Hartridge spectroscope - any good?

[bojan]

Hi guys,
I just picked up a Hartridge reversing spectroscope on the flee market.
It is in very good shape, complete with wooden box and light source, and apparently calibrated quite OK, I can measure the wavelength with 0.2nm resolution using the built-in micrometer.
Anyone has any information about this instrument?
I am especially interested in assembly drawings (before I start improving it :eyepop:).

[Merlin66]

Can you post a couple of photos?
I've got some old books on spectroscopes/ spectroscopy which may have some info, but probably no detailed drawings...

The Hartridge Reversion scopes work by displaying two spectra in the ocular. The two spectra are arrayed in opposite directions one a mirror image of the other. You decide which line or band you want to know about and you turn the micrometer till the same band on both spectra are lined up adjacent to one another. Then you look at the micrometer and read the wavelength to 0.2nm.

[mswhin63]

amazing what you find on the fleamarket

[bojan]

Ken,
yes, this is it:
http://gemologyonline.com/Forum/phpBB2/viewtopic.php?f=58&t=4027
http://www.worthpoint.com/worthopedia/vintage-beck-london-hartridge-reversion-spectroscope
http://www.dhub.org/object/371498,Professor

On the paper that came with it is seems that it was meant to be used for determining CO in blood (accessories that came with it suggests the kit was supposed to be used for analysis of liquid specimens) .
I tried to google a bit, what I 've got are mostly the articles describing various applications of this instrument (medical, gemology).

What I am interested in is its optical layout.
I am guessing, it uses Amici prism and on the the moving part there must be a mirror (to reverse the spectrum). But, how exactly the second spectrum is reversed? It must be more than just one mirror involved, because the spectrum is actually rotated, and the overlap between two images is controlled by the width of the spectrum band. The spectroscope part is not very big, measuring 170mm in length.

Last night I tried it on street lights, and the plan is to mount it on my MTO-1100A... but it would be nice to know more details of it's optical layout before mechanical details (adapters and so on) could be designed and made...

On the other thought, if this is a collectable of some sort (as suggested by some websites) the better approach would be to sell it to someone who values those historical things (the whole kit is in very good condition - some parts (like optical wedge, I assume it should've been be there) are missing - but my overall impression is it wasn't used much) and then spend the money for less valuable, but more appropriate for astro-work gadget? I hate the idea of destroying something that works - those mods are always risky to some degree.

Attached below is a spectrum from 20W white lamp (4100°K), on my workbench. Focus is obviously not good, and camera was moving as I was holding it in hand trying to keep it aligned with the eyepiece (exposure was automatic, couple of seconds)

[robz]

Looks fascinating bojan ! :thumbsup:

I'd say for sure this works with a prism assembly as I recall seeing one here at work when we had a Science Department and recall ''prisms''being mentioned.
Of course I wanted to borrow it to try on my 6 inch reflefctor at the time but they guarded it with all the kings men!!!:shrug:

I would love to see if it works on your scope..........even a make shift arrangement will do ;)

Rob.

[bojan]

Robert,
I will try it as soon as I can.. the scope adapter is not too hard to make, it should go in the thread instead of slit assembly (which is pretty much useless in stellar spectroscopy anyway).
The harder part will be a camera adapter, because the eyepiece part is movable and of very light construction - I'd say it can't support much more than 100g (so the camera will have to be a small one, hires webcam (long exposure will be an issue then - spectrum is pretty stretched, so exposure times will be very long.. like with all spectrographs).

[robz]

Yes bojan, I get your drift here.
Light weight webcam would be the way to go although a limit of 100g as you say is a bit of a bummer:question:
I suppose that a heavier camera could be employed, but it would need to be braced somehow from a part of the scope rather than the spectroscope.

Anyhow, let us know how you go.

Cheers,
Rob.

[bojan]

And this is the problem.. because the eyepiece moves (rotates around a certain spot inside the prism) with the position of the micrometer (changing the angle from optical axis with the wavelength).
So I can't have it supported from anywhere else.. unless I dismantle and re-design the whole thing (and I am still reluctant to do it, before I know what exactly I am dealing with here).

[robz]

Hmmmmmm.......yes, I see.:question:

Guess that some more research will be required on this as it is obviously different to most spectroscopes.:shrug: ?

[Merlin66]

Bojan,
IMHO I'd clean it up and sell it on...it's definately a collectors item.
With the funds you get you could either build a nice reflection grating "Classic" design spectroscope or get a Star Analyser grating.

[bojan]

Hi Ken,
I feel you are right here... that is why I don't want to start doing much else (apart from testing already done, and all this was non-destructive so far) In your opinion, what would be the value of this instrument these days?

[Merlin66]

Don't know exactly - depends on the actual condition, boxes documentation etc, but I do see "similar" old spectroscopes (Browning/ Hilger etc) going here in UK for around 120gbp to 200gbp.
Hope this helps.

[bojan]

I was just thinking how this thing works... how the spectrum is reversed (rotated) ? ?
The action must be inside the eyepiece barrel, as this is the only part that moves (with micrometer).
Also, the eyepiece actually consists of two parts, I can see it is cut in two halves along optical axis - one half for each spectrum. Two halves are not identical, from what is visible from outside..
The only explanation I have is, one half reverses the image (simple plossl eyepiece lens perhaps) , and the other one doesn't (terrestrial eyepiece.. it has to have similar magnification but field of view is visibly narrower).

I simply have to confirm this theory....
It seems at the end of the day there will be nothing left to sell to collectors :eyepop::lol:... (except maybe wooden box... oak, most likely)

[Merlin66]

I would have though there may have been a dove plate (?) splitter on the end of that roughly triangular arm which moves with the micrometer?
You can always send it over to me and I'll give you a full report.;)

[bojan]

Here it is.. doveplate inside one half of the eyepiece.
So, If I removed it, what's left would be a perfect astro spectrometer...

[Merlin66]

Looks like it....
IMHO the resolution of the prism, based on your earlier images is pretty low....I'd still recommend a good grating...
Just make sure there are no bits left over when you re-assemble the Hartridge for future sale.;)

[bojan]

Resolution is a linear function of distance from prism... double the distance, double the resolution. Brightness of spectrum should be better with prism than with grating. The real advantage of grating is linearity.. but Amici prism is pretty linear anyway.
The image above is a whole, un-cropped frame.

However, I will be careful :thumbsup:..

[Merlin66]

Linear resolution maybe, but the dispersion is based on the prism material, and the physical size of the prism.
So magnifying the size of the spectrum (greater distance) won't give you more detail... it's not there to begin with...like "empty magnification" and the analogy of magnifying newsprint images v's resolution.

[bojan]

True....

So, are you interested ;) ?

[Merlin66]

PM sent.

[bojan]

Very quick test with Toucam (objective replaced with lens from small hand-held scanner)... same source (20W white bulb on my workbench).
This is the whole image (no cropping).

Next test will be on star (hopefully this weekend).
Resolution could be better, as slit could be closed a bit more (too much backlash in mechanism, I will try to reduce it later)

[Merlin66]

The double lines in the mid spectrum are Hg lines and 20A apart.
This gives you some idea of the dispersion/ resolution.
Line them up and see what answer the micrometer gives......

[bojan]

It is 545.6 and 542.8 nm

Focus is better in camera, actually

[Merlin66]

Hmmm
According to my reference sheet (http://www.astrosurf.com/buil/us/spe2/hreso14.htm)
the lines are at 5769.60 and 5789.66 A
There should be a nice definate line in the blue at 4358.33 - does that measure up OK?

[bojan]

Yep, spot on.
I set the micrometer first and then had a look.

[bojan]

I tried the numbers you gave me, there is nothing there...
Maybe there is a need for calibration.
Or, there is no mercury in the lamp. Then again.. how come the blue line is there, spot on?

BTW, none of Christian's pages are working for me.

[Merlin66]

http://astrosurf.com/buil/us/spe2/hresol4.htm
Try this link...it seems to be live...

[bojan]

5460.735 is closest to my reading ( 545.6, the brightest one on image).
Actually, I managed to identify and measure all brightest lines here, within +-1.5 nm accuracy:
http://astrosurf.com/buil/us/spe2/calib2/osram_1.gif

Anyway... not bad for the start .

[DavidU]

Interesting thread Bojan.

[bojan]

It was a clear nigh yesterday and I tried it visually on Sirius and Betelgeuse.
I had to remove the cylindrical lens (just one grab screw is holding it in place) to be able to reach focus.
While Sirius spectra appeared to be smooth (no dots), I saw bands in Betelgeuse's.

Next step: a photo of spectrum.
This will be a trickier part because I don't have Toucam modified for long exposures... so I have to do this first (plus an adapter to fit on the eyepiece. The spectra images earlier in the thread were taken from hand, and with plenty of light available for short exposure).