Via Flickr:
Camera mount in the background
2011-05-21
2011-05-19
Lots of clearance
I didn't break anything, although it looked a bit dangerous at times. I had a small measurement error, so all holes needed to be enlarged a tad.
Drilling
Making a hole for the main lens. The small central hole was used to align all boards for threaded rod holes and as a guide hole for the cutter tool. Everything should be fairly well centered for getting the measurements right for the actual OTA.
Raw material for test rig
Via Flickr:
Thick, 27mm plywood for the main lens, thinner 10mm ones for negative lens and camera mount. Four holes will be drilled into each, three for threaded rods and a big one at the center for optics.
Thick, 27mm plywood for the main lens, thinner 10mm ones for negative lens and camera mount. Four holes will be drilled into each, three for threaded rods and a big one at the center for optics.
2011-05-18
Astrograph project starts
My mystery optics order from Surplus Shed of a very fast air spaced triplet and negative doublet arrived today. The weight is a bit of a concern, the triplet lens (D=155mm, f/1.23) weighs a whopping 2.5 kg and creating a stable focusable system for these two is going to be challenging. The smaller, but not lesser, negative doublet weighs "only" 414 grams, and is unmounted, edges painted black with elements glued together. I took a chance on these, as the big lens for half off, and at a total price well below 200€ shipping, taxes and customs included wasn't too bad if these can be combined to even a reasonably good fl=465mm f/3 astrograph. Since I'd use mainly narrow band filters with it, I'm not too concerned about color aberrations, mainly about the image plane flatness for the fair size CCD sensor in SXVR-H18.
The next step is to create a temporary rig for determining correct spacing between elements in order to reach the desired focal lenght, the thin lens equations say it's in the order of 150-160 mm, but this is now the real world. In theory short test exposures should be doable with it as well before creating the actual tube assembly.
The structure for the OTA served a challenge, as the back focal distance from the negative element to image plane at infinity focus is fairly short, in the order of 80 millimeters at desired focal length. This leaves out the option of building a rigid tube and attaching a commercial focuser at the back, but I realized I might just be able to construct a Huge Crayford focuser and put the optics into the inner tube and attach the camera to the outer tube, eating only 15-20 millimeters of the focus travel. As a result the final tube would end up around 20cm diameter and 20cm long looking more like a snare drum than a telescope, but who cares.
The next step is to create a temporary rig for determining correct spacing between elements in order to reach the desired focal lenght, the thin lens equations say it's in the order of 150-160 mm, but this is now the real world. In theory short test exposures should be doable with it as well before creating the actual tube assembly.
The structure for the OTA served a challenge, as the back focal distance from the negative element to image plane at infinity focus is fairly short, in the order of 80 millimeters at desired focal length. This leaves out the option of building a rigid tube and attaching a commercial focuser at the back, but I realized I might just be able to construct a Huge Crayford focuser and put the optics into the inner tube and attach the camera to the outer tube, eating only 15-20 millimeters of the focus travel. As a result the final tube would end up around 20cm diameter and 20cm long looking more like a snare drum than a telescope, but who cares.
2011-02-15
The Great Orion Nebula narrowband
January 2010 version of M-42
I've learned a few things over the fairly short period I've been trying to do astrophotography, here's the ever-so-cool M42 with my current capabilities. As a comparison, side-by-side from January 2010 and February 2011 the same target. Naturally, part of the difference comes from changes in equiment used, the 2010 was shot on a Canon 350D thru an el-cheapo achromatic fl=1000mm f/10 refractor with racket-and-pinion manual focuser seated on tripod-mounter HEQ5 mount and no guiding. For the 2011 version I used Starlight Xpress SXVR-H18 CCD-camera, high-quality Baader filters, guided exposures with dithering and for optics I have now access to the astro-club's William-Options 110-FLT on pier-installed EQ6 mount.
Many small changes a small change in image makes. Oh, and the image on left was taken at nearly new moon, and the newer version is 70% full moon glaring right above Orion.
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