Lens Question? F4.7-5.6?

TwistMyArm

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When looking for new auto focus zoom leses what are some things that I should be looking for. I'm more intrested to know what the F4.7-5.6 refers to when I see this in regards to the lense.
For example, "PENTAX SMC FA ZOOM 80-200MM F4.7-5.6 LENS". How does this affect the lense?
Any info would be appreciated.
 

Chase

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The 4.7-5.6 refers to the f-stop value of the lens. The lower the number, the more light the lens is capable of letting in.

You'll often find two of the same zoom range lenses, say 28mm-80mm, but the prices will be a huge difference. Usually in this case, you will see a major difference between the f-stop rating. The less expensive one will usually be in the 4 range, where the more expensive may going to around a 1.8 in some cases.

I'm sure some of the others in here can give you much better information on this than I can, but hopefully this helps a little.
 

ismael

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That refers to the aperture of the lens. The bigger the aperture (smaller the number) the more light goes thru the lens. In numeric terms, F2 or 1:2 is better than F4 or 1:4, since more light means faster shutter speeds are possible. In zoom lenses, it refers to the aperture at the widest and closest settings accordingly. In your case, the lens is F4.7 @ 80mm and 5.6 @ 200mm
Those are typical values for these lenses. When you see a sport photographer with a HUGE lens, the size of a car muffler, it is not necessarily a super telephoto, but usually a wide aperture. I've seen 600mm lenses with F4 or better. But they are REALLY $$$ expensive.
Hope this helps.

Thanks,
Ismael
 
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TwistMyArm

TwistMyArm

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I know what the FStop is I was just confused with the F4-5.6. That makes a lot more sense now though F4 beeing the widest value at 80mm and F5.6 beeing the widest at 200mm.
Thanks for the help
 

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