wHAT MAKES A FAST AND LENS AND WHATS IS IT USES


organicimagery

Link Posted 05/09/2009 - 12:00
Hello folks, hope all is well, I have a question, I asked a pro photographer the other day (5dmk2 man)this and he was stumped! So here it goes,I have a fa 50mm 1.4 lens and every one says how fast the lens is, but in real terms what makes a fast lens, what use is a fast lens and how much better does it perform in what situations to a slower lens, Thanks, i appriciate the comments
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scottthehat

Link Posted 05/09/2009 - 12:02
it has a big apature which lets more light in making it better for low light and also the more light it lets in the faster shutter speeds you can use,
just keep snapping,

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CAMERAS = k200d + battery grip.
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LENSES = tamron aspherical DII 18-200mm f3.5/6.3,
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sigma 150-500mm apo dg hsm os
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mikew

Link Posted 05/09/2009 - 12:05
Or possibly you buy one so that you can apply selective focus as the DOF of the very wide aperture available on a 'fast' lens wide open is very small and hence isolates your subject well. This is why I bought an f2.8 17-50 Tamron.

Bear in mind a fast 50mm lens is considered to be f1.4. A fast 300m is probably f4 so there are no hard and fast rules.

mike
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johnriley

Link Posted 05/09/2009 - 12:15
"Fast" refers to the lens compared with the norm for lenses of that focal length.

So in 50mm lenses, f1.4 and f1.2 are fast. F1.7 and f2 are the norm. F2.8 is slow and often a macro lens.

An 85mm f2 would be the norm an 85mm f1.4 is fast.

f2.8 zooms are fast.

And so on.

Fast lenses are heavier, bulkier, need more elements and are much more expensive. They do allow easier manual focusing in dull light and also higher shutter speeds if the reduced DOF at wider apertures is acceptable.
Best regards, John

Mannesty

Link Posted 05/09/2009 - 17:39
One benefit of 'fast' lenses not mentioned so far is the brighter viewfinder image you get making focussing in low light much easier than with a normal speed lens.
Peter E Smith

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organicimagery

Link Posted 06/09/2009 - 17:32
so my 28-200 3.5-5.6 is snail slow then really. Any other main advantages on haveing a fast lens?
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johnriley

Link Posted 06/09/2009 - 17:38
The photographer's sense of self image? I know people who sport their f1 lenses with pride! Just kidding...

Seriously, in the days of 50mm standard lenses f2.8 would be considered very slow indeed. We would probably buy the f2 or f1.8/1.7 lens and aspire to the f1.4. When the f1.2 arrived that was but a dream.

The old Canon f0.95 was actually often referred to as the "Canon dream".
Best regards, John

lemmy

Link Posted 06/09/2009 - 23:37
I read some tests on that lens at the time (the early 60s as I recall) in the BJ. It had, they said, wide open, a soft, plastic quality. Maybe that was why it was called 'dream'. I think they probably meant fuzzy.

But hey, for a press man, you had an image, never mind the quality, feel the image!
lemmy
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johnriley

Link Posted 06/09/2009 - 23:44
I have a comparative test of 50mm f1.2 lenses from Creative Photography, a long defunct magazine that lasted a splendid 13 issues.

The Pentax one equals the performance of the other 50mm lenses in the range when stopped down, with lower resolution and contrast when wide open. However, it has excellent control of point light sources, which is logical considering its likely uses.

I'll try to remember to look out all those lens tests tomorrow and see what interesting snippets I can find.
Best regards, John

organicimagery

Link Posted 08/09/2009 - 01:48
ok great will keep looking on thread
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edumad

Link Posted 08/09/2009 - 09:56
Fast probably was a term that originated from those photographers who bought them for the ability of using faster shutter speeds they required.
I've also heard bright lenses, maybe coming from the desire of having the ability of more easily having a good view in the viewfinder or allowing easier photography in low light.
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