Robert_Lay wrote:
So, when using the 18 mm lens the Rebel has a smaller depth of field (sharper plane of focus), which I believe was the point you were trying to make.
Robert,
Yes ... that's what I mean.
I assume you are talking about distance in feet (because I get the same values at www.dofmaster.com
you gave in your calculation).
However ... to have the same focal length on the 350 as 7.2 on the G6, you'll have to use 21.9 mm (35 mm equivalent), so you arrive at a total depth of field of 1.21 ft (4.47 ft - 5.68 ft) which is an even bigger difference to the 4 ft of total area in focus that the G6 gives you.
However ... 35 mm equivalent focal length is not a very good example for a 'shallow depth of field' photo ... (apart from the fact that the only DSLR lens capable of giving f/2 is the Sigma 20/1.8 lens) ... I'd rather look at the 80 mm focal length (classic portrait focal length, 16 mm on the G6, 50 mm on the 350D) and a subject distance of 10 feet, with an aperture of f/2.8.
Here the values are:
G6: 4.19 ft total in focus (8.33 ft - 12.5 ft)
350: 1.29 ft total in focus (9.39 ft - 10.7 ft)
so you have the same ratio ... ~3x the depth of field, which is roughly equivalent to the difference in sensor size (makes sense, huh?)
If you continue to experiment, you will realize that the setting that will give you a comparable image on the 350D (as far as depth of field is concerned) is f/9 ... and everybody who has done a bit more intensive (I dare not say 'serious'
) portrait photography will know that f/9 is maybe not the optimal setting to achieve good background separation.
Point is, on the G6 you can not use a larger aperture than f/2.8, so you are pretty much limited to that effect. On the 350D, with the 320$ 50/1.4, you can get the area in focus down to 0.65 ft (9.69 ft - 10.3 ft), which is pretty shallow. It means that the eyes will be sharp, but the ears can already be out of focus ... if that is the effect you are going for.
Hope that helps 
If you want to have a less technical demonstration... take a look at this image by Sikario (linked in another thread)
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Sophia ... I'm pretty sure that you will love your G6 once you know how to use it ... getting blurry images is not necessary, the most important limitation of the camera normally is the expertise of the person using it.
Best regards,
Andy