Question on Lenses and F-Stops

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Dan_The_Man

Active member
Hi there,

I am looking to buy a Canon 7D and get a couple of lenses with it. I want a 50mm and have found 50mm 1.4 lenses for around £250-300. I have also found a 50mm 1.8 lense for £70! Can someone explain to me why it is so much cheaper just for the 0.4 f-stops?

Dan
 
The difference is much greater than you think. To close down a lens a "stop" means that you need twice as much light to get an equivalent brightness. Half a stop means 50% more light and so on.

More over, f-stop is a logarithmic scale so .4 is actually equivalent to 2/3 stops and not .4 stops. So the difference is considerable.
 
Also the difference between those two particular lenses is pretty large. The 50mm 1.8 is a good lens but it is built to be a cheap as possible, meaning that everything (except the glass elements) is plastic and the focus ring is tiny. The 50mm 1.4 is a much better built lens with better glass in it and a full-sized focus ring.
 
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