[Twix]

A couple shots I took today after getting my car lowered. I took the top one with a standard 18-55mm that my T3i came with. The second I took with a fixed 50mm at f1.4. I don't see any real differences, therefore, I must be using the fixed lens incorrectly. Anyone shed some light? I took what I think is a cool shot with the fixed lens on some Lego I had built. (pics below)

[Itsed65]

What were you looking for? If you notice, in the shot you took with the prime, the fence and house behind the car are slightly blurred from the narrower depth of field. If you were looking for more "Bokeh" you would need more separation between the car and the fence, because as you back up enough to get all the car in the frame, your depth of field increases.

Your X1 looks great btw!

[Twix]

I see. If I wasv to take more of a 1/4 shot than I would get more of a blurred background?

[Billup]

The overall distance between the fence and car is where you notice the effects between the two. First picture captures everything in focus, and your fixed lens gives the background a more blurred appearance keeping your car as the main focus.

Good looking ride, looks great lowered!

[Veritable]

Here is probably the best Canon resource I've ever found: http://www.the-digital-picture.com/

Especially check out the Lens Image Quality tool: http://www.the-digital-picture.com/R...ple-Crops.aspx

Aperture setting controls how much light you are letting into the camera sensor, and thus how much of the scene is in focus. That also directly affect how fast your shutter speed can be in order to maintain proper exposure.

You don't want to use the lowest f-stop number your lens is capable of, unless you can't help it, because that is like revving your engine to redline; it doesn't have more to give. You also don't want to use high f-stop numbers, because your camera sensor has a Diffraction Limited Aperture of f/6.8 according to calculations.

So, you can try to do your own Image Quality test. Use Av (aperture priority) mode for your camera. At the same scene and same condition, take your 18-55 and set it to f/5, zoom in to 50mm, and take a picture. Then, take the 50mm and also set it to f/5 and take a picture. Keep the ISO setting the same (lower the better, of course).

You will find that in order to keep the exposure in check, you will have to change your shutter speed depending on the lighting condition. You will also find that your 50mm will out-perform the 18-55 @ 50mm.

I have a 50D (with DLA of f/7.5) paired with a 17-55mm f/2.8 IS USM. I will always shoot at f/7.1 until I lack daylight, and then start dropping down the number. I will not use the f/2.8 setting unless I'm indoors.