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

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

In part one of this series we talked a little about the physical differences between a full frame sensor and a “cropped” sensor. Now let’s see what happens where the rubber meets the road.

This is where it gets a little complicated and the arguments start. For the sake of simplicity we will only deal with “full frame lenses” and not “cropped sensor lenses”. After reading the first post some of you may have wondered aloud, “If the sensor only uses a small part of the circle, then why not make a smaller lens with a smaller circle?” Well, they do. Canon, for example, makes a few lenses called EF-S that are designed specifically for the Crop Sensor cameras and are meant to be cheaper. The downside is that they do not fit on a full frame camera. In the interest of trying to compare apples with apples (if you are offended by that reference you are just looking for trouble) we will only compare full frame EF lenses.

The original listener question asked if there was a difference in the DOF when shooting with a 50mm 1.8 on a Crop Sensor camera vs a Full Frame. The answer is “NO, there is no difference.” Wait a minute. Sort of. So, “YES, there is a difference”.

Since I own a 40D (crop), a 5D mkII (full frame) and a 50mm f1.4 lens I decided to put it to the test.

Let’s deal with the “NO DIFFERENCE IN DOF” answer first. In order to demonstrate the difference I set up the shot with as many constants as possible- the cameras mounted on a tripod so the distance to subject is the same, aperture set to F4, shutter to 160, WB to Daylight, and the same 50mm lens for both shots. The only difference is the two cameras. Let’s compare the result-

Ignoring the obvious, let’s focus our attention solely on the DOF. To my eye it looks close enough to be called identical. And so it should, nothing has changed optically. Since the DOF is a function of the aperture, focal length, and distance from the camera and those values are identical in each shot we achieve the same DOF.

Remember though, that I did say it DOES affect our DOF. That part is still true but to illustrate we need to explore what is causing the obvious differences in these two shots. We’ll do that in part 3.

Stay tuned.

PART THREE

Adam and I have been talking quite a bit about flash photography on the show lately. The technology is such that shooting basic flash photos on AUTO settings is fairly straightforward and yields pretty reasonable results. But moving into more manual settings, while ultimately rewarding, can be daunting at first. However, if you can grasp one simple concept you will be well on your way to making great looking flash photos.

When shooting with flash you are essentially making 2 exposures. One for the ambient light, and one for the flash.

Allow me to illustrate with a couple of examples. Here you can see a photo I call “Flowers In The Hallway”. It is undoubtedly a terrible picture but it helps me illustrate my point and there’s no sense distracting you with a Rembrandt.

In this first set we establish the ambient light setting (i.e. the existing window light) and then adjust our bounce flash accordingly. First we start with no flash.

Next we add very little flash.

That barely makes a dent so we add more.

Starting to see some results so we add still more.

And a little more.

And finally we max out.

Full power is clearly too much so we would scale it back a little to get the effect we wanted. Notice in each picture that even though the flash was getting brighter we left the ambient light (the window) consistent? Now let’s try the opposite effect. We’ll leave the flash output consistent and adjust the window light.

In the first shot we overexpose the window to blow it out a little.

Next we reduce the exposure to include less ambient light.

And even darker.

And still darker.

Like our first example, notice how the flash exposure remains consistent while we alter the ambient exposure.

Tune in next week to hear Adam and I explain how to build a flash photograph and balance the two exposures. www.twohosers.com