Elmo-like webcam - Page 1
Forum section: electronics / general

author: FrankT
author_rank: Regular Contributor
timestamp: May 18, 2012, 10:24:37 pm
content: Does anyone know if you can get a webcam that does what the elmo does in Daves vblog? Something that has high optical zoom (x20 or more), but with a long focal length (5-20cm).There are lots of USB microscopes on ebay, but they seem to have a focal length of 1-2mm.Is it possible to modify an existing web cam by mounting a lens in front to do this?And of course, I want it cheap!Frank

author: Unknown
author_rank: Unknown
timestamp: May 18, 2012, 10:50:44 pm
content: You appear to be confused about terms like zoom and focal length. Focal length is the distance between the lens and the focal point of a parallel beam (i.e. focused at infinity). To focus it closer, you increase the distance between the sensor and the lens. To produce an image on the sensor at the same size as the object, you would need a distance between lens and sensor of 400 mm and a distance between lens and object (working distance) of 400 mm. This assumes ideal thin lenses, things get more complicated with objectives consisting of multiple elements, as used in microscopes. Zoom is the ratio between shortest and longest focal lengths, and only applies to zoom objectives. A single lens has a zoom of 1, since it's fixed focal length.You could mount a lens in front of a webcam, but I doubt whether you'd get anywhere close to microscopy-level magnification. You would need a fairly short focal length (high curvature) to have any effect. Focal lengths add up as the reciprocals, so 1/f_t = 1/f_1 + 1/f_2. The unit of reciprocal focal length is diopter. If the focal length of the webcam lens is 4 mm (250 diopter), then you would need approximately another 250 diopter to get it down to lifesize (image size = object size) magnification, at an impractical working distance of 4 mm. Increasing the working distance would require increasing the distance between sensor and lens or more complex arrangements like relay lenses. Corner quality is probably going to suck for a single element lens, which is not exactly optimized for performance at 4 mm.

author: FrankT
author_rank: Regular Contributor
timestamp: May 18, 2012, 11:13:23 pm
content: Thank you for your polite and informative reply. It has been a long time since I've studied optics at school.It sounds like it is going to be either too hard, or too expensive.

author: Rerouter
author_rank: Super Contributor
timestamp: May 18, 2012, 11:19:51 pm
content: personally i have used the lense off this on a better webcam (better quality and more sensitive one)http://www.whitegadget.com/attachments/other-gadget/9785d1212143471-nightvision-usb-webcam-nightvision-usb-webcam.jpghowever as stated by alm, you need to be millimeters from the surface to get a nice clear picture, e.g. 1.5mm to clearly read the label on a 0402however to do it properly you would need to use something like thishttp://hackaday.com/2012/03/01/a-zoom-lens-for-your-webcam/

author: EEVblog
author_rank: Unknown
timestamp: May 18, 2012, 11:37:58 pm
content: I saw someone had hacked a big canon/nikon zoom lens onto a webcam in a jiffy box or some sort. Said they could zoom into SMD soldering easily from 1m away.Was it on this forum somewhere?Dave.

author: Psi
author_rank: Super Contributor
timestamp: May 19, 2012, 01:04:21 am
content: Yeah, you would get some really good results with a cheap dslr (that has video out) and a good macro zoom lens.But obviously it's not the cheapest option.

author: jusanother
author_rank: Contributor
timestamp: February 12, 2014, 07:44:31 pm
content: Quote from: EEVblog on May 18, 2012, 11:37:58 pmIt was here:https://www.eevblog.com/forum/manufacture/an-idea-home-made-video-microscope-for-smt-work/msg110129/#msg110129