bodger: girls in photo booth (photobooth girls)
I've had a Kiron macro zoom lense for quite a while. It's not a fancy sort, but it works nicely - especially for macro shots where I want good depth of field. Most macro lenses are close-focussing ones with a razor-thin depth of field. This beast works in macro mode at a fair distance, with the attendant advantages in depth of field. Granted, it needs a lot of light to work, and shooting faraway subjects with magnification makes vibration an issue, but these are dealable with - an off-camera strobe helps enormously. These days, that's mostly what I use it for. I was trying to get a good picture of the character matrix of a monoscope, and realized the zoom macro would be the tool to use. It took me a while to find it, it had ended up in a camera bag in the basement, where it had lain for quite some time. Unfortunately, it's damp in the basement, and it had gotten fungus or something on the back of the front element. To clean it would require disassembling the lense.

I have a lot of good camera and lense tools, so I grabbed the lense spanner and the lense and peered at it for a while, realizing that the lens retaining ring didn't have spanner grooves. Some research on the internet revealed that some people simply saw grooves into the front ring and remove it that way, but I didn't want to, as it's really easy to ruin something in the process, and the front of the barrel had been dented at some point in the past, so the threads were in poor shape. However, the same research revealed a downloadable copy of the repair manual for it. It turns out this is a popular lense, and has been offered in a variety of versions and configurations over the span of a few decades. The one I had didn't match the repair manual, but it was close enough for me to realize the tiny dimples at the front were actually tiny setscrews covered over with (essentially) black nail polish. With the setscrews removed, the front lense element assembly should simply unscrew.

I rounded up my Wiha precision screwdriver set and selected a bit that would just fit in the setscrew opening. A few turns abraded away the black nail polish, exposing the head of the setscrew. Some careful digging cleared out the slot, and I was able to back out the setscrew nicely. It's a really small screw, about the size of a grain of pepper. There was one each in front of and behind the line delineating the front lense assembly. So I removed both of them. Then I tried to unscrew the front of the lense. It didn't budge. So I found one of those grippy pads used to remove stubborn jar lids, and cranked away at it with that. Success! The front unscrewed smoothly. Now that I had access to the back of the lense, it was simple enough to carefully remove all the fungus without damaging the antireflection coatings (as far as I could tell, anyway). Then I screwed it back on. Replacing the tiny setscrews was tricky, as they wanted to lie in their openings sideways. I finally ended up lightly magnetizing the screwdriver and using it to place the screws in position. That worked a treat, I replaced the screws, and the lense works properly!

With it, and the last sunshine before this afternoon's thunderstorm, I got some good shots of the character matrix, in acceptable focus from edge to edge (I have to photograph it edge-on due to the construction of the tube).

bodger: girls in photo booth (photobooth girls)
I was taking some low-light pictures with my DSLR a while back, and was having poor luck getting sharp focus. The wide aperture was exacerbating a problem I've noticed for a while. It also got me to thinking. I never had that problem with my old SLR, was my vision going or what? I really missed the split prism and microprism focusing aid in the SLR. And that was the clue I needed. Modern DSLR bodies are generally designed to be used with autofocus lenses, but most my lenses are older models that are optically just fine, but don't have any autofocus ability. Because they're designed for autofocus, they don't have the manual focusing aids I'm used to. The LCD screen is useless for fine focusing, and it's hard to get it exactly right using just the viewfinder.

Fortunately, there's a market for retrofitting old-style microprism focusing screens into modern DSLR bodies. A little poking around and reading reviews yielded two main contenders that have offerings for my camera. Haoda and focusingscreen.com. Prices between the vendors are basically similar (not exactly cheap at around $72, but this is a specialty item and genuinely useful), and presently I decided to go with focusingscreen.com, as they offered more choices (four) for my target camera, and generally seemed to have more info (such as installation instructions with pictures) available on their site. I opted for the Nikon-style K3 screen, as it was similar to the one in my old F-series body, with a split prism in the center and a microprism ring around it. I'm accustomed to this arrangement, and I know it works well for me. There's a nice writeup of screens there and focusingscreen.com offers a comparison of their offerings there (odd url, "privacy.php", and I like the page heading reading "Let's see what we have here"). The English on the site is a little dodgy, but easily understandable. The installation procedure looked like something well within my skills, so I wouldn't need to take the camera to a shop.

The site mentioned that the machine that cuts the focusing screens would be down for maintenance, but I went ahead and ordered anyway, figuring I'd get one that was cut with a freshly serviced machine. Shipping from Taiwan was fast, it was sent on the 22nd and arrived two days later. I picked it up today (I had to go to the post office to sign for it). It was very well packaged in a sealed bag in sealed bubble wrap in a box in a plastic shipping envelope, and included a very nice container for the screen itself, a plastic tool to manipulate the screen without scratching it, a nice pair of fine-point tweezers, two finger cots, and a pair of transparent plastic shims for fine-tuning the focus plane. The focusing screen box was shrink-wrapped with a little sticker reading "Opened packing can't returns." There was a sheet of paper reading "Dear all, Thanks for your using very much. Please read the instruction before installation to make it more smoothly." It also listed their URL to access the detailed installation instructions.

After dinner tonight, I decided to give it a whirl. I fed the (Chinese) installation instructions page to Google translate (it's clear enough from the pictures alone, but I wanted any useful details from the text). It starts off "Please send your little brother", which I assume means you don't want kids running around whilst performing surgery on your nice camera. It also suggests turning off fans and windows and so forth to keep down dust. The installation was actually pretty easy. Remove the lens, invert the camera, pop free the retaining bail, remove old focusing screen, put in a shim and the new screen (right side up, with notched corner on the left, toward me), snap the retaining bail back into place. Easy.

Then I installed a lens, cranked the aperture all the way open, and did several test shots. They were pretty close, but the camera was focusing slightly too close. This meant I needed to move the focusing screen in or out slightly. I mused on how the optics worked briefly, and decided that I needed to move the focusing screen out, away from the lens. So I opened it up again, removed the shim, and put it all back together. Another trial showed that it was focusing correctly now (in effect, the focusing screen was the same distance from the lens as the film plane). Now it's easy for me to use my nice old lenses with the new camera and get sharply-focused shots.

bodger: me at Carabelle beach, FL (beach monster)
I was watching TV the other night, and saw an ad about the face recognition in iPhoto 9. I have a copy, but hadn't been aware of that feature, so I went off to play with it. It's actually surprisingly good, and makes guesses of people's faces fairly well, even at odd orientation, partially obscured, bad lighting, poor focus, etc. A quick way to catalogue a lot of photographs by who is in them.

However, it is, of course, not perfect... )

bodger: xkcd android girlfriend arc weld cherry stem (Default)
A while back, I bought a big, weird-looking tube on eBay. I had more-or-less forgotten about it until I came across it again whilst moving house. Curious, I endeavored to determine what it was. After some research, I found out it was a "finebeam tube" (Fadenstrahlröhre). In fact, my tube looks like the one in the picture, and bears the same part number. However my unit sports an oddball plug instead of the ordinary pins on the (supposedly more modern one) available for sale today (for a whopping US$1,858!).

The tube contains a simple electron gun, a set of deflection plates, and gas (generally helium, hydrogen, or neon) at very low pressure, enabling the beam to be observed. It's used to illustrate electron physics, the effects of electrical and magnetic fields on electron beams (with an additional set of Helmholtz coils and a variable power supply), and even compute the specific charge of an electron.

Some searching failed to reveal a socket for it, or even a pinout. There are only six pins, and their functions were reasonably well documented (heater, heater/cathode, Wehnelt [focus] cylinder, anode, and two deflection plates). Probing the connector, I found two pins with continuity. This showed that the tube was at least electrically intact, and those would be the heater pins. The various tubes on the web seem to want between 4 and 7.5 volts on their heaters. May as well try to light it up! I rounded up a tube tester, and wired a couple of its socket pins to the heater pins on my tube. Gradually bringing up the heater voltage in a darkened room presently resulted in a dim orange glow.

Encouraged, and motivated by the possibility of actually seeing an electron beam with my own eyes, I rounded up an adjustable regulated power supply (Heathkit IP-32) capable of delivering zero to 400 volts. The procedure was a bit tedious, as I'd have to connect a wire to a prospective pin on the tube, turn on the supply, turn off the lights, and wait for my eyes to adapt to the darkness to see if there was a visible beam.

I got a beam! )

It was dim and fuzzy, but definitely there! I brought [profile] fizzygeek down to see it, and she was able to see the beam easily (I suspect her years of darkroom experience helped).

I wondered if I could photograph it. I grabbed a tripod and borrowed [profile] fizzygeek's Canon G9, as it has a reasonably fast lense and sensitive (ISO 3200 equivalent) sensor, but no joy. No worries, just an excuse to get out the big guns. In this case, a DSLR and a cable release. Unable to get good focus with a generic 55mm lense, I got an ancient Micro-Nikkor I had picked up on eBay for $15 a few years back. Now to figure out exposure. I generally have a good eye for such things, but this was a bit far out on the reciprocity curve. I tried a few seconds, but just obtained a faint smudge that I assume was the glowing cathode. Cranking the camera all the way to its 30-second limit, I still didn't have much. Then I realized I hadn't checked the aperture! Sure enough, it was pretty stopped down, so I cranked it all the way open. Bam, bright screaming overexposure! This surprised me a little, as I didn't think there was that much light available, but I happily tweaked settings until I got a decent exposure. I took the memory card upstairs to view the results on the big calibrated LCD monitor.

I figured the next thing to try was to deflect the beam using the built-in deflection plates. The power supply included an additional "bias" output, variable from zero to -100 volts, so I strung another wire, and started trying pins. Sure enough, I was able to deflect the beam. Since electrons are negative, and I was applying a negative voltage, the beam deflected away from the plate I was connected to. This way, I was able to figure out which pins went to the deflection plates.

pictures of a bending electron beam )

I noticed that the anode cone was glowing in the pictures. Very pretty, but I didn't remember a glow. The purplish cast to the photo gave me the missing clue: that particular DSLR was the UVIR version (thanks [personal profile] gravitrue!), sensitive to ultraviolet and infrared light as well as the visible spectrum. And I hadn't moved the UV+IR blocking filter when I changed lenses.

I went back downstairs, screwed on the filter, and tried again. Sure enough, the exposure was now about what I expected (the additional light outside the visible range was what had thrown me off). And indeed, in the visible-only exposure, I didn't see the anode glow, and the heater glow was a more appropriate intensity and dull orange colour (the copious IR had made it unnaturally bright, and tinged it an otherwordly lavender).

more pictures )

January 2014

S M T W T F S
   1234
567891011
12131415161718
19202122232425
2627 28293031 

Syndicate

RSS Atom

Most Popular Tags

Style Credit

Expand Cut Tags

No cut tags
Page generated Jul. 25th, 2014 07:56 pm
Powered by Dreamwidth Studios