Optical Ed’s
Solar Projection
Imagine!
A huge 9.5 inch diameter projected sun image with the same resolution as a 4 inch telescope! When it comes to group viewing of the sun nothing surpasses my solar projector. Nothing could be easier to set up and use. It mounts on a camera tripod so the set up is much easier to carry around than a telescope. If the air is steady you can even see the solar granulation. The projector consists of a very long plano-convex lens, roughly 86 feet mounted on an oak board and fed by a flat mirror on an adjustable mount.
Although not color corrected because the focal length is so long the color dispersion is less than the theoretical resolution of the lens resulting in absolutely no color aberration. You see the true color of the sun as well, not some shade of blue, orange or other color. Once near sunset I discovered that there is a red edge and a blue edge on the sun due to atmospheric refraction. I could have added a drive but I find it really unnecessary. Since the image is good over a huge area you can simply use a larger screen and you'll only need to move it when it drifts off the screen. It’s a really awesome way to watch a solar eclipse too.
For best results it's best to bring the image indoors or into the shade for better contrast. You can shoot it down the hallway of a school or through an open window. For the best viewing it's best to keep the light path away from hot areas like concrete or asphalt parking lots.
Set up is a breeze. You mount the projector on a camera tripod and set up your screen 86 feet away. You sight along the edge of the board and aim it at the screen then you move the mirror to bring the sun onto the screen. Easy!
Price$200
Safety: My solar projector is absolutely safe. It never concentrates the sun to where you could accidentally get burned as a telescope would. For more information contact me at: solarview@isoc.net
Picture of sun taken with solar projector Compact and very portable
Optical Testing
I acquired a Zygo GH interferometer and put it back in working order. It lacks phase shifting capability but is more than adequate for telescope optic testing. I made Offner null reference lenses and motorized stages to allow interferometric testing of telescope mirrors up to 20 inches currently.
203 mm parabolic mirror
Optical Design
I suppose I’ve designed every sort of telescope you ever heard of (and some of my own designs too) using Zemax optical design software. I have a lot of experience with Zemax in telescope design and testing.
Optical Fabrication
I have a small number of lapping and polishing machines in my basement for optical work that I do.
8 Inch Folded Herschelian
This scope has an 8 inch F/10 primary. My wife guessed a bird house, I can see where she got that.
This scope is an all spherical folded Maksutov-Herschelian consisting of an F/10 spherical primary, a folding flat and a doublet meniscus correcting lens. The corrector could be one element with wedge but I found it easier to cement two lenses decentered to get the required wedged lens. This is a high performance unobstructed planetary telescope. I call it my Dob from hell. It was featured in Sky & Telescope Feb. 2005.
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Spot Diagrams
The scope is very well corrected on axis but has considerable astigmatism in the field. However for my next Herschelian I was able to improve the off axis performance to diffraction limited over a half degree field.
Window Scope:
Imagine sitting in a comfortable chair on a cold winter night observing the planets. Here is the optical layout of my latest scope. See details:
8 Inch Jones CHiefspiegler
When working on my window scope I explored different types of correcting lenses. The Maksutov corrector was easy but not well corrected in the field. In Jan. 1971 S&T Bob Cox built a catadioptric Herschellian designed by Richard Buchroeder. It used a spherical primary, flint and crown correctors and was limited to F/10. Off axis it was not any better than the Mak corrector. Then I discovered a design with much better performance. I later discovered that it would work well at F/7 (I’m working on a 12.5 inch F/6.7) making it one of if not the fastest and simplest schiefspieglers. It is distinctly different than Buchroeder’s design, however, since the primary isn’t spherical, it doesn’t use flint and crown correctors, and the field performance is significantly better. I call it the Jones CHiefspiegler (a play on words from Catadioptric Herschellian schiefspiegler). I first built it folded at 90 degrees like a Newtonian which worked well but then when I put it on my equatorial platform the eyepiece was high enough that I had to go on tip toes. To fix this problem I tried tilting it at 45 degrees to the side. This turned out to be a can of worms from an opto-mechanical standpoint, way too complex! I almost made it work but then decided that folding it straight back as shown in the picture was much simpler. This worked great and now the length from the bottom of the scope to where your eye is located is about 44 inches. This is equivalent to a popular F/6 Newtonian. So why have a Newt when you can have an unobstructed scope?!!
The contribution of the correcting lenses is minimal, most of the aberration comes from the primary mirror.
8 inch CHief on an equitorial platform
Another nice feature is that the control of stray light is surprisingly good compared to a Newtonian.
For more info click here
12.5 inch F/6.8 Chief
I found a 12.5 inch f/6.8 mirror on Ebay for
a good price so I decided to scale up my 8 inch Chief design. Finished in June
08 here it is:
Optically this scope performed great as Zemax said it should. However the eyepiece position was too inaccessible. Time for a redesign. Note the rocker box is leaning forward to reposition the COG correctly.
What I needed to do was rotate the whole optical assembly 90 degrees. The beam was in the way so I had to re-make both the mirror box and rocker box to look like this:
This arrangement worked much better and I was glad to get rid of the crappy Baltic birch on the other rocker and mirror box too. Most of the time I don’t need any help except when looking straight up I need a 6 inch stool. The top of the beam comes apart for easy transport . Should have built it this way to start.
As with my 8 inch I have 2 knobs below the focuser to adjust the lens tilts and a screen on a stick to make alignment a breeze. The focuser is a Wyorock refractor focuser and I use an extension except when I use a star diagonal (viewing near the horizon).
All in all this scope exceeded my expectations, it has a refractor like dark sky background, unobstructed reflector like image, the best of both worlds.
Alignment Procedure for CHiefspieglers
Mirrors
1 Using a simple laser I make sure the laser hits the middle of the secondary, then the center of the primary by adjusting the secondary and
2 By adjusting the primary the laser the laser should hit a mark on the alignment screen. I have a line on the screen 6.25 inches from the beam on the X axis.
Lenses
3 The lens tilts should initially be set using an angle gage as best as possible. The lens tilts are adjusted at the eyepiece by going in and out of focus on a star at high power.
4 Make an adjustment in lens #2 then if the size of the astigmatism decreases then make another adjustment in the same direction. Make another adjustment in the same direction if it gets better, if not move it in the opposite direction.
5 When you get it the astigmatism as small as it gets make a small adjustment to lens #2 and go through step #4 again. It’s an iterative process, you change the first lens then find the best position of the second lens.
6 Astigmatism causes the star image to be football shaped or elliptical along one axis and then switch 90 degrees on the other side of focus. If you’ve gotten the astigmatism as small as you can but there is some residual astigmatism not orthogonal to the X or Y direction then the primary is adjusted slightly left or right keeping the same distance from the beam.
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