drewdam said:
hi,
am using a FZ20 now, which has a zoom range of 36mm-432mm, can i say that the dslr lens with 80-200mm is the 1:1 ratio to my FZ20 200mm zoom? or should i say at 200mm is about 5x the optical range?
reason for this is i am used to such the long range and if i will to go into dslr..i need to work up the budget..:sweat:
1) 432mm/36mm =12x
That's why they call it 12x optical zoom.
2) For the FZ20, the actual focal length at 12x optical zoom (i.e. 35mm format equivalent of 432mm) is only 72mm.
But because of FZ20's small 1/2.5" sensor, the subjects in the frame appear as if they're taken at 432mm focal length on a full frame 35mm format sensor/film.
That's why the 35mm format equivalent of the FZ20 at max. focal length is 432mm.
3) To have the same subject sizes in the DSLR's frame as the FZ20 at 12x optical zoom, the subject sizes on the DSLR frame should be as if they're taken at 432mm focal length on a full frame 35mm format sensor.
This means that
a) if the DSLR has a full frame sensor, then the lens used must have at least 432mm focal length to match the FZ20's subject sizes on the frame at 12x optical zoom.
b) if the DSLR has an APS sized sensor (which most DSLRs currently have), its sensor frame is actually about 1.5 times smaller (which is commonly called "crop factor", as measured by both length and breath are approximately 1.5x shorter and area size therefore 2.25 times smaller) than a full frame. Therefore the focal length necessary to achieve the same subject sizes on the smaller sensor as 432mm lens on a full frame = 432/1.5 = 288mm.
This means that 288mm would also be the focal length for a DSLR with a crop factor of 1.5 to achieve the same subject sizes as the FZ20 at 12x optical zoom.
Crop factors range from 1.4-1.6 for most DSLRs with APS-sized sensor.
So the approximate SLR lens focal length you're looking at to get the same subject sizes as the FZ20 at 12x optical zoom would be about 300mm.
c) For the reasons above, different cameras capture different levels of details at the same 35mm format equivalent focal length because the actual focal length used are different for different sensor sizes. (72mm for FZ20, about 288mm for APS-sized sensor DSLR, and 432mm for a full frame sensor DSLR or film camera).
Summary : You should be looking at 300mm lens if yours is an APS-sized sensor DSLR.
Hope the above answers your question.