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.
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?
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.