... about reading/comparing Specs, reviews, ISO performance comparison and megapixels.
Photo by Kristopher Laurin-Racicot
I’m sorry, I’ve heard too many atrocities in digital photography statements today based on read stuff, stuff on the net to really stand and do nothing. This blog entry can get a bit technical so I’m sorry if I lose you in the process. I will include pictured examples when I have time. Right now I just want to rant my ass off. The ranting continues..
The second factor is the sensor size.
Recently, I’ve heard that the Canon 1DmkIV matches the Nikon D3s for image quality and aces it for 4 additional megapixels. Now I wonder if the voices I’ve heard really know about the influence of the sensor size over a picture’s visual appearance…
I’d just like to resume what that amazing Cambridge in color article is trying to explain about how sensor size influence photography.
Say, a sensor and a lens.
The sensor is a light gathering surface. A bigger surface records more information like the color tones and dynamic range that make a photo file. A bigger surface makes a bigger coverage on a lens.
A lens is made out of many glass elements. Depending for what sensor size and aperture the lens is made; the glass elements vary in diameter. Normally, the glass elements needs to be a least as big as the sensor. In the best cases, a manufacturer makes the element bigger than the sensor to minimize the common physical lens defects like corner softness, chromatic aberrations (the pink/purple/blue highlights on the corners of lenses) and vignette (the dark corners of a lens).
In common dSLR lens libraries, there are lenses made for full frame sensor and cropped sensors, each with glass elements built to the size of each sensor. Full frame lenses can be used on cropped sensor: the cropped sensor only sees a part of the full frame glass element. Such thing is called a crop factor.
The crop factor was created to give the visual appearance of a lens for the 35mm equivalent value in focal and aperture values for cropped sensors. So… say a cropped sensor has a crop factor of x1.5, it multiplies both focal and aperture values by the crop factor. So in the case of a 50mm f/1.8 lens, 50mm x 1.5 becomes 75mm in focal range and f/1.8 x 1.5 becomes f2.7 in aperture visual appearance. The light gathering of the 50mm f/1.8 doesn’t change but the visual appearance will. Crops are convenient in terms of weight because the lenses used on crop sensor cameras are usually smaller and lighter to achieve the 35mm equivalent focal range. The trade off is the less apparent background blur.
The background blur is more present when the aperture value of a lens is small. The technical term for this is depth of field. The depth of field or DOF determines what’s sharp and blurry in the shot. It is usually measure in thickness. A thinner depth of field strengthens the presence of the background blur.
Do you notice that the closer you get to an object the more background blur you get? Well when the sensor covers the whole frame, you can use the whole glass element to cover whatever you are covering. The crop factor is x1 so a 50mm f/1.8 lens gives the visual appearance of a 50mm f/1.8. In practice, you can move in more closely and get a thinner DOF than the cropped counterpart. This is an artistic trait widely (though subjectively) appreciated in photography because it isolates the subject very well in most cases.
In comparison, a medium format sensor is bigger than a full frame dSLR sensor. This means bigger glass elements and a thinner DOF.
As such, it is truly wrong to seriously compare camera sensors size on image quality comparison points we are used to see in reviews like ISO performance and megapixels mainly because they don’t give the same native visual appearance (I say native because Photoshop can tweak pretty much anything nowadays…). People just got to know what kind of photography they are into before defining their needs. Cropped sensors usually suffice for general applications. For classic artistic usage where thin DOF is needed, a bigger sensor gives better results.
The sensor is a light gathering surface. A bigger surface records more information like the color tones and dynamic range that make a photo file. A bigger surface makes a bigger coverage on a lens.
A lens is made out of many glass elements. Depending for what sensor size and aperture the lens is made; the glass elements vary in diameter. Normally, the glass elements needs to be a least as big as the sensor. In the best cases, a manufacturer makes the element bigger than the sensor to minimize the common physical lens defects like corner softness, chromatic aberrations (the pink/purple/blue highlights on the corners of lenses) and vignette (the dark corners of a lens).
In common dSLR lens libraries, there are lenses made for full frame sensor and cropped sensors, each with glass elements built to the size of each sensor. Full frame lenses can be used on cropped sensor: the cropped sensor only sees a part of the full frame glass element. Such thing is called a crop factor.
The crop factor was created to give the visual appearance of a lens for the 35mm equivalent value in focal and aperture values for cropped sensors. So… say a cropped sensor has a crop factor of x1.5, it multiplies both focal and aperture values by the crop factor. So in the case of a 50mm f/1.8 lens, 50mm x 1.5 becomes 75mm in focal range and f/1.8 x 1.5 becomes f2.7 in aperture visual appearance. The light gathering of the 50mm f/1.8 doesn’t change but the visual appearance will. Crops are convenient in terms of weight because the lenses used on crop sensor cameras are usually smaller and lighter to achieve the 35mm equivalent focal range. The trade off is the less apparent background blur.
The background blur is more present when the aperture value of a lens is small. The technical term for this is depth of field. The depth of field or DOF determines what’s sharp and blurry in the shot. It is usually measure in thickness. A thinner depth of field strengthens the presence of the background blur.
Do you notice that the closer you get to an object the more background blur you get? Well when the sensor covers the whole frame, you can use the whole glass element to cover whatever you are covering. The crop factor is x1 so a 50mm f/1.8 lens gives the visual appearance of a 50mm f/1.8. In practice, you can move in more closely and get a thinner DOF than the cropped counterpart. This is an artistic trait widely (though subjectively) appreciated in photography because it isolates the subject very well in most cases.
In comparison, a medium format sensor is bigger than a full frame dSLR sensor. This means bigger glass elements and a thinner DOF.
As such, it is truly wrong to seriously compare camera sensors size on image quality comparison points we are used to see in reviews like ISO performance and megapixels mainly because they don’t give the same native visual appearance (I say native because Photoshop can tweak pretty much anything nowadays…). People just got to know what kind of photography they are into before defining their needs. Cropped sensors usually suffice for general applications. For classic artistic usage where thin DOF is needed, a bigger sensor gives better results.
This is why I’m convinced that for the pictures I’m taking, a smaller sensor will never beat it’s larger counterpart. Yes I truly think that a 12 megapixels full frame sensor camera (even there was to be a 6 megapixels full frame sensor) would beat a 18 megapixels cropped sensor camera. But for now, I can’t afford a bigger sensor so I’m sticking with what I have. I’m just frustrated at the people who have bigger sensor cameras that mostly shoot the same stuff I do complaining about cropped sensor cameras that have better performance then what they have… They are not photographers. They are an insult to photography. They are just tech toy users. Damm them.
OMG I just wrote another 700 words on my second part! Am I done? FUCK NO!
read part one
read part three
2 comments:
First problem here. Lens aperture does not multiply with crop factor, only they focal length is multiplied.
Reason for this is simple, if you use a 50 1.8 lens on a 1.5, or 1.6 crop factor (like me that is Nikon/Canon difference) it will behave like an 75 1.8 or 80 1.8 lens (in my case). Lens blur and background blur are not affected by the crop factor, only thing you get is less viewing angle, but all other lens performance stays the same.
If a full frame lens is used on a crop factor body it will still give the same amount of light as it would on a full frame body, it will still give the same background blur as if used on full frame body, and it will still have the same depth of field as on full frame body, but you will just see less of it in the photo (you will just capture a portion of that view).
Sure, 50 1.8 will not behave same as 80 1.8 lens, those lenses have different background blur, but that is do lens design, and combination of focal length and aperture size. If you check out 1:1 crops from a same lens on a full frame and crop factor you will not be able to distinguish which one was taken on what camera. Since all of the lens performance stays the same.
The last important difference is the crop factor and multiplication of aperture size. It's not linear. 1.6x extension tube gives a whole 1 aperture value to your lens. So, if you would use a 1.6x extension tube on Canon 100-400 f4.5-5.6 L IS USM it would behave like an 160-640 f6.3-8 lens.
So, if you would use that logic on crop factor, not that I'm saying it would work, on a crop factor body, a full frame 50 1.8 would behave like 80 2.5 lens.
The more extreme example is using 70-200 f2.8 lens on a 2x extender. It will then be an 140-400 f5.6 lens, and if you use crop factor body, it will then become 224-640 f5.6 lens. Just because you will still have those f5.6 light gathering possibilities, and that's the primary use of f stops - the amount of light you get from the lens.
A simple answer for all users who are asking should they go full frame is the question: "What do you shoot?"
Long lens sport photographers would love the crop factor, as it simply gives "longer" lens, but a wide angle close encounter extreme sports photographer like me would easy trade those high fps for a wider field of view.
Don't tell me you read stuff before you shoot too?
Have you shot with a 50 1.8 on both full frame and crop? And have you once tried looking at how the DOF become thinner when you move in closer?
It's a question of visual appearance difference (mainly the DOF) not of behavior (just because you can get in closer with the subject). I said the light gathering ability of a f/1.8 lens remains the SAME.
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