Sensor Size Confusion

The imaging sensor size in your camera does affect how you make your photography and some make a huge deal out of it. It’s my goal today to make a big deal out of nothing, or at least to help you understand my approach to it all.

This is Latitude Photography Podcast, Episode 61 for December 15, 2019!

Links Mentioned in today’s show:

Show Sponsor: Golden Hour Podcast by Polar Pro Filters

Neil Van Niekerk blog post on Depth-of-field comparison between sensor sizes:

The BEST DOF calculator out there by Cambridge in Colour

Fstoppers article

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Main Topic.

Today, we are talking about the effect that sensor size has on our image making. I’ve come across a few articles recently and have had some conversations about this with a few photographers, so it’s really fresh on my mind. 

I had planned on doing a gift guide, but I then decided that really just adds to the commercialism of Christmas and we have enough of that already, it seems that everyone and their brother is publishing a gift guide of some sort, so I decided to do something that’s a bit more in tune with what I’ve been thinking about these past few days.

The first article I want to bring your attention to was written over 5 years ago by Neil van Niekerk. It’s a good rundown of what happens to your image when you shoot with a full-frame vs. a crop sensor. The second article is one that was published recently by Nando Harmsen on the website. 

This article is less technical and simply draws attention the the many different sizes of sensors and things like different lenses needed to achieve the same field of view are discussed. 

But the final link I want to bring your attention to is the best Depth-Of-Field Calculator I’ve yet found which demystifies this whole thing. It gets rather technical so I’ll do my best to break it all down here for you, so let’s get started.

(review of crop factor etc)

To sum up the first article, the author goes through a very detailed step by step guide as to why we have shallower Depth of field on a crop sensor camera. What he fails to explicitly articulate is that by doing this comparison the way he’s doing it, we absolutely will get longer DOF simply because you need a shorter lens to get the same field of view. He referenced this article on Depth of Field by Cambridge in Colour but missed out one very key element. That is when we calculate DOF, we have to have a standard for interpretation. Since DOF is a sliding scale of sorts, who’s to say what’s in focus for me is also in focus for you?

That’s why we call DOF to be the items that are in acceptably sharp focus.

If you used a standard DOF calculator such as Photo Pills, and you were to put in the parameters of a Sony crop sensor camera, 28mm lens, f/8 and subject distance of 2 ft your calculated DOF is 5 and 21/32 of an inch. Switch that to a Sony full frame with the same paramaters, and your calculated DOF is 8 and 25/32 of an inch. 

Wait a minute. This means that the smaller sensor is shallower DOF? How can this be?

This is where most folks usually, including me, just give up. 

I used to like to say this is all bunk because what if you have that full-frame Sony, and you shoot an image in crop mode and one in full-frame mode. You’ve done nothing else yet the DOF still changes!? How can this be. It’s stupid right? Yet it does change, even if you’re on the same exact camera.

Further explanation

This is where we bring in this idea of the circle of confusion. In short, the COC is simply the smallest perceivable detail for what you’re looking at. So a standard must be set for calculating DOF. You probably didn’t realize it but in general, all your DOF calculations have been based on your photo being translated to an 8×10 print and being viewed the distance of 1 foot. It’s important to know the physical size of the image because that means that the physical size of the sensor is also important in determining DOF. 

Since the physically larger full-frame sensor doesn’t have to be enlarged nearly as much, it has LONGER DOF all things being equal. Please notice, if you leave all things equal you will have a different field of view between the full-frame and crop sensor cameras. If your goal is to have the same perspective between the two systems (FF and crop sensor) then you will alter your DOF because you’re using a physically shorter lens. 

Let’s examine this one more time using the DOF calculator on the Cambridge In Colour website. Here’s my parameters:

Max Print dimension: 10 inches

Viewing Distance: 25cm (almost one foot)

Eyesight: standard

Camera Type: 1.5 crop factor

Aperture: f/8

Focal Length: 28mm

Focus Distance: 2 ft.

Total DOF: .51 ft.

Those of you with magnificent memories will remember that my previous calculations were just under (barely) six inches. That was also based on a slightly longer viewing distance of 12 inches, not the slightly less 25cm as this one is. So we’ll go with this calculator from here on out.

Let’s change it to a full frame, that’s the only change.

Calculated DOF goes from .51 ft to .79 ft. That’s the same type of adjustment we saw in the previous example where I was using the Photo Pills App.

Now let’s leave it full-frame from here on out. And let’s leave the camera settings alone. Let’s change the print size to 14 inches and see what happens to our DOF.

The DOF goes from .79 ft. to .55 ft. WOW. So when you make the print larger, the DOF gets shallower! Nothing else changed! I don’t know about you, but this is blowing my mind. Let’s now change the viewing distance to 50cm.

We’ve about doubled the DOF just by increasing our print viewing distance. It’s now 1.17 ft. 

So what does this really say about DOF and all that?

It means that DOF is truly subjective based on many different parameters beyond your camera, lens and distance to subject. It’s based on the perception of acceptably sharp focus. As you move that print further and further away you’re less and less able to see the fact that something is literally out of focus. Therefore we define acceptably sharp focus to be a greater depth within the frame.

One more calculation, changing it to 1 meter print viewing distance increases the total DOF to 3.08 ft. 

So in review, just by changing our print size from 10 inches to 14 inches we decreased the DOF. But by increasing our viewing distance on that 14 inch print we then increased the calculated DOF. This, of course, assume you have standard vision. If you have 20/20 vision the DOF on that large print at 1 meter in distance goes from 3.08 ft to .75 ft again. So if you have good eyesight calculated DOF is different for you too. Makes sense, with out glasses calculated DOF is terrible for me because everything is a blur. With my glasses I have near 20/20 vision so that’s where I would want to look for calculations that have meaning for me.

Your takeaway

It’s easy for us to get bent out of shape over sensor size and how the DOF is a reason for one way or the other as you argue the benefits of one sensor size over the other. 

In reality, we’re usually way more concerned with the perspective and field of view of the scene first, and in that case, yes, a smaller sensor will need a shorter lens to render the scene before you the same as a larger sensor camera, therefore giving you much more DOF. But the primary reason that’s changing is that the lens itself has changed. 

that’s something that’s easy to see and understand. But it goes so much deeper than that. There’s perception and viewing that’s part of it too. And understanding DOF and how it really works in camera may help explain why your focus stacked image didn’t work out the way you thought it would. It might explain why f/4 on that shot really isn’t working the way you envisioned it. Are you viewing it on your phone or a large print? The calculated DOF will be different for those two very different viewing experiences. 

Assignment for January

In keeping with this theme I have an assignment for you. I want you to go out and shoot something with a long and shallow DOF. Same subject, same framing as much as possible anyway. And then post them to the FB group with your commentary on why you like one over the other. Have something distinctly present in your foreground and have a reasonable background. Do this by January 3, 2020 and I’ll talk about the results in a future episode in January. You can also email them to me at if you’d rather not email. I will plan to put these into the show notes and a new fb group post for the show. Please give me a link you’d like to send folks too as well and we’ll be sure to link that in the show notes.

Tip of the week

Today’s tip of the week has nothing to do with DOF, lenses or anything like that. That would be too easy. Today’s tip is to shoot without actually looking through the viewfinder or the LCD screen. It can be from your hip or hold the camera high. You should look at something, concentrate on it, zoom your lens or walk closer or further away to frame your subject in a way that you envision. Once you’re done go ahead and check your results. Do this over and over with different subjects until you get “good” at it.


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