1-4cm focal usb camera - Page 1
Forum section: electronics / projects

author: VeryFastSnail
author_rank: Contributor
timestamp: December 18, 2019, 05:36:26 pm
content: Hello everyone, I’m currently am working on one project that requires close focusing camera, perfectly focus distance would be 1-4cm. This cam will take static pics, and quality is not that important. Pics will be converted to black and white. Picture size could be small, but cam has to be cheap, perfectly under 10$$$What I already tried to do:Looked at webcams that are comonly availablewith little to no success, focal lenght is common at <15cmUse laptop webcams,same problem as aboveLooked on aliexpress for camera modules,found some, ordered, will test soon.focus distance is unknown btwThought of adding some kind of lens to decrease it’s focal lenght,maybe someone is better at optics then I’m and could help me with type of lens to useThere are those endoscopic cameras, focal lenght is 3-8cm, but I dont want to dissasemble it...What do you think is the best solution?

author: Siwastaja
author_rank: Super Contributor
timestamp: December 18, 2019, 05:53:31 pm
content: Just move the existing lens further away from the chip to focus closer.

author: magic
author_rank: Super Contributor
timestamp: December 18, 2019, 05:59:46 pm
content: Focal length is not the same as focusing distance. Focal length is property of the lens and it cannot be changed (except for zoom lenses).Focus distance depends on focal length and the distance between the lens and the image sensor, per well known formula: 1/f = 1/x + 1/y.You can focus arbitrarily close by moving the lens further from the sensors. For a webcam, disassembly of the case may be required. This will not be a problem in those AliExpress modules, you can unscrew the lens as far as you want until it falls out. If the distance still isn't enough, extension rings for webcam/CCTV lenses are available. This lens system is known as "M21 mount" or "S-Mount".The lens will be operated outside its intended conditions and image quality may suffer. For serious macro operation (object distance < sensor distance) you may get improved results by inverting the lens (front to the sensor, back to the object).Another possibility is diopter adapters / lens stacking: attach an additional lens to the front of the fixed one. Either a simple high diopter magnifying glass or an inverted webcam lens.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 18, 2019, 06:32:20 pm
content: Look for a USB microscope instead. Generally they will specify their focus distance, but they'll be optimized for up close, and if you get something with a Barlow lens or with a long working distance specified, they'll be able to focus from farther back (not just within a couple of CM), and generally they have lower magnification.Because of the way the optics work, a regular USB camera that can focus very close is already magnifying (unless your output screen is the size of your field of view), so relatively low magnifications will just look like an up-close camera put on a bigger screen, whereas higher resolutions will look more of what you're expecting from an actual microscope.In any case, cheap decent quality (at least for stills) USB microscopes can be had fairly inexpensively.

author: VeryFastSnail
author_rank: Contributor
timestamp: December 18, 2019, 07:15:31 pm
content: Thank you for all your answers they are very informative. I will look into it.

author: magic
author_rank: Super Contributor
timestamp: December 18, 2019, 08:59:59 pm
content: I think you could start with extracting some webcam from its case and unscrewing the lens further than normally possible. That's certainly the quickest and cheapest thing to try.Quote from: DaJMasta on December 18, 2019, 06:32:20 pmWhat is actually the resolution of those things, in terms µm per pixel, DPI or similar units?I have never seen it specified that way, only one single "magnification" number whose meaning completely eludes me.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 18, 2019, 11:47:20 pm
content: Depends on the model, generally the better ones will be more verbose with how they function, but generally their stated magnification is for an assumed monitor size, say a 21" 1080p screen or something, and you can kind of work backwards from there.Since the focus is widely enough variable (a nominal 200x magnification microscope can often go down to 50x or 20x just by backing it out) and the magnification number is also dependent on the displayed image out of it, they probably should just specify a nominal pixel size at the rated magnification, but that doesn't seem to be a priority on the cheap end.For more expensive options, like Dino-Lite's microscopes, they specify X and Y dimension field of view for a given rated magnification and working distance, so you can resolve the width of a pixel just knowing the sensor resolution. There are also a number of microscopes that have companion applications that have a measurement tool, so if they can read the focus adjustment, they know how large a pixel should be when in focus.

author: magic
author_rank: Super Contributor
timestamp: December 19, 2019, 08:44:44 am
content: Quote from: DaJMasta on December 18, 2019, 11:47:20 pmThat's finally something we can work with.I checked a few of their models and it seems that in every case they take 40×30cm FOV as "1x magnification". So the spec is a ballpark estimate of magnification going from the object to a full size PC monitor. Probably some variation exists between vendors.editSome of their products look quite suspicious. Takethisfor example, with ~500µ field of view. Since they can't have over unity numerical aperture in air, they would be lucky to get resolution of 0.3µ per pixel. For NA=0.5 we are talking 0.6µ. 5MP sensor is a complete overkill for such optics and it's a $1k product, not some $10 junk from AliBay

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: December 19, 2019, 06:15:10 pm
content: Not exactly in your budget but we used a couple of Logitech C910 and C920 for close up shots.You can bypass the auto-focus and set it just right from software with no effort.