Explaining Sensor Crop

mtracerz

mtracerz

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Ok, been reading up on basic photography, and i'm reading about the sensor cropping issues.

A quote from the book says:

A useful 35mm wide-angle lens view, becomes the mundane 56mm normal lens perspective
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Can someone explain why the lower number of mm the lens is, the wider the view it produces.
And also some more info on the sensor crop would be handy.

Finally, which dslrs offer the full frame? I know they will be pricey, just out of interest.
 
mtracerz said:
Finally, which dslrs offer the full frame? I know they will be pricey, just out of interest.
Click to expand...

Sony A900
Canon 5D, 5D2, one or two of the 1Ds bodies iirc
Nikon D700, D3, D3s, D3x

that's all.
 
mtracerz said:
Can someone explain why the lower number of mm the lens is, the wider the view it produces.
Click to expand...

The "mm" is the effective focal length of the lens.

To see why for yourself take a cardboard tube, hold it to your eye and look at something, then cut the tube in half and look at the same thing. With the shorter tube you will see a wider view, cut that piece in half again and you will see an even wider view.
 
Martyn... said:
....To see why for yourself take a cardboard tube, hold it to your eye and look at something, then cut the tube in half and look at the same thing. With the shorter tube you will see a wider view, cut that piece in half again and you will see an even wider view.
Click to expand...

Great explanation Martyn :thumbs:

mtracerz, there are far more knowledgeable people on here who know about the technology involved, but there are basically a handful of sensor crop factors; full (there or thereabouts the same as 35mm dimensions), 1.3x which is found on the 1DI/II/III (not the S versions); 1.5x on most Nikons; 1.6x on Canons like the 30D; FourThirds, which is I believe half the size of APS-C sensor, so will give a 2x crop factor - someone correct me if I've ballsed this up, my memory is a bit rusty ;)

Although I would like the benefits of FF for large scale reproduction in magazine, I actually prefer the 1.5x crop on my D2X because it gives me that little bit extra out of my long lenses; I use a 80-200mm f/2.8, which has a field of view (in 35mm terms) equivalent to 120mm- 300mm, still retaining the f/2.8 constant aperture. That lens cost £700 but to buy a 300mm with the same aperture for FF would be in excess of £2,000. If I used that lens on a D700 for example it would still be a 80-200mm f/2.8 but the long end wouldn't be nowhere near as long, if you get my drift.

However, at the wide end the crop factor limits my options with my standard 17-50mm so I've had to buy a 12-24mm to get the equivalent of an 18mm on FF. That's probably the biggest downside of the whole crop factor issue, the availability of truly superb wide lenses.

I'm also sure that with the crop factor there will be some compromise when it comes to DoF but I'm not the person to explain that effectively.....
 
Martyn... said:
The "mm" is the effective focal length of the lens.

To see why for yourself take a cardboard tube, hold it to your eye and look at something, then cut the tube in half and look at the same thing. With the shorter tube you will see a wider view, cut that piece in half again and you will see an even wider view.
Click to expand...


Nicely put.


You can use Martyns idea to imagine cropping too ..simply make the cardboard tubes narrower (like a cropped sensor is smaller) and perform the same set of views.
 
...oh, and there are medium and large format digital sensors available that give 'full frame' images but these are well pricey.
 
Martyn... said:
The "mm" is the effective focal length of the lens.

To see why for yourself take a cardboard tube, hold it to your eye and look at something, then cut the tube in half and look at the same thing. With the shorter tube you will see a wider view, cut that piece in half again and you will see an even wider view.
Click to expand...

That pretty much summed it up for me :thumbs:
Thanks for that :D
 
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