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-   -   Question regarding zoom. (https://forums.steves-digicams.com/general-discussion-11/question-regarding-zoom-95128/)

Morag2 Jul 12, 2006 9:54 PM

Hey everyone, I have a Kodak P850 with a fixed 36-432mm zoom. So I was wonder how zoom works on an DSLR camera. Say I bought two lenses for my DSLR. One with a 50-400mm lens and one that is 400-800mm. So here is my question.

For the 50-400mm lens, would it, when fully zoomed look similar to my camera does at full zoom? And the 400-800mm lens, even when it is at it's lowest zoom would it still be similar to my camera at maximum zoom?

Basically, I just want to know if the numbers given on SLR lenses are comparable to those on fixed lenses? If I bought that 400-800mm lens, would it seem like a 24x zoom after using my camera with 12x?

Sorry for the long post, my question is kind of hard to explain.

Sintares Jul 12, 2006 10:09 PM

Basically, I just want to know if the numbers given on SLR lenses are comparable to those on fixed lenses?

The lens are given in the 35mm format equivalents. So a 432mm fixed lens has the same reach as a slr lens of the same length.

One thing to note however is Dslrs have a smaller sensor than the sensor of a film camera (the film !).

From the Dpreview glossary

As a consequence, a sensor smaller than a 35mm film frame captures only the middle portion of the information projected by the lens into the 35mm film frame area, resulting in a "cropped field of view". A 35mm film camera would require a lens with a longer focal length to achieve the same field of view. Hence the term Focal Length Multiplier (FLM). The FLM is equal to the diagonal of 35mm film (43.3mm) divided by the diagonal of the sensor

So in other words a Dslr with a FLM of say , 1.5, with a 300mm lens would have the field of view of a 450 mm lens on a film camera.. Whilst this is great for telephoto lens, that expensive 18mm wide angle lens becomes a 18x1.5 = 27mm, not so good.

See http://www.dpreview.com/learn/?/Glos...tiplier_01.htm


Also be careful when talking about zoom as x10 or x12 etc

The zoom on a lens is longest focal length/shortest focal length, so 432/36 = a x12 zoom, however a lens with the range 10-120 would also be a x12 !

And the "zoom" figure does not indicate actual magnification either, basic human eyesight is said to be roughly equivalent to a 50mm lens, so a lens at 432mm , x12 zoom is only roughly x8.6 magnification..

Morag2 Jul 12, 2006 10:17 PM

So that focal length multiplier, if I understood correctly, does it actually help you get a closer shot from a distance? (You said 300mm becomes 450mm). I see the dissadvantages for taking wide angle shots of course, but I'm much more interested in getting close than in getting further away. (My camera has 12x zoom and I'm already wishing for more)

Sintares Jul 12, 2006 10:31 PM

It will "look" as if you are closer, due to the cropped field of view, see Case 1 at http://www.dpreview.com/learn/?/Glos...tiplier_01.htm

Be careful discussing this, as this board has the odd fanatic :lol:that will rant and scream that you are not really getting closer , its just the cropped fov making it look that way...

However with your Kodak, just buy a good tcon, Sony has a nice one the VCL-Dh1758 x1.7 to take you to 734mm (x20)


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