The following series of posts were recently referenced on Episode 56 of The Two Hosers Photo Show.

I recently dusted off my Sigma 30mm f1.4 lens that I had been using with my Canon 40D. Once I upgraded to the 5D I figured that setup became redundant because I could achieve the same (except better) result with the full frame camera and the 50mm f1.4. I was right.

Then my “40D Walking Around 17-85mm” broke so I unretired the 30. I found myself in situations where I wanted to bring a DSLR but really didn’t feel like carting along the tool that buys my kid new shoes. Not that I would be thrilled if somebody spilled punch on my 40D but it wouldn’t be nearly as drastic.

So with that epic backstory behind us I decided to shoot a quick test comparing the 30mm on a crop vs the 50mm on a full. Buckle your seatbelts, here we go.

I tried to shoot both photos from the same angle and distance as best I could. Both cameras have identical settings but you can see slightly different exposure/colour results.

The first set was shot at f2.8 with the focus being set on one of the leaves of the tree on the beige t-shirt. Aide from the slight framing differences (I based framing on the focal points in the viewfinder. Turns out they are not identically placed in each camera…..) the images dont look wildly different to me. I would suggest there are subtle differences in the DOF as evidenced by the lettering on the beige t-shirt but if these weren’t viewed side by side I think you would be hard pressed to distinguish.

Where we do notice the difference is in the shape of the suitcase. Because we are using a wider angle lens to achieve the same framing as a standard 50mm lens, our perspective changes slightly. This results in the slight distortion of the suitcase. Once again I feel that if these photos were viewed independently nobody would complain about the warped suitcase, but when shooting a close up portrait of someone we might not be doing them any favours.

Next, I moved in slightly and cranked both lenses wide open to f1.4. In this case the focus is on the “A” in nature. This comparison illustrates the subtle difference in the shallow DOF.

I much prefer the image from the 5D but only when compared side by side.

Conclusion? This test confirms my earlier assessment that full frame is awesome and I recommend getting one if you can get it to pay your bills. If not, go with the crop sensor. You’ll save a few Deutschemarks and the chicks will still dig you.

The following series of posts were recently referenced on Episode 56 of The Two Hosers Photo Show.

One last note about crop sensors for now (I have not talked very much about EF-S lenses and I am not going to).

One of the catch phrases you hear with the crop sensors cameras is the “Equivalent Focal Length” or some variation. With the Canon sensors you get a crop factor of 1.6 (Nikon is 1.5) so you’ll hear a lot of folks saying things like “The 50mm lens on the 40D is the equivalent of an 80mm lens”. While there is some truth to this statement it is essentially a shortcut to explain what is actually going on.

True, the “Field Of View” is roughly equivalent to an 80mm lens in terms of how wide the camera can see but that’s about where the comparisons end. Because it is still a 50mm focal length cropped you get the characteristics of a 50mm lens.

I shot a couple of test pics to try and illustrate this point. The first photo was taken with a 50mm lens set to f4 on a Canon 40D (crop sensor). Next I made the exact same shot, from the same distance with a Canon 5D mkII (full frame) and a 70-200mm set to 80mm at f4. (Okay, I missed slightly and it was actually 78mm if you want to split hairs). Do these images look identical?

The two photos are fairly similar but on close inspection you can see the subtle differences you get when using a proper 80mm lens. In order to further illustrate this let’s try an experiment.

I shot two images of the same subject with my Canon 40D using my 17-85mm lens. I made the first shot zoomed all the way in at 85mm.

I then attempted to recreate the same shot zooming all the way out to 17mm. I didn’t change any other parameters (specifically distance from camera to subject). I then cropped in post to give me a similar framing, just as a crop sensor would do.

You can see a big difference in these two images in terms of Depth Of Field. Shooting a 17mm lens on a smaller sensor (crop factor of 5x in this case) is clearly not the “equivalent” of shooting with an 85mm lens.

Keep in mind that the results here are exaggerated by the 5x crop factor vs the 1.6x that we normally get. So while it is “similar” it is not “equivalent”. As I mentioned in the previous post however, I wouldn’t toss my 7D in the bin just yet.

PART FIVE

The following series of posts were recently referenced on Episode 56 of The Two Hosers Photo Show.

In parts one and two we talked a little bit about the difference between crop sensor cameras and their full frame cousins. Specifically we were asked about the effect on Depth Of Field. The basic conclusion was that sensor size does not affect DOF- when all things are equal.

That means that the same lens, same aperture and same distance from camera to subject yields the same DOF results. But obviously the pictures themselves are quite different. The initial assumption is that the crop frame sensor “zooms” in on the image but that is only partly true. In reality since it only uses the center part of the image it is in fact “cropping” the image but when printed the same size (in this case 800 pixels wide) it effectively zooms the image. Because the “zoom” is done in post it doesn’t have the same effect optically as a true in camera “zoom” would. Let’s have a look. (To recap- all images were shot with a 50mm lens at f4).

Here’s the full frame image again.

Now here is the image from the crop sensor as it would appear in relation.

Looking at the image you can see where the rest of the picture would be captured if we used a full frame. (NOTE- I actually tried to centre the image better than that but I missed. Sorry.) But to illustrate the point even further, let’s look at the two images laid on top of each other. The black and white is the extra picture captured the 5D’s full frame sensor.

So that’s where sensor size doesn’t affect DOF. Now let’s see where it DOES change the result. In order to achieve the same framing as one would get with the full frame 5d, the crop sensor user has to back up. Since one of the main factors of DOF is distance from subject to camera, and we are now changing that distance we can expect the DOF to increase (less blur).

Not only is our DOF affected, our perspective also changes slightly. Another way to achieve similar framing would be to use a wider lens on the crop sensor. For instance the 30mm 1.4 from Sigma is popular as a 50mm equivalent. However, since another main factor of DOF is focal length, using a shorter focal length with also result in a deeper DOF and a different perspective.

In the end the results in DOF don’t appear to be overwhelmingly different so my advice is to be happy with your crop sensor camera and go out there and make some great photos. Remember, it is likely 10 times the camera you were shooting with just a few years ago.

PS- I did shoot one more test, the results of which I will share in the final post in this series. Stay tuned.

PART FOUR