More solar observing experiments

I am continuing to experiment with my solar projector, which uses a hard disc platter as a heliostat mirror, and two Surplus Shed lenses, one positive with 2600mm focal length, and one negative with -800mm.  While I can see sunspots, I can't see almost any structure in them, and there is a lot of chromatic aberration.  A bit of experimenting suggests that most of the chromatic aberration is due to the negative lens, so I've ordered a -1000mm achromatic lens.  We'll see if that improves things.

While ordering from Surplus Shed, I also ordered a 15mm focal-length Hastings triplet.  If it does not make a good planetary eyepiece--I will certainly will try--I will have a nice 15X loupe, replacing my 15X plastic-lens loupe (which is usable, but only in the center of field).

Solar observing mishap

I was experimenting with solar projection with my 8" scope.  I first stopped up the aperture to about 3".  All was well.  Then I went for full aperture.  The images were sharper.

But then the images went foggy.  And I couldn't get them in focus.  And smoke started coming out.

I disconnected the Kellner and noticed the lens was fogged up.  Turns out that while the eyepiece housing was metal, as it should be for solar work, the eyepiece lenses had a plastic spacer.  Which melted.  The spacer is the black thing to the left of the lenses.

The lenses cleaned off fine with acetone.  But I wonder how I can find a metal replacement spacer.

So, that's a warning for solar work: don't assume that just because the eyepiece tube is metal, the inside is metal, too.

Home-made fine-tuning rings for Hyperion eyepieces

The Baader Hyperion eyepieces accept fine-tuning rings which increase the magnification.  One unscrews the lens group at the bottom, screws in one or more fine-tuning rings, and screws the lens group onto that.  One can buy the fine-tuning rings, of course, for a modest price.  But cheap as I am, I decided to save.  Instead, I purchased two bunches of 48mm camera filters on ebay.  The latest bunch was a lot of ten Niko skylight filters for $13 shipped.  One then removes the glass from the filters, and screws the filter housings into a tube.  The tube is very rigid.  (Removing the glass destructively is easy.  Put filter in some thick bag, hit with hammer or screwdriver or handle of butter knife through the bag.  If the glass breaks, it is easily removed from the housing, though of course one should wear some kind of safety gloves and be careful not to let the glass out of the bag.  Eye protection and a breathing mask are a good idea.  Surprisingly, a number of the Nikos had the glass survive the procedure.)

The ten Nikos add up to 43mm total, and the three Gemkos I have from an earlier purchase give me 14mm.  I could control the length of the fine-tuning tube in increments of about 4.5mm by adding and subtracting one filter housing at a time.

For a total extra price of about $20, my single 13mm Hyperion varies in increments of under a millimeter of focal length between 13mm and about 7.5mm.  The views are really good, though the focus has to be close in with all 57mm of rings attached.  The apparent field of view increases very significantly, which is nice (at full extension, I need to press the eye into the eyeguard to see the whole field of view).  I guess this is because the field stop doesn't increase.  The eyepiece becomes absurdly long, and maybe some focusers won't be happy with the added torque.  I suppose for added fun, I could put in a Barlow, but then the magnification would be more than I can really use.

Astronomy gear and microscopy

I wanted to show the kids the grooves on a CD.  With the medium magnification objective on our microscope, one could just see shimmering graininess.  And I couldn't get the highest magnification objective to focus in on the graininess.  I think the problem may have been that the condenser light couldn't go through the CD, and so I was lighting it with a hand-held flashlight, and that objective has to go so close to the object that blocked the light.  So I got out my 6mm TMB/BO planetary eyepiece (equivalent to about 40X as a microscope eyepiece), popped it in a 1.25" - microscope adapter, and went back to the medium magnification eyepiece, and while we couldn't see it too well, it was obvious that there were pits, and that they were arranged in a line-by-line pattern.

That "1.25" - microscope adapter" is home-made, of course. I cut a 1" segment of 1.25" poplar dowel. I then drilled out the inner 1" of it with a Forstner bit, making a wooden tube with 1/8" walls. I cut a 1.5" segment of some 1.25" ID aluminum tubing (well, actually, a little less than 1.25" ID--I had to sand it out). I then nested the two, with the wooden tube sticking out of the bottom of the aluminum tube, and the aluminum tube extending on top about 1/2" past the top of the wooden tube. (See diagram: gray is aluminum and brown is wood.) They fit snugly, but I put in a couple of drops of CA glue for safety.

The whole assembly then fits around the focuser tube of the microscope, with the top of the wooden tube being flush with the top of the microscope's focuser tube. Eyepieces then fit in the aluminum collar that sticks out on top. The nice thing about making the adapter fit around the focuser tube instead of the more obvious inside is that it doesn't contribute any vignetting.

Of course, it would have looked a bit neater to make the inner tube of aluminum. But ordering an aluminum tube would cost about $8, while a dowel cost $4, plus I wanted the dowel for another project. Moreover, there is an advantage to using a wood inner tube--it won't scratch the outside of the microscope focuser tube as much as metal would. I suppose PVC could have worked as well, but the closest I could find in PVC was 1.29" OD, and I didn't relish the thought of sanding that down to 1.25" OD to fit inside the aluminum tube.

Hastings triplets

About two weeks ago, I ordered one of the super-cheap "30X" triplet loupes on ebay for less than $2 shipped (see photo on right). 30X should be 8.3mm (FL = 250mm / magnification, for magnifiers). It came a couple of days ago. To my disappointment, it has turned out to be about 8X (looking on amazon reviews of similar products, this isn't uncommon), i.e., about 31mm. Handheld in my F/4 8" (not the ideal test-bed for this eyepiece!) and pointed at Jupiter it showed significant CA on axis (but it was hard to keep on axis, so I can't swear that the CA was on-axis). I did see one cloud belt, which is about all I can see with that scope. I also tried it on the Double Cluster, and it looked OK, but the AFOV was low.
Today, I used the lens it in a Spenser microscope (just placed it right on top of the eyepiece tube). There it came into its own. I compared it to the Leitz 10X eyepiece (I don't know of what variety) that the microscope came with. The magnification of the triplet was slightly lower. AFOV was about the same, maybe around 30 degrees. Eye-relief was huge (which isn't a plus for me--I like short eye-relief eyepieces). But what was really impressive was the vibrant color and on-axis detail, both significantly better than the Leitz 10X. Despite the magnification being slightly smaller, I could see detail better. The sharpness dropped off significantly in the last 30% of the field.  (Visually, the image was much sharper than in this photo, and the usable area bigger.)
Reading Amazon reviews of similar products led me to the following hypothesis. There are two very-similar loupes being sold out of Asia, both marketed as 30X triplets with 21mm diameter lenses. One variety has "TRIPLET 30X21mm" stamped on it, and it actually is a 30X. The other variety has "30X21mm" stamped on it, and it is close to 10X. It is, nonetheless, a nice piece of glass, but only 10X. (The seller is refunding me my $2.)
Friday night, for $6 shipped, I ordered one of the ones stamped "Triplet" from a US seller whose ebay ads warn against being duped by competitors. The seller avers that his are genuine 30X triplets, and based on an email exchanges with him, I am inclined to trust him (after all, if it's not 30X, he'll have to refund the money, and if he doesn't I'll put in a paypal claim). I should be getting mine in a couple of days, and will report.  I am not posting a link until I've actually tried out the lens.
If that fails, I know a third loupe vendor, out of Canada, who has actually had his optometrist test his 30X Hastings triplets, and found that they are not only 30X, but have AR coatings on one of the surfaces. He sells them for $22.
When it comes, my plan is to bore out a 1.25" dowel and stick the 30X lens in. If it works out, I might even sell a few super-homemade (and not filter-threaded) hardwood triplet eyepieces for some very low price. Or at least give them away to friends. :-)