First of all: The Digital Picture.com has an excellent page where you can compare the sharpness of different lenses and different apertures.
But recently I did some quick tests with my 50 mm f1.4 myself. It’s a decent lens and regarded excellent for the price range. And it’s pretty fast, featuring an aperture of 1.4. But lenses loose sharpness and contrast at low apertures, and I wanted to know exactly how much. In this lens the difference is huge. Here are two 100% crops:
50 mm @ f5.6
50 mm @ f1.4
Yes. That’s the same lens, the same camera and the same conditions. Only a different aperture value. But will you see the difference if you snap an image at full resolution and reduce the size down to what you’ll need on a web page? Let’s have a look. 21 megapixels from my Canon 5D MarkII reduced down to an image that is 500 pixels wide.
50 mm @ f5.6
50 mm @ f1.4
And I guess you’ll need a slightly trained eye to see the difference clearly. First of all you see the vignetting: darker corners. Then you see that the DOF is more shallow and that the cars at the bottom of the image in the f1.4-version is not completely focused. This is how it should be. A shallow depth of field is one of the beauties of a low aperture value.
But if you look closely you’ll see that the overall sharpness and sense of depth in general in the f5.6-image is better. Even when the image is reduced down to this size.
So, if you want the ultimate in technical quality you should plan your aperture. And buy very nice lenses…
There are three main factors that influence the quality of a digital image. The resolution is probably the most common. How many megapixels is your camera? Then, we have the compression. If you compress an image to make a smaller file using the JPEG-system you will loose some quality.
The third factor is the so called dynamic range. Can you take care of the details in both the highlights and the shadows? Here’s an example. You have a scene where the sky is dramatic and interesting. But you also want some details on the ground. In the following image I adjusted for the sky. And as you can see the ground is only a silhouette.
So you need to let in more light. Open up the aperture or add some time to the exposure. Very nice scenery, but no dramatic sky. As the next image shows.
Seems like you can’t have it all. Or maybe you can? There are actually a couple of solutions. One of them is called HDR, or High Dynamic Range photography. To put it simple, you combine several exposures into one using some magic mathematics. And the good news is that you don’t need to understand much of the mathematics, there are several tools to make HDR images and you can use most digital cameras when shooting for HDR.
For the image in my example I actually shot three versions. One standard exposure, one with +2 stops and one with -2 stops. All the three exposures are loaded into the HDR software to make an image that will show both the dramatic sky and the forest.
What do you need?
When you’re out in the field you need a digital camera that let you manually adjust the exposure value and a tripod or something to support the camera. The three exposures need to be identical. Or at least nearly identical. Some of the HDR software out there will try to adjust if you have moved the camera slightly between exposures.
When you get back you need a computer and some HDR software. I am using Photomatix Pro. Available for both Mac and Windows. For Mac you can also try the free DRI maker. It doesn’t make true HDR images, but will help you with that difficult dynamic range by combining several images in a different way.
And if this quick introduction was interesting you can go further by having a look at the HDR group on Flickr. Lots of examples, tips and links.
Oyvind adds two good links to tutorials for HDR in Photoshop in the comments. One from luminous-landscape.com and one from backingwinds.
And you can have a look at some of the other HDR images I have made recently. These three are from the beautiful Røisheim Hotel in Bøverdalen in Norway.