Staring @ the Sun, 62

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11/2/2012. It was cement to be?
So a couple of weeks back, I discovered that the ERF filter in the 152mm Frankenscope was split right down the middle. I noticed when I looked down the telescope's throat to see if there were any obvious problems that might account for its low contrast. This cracked filter wasn't obvious, and I don't think it accounts for much of the lack of contrast (because this solar 'scope has never shown the contrast I think it should), but I do think it caused some wierd doubling of detail down near the border of resolution and noise. That it was cracked was apparent only because the reflections I saw coming up from each side of the filter didn't exactly meet in the middle. I went in to have a look and the filter came out in two neatly split halves:




On the far right is a 72mm clear-glass photo filter; on the left, the cracked Lunt ERF. I compared reflections from a known-to-be-mounted-right ERF in my 60mm Lunt solar 'scope with the reflections from each side of this filter to be sure which had the IR-rejection properties. Then I cleaned the opposite side using a Baader cleaning kit formerly sold by A-P. I did the same to one side of the photographic filter.

I put three drops of optical cement (Norland Optical Adhesive #61, bought from Edmunds) on each half of the ERF. That was probably too much. Two would have been plenty. And I pressed the cleaned side of the photo filter onto the ERF. Squoonched and rotated it around some to distribute the cement, pressing down to insure good contact, working bubbles out from between where the drops of cement met. I prepared this open-face optical sandwich on an aluminum plate padded with a lint-free lens-cleaning tissue to assure solid, flat support, and I worked in the shade, indoors, because the UV from sunlight (absent the specified 100w "mercury lamp") can be used to quick-cure the cement. Once happy-ish with the arrangement, I removed the tissue and carried the filter and aluminum plate outside into full, clear sunlight.




That's when it occured to me that the "clear photo filter" just might be a UV filter, but, well, what's done is done, and I hoped it wasn't a very good one. Whatever. In 15 minutes, the sandwich was semi-set and in a couple of hours it was nicely so. Then I discovered that some of the excess cement had leaked through the fissure in the ERF and spread out on the IR-rejection side. Panic! Don't glue it to the aluminum, don't make a translucent mess on the surface, don't disturb the bond... I brought it all inside, filpped the sandwich, cleaned the cracked surface (and the aluminum) as aggressively as I dared, and took it back outside. S'OK, I think. Several days later, the bond was as good as it's going to get:




That's the repaired filter reflecting a page of the Slowblog from the ERF side. I don't see any discontinuities there and you have to look to see a line through the middle of the filter when viewing it by transmitted light.

Sky trials to come.


11/3/2012. But not today. I let the batteries get weak, both the gel cell that drives the mount and the internal battery in the computer, and I ended up powering both devices at one time or another from the Honda's 12v auxilliary plug (the one that used to be called the "cigarette lighter"). Mostly I just wanted to keep my hand in on a day of low solar activity, reasonably good transparency, and mediocre seeing. Practice, Mister, practice:










The bottom image is a two frame mosaic of 1602 and environs made from 1.5 GB clips for each panel; the rest are distilled from 1GB clips. All these images use about 150 frames (10-15%) from available clips to knock down electronic noise and still retain some semblance of a seeing filet. I used a gamma of 1.9 for the top shot and 0.5 for the rest. I'm trying to retain some detail in the chromosphere when seen in profile; it's naturally easier at higher gamma but there's a balance to be struck between the ease of retaining surface and limb detail, as always. So far, so good. Also, the chromosphere at the limb is easier to catch with increasing aperture; 90mm seems sufficient, but if I recall correctly, it's much more obvious with 152.



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Except where noted, solar photos are made with a Point Grey Research Chameleon camera behind a Lunt Solar Systems 60mm THa solar telescope double-stacked wtih a 50mm front etalon for an achieved bandwidth of about 0.55 Angstroms. The telescope uses a B600 blocking filter and is mounted piggyback with an Astro-Tech 10-inch Ritchey-Chretien (carefully capped!) on an Astro-Physics Mach1GTO mount. An Acer Aspire One netbook running Point Grey's Flycap software provides camera control and capture services via USB 2.0. Images typically begin as 20 second AVI's captured at 15 fps. 300 frame clips are aligned and stacked using Registax 6 or AVIStack 2.0. The resulting files are processed via wavelet functions in Registax and / or the FocusMagic 3.0.2 deconvolution plug-in in Photoshop CS4. (PixInsight is rapidly supplanting some of those steps.) The imaging train usually includes an Orion "Shorty" 2x barlow screwed into the 1.25-inch prime-focus snout. Exposures are on the order of 4-8 ms with gain set to 10-12 db, or 12-18ms at 0 gain. The barlow is sometimes replaced by an Antares 0.5x telecompressor sandwiched between the 1.25-inch snout and the C-adapter on the PGR Chameleon; this produces a full-disk image (during most of the year) and allows exposures in the 1ms range with slightly less gain. A RoboFocus motor with a timing belt looped around the stock (or, sometimes, a Feathertouch) focus knob enables remote operation.


                   © 2012, David Cortner