingy till nowAnd don't forget, when shooting with a large aperture, the longer the focal length, the shallower the apparent DOF (perceived blurrier background) also.

aparmley
07-01-2005, 04:00 PM
And for good measure, always remember that when shooting at the largest aperature you are not going to have the sharpest picture. so if the shot allows for it and you know you need a sharp picture, increase your aperature to 8, use a tripod if the shutter speed slows down to much and use the timer or a shutter release, and don't forget to breath, in through mouth out through nose, very very important.

eastbluffs
07-26-2005, 12:33 AM
With Digital SLRs, it is often necessary to use f/16-f/22 to get the widest depth of field. F/22 is similar to f/8 on most point and shoots. Hey Obi -
What's the difference on F stops vs DOF between P&S and Digital SLRs?

If this were a multiple choice exam, I'd guess it has to do with film (OK, cyberfilm) plate size. But if I were pressed for an explanation, I just can't figure it.

"F stop" is the focal length divided by apeture diameter. Its a ratio and not a hard measurment. Therefore, f8 on a 500mm is 10 times wider than f8 on a 50mm lense. And since longer lenses (given the same subject distance) give considerably less DOF, it follows that DOF is determined by the physical (hard measurement) of the apeture width.

Probably some web site has a fancy diagram showing little lines with arrows bouncing off the lense mirrors like billiards.

Since a Digital SLR uses the same lenses as a 35mm lense, the actual plate will be positioned exactly where the 35mm film would be, so DOF would be identical between DSLR and 35mm-Film-SLR. Correct so far?

I get real fuzzy on this coffeeshop logic where different lense sizes, much smaller pixil-plate sizes, and therefore physically smaller lenses are used (as in P&S cameras). After all, we normally only hear about the efl (Equivilant Focal Length) of those cameras. Who knows what the actual focal length is in mm on a Canon Elf shooting at 38mm(efl 35)? Its surely tiny. Maybe 20mm?

So, let me breath (properly, oh Obijuan), and rest those hampsters running around my brain, while you elaborate the ying and yang of DOF.

TheObiJuan
07-26-2005, 01:00 AM
Hey Obi -
What's the difference on F stops vs DOF between P&S and Digital SLRs?

If this were a multiple choice exam, I'd guess it has to do with film (OK, cyberfilm) plate size. But if I were pressed for an explanation, I just can't figure it.


You got it. Because the sensors are so darn small on point and shoots, they have huge depth of field. The actual lenses on these p&s cameras are actually only a few millimeters. Some as low as 4mm!



"F stop" is the focal length divided by apeture diameter. Its a ratio and not a hard measurment. Therefore, f8 on a 500mm is 10 times wider than f8 on a 50mm lense. And since longer lenses (given the same subject distance) give considerably less DOF, it follows that DOF is determined by the physical (hard measurement) of the apeture width.

Probably some web site has a fancy diagram showing little lines with arrows bouncing off the lense mirrors like billiards.

Since a Digital SLR uses the same lenses as a 35mm lense, the actual plate will be positioned exactly where the 35mm film would be, so DOF would be identical between DSLR and 35mm-Film-SLR. Correct so far?

Yep, right thus far. DOF is a product of aperture, focal length, and image size.
Adjust any of these three and you get different directly proportional results.



I get real fuzzy on this coffeeshop logic where different lense sizes, much smaller pixil-plate sizes, and therefore physically smaller lenses are used (as in P&S cameras). After all, we normally only hear about the efl (Equivilant Focal Length) of those cameras. Who knows what the actual focal length is in mm on a Canon Elf shooting at 38mm(efl 35)? Its surely tiny. Maybe 20mm?

So, let me breath (properly, oh Obijuan), and rest those hampsters running around my brain, while you elaborate the ying and yang of DOF.


Here is a great link for calculating the DOF of your camera, (our) and your lenses. Be sure to use the actual, not effective focal length, as your sensor is essentially cropping the center of the lens, so the physics stay the same.
http://www.dofmaster.com/dofjs.html

I could go on and on about DOF, and there is a lot to go on and on about. Especially formulas.. but Bob Atkins does it best here:
http://www.photo.net/learn/optics/dofdigital/

TheObiJuan
07-27-2005, 08:32 PM
snip


With a small sensor, you get to use really small, true focal lenght lenses, like 5mm. At 5mm and f/2.8, the DOF will be many feet. If it were a big sensor, and a 5mm lens were used (I think impossible, 8 is bad enough), then their would also be greater dof at f/2.8 than a 50mm lens.


Once again, the smaller the sensor, to smaller the lenses, the greater the dof.

'Macro' shots, on any camera, will yield very little DOF. The closer you get, the more pronounced the small DOF becomes. With DSLR, f/16 is considered shallow for macro photography.
Try f/2.8, at any focal length, for 1:2 or greater macro shots on a dslr, and you will see, it will be very frustrating. But with a small sensor/short focal length lens, on the point and shoot. f/2.8 works out beautifully!

Honest Gaza
07-28-2005, 07:36 PM
The aperture determines how much light enters the camera.

Here is a link to as easy (yet in-depth) an explantion as you can get...
http://www.photoxels.com/tutorial_aperture.html

Sorry...I'm still confused. As Denzle Washington once said...."explain it to me like I'm a 6 year old".

Referring to the link given, it explains "The aperture of a lens is the diameter of the lens opening..."
From this, I can understand that the greater the opening, the more light is let in (so far, so good). In garden variety English, I would have thought if I have an opening of 10mm (therefore an Aperture of 10mm), and compared it to an opening of 5mm (therefore an Aperture of 5mm), then the 10mm would be the larger aperture of the two. Am I correct, or have I lost the plot already ?

If I'm still on the right track how then, does this suddenly mean that an F2.8 setting results in a larger aperture than an F16 setting ?

What is the relationship other than "remember, the smaller the F-stop, the larger the aperture". I want to know why !!!!!!!!!!!

Is it the mechanics of the shutter, is it white man's magic....what is it ?

Help please.

TheObiJuan
07-28-2005, 07:42 PM
Sorry...I'm still confused. As Denzle Washington once said...."explain it to me like I'm a 6 year old".

Referring to the link given, it explains "The aperture of a lens is the diameter of the lens opening..."
From this, I can understand that the greater the opening, the more light is let in (so far, so good). In garden variety English, I would have thought if I have an opening of 10mm (therefore an Aperture of 10mm), and compared it to an opening of 5mm (therefore an Aperture of 5mm), then the 10mm would be the larger aperture of the two. Am I correct, or have I lost the plot already ?

If I'm still on the right track how then, does this suddenly mean that an F2.8 setting results in a larger aperture than an F16 setting ?

What is the relationship other than "remember, the smaller the F-stop, the larger the aperture". I want to know why !!!!!!!!!!!

Is it the mechanics of the shutter, is it white man's magic....what is it ?

Help please.

that's because it's NOT F16, it's f/16, get it?
The bigger the number, the smaller the aperture.
1/2 a candy bar is much larger than 1/16th of a candybar, no?
Hence, f/2 is MUCH larger than f/16.


f/2.8 on a 50mm lens is the same ratio, but much smaller actual size in mm aperture than f/2.8 on a 300mm lens.

Honest Gaza
07-28-2005, 08:01 PM
Thankyou....this is obviously the critical element I was missing. The fact that the aperture value is a denominator when referring to the F-Stop.

eastbluffs
07-29-2005, 12:21 AM
With a small sensor, you get to use really small, true focal lenght lenses, like 5mm. At 5mm and f/2.8, the DOF will be many feet. If it were a big sensor, and a 5mm lens were used (I think impossible, 8 is bad enough), then their would also be greater dof at f/2.8 than a 50mm lens.


Once again, the smaller the sensor, to smaller the lenses, the greater the dof.

'Macro' shots, on any camera, will yield very little DOF. The closer you get, the more pronounced the small DOF becomes. With DSLR, f/16 is considered shallow for macro photography.
Try f/2.8, at any focal length, for 1:2 or greater macro shots on a dslr, and you will see, it will be very frustrating. But with a small sensor/short focal length lens, on the point and shoot. f/2.8 works out beautifully!

I get the feeling that saying sensor size is a determining factor in DOF is an oversimplification, but the manifestation is none the less true. I just spent an hour trying to work out the physics of it all and the fact that it wasn't 100% successful doesn't change the usefullness or acceptablitiy of that fact. I predict a few odd dreams in the next week or 2.

Thanks for the tips and the great links!

BobSeber
08-05-2005, 05:25 PM
I get the feeling that saying sensor size is a determining factor in DOF is an oversimplification, but the manifestation is none the less true. I just spent an hour trying to work out the physics of it all and the fact that it wasn't 100% successful doesn't change the usefullness or acceptablitiy of that fact. I predict a few odd dreams in the next week or 2.


I've had a go at the physics - check this out:

http://www.robertseber.com/calculators/backgroundblur.html

TheObiJuan
08-06-2005, 02:06 AM
I've had a go at the physics - check this out:

http://www.robertseber.com/calculators/backgroundblur.html

Nice link, Bob.
I bookmarked it.
It sure did quantify the info I knew and neatly organize it, too. :D

eastbluffs
08-07-2005, 11:16 AM
I've had a go at the physics - check this out:

http://www.robertseber.com/calculators/backgroundblur.htmlVery elaborate! You did all this? What is your source, you build cameras for NASA or something? Are these accurate or just illustrations of a trend?

I'm not a mathametician so wouldn't understand the mathametical proofs and formulas, but can probably manage logical relationships.

Enter my confused thought process:

First, I was thinking of defining "what is focus" as the arrival of the light at the correct spot on the 2 dimensional frame of the sensor, as related to all the other light gathered from the subject. So instead of just "DOF", it would be a more scientific DOF-Spread, measurable as what percentage of light arrives elsewhere, and how far it spreads. Bohek would be the incidental patterns of misdirected light.

I was trying to take the focal length as a unit-of-measure for measuring all subject distances, somehow applying that to the degrees of concentric circles going out from the center of a lense, or apeture, (maybe weighted against the area of the sensor), etc. So, taking the distance to subject as a fraction of the focal length would cause a smaller number to measure distance to subject as the focal length widens, explaining why longer focal length would give less depth of field given the same apeture. But this fraction is only multiplier of the initial DOF-Spread potential caused by apeture.

Anyway; I'm not trying to solve some hither-to unsolved natural phenonemum like gravity. Its a man-made thing that lots of people (like maybe you) know all about. It would be a question of finding a lay-person's explanation, or someone patient enough to create one. Its either that or go study triganomatry (and learn to spell same), ummm, or just accept what people like you say in these calculators and leave it at that. I just feel that understanding the reasons would make it all so much easier to apply.

BobSeber
08-08-2005, 05:00 PM
Very elaborate! You did all this? What is your source, you build cameras for NASA or something? Are these accurate or just illustrations of a trend?
I took some thin lens equations off a website and re-arranged them to show what I wanted. I studied Engineering, so my maths was once pretty good. I did a real-world test with a pen-torch and one of my lenses (I might add a page on how to do this). The equations are a bit theoretical, and don't allow for the thickness of the lens, but my real-world test showed that they work well enough.


First, I was thinking of defining "what is focus" as the arrival of the light at the correct spot on the 2 dimensional frame of the sensor, as related to all the other light gathered from the subject. So instead of just "DOF", it would be a more scientific DOF-Spread, measurable as what percentage of light arrives elsewhere, and how far it spreads. Bohek would be the incidental patterns of misdirected light.

It's not that intuitive (I was surprised too), but lenses actually project everything as quite well defined discs. The smaller the discs, the more in-focus things appear. Try it for yourself - point your camera at black dots on a piece of paper, or at a point light, and deliberately focus short of it. You'll see the discs, and they have quite firm edges. Nikkon actually design some lenses to have variably fuzzy discs, but pretty much all other lenses produce firm edged discs. When something doesn't have much contrast you can't really see the discs as they all merge together. Some lenses even project hexagons (6 blades) or doughnuts (e.g. the DO lenses).

I think that DOF can be very confusing itself. It's useful, but people use it to explain things that it doesn't explain properly, like background blur.


Anyway; I'm not trying to solve some hither-to unsolved natural phenonemum like gravity. Its a man-made thing that lots of people (like maybe you) know all about. It would be a question of finding a lay-person's explanation, or someone patient enough to create one. Its either that or go study triganomatry (and learn to spell same), ummm, or just accept what people like you say in these calculators and leave it at that. I just feel that understanding the reasons would make it all so much easier to apply.
I think the way to demonstrate the "why"s would be to have a diagram of an enlarged cross-section of a camera. Sliders could be used to adjust the parameters, and the diagram would adjust accordingly. That'd be kinda cool! Maybe a simple diagram would do for now...

Within
08-12-2005, 07:31 AM
Can I get this straight,

DOF is the result of the amt. of light reaching the camera sensors, correct?

The amt. of light can also differs the focus length, thus, causing blur backgrounds, am I correct till here? Is this the supposed conclusion of Bob's test.

By adjusting the aperture and shutter speed, the focus length would increase or decrease prior to the amt. of light reaching the CCD would differ the focus length. I hope that this is understandable and relevant up to here. If I made a mistake, I would like to be corrected, thanks!

Amt. of allotted time, shutter speed, and area for light, aperture, to pass through are factors that affect the amt. of light reaching the CCD or CMOS. The value of the factors differ to different aperture or shutter speed values.

Does my inferences make sense ?

BobSeber
08-12-2005, 08:49 AM
DOF is the result of the amt. of light reaching the camera sensors, correct?

Depth Of Field is the distance which is in acceptable focus e.g. 20mm. If you choose to control the amount of light reaching the sensor by altering the ISO speed or shutter speed then you will not affect DOF. The DOF is not, therefore, a result of the amount of light reaching the sensor. If you control the amount of light by altering the aperture you will also change the DOF.


The amt. of light can also differs the focus length, thus, causing blur backgrounds, am I correct till here?

The amount of light falling on the sensor doesn’t change with focal length unless the camera and lens you are using changes the f-Stop at the same time. A 70mm f/4 will let in the same amount of light as a 200mm f/4. A 50-200mm 3.0-5.5 would change the f-Stop as you move from 50mm to 200mm.


By adjusting the aperture and shutter speed, the focus length would increase or decrease prior to the amt. of light reaching the CCD would differ the focus length.

Adjusting the aperture or shutter speed has no effect on the focal length.


Amt. of allotted time, shutter speed, and area for light, aperture, to pass through are factors that affect the amt. of light reaching the CCD or CMOS. The value of the factors differ to different aperture or shutter speed values.

I think that your understanding is correct on those points, although I am unsure what you mean by “allotted time”.

Ali_baba
08-29-2005, 12:13 PM
This thread deserves to be a sticky post

normie_5
08-10-2008, 04:00 PM
The aperture ratio or relative aperture, more commonly known as the f-number, is a number defined as the focal length of the lens divided by the effective diameter of the aperture. A smaller f-number implies a larger diameter lens and therefore more light available for high-speed photography, or for work in poorly illuminated areas. However, small f-numbers involve small depths of focus.

So that means f8 = 1/8 and f16 = 1/16. So f16 is half the diameter of f8

Hope this helps.