Wednesday, March 30, 2016

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!

Sunday, March 27, 2016

More Photo Phocus-Stacking Phun!

After the fun I had with the focus-stacking theme of the last post, I decided more was in order. Of course, there is the Desert Museum, which would be a great choice, but cheapskate that I am, I opted for B&B Cactus Farm on the far-east side of Tucson. While both are about the same drive for me, B&B not only let me gawk and photograph as much as I wanted, the helpful staff pointed me to out-of-the-way places where the early cacti were blooming. Yes, turns out I was a little early - they are saying the peak blooming of the cacti they have will likely be next week - so a warning to the local folks here - next Saturday might be good for a cheap date at B&B!

Hedgehog Cactus, 11 Frame Focus-Stack
Hedgehog Cactus, 8 Frame Focus-Stack
First to attract my attention were several
variety of Hedgehog cacti with their brilliant red and scarlet blooms. Don't forget that the focus-stacking technique I'm working on here are specifically for showing the finest details in close-ups, so most of these might be a more narrow shot.  There are a few single-exposure wide shots, but if you want to see more of the plants themselves, go to the Google, or better yet, go to B&B! Every variety of cacti are different, but the Hedgehog's have the recognizable red-orange flower with the bright green stigma

Robust Hedgehog, 21 Frame Focus-Stack
But just to throw a curve, here is another type of Hedgehog - a "Robust" Hedgehog, according to the tag. Note the markedly different color, though still has the contrasting green stigma.

The focus-stacking technique again, utilizes multiple images shot at different focus settings to extend the zone of sharpness of the image. For instance with this image, when the close edge of the flower was in focus, the rest was necessarily out of focus. There are some minor artifacts, seen just over the near edge of the flower petals, and right around the stigma where the out-of-focus edges in the original image shadowed the details beyond. Photoshop does a good job of putting them together, but it isn't quite perfect... Still, an amazing technique. I'm wondering if the software dedicated to focus-stacking (Zerene, Helicon Focus) would be any better?

Mammillaria rubragrandis, 14 Frame Stack
After the red-end of the spectrum, I was enchanted by other colors - in this case, white with accents! At left is a pincushion cactus with some beautiful white flowers and the palest of pink accents. Labeled Mammillaria rubragrandis, it was a spectacular cactus on its display rack. I felt sorry I didn't take a wider shot, then later found a larger one for sale in the store inside and took the shot at right.

Mammillaria muehlenphfordtii, 14 Frame Stack
Mammillaria rubrograndsis, 17 Frame Stack
And while on the Mammillaria cacti, at
left are some tiny flowers, less than 5-6mm in diameter on a Mammilaria muehlenpfordtii - such a big mouthful for a small cactus! Make sure you click to download the full-size frame to see the details in spines and hairs of the cactus.

Another family member is at right, this time a Mammillaria rubrograndsis. Again, the range in color tints is very striking!

And some colors were more unexpected than others... I know there are some cholla cacti that are about the only plants with green flowers. Too early for them this time of year, but spotted these with brown/tan colors with bright pink stigma. At right is a single wide shot of another plant showing the dark brown flowers.

Golden Barrel, 5 Frame Stack
Nearing the end of my shooting, I headed towards the retail store and spotted a pot nearly 4 feet (1.2 meters) in diameter that held 3 golden cacti that had to be about 18" (.45m) across. Yet they had the most spectacular little yellow flowers. At left is shown the cactus in the pot, and the close-up at right shows the blossoms. Click the image and you can see the yellow petal-tips are brown, making a subtle accent to the flower. Seeing all the dried blossoms, there must be times when it must appear spectacular!

Mount Lemmon Anaglyph - Red/Blue Glasses needed!
Finally, before leaving, I passed through the sales store and found some more of the spectacular cacti and other things for sale. Along with the white pincushion cactus above, I found another, whose flower was bigger than the cactus itself! Shown at left is the Lobivia wrightiana. It is a small cactus - see my thumb in the picture for scale! I couldn't get out of the Cactus Farm without buying something... I ended up getting a couple totem pole columnar cactus babies about 6" high after admiring my neighbor's growing in his yard over the years. Melinda also needed a new pot to transplant her ivy into, and I also got some cactus potting soil. But with all the images I got (almost 300!), I think I still came out ahead...

Oh, and if you thought you could get by without a 3D image, you would be wrong! I was so focused (excuse the pun!) on the focus stacking, I didn't take any 3D of cacti, but as I was headed out, realized as I drove back that there might be a nice one of the Catalina Mountains to the north. We were far enough away to clearly separate the front range from Mount Lemmon itself, so took a few pairs, figuring a couple hundred yards will do it - so grab your red/blue glasses and check out the image at right.

Thursday, March 24, 2016

Springtime - With A Vengance!

Yes, we see the calendar - we're a couple days into Spring, but Tucson never really had a Winter! A quick check of the National Weather Service data shows that all Winter, every month had some days over 80F (27C). We've already broken 90F (32C) on 17 February, and the local NBC affiliate has started the contest to name the time the official temperature reaches 100F - grand prize is a $7500 central AC unit! The "normal" date is mid-May, but with 90F broken already 5 weeks ago they are being cautious. And even though it was supposed to be an el Nino winter with above-average rain for us, since the first week of January, we've had under .3" of rain, so we've already taken to occasionally watering the native desert plants to keep them from stressing so soon. So with the higher than normal temps and lack of rain, we didn't get many wildflowers, but the cacti are starting to bloom, seemingly the smallest ones first!

Recently I was reminded to shoot some springtime shots - I was complaining to my bloggin' buddy Ken Spencer on a recent post where his shot of tree buds was mostly out of focus. He should have combined a few frames with slight focus change between them and combine them in Photoshop to "focus stack" and extend the range of sharpness. So I should lead by doing, so here we go... Down at the end of the street, our neighbor Mike has a few potted cacti and has some nice little mammallaria cactus covered with flowers and buds. Since the biggest is less than a cm across (less than 1/2"), time to break out the macro and extension tubes for some ultra-closeups! At left is that 1cm blossom with a 12-frame focus stack, where 12 exposures were combined with slight focus shift between them to keep everything of interest in focus. For comparison, at right is one of the single frames, which were all shot at F/8. Make sure you click on the image to examine the full-size version to see the finest details available. At this magnification, only a narrow range of the flower is in sharp focus - that is why the focus stack is such a powerful technique.

This next one used the same technique on a similar blossom atop the cactus, so the flower was seen more in profile. Again, a dozen frames were combined to make the image - interesting how it takes about that many for these shots... Now someone might ask that instead of taking a dozen shots and spend the 10 minutes on the computer to do the focus stack - can't you just stop the lens down to a smaller aperture to increase the depth of field? Good question and yes, you can! A smaller aperture extends the focus range, but there must be drawbacks - well, yes there is that. With stopping the lens down, the exposure is correspondingly longer. These cacti are pretty sturdy, and since I was shooting with a tripod, there wasn't an issue with using a tenth of a second exposure (at F/32) compared to 1/250 second at F/8 for the others. There is another drawback - at the smallest apertures, the laws of optics fight you and diffraction effects start fuzzing out details again. At right is shown the comparison at full camera resolution, showing the single shot at F/32 with the focus stack at F/8. While the stopped-down exposure does extend the focus range the focus stack wins hands down with incredible sharpness down the pixel scale.

With the mammillaria cactus well-covered, I moved the 40 yards closer to home. My neighbor Susan's prickly pear was forming flower buds - another natural subject. I like the "shooting into the sun" angle, making the needles look almost translucent. While the plant has a few big showy spines, the truly dangerous ones are the multitude of little spines that are hard to spot should you brush against it. On a hike in the wilderness, you nearly need magnifying glass and tweezers to remove most of them. Still, it can be a long-term painful experience! On the right, our Indian Hawthorne in our front planter is almost in full bloom. Interestingly, these plants get almost no direct sunlight, being under the north eave of the house, depends on me for occasional watering, yet has survived for the nearly 30 years I've been in the house. Not really a desert plant, it is likely the constant shade that has allowed it to survive. The flowers are short-lived, but for a couple days are a nice accent to the front of the house. The prickly pear buds were a 9-frame focus stack, the Hawthorn a 12-frame.

While the above pictures would likely have been enough for an early-Spring post, I wanted a little more, so went in search of denizens of the yard. On the Rhus Lancea tree in the back yard, I spotted some aphids and moved in close! These little sap-suckers are small and tough to spot, only about 1mm across. With the maximum 50mm extension tubes on the 100mm macro, the front of the lens was only a couple inches from the little guy. The shot at left is a 12-frame focus stack of a sprig on the tree where the new growth is soft enough for the aphids to take in the sap. I was surprised to only find the one on the higher sprigs (easily accessed without getting down on the ground). After taking this sequence, I looked harder and found a whole herd of aphids being attended by ants. Reading up on the phenomena, it turns out to get enough protein, the aphids take in a huge amount of sap and literally "poop" sugar water, which the ants love. Ants watch over the herd of aphids, moving them to different parts of the plant where there is new growth. Since the ant was so active, a focus stack wasn't going to work, so I went to some effort to get everyone in the same focal plane, and used the flash to freeze the ant's motion. Again, at right is a full-resolution blow-up of the ant watching over the aphids, the left image is a 12-frame stack.

And of course, it wouldn't be a "flora and fauna" post without some 3D images! So get out the red/blue anaglyph images for the following images. Macro shots are a little harder to get good 3D - they are very sensitive to scale, and the baseline between the image pairs are smaller than your eye separation, otherwise the 3D effect gets uncomfortably large and tough to focus. The little mammallaria cactus at the start of the post was a great subject, with only about an inch baseline between images. Shown at left, it is a great stereo shot, but the flower color is close to the glasses filters color and weird shifts occur! The flowers come out a blue/purple - interesting, but totally alien in appearance! So go to the top images in the post and imagine THAT color in the anaglyph at left. At right is the only non-macro shot today. I think it is a mesquite or palo verde tree whose flowering branches would make a good 3D image. It was taken with the kit lens and has a stereo baseline of about your eye separation, so should look pretty natural.

So that is what I've got so far this Spring. I'm keeping an eye out and will continue to see what looks interesting...

Tuesday, March 15, 2016

Birthday Gurl!

Today is Melinda's birthday! Six decades on this earth as of today! As seems normal in her family, it is appropriate to post an embarrassing photograph, so at left is one of her dad's favorite images of her (carried it around in his wallet to show his friends). As a little girl of about 2 she is shown sleeping on the potty! Dad must have found some humor in it, and he was carrying it when he died 10 years later, so present it to brighten your day as well.

Melinda is doing fine - in the middle of cycle 2 of Navelbine, gets her 5th infusion on Thursday, the 6th the following Thursday (24 March), then her next PET scan to monitor progress on 4 April. She had enough energy to go out for dinner tonight - her choice was Red Lobster - always one of her favorites! She was inundated with cards, texts and phone calls today. For her birthday I got us tickets to David Crosby (of Crosby, Stills, and Nash) who makes a stop in Tucson on a solo tour next Friday. She's a fan, so should be a nice evening. Oh, and while I offered to reproduce a present-day shot of her dozing on the potty, she declined, posing instead with the piece of carrot cake I got her for dessert. Happy Birthday Hon!

Sunday, March 13, 2016


Da planes, da planes!
This weekend was a "two-fer" here in Tucson - the very popular Book Festival held at the U of AZ campus and also an air show at Davis-Monthan, the local air force base. Not a fan of crowds or long walks to heavily-attended events, we tend to avoid such things, though I did brave traffic early both Saturday and Sunday to do some work at the Mirror Lab. And while Melinda wasn't up for a long trek to the air show, I convinced her we could drive to a spot adjacent to the AFB to watch the Thunderbird show. Since that sort of an exhibit extends well past the edges of the base, you can see parts of it from almost any part of town. We chose to go down near the Stellar-Vision Astronomy Shop, parking at the Dodge dead end near Alvernon, a mere stone's throw from the base fence. Arriving right at the appointed hour of 3pm, we depended on better-placed spectators with a better view (at left) to point out that the planes were taking off.

Seen Against The Catalinas
Fast Approach
But even though we didn't hear them launch, we soon were enveloped in the roar of jet engines. After a high-speed pass they were spotted cruising in formation in front of the Catalina Mountains. While they don't look far, witnessing part of the show from Midtown today, they are likely a good 5 miles away!

Melinda watched from a comfy chair near the van, I wandered about 40 yards away in the shade of a rhus lancea tree to avoid shooting through power lines. Being near the path towards the runways, they made frequent passes over us, some just under the speed of sound. As a result, there wasn't much warning they were approaching. From my vantage point, I could see them from quite a distance and motioned to Melinda they were coming. Trying to shoot them, as low as they were flying, at least their motion allowed some good close-ups.

They repeated some of their maneuvers, so some of my images were very similar, even taken 10 minutes apart! A good example is this one of a big loop, both with smoke generators. The one at left had 5 planes, at right only 4. One I made into a vertical format orientation, the other horizontal. I couldn't decide which I liked better, so include them both.  The horizontal orientation lends itself to better viewing on a computer screen, but the vertical structure is a natural for the loop.

Similarly the various formations of 4 or 5 F-16s were similar, and include them both as well...

All of these images were taken with the 300mm F/4 and XSi on a monopod. That lens worked great at zooming in on the action while comfortably ensconced under a shade tree!

copyright: Kelly Presnell / Arizona Daily Star
And I'll close out my contributions with a closeup of one of the solo F-16s making a high-speed pass at left. I think it was the lowest and closest I got to one of the planes.

But my favorite image from the show was from the Arizona Daily Star, with the 5-plane formation flying past the moon. I had spotted the moon from my vantage point and thought about trying to catch the jets in the same field, but would have been tough. Hopefully Kelley didn't Photoshop the image, but can only assume it is a "real" image!

Wednesday, March 9, 2016

The Seven-Week Ordeal

Don't you just hate it when the littlest things in life misbehave and just kick you in the butt?! The latest case-in-point just came to a conclusion today, but began 7 weeks ago! I was flossing before bed one night in January, and one of my crowns popped off. I was thinking that my dentist could just glue it back in, but Dr Chang pointed out that the little stump it was glued to came off with it, so that couldn't happen... I needed to go to an oral surgeon for a "crown lengthening", trim away the gum line and remove some underlying bone to expose more of the tooth to hold a new crown securely. Sounds fun, eh? At left is shown the offending crown that broke off. No response from the tooth fairy - I guess she's not responsive to fake teeth (crowns)!

So I make an appointment to the recommended oral surgeon - of course, 2 weeks away. In the meantime, no chewing on my right side. Finally the day comes - consultation only, it turns out. It also turns out that I've been there before - a good sign as I recall none of it! Evidently I was there 10 years ago for the same procedure on the tooth in back of the one he is working on this time! He said the job was no problem, appointment was 2 weeks away.

Turns out those 2 weeks were needed. Since I'm on blood thinners (artificial heart valve), I need to be off them for the minor surgery. The gold standard is to go on Lovenox for a few days before to bridge my being off Coumadin. While my drug store stocked it, insurance wouldn't pay it unless it came from Walgreen's Specialty drugs from somewhere in Texas. But to get it, the script from the surgeon that went to CVS somehow had to go through the clearinghouse in Columbus, Ohio to the distribution in Texas. It came the day before I needed to start taking it! Close call!

Surgery day came, my INR (measure of blood clotting) was right where the doctor wanted, and the procedure went fine. He used Versed for the anesthetic - same as used for colonoscopies too. So I was awake, but mostly out of it. Melinda came along to drive me home later - all was well. Until the next day... I had started my Coumadin back up, and sometime on Thursday, the tooth, which was well-packed under gauze and tape, started bleeding and wouldn't stop. Not gushing, but steady enough to have big clots of blood in your mouth every 10 minutes. Hard to sleep through the night that way, but showed no signs of abating, so back to the surgeon, where his assistants worked on me (he was out at some insurance meetings). She got it to slow down if we packed rolls of gauze and I bit down hard, so left it at that - after she supplied me with what seemed a case of gauze! Still bled into Friday, when I involved the INR clinic at the hospital. She had me stop taking the Lovenox after my Friday morning dose and that is what did it - full bleeding stop on Saturday - no more issues. Saw the surgeon a week later - I was fine and he okayed 3 weeks to a new crown.

So today was new crown day! For a fan of technology like me, getting a crown is kind of fun these days. A decade ago when I had my first one, it was the 3-week wait for the permanent crown to come back from the lab. These days, there is a new computer-driven system called CEREC that maps out the tooth with a 3D camera, the dentist designs the tooth on a computer CAD (Computer Aided Design) program. And a little diamond milling machine cuts it out of a block of ceramic in the room next door. After a test fit it is baked in a high-temperature oven and it will be harder than your original teeth! And it usually takes about an hour for the entire process! At left is shown the screen where the dentist designs the tooth to fit the stump below, and at left is the typical fit into place.

New Crown in the Middle
The last one Dr. Chang did for me took 57 minutes! This time we started without anesthesia, but I had some twinges, and he saw another patient for 15 minutes while the novacane took effect. As a result it took about 90 minutes, but better than a 3 week wait.  Oh, and the best part as he said goodbye - since the crown that came off was put on just 3 years ago, he didn't charge me the normal $500! What a guy!  And his last words - don't chew on your right side for 24 hours! Can't wait for tomorrow!

Day Old Moon!

It was just yesterday, exactly 24 hours ago, in fact, that there was a total solar eclipse on the other side of the world! We've got a couple friends on a ship somewhere between Indonesia and Malaysia that went to see it. While we've not heard from them, have seen a few images online. Meanwhile, after a busy day here, around sunset while feeding cats, I thought to look for the exactly 24 hour moon to the west. The "moon clock" starts at new, and you can't get any newer than a total solar eclipse! With the ecliptic at sunset nearly vertical, I was thinking it would be easy to spot, and sure enough, found it early and had enough time to go get the 70-200 zoom and set up for a shot in the front yard. The nearest palm tree is near enough to be slightly out of focus, but some vegetation was moving in the breeze for the .4 second exposure, F/9 at a focal length of 165mm. If you click on the image, the moon is the skinniest of crescents, and you can also see the "dark side", illuminated by the nearly full earth as seen from the moon. The moon will continue to wax (grow in phase) for the next 2 weeks, reaching full on the morning of the 23rd. Enjoy it as the weather allows!

Sunday, March 6, 2016

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.

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!