Canon A710 IS vs Canon A640

[zzmiller]

Of these two cameras I am interested in knowing how one answers this question as it may also apply to any camera with 10MP as compared to the A710:

If I take a picture and then want to crop the picture, lets say to 50% it size, and still get a good high quality picture, which camera is better?

The A710 (7 MP, IS, 6x optical) will allow you to zoom 2x farther than the A640 (10 MP, 4x optical, no IS) but the A640 will allow you to capture 3 MP more of data. So if you have full optical zoom with the A710 and then cut it to half the size would you get a ppicture with 3.5 MP? And similarly, if you do that with the A640 it seems you would need to crop to 1/3 of the original picture to get the same size as half the A710, meaning you would have 3.3 MP. Do I have this right or am I looking at it too simply? If that is true then it seems the A640 might be the better choice since you might rarely use full optical zoom, especially indoors.

However, on other hand, if you are indoors would it be more advantageous to also have access to IS? More specifically to that question is the greatest attribute of IS the ability to take low light pictures better?


Thanks for any input!

[David Metsky]

If you cut the dimensions of an image by half (was a 10x8, now is a 5x4) you've lost 75% of your pixels.

Both cameras will do fine for what you are asking, the difference is fairly small and frankly not very noticeable. In general, optical zoom is more powerful then cropping. And extra megapixel or two doesn't give you much extra reach.

A more important issue for image quality would be the sensor size. The A640 has a bigger sensor, and produces better noiseless images then the 710's smaller sensor. Still, both are quite good.

IS is very nice, but mainly if your subject isn't moving. If your subject is moving around (like kids) it's not going to help you.

[reppans]

I'd agree with everything David mentions above. Also, cropping doesn't give you the true distance compression that I happen to really like in a good zoom (imagine cropping a 20 megapixel 28mm equiv photo).

My short list was between the G7, S3, 640 and 710 (price was not a concern) and I went through this process of elimination:

- G7 dropped due to the proprietary Li-ion
- S3 dropped due to size, I just wouldn't carry it with me ALL the time.
- 640 dropped due to zoom power, and perhaps of lesser concern IS.
- 710 also gained points for being the smallest and lightest, including only having to carry 2 back-up batteries (surprising important for me).

[reppans]

...However, on other hand, if you are indoors would it be more advantageous to also have access to IS? More specifically to that question is the greatest attribute of IS the ability to take low light pictures better?

Here's an example of IS in action... I just happen to be passing through Barnes and Noble today... :D.

http://farm1.static.flickr.com/164/430974233_42849dd615.jpg

The shot was taken with a slight zoom (80mm equiv) at 1/13 of a second, handheld. Normally, the rule of thumb for handheld is to shoot at the reciprocal of zoom (an 80mm zoom should use 1/80th or faster). This is nearly 3 stops slower, about right for IS, and only one try.