Why can't my newer cameras focus on my hands and something behind them at the same time? [duplicate]

Question

I've got this thing where I go around the world and hold their famous monuments with my hand through perspective photography. For example, holding the learning tower of Pisa. The pictures I've taken a while back with my Canon SD630 came out the best with both my hand and the tower in focus. Now a days, I'm using a Canon S100 and a Canon t4i. The problem is I can't get them to focus on multiple points or not focus on any points at all like I could do with my SD630. The same picture with Pisa with these two cameras, it's either my hand in focus on the tower, never both that was possible with the 630.

I'm still new to photography, what's causing that and how can I get around it?

Answer 1

All lenses can really only focus at one distance from the camera. Everything in front of or behind that point is increasingly blurry. In practice, there is a range of distances where the blur is imperceptible, or close enough. We call this the depth of field.

It sounds like you are looking for a very large depth of field. Your older camera had a very high apparent DoF because it has a tiny sensor and because blur is less apparent at lower resolutions. Your SLR in particular has a much larger sensor, and the S100 a slightly larger sensor, and both have much higher resolution. This makes depth of field much more of an issue.

You can get a higher depth of field by stopping down — that is, using a smaller aperture, one with a higher value. It looks like the SD630 had a smallest aperture of f/4.9 (when zoomed in), which is roughly like setting your DSLR's lens all the way down to f/22. Try that, and maybe try scaling the image down to 6 megapixels to mask more of the blur, and see if that approaches more of what you're looking for.

More detail on topics raised here at:

• What exactly determines depth of field?
• What is a "small" aperture?
• What is aperture, and how does it affect my photographs?

And

• How can I take photographs with a large depth of field without diffraction?

Answer 2

The problem, at least with the DSLR, is that the sensor is larger and therefore you use a longer focal length and get a shallower depth of field. The depth of field is the distance that is perceived as in focus when an image is captured and a shallow depth of field means that things go out of focus more quickly.

On a point and shoot with a very small sensor, the crop factor is very high, so an 10mm lens may be the equivalent of having a 50mm on a DSLR with a much smaller crop factor. The crop factor is based on the sensor size and describes what portion of the image circle of a conventional full frame 35mm frame is used by the sensor.

This very short focal length on the point and shoot results in a very wide depth of field, such that your hands and the background are both able to be in focus. On a larger sensor, the focal length is much higher and the depth of field much more shallow. The way to get around this is to increase the aperture (the f/number) to a higher number. This will make the aperture let in less light, but it will also increase the depth of field and allow you to get both your hands and the background in focus. Note, however, that you will either need lots of light or a long shutter time in order to let enough light through the small aperture.