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

or “Much Ballyhoo About A Molehill In A Teacup”.

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

I’ve been meaning to write about this one for a long time but never really got around to it until I got an e-mail from a listener asking about it. So let’s wade into the murky waters of Sensor Croppery.

This topic inspires a whole lot more confusion and argument than it really should. It’s both simple and kind of confusing simultaneously. Maybe because there are a lot of different misinterpretations floating around the web and people have dug their heels in on what they think is going on. On that note, I’ll do the same.

Keep in mind I am not a Camera Designer, nor a Sensor Engineer. Aside from the time me and a buddy created Kelly LeBrock I am not really a scientist. Weird. So what follows is MY UNDERSTANDING of what crop sensor is vs full frame.

Why The Difference?

(NOTE- Aside from mentioning it right now, we will not talk about megapixels in any of these posts. It is irrelevant to this discussion.)

Traditional 35mm film got it’s name from the fact that it is 35mm wide. Almost. In truth it is 36mm wide by 24 mm high. When the transition to digital was made that physical sensor size was mimicked. Really awesome, very expensive. But smaller sensors are cheaper so they started making those in order to make DSLRs available to more people. Different camera makers opted for different sizes (slight variables) but since I shoot Canon I’ll refer to those.

The so called “crop sensor” cameras feature a physical sensor 22.2mm by 14.8mm. These also became known as 1.6 sensors since 36/22.2 is approx 1.6. (And by extension the “true” focal length of lenses on a crop camera could be calculated by multiplying by 1.6. Thus, a 50mm lens is the equivalent of an 80mm on a full frame camera. Or is it? More on that in a later post.)

Before we dive too far into all the math involved let’s have a quick look at what is physically happening here through the use of a couple of diagrams. In the first one we see an approximation of the image your lens registers. Since your lens is circular, so is the resulting image.

The only thing is, we don’t capture the whole thing since we deal with rectangles. So when we employ a full frame (36mm x 24mm) sensor we capture this portion of the image.

And when we employ a cropped sensor (22.2mm x 14.8mm on the Canon) we capture this much of the image.

As you can see the smaller sensor captures what appears to be a crop of the larger image, hence the term “Crop Sensor” or “Crop Factor”.

So, does it matter? Well that depends. Some people say it matters very much and others insist it is entirely irrelevant. Good news is that both camps are right. I’ll explore how this all affects our image making (especially DEPTH OF FIELD) in the next few posts.

Stay tuned.

PART TWO