*update: I’ve been having weird trouble with photos going missing from flickr. It’s fixed again, hopefully this will stop! Sorry guys, thanks for all the feedback though. Also, for those looking for a very technical discussion, you won’t find it here. These articles are meant for those who have just enough understanding of these things to be confused and are meant to serve as a simple explanation, thus the title.

I’ve gotten the “what camera and lenses do you use” question enough lately that I’ve decided to start a section on the blog for photographers. After all, I have learned just about everything I know from other people’s blogs, so why not share the love? There’s a lot of great stuff to learn out there, but there’s a few things I had a hard time really grasping that no other website was super helpful with, so I’m going to dive into some of those things. Today we will talk about full frame vs. crop frame sensors, perhaps the most worn out subject of all in many forums!

First of all, I use a Canon 5D 12.8 mp SLR. I love this camera solely for it’s sensor, which is full-frame. Full frame means that the sensor is the same size as a 35mm film negative. Any digital SLR that is not a 1Ds, 5D or Nikon D3 has what’s called a crop sensor, meaning that the sensor is about 1.6 times smaller than full-frame. I’d say it’s safe to say that it’s not the size that matters, it’s what you do with it, but there’s a lot of things you just can’t do without a big sensor.

Here’s the best way I’ve found to demonstrate this: Hold your finger up close to your eye, as close as you can get it and still focus your eye on your finger. Notice how everything behind your finger is blurry? Now, move your finger farther away while still focusing on your finger and notice how the background comes more into focus. This is called depth of field, or DOF. (aspiring photographers posing on forums and flickr really love their abbreviations)

To understand the differences between full-frame and crop sensors, let’s use that same test but with a camera. Here is my finger at the closest focusing distance to my 5D with the 35L attached, set to f/2.

The background is very blurry, like how it was with your eye, right? Now here is what happens when I move my finger away from the camera:

Notice how the background got less blurry? Now on a crop sensor camera, that first picture would look like this:

The smaller sensor sees less of the same picture, thus it has the effect of zooming in closer. To make a crop camera have the same basic proportions as a full-frame, you need to either zoom out with your lens or step back with your feet. So, if we wanted to make a crop camera take a picture of my finger with the same proportions as the first full-frame picture I showed you, it would look like this:

Now compare that again with the full frame version (I realize they’re not EXACTLY the same):

So, because of the smaller sensor, the depth of field is diminished in the same picture because of the greater distance between the subject and the camera. Additionally, the crop sensor changes the field of view of the lens. Notice how on the bottom picture there’s two computer screens almost completely in the frame, but in the top just the corner of each is visible? The crop sensor causes the 35mm lens to act more like a 50mm, which has a narrower field of view. 35 x 1.6 = 56. But if I put a 50mm lens on the full-frame to try and make it look like the 35 on the crop, there would be even MORE background blur on the full-frame version because of the longer focal length. (or LESS depth of field, however you want to call it)

Who cares about blur? (Photographer’s geek word for this is Bokeh, pronounced Boh-ka) Well my friends, if you think about it, this is the only thing pictures have the upper hand on over paintings. I’ve seen some really realistic looking paintings, but they can never reproduce the way our eyes blur things to create depth like a camera can. Personally, I use this effect a lot, shooting with mostly prime lenses at f/2-ish a lot.

Here’s a few real-world examples:

It’s a subtle thing that the full-frame does, but by blurring backgrounds a bit more at all f-stops, it causes the in-focus parts to seem to stand out more, thus looking more 3D. It’s that “jump off the page” sort of thing.

Now, there are times when you don’t want the background to be blurry.

This picture would have looked about the same on a crop camera at 10mm (10 x 1.6 = 16) as it did on my camera at 17mm. Everything’s in focus because it was shot at f/11 or something like that. But that brings us to one more full-frame advantage: fidelity.

The new Canon Rebel Xsi has a 12.2 megapixel sensor, but it’s a crop sensor. This means that the pixels has to be a lot smaller to fit on the smaller area. The 5D has 12.8 megapixels on a bigger surface, making the size of the actual pixels bigger.

Imagine putting out a bucket and a drinking cup in the rain for a half hour. Which would gather more water? Obviously the bucket, it’s wider. Well, it’s the same concept for pixels, except they gather light in photons and they’re really, really small. Since the 5D’s pixels are bigger, they gather more light than the Xsi’s pixels, even though there’s about the same amount in each camera. More light means more information for the camera to deal with. Thus the colors are better and the image noise is better. At 1600 ISO this difference is noticeable, although Canon has done some amazing things to make the Xsi’s noise low.

Here’s the best example I can find, here are two pictures of the same thing taken with a 5D and a Rebel XT. The 5D had an 85L lens attached, the XT had a 24-70L. I processed both with the same program to look as similar as I could. Nevertheless, the differences in color and “pop” are huge.

First the 5D

Next the Rebel

Obviously not a completely fair comparison because of different perspectives and focal lengths, but you get the idea.

There is one other difference between the two sensor types, and that’s price. Crop sensors are way cheaper. However, times are changing. A new 5D can be had for $1900 or so, and used ones go for much less than that. (I bought mine used two years ago) A new 40D can be had for $1100 or so, and it has more bells and whistles than the 5D has. Plus, the 5D mkii is bound to come out soon, as is Nikon’s rumored D700 full-frame and Sony’s rumored A900 full-frame. Finally Canon will have competition in the pro-sumer full-frame market and if nothing else, it will drive the cost of the old 5D way down. So stay tuned!

Are there any advantages to a crop sensor? Yes! If you shoot with long telephoto lenses, you may like a crop sensor. It makes your pictures look like they were taken with a longer lens without having to crop anything out. Bird people and sports people would like this. Since I’m neither of those things, I’m biased but it’s worth mentioning.

So, now you know the differences between crop sensor cameras and full-frame cameras. Are crop sensor cameras bad? Not at all. Many amazing photographers started with them and many still use them. It’s really the person doing the button pushing that makes a photo good or not, but there are things that can help, and a full-frame camera is one of them.

If you REALLY want to nerd out on this and you find this explanation too simplistic (which was on purpose), go here:

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

(thanks to the guys at Dyxum for that one and for correcting me on some wrong phrasing!)

Comments? Questions? I’d love to hear them!

Up next: Primes vs. Zooms