A New View!

Long time readers know I'm justifiably proud of some of the Mirror Lab accomplishments, including the twin mirrors of the Large Binocular Telescope, each 8.4 meters (about 27.5 feet) in diameter. In particular, I've been on a quest of sorts of imaging the telescope while it does interesting things. It seems to have culminated last Spring when I caught the ARGOS laser propagating into the sky from a distance of 12 miles. From the town of Safford, through a small telescope, I almost had a front-row view of the instrument, visible at left, which is used to project a constellation of artificial stars in the field of view of the telescope to partially correct atmospheric turbulence. Several hundred similar frames were combined to make a short video seen here.


Well, without permission from the powers that be to get any closer (made more difficult by the recent severe fire this last spring that approached within 50 meters!), my most recent query was - from how far away can you see it?! From a post a few years back, I knew that LBT was line-of-sight from Kitt Peak National Observatory, very close to 120 miles away! The image at left is from that post and demonstrates that if you can see KPNO from LBT (flat-topped mountain in center), you can see LBT from KPNO!




So last night after work (working evenings this week at the Mirror Lab), I found my way driving westward - this after confirming with the LBT telescope operator that indeed ARGOS was operating properly. Being that it was dark-of-the-moon, I parked on the last pullout before turning towards the Observatory so that my lights would have no effect on operations there. It was an interesting night - totally clear, but obviously above an inversion layer. I watched the thermometer climb as the van ascended. It was 60F at the base of the mountain, 70F on top! The wind seemed a little blustery, alternately blowing out of the south or the north - weird! But fortunately, I was very comfortable in shorts and a long-sleeved t-shirt.

I had several optics to try - the first was easiest to set up - the 500mm F/4 "big bertha" telephoto. I had it up, pointed and focused on the lights of Tucson in a few minutes. It took me a couple shots to find where the LBT would appear - I'd never seen it from Kitt Peak, as it is quite small. But I knew it would be left of the red-lit radio transmission towers atop Mount Lemmon, so used that as my guide. About my 3rd shot - there it was! The green laser standing out from the occasional star and headlight visible on the Mount Lemmon Highway. At left is shown a 6-frame panorama of part of Tucson. with the green spot of the 18 watt ARGOS laser visible. At right is a single frame at a little larger scale better showing the laser beam.


I then broke out the big gun - the TEC 140 - a 5.5" diameter telescope with 1,000mm of focal length. Again, because of the large magnification, it took a couple practice frames to get it pointed properly. Note that at NO TIME was the ARGOS laser visible to the naked eye or even visible in the camera viewfinder. It was only the power of a 20 to 30 second exposure that revealed it was there. I had started an exposure sequence for a possible time-lapse, and interestingly, the inversion layer is visible just under LBT. In a couple minutes of exposure, it slowly dropped and became a little brighter in the less-affected air. Also visible in the exposure is the south slope of the mountain, brightly illuminated by the lights from Ft Grant prison at its base.


Most of my outings, I usually finish with a practice shot or mini-project that can be completed while putting away gear. This night, approaching 1:30 in the morning, I mounted the 16mm fisheye on the Canon 6D and took a couple frames of the sky from Andromeda to the rising Winter Milky Way. What is most interesting, besides the reddish airglow that looks like clouds to the west (right), is the oval glow just below center. This is called the Gegenshein, or counter-glow - a spot defined by being opposite to the sun in the sky. An optical effect allows sunlight to reflect from meteoritic dust back to us. This may be my best photo of it, and from only 2 stacked exposures shown here. Each of the 2 exposures were 2.5 minutes with the fisheye working at F/4.

Always great fun to be under a clear dark sky, and while chasing an ARGOS viewing might be only an excuse, it doesn't take much to get me out looking up!

Adler Planetarium

One of my obligations on this trip to "Ketelsen East" was that I had agreed to speak at the September meeting of the Chicago Astronomical Society - at Adler Planetarium! I think it was a big deal because Adler is a big deal! It is the oldest planetarium built in this country and is part of the lakeside museum complex where Chicago meets Lake Michigan. In fact, flying into O'Hare the day before speaking, we flew out over the Lake before turning and landing towards the west, and had a great view of the downtown area, including the shot at left of the museum complex. This is a full resolution (cropped from the full image) and labels added to identify some of the major structures. The planetarium is on a manmade island which also used to have a small plane airport (Meigs Field). The airport was demolished in 2003 and "North Island" is now entirely park land, as is much of the lakeside. From the base of the stairs at the entrance, mostly only the original marble building is visible with the projection dome at center.

The original building was a 12-sided structure, and perhaps you can make out in the wide shot above, that each corner of the building had one of the signs of the zodiac. Four of them are collected in the collage at left - I just love the art deco design of these! Unfortunately, most are hidden by building expansion and while some are visible inside the additions, I suspect not all 12 can be located (I didn't have the time!). If you get a little further from the structure, you can see some of the newer additions that wrap around the lakefront side of the original building, also, you can pick up the figure of Copernicus seated on a marble plinth in front of the planetarium! The photo at left was taken shortly before sunset...


And you can imagine that with Adler located on a spit of land so close to Chicago, that the view of the city is great - and you would be right! At left is a 2-frame panorama looking down Solidarity Drive towards the west. Not exactly looking towards the skyline, which is a little more to the north, that would be the image at right! The image needed someone in it and luckily these two girls served the purpose well! The skyline view is great and in fact, there is a webcam atop the Adler dome, but I've not found a public-available view of it! It is used for several of the local TV weathercasts as it is a good indicator of weather and cloud cover, so perhaps it is now a "pay for play" camera!

Fortunately, I had an escort to make sure I got to the Adler from "Ketelsen East" in the far-western suburbs! Mark met me at the Geneva, IL train station and guided me through the station downtown where we were picked up by Tony of the CAS for the drive to Adler. If not for all this, it would have been tough for me to make it on my own! Melinda and I made it to Adler once in the last 10 years, and it was a tough drive, needing a navigator, then paying $20 for parking once arrived. The train was a nice method, but introduced its own set of "need to know" facts!

Anaglyph - use red/blue glasses to see Gemini 12 in 3D!

We had a couple hours to go through some of the displays. One of my favorites was an entire gallery devoted to "local boy" astronaut Jim Lovell. There was quite a collection of his papers and artifacts of his growing up and time in NASA, including the Gemini 12 spacecraft on display! That is it on at left - amazingly small for 2 people to spend 4 days out in space! BTW, that is a 3D anaglyph at left, so get out your red/blue glasses to see it in 3D. For those of you without glasses or only one eye, check out the similar image at right...





At an institution like this, you expect a good collection of instruments both historical and more recent, and they had a very good collection. At right is a selfie image of me taken with a thermal IR camera demonstrating invisible wavelengths not visible to the eye. I was wearing glasses, and carrying my camera that took this photo of the monitor, so they are near room temperature, and it appears my cheeks are the hottest (brightest) exposed part of me... I was also wearing a hat, so the top of my head is clipped too... At right, Tony and Mark examine a collection of antique telescopes from the early 1800s...

Of particular interest to Tony and Mark was a large refractor (18.6" diameter) Clark refractor that was on display. There was some discussion whether it still belonged to the Chicago Astronomical Society as it once was. There was some uncertainty in that...


Adler officially closed at 4:30 until the evening programs started, but we had arranged a tour of the adjacent Doane Observatory which serves as a public telescope at the facility. Located on the lake side of Adler, it is blocked from direct lights of the city. Our tour was given by long-time employee Michelle Nichols who apparently wears many hats including director of public observing. That is her standing in front of the facility at left, and in front of the 20 inch telescope at right. We were debating the various effects on seeing of the building - Mark thought the concrete walls would heat up during the day, but my thought was that the ivy shaded much of that effect. The dome is a little unusual in that it is the truncated cylinder as shown in the image. Because one side of the "dome" is heavier, the wheels wear unevenly and require frequent inspections. There also seemed to be an ongoing issue with collimation of the telescope affecting the image quality, of which all three of us offered assistance to inspect and adjust. While my time in Chicago is limited, Tony and Mark may get put to work to try to improve the images.


After Michelle's tour, we had "dinner time" on the schedule and while we had talked about a ride over to Millennium Park to enjoy "The Bean" and get a snack, we stayed adjacent to the planetarium and talked about things over a couple chili dogs at the stand a few feet from the steps.

Eventually my time came and my talk about working on the GMT project at the Mirror Lab was very well received. It was under attended though - evidently the thinking was that with a local concert, the parking was enforced at $35, which might have turned off a lot of club members - a significant jump over the normal $4 for night time parking! And even with us amateur astronomers preaching against light pollution, I had to admit that the night time view of the Chicago skyline was quite striking! I've got more from this visit to post - stay tuned!

A New View of LBT!

It is never my intention to go a month between blog posts - it just seems to work out to that lately - I have no excuse! Case in point is this post about the Large Binocular Telescope (LBT) - the photos were taken nearly 2 months ago! I was initially looking for permission from their director to ok the release of the images, but after so long, I guess I'll be looking for forgiveness rather than permission if they complain!


I feel sort of possessive of the LBT telescope as I supervised the polishing operations on the primary mirrors. Entering "LBT" in the upper left search window will return a number of posts, including some on the ARGOS instrument - my current favorite. ARGOS, of course, stands for "Advanced Rayleigh guided Ground layer adaptive Optics System" - an instrument mounted on the telescope that uses lasers to focus 10km above the telescope, those artificial "stars" are used to analyse and correct the atmospheric turbulence along the path. It really is exciting stuff, as it can improve seeing over a relatively large (up to 4 arc-minutes) field by a factor of 2 or 3.  While a factor of 2 or 3 doesn't sound that groundbreaking, note that the INTENSITY or brightness of a focused star goes up a factor of 4 or 9, by improving the sharpness that factor of 2 or 3.  Improving your star detection ability by a factor of up to 9 really is a big deal! This post really isn't about the instrument, merely observations of the lasers involved. For more information of the system and results, even from this run, go to the Max Planck Institute site - the sponsor of the instrument.

There was an ARGOS run in early March. With fresh snow on the mountain, I didn't even consider an observing site on Mount Graham, instead, went to the town of Safford, some parts of town enjoying a direct view of the telescope. I had obtained telephone permission to observe from the Discovery Park campus, but their view was a bit too obscured, so moved about a mile eastward for the good view shown above right at about sunset. You can see in the photo if you go west or north, the rise to the right of LBT starts blocking it. From my vantage point, LBT was 12 miles away - the closest I've been for an ARGOS run! The image at left shows my setup - from 2 sturdy tripods I was running a 500mm lens on the Canon 6D (full 35mm format) for a wide angle shot of the telescope, and the TEC140 (1,000mm with Canon XSi APS format) for the narrow field-of-view.

Looking very carefully at the above image, the laser projecting upwards from near the peak of Mount Graham can barely be seen. It was much more obvious through the optical aid of the telescopes and telephotos! At left is the view through the 500mm. Coupled with the larger format of the 6D, it gives a very nice wide field of view.

Through the TEC140, as with the photo at the top of the post, lots of details can be seen, including antennae in the sunset shot above! I took a series of photos with both setups, typically 30 second exposures under the nearly full moon was sufficient to get a good histogram. In the wide shot above, a wisp of clouds can be seen hugging the mountain. There was a layer of smoke that I suspect was from a controlled burn from the Tucson water treatment plant. The "Sweetwater Wetlands" had a burn of vegetation to control mosquitos, and can be seen as an enhancement in the laser scatter just over the telescope in some of the shots.

I chose to use only the narrow field in making the time-lapse of the evening, since the details were so stunning. In addition, I was able to start taking images before the dome opened, another advantage of knowing the phone number of the telescope operator and getting briefed on the observer's plans. So shown here are about 270 frames taken over a 3 hour period covering the dome opening, setup and following the first object of the evening. While it looks like the telescope is tracking across the sky much more slowly than the stars in the field, realize we are looking just over the horizon with a considerable focal length while the telescope is looking much higher in the sky.




Note that at no time was the green beam of the ARGOS laser visible to the naked eye. Even in my decent pair of 9X63 binoculars was it barely seen. Of course, as seen above, it photographs well! Finally as I was driving home with the telescope on its second object, I could barely detect a "green star" from inside the enclosure directly by eye, but that was all that was visible in my nearly 4 hours there! I've heard rumors that locals are upset at the lasers, but as you need optical aid to detect them, it hardly seems obtrusive! At the same time, with the gains in observing efficiency they are seeing it is proving its worth.

Before leaving, I took a few frames of the Discovery Park campus a mile to the west from my location. It is a cool place with interesting displays of both historical interest from the region, and the ground-breaking science going on at LBT and the optics from the Mirror Lab, including a cool 20" Tinsley telescope in the dome. Shown here is a 2-frame mosaic illuminated by ambient moonlight, and some security lights on the grounds that give it a nice glow...

Brush With Celebrity!

Congresswoman Gabby Giffords, April, 2010

Congressman Ron Barber, Aug, 2013

Working at a high-profile location like the Mirror Lab, we get our occasional VIPs and celebrities. Frequently some of these groups are lead by the College President or more likely by founder Roger Angel or former Director Peter Strittmatter. The Lab is quite the local source of pride - and so it should be! I think I recall spotting Senator John McCain once, but have recorded two congress-persons, Gabby Giffords, shown at left, and her replacement Ron Barber at right. Gabby's photo was taken at a solar power technology meeting hosted at the lab and the photo is of a solar-powered car an engineering team had built. The photo was taken 8 months before she was shot in the head in an assassination attempt. Ron Barber's photo was taken in the Lab as he was hounded by the media! Since these photos we've also seen their Republican replacement Martha McSally...

Mike with Bill Walton

Linda and Bill, photo by Steve West

But I've never quite seen the excitement that was caused by a VIP last Friday. After announcing the UA/ASU basketball game at McKale Center Thursday night, Former UCLA and NBA standout, and now sports commentator Bill Walton was taking in a tour from engineer Mike Tuell! Evidently Mike had contacted him nearly a year ago through Bill's website offering a tour and it finally happened last week! Now you have to realize that Mike towers over most everyone at the Mirror Lab, so it was a bit unnerving to see someone, anyone, towering over him! And later I saw a photo that I also had to share - the same grinning Bill Walton REALLY towering over our receptionist Linda - who I always considered normal height, but appears deficient by comparison here... Oh, and his actual height - Mike claims it is 7', but there was some conspiracy involved for listing it officially at 6'11"...

Anyway, there was excitement in the lab as he was recognized by most, signing autographs and posing for pictures. Congressmen and Senators, I guess are dull by comparison compared to a famous athlete!

A Rare Optical Alignment!

The first day of work in 2017 at the Richard F. Caris Mirror Lab and what should I find, but a first-ever (that I'm aware of) alignment of the first 3 mirrors of the Giant Magellan Telescope! There are 4 mirrors in various stages of completion in the lab, but today GMT1 was moved from the test tower where it has resided over the holiday shutdown, out into the integration lab while both machines are undergoing some upgrades. So as seen at left, from right-to-left are GMT1, GMT2, and GMT3!

GMT1, the blue-colored one at right is finished, but will likely serve as reference to measure all the other mirrors, so may be the last to be delivered! It has a brush-on blue coating to protect the finely-polished surface.

The center mirror (with Leslie standing in front for scale!) is GMT2 and is diamond generated and awaiting fine-abrasive lapping and polishing. In the rear is GMT3 - currently face-down, with rear work of applying load-spreaders and thermocouples complete. It will soon be flipped over and work started on the front concave surface.

All of these mirrors are our standard-size 8.4 meter diameter substrates. That converts to nearly 28 feet in diameter. If you go to the GMT website above, that telescope will consist of 7 of these mirrors combining to form a single HUGE telescope... As seen at left, these 3 mirrors nearly fill the integration lab completely, with barely room to walk between them. You can see that both polishing cells are nearly identical, with a plumbing skirt to contain polishing and generating fluids around the outside. Visible on the GMT2 cell at left is the inflatable pressure seal at the backplate which allows pressurizing the cell plus mirror to match the polishing pressure to reduce print-through in the finished mirror surface.

And some of you may well wonder why the rear of the GMT3 mirror is covered with foam. Nothing secret certainly, just protecting the rear surface with the now-attached load spreaders which will interface with the supports in the polishing cell and the eventual telescope cell. At left I've pulled back one of the foam sheets to show loadspreaders and the thermocouple wiring so that mirror and air temperatures can be monitored during polishing or in the telescope.



And just because it is MY blog, here are some 3D anaglyphs! Grab your red/blue 3D glasses and enjoy the following shots. By adding another shot an inch or two away from the loadspreader shot above, you can make the 3D shot at left.

And while I was on a ladder taking the above shots, Looking back across the lab, I took another stereo pair of GMT1 and GMT2, shown at right.

We're continuing machine upgrades, and need to run some experiments to checkout machinery and software before continuing work on the GMT mirrors. Stay tuned!

Optics Ole'-Timers

Everybody's friend Bob Crawford died a week ago (7 April) on his 77th birthday. Well, I should say that if you had ever met him, he was a friend. One of the nicest folks I've ever known, he was on staff at the Optical Sciences Center's optics shop where I worked for a few years in the 1980s. He was a veteran Master Optician, and as a newcomer to optics after nearly a decade of astronomy in college and Kitt Peak National Observatory, he was quick to help and teach the newbie (me!) in any way he could in my new profession. Even though my duties were mostly in metrology and engineering, he answered my million-and-one questions about fabrication, and slowly I absorbed from the master...

One day I brought in my 4X5 view camera and took some pictures, including these of Bob beside what I recall was a spare mirror for the Multiple Mirror Telescope. I was called on it today by one of the old-timers from the period, but I wasn't around for the original six-mirror fabrication, so this had to be the spare, made out of the same surplus Air Force egg crate fused quartz substrates. In the other image, MMT engineer J.T. Williams was assisting Bob in measuring some of the physical parameters of what was likely a nearly-finished mirror in its handling ring. These negatives have never been printed, but this week I got them scanned and prints made for today's services.

The memorial today was absolutely amazing!  Everyone in the Tucson optics industry was there - a testament to Bob's outgoing personality and how he was loved wherever he went. Former OSC directors, secretaries and former co-workers and staffers of all levels came to pay their respects to Bob's memory, his wife of 52 years Joan, and adult children David and Jennifer. As is always the case (last time was the passing of another OSC optician Ed Strittmatter 2 years ago) it is a shame it takes the death of someone so loved to bring everyone together to catch up on our lives.

Melinda and I had just seen him a couple weeks before his passing while at the cancer center. Melinda was in getting blood tests, and Bob and Joan were on their way home after an oncologist appt. I'm sure he was feeling poorly, but we chatted for a good long while, waiting for Melinda to get out of the lab so they could talk to her and see how she was feeling too. But that was how Bob was - always wanting to be brought up to date, hear a story, a joke, bring out a smile. Thanks Bob - for everything!

March '16 ARGOS Run

Regular readers know that I love recording things in the sky. While the Large Binocular Telescope (LBT) and the ARGOS system are not a natural phenomenon, since I worked on the fabrication of the mirrors of the huge telescope, I feel a natural bond to it atop Mount Graham. I've posted about it many times before - most recently in October, I was in position at a new observing spot about 20 miles south, but a stubborn cloud cap remaining from a clearing storm prevented their opening while I waited below. However, that post resulted in my finally putting together a nice time-lapse nearly 2 years earlier from November '13. A more general post describing the instrument and the other telescopes atop Graham is from that earlier date. This time (a couple weeks ago on 12 March) the weather was great, though a little chilly with a bone-chilling breeze. I was set up about a mile south of a small development, and about 16 miles south of the brilliant lights of Fort Grant, a State Prison, visible at the left side of the above image. From 20 miles, the laser was barely visible to the naked eye, but with binoculars could be spotted nearly to Polaris about 30 degrees high! In this image, I'm lit up by a several-day-old moon in the west, that was to set about 11pm.

Once the scope and telephoto lens was set up, you realize how difficult it is to align and focus in pitch black conditions! I ended up focusing on the rising stars of the Big Dipper's handle, but alignment on the LBT (before the laser started up) was tough requiring many short exposures as trial. It would have been much easier to get there an hour or so earlier, but time seems a rarity lately!

Finally success, as shown at left is the view of Graham with LBT and ARGOS with the 70-200 zoom set to 70mm. You can spot some of the local lights and how much the lights of the prison illuminate the southern flanks of Graham. At right in this wide image is Heliograph Peak, and while it looks to be the tallest peak, because of perspective (it is a little closer to my position) it isn't... At right is a shot of the mountaintop through the TEC 140 with its nearly 1,000mm of focal length, and the scopes atop the peak labeled. You can even spot the illumination from Fort Grant on the side of the LBT enclosure! Amazing what a minute will show in the exposure, since the laser was barely imagined to the naked eye.

All was going swimmingly - I ended up shooting over 2 hours of images with the TEC 140, potentially for a time-lapse (see below!). But when I took a first-look at the images later, I found a surprise! Shown at left is an image taken less than an hour into my shooting. While LBT had moved on to its second object of the night, there appeared to be a second "laser" appearing to emanate from the Sub-Millimeter radio telescope. But there were 2 clues about it's real source. First, clicking to load the full-size image, you can see wiggles in it as the source was affected by atmospheric disturbances, like the distant stars themselves... Also the telephoto caught part of the trail as it was disappearing behind the mountain. It was likely a distant sun-illuminated satellite disappearing over the horizon... Unfortunately, using Heavens-Above, I couldn't locate any possible candidates...


And yes, I did put together the time-lapse sequence, after editing the 140 images taken that evening with the TEC 140, and uploaded it to Youtube for your convenience! Note that the change in lighting over the time-lapse is due to the moon setting towards the end.




In conversations with the LBT director, he ended up using the shot of mine of the satellite disappearing over Graham in the LBT blog, which also includes highlights of the ARGOS run. Evidently ARGOS, which projects laser spots 10km up for partial correction of atmospheric turbulence, improved the seeing over a moderate field of view to .2 arcseconds. See the blog entry for more info.



Addendum: When I published this post late last night, I totally spaced that I got more shots of this run from a different perspective a few days later! Joe Bergeron, visiting from out of town, and I went up to San Pedro Vista on the Mount Lemmon Highway and spent an hour or so shooting towards Graham. Four days later and the moon was a lot brighter, and we were over twice as far away as above at nearly 50 miles. As a result, it was sort of murky and bright, but managed a few frames. Three images were stacked together to make the image at left. You can see a moderately bright star, heavily reddened by the the low elevation rising past the telescope and ARGOS laser. There is also enough ambient light that you can see snow on some of the higher slopes of Graham.

Another thing I've found in the last 24 hours is that when you play the above time-lapse, one of the clips it will auto-play is one made by the ARGOS team from adjacent to the LBT! It is a spectacular clip, showing what is possible with the short exposures and wide angle lens as a result of being 40 yards away, as opposed to shooting from 20+ miles with a meter-long focal length! Impressive stuff - copied here for your convenience - enjoy!

Glass Recycling!

I hate to throw stuff away that might have another use - especially when it comes to optics and telescopes. Amateur telescope makers are known as scroungers - even going to the trouble of making mirrors from television cathode ray tubes! I won't go to that much trouble, but a couple decades ago, in the early days of the Mirror Lab, we performed some diamond generating experiments, using some 48"X48" sheet Pyrex we happened to have in storage. After the experiments, I was told to put them in the dumpster, but I set aside some of the nicer pieces, using a hammer and chisel to "score" a line, set the line on a 2X4, and jump on the piece to snap the pieces into manageable sizes. "Snapping" Pyrex up to 1.5" thick was no simple task, but I took a few pieces home where they've been sitting for the last few decades, as shown at left. While 1" to 1.25" Pyrex is a little thin for large mirrors, it is fine up to 16" to 20" diameter (I guess some might consider that large!).

With the arrival of Spring, I thought it was time to try to do something with the glass pile, so picked out a nice piece to take to a local machine shop. Shown at right (leaning against Melinda's Jeep tire) as I was leaving the house, I figured they might be able to cut out a 16.25" diameter piece of glass.  The white marks on the glass are shallow diamond generator marks on one side of the Pyrex sheet.

I've used and mentioned A-1 Fabrication They cut some 2" thick steel counterweights for my AP 1200 mount, and also did some very nice welding on the aluminum mount for my TEC 140 scope. Supposedly their water jet cutter should be able to make my irregular pieces a more useful round shape, so went to them last week to try them out when it comes to glass. I've not talked about water jet cutters before, but it uses high-pressure water with added abrasive to cut through most anything. Miguel offered to cut out my round for $80, which sounded great to me! It would have been a couple hours of tedious work to rough in the shape with a brick saw, then diamond generate the edge round. Remembering too that a 16" Pyrex substrate would likely cost in excess of $500 or so, $80 in addition to my recycling storage fee sounded good! So I dropped off a sketch and the glass about a week ago - they said it would be a few days. When I hadn't heard in the week, I called and they said they would do it that day (Friday). Sure enough, I got the call a couple hours later and picked it up.
before.

I looked near-perfect! It was chip-free, and perfectly round to better than .030" or so. Miguel showed Roger and I the machine in use. They were cutting a piece of half-inch stainless steel, and said my 1.25" Pyrex cut at the same speed of 3" per minute. With my 16" having a circumference of 50", it would have taken about 17 minutes for the full disk. The "kerf" (width) of the cut was only .030", so there was almost no waste, and there appeared to be little or no widening of the high pressure water cutting edge over the thickness of the glass. The first thing I did was use a diamond pad to put a little bevel on the sharp edges to prevent chipping, There were some subtle marks along the edge as the water pressure, abrasive feed or linear motion surges during the process. Shown at left, they should have no effect on its performance as a mirror blank.

Now that I know they can do work like that, it is easy enough to mark out and get the other chunks cut to size. All I need is more projects to work on, but those seem to spring up as soon as the pieces appear!

Progress On GMT4

I love posting about the work that goes on at the Richard F Caris Mirror Lab. In my nearly 30 years there, I'm justifiably proud of the work we're doing - making telescope mirrors upwards of 28 feet (8.4 meters) in diameter is an interesting juxtaposition of steel mill technology and the finest measurements you can imagine (thousandths of a human hair). Unfortunately, I can't post about my current work (not secret, just sensitive), but the Lab is making some good progress on major projects. A couple months back, I posted about the unveil of our latest glass casting - another 8.4 meter mirror destined for the center position of the Giant Magellan Telescope. Once out of the oven, the work starts, and I've brought the camera in a couple times to document the newest glass.


Since the post linked above, as shown at left from 27 January, the outer Inconel bands have been removed, as have the outer tub walls and the soft refractories have been scrubbed from the outside diameter of the substrate. At right is a 2-frame panorama showing the long view past the central hole. The streaks are the last remnants of soft refractories that have yet to be cleaned off - which they likely were the next day! The next step is to lift the glass off the oven to start mold removal, which is encased inside the glass. The crew hadn't let the moss grow as the mirror cooled in the oven - the lifting fixture had already been assembled in advance!


When I next brought in the camera a couple weeks later, the lifting fixture, called a spider because of its spindly structure was in place on the curved surface of GMT4. Still attached to the crane, they were adjusting the individual substars to properly balance the weight between them.

The closer image at right shows each of the 6 points of the spider was sitting atop a jack stand, fine vertical motion through a screw jack and load cell with readout to measure the weight distribution of the spider.  On the mezzanine level in the background, the top "cone" of the oven can be seen in its storage area.  Once the spider was centered properly and the 36 annular attachment points were properly adjusted for load sharing, the next step was gluing the spider to the front face of the substrate.





A few days later and that was accomplished too! In the image shown at left, some of the annular pads can be seen with black RTV oozing out. Not shown here is a metering dispenser that mixes the 2-part RTV adhesive from 5 gallon containers and pumps it out a hose that is held in place in those holes to pump the compound into the gaps between the steel annulus and the glass. Once it hardens it will be strong enough to lift the substrate plus mold, and hold it upright in the cleanout stand for mold removal, which will take a couple months. Just the glass of the 8.4 meter mirrors weighs about 20 tons, and the weight of the mold plus hard refractories almost doubles the weight to 35 tons. But with time, as the hard refractories attached to the back of the mirror, and the soft refractories imbedded in the glass are removed, slowly the weight will drop to the glass-only weight.

So in the next week or so that they give the glue to fully cure, the casting crew will put on their hardhats and protective gear for steel construction - assembling the washout stand that will provide an environmental enclosure for protecting the mirror against thermal shock (high-pressure water is used for soft refractory removal, and in low humidity can give dangerous temperature gradients), as well as providing safe access to all parts of the mirror for mold removal. The pieces are shown at right with the handling ring in the upright position - in a couple more weeks, the mirror will be mounted within the ring and steel structure providing a cocoon of protection around it.



WARNING: 3D Anaglyphs beyond this point!

Now for the good stuff! Anyone who knows me knows I'm a 3-D stereo nut, and more and more am shooting image pairs to make anaglyph images to view in stereo. So grab your red/blue glasses and be amazed at the following shots. Some of these from above are one image of the pair, others weren't used above, but these are my favorites of those I've taken recently. Most are likely hyperstereos - where the separation between the two images are a little wider than your eyes. The stereo effect is exaggerated somewhat, but oftentimes, that is welcome in complicated structures like the spider, shown at left. The image of just the curved substrate is more subtle at right, where there is not a lot of structure to focus on to provide depth clues. In fact, I'm glad the streaks are still there as they provide something for your eyes to focus on to provide depth.

Here are a few more - at left is another before the spider was placed, but from a different perspective than the one just above. The mezzanine level is shown, though dark, with subtle depth across the mirror till the pipes and tubing on the far wall are encountered.

At right, another wide shot showing the spider in place, this time with the lights on in the mezzanine level - strong 3D effect through the spider structure and even up past the oven cone.








Wrapping up with a couple close-ups of the spider atop the GMT4. I like the view at left that shows a bare strip of glass across the entire mirror chord, showing both the hexagonal structure of the casting, as well as the lines of annular supports.

At right is a close-up of an annular support after gluing, showing the port into which the RTV was injected. If you look carefully under the center support, you can see where the RTV oozed through the annulus of the steel ring and seeped into its ID.

The casting crew is making fast progress - the place looks drastically different almost every day.  I'll try to keep up in some documentation, including the 3D if you enjoy them - comments always welcome!  I'm thinking about a bulk purchase of the anaglyph glasses, so do let me know if you don't have them, or would like me to find some for you...