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Lens
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can i ask another question ; when people buy a lens say 50mm for a dslr i have heard people say that it is equal to Xmm on film lens can anyone explain why this is and how do i work it work out (X meaning a different mm number )?????
Hi Naja – I’m no expert – but I think I am right in saying that when you put a 50mm lens on a Film camera (35mm) – you do indeed get a 50mm focal length.
When you put a 50mm lens on a FULL frame DSLR (EOS 1D, 5D, Nikon D3 etc) – you also will get a 50mm focal length.
However – most consumer DSLR’s have a smaller “Cropped” sensor – and many have the APS-C size – that is – giving a 1.6x increase in focal length on a lens. Not sure technically how the smaller sensor increases the focal length – but it does.
So – a 100mm lens on a 35mm or full frame DSLR camera – will be a 160 mm lens on a APS-C camera. You just multiply the lens focal length by the lens focal length.
This can be a help or a hindrance – depending on the lens and required use.
A 100-400 on a Canon 540d will give a super zoom of 160-640mm focal length – great for sports or wildlife.
Hope this helps.
bren
It depends on the size of the sensor. Very expensive digital cameras have sensors the same size as 35mm film (and are hence called Full Frame cameras), so the lens specification stays the same. However, most entry level SLRs have much smaller sensors to reduce costs. It is the ratio between the actual size of the sensor and the reference 35mm that is used to calculate the X. Common ratios are 1.6 and occasionally 1.3.
So 50mm on a full frame camera will be (50mmx1.6=) 80mm on an entry level camera.
Think of it along the lines that a smaller sensor will see less than a larger sensor – just the central bit of what comes through the lens. This is the same as if you zoomed in to that central bit, therefore leading to the calculation above.
thanks guys for taking the time to answer that has really helped
kind regards
henryJust a point to note. Although the lads are correct in their explanations, the 50mm lens will have a field of view equal to an 80mm lens with a sensor of a 1.6 crop factor, but the actual magnification of the subject in the lens will remain the same as 50mm.
A camera lens captures a circle “image”, while length of the lens determines the maximum angle of view which it´s able to capture.
And the smaller part of this circle you capture with the sensor, the smaller angle will be visible in the photograph.The crop factor number tells you the ratio between a “standard” 35mm full frame sensor and the sensor which you use in your camera.
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