I received a question just recently from a member who is upgrading to the Sony SLR. She was wondering if a particular lens was wide enough for shooting interiors.
You might think the answer is as simple as looking at the size of the lens itself, if only that was the case!
The physical dimension of the digital sensor actually determines the true focal length of a given lens.
Generally speaking the standard of measure for SLR's is 35mm. This of course refers to the size of ye olde 35mm film. In the digital world this is called Full Frame (a sensor the full size of a 35mm frame). The good news is when you attach a lens to a camera with a FF sensor the lens focal length is a true 1:1. Simple enough.
However, full frame sensors are big and costly to manufacture. In fact there are only a handful and they reside in expensive cameras.
Solution? Most digital SLR's (such as the sony) employ digital sensors smaller than full frame, to keep costs down.
The most common of these is APS-C. These are called Crop Sensors (a sensor which is smaller and therefor shows a smaller image than a full frame). These cameras have a multiplier (more on that in a second) which actually push a given lens to become more telephoto than you would think based on it;s mm rating.
Let's take a look at an example (sorry for the large picture, I want to make sure this is clear):
In the example above the picture as a whole, represents a 35mm full frame digital shot.
- The WHITE rectangle represents 1.5x crop sensor (the sony uses this crop btw)
- The RED rectangle represents a 1.6x crop sensor (very common in many pro-sumer DSLR's)
- The Blue rectangle represents the 4/3 system used in most point and shoot cameras
- The Green rectangles represent very small P&S cameras as well as cell phone cameras.
- There's a couple other specialized crops (such as the 1.3x) which I'm not going to delve into at the moment.
As you can see, sensor size has a pretty big impact on how wide you can actually go. The smaller the sensor the more telephoto the lens becomes / the less wide angle it becomes. This is great if you are shooting far away subjects (free telephoto bonus!) but a real curse when you are shooting interiors which is why you'll always find a full frame sensor in the main camera of any real estate / architectural professional photographer.
Oh, I almost forgot...it's actually quite easy to determine what your actual focal length is. Just multiply your crop factor by your lens mm. For example, a 50mm lens on a 1.6x crop camera (like the canon rebel for example) would actually behave as an 80mm. 50*1.6=80. Voila!
A few last quick notes on sensor size:
- Larger sensors produce inherently better signal to noise ratios, they record cleaner / richer images and allow for higher ISO performance
- Larger sensors allow for more narrow depth of field (Boke), at aperture 1.4 or smaller combined with a full frame sensor the depth of field is so narrow that a crop sensor would need a lens with an aperture of 0.9 to compete...a virtual impossibility with any lens a mortal could afford
- As I hinted at above, some crop sensors are highly desirable depending on the type of photography you are doing and they do have the advantage of relying more heavily on the center of the lens (which typically provides better image quality than the edges)
Hopefully I haven't put you to sleep. Please feel free to ask any questions. :)
Cheers, -B
Architectural-Photographer
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Bryce - I never really understood how the sensor size worked. Thanks for clearing it up. Love the shot of the aquarium.