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Saturday, June 10, 2006

'Vignetting' 101

A man named David R. Stout has posted an interesting thread about vignetting issues with the Canon 5D camera on the dpreview Canon EOS-1D/1Ds/5D Forum (if our link doesn't work for you, go to the dpreview Forums and search for a thread called "5D Vignetting Survey."

The thread is illuminating (sorry) for a couple of reasons, and amusing for a few more—not least of which is the escalating level of David R. Stout's exasperation at having to deal with blusterers and blatherers who are obviously not reading his posts carefully, if at all. It does devolve into some smoldering and smoking, if not outright flaming, but along the way there are some interesting issues raised.

If you don't feel like reading the whole thing, the upshot seems to be that vignetting with the 5D can be a significant issue, unless you use the Canon 24-70mm "L" lens, which doesn't seem to suffer from it at all.

An 1886 carte de visite of a distant relative.

Vignetting (seen as excessive darkening of the corners of a rectangular image) is a tendency, of course, and like many issues in photography it's not entirely a technical issue, but partly an aesthetic one. Here are the Vignetting 101 Rules o' Thumb:

---------1. The actual technical term is "illumination falloff" or just "falloff." "Vignetting" really refers to isolating an image by letting the edges fade to nothing (see illustration above). Nevertheless, "vignetting" is what it's referred to, and you know how lenient I am about demotic usage, so I'll refer to falloff as vignetting like everybody else does. (Whee! Who, me, standards? It's a noun-issue.)
---------2. Vignetting is mostly a lens characteristic.
---------3. Vignetting is not entirely a lens characteristic (unless you're viewing an aerial image). It is in part an interaction between the lens and the recording media. Thin- or single-emulsion films, for instance, will exhibit more vignetting in the exact same circumstances (same camera, lens, scene, etc.) than thick-emulsion films. And of course we all have read many times about the requirements of digital photosites for perpendicularly-impinging light.
---------4. Some vignetting, called "physical," is just a matter of geometry. To illustrate this to yourself, cut a circle out of the middle of a piece of paper. Look at it straight on, then gradually angle the page until you're looking it it edge-on. Imagine the circle as the camera aperture, and you've just seen physical vignetting go from 0% to 100%.
---------5. Vignetting tends to be worse...
------------------a. ...the wider the lens (with the wider end of zooms being particularly prone),
------------------b. ...the faster the lens,
------------------c. ...the wider the aperture you use.
---------6. Vignetting is often hidden by complex subject matter, so it's more visible in clear skies or featureless walls and so forth.
---------7. Vignetting isn't always bad!

Illumination falloff incorporated to good effect in a Sally Mann photograph
(probably aided and abetted by burning and dodging)

In re #7, personally I would venture to say it's an advantage more often than it is a problem, for most people anyway. Master printers routinely "edge-burn" or "corner-burn" a print to "hold it in." This is trivial to do in ACR or DxO.

The funniest thing about David Stout's thread was a passing suggestion: if vignetting on the 5D bothers you, you can always crop the image.


That one got a laugh from me. Let's crop the sensor down to, let's say, 22.5 x 15mm....


Featured Comment (anonymous): "
For those interested, Here's a link to the best explanation I've seen about vignetting (falloff)."


Blogger falmanac said...

My 5D doesn't vignette any more than my 20D did with an S lens attached. (Specifically the 17-85S & the 10-22S) And heck, there's a great little tool in Photoshop that'll fix the problem in no time flat. (Disclosure: In the grand scheme of things I am an amateur photographer who'd most likely be called an indifferent printmaker by those who think of themselves as consummate printmakers. So feel free to take this with a grain of salt.)

4:44 PM  
Anonymous Anonymous said...

i just read some of that thread. geez, i love cameras, reading about cameras, talking about cameras... but reading the forums on that website just make me cringe at this point. i guess i just don't understand or relate.

has the age of the internet and the computer camera made the gearheads crazy? or just crazier? was it always like this?


7:51 AM  
Blogger Mike Johnston said...

Just crazier. It was always like this, but it's worse now.

My 2¢, anyway.


7:53 AM  
Blogger scotth said...

I wonder if the vignetting looks worse because of what digital does to the tonal range. I know when I look at some scenes I wil have more contrast in the file then I am seeing with my eye. I wonder if that same effect is making the vignette pop a little more.


11:28 AM  
Blogger Mike Johnston said...

Yes, high contrast and compressed dynamic range can both exaggerate tonal changes.


1:50 PM  
Anonymous Anonymous said...

For those interested, Here's a link to the best explanation I've seen about vignetting (falloff).

9:37 AM  
Blogger Mike Johnston said...

Wow, what a great page. Yep, that about covers it, with very nice illos too.


9:49 AM  
Anonymous Anonymous said...

An interesting read that sheds some light on full frame sensors and how Olympus adressed the vignetting & image quality issue, and why a bigger sensor won't help if you don't also scale the lenses accordingly:

11:57 AM  

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