In regards to the two mirror Hale spectroscope design (Czerny-Turner) for a spectrohelioscope, you must keep the mirrors somewhat close, also the slits in line with the two mirrors. Use graph paper to see the relationship of the optical axis of the mirrors relative to the grating and the slits, also for construction in order to keep down errors. With long f.l. mirrors about 12 feet (3 meters), the mirrors can be a bit apart, but not too far apart. But for short f.l. mirrors, say about 4 feet (one meter), keep the mirrors close together always. Do not have diverging and converging light paths to and from the mirrors in relationship to the grating. Never. You get too much H alpha lag. For fixed slits synthesizers , the H alpha lag is no problem. For moving slits synthesizer, the H alpha lage can be too much, causing a problem.

What is H alpha lag. Well, with a moving synthesizer and slits, as the entrance slit moves up, say about 6mm, the H alpha line at the exit slit does not move exactly down the same 6mm, but it lags about 25 to 50 microns, depending upon design of the optics. Vice versa when the entrance slit moves down. So total up and down movement of entrance slit will be 12mm, depending however you design it.The result is the field of view of the solar disk in H alpha light will be all pure H allpha light in the center, but the extreme top and bottom of the field will be a slightly different wavelength, namely about plus or minus 0.1A to 0.2A. The latter is not a problem most of the time.

With fixed slits for a synthesizer, there is no H alpha lag and the field of view of the solar disk will be all pure H alpha light. There are many types of synthesizers. Some have fixed slits and some have moving slits. This gives you an enormous advantage to design a spectrohelioscope as you wish it.

Read in my 119 page book on Spectrohelioscopes. There is discusson on H alpha lag, spectroscope designs, otherwise. It is all there.

Fred Veio "You should make a solar spectroscope!"

You should make a solar spectroscope. You must mount it separately and parallel to the Coronado or Daystar H alpha filter. There is much interestng solar disk and solar limb details to easily see. A spectroscope is much easier to put together than a spectrohelioscope, and the adjustments are less critical. With a cross hair you can pin point events exactly so, not difficult to do, not need a monstrosity. 

Apogee and a few other companies sell achromats of somewhat long f.l. Prices are reasonable too. Average cost about $130. Do not complain. A few other places sell for about triple that price. Test the achromat for spherical aberration. If you got 1/6 was, stop down a bit, will improve to about 1/8 wave on the wavefront at infinity focus.

Use one for the spectroscpe section, and another for the telescope section with a 2x barlow. about -500mm fl, to double the efl.

For the telescope about 80/1300 or related achromat is excellent, use with a 2x barlow get about 2600mm efl, giving a one inch (25mm)diameter solar image on the entrance slit. The spectroscope can be a similar achromat of about80/1300mm. The grating can be about 25x50mm with 1800 gr/mm 50% theoretical resolution, resolving power about 0.2A,not too expensive, say about 150 dollars. If you got a 50x50mm grating, can stop down on the sides to about 25x50mm to improve resolution.

Tilt the grating to the yellow near the sodium lines, with the slit over a bright hot plage you see the heliumm line in absorption easily, two very faint atmospheric lines nearby will cause no problmes. sometimes the helium line is in emission, do not need a flare, just a local very hot local area. Sometime the helium line is seen in absorpton and in emission.

Tilt the grating to the H alpha line, with the entrance slit over an emerging magnetic flux region, you will see the H alpha line being distorted, displaced very easily, does not change fast, only very slowly. With the grating tilted into the second order in the green, and entrance slit over a penumbra, you see the photospheric lines becom thicker due to Zeeman effect.

For a surging prom the H alpha at the solar limb in emission has zig zag here and there that are easy to see. Entrance slit on a surging filament on the solar disk will show parts in absorption shifted easily away from the main H alpha core line.

Miscellaneous solar events are seen too. Point is that you are missing much easy to see events with the human eye, which has cones about two microns diameter. Film is about five microns for lines. CCD pixels are about ten microns. The human eye is your best friend. Just keep the focal lengths long, say bout 1300mm thereabouts.

You do not have to make a SHS, just a spectroscope, simple.

Fred Veio writes on the Arcetri spectroscope design with a basic telescope

Here is a basic spectrohelioscope design again.Total costs about 600 dollars, portable, compact, easy to make, wood and nuts and bolts, simple tools. I suggest that you keep it all as simple as possible for the sake of other interested amateurs. If you make it very fine, complex construction, other amateur will tend to think that is the way it must be. Not true.

Two basic SHS designs. One has the spectroscope section in the Arcetri design with Arcetri solar image synthesizer. The other has the two mirror Hale design with the Young knodding mirror solar image synthesizer. The telescope for both can be a long achromat with 2 x Barlow to give about 2.7 meters e.f.l.

The below discussion is for the Arcetri spectroscope design with a basic telescope.

For the spectroscope section, use two 60/1000 or 60/900mm achromats (about $20 each), one diagonal with minor axis about 60mm and 1/8 wave, grating of 32x30 mm ruled area with 1200 gr-mm good ($360 from Diffraction Productrs) but 1800 gr-mm better($380). A green 5000A blazed wavelength or an orange-red 6000A blazed. Use the solar image synthesizer of sideways moving slits, movement about 12mm average sideways, slit width about .004 (100microns) to .005 inch (125 microns) for a passband about 0.5 to 0.6A. Diffraction Products USA gives a 15% discount to amateurs. The two achromats might not be the same f.l., does not have to be, can shim optically the focal length difference with a good quality optical  window from Edmund or other place, flat about one to two waves is all right, not expensive.Do not use house window glass.Say difference in f.l. is about 5mm, then an optical  window about 15mm thick will shim forward the difference by one third of the thickness, namely about 5mm.Two pieces of glass (about $10) can produce 15mm thickness.

For the telescope section, buy achromat about 80/1300mm to 90/1300mm thereabouts (about $150), not critical, use long f.l. Barlow about -250mm for about 2X, to get about efl 2600mm, gives a one inch (25mm) diameter sun image on the entrance slit. Heliostat will be a 90mm minor axis diagonal (about $80), 1/8 wave at least, cheaper than a round more expensive flat mirror ($300). RA gear drive will be a total gear reduction of 2100:1 ratio with one rpm motor. Use two eyepieces (each about $10)of single achromats about 50mm for the spectroscope mode and about 110 to125mm f.l. for the SHS mode.

Buy the achromats from Apogee, Sky Instrument or SurplusShed. Not expensive. Test them for spherical aberration with Ronchi test. Mount the achromat at end of a piece of plastic tubing, point at a bright star or a planet, hold Ronchi ruling at the other end. If get three straight black parallel bands, this is equal to about 1/10 wave on the wave front at infinity focus, namely excellent. If about 1/6 wave, can stop down the achromat to 50mm to give about 1/8 wave at infinity focus. Just juggles a bit here and there. Do not try to be a perfectonist, go nuts, there is leeway here and there, lot of details are not critical at all, do not have fear of the instrument. And read my book here and there as pertains to setting up and focusing and what not.

Fred Veio writes on SHS optics

You should use long focal length optics for the spectroscope in order to stretch out lengthwise the solar spectrum. About 60mm by 900mm focal length  or 60mm diameter by 1000mm focal length  will be excellent, not cost too much from Surplus Shed, which now is advertising in Sky and Telescope, look in the back ad pages.

And use a 45% theoretical resolution diffraction grating from Edmund, cost about 90 dollars approx, 1800 gratings/mm will be best, 25x25mm ruled area, further stretching lengthwise the solar spectrum. The result will be about 8A/mm, passband about 0.8A wide.  The latter is ok for prom but contrast average  for the solar disk in H alpha light. For excellent contrast use a 90% theoretical resolution grating, cost about $350.

 The telescope can be about 80 by 1300mm or related achromat, also use a long  negative focal length  Barlow to give about 2X,  making the effective focal length about 9 feet focal length .(2.7 meters) for a 25mm diameter sun image on the entrance slit. The sideways movement of the slits is called the Arcetri (Are-che-tree) synthesizer. The 60-foot solar tower in Florence, Italy, uses a similar motion for the slits for spectroheliograms of the solar disk.

The sideways movement should not be too much, say about 12mm back and forth, this better guarantees that the synthesizer will work ok. If 12mm is good, then you can try about 18mm. The idea is to go step by step just to be use all is mechanical and optical working. The two 60 by 1000mm focal length  achromats ideally should be the same focal length . If not, you can use a glass shim to make up for the difference. Assume one achromat is 990mm focal length  and the other is 995mm focal length  Then you have a difference of 5 mm. So get a good quality optical window about 15mm thick. Can use two pieces of glass cemented together. Surface flatness about one to two waves is good, not so expensive. The glass thickness will shift forward the solar image by one third of the thickness. So in this case, about 5mm shift forward. Result will be the two achromat will be almost exactly the same focal length  For the heliostat, use a diagonal about 60mm minor axis, Pyrex, about 1/8 wave flat will be good enough.

Total costs will depend upon the grating used. Average costs will be about $400. You do not have to copy the prototype by Fred as published in Sky and Tele in 1969. There are many possible designs. The main thought is to keep the focal lengths long, and test the optics to be sure that they are 1/8 wave corrected for spherical aberration at infinity focus. A Ronchi screen from Willman-Bell is low cost, 50x50mm size, about 100 gr/inch is good, about $4.Mount on piece of optical window glass, about 99% flat is ok. A glass Ronchi screen from Edmund is about $25.

This was in response to a note by Dave Groski

I recently  received a number of old Sky and Telescopes from the 60's
and early 70's to further my collection. While going through them I found
and interesting article in Oct. 1971, " A Compact Prize-winning
Spectrohelioscope". The article discusses the construction of a simple, low
cost SHS made from two binocular lens and a 600 lines/mm transmission
grating. The optics are layout in Arcetri design  and uses a 60mm refractor
to form the image of the Sun on the entrance slit. The movement of slits is
with a toy motor and whole assembly is made out of what looks to be 1/4"
plywood. The unit was build by a 10th grade high school student. A quick
check of  Surplus Shed shows that  similar  lens cost about $7 each  and
grating is $15 so one should be able to construct  similar unit for around
$50. The linear dispersion is about 85 A/mm so with a 0.06mm (0.002 inches)
slits width, one would get a 5 A bandpass which would be fine for viewing
prominence and the unit could also be tuned to the Ca-K line, for observing
there. A unit like this would allow one to enter into H-alpha viewing which
out a large out  lay of money and also give one experience in building a
SHS that can be used in  constructing  a larger and higher resolution
instrument. I have already started to build one to see what it will show.

                                                             Best Regards,
                                                                Dave\

I only recently got wind of this group and thought you might
be interested in my shs project.  Based on Maurice Gavin's
reflective needle-slit instrument  (http://www.astroman.fsnet.co.uk/
it will use a polished needle (actually 1mm hypodermic needle
tubing) and an 8-inch f5.7 mirror in place of his 9-inch lens. I was stumped for several months on two aspects and worked on other projects until my mind could let go of the problems and
come up with the solutions.
First, I wanted to use needles for both entrance and exit slits.
There were countless drawings of mechanisms for driving two
needles in sync that led nowhere, I finally went back to Gavin's
idea of a single pivot and driver.  In my case using one half
the needle for the entrance slit and the opposite half for the exit.
A cool driving mechanism was discovered in this arrangement:

         {           <- small spring to constrain motion
  -------o--------   <- needle on pivot
         |           <- brass strip wrapped around pivot and magnet
         O           <- itty-bitty mighty magnet from Radio Shack



  |             |
  |------o------|    <- two strong magnets on motor
  |             |

When the motor is spun up and moved in close, the needle
mechanism oscillates.  It works best if the motor is turned
90 degrees so the magnets come over the top and go around
back, perpendicular to the motion of the needle.  I used
two magnets removed from hard-drive head mechanisms.  The motor
is a muffin fan with the blades cut and sanded off, very low
current and designed to run forever.  Balancing the magnets
and mounting the motor on rubber feet there should be very
little vibration transmitted to the instrument.

The mirror will create a focused image about .4-inch ~ 10mm
and the needle will cover about 1/3 of that.

The second snag was getting a good polish on the needle.  This
was overcome by using a suede leather pad painted with 500-grit
silicon carbide, folding it over the needle (mounted in a hand
drill), and pressing hard between two boards.  Spin the drill
as fast as it will go for a minute, keep moving it in and out
to prevent rotational marking.  Then move the needle to a fresh
spot on the pad and go again.  Repeat about 10 times.  Replace
the pad with one painted with 9-micron aluminum oxide and repeat.
A gorgeous finish.  I tried improving it with cerium oxide but
could not tell the difference with a high-power lens.

The optical sequence, with needle and mirror at opposite ends
of the box, and reflective grating toward needle end:
  - sunlight enters through 3-inch aperture beside needle
  - mirror focuses image on needle-side-1
  - reflection back to mirror for collimation
  - collimated rays to grating for dispersion
  - dispersed rays back to mirror
  - mirror focuses dispersed image on needle-side-2
  - diagonal mirror directs image to eyepiece

With the grating located near the needle I should get twice
the dispersion of Gavin's instrument, since the rays have to
pass the length of the box twice from there to the needle.

I am a little hung up on where to place the diagonal so it
does not block the rays coming from the mirror to the needle,
if I can't find a good location I will try substituting a glass
plate (microscope slide) turned 45-degrees to the light path.
That will pass the rays to the needle and reflect the image
to the eyepiece with a substantial loss in brightness, but might
work.  If not I'll just go back to a slit like Gavin.

My dream is to use a 12-volt solar panel to drive the instrument.
A local retailer has ones that produce 300+ milliamps which
is just about enough for an alt-az drive and muffin fan motor.
Maybe.

Paul Kline
pk6811s@acad.drake.edu

 Well boys, Im here!  I figured the same people on this group are probably on the solar observers group. In case not one of you lucky persons will soon help me make a scope (maybe).  First on my list is a solar newtonian, spectrohelioscope will be next. unless you want to try and talk me out of it.  At the moment I use a 7" meade mak with a .45 daystar U. I image with a Nikon 990, and soon will pick back up on the 416 ccd for higher resolution. Heres my latest image.  

Tony Grigsby  http://alltel.net/~tony7