So you think your microscope has a long working distance? - Page 1
Forum section: electronics / general

author: Carl_Smith
author_rank: Frequent Contributor
timestamp: June 26, 2017, 11:25:52 pm
content: So you think your microscope has a long working distance?I remember being amazed years ago the first time I worked with a binocular boom type microscope to work on circuit boards. Previous to that, my experience with microscopes were the type used in school biology class, where the distance between the objective lens and the slide was probably 5 mm, and if you racked the focus down too much you could hit the slide with the lens.So I thought it was really cool that they could do some optical trickery to give enough working distance to actually have room to solder on a circuit board under the microscope.But last week I witnessed a whole new level of optical black magic. Our local hospital mega-corporation recently spent over half a billion dollars to build a new hospital in my city and they gave tours to the public. In one of the operating rooms they had a camera mounted on the huge light over the operating table.They had this camera zoomed in so much that a US penny coin filled the whole field of view on the monitor. But the camera was over 3 feet above the operating table on the center of the light.Amazing - a working distance of a meter zoomed in to less than 20mm field of view.

author: Brumby
author_rank: Unknown
timestamp: June 27, 2017, 12:10:22 am
content: The magnification given by the OP is something quite achievable with optics alone. It's roughly equivalent to a 2,000mm telephoto lens on an old 35mm film camera. Nikon first produced lenses like this decades ago.Yes, they were big. So big, you mounted the lens on a tripod - and attached the camera, but part of the reason theywereso big was so that they had a large collection area for light. In a medical setting, lighting is usually pretty darn good, so this isn't quite so demanding.The other thing is that medical equipment is - quite consistently - up near, if notthe, best that is available. Cost is less of an issue where lives are at stake - so the designers can opt for higher quality designs. Many years ago, I saw a macro zoom lens suitable for medical use, which had a ring flash around the lens for shadowless photography. The price was mind blowing - but so were the images.You must traverse this optical path before you can enter the realm of image sensors and processing, but the state of the technology in that department does present a wonderful complement and incredible capability.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 27, 2017, 12:50:58 am
content: Yeah but why did the guy eat a coin? Did House find it?

author: Carl_Smith
author_rank: Frequent Contributor
timestamp: June 27, 2017, 01:45:37 am
content: Quote from: wilfred on June 26, 2017, 11:43:50 pmAgreed. I referred to it as black magic because I understand just enough about optics to understand that this is not a trivial thing to do but not enough to understand how it's actually done. Like when people refer to antenna design as black magic.Quote from: wilfred on June 26, 2017, 11:43:50 pmI was thinking it was done optically. However the image was displayed on what looked like a standard computer monitor, and I have no reason to think it was anything special like a 4k monitor. A standard 1920x1080 monitor is only 2 megapixel, so I guess you could use the center of a higher resolution sensor and still not see any loss of detail on such a monitor.I would think that they wouldn't do any image enhancement since they wouldn't want any artifacts introduced. You'd want any details seen to be real detail.Quote from: Brumby on June 27, 2017, 12:10:22 amJust from memory the camera assembly that I could see on the light was maybe 4 inches long and about 1.5 inches in diameter. I didn't get a look at the end of the unit to see what the lens actually looked like.There was no shortage of light since this thing was in the center of a huge operating light, and there was a second similar light also showing on the area.I imagined having a camera like this at my workbench so I could make Youtube videos of circuit board work without having a camera in the way. Of course, it's way overkill for that...

author: Kleinstein
author_rank: Super Contributor
timestamp: June 27, 2017, 04:25:08 pm
content: With microscopy or close up photos there is a trade of between optical resolution limited by diffraction and depth of field. So to get really good resolution, the lens and aperture need to be rather large - so the small lens (1.5 inches at 2 m is still a small aperture compared to a real microscope) must have a somewhat limited resolution. A much larger lens might not help very much, as the depth of field would get rather small then. It can still be impressive though.They might use some software to improve contrast for the higher image frequency to somewhat make the diffraction limit a little less visible. There are not that many artifacts with this - just more image noise. So with sufficient light it can help.