Focal Length
The focal length of a lens determines its angle of view, and also how much the subject will be magnified for a given photographic position.
Focal length also determines the perspective of an image.
Longer focal lengths require shorter exposure times to minimize burring caused by the shake of hands.
The Focal Length means how much can your camera see.
Aperture
The aperture range of a lens refers to the amount of light that the diaphragm can let inside the camera to reach the sensor.
Apertures are listed in terms of f-numbers (expresses the diameter of the entrance pupil in terms of the effective focal length of the lens; It is the quantitative measure of lens speed), which are marked on the lens.
On a camera, the f-number is usually adjusted in f-stops.
Each “stop” is marked with its corresponding f-number, and represents a halving of the light intensity from the previous stop. Modern electronically-controlled interchangeable lenses, such as those from Canon and Sigma for SLR cameras, have f-stops specified internally in 1/8-stop increments, so the cameras’ 1/3-stop settings are approximated by the nearest 1/8-stop setting in the lens. The F number can be displayed as 1:X instead of f/X(like in our example).
Lenses with larger apertures are faster because, for a given ISO speed, the shutter speed can be made faster for the same exposure. A smaller aperture means that objects can be in focus over a wider range of distance (depth of field).
Portrait and indoor (sports and theater also) photography often requires lenses with large maximum apertures in order to be capable of faster shutter speeds (and narrower depth of fields) in order to combat the low light problems with no camera shake.
The narrow depth of field in a portrait, as well as in macro photography, helps isolate the subject from the background.
Minimum apertures for lenses are almost as important as maximum apertures. This is primarily because the minimum apertures are rarely used due to photo blurring from lens diffraction, and because these may require long exposure times.
For cases where extreme depth of field is desired, then smaller minimum aperture (larger maximum f-number) lenses allow a wider depth of field.
It’s also good to know that lenses typically have fewer aberrations when they perform the exposure stopped down one or two f-stops from their maximum aperture.
Tags: lens, focal length, aperture, f number, f stop, depth of field, dof, angle of view, perspective, wide, tele, exposure time
March 24th, 2007 at 8:48 pm
Thank you for your advice on photography. I have your site bookmarked.
Regards,
Bryan
March 24th, 2007 at 8:51 pm
Wow, that’s really clear.
I am not really into photography but of course I have seen those terms just forever; I just had no reason to look in to what they meant.
It is a waste of time an money for me to use anything but a point and shoot –I have carried a single use camera in my glovebox for years in case I had to document the scene of an auto accident but that is the extent of my skills.
March 24th, 2007 at 10:24 pm
Clear practical description for the novice, but should mention image sensor size and the related multiplier for field of view, or at least say that the specific examples are for a 35mm camera.
March 24th, 2007 at 11:19 pm
Hmmm… This is an ‘okay’, back of the envelope, explanation. However it’s riddled with minor technical inaccuracies that for the most part can be overlooked.
Except for one… “Focal length also determines the perspective of an image.”
Sorry, focal length has absolutely NOTHING to do with perspective. The ONLY factor which affects perspective is the camera’s location with respect to the subject. Focal length certainly affects magnification, and a longer focal length lens can produce an image of an object of equivalent size from farther away when compared to a lens with a shorter focal length. But in the process you’ve also changed perspective.
They only way to change perspective is to move the camera!
strider
March 25th, 2007 at 12:23 am
Very practical and easy to understand information.
Thank you very much Lau!
March 25th, 2007 at 2:12 am
I was going to correct the author on his erroneous statement about perspective, but Strider beat me to the punch. Strider is correct.
March 25th, 2007 at 2:31 am
I think this is a gr8 article explaining the concepts but one question, what is the significance behind your profile photo on the website? It has a certain sadness and mystery to it!
March 25th, 2007 at 10:12 am
Thanks for this information.
March 26th, 2007 at 5:07 pm
FINALLY! A no nonsense, straight to the point explanation! Thank you! I spent weeks looking for something like this a few months back and never found it.
Very informative.
March 26th, 2007 at 5:20 pm
[...] Focal Length and Aperture Explained for the Photography Novice [...]
March 26th, 2007 at 5:28 pm
the less than 21mm IS NOT an architecture lens. Problem is the massive amounts of distortion, and barreling effect that the wide lens causes.
The tilt lens is more of an architecture lens.
March 26th, 2007 at 6:23 pm
[...] Read More… [...]
March 26th, 2007 at 8:12 pm
Let’s see, since this is a beginners description, I don’t think it matters as to the nuances of architectural lenses. This is aimed at those who have the 18-55 kit lens with their 350D.
As for focal length and perspective… perspective is more than just camera placement.
Here’s another great website for a more in depth but understandable explanation of f-stops:
http://www.uscoles.com/fstop.htm
March 26th, 2007 at 8:21 pm
I like to think of aperture and exposure in terms of a water faucet. Aperture is the size of the faucet’s opening and exposure is how long you open the faucet. A faucet with a small hole (i.e. large aperture number like f16) means only a little bit of water trickles through. A faucet with a huge opening (i.e. small aperture number like f2.0) means a lot of water pours out. Now, if you were trying to fill 2 buckets of the same size, if you have a small opening you have to leave the tap on longer. To get the same volume of water with a large faucet tap, you leave it on shorter.
In photography, the “water” is the light and the bucket is your film. To capture a photo where you “faucet size” changes, you have to adjust the “time the faucet is on”.
Just remember, for aperture the smaller the number (1.0, 2.0, 2.8), the bigger the opening, so the more light flows through quicker (i.e. “faster” lens)
March 26th, 2007 at 9:05 pm
The extreme wide angle is better geared for landscapes and fisheye style photography than architecture.
It’s better to let beginners know architectural photography is a special discipline that strives to AVOID weird distortions. LInes need to be clean and straight.
March 26th, 2007 at 10:11 pm
[...] Focal Lengh and Aperture Explained for the Photography Novice: http://www.photoaxe.com/understanding-the-lens-focal-length-and-aperture/ [...]
March 27th, 2007 at 4:01 am
[...] Focal Length and Aperture Explained for the Photography Novice 27 03 2007 Focal Length and Aperture Explained for the Photography Novice [...]
March 27th, 2007 at 7:07 am
just curious as to why when we increase the focus of the lens the aperture of the lens becomes smaller? im using finepix s9600 model. hope anyone can help and explain. im new to photography and i want to learn more.
March 27th, 2007 at 11:56 am
[...] Focal Length and Aperture Explained for the Photography Novice [...]
March 27th, 2007 at 7:55 pm
[...] Focal length and aperture explained simply [...]
March 28th, 2007 at 6:42 pm
[...] [...]
March 28th, 2007 at 8:41 pm
[...] Focal length and aperture [...]
March 28th, 2007 at 9:23 pm
[...] Focal Length and Aperture Explained for the Photography Novice Article for beginners explaining focus and aperture. (tags: photography reference camera tips howto photo aperture) [...]
March 30th, 2007 at 4:01 pm
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April 1st, 2007 at 1:41 am
[...] Spring is here! 31 03 2007 Its been almost a month since I scribbled in my blog. Been awfully busy the whole of this month partly due to Wordpress downtime and partly due to personal errands. Anyway finally got some time to scribble. Found this interesting article useful on Photoaxe for wannabe photographers like me. It gives a no-brainer information about focal length, apertures etc and much more. [...]
April 2nd, 2007 at 9:15 am
Nice tutorial on Focal Length and Aperture.
Still being a novice, how to read lens desriptions like “VF-58CPKS” of Sony, please explain
April 7th, 2007 at 12:04 am
Focal Length and Aperture Explained for the Photography Novice…
The focal length of a lens determines its angle of view, and also how much the subject will be magnified for a given photographic position. The aperture range of a lens refers to the amount of light that the diaphragm can let inside the camera to reach…
April 7th, 2007 at 1:42 pm
Very clear and well written. Thanks
April 13th, 2007 at 5:24 pm
[...] PS. If you are new to my blog check my best tips: Focal Length and Aperture Explained for the Photography Novice 3 Simple Solutions for Shooting Against the Light in Photography that Work How to Make a Killer Photo using 8 Simple Composition Rules How to Shoot Roads in Photography …and more other here More: Share and Enjoy:These icons link to social bookmarking sites where readers can share and discover new web pages. [...]
April 16th, 2007 at 6:20 pm
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April 22nd, 2007 at 2:11 pm
This is a pretty good explanation and the pictures really help.
April 29th, 2007 at 11:44 pm
like the vast majority of novices, i sorta, kinda know what ISO is… but when asked to explain ISO and apertures and f stops, i scramble.
this makes more sense! thanks!
May 5th, 2007 at 2:51 am
this is kool im a 11 year old kid
May 7th, 2007 at 10:55 pm
still confused about one thing: the specs for a digital camera (a Canon)I’m interested in say the lens is “7.3-29.2mm f/2.8-4.1 (35mm film equivalent: 35-140mm)”. why is the digital camera spec 7.3-29.2 expressed that way instead of just as the 35-140mm? Can anybody explain this to me?
June 20th, 2007 at 1:19 am
[...] Focal Length and Aperture Explained for the Photography Novice (tags: camera photography reference) [...]
August 13th, 2007 at 3:35 pm
[...] Longitud focal y apertura explicados [...]
August 29th, 2007 at 12:07 pm
[...] Focal Length and Aperture Explained for the Photography Novice - Part II Before looking at the following video, take a read of this article: Focal Length and Aperture Explained for the Photography Novice - Part I. [...]
September 25th, 2007 at 10:09 am
[...] read more | digg story [...]
December 23rd, 2007 at 4:03 pm
This is another site worth looking at to explain f.stops
http://www.paragon-press.com/lens/lenchart.htm
Cheers
Lindsay
December 23rd, 2007 at 5:40 pm
That’s a good one. Thx for sharing Lindsay!
May 11th, 2008 at 1:22 am
I don’t understand something after having read the above information. I have a new Canon XSi Digital Camera. I have an extra lens, a telephoto lens which says on the box F/4-5.6 but when I use it on my XSi, the display shows a range of F/4-32. Why am I not seeing the true aperture range that is on this lens?
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