Using the digital Zoom/Tele converter on the Canon PowerShot G9

(Discussing differences in recorded picture quality) 

By Rob van de Wijngaard
www.geckophoto.zenfolio.com
(The Netherlands, February 29^th  2008)

Experimenting with the zoom function of the Canon G9 PowerShot, I noticed something remarkable when using the digital tele converter. The dimensions of the picture always stayed the same at 4000x3000 pixels. Before discovering this I was thinking digital zoom is something like “in camera” cropping but as you will see, this is not the case at all. It looks like the Canon PowerShot G9 is extrapolating the “cropped” image up to 4000x3000 pixels.

The Canon G9 (and G7) camera’s has 4 different ways to apply digital zoom.

To select any of the zoom/tele converter settings, push the “menu” button and scroll down to “Digital Zoom” in the camera menu. Use the left or right button to choose one of the following options:

• Off
• 1.5x (1.4x for the G7)
• 2.0x (2.3x for the G7)
• Standard

Push the “menu” button to confirm your choice.

Short explanation of each of the different settings applicable to the G9:

• Off; only the optical 6x  zoom function, from 7.4 to 44.4 mm (35-210 mm in 35 mm equivalent) is available
• 1.5x; this is a fixed digital zoom factor 7.4 mm becomes 11.1 mm (52.5 mm in 35 mm equiv.), 44.4 mm becomes 66.6 mm (315 mm in 35 mm equiv.) So the effective zoom factor stays 6x but now from 11.1 to 66.6 mm.
• 2x; this is a fixed digital zoom factor 7.4 mm becomes 14.8 mm (70 mm in 35 mm equiv.), 44.4 mm becomes 88.8 mm (420 mm in 35 mm equiv.). As with the 1.5x setting the effective zoom factor remains the same but now from 14.8 to 88.8 mm.
• Standard; in this setting the camera use the optical zoom first from 1x to 6x (7.4 - 44.4 mm) and above 6x zoom, digital zoom is applied from 1x to 4x  resulting in a impressive overall zoom factor from 1x to 24x, 7.4 to 177.6 mm (35 to 840 mm! in 35 mm equiv.) 

The following are remarks when using digital zoom:

• It is not possible to shoot RAW in combination with 1.5x, 2x or standard zoom settings (G9).
• In the “SCN” setting “ISO 3200”, “Color Swap” and “Color Accent” are not available.
• The 1.5x and 2.0x digital tele converter settings are not available when shooting movies, the Standard setting can be used.
• By using the 1.5x or 2.0x you “lose” the wide end setting of the camera just like using a normal tele converter on a SLR camera. There are situations when you don’t have time to switch off the digital converter and you might miss the shot.
• Using the standard setting leaves everything normal from 1x to 6x zoom so the wide end setting of 7.4mm is always within direct reach.
• The optical viewfinder zooms only from 1x to 6x  and is of no use when you choose to use 1.5x, 2x digital zoom or Standard (Standard used above 6x zoom).
• Using the digital tele converter enables the use of faster shutter speeds at the same focal length compared to the “off” and “standard” settings.
• Using the 24x zoom has a big disadvantage; it is very hard to keep your subject framed on the display of your camera when hand holding it. Using a tripod is highly recommended in this case.

The test

I used the small poster (picture 1) as a test target and made pictures from it from a fixed position, about 2.5m away. The camera was mounted on a sturdy Berlebach Report 8043 tripod. Image Stabilizing was set off.

To avoid vibration the 2 sec. self timer was used, the Canon PowerShot G9 was set to ISO 80 to minimize noise. Since RAW is not available using Digital Zoom the best JPG setting was used; Large, Superfine compression. One shot was made in RAW as a reference. The RAW file was converted to TIFF using Raw Image Task.

For reference there were also made some “real life” shots from a building (picture 2) from a distance of about 50m. This building, a few minutes by feet from my office, is great for testing because of the detail and colours.

To accentuate the differences between the various settings crops were made at 200%  and the same amount of un-sharp mask (USM) was applied (amount 100%, radius 0.7 pixels, threshold 0 levels). I had to go up to 200% (!)  to make the difference visible between the RAW and JPG non digital zoomed images.

Test 1, results at 44.4 effective focal length

There are situations that you are able to come close enough to frame the subject effectively when zoomed in (digital zoom = off). So what are the consequences having digital zoom on (1.5x or even 2.0x) in this situation. As mentioned in the example above the focal length will be less resulting in a lower F-stop number and an up to two times faster shutter speed.

But what about image quality? :

The results speaks for themselves, the RAW and JPG non digital zoom pictures are very close to each other. With a slight edge to the RAW file which has less artifacts.

Although the “in camera” JPG conversion does a very good job, when you require best quality, and maximum latitude in post processing, it’s a no brainer shoot RAW.

An extensive comparison between RAW and JPG isn’t within the scope of this article so I won’t go further into detail.

The 1.5x and 2.0x digital zoom pictures are clearly softer, the 2.0x picture being more soft than the 1.5x picture So in this case digital zoom is not recommended

Test 2,  results at max. effective focal length

There are also situations when it isn’t possible to come close enough to your subject, for instance making pictures of small animals in the Zoo where a fence won’t let you come closer. In this case you can choose between

• Using maximum optical zoom and crop and “upres” later or
• Using optical zoom combined with 1.5x or 2.0 digital zoom
• Using standard zoom for an impressive 24x zoom (6x optical, 4x digital)

2a; Digital zoom off, focal length 44.4mm, cropped and upressed to match 1.5x digital zoom

2b; Digital zoom 1.5x, focal length 44.4mm, eff. Focal length 66.6mm

2c; Digital zoom off, focal length 44.4mm, cropped and upressed to match 2x digital zoom

2d; Digital zoom 2x, focal length 44.4mm, eff. Focal length 88.8mm

2e; Digital zoom off, focal length 44.4mm, cropped and upressed to match 2x digital zoom

2f; Digital zoom 4x, focal length 44.4mm, eff. Focal length 177.6mm

Things are a bit different here; although the upressed pictures looks sharper than the digital zoomed pictures there are more artefacts to been seen in the upressed pictures. Do keep in mind that these examples are shown at 100% It is likely that one would hardly see any difference at small (10x15cm) prints.  To my opinion there is one exception; pictures made with the combined optical and digital zoom, resulting in 24x zoom are very soft. The upressed picture may look quite coarse but keep in mind this is a crop of a picture when printed 225 cm (“88) long and 169cm (“66.5) high! (resolution 180pix/inch) 

Note: Upressing was nothing special here, I simply increased the number of pixels in the Photoshop “Image size” menu. There are a lot of other methods, using different types of software which will improve the results of upressing even more. 

Some real world examples 

These pictures were made on a overcast day, distance to the building aprox. 50m .

The Canon PowerShot G9 was set to ISO 80 to minimize noise. Since RAW is not available using Digital Zoom the best JPG setting was used; Large, Superfine compression.

Pictures are resized to 800x600 pixels, sharpened 100% , radius 0,7 pixels, threshold 0 levels.

There are differences to be seen but if the pictures are only be used on the internet and/or documentary the “punishment” for using digital zoom is not that hefty.

Digital zoom off, optical zoom 6x (44.4mm)

Digital zoom 1.5x, optical zoom 4x ( 29.2mm)

Digital zoom 2x, optical zoom 2x (22.2mm)

Digital zoom off, optical zoom 6x (44.4), to JPG converted RAW