Wikipedia:Reference desk/Archives/Miscellaneous/2022 May 1

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May 1

hacksaw

For a dumb project I want to cut up some sheet steel. I have the crappy style of hacksaw, like this, i.e. the blade is supported at just one end, sort of like a keyhole saw. Is that going to take a lot more sawing effort than the normal type of hacksaw where the blade is under tension in a frame? I could buy the other kind if it will really save a lot of work, but I'd otherwise rather use what I have. I'm not worried about the cuts being clean. It is called hacking for a reason, heh. Thanks. 2601:648:8202:350:0:0:0:4671 (talk) 02:16, 1 May 2022 (UTC)

The saw you have will be much harder to put pressure on, and the extended blade will wobble around, resulting in a wider cut, more friction on the side and more effort. however for a large sheet, the regular hacksaw will not be able to cut much width. Tin snips will be much quicker, and if it is thin, you may be able to use scissors to cut it. Graeme Bartlett (talk) 04:37, 1 May 2022 (UTC)

It's too thick for normal household scissors. Tin snips would work but I'd have to go buy some, and a tension hacksaw might be a better bet at that point. Anyway I'll figure something out. The amount of cutting needed is not huge, so if the one-ended hacksaw is usable at all, maybe I'll just slog through it. Thanks. 2601:648:8202:350:0:0:0:4671 (talk) 06:50, 1 May 2022 (UTC)

In the image the blade is hidden by the packaging. Isn't the lower part of the blade tight? If you use only that part to cut, the wobble will probably be acceptably small. The maximal depth of the cut is rather small, though, being the distance between the blade and the parallel part of the frame. By cutting from two sides you can double that distance and then finish the rest with the protruding part of the blade. Make sure the sheet you're cutting is held steady and tight, so that it won't wobble either.  --Lambiam 07:06, 1 May 2022 (UTC)

The lower part of the blade is supported so it won't flop around, but it's not under tension like a real hacksaw. But yeah, that approach might work, so thanks. I also looked online and it turns out suitable tin snips are less expensive than I expected, and are probably the best way to do this, so I might just buy a pair. I'll find other uses for them too. 2601:648:8202:350:0:0:0:4671 (talk) 15:24, 1 May 2022 (UTC)

Is the sheet metal thin enough that it could be folded over? --←Baseball Bugs ^{What's up, Doc?} carrots→ 08:44, 2 May 2022 (UTC)

It is thin enough, but it's not flat, so I can't fold it. The project is a hobo stove so I want to cut out part of a cylinder, either from a large tin can or from a silverware strainer. I think tin snips or other heavy duty scissors are the right answer. My regular household scissors are just too wimpy. It occurs to me that I have a coping saw too, so maybe I can get a metal-cutting blade for it. 2601:648:8202:350:0:0:0:4671 (talk) 23:18, 3 May 2022 (UTC)

Glow on old videos

Apparently many older videos from 1980s or 1970s have a peculiar glow when light hits some reflective surface, like here on metallic parts, with reddish glow. Why is that? Older optics of cameras? 212.180.235.46 (talk) 18:35, 1 May 2022 (UTC)

For videos of things on stages, it could well be due to lighting. Perhaps there is a red light as well as white lights shining there. Could also be due to chromatic aberration, though this would usually show blue on the other side. Things recorded on NTSC video tape can have poor colour reproduction, particularly showing green skin. Graeme Bartlett (talk) 00:49, 2 May 2022 (UTC)

It's catching direct reflections from the stage lights, which would be super bright.

But you knew that. The real question is why do flashes of really bright light look so weird on old video formats?

It has to do with what happens when a Video camera tube is overloaded. Those tubes had a Photocathode that was supposed to be electrically charged wherever light touched it. But if too much light hit it, there would be too much charge, and the charge would bleed into neighboring areas (causing a halo) and not dissipate as fast as it was supposed to (causing "trails").

Unfortunately, Wikipedia doesn't seem to have a good article on this. If you look up "Blooming" you get redirected to Charge-coupled_device#Blooming, which is about a similar effect you see in video from the 90s. But it's different, because instead of a tube, a microchip is used and the bleeding tends to favor the direction that the elements are wired together, causing vertical stripes ApLundell (talk) 19:34, 2 May 2022 (UTC)

But are the red (purple) trails (clearly visible when the microphone stand moves at 3:03 in the video) the result of the red photocathode being overloaded, or is it because the red one isn't overloaded, but the green and blue are, causing a dark halo in those colors? Prevalence 10:39, 3 May 2022 (UTC)

"All vidicon and similar tubes are prone to image lag, better known as ghosting, smearing, burn-in, comet tails, luma trails and luminance blooming. Image lag is visible as noticeable (usually white or colored) trails that appear after a bright object (such as a light or reflection) has moved, leaving a trail that eventually fades into the image."

From Wikipedia Vidicon. 74.92.173.225 (talk) 22:57, 3 May 2022 (UTC)