SolarChat!

I am missing something. While I can get wonderful images projected onto something with the Lockyer, that is about it. So far this is what I have:

the focused disc of the sun is on the slit, a lens is then focused onto the other side of the slit and the light passes through the prisms, then a second small telescope is used to view the spectrum. What I am missing is, I think, the focal length of the collimating lens. where should the focal point be relative to the smaller telescope?
Cheers in advance.
Chriso

Chriso,
From your brief explanation you should be able to see the solar spectrum
It could be that the prisms are not properly aligned??
What about an image of your set-up?

I believe they are aligned, I used a UV, and a red laser to find the minimum deviation.
Here are the pictures, they were on another device...
It projects nicely, but I want a 'wider' swath

The collimating lens is off in this picture

The originals are much nicer...

I can only project the spectra, not magnify it. Or do I need to adjust my thinking of how this works. I'm going from old textbooks and photos of examples. I really want to recreate an old one, as they will be used for living history exhibits. I'll make a more modern diffraction grating scope later.
thanks!

Hmmm, a very neat piece of work!
I don't see the collimating telescope???
There should be a small telescope 25-30mm aperture and a focal ratio to match the telescope say an f12 telescope = f12 collimator.
This it fitted between the prism plate and the rear of the entrance slit on the telescope, focused on the slit gap.
The imaging "telescope"/ lens can be anything to best match the camera/ CCD.
Does that make sense?
Ken

The collimating lens is off in the picture. Is it a full 2 lens telescope, or a single lens? I was under the impression that it was a single lens (or a doublet, but I'm sure you get my meaning) The focal ratio is what I was missing. the telescope is an 80mm f/11.5 (900mm fl) I'll poke through my lens box and see what I can dig up. I had tried several different lenses with mixed and unimpressive results.

The books I have been using are Lockyer's and Browning's I have several others, but they are physical books and I don't have them with me. The other two are on Google books.
And... you're Ken Harrison? wow! I read through your Astronomical Spectroscopy book. Fantastic writing, it kind of inspired this project, well encouraged it really. (I suffered a concussion yesterday and things are still a tad fuzzy, so please excuse the babbling)
Here it is with the collimator. it isn't permanently attached yet, due to the issues I have been having.

Looking good...just make sure the center of the slit, the collimator, the prisms and imaging lens are all located on the optical axis.
Look forward to seeing your successful results.

Real nice metal work
You were not kidding about
Accurate reproduction!

How much does that rig weigh ?

Thanks! The lower picture is an old one example made in the 1890s, that I used as reference. The one mounted on the telescope is mine. It is pretty heavy, the brass tube is 7 pounds, objective lens 1/2, eyepiece is pretty solid so a pound. The prism plate is another 2+ when it is all said and done, so total I'd guess 11 pounds (5 Kg)
I am just barely getting the hang of making things so they don't look like they were made with a lump hammer on a rock. I'm working on a gear train to rotate the prisms in unison. Making gears is hard. I need the practice, though a grating engine is in the works. I should be able to do 500 or so lines per inch. \
cheers!
chriso

Eleven pounds not bad
I notice one has odd number of prizm
One has even
I thought you need odd no?

John,
There is no restriction on the number of prisms, any where from 1 to 9...the more prisms the greater the dispersion but also the greater the light losses in the train.

Yea but odd numbers only?
I don't get how even numbers would work
Newton experiment
One prizm dispersed light
Second prizm combines colors back to white light
So third color, forth wHite light

Get where I'm going?

John,
No, you're on the wrong tram.....
1st prism disperses, 2nd prism disperses, 3rd prism disperses etc etc etc.
The sum total of the dispersion is equal to the combined "base width" of all the prisms.

(Newton's experiment - see "Astronomical Spectroscopy for Amateur's", page 4 showed that the second prism did not break down the light into further colours. But it does increase the dispersion - the spread of the spectrum)

John, I believe you are thinking of what happens when you stack equilateral prisms rotated 108 degrees. kinda like this: /\/\/\ Mine are set at the dispersion angle

Ok so angle counts
Learn something new

Newton was single primary color
Can not be split again

One thing to remember,the photo of Lockyer's instrument is contemporary, it was changed and used by others after the historical observations were made. The drawings in his "observations part II": http://rstl.royalsocietypublishing.org/ ... l.pdf+html tell much more. Another instrument, built for one of Lockyer's contemporaries (Charles A Young) can be found here: http://americanhistory.si.edu/collectio ... ah_1187502. It uses a different system for changing wavelength while maintaining minimum deviation. It also double passes the prisms with an ingenious arrangement.

Oh, I should add, this is an impressive project, and well executed!

Thankyou! This is the document I have been looking for! (Oh, my 108 degree should be 180 in my last post.) What I need now is a day of sun when I'm not working. I would love a double pass unit, but the 25mm prisms I'm using are a tad small. Once I get more precise with my machining I'll add that feature. On another note, my glass plate holders for the photoheliograph replica are finally getting built. I'm cheating and using the laser cutter at the library. Here's to repeatability!
cheers!
chriso

A lovely instrument. Nothing more beautiful than brass (and wood) construction!
Wishing you success in achieving some imaging.

Cheers.
Peter.

do you plan to use this project to generate a spectroheliogram?

I may attach a camera on it at some point, I have another non period telescope with the same objective on it that I'll use for a more modern setup. The oscillating slits will ab a tad difficult with this one. I'd need a roof prism to send the light back, or figure out a reliable system of linking the slits. It is in the works eventually.