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Old Apr 29, 2005, 12:41 AM   #1
alg
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I just got my first DSLR, XT.

Most affordable DSLR zoom Lens start around f3.5. A f2.8 SLR zoom lens seems very expensive.

However a lot of Prosumer Cameras (eg FZ20, C8080, G6) have lens speed starting at f2.8 or faster.

Is the SLR lens f number comparable to the prosumer. i.e. If I get a f3.5 SLR lens and a prosumer lens also at f3.5, will the images taken with each camera appear equally bright and with same DOF (Assuming the ISO speed is the same) ?

DOes this also mean that unless I get a very expensive SLR lens, using a prosumer camera I will be able to get brighter pictures for a given ISO speed.:?

Alg






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Old Apr 29, 2005, 5:23 AM   #2
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alg wrote:

Quote:
Is the SLR lens f number comparable to the prosumer. i.e. If I get a f3.5 SLR lens and a prosumer lens also at f3.5
Yes - the aperture is always a ratio of the effective focal lenght over the 'effective' lens opening -> Any lightmeter (even an external) would work the same...



Quote:
... will the images taken with each camera appear equally bright
Apple vs oranges - With one you see through the lens, with the others you see through a separate viewfinder or EVF with a brightness that is adjustable



Quote:
and with same DOF (Assuming the ISO speed is the same) ?
NO - the smaller the sensor the larger the DOF - i.e. you can't really get a good 'Bokeh' on a prosumer cameras unless you maximize the effect by using the zoom setting and get in close...



Quote:
A f2.8 SLR zoom lens seems very expensive.
... and everyone agree, again the aperture is a ratio:
Fast lenght must have big opening -> bigger optic -> more glass means more metal to keep it whole -> which is what you're paying for $$$ :lol:

The benefit being two folds:
1. The better 'Bokeh' - DOF
2. A more precise focus since a higher resolution AF sensor is used
The flip side is they tend to be heavier because of the extra materials used - only you can make that trade-off: less weight(or IS) vs 'Bokeh' :?



Quote:
DOes this also mean that unless I get a very expensive SLR lens, using a prosumer camera I will be able to get brighter pictures for a given ISO speed.
Yeap - it's that 'Bokeh' again isn't it (and the noise at high ISO)??? - But it's even lighter!!! :idea:
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Old Apr 30, 2005, 10:56 AM   #3
alg
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Thanks, NHL

You have answered all my questions



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