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Qualian
04-08-2010, 07:14 PM
Hello,

I want to do one of those anamorphic distortion pavement drawings that look like they are standing up from the floor due to getting bigger as they get further from the view point, to negate the effects fo perspective making things seem smaller in the distance. Something like this:
http://www.quickonlinetips.com/archives/wp-content/uploads/waterfall-painting.jpg

To make it easier for myself, I want to take a photo of the street scene I intend to do the drawing in/on, with the camera at the viewing point that a human viewer would look at it from with their naked eyes. I would then get this photo and use it to plan the drawing.

For this to work, i need the lens angle of the camera I take the photo with to be the same as the lens angle of the human eye, or at least very close to it. Can any optics experts out there tell me what camera settings and lens I would need to do this? Ultimately, I would be able to tell if it has worked by tracing the photo as linework onto a piece of glass, then took that piece of glass out to the photographed street scene's viewing point, held it up in front of my eye and found out the lines on the glass register pretty closely with the real world scene seen thru the glass/linework.

Thanks.

halen
04-09-2010, 11:06 AM
Traditionally 50mm lens with 35mm film/sensor cameras is consider having similar perspective than human eye, with crop factors (http://en.wikipedia.org/wiki/Crop_factor) 1.5 (Nikon cropped SLRs) or 1.6 (Canon cropped SLRs) its around 32mm or 33mm. If using pocket camera you need to know the crop factor or just experiment and check info from images metadata.

Angle of view is different for every person, something (hints of a movement) can be seen almost straight to the side and then there is just quite narrow area of accurate view. Humans also tend to move eyes rapidly when looking at something. But what you probably need is that perspective is quite similar with those lenses mentioned. Formulas for calculating angle of view with lenses can be found here (http://en.wikipedia.org/wiki/Angle_of_view). There is already an example for that 50mm lens.

jeremybirn
04-10-2010, 04:32 PM
The most important thing to match is the POSITION of the camera. Your "perspective" really comes from the position of the camera, not from the lens.

Think about how tall the average viewer will be (ie. if there are a lot of kids in your audience, choose a lower average height), and how far back they'll be standing where you want the maximum effect, and then snap the picture from there.

Use a prime lens (a lens that isn't a zoom), or a good quality zoom lens with low distortion (you don't want barrel or pincushion distortion warping the image.) Yes, something in the 25-50mm range lens on a dSLR might be great. But if a wider view of the scene from an 18mm lens would let you plan the drawing out better, remember that changing the lens length by itself won't change the perspective.

-jeremy

halen
04-11-2010, 08:03 AM
The most important thing to match is the POSITION of the camera. Your "perspective" really comes from the position of the camera, not from the lens.

Agree with half of this - average position of viewer is important and any of this thing with lenses has any meaning after it is set. Earlier just assumed that this has already been done. :) But after that, lens really has an effect too - if you take that average position and switch from tele to wide, you'll get quite different images. Tele tends to flatten perspective and wide lenses tend to give more artificial depth (with wides things are getting smaller towrads horizon mutch faster than with teles, if that's not change in perspective I just probably don't know the right words, but there is a change in how you'll see the image). If you want to stand in that position where you think that your average viewer is looking the image and see it the same way - you'll need to select lenses accordingly.

But if a wider view of the scene from an 18mm lens would let you plan the drawing out better, remember that changing the lens length by itself won't change the perspective.

Or you might just take several ovelapping pictures and stick them together and keep the lens closer to the "right". But since with these kind of images there is probably no way to set only one viewing point and there are already a lot of averages - I'll think that you'll get good enought result just by going there and taking enought references by approximating it right. :D

Good luck with the image. :)

Quadart
04-11-2010, 01:05 PM
Jeremy’s statement “The most important thing to match is the POSITION of the camera. Your "perspective" really comes from the position of the camera, not from the lens.” is wholly true.

At fixed camera positions, different focal length lenses merely zoom in or out from a particular area of a scene. If you take a photo of a car parked 300 feet down a road with a 200mm lens and then with a 50mm lens you will notice a size difference between the cars in the photos, but the perspective and framed area of the telephoto image will be the same in the wider shot. The entire telephoto scene is simply reduced within the image produced by a wider angle lens. Telephoto lenses produce images with ‘flattened perspective’ because they zoom in on distant subjects that are in regions of more compressed perspective to begin with. The rate of perspective compression or diminution decreases with distance, hence the effect of perspective flattening as you use lenses with greater magnifying focal lengths.
-----

Here’s a quick tute on making anamorphic sidewalk art:

http://www.instructables.com/id/How-to-do-3D-Anamorphic-Artwork-and-Sidewalk-Stre/

halen
04-11-2010, 01:34 PM
My apologies. :shrug: You are right about the perspective. I engaged my writing before my brain - which seemed to be stuck first with different angles and then with the idea of taking the "same" picture (an image with same crop) with different lenses, where obviously camera has to move and perspective change. I'll live and learn...:cool:

Still I'd use "normal" lenses for easiest match. :D

Qualian
06-29-2010, 01:36 PM
Thanks for your help so far...another question that might make me sound like an idiot and certainly makes me realise I have forgotten all my college photography:

When we say a '50mm lens', are we talking about the distance between the lense and the surface that records the image (film or sensor)? And the greater the distance from the recording surface the less curved the lens must be?

I want to simulate this in Maya - so in Maya, I have entered the Focal length as 50 - but is that entry field in millimeters? if so, is the world units in MM? In other words, if i want to view a 10meter X 10meter surface throught a 50mm lens, should I create a surface of 10000(mm) X 10000(mm) to be viewed through a lens with the number 50 entered into the focal length field? I might sound silly here, but I'm not sure if Maya keeps its units consistent in all entry boxes.

Then, what would I enter the Angle of View as, to match as closely as possible the average human eye?

And what is 'Camera Scale' in Maya? Should I leave that at 1?

jeremybirn
06-29-2010, 06:21 PM
Maya's 50mm is indeed like a 50mm lens on a real camera. The default "camera aperture" settings of 1.417 x .945 inches mean it matches a lens on a 35mm (still picture) camera. (With different film gate settings, it could match a 50mm lens on cameras with other film formats or sensor sizes.) Yes, leave the camera scale at 1.

See my answer above regarding the focal length (or angle of view) of a human eye. Focus 100% of your attention on matching the perspective (camera position) of your viewers, and then set the focal length or angle of view so as to fully cover the scene you need to depict from that perspective.

A human eye sees most of it's detail within a very narrow field of view, like looking at one word on a printed page. It also samples with a much wider field of peripheral vision at a lower resolution, with more attention to moving objects than still in this area. But the eyes are always darting around, sampling different parts of the image at a high resolution, and your brain puts together a bigger higher-resolution perception based on that.

People's eyes will be scanning the image you rendered just as they would scan a real scene. The eye is not something that needs to be simulated, because it's really there, whether people's eyes are looking at the scene you rendered or a real environment. What you are simulating is the scene you put in front of a person, not a person's eye. The person's eye will still be there when they are looking at your rendering, so just focus on matching the perspective correctly without regard for the size of the print or the field of view.

-jeremy

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