Hi all. I am gonig to ask a stupid query , bear with me on that. Being a physician I can give lectures at end on the human body but I suppose I am a newbie in cameras though I read a lot.
Aparmley very well described that a big window lets more light and hence a 2.8 lens will be very big. I have the following queries
1)how have panasonic compressed that same 2.8 into a small lens in the Lumix Fx30 also giving a 420 mm zoom? I need a tech explanation? I know of course that the sensor is smaller that Rebel xt and quality wont be the same , etc etc. The sony 828 also gives a lens with F 2.8 @ 200 mm.
2) already technology has compressed the size of the 70-300 DO lens though the aperture is still 5.6- agreed that the results are not too good with odd flares
3) Is it possible that one day we will have lens of the DO size with a 2.8 f all the way?
thanks for all help
1)how have panasonic compressed that same 2.8 into a small lens in the Lumix Fx30 also giving a 420 mm zoom? I need a tech explanation? I know of course that the sensor is smaller that Rebel xt and quality wont be the same , etc etc. The sony 828 also gives a lens with F 2.8 @ 200 mm.
Because the sensor (area of exposure) is a lot smaller. In terms of area, the FZ30's sensor is about 1/16th the area of a DSLR sensor. What this means is that the FZ30 doesn't need as a large a lens to gather enough light for the sensor. The reason why DSLR's have such big lenses is because the sensor size is huge.
2) already technology has compressed the size of the 70-300 DO lens though the aperture is still 5.6- agreed that the results are not too good with odd flares
The difference between a f/5.6 lens and a f/4 lens let alone an f/2.8 lens is enormous. This increases by a quadratic factor, so it takes TWICE the amount of light between each step.
3) Is it possible that one day we will have lens of the DO size with a 2.8 f all the way?
Yes, it'll eventually happen, but not for a while (we're talking many years). And it will be very expensive to begin with.
Rex
Thanks a lot for the very prompt and detailed reply. Really appreciate it. It is very clear to me now. I think I will now focus on the canon 70-200 F4 which is not as heavy as the 2.8
regds
Krishna Raman
I may be mistaken, but wonder if a short explanation of how F-Stops are measured could help.
Rather than making a hard calculation such as mm, they use a ratio of the focal length. So f-8 for 100 mm focal length has an apeture diameter of 1/8th of 100, or 12.5 mm. However; on a tiny sensor a P&S may be more like 6 mm to achieve the same field of view as the 100mm on the normal film camera, but for that, an f-16 apeture would be less than 1/2 mm.
Amount of light goes by Area, not diameter. Well, you can do the math.
f-stops go 1.0, 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22, each successively double the light.
At 50mm on a normal 35mm film camera lense, f1.4 apeture has an area of 1,002 mm, where f2.8 has an area of 250mm. That's 4 times the light!
Point being; not everything we normally think about focal lengths translates directly to P&S.
As for zooms; I'm also curious why prime lenses (non zooming) can have such dramatically larger apetures than the largest apeture on a zoom.
I apologize for boring you if you were already aware of this. Just thought it might illuminate the subject a little if you weren't.
2.8 lens for rebel xt vs Lumix Fz30 2.8 lens
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