Crop Factor : Multiply Your Aperture
- Thread starter daniyal
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Bamboopictures
Senior Member
The video is very misleading but also quite typical of the misinformation on optics among photographers.
From the presenter's example at 3:11,
subject size, subject distance, fstop, shutter, ISO are the same but the background is blurrer for FF compared to MFT.
So he concluded that same f-stop produce different DOF for different sensor size?
But what about the effect of focal length on DOF?
He forgot he had doubled his focal length on the FF to get the same framing as the MFT.
Multiplying the aperture by the crop factor is downright crazy considering the implications:
M43 shooters must use a slower shutter speed for their f2.8 MFT lenses vs their f2.8 FF lenses?
A 50mm f1.4 full frame lens will give M43 shooter shallower DOF than a 50mm f1.4 M43 lens?
Clearly, it is illogical.
I think, his message is: don't expect to use the same lens to get the same results with cropped sensors.
But his suggestion to label APS-C /MFT lenses against mathematical convention is seriously flawed.
Just imagine what the aperture rating for compact cameras will be using his math. 2mm /f128 anyone?
For the real formula:
http://en.wikipedia.org/wiki/F-number
From the presenter's example at 3:11,
subject size, subject distance, fstop, shutter, ISO are the same but the background is blurrer for FF compared to MFT.
So he concluded that same f-stop produce different DOF for different sensor size?
But what about the effect of focal length on DOF?
He forgot he had doubled his focal length on the FF to get the same framing as the MFT.
Multiplying the aperture by the crop factor is downright crazy considering the implications:
M43 shooters must use a slower shutter speed for their f2.8 MFT lenses vs their f2.8 FF lenses?
A 50mm f1.4 full frame lens will give M43 shooter shallower DOF than a 50mm f1.4 M43 lens?
Clearly, it is illogical.
I think, his message is: don't expect to use the same lens to get the same results with cropped sensors.
But his suggestion to label APS-C /MFT lenses against mathematical convention is seriously flawed.
Just imagine what the aperture rating for compact cameras will be using his math. 2mm /f128 anyone?
For the real formula:
http://en.wikipedia.org/wiki/F-number
Last edited:
Deunamist
Senior Member
yeah, it doesn't really make sense. cropped sensors are already receiving less light than full frame due to their size.
your real aperture is the T-Stop of the lens, not a multiplied F-Stop number. because F-Stop is how much light you allow your lens to take in, while T-Stop is the amount of light that actually hits your sensor.
your real aperture is the T-Stop of the lens, not a multiplied F-Stop number. because F-Stop is how much light you allow your lens to take in, while T-Stop is the amount of light that actually hits your sensor.
Bamboopictures
Senior Member
I think for APS-C and MFT shooters, it will be useful just to note that for any given composition, you will be forced to use a shorter focal length than if you were shooting full-frame. Eg, to get a framing similar to an 85mm on FF, NEX shooter will have to contend with a 55mm on APS-C. Obviously the DOF will be shallower on the 85mm.
In terms of subject distance, a FF shooter can stand nearer to the subject than a NEX shooter can to achieve same shot size using the same lens. Since the subject distance is shorter for the FF shooter, the DOF can than be shallower.
However with a speedbooster NEX and M43 shooters can achieve almost FF light gathering, FOV and DOF.
The interplay between f-stop, subject distance and focal length can be studied here http://www.dofmaster.com/dofjs.html
In terms of subject distance, a FF shooter can stand nearer to the subject than a NEX shooter can to achieve same shot size using the same lens. Since the subject distance is shorter for the FF shooter, the DOF can than be shallower.
However with a speedbooster NEX and M43 shooters can achieve almost FF light gathering, FOV and DOF.
The interplay between f-stop, subject distance and focal length can be studied here http://www.dofmaster.com/dofjs.html
This is what I gather on the internet >>> http://photography-on-the.net/forum/showthread.php?t=557405
Bamboopictures
Senior Member
DOF is affected by only 3 variables:
1.subject distance,
2. aperture and
3. focal length.
Sensor size is NOT a direct variable.
A point and shoot has very deep DOF because the real focal length of the lens is very short, often 2-6mm. But because of the crop factor,
2-6mm has the FOV of a 35-100mm (eg) FF lense. The confusion happens when manufacturers label their lenses using the "35mm equivalent."
Many consumers wonder why the 28-70mm zoom on their pocket camera cannot give them the same foreground isolation as a 28mm-70mm DSLR lens. Then they read about sensor size and conclude that the large the sensor, the shallower the DOF. This is a misconception.
Just like a pocket camera, a FF camera will not be able to achieve shallow DOF with a 6mm lens. The only difference is, a 6mm for FF is an ultra wide lens but for a pocket camera, the sensor is so cropped that only a small area of a 6mm image is captured, resulting in a telephoto FOV.
1.subject distance,
2. aperture and
3. focal length.
Sensor size is NOT a direct variable.
A point and shoot has very deep DOF because the real focal length of the lens is very short, often 2-6mm. But because of the crop factor,
2-6mm has the FOV of a 35-100mm (eg) FF lense. The confusion happens when manufacturers label their lenses using the "35mm equivalent."
Many consumers wonder why the 28-70mm zoom on their pocket camera cannot give them the same foreground isolation as a 28mm-70mm DSLR lens. Then they read about sensor size and conclude that the large the sensor, the shallower the DOF. This is a misconception.
Just like a pocket camera, a FF camera will not be able to achieve shallow DOF with a 6mm lens. The only difference is, a 6mm for FF is an ultra wide lens but for a pocket camera, the sensor is so cropped that only a small area of a 6mm image is captured, resulting in a telephoto FOV.
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