full-frame vs crop-sensor comparison :  depth-of-field & perspective

When the differences between full-frame and crop-sensor cameras are discussed, there is an inevitable question about whether the crop sensor multiplies the focal length. Whether a 50mm lens on a crop-sensor acts like a 75mm lens (on a 1.5x crop sensor) or 80mm lens (on a 1.6x crop sensor).

The answers given on the photography forums are confusing – yes, the focal length effectively increases. No, it doesn’t. Two polar opposite answers. The discussion (which tend to devolve into arguments) are convincingly made for both sides. The reason is because the topic is a complex one … and therefore the answer is (kinda) complex too.

One argument goes along the lines that the crop sensor is just that, a crop. An enlargement. That nothing changes – you just get less of the scene. And that there is no “equivalent focal length” when you go to a crop sensor camera. But what really happens is more complex than that.

With this article, I want to help analyze what happens when you change lenses between a full-frame camera and a crop-sensor camera. And we’ll analyze whether there is actually an equivalency between certain focal lengths, when using a crop-sensor camera. In other words, whether your 50mm lens becomes “equivalent to” a 75mm or 80mm lens when used on a crop-sensor camera.

Since this article ended up being a long meandering discussion, I thought it best that we start with the final summary. Just to save the impatient people some work.


Yes, a 50mm lens does indeed behave like an equivalent focal length of a 75mm lens (on a 1.5x crop sensor), or an 80mm lens (on a 1.6x crop sensor) … however, the depth-of-field increases by about a stop.

Yes, a 100mm lens on a crop-sensor camera will give you the same perspective as a 150mm / 160mm lens (on a full-frame camera), if you don’t change position … however, the DoF increases.

But let’s discuss this with some images:

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Using your lens’ bokeh as a design element

In previous articles we could see how a fast 85mm can be used for shallow depth-of-field to shoot nearly anywhere by melting away the background. There’s another aspect to this – the bokeh of the lens. The bokeh is a reference to how the quality of the background blur is rendered by a lens. It can be smooth, or have “jittery” patterns to the edges of objects, and the highlights.

Do note though that bokeh and shallow depth-of-field are not quite the same thing. While the DoF / choice of aperture does affect the appearance of the bokeh of a lens, the shallow depth-of-field look isn’t “bokeh”. Similarly, you can’t do something like “add more bokeh”. Bokeh is the quality of that background blur. It’s mostly an aspect of the lens design.

Now, very often, when a fast prime lens is used wide open, there’s a kind of swirly feel to the background blur – and if you’re aware of this, and find an appropriate background, it can really accentuate the portrait.

The image at the top of Jen & Corby, was shot at f/1.4 and you can see how the background behind them has a distinctive circular swirl to the out of focus high-lights.

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bokeh comparison: Sony RX1 vs Nikon 35mmm f/1.4G

Sony has been on fire recently with their new camera releases. The Sony RX100 is arguably the best point&shoot on the market right now. The full-frame Sony A99 DSLR has been getting great reports … and then there is the new Sony RX1 (vendor) – full-frame goodness in a compact camera with a fixed 35mm f/2 lens.

And just in anyone has missed the crucial news – Sony cameras use Zeiss lenses. The word “legendary” is usually automatically associated with the word Zeiss.

A quick summary of what makes the Sony RX1 unique:

The full-frame sensor promises excellent high-ISO noise performance, and the Zeiss optic promises stellar performance from the lens. With that, there’s been a lot of buzz about this camera … and I have one in my hands.

So far, I am hugely impressed with this camera. The build quality is solid. It has a certain heft for such a small camera. The lens is incredibly sharp. (More about that later.) The 1/3rd stop indents on the lens smoothly click into position. This camera just speaks “quality!” Even the lens cap that clips on solidly, is made of metal!

Instead of a breakdown of the specs though, I thought it might be more interesting to look at one specific aspect of this camera & lens – the bokeh of the lens.

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photo session using various 85mm lenses  (model: Jess B.)

A fast 85mm lens is an essential addition to any camera bag, whether an f1.8 or f1.4  or even an f1.2 aperture. With their shallow depth of field, and the pleasant perspective for portraits (when not used with a super-tight composition), these lenses will have your subject just pop from the background.

Jessica and I are busy with a new project – testing various 85mm lenses – specifically for how their bokeh appears in comparison. It is proving a tad more difficult than I had hoped for to show when poor bokeh is truly distracting, and when a lens with great bokeh is immediately superior. But then, the deep-freeze temperatures here recently hasn’t helped us either in scouting for locations. But we’ll still get there. (So this is not the comparative review yet.)

In the meantime, I wanted to show a few images off. They were all shot at wide apertures, using only the available light wherever we were.

The photograph above was taken on the steps inside a train station, using only the available light streaming in. In posing Jessica, I made sure that the direction of light made sense in creating open light on her face.
1/250 @ f1.4 @ 800 ISO
Canon 5D mk II (B&H);  Canon 85mm f1.2 II (B&H)

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creating a background with narrow depth-of-field & great bokeh

Shooting images for the review of the Nikon 85mm f1.4G AF-S lens, it struck me how truly superb this lens is. It improves on the legendary Nikon 85mm f1.4 AF-D lens in some key areas. (For me the updated lens was an immediate upgrade.)

But ultimately, you could get similarly beautiful images with any short portrait lens that gives you a very narrow depth-of-field AND has great bokeh. (Just to reinforce that again .. narrow DoF and bokeh are not the same thing. But I digress.) So, whether you’re shooting with a Nikon 85mm f1.4 lens (B&H), or the Canon 85mm f1.2 (B&H), or Canon 85mm f1.8 (B&H) … these images are easily attainable. It is more about the technique and thought-process and approach, than any specific piece of equipment. However, you do need photo equipment that enables you to achieve what you want to, technically and stylistically.

So walking around with Anelisa in New York, looking for great backgrounds I saw this fantastic Art Deco styled exterior of a diner. And I knew that with the various colors and shadings in the late afternoon, it would give beautifully colored reflections at various angles. Here is the pull-back shot …

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bokeh – a few notes

October 26, 2010

bokeh – quality of lens blur

The way that a specific lens renders the out-of-focus areas in the background (ie, the bokeh of the lens), is always an interesting aspect of any lens’ behavior. If the out of focus areas show hard edges, or highlights with a kind of double edge, then the bokeh can appear intrusive. Then it is called harsh bokeh. If the out of focus areas are smooth without the edges being defined, then the bokeh is described as being pleasant. And then on occasion, you get bokeh that is … well, let’s just call it ‘interesting’.

I noticed that the Nikon 105mm f2.8 VR macro (B&H) can at times show a weird circular swirl in the background. It is especially noticeable if there are bright out of focus highlights. The photo at the top shows this clearly, even with a background that should appear smooth. In comparison, we can see how the famed Zeiss Makro-Planar T* 100mm f/2 ZF (B&H), renders the highlights. Smooth. Just as you’d expect from a lens with such a reputation.  (Both images were shot at f2.8 although the Zeiss is capable of f2 which is exceptional for a 100mm macro lens!)

Just for interest here, I thought of showing how a few other lenses compare in how they render the background …

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shallow DoF / depth-of-field is not the same thing as great bokeh

The first thing you might notice in this image is our super-cute model, Johannie.

Next you will probably notice either:
– the strange background pattern, (due to this lens’ bokeh),
– or the wafer-thin depth-of-field of the Nikon 50mm f/1.4D used wide open
– or the lighting on her, (a reflector),

These are all inter-related in some way for this photo …

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bokeh – the quality of blur

Bokeh is the term used to describe the quality of background blur in a photo,

i.e. how pleasing the blur looks of the background areas. Since the softness of the background blur is usually more important than how the foreground items are blurred, bokeh usually relates to the background blur.

The bokeh of a lens is influenced by numerous factors, including
– the lens design,
– specifically, how spherical aberrations are corrected,
– the number of blades in the aperture mechanism,
– focusing distance,
– the actual aperture used will also affect bokeh to some extent,
– the distance of the out-of-focus objects,
– and in the case of the Nikon DC lenses, by how certain aberrations are selectively introduced.

Bokeh is usually described as being subjective, and it largely is.  However, when you’re able to recognize the difference between good bokeh and poor / harsh bokeh, then it becomes less subjective I believe. When you see good bokeh, you’ll recognize it. Same with bad bokeh.

To illustrate how good bokeh appears, and what poor bokeh looks like, I had set up this simple shot.

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