Sunday, April 22, 2012

G1X: Digital Zoom and Resolution

Slide Show 1: G1X digital zoom examples

I made a mistake in an earlier post about the digital tele-converter feature of the G1X. My rationalization is that I’ve rarely used any sort of in-camera digital zoom because it is really just cropping; in other words, I’m not experienced with digital zoom.  If a picture is to be cropped then my preference is to crop in Photoshop. My mistake was in thinking that the standard digital zoom was not up-rezzed whereas the digital tele-converter zoom (the fixed 1.5 or 1.9 zoom) in the G1X was up-rezzed. I was wrong. Both standard and tele-converter digital zooms are up-rezzed to the full 4352x3264 resolution of the G1X.

My error has unnerved me and I now wonder if there is a possibility that other posts may also contain errors!

The slide show above illustrates the G1X digital zoom at several settings but here’s some background information. The G1X lens has an optical focal length of 15.1mm to 60.4mm – a 4X zoom. For small sensor cameras, optical focal length is often stated in terms of equivalent full frame 35mm film camera focal length. For the G1X, the equivalent focal length is 28mm to 112mm. Instead of writing out “equivalent” every time, I prefer to use “mme”. With digital zoom (cropping) the effective equivalent focal length of the G1X is 28mme to 448mme – a 16X zoom.

Digital zoom choices are made in the Main Menu. The menu item reads “Digital Zoom” and does not indicate “digital tele-converter”. Options are: OFF, 1.5X, 1.9X and Standard. The 1.5X and 1.9X options are “digital tele-converter”. In terms of image size, all options produce 4352x3264 pixels in 4:3 aspect ratio frames. Digital zoom is not available for other aspect ratio frames and not available in RAW mode.

Using Standard digital zoom, digital cropping begins once the optical zoom has reached its maximum. That is, digital cropping begins above the 112mme focal length. This also means that the largest aperture is f5.8 for standard digital zoom on the G1X.


Slide Show 2: G1X digital tele-converter examples

In contrast to Standard digital zoom, the digital tele-converter zoom factor (1.5 or 1.9) applies to all optical focal lengths. This means that the optical 28mme becomes 42mme and the optical 112mme becomes 168mme when the 1.5X digital tele-converter is activated. Additional digital zooming is not possible when in the digital tele-converter mode of digital zoom.

The advantage to the digital tele-converter is that larger apertures are available in comparison to the optical or Standard digital zoom. Suppose, for example, a given scene is best photographed at 85mme. The largest aperture for 85mme optical focal length is f5.6. Standard digital zoom applies only to focal lengths larger than 112mme. Using the 1.9X digital tele-converter feature, the same composition is available at an optical focal length of ~45mme for which the maximum aperture is f4. Therefore this scene could be captured at f5.6 with pure optical zoom or at f4 by using the 1.9X digital tele-converter.  Using the larger aperture means that a faster shutter speed or lower ISO can be used when in digital tele-converter mode.

To my surprise, the combination of digital tele-converter and larger apertures did not increase the amount of background blur, see Slide Show 2 above and notice the blur in the far background.  The explanation is that depth of field is increased at shorter focal lengths and this increase more than offsets the slight change in aperture even when the image is cropped.

Although my preference is to crop in Photoshop, the digital zoom and digital tele-converter features do have their place. 


hongsi said...

Thank you very much for your post about G1X's digital tele-converter. I don't have a 250D filter. I set f2.8 and micro as C1 for the micro shooting. And usually I will use this mode with 1.5X or 1.9X digital tele-converter for shooting food, tickets and some close object. Before I preferred crop in Photoshop, but using 1.5X or 1.9X I can focus more on the composition of shooting.

MedicineMan999 said...

Great article on the digital extender. I have 2 G1X's and didnt know it existed! I've always shot .raw so maybe never noticed in the menus due to that...regardless I'm playing with it now! thanks!