The rule of thumb you seek is the total zoom is proportional to (optical_zoom)*SquareRoot(pixel_count).
A factor of 2 in optical zoom is equal to a factor of 4 in mp count..
The above is for good enough lenses and looking at the final picture at so many pixels per inch..
Dave..
The short answer is: No..
You can have a little more zoom by cropping but it is not so much. As an example if you have a camera with 8 MP and 105 mm zoom you can get a crop of 4 MP like it was 148 mm without the effects that this increase of focal length implies (shallower DOF, distance compression, etc.).VictorBucuresti, Romaniahttp://s106.photobucket.com/albums/m268/victor_petcu/..
An 8Mp camera cropped to give 2X or a 2X digital zoom uses 2Mp of the sensor. So if you crop to get the equivalent of a 6X zoom from an 8Mp camera with a 3X optical zoom you are using only 2Mp of the sensor. Obviously Mp doesnt make up very much for optical zoom...
Here's an article which allows one to both see the discussion but also pretty easily plug in the numbers for diferent cameras..
Http://www.digicamhistory.com/Figure%20of%20Merit.html.
The method is framed around trying to decide which camera would allow the largest image at the same pixel count/resolution, kind of "Which gets me closer?".
But all this does is give an image size comparison at the same resolution and doesn't give any insight into optical quality, handling of distortion or color aberrations, etc. So at full zoom, Camera A may give a "bigger" picture of the subject, quality wise, it may be less pleasing...
If you are just talking about the area covered, equations can be developed, but if it is the final image quality, lots of factors like the camera, lenses, setting, lighting etc will matter...http://budding-nature-photographer.blogspot.com/..
Sounds good in theory. However in practice a cropped image is pushing the optical sharpness of the lens to it's limits. At the same time sensor noise and sharpening artefacts (from a jpeg image) means the results will be a compromise, and unlikely to be a good as zooming (or physically getting closer) in the first place.Regards,Peter..
Craig Gillette wrote:.
Here's an article which allows one to both see the discussion butalso pretty easily plug in the numbers for diferent cameras..
Http://www.digicamhistory.com/Figure%20of%20Merit.html.
The method is framed around trying to decide which camera would allowthe largest image at the same pixel count/resolution, kind of "Whichgets me closer?".
But all this does is give an image size comparison at the sameresolution and doesn't give any insight into optical quality,handling of distortion or color aberrations, etc. So at full zoom,Camera A may give a "bigger" picture of the subject, quality wise, itmay be less pleasing..
Indeed, it's a "other things equal type" of comparison using this formula, a good way to trade off zoom vs megapixels. Of course when it comes to image quality, this formula does not compute that, there's lots of factors involved in that question!.
I haven't updated the table in a while, but there is a newer version than the one in the FoM article above:http://www.geocities.com/digital_ray_of_light/zoomzoomv7.html.
Comprehensive 2007 speculation and predictions: http://1001noisycameras.blogspot.com..
Baloo_buc wrote:.
The short answer is: No.You can have a little more zoom by cropping but it is not so much. Asan example if you have a camera with 8 MP and 105 mm zoom you can geta crop of 4 MP like it was 148 mm.
Yeah. That's about right.... .
Without the effects that thisincrease of focal length implies (shallower DOF, distancecompression, etc.)..
Ahh.... But that "without" is NOT right, Victor. Sorry..
It doesn't matter how we crop either by using a longer lens, or physically cutting the image down around the outsides we DO get images that are the same in DoF and distance compression... no difference..
Just thought I'd mention it, for the sake of accuracy. .
Have a nice day. Regards,Baz..