wrapping head around lens markers and "equivalents"

[Mike Barber]

i don't shoot with an EX1/3, but i need to send someone remotely with an EX1 out into the field to do a shoot and i'm afraid they're a bit green when it comes to the more nuanced aspects of cinematography. i want to make sure that when they set up their interview shoots, that medium-wide shots aren't distorting the body (as i have seen on a few shots where they shoot too wide).

so i want to give them guidelines on what to set their camera to when it comes to shooting the interviews, but i don't entirely understand the "35mm equivalent" markings on the camera, and it's causing some confusion in some discussions.

ok, i get that different cameras will have different crop factors depending on their sensors that can be explained with "35mm equivalent" figures to help one correlate fields of view.

so if one were to have, say, an A camera that's a full frame canon 5d and a B camera that is an EX1, and both needed to have similar framed wide shots (say the 5d used a 28mm prime), one would need to calculate 28mm x 0.6 crop to get 16.8mm for the EX1, so that's the marking that they would use on their lens, right?

but that's just to match the field of view, right? all we're talking about is matching frame sizes, right?

what about z-space compression? isn't that EX1 sets at 16.8mm going to act like a 17mm lens where distortion and z-space is concerned?

if i want a close up to look like it was shot with a 50mm prime (regarding spatial compression, not necessarily DoF or FoV… so ignore cropping for the moment), then am I telling them to set the EX1 lens at 80mm??

[Zoran Vincic]

Originally Posted by Mike Barber

so if one were to have, say, an A camera that's a full frame canon 5d and a B camera that is an EX1, and both needed to have similar framed wide shots (say the 5d used a 28mm prime), one would need to calculate 28mm x 0.6 crop to get 16.8mm for the EX1, so that's the marking that they would use on their lens, right?

you've got that wrong.

5D is a 35mm full frame camera and ex1 is 1/2'' sensor camera with a crop factor of 5.4.

28/5.4 = 5.2 - that's the focal length you need on the ex1

16.8mm on the ex1 equates 90mm in 35mm format, not even close to wide angle.

if i want a close up to look like it was shot with a 50mm prime (regarding spatial compression, not necessarily DoF or FoV… so ignore cropping for the moment), then am I telling them to set the EX1 lens at 80mm??

no, you'll want it at roughly 9.2mm

[Doug Jensen]

Mike,

You might find this FoV calculator at Abel helpful.
AbelCine - Field of View Calculator

[Mike Barber]

Originally Posted by Zoran Vincic

no, you'll want it at roughly 9.2mm

ah, so i had my numbers mixed up…

the ex1's lens focal length (zoom) range is 5.8mm to 81.2mm…

so in terms an ex1 user would clearly understand -- to refer to the zoom marking on the ex1 lens -- if i want to specify a focal length that is akin to what a 35mm shooter would use for a portrait (between 50mm and 85mm), then i should tell the camera op to use between 10 and 15?

[Olof Ekbergh]

The classic portrait lens is 85mm (or 70-100 range).

The reason for this is that the features of a face look the most like what the human eye sees.

If you go wider the nose gets bigger and the ears smaller.

If you go longer the face gets squashed, ears seem bigger and nose smaller.

This does not change with the size of the chip. Only the angle of view changes. This is one of the main reasons the 5D's and even C size cameras are so popular for talking heads. I now use a FS700 for most of my interviews, but I also use a 5DmkII and a 7D at times for multi cam setups. In my opinion the 1/2" chip cams still are the best ENG cams, they are so easy to nail focus with. My EX3 is my go to ENG cam still.

Another advantage to the 85mm range is that the BG is nicely out of focus, f4 is a nice setting for an interview with this focal length.

Yes this does mean you have to back up more with smaller chips. And with larger chips you can be closer.

Like any "rule", it should not be always obeyed but is a guide. With my EX3 I tend to shoot a lot of interviews at about 50mm, this is a pretty good compromise in tight situations.

And don't forget the eye light, the new compact LED lights are great for this.

[David Heath]

Originally Posted by Mike Barber

so in terms an ex1 user would clearly understand -- to refer to the zoom marking on the ex1 lens -- if i want to specify a focal length that is akin to what a 35mm shooter would use for a portrait (between 50mm and 85mm), then i should tell the camera op to use between 10 and 15?

This is becoming overcomplicated, and some points made are just wrong.

Let's understand exactly what the potential problem is, and that is distortion of the body through perspective. You'll get the problem when the distance to the subject (measured to the eyes, which should be the point of focus) is not SIGNIFICANTLY more than the nose-ear distance. Big question then becomes how much is "significant"? Personally, I'd say about 10x is a decent minimum, so if we take about 4" as a figure for how much the average nose is in front of the ear, what it boils down to is that camera-subject distance should always be AT LEAST about 1 metre to avoid the worst effects of distortion of features.

And really, that's it. No need to worry about focal lengths, 35mm equivalents etc - to avoid distortion - just don't get too close. End of story.

If you say "use a focal length on your EX1 of Xmm", and the cameraman finds themselves in a confined space, it's not stopping them filming from (say) 50cm away - and getting both a too tight shot AND distortion!!

Now the figures of 10x, 4" and 1 metre are obviously open to debate, and I'll accept that there may be an argument in favour of more than 10x, therefore further than 1 metre. But it becomes a law of diminishing returns. The further back you go, the less the difference becomes and a bigger distance can cause practical difficulties in all sorts of other ways.

And the further back you go, then obviously for any given focal length lens, the more of the body that gets seen. Which is where the 80mm focal length comes in, and here I must fundamentally disagree with what Olaf says. There is nothing magical about that number, and it has EVERYTHING to do with the size of the chip. (Or photographic negative, when I first did my theory!)

Quite simply, 80mm is the focal length needed *for full frame 35mm* to get a normal head and shoulder portrait whilst keeping the camera about 1-2 metres from the subject.

For full frame 35mm it's the focal length that gives an acceptable angle of view for a normal portrait, without getting so close as for features to become distorted.

For a large format camera, 80mm would give far too wide an angle - you'd need to either accept a portrait of far more than head and shoulders - or go closer and get the distortion. For a negative or chip size smaller than ff35mm it won't give distortion - but will mean that for normal size framing the camera must be what may uncomfortably far back.