spectro-aras.com

Hello,

For those who own LHires III and interested in the very near UV world, let me publish here my measurement of a banknote checker (BLB-T5/6W).

Here I managed to calibrate and identify the Hg lines: Initially tried to use the internal lamp, but found it is falling apart more quickly than the Hg lines of this lamp.
The 3 prominent lines I used for calibration (order 3):
3650.153
4046.563
4077.834

Some other visible, but somehow makes calibration incorrect (would need smoothing the background precisely):
3650.153
3654.836
3663.279
3906.37 (weak here)
4046.563
4077.834

Of course, there are some more weaker lines visible at higher resolution. Let's see how the interval look around the H,K lines: Now I can see 3 issues:
- indeed, I do have ripples in UV, too (ATIK 414 EXm), the error is +/- 1.5% of the actual signal - whilst the internal lamp didn't show any ripple...
- internal lamp's flat shows only dusts + reflections from visible; now I see reflections must be removed if someone intends to use it
- internal lamp's flat becomes fully useless with a photometric slit (too big reflections)

I'm going to use now this pair of "BLB-T5/6W" tubes for creating flats, to correct my ripples (canceling the lines at 3901.87, 3906.37 manually on the flat in 1D).

Other experiments I did, to test materials as a diffuser:
- a white T-shirt removes UV signal; but some weak transparency or most likely fluorescence (!) it provides towards 4000A
- A4 paper fully removes signal below 400nm
- white plexi fully removes all signal
- clear plexi transmits mostly everything as-is; best diffuser I've found so far

Furthermore, this BLB-T5 tube is written typically to peak at 367nm. On my graph, peak is at 376nm. Therefore I suspect this must be the honey spot where my optical system become inefficient (including the 250/1000 newton + APM 2.66x barlow I used for now).

A positive surpise, that the 3 Hg lines at 3650, 3654, 3663 seems to be still focusable with the doublet, where the internal Ar lines become fully vanished!
It would be nice to see where the real peak should be, to do an assessment of efficiency how deep it's worth to go with this instruments.

About further flat lamps possibilities, I did find UV Leds - but their half width is only about 15nm, and many of them needed (with much more planning care and soldering skills). Found also no prepared "LED array" stripes for the UV - as it exists for visual range very cheap... I think it's for future. Currently I was able to disassemble the banknote-lamp quickly without any soldering or high DIY skills, already assembled it on a plexi. Hope I can use it for observations around H,K line at high resolution.

Of course, it would be nice to see other spectrographs testing with a similar lamp.

- Peter

To: Peter,

I'm going to try to use this KOBRA UV Black Light Flashlight 100 LED illuminator (with a "thin" plexiglass diffuser) for Hb-H11 spectral flat:
https://www.amazon.com/gp/product/B01IA ... UTF8&psc=1

Now I'm looking for a 1.25" diameter 1.4x barlow for the LhiresIII to change my light cone from F/6.8 to F/10.

James

James,

Anything is better in UV than the 2700K lamp in the Lhires! (that you won't notice it's not the right flat...) - of course, for the green/red region, the internal lamp still useable with good comfort.
My "BLB" is also imperfect, have a few spikes in the CaII region, need to remove it separately (marking their position). By chance, the H13-H9 region is free of emissions...
This is an emergency solution only, as the ATIK 428 has a bigger 50A wide variation on the flat (unlike the 414), and a LED I was trying was not wide enough, and I exactly use that flat assuming it's continuous enough for my short coverage at 2400/mm grating... (not fully proven, just seeing in practice it works)

Of course, once you post here that lamp's flat, that would be fine!
Also you can try a higher temperature Halogen, as seen somewhere in these posts (I also wanted to try, just need more time to look after, and parasite/reflected light common towards blue with the LHires makes me fear of this).

Basically everything is imperfect in the UV, starting with the collimator lens - why not someone ordering to try a UV designed objective from Edmund Optics? I'd be the next to follow once it works. It's a special case that I can use it for 1 star (question till when), for a rare event - hence my hesitation to invest too much for UV.

As for the Barlow to make your scope f/10, you should ask others (yahoo group) who have experience in optics or attached an LHires to f/7 scope, and do tests. It is a tricky area, e.g. you can play with the focus distance to adjust the magnification factor with some TV Barlows!

Happy experimenting!
Peter