| Author | Thread |
|
|
02/16/2005 09:21:01 PM · #1 |
I'm sort of confused.....
I was reading a review comparing two different F2.8 lenses. The reviewer remarked that one lens was brighter than the other (when looking through the view finder).
Does an aperture of F2.8 represent a 'measured size' of the aperture - or - the 'actual amount' of light that a given lens will let through to the camera sensor?
|
|
|
|
02/16/2005 09:31:20 PM · #2 |
Originally posted by casualguy:
I'm sort of confused.....
I was reading a review comparing two different F2.8 lenses. The reviewer remarked that one lens was brighter than the other (when looking through the view finder).
Does an aperture of F2.8 represent a 'measured size' of the aperture - or - the 'actual amount' of light that a given lens will let through to the camera sensor? |
You might want to post the article.
In answer to your question it is the 'actual amount' of light that any lens will let through to the camera sensor.
|
|
|
|
02/16/2005 09:34:19 PM · #3 |
Someone correct me if I'm wrong, I may well be...
My understanding is; The F number is the ratio between the diaphram diamater, and the focal lenght. So at F2.8 on a 50mm focal lenght, the diameter of the diaphram should be 50/2.8 = 17.85mm
So two lenses of the same focal lenght and aperture, should let through the same amount of light. Where as F2.8 on a 100mm lens means the diaphram diameter is somewhat bigger....
Can someone tell me if I'm close? |
|
|
|
02/16/2005 09:40:05 PM · #4 |
Originally posted by Simonjw:
Someone correct me if I'm wrong, I may well be...
My understanding is; The F number is the ratio between the diaphram diamater, and the focal lenght. So at F2.8 on a 50mm focal lenght, the diameter of the diaphram should be 50/2.8 = 17.85mm
So two lenses of the same focal lenght and aperture, should let through the same amount of light. Where as F2.8 on a 100mm lens means the diaphram diameter is somewhat bigger....
Can someone tell me if I'm close? |
Very. At f/2.8 the amount of light hitting the sensor will be the same if using a 50mm lens or a 300mm lens even though the physical aperture diameter is different. Has to do with the angle at which the light travels through the lens.
|
|
|
|
02/16/2005 09:51:45 PM · #5 |
Originally posted by nsbca7:
Originally posted by Simonjw:
Someone correct me if I'm wrong, I may well be...
My understanding is; The F number is the ratio between the diaphram diamater, and the focal lenght. So at F2.8 on a 50mm focal lenght, the diameter of the diaphram should be 50/2.8 = 17.85mm
So two lenses of the same focal lenght and aperture, should let through the same amount of light. Where as F2.8 on a 100mm lens means the diaphram diameter is somewhat bigger....
Can someone tell me if I'm close? |
Very. At f/2.8 the amount of light hitting the sensor will be the same if using a 50mm lens or a 300mm lens even though the physical aperture diameter is different. Has to do with the angle at which the light travels through the lens. |
So I assume this to mean that a Canon/Sigma/Tokina etc., lens of the same focal length and aperture would look equally as bright through the view finder or otherwise, right? (Not necessarily as sharp)
|
|
|
|
02/16/2005 09:59:51 PM · #6 |
Originally posted by casualguy:
So I assume this to mean that a Canon/Sigma/Tokina etc., lens of the same focal length and aperture would look equally as bright through the view finder or otherwise, right? (Not necessarily as sharp) |
No. The same amount of light will theoretically hit the sensor at any given aperture (regardless of the focal length), but one lens might not appear as bright as another to the naked eye. I think what the reviewer may have been refering to is contrast, not the actual amount of light. Some (better) lenses are more contrasty then others. Has to do with lens coatings, lens configurations, ect...
|
|
Home -
Challenges -
Community -
League -
Photos -
Cameras -
Lenses -
Learn -
Help -
Terms of Use -
Privacy -
Top ^
DPChallenge, and website content and design, Copyright © 2001-2025 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 09/14/2025 12:34:36 PM EDT.
