Ask MetaFilter posts tagged with optics

Bokeh galore

johannahdeschanel — Fri, 12 Sep 2008 13:38:55 -0800

What are some of your favourite bokeh lenses and settings for head-and-shoulder portraiture?

No, I won't just mug a FIOS installer

boots — Fri, 01 Aug 2008 12:58:43 -0800

Where can I buy fiber optic cable in a brick-and-mortar store in NYC? Small quantities only. Thanks.

What's that material that swaps between images as you tilt it called?

paul_smatatoes — Sun, 01 Jun 2008 07:26:22 -0800

What's the proper name for that kind of image-switching material that switches between two pictures as you tilt it? I mostly associate it with novelty baseball cards, toys, children's books, and so forth. That plastic-y corrugated stuff? If I wanted to order a bunch of postcards printed with it, what am I looking for?

Tips for working with optical fiber?

Mapes — Thu, 03 Apr 2008 11:09:54 -0800

Tips for working with optical fibers (stripping, cleaving, aligning, etc.)? I'll soon start working with an infrared laser and optical fibers as part of my research. Unfortunately, my lab colleagues don't have much experience in this area. Can you recommend any books or websites that would have useful tips on operational details such as stripping, cleaving, and aligning? Really, any tricks of the trade would be appreciated.

(Regarding safety: I'll have the safety folks approve any setup before I start working with it. This is a 1W 1064nm laser accompanied by a visible guide laser, output from an uncollimated single-mode fiber, and it will be used inside an enclosure in a light-tight room by an operator wearing OD 5 eye protection.)

Is that a UFO or just some guy in a BMW?

le morte de bea arthur — Mon, 03 Mar 2008 02:02:09 -0800

I've noticed that many cars seem to have headlights that change colour depending on angle. Is this deliberate or unintentional, and how do I avoid buying bulbs that do this? What I've observed is that these colour changes occur as the road rises and falls, or as I round a bend. This is not a subtle effect - I see all kinds of vivid colours flashing in my rear view mirror. I find this very distracting. At just the right angle these lights can briefly mimic the lights of an emergency vehicle, which is obviously not a good thing.

My initial guess is this is due to chromatic aberration or something, rather than being intentional. But is it? Can anyone enlighten me further? Are these things legal (specifically in the UK)? What should I look for in a new set of headlight bulbs so that other drivers won't curse me at night?

Are square lenses better?

Popular Ethics — Mon, 03 Dec 2007 20:45:37 -0800

Optics geeks: Why do some cameras matte off a rectangle in front of the lens like this? I see this a lot with (cheaper) point and shoot cameras, film cameras, but not SLRs. Does masking this way cut down on flare? Would the square aperture reduce light to the sensor. Would it make for funny diffraction or bokeh?

Just curious why the two approaches.

What to do with a ruined zoom lens?

kcds — Tue, 20 Nov 2007 08:39:02 -0800

What can I do with a "ruined" autofocus SLR zoom lens? Anything cool/neat I can turn it into? Any fun optics demonstrations I can do with the lenses inside? I have a Canon EF 35-105mm zoom lens that has recently become surplus to my requirements. When I tried to sell it to a camera store, they examined it and said "no thanks, it's got fungus inside it" - and sure enough, when you hold it up to the light, there is some kind of crap inside it, and I'll take their word for it that it's fungus. I could probably sell it on eBay 'as is' for $5, but I'd much rather doing something fun or neat with it, especially given that it's basically otherwise worthless, and I can't really do any more harm to it at this point.

Any neat project ideas? Can I turn it into a $10 Lensbaby ripoff? A $5 telescope? Anything cool I can do with the focusing micromotor?

Light source that compensates for orange mask in negative film?

Joakim Ziegler — Thu, 20 Sep 2007 20:27:02 -0800

Let's say I'm toying with the idea of making my own scanner for negative film. I've found a suitable sensor, and the rest of the mechanism looks manageable. Can I get a suitable light source that will compensate for the orange mask, at a reasonable price? Basically, I'd like suggestions for a good, stable, even light source of a color that will compensate for the orange mask in negative film. I could just do this by trial and failure, but I'm sure there are some standard light sources for this somewhere, perhaps something used to optically duplicate negative film? I'm basically going to put a high-res CCD camera on the other side of the film, focusing through something like a Printing Nikkor, so what I need is a light source that'll light one frame of 35mm film evenly, with a color that will get rid of as much of the orange mask as possible (I guess I can do some detailed calibration in software afterwards).

How do hybrid EO/IR systems work in UAV applications?

arimathea — Thu, 30 Aug 2007 09:38:07 -0800

How do hybrid EO/IR systems work in UAV applications? I know next to nothing about optics or optical systems and i'm pretty weak on physics, but i've recently become very fascinated with UAVs. I've been reading about hybrid EO/IR systems, where the aircraft senses both optical information (e.g. pictures) as well as infrared photos. I understand roughly how a gimbal and gyroscopes work for positioning the camera as well as how the camera knows what it is looking at in terms of positioning, but what I don't understand is what an actual assembly looks like. Is there a lens that is used to magnify the incoming IR wavelengths? Is it usually the same lens for multiple sensors with some kind of prism or beam splitter? Can you provide more detail? I've tried to do a little research but the background I'd need in optics is more time consuming than makes sense for me.

Optics n00b question

garethspor — Tue, 15 May 2007 18:36:18 -0800

Optics n00b question: I'm working on an art project wherein I etch drawings onto glass and then project shadows of said srawings onto a wall. I've done this before using an overhead projector as a light source and it worked great. This time around I bought some lights that don't work quite as well... I bought a couple of these, learning the hard way that what I need is some sort of point source lighting to make the kind of crisp shadows that the overhead projector made. What I'm wondering is if there is some sort of optical apparatus such as a lens or whatnot that I could mount to the front of these lights to change their properties. Or, failing that, some sort of cheap alternative to buying more overhead projectors? Any help is appreciated!

tap that glass

fake — Thu, 28 Dec 2006 13:51:50 -0800

I'm interested in fitting odd lenses -- and making custom lenses -- to/for digital cameras and digital video cameras. I'm not terribly concerned with the electronic side of things, so you shouldn't be either. What I'm looking for is a crass/crash course in optics -- something (a book, a video, a class, a kit) that will teach me the basics of optics and allow me to force photocopier lenses, telescopes, and microscopes onto unsuspecting recording devices.

optics on different cameras, how can I get consistency?

tip120 — Wed, 13 Dec 2006 07:48:49 -0800

2 different cameras, 2 lenses, how can I get the closest possible recreation? Using this firewire camera as a reference, with a lens that has a focal length of 2.8mm-8mm, what sort of lens would i need on a 35mm camera, or digital SLR, to recreate the angle on an object from 7 feet away?

Please if it's the same super, and please forgive my ignorance. If it is indeed something different, what's the equation to figure it out?

Weird optics

aye — Sat, 21 Oct 2006 20:44:20 -0800

Let's say I find a shiny spherical object and under point lighting, I move it very close to my eye. I then focus on the bright spot, but focus at a distance of 1-2 feet until the patterns are in focus. At this point, it looks like a bad microscope. Am I looking at part of my own eye? Is this a documented phenomenon I could read about?

Peering into the depths of AskMe

Popular Ethics — Thu, 20 Apr 2006 21:17:54 -0800

Attention optics geeks: Will a flat water/air port affect a lens' minimum focus distance? I have a very specialized lens application at work. We need a long telephoto zoom lens (>500mm) which will look through a flat port into a tank of water. I have found a lens [pdf] which meets all of our specs except for one - the minimum focus distance is too long (5m, we need to focus as close as 4m).

I know that the water/air port will increase my effective focal length by about 33%. What I'm wondering is whether the light-bending power of the port might also reduce the minimum focus distance from the manufacturer quoted air-value.

(This isn't my area of expertise)

Do children see darkness as "blacker" than adults?

bugbread — Sun, 09 Apr 2006 07:05:59 -0800

Do children see darkness as "blacker" than adults? When I was a child, I noticed that in supposed "pitch darkness", I actually saw a large number of really small red, blue, green, and other colored points (somewhat like if you look at a low res digital camera photo of darkness). As an adult, it seems that there are more of these points than there used to be.

I can think of 3 possible likely interpretations:
1) Adult eyes, for some reason, do in fact see more of these dots.
2) It varies from person to person
3) It's my imagination that the number has increased.

Which is it? And, if #1 or #2, why is it?

best binoculars?

snsranch — Mon, 30 Jan 2006 20:03:26 -0800

Re: binoculars. What do I look for and what is the best for my money? We are hiking/mountaineering with kids. We are ramping up for some serious hiking and exploring in the coming months. We have been hiking alot but I am always sad when the kids (my boys) miss being able to witness the occasional Golden Eagle, coyote, mountain lion or big horned sheep because we don't have field glasses/binoculars. What would be the best for us? Keep in mind that we will be visiting mountain tops with incredible long-range views. Looking at the moon and stars is good too! Thanks in advance.

Lens flare or something else?

edd — Wed, 23 Nov 2005 09:23:31 -0800

The image on the left side of zeus.com shows a photo of a man with some sort of optical effect partially overlying his head. Any ideas on what caused this? Both a name and a simple explanation if possible? Suggestions I've heard so far include lens flare or reflections on an intervening pane of glass but noone seems entirely sure of it.

Depth of Field and Focus. How do they work?

odinsdream — Tue, 04 Oct 2005 23:52:29 -0800

Selective Depth-of-Field in Six Feet Under, and a question about lens flares. In the commentary for either the first or last episode of Season 1, the director mentioned a lens technique that would put two subjects in focus when they're each positioned at different depths. He couldn't recall the name of this technique, or even how it worked. What is it called, and how does it work?

I've taken some screen shots of examples here and here. (~150KB jpegs) They aren't the best representations available in the show, but it was tedious to find them. Many are in the kitchen, where the characters are very far apart. In the first example, note that both characters are mostly in focus, while the edges of David's face and the arm of the chair between him and Nate is not. Similarly, in the second example, Ruth's face is in focus, as is the background, but her dress is not entirely in focus.

And, more of a general lens question, what determines the shape of lens flares or point light sources thrown out of focus? In this example, the lights appear as 9-sided regular polygons. I've seen everything from stars to perfect circles. What are the physics/optics behind these shapes?

A Vision Question.

Framer — Tue, 19 Jul 2005 04:57:25 -0800

When I look at something (without my glasses) that's about 100 feet away, it looks a little blurry. If I look at a photo that includes stuff that's 100 feet away from the perspective, it's not blurry, of course, it's just smaller. BUT, if I look in a mirror, let's say a rear view mirror of a car, at something that's 100 feet behind me, it looks blurry, rather than just small. So why doesn't a mirror act like a photo and just make me see the thing smaller? The plane on which I'm seeing the object, after all, is just a few feet away, same as a photo. How does a mirror actually maintain the depth of field, but a photo doesn't?

(Any auto accidents resulting from Me-Fi'tes playing with this optical trick themselves on their way to work this morning are not my responsibility.)

What should I look for when purchasing a camera lense?

odinsdream — Thu, 07 Jul 2005 16:05:59 -0800

Canon 350D Digital Rebel XT: Should I get it with the kit lense or without? If without, what lense would you recommend? What are your experiences with this camera and lense? I'd like to get an additional wide-angle lense even if I do opt for the kit lense, but if I were to go without the kit lense, what lense should I get to replace it? I've got very limited experience with lenses in general (due to lack of funds, until now), but plenty of manual SLR experience (using a small prime lense that came with the Minolta).

What should I look for on my lense-purchasing journey? Is my assumption that a wide-angle would be awesome naive?

Question number 6434

troutfishing — Sat, 10 Apr 2004 10:07:37 -0800

Pizza induced visual field distortion : When I chew - as on a piece of pizza (or whatever) and stare at a computer screen, especially from it distance, I perceive a "ripple" (or a "flicker") on the screen which is congruent with my chewing action. (more inside)