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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/16/2014 at 16:34
Skylar McMahon View Drop Down
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Ted and I discussed this and I wanted to share it, because it supplies a breakdown that is very understandable.
 
 

LOWER f-number = LARGER aperture. Larger aperture = shallower depth of field and faster shutter speed…because more light is hitting the sensor. Shallower depth of field means there’s less in focus fore and aft of the actual surface you’re focusing on, resulting in a soft background.

 

The reason lower f-numbers mean larger aperture diameter and larger f-numbers mean smaller aperture diameter is because the “f” is the numerator (top number) and the number is the denominator (bottom number) in a fraction that equals the actual diameter of the aperture. That’s the reason there’s always a “/” (divided by) after the “f”, as in “f/4.” The “f/4” is a fraction, where (f= focal length) / (number divided into the focal length to equal the actual aperture diameter). For example, say you have 100mm focal length and you’re shooting with an aperture size of f/2. The fraction would then be 100/2 = 50mm aperture diameter. In the same example, if you were shooting at f/4, your aperture diameter is 25mm, because 100/4 = 25. f/10 would then be a 10mm aperture diameter.

 

The reason aperture diameter is expressed as “f-stops” that way is because even though f/4 at 100mm focal length (25mm aperture diameter) is a different actual aperture diameter than f/4 at 85mm focal length (21.25mm aperture diameter), the effect on field of view and light reaching the sensor is exactly the same, because focal length has an effect on light transmission and depth of field just as the aperture. So, in that example, you have to use a larger actual aperture diameter at 100mm to gain back the same amount of light than you’d need at 85mm, even though both are set at f/4. Remember, the same rules apply for riflescope magnification (equivalent to the focal length), objective size (equivalent to the aperture) and amount of light (exit pupil diameter) reaching your eye (the sensor). As you crank up magnification, you need a larger objective to get the same amount of light to your eye. And, as you increase magnification in any optic, the depth of field always gets shallower. Make sense?

 

The other things that will soften the background in a photo (creating “bokeh”) besides using the largest possible aperture (again, smaller f-stop number) are using a long focal length (higher magnification) and putting more distance between your subject and the background and/or less distance between the lens and your subject.

 

Figured if there is any other beginners in the same boat that I am in with learning more and more regarding SLR cameras, settings, and uses, this would put more into perspective.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/17/2014 at 09:17
Dale Clifford View Drop Down
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another thing to keep in mind is the perspective given to the final picture because of the magnification being used. Camera lenses are standardized to use 50 to 55 mm as a normal viewing distance mostly duplicating the human eye's and interpretation by the brain of the spacial relationship between the objects in the photo. wider angle ie. lenses with mags. less than 50 mm change this relationship while including them in the same picture. These lenses give greater depth of field and are usually "slower" in f stops without giving up utility in ambient light requirements. Higher lenses above 50 will "stack" the perspective. If you look closely at a picture, and lots of practice, one can pretty close to guessing what magnification of lenses was used in the shot by the stacking. The resultant effect is the need for more light (lower f stops).

Portrait lenses will usually fuzz the lowest f stop to "soften the features" of the person and are usually pretty fast (lower f stops), around 85mm and expensive.

macro lenses need depth of field, so usually are not very fast. (higher f stops). and the focal length is based on how close you can get to the subject. and are expensive.

great pictures are taken by anybody having a camera at the time, and many occur daily because of camera phones, however they are not technically great shots.

being able to choose the equipment by seeing the final picture in you mind before makes the difference

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/17/2014 at 09:21
Dale Clifford View Drop Down
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another easy rule of thumb is

if 50 mm is the "normal perspective" then 100 mm is 2x (2x power handgun scope) and a 200 mm is a 4x etc.

digiscoping adds new dimension because the mags can get from 10x-40x -- lots of planning for these shots.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/17/2014 at 09:23
Skylar McMahon View Drop Down
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Originally posted by Dale Clifford Dale Clifford wrote:

great pictures are taken by anybody having a camera at the time, and many occur daily because of camera phones, however they are not technically great shots.

being able to choose the equipment by seeing the final picture in you mind before makes the difference

 
That couldn't be more true.  There is a social site that I'm on frequently because there are some photographers I follow as well as Nation Geographic, but  many others that show up in my feed are camera phone artist.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/17/2014 at 09:24
Skylar McMahon View Drop Down
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Originally posted by Dale Clifford Dale Clifford wrote:

another easy rule of thumb is

if 50 mm is the "normal perspective" then 100 mm is 2x (2x power handgun scope) and a 200 mm is a 4x etc.

digiscoping adds new dimension because the mags can get from 10x-40x -- lots of planning for these shots.

 
Thanks, Stephanie who works here is very interested in Digiscoping.  We may have to do some experimenting.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2014 at 02:51
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   Just a little something to add. Most Nikon DSLRs use ccds that are smaller than a frame of 35mm film. Therefore, if you have a DX type camera, which is most of them, your focal length is actually 50% larger than the lens your using. For instance, a 50mm lens, close to the same focal length as your eyeballs, is actually 75mm when attached to a DX camera. If you want "normal" you really need something close to a 35mm lens.
    Here's an example of depth of field vs distance from subject. These are from the same photo I took a few months ago of a walking stick. I used a 100mm F3.5 macro lens set at f7.1. If I had opened it up to f3.5 the depth of field would be even less. As it is, it's only sharp to for the first 1/8 inch or so of depth. I was only a few inches from his head.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2014 at 02:54
tejas View Drop Down
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The other pic wouldn't load on the same post.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2014 at 05:37
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umm......I always thought my 50mm lenses made things appear a little wrong.  My lawn always looked too big. The fence looked farther away than my eyes saw it.  The valley looked farther away than when I was standing up on the hill.....

I always thought that 80mm was basically duplicating your eyesight....

Anybody know about this?   
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2014 at 22:00
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Originally posted by tejas tejas wrote:

   Just a little something to add. Most Nikon DSLRs use ccds that are smaller than a frame of 35mm film. Therefore, if you have a DX type camera, which is most of them, your focal length is actually 50% larger than the lens your using. For instance, a 50mm lens, close to the same focal length as your eyeballs, is actually 75mm when attached to a DX camera. If you want "normal" you really need something close to a 35mm lens.


The focal length equivalence part is correct. However, the focal length of any lens is always the same no matter what camera sensor size it's being used with. The DX sensor size (APS-C) just crops the scene more, giving the appearance of greater focal length. It doesn't actually cause an increase in the focal length, the sensor is just smaller, so the image projected onto the sensor takes up more of the sensor area. Another way to look at it is the DX sensor crops the scene by a 1.5X factor vs the full frame (FX in Nikon nomenclature) 35mm equivalent sensor size. So, a given lens on a DX camera body provides an "35mm equivalent" FOV of a lens having 1.5X greater focal length, but the effect the focal length has on the subject remains the same as if the shot were taken with an FX sensor.

Other sensor sizes have an even greater "crop factor." For example, a micro four thirds sensor has a 2X crop factor, so a given focal length on a MFT sensor camera has a FOV equivalent to a lens having twice the focal length on a full frame sensor camera.

Some Canon APS-C sensors have a 1.3X crop factor and others have a 1.6X crop factor.

The Nikon 1 cameras have a 2.7X crop factor.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/22/2014 at 22:06
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Originally posted by Son of Ed Son of Ed wrote:

umm......I always thought my 50mm lenses made things appear a little wrong.  My lawn always looked too big. The fence looked farther away than my eyes saw it.  The valley looked farther away than when I was standing up on the hill.....

I always thought that 80mm was basically duplicating your eyesight....

Anybody know about this?   


I always thought the same thing, Ed; somewhere around 75 - 85mm looks more equivalent to normal vision to my eyes as well.

However, 50mm is the generally accepted "rule of thumb" (full frame equivalence) in the camera world for normal human vision equivalence.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/24/2014 at 09:09
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80mm seems like it has a much narrower FOV than my eyesight.  The accepted "normal" 50mm seems just about right to me for a "normal" FOV, FWIW.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2014 at 12:38
Son of Ed View Drop Down
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" Bitterroot wants to see it WIDEWAYS correctly.....but FRONTWARDS can be all fouled up!!  He's been smelling elk droppings too long! "    






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