The View Up Here

Random scribblings about kites, photography, machining, and anything else

Archive for January, 2015

Still Sick

Posted by Tom Benedict on 23/01/2015

The day after I posted Sick Lizzid I went back to work to put our wide field imager back together. (While I was out sick it had yet another failure. Grrr!) We got a lot done, but working in the cold at altitude is a recipe for relapse. I was out sick again yesterday and today.

So I spent my lucid reading time going through The Strobist. I finished Lighting 101 and started on Lighting 102. The second course goes into a lot more detail than the first, and includes student exercises (yaaay!) I had a little more energy this morning, so I went though the first several. These are more to familiarize the photographer with how light behaves than anything else, so I won’t post any of the pictures I made. I do, however, urge everyone going through the L101 and L102 classes to do every exercise. As pedantic as some of them may seem, nothing beats time in the saddle when it comes to learning a thing.

One of the things I like about The Strobist is that it’s very nonlinear in nature. Lessons do follow one another, but if something is relevant to the discussion there’s a link you can follow. Lighting 102 2.2 – Specular Discussion had a link to an article called Stainless Steel and Cookies, which in turn had a link to an article called Pretty, Shiny Things that discussed a technique called double diffusion. I’ve used this at work to get a relatively flat diffuse source. The flat field source I made for characterizing the linearity of our infrared wide field imager used double diffusion to minimize roll-off at the edge of the field.

The exercise for L102 2.2 was to play with specular reflections. I took a cue from the Pretty, Shiny Things article, in which the author was photographing wheat beers. I’m fresh out of decent beer, and too sick to drink anything, anyway. So I grabbed a bottle of Grand Marnier out of the cabinet and started playing.

Grand Marnier

I tried bare flash (eeks!), a shoot-through umbrella (better), and this, a double-diffused setup using the same umbrella with a Fotodiox shoot-through diffuser between the umbrella and the bottle. I didn’t think to try it without the umbrella until I’d already taken the setup apart, but by then I’d sapped what energy I had, and had to quit.

I’m really enjoying going through the lessons and exercises on The Strobist. It sounds weird, considering I’ve spent close to twenty years doing landscape photography. But I’m getting a real kick out of learning new ways to control light.

– Tom

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Sick Lizzid

Posted by Tom Benedict on 20/01/2015

There’s some kind of flu going around. I should’ve known when I saw the papers the other day at work. The headline read something like, “There’s Some Kind Of Flu Going Around!”. (Actually I think it said something derogatory about how the flu shot should’ve stopped this and didn’t. Hey, mutation’s the name of the game.) I tried to press on and not catch it until we’d finished all the work on that lens, but it finally caught up with me Saturday evening. I’ve been getting worse ever since.

I spent most of Sunday flopping around the house like a semi-fevered jellyfish. When I didn’t have the energy to flop around I read The Strobist. I know it’s been said a zillion times, but that’s hands-down the best site I’ve found for learning how to light photographs. But there was only so much reading I could take. I finally reached critical idea mass and just had to set up and play. No one was willing to model for me, so I set out to do a self-portrait.

I wanted to do basic corner lighting. It’s a straightforward single-light setup that lets you balance main and fill light on the subject as well as background light just by varying the distance between light and subject, and light and background. All you need is a corner with two light colored walls to work with.

That’s when I figured out I don’t have a corner with two light colored walls to work with. All the corners in my house either have furniture in them or one of the walls is actually a window. In desperation I finally wedged all my gear into the entryway to my house – a tiny 4’x4′ area. The only way it constituted a “corner” was if I called my front door a wall. Good working distance? Nope! Room for lighting? Not really. Desperate? You bet!

I didn’t really have room to do any balancing since I couldn’t move away from my background and I couldn’t get the light any closer to me than the edge of the entryway. I probably should’ve been frustrated, but the bigger problem was that no matter what I did, all the pictures I made looked like a sick guy who’d crammed himself in the entryway to his house and wedged himself in with camera gear. I’d have cried if it wasn’t so funny.

So instead I stuck a 100mm macro lens on my camera and took pictures of my eye. But what with the puffies, the redness, and everything else, it was just as bad as the self portraits. Come to think of it, it was probably worse.

When life hands you lemons, make margaritas.

I decided to do some creative editing instead. I like selective color eye photos, so that’s where I started. I left the iris alone, but desaturated the rest of the frame. It was kinda blah. So on a whim I started going through individual channels instead. The red channel smoothed everything out, but looked even more blah. Green was more interesting. But the blue channel was COOL. I looked like an alien. Or a lycan/vampire hybrid or something. Now we’re cooking!

My iris needed some work. So I bumped the saturation and vibrance, and toyed with the clarity a little. (MAN the new terms Photoshop CS6 has made me learn…) Then I tried rotating hue. A little fine-tuning and…

Lizzid EyeLizzid Eye!

Well… A sick lizzid, anyway. But hey, I’ll take it.

– Tom

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Heavens and (Optical) Hell

Posted by Tom Benedict on 19/01/2015

In an earlier post I mentioned we were in the middle of a big investigation into the degradation of one of our instruments. My active role in the investigation finished up Friday, so I’m breathing a big sigh of relief. Meanwhile I started processing all the photographs I made in the course of the investigation to document the work done. I ran a couple of time lapse cameras, so the photos number in the thousands. I only used a couple of the time lapse photos, though, so the number of “keepers” was a lot smaller.

I picked a subset of the keepers to narrarate the story thus far:

CFHT with Megacam

A couple of months back one of our astronomers analyzed the images coming off of our wide field imager to measure the zero point of each filter. A zero point is the measurement of the transmission of the instrument is in a given band. Because of dirt and grime building up on our primary mirror, we expect some drop in the zero point over time. What we didn’t expect was what he saw: a 20% drop in performance in g’ band with slightly less extreme drops in all the other bands. What made this worse was that we had just re-coated the mirror. We expected to get a marginal gain, not a dramatic loss. Clearly something was wrong. When the instrument came off the telescope we went up to take a look.

First Look - Something Wrong

I’ve done plenty of sunset photography at the beach. Most days I get away with some good frames and a camera that needs a damp wipe. Other times I get stuck in an onshore and my gear winds up covered in salt spray. But even at the worst of times, I’d never seen a lens that bad.

One of my co-workers spent an entire day trying to clean the lens. Stuff seemed to move around, but he found it almost impossible to actually take stuff off. By the end of the day the lens looked cleaner, but it was still bad. We all took bets on what the performance would be the next time it went on sky. I thought we’d see at least some of the performance restored from his cleaning efforts. None of us expected what happened, though. That 20% increased to a 50% loss of light. We’d made things worse. We pulled the instrument off the telescope and went up the next day to take another look at that lens.

Winter on the Mountain

We’d just had the worst ice storm of the season. The roads were still closed to the public while the road crews took the snow blowers up to clear the roads. When we finally got to the observatory and took a look at the instrument, what we saw wasn’t promising. After a very brief hands-off investigation, we started taking things apart.

Removing L1

Our first thought was that we were dealing with a contaminant, so that’s how we proceeded. We tried every solvent we could think of to take the “stuff” off the lens: DI water, methanol, isopropanol, acetone (I cringed at this one), toluene… None of it seemed to do a thing.

Early Testing

We did eventually find some chemicals that had an effect, but the amount of scrubbing necessary to make them do anything at all was really discouraging. Eventually we found that weak acids had a stronger effect, and required less scrubbing.

Finding what Cuts the Goo

We used two techniques to image the glass throughout the process: reflected light photography and dark field photography. Reflected light photography highlights differences in thickness in thin film layers through color change. Dark field illumination highlights contaminants like dust and other particulates. We used reflected light to show the spot of “clean” we were able to make with a weak acid.

Dark Field Illumination Technique

As splotchy as the reflected light photos were, it wasn’t until we used dark field illumination that the true extent of the “contamination” became apparent.

Dark Field Image

We made a comprehensive dark field survey of the lens to see what we were dealing with. A couple of features stood out: The center of the lens appeared to be cleaner than the rest of the surface. This is likely because of the cleaning technique used earlier – radial strokes from the center to the edge. The center was the starting point of each pass across the glass, so it got the most cleaning.

Another feature we saw was the dark ring about 1/3 of the way out from the center. Our optical engineer said this is the mark left by the vacuum fixture the lens manufacturer used to manipulate the glass during final polishing and coating.

The rest of the glass appeared to be covered by a blotchy layer of… something. We took samples and sent them off to a company so they could perform an assay to tell us what the heck was going on.

Using the Microscope

Meanwhile we borrowed a digital microscope from one of the other observatories on the mountain and set it up to take a closer look at what this contaminant was. Under that much magnification we were running into issues with vibration, so we put everything on the table and tried not to breathe when we were taking exposures.

(As a quick side note, that’s my Bogen 3021 legs and 3047 head I got for doing large format photography work back in ’95! It’s the most solid tripod I’ve ever owned. Despite having one of its feet burned off in lava in 2001, it’s still going strong. I love good gear!)

Microscopy - The Problem

What we saw under the microscope wasn’t encouraging. Either the entire lens was covered in bumps of… something… or we had a bigger problem. Were those craters?

We tried illuminating the patch under the microscope from various angles to see if we could figure out what was tall and what was short. But it wasn’t until we moved the microscope to the edge of the glass that we knew for sure.

Microscopy - Even the Edge is Bad

We were looking at pits in the coating. Something had killed the anti-reflection coating on our lens.

This is when the investigation divided forces. One side of the investigation pursued the question of what had caused the damage. The other side pursued the question of how we were going to recover and get the instrument back on the sky. We collected a new set of samples to send out for assay and moved the lens to another lab to begin the next stage: fixing whatever had gone wrong.

Test Swabbing

After an understandable amount of deliberation and debate, the powers that be decided the best course of action was to remove the coating from the lens. At its very best, an anti-reflection coating cuts the reflectivity of an air-glass interface by about 4%. Typical coatings recover more like 2% of the light that is normally reflected. We were looking at a 50% loss due to scattering from the damaged coating. Removing the coating would get us back in the 2-4% range. It was an irrevocable step to take, but it was clearly a win.

So we went back to the weak acids that had worked earlier, and began to experiment with concentration. The trick was to strike a balance between an acid that was strong enough to remove the coating in no more than a handful of applications, but not so strong it would attack the underlying glass. Our optical engineer identified a handful of acids that would be reasonably safe to use on the glass, and maximum exposure times we could use without damage. Hydrochloric seemed to be the best match, so we went back to testing.

Test Swab Technique

At 4% concentration, HCl was clearly removing the coating after only ten seconds of light scrubbing with a swab. The only problem was that even at 4% it was stronger than the concentration used by the glass manufacturer during their own testing.

Reflected Light Image - HCl Concentrations

We switched to a weaker solution: 50:1. At the same time we also wanted to minimize mechanical abrasion of the glass, so rather than going for a more aggressive swabbing action with the weaker acid, we tried a prolonged soak using a lens tissue saturated with acid.

Reflected Light Image - First Successful Soak Removal

After five minutes with an approximately pH 1.0 solution, we finally had something we could turn into a real procedure for stripping the lens.

At these concentrations the acid was about as strong as the white vinegar we’d tried earlier, and vapor concentrations were low enough not to require respirators. Respirators can be uncomfortable at the best of times, but at 14,000′ of altitude the restricted breathing is more than just a matter of comfort. It can mean having to break up work shifts to give people the chance to breathe. Working with just gloves as PPEs made life a lot easier.

Highway to Hell - Putting Acid on a Lens

There is something incredibly wrong about deliberately pouring acid onto a coated optic. Even knowing that the coating was shot, and that we couldn’t operate with that coating in place, I felt dirty when we loaded the first of several “patches”. Some part of me whispered, “You’re going to optical hell for this, boy.” With my heart in my throat I poured spoonful after spoonful of acid onto the patch.

Making of - The Work Begins

All of this was complicated by the fact that I was still doing photography of the procedure as we went. (Now you understand why I used time lapse cameras!) At times the cameras got in the way and slowed things down, but we all agreed that having a good documented record of the work was more important in case we missed something and had to re-establish what we’d done at some later date.

Dark Field Image - The Work Begins

It certainly helped that the technique worked. It wasn’t perfect, but it worked. We set up the next patch and began working in earnest.

Staying the Course - The Work Continues

There were a couple of features on the glass we weren’t certain of. One was the dark ring a third of the way out from the center – a ring left by the vacuum fixture the manufacturer had used to handle the glass. Would the acid work on that area? When we looked at it under the microscope the coating appeared to be less damaged than in other areas. Would that make it tougher to remove? Or easier?

Reflected Light Image - The Ring

The answer, as we learned, was tougher. The coating at the ring was less damaged than in other areas, but it was still damaged. It still needed to be removed. We only hoped that longer exposure to acid would eventually take it off.

Dark Field Image - End of Day 1

By the end of the first day we’d made some real progress. We were clear out to the dark ring, and had started on another potential problem area of the glass. After doing a DI water wipe to remove any remaining acid we made a dark field image to see how we were doing. The prognosis? GOOD!

For the record, the apparent scratches in the center of the lens are actually on the lens cover we bolted to the bottom of the lens. The glass itself is scratch-free.

Finishing Touches - Pipette Works Better

Day two was more of the same. We worked our way out toward the edge of the lens and continued to work on problem areas like the dark ring and a couple of other spots. As the problem areas got smaller, our patches also got smaller. At one point someone remarked that it looked like the lens had had a massive shaving accident. By then we knew the technique was clearly working, so the joke wasn’t as forced as it might’ve been earlier in the week. We could actually laugh without wincing.

As we neared the outer edge of the lens, the slope of the glass made it more likely that acid would run off our patches and down to the RTV that held the lens in its cell. Rather than spooning it on as I had the previous day, I switched to a pipette. Over the course of the day I put about a third of a liter of acid on our lens 0.09ml at a time. By the end of it my thumb was tired.

The lens has a 20mm wide baffle that fits around the outside diameter of the glass. This shadows the transition onto the AR coated surface, and covers the first 10mm of coating. We decided to leave the coating on the glass in this area. It wouldn’t affect the lens’s performance on sky, and it meant we had something of the old coating left in case we decided to get more chemical assays done in the future.

Edge Effects - Something Still there

In the areas we did remove, though, we saw a curious thing: We could still tell where the AR coating had been. Something was still there. Whether it was an undamaged underlying coating or just a chemical stain on the glass we couldn’t tell. It didn’t seem to scatter light the way the damaged coating had, though, so we left it alone.

Reflected Light Image - Coating Gone Lens Back

At the end of the second day the lens looked like… well… like a lens again. We did a final rinse with DI water and a final clean with methanol, then reinstalled the baffle and called it good.

Last Dustoff

The next day we blew it off with our version of canned air: high purity nitrogen and a regulator. In volume it’s cheaper than canned air, runs no risk of depositing stuff on the glass by accident, and lets us cover a lens this size in a matter of minutes. It’s a heckuvalot faster than the little Rocket Blower I use on my camera gear!

Last Look - Something Right

With the lens back on the instrument and the baffle back in place, we took one last look before putting it on the telescope. This is almost the same lighting that we used the first time we looked at the lens several weeks prior. The difference is striking. Before, I couldn’t even get my camera to focus on the bolt heads inside the optical tube assembly. This time? Not only could I focus on each of the bolts in the OTA, I could see all the way up to the pickoff mirrors for the guide cameras, and focus on the optics of the guide cameras themselves. Now that’s what a lens is supposed to look like!

Of course the day ran late. We were all getting used to leaving the mountain later than normal. With the instrument reassembled, we all sighed a big sigh of relief. And I finally got back to doing the kind of photography I prefer: landscapes.

Winter Ice

A little less snow and ice than when we started, but I couldn’t pass up the light.

We went up the next day to put the instrument back on the telescope. Everyone was eager to hear the news: Did we get the light back? A couple of people stuck around headquarters after the exchange to watch the first images come off at the beginning of the night. I opted to go home and spend the evening with my family. About 7:30pm I got a call from the remote observing room: The images looked great! The light was back! It was the best news I’d heard in weeks.

At 8:30pm I got a second call, this time from my boss. The filter mechanism had jammed. “When do we go up?” I asked. I knew the answer. It was bound to be some version of “Right now!” We drove back up and cleared the filter jam. While we were working on it the glycol chiller system stopped working, so we purged that. Then our all-sky infrared camera stopped working, so we worked on that. It was almost 2am by the time we finally headed home for the second time.

“Hey, is that the volcano?” my boss asked. Off in the distance we could see the Halemaumau vent lighting up its cloud of volcanic gases. “Sure is!” I replied. “Pull over and take a picture,” he said.

This is the thing I love about the people I work with. My boss had been up the night before doing on-sky engineering. We’d just been through weeks of hell trying to get this instrument back on sky. Its first night back, two more systems on it fail. By the time we finish it’s two in the morning and we’re zonked. But people still take the time to appreciate the beauty of the place we live, work in, and call home. I pulled over and set my camera down on a rock so I could take a picture of the volcano at night.

Volcano and Stars

It was a good day.

– Tom

Posted in Astronomy, Engineering, Hawaii, Photography | 6 Comments »

Even More Cowbell

Posted by Tom Benedict on 11/01/2015

I still haven’t used my new strobe gear to do portraiture. Which is kind of odd, now that I think about it, because that was one of the things I had in mind when I got it. I put some of this down to portraiture being a relatively new form of photography for me, so I’m not as driven to jump in. And some of it has to do with my only having one light and no reflectors. It’s tough to do good portraiture without at least a bounce card. (I know, I know… A bounce card is no more complicated than a piece of posterboard. I’ll get to that in a second.)

The real reason? NO ONE wants to be a subject, much less hold a piece of posterboard I tell them is actually a bounce card. (See? I told you I’d get to it!)

But that didn’t stop me from hoarding all the gift cards my family gave me for Christmas and using them to get  a second strobe, light stand, and umbrella. And it sure didn’t stop me from adding a 42″ reflector and flash diffuser to my cart while I was at it. As I placed the order I told Rydra that she and our little minions were now fair game. Oh yeah, baby! The portraits will roll! (Unfortunately, all of them know where I sleep, and know how to pull the batteries out of camera gear. So maybe this won’t work out as well as I’d hoped.)

Meanwhile I’ve been enjoying my single flash a great deal. No portraits, but I’ve been using it at work a ton. Most recently I’ve been using it while we’ve been investigating an issue on a much larger camera than anything I carry in my bag.

Megacam on CFHT

This is Megacam. When it was built it was the largest digital camera in the world. It’s a 320 megapixel focal plane fitted to a wide field corrector that’s optimized for use on our telescope. (And yeah, it came with Linux drivers.)

My real involvement with Megacam started as it was being integrated for use on the sky. Shortly after it saw first light, people figured out that it needed something that wasn’t part of the original design: a light baffle. That was my first large-scale project at the observatory: design and build a baffle for Megacam. The big black can on the bottom that looks like a silencer is what I came up with. It’s about 2m high and about 1.2m wide. To date it’s the largest lens hood I’ve designed and built. Tucked up above it is the wide field corrector assembly: four lenses and one image stabilizer (heck yes it includes image stabilization!) And it’s there that the story begins.

A few months ago one of our astronomers alerted us to what looked like a steady degradation in instrument performance. We investigated and found that the bottom-most lens in the corrector was dirty. One of the guys at work tried valiantly to clean it, but even his best efforts left the lens looking… ooky. To make a long story short, we took everything apart, looked at it through a microscope, and figured out what was going wrong. To our dismay we found that the optical coating on the lens was literally falling apart.

I wind up doing a lot of the documentation photography at work. Any time something goes wrong that we need a record of, I’m asked to pull out my camera and get busy. As part of the investigation of this lens I had the opportunity to do ambient light photography, dark-field photography, and (you guessed it) flash photography.

I needed a set of reflected light photos of the outer edge of the lens, but the room lights were killing me. So I turned them all off and pointed my flash at the ceiling to use as a giant white card. It worked great.

MC WFC L1 Acids

It’s not perfect. You can see the light fixtures in the reflection of the ceiling. But we’re not trying to do image analysis with these. The point was simply to record the state of the coating at several points around the edge of the lens. I couldn’t have pulled it off in the time I had available without my strobe.

I’m sure my second flash head will find its way into the photography I do at work. But what I’m really excited about is finally finally jumping into portraiture.

– Tom

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