Merlin66

It’s easy to measure the focal length of a Barlow lens. measure the front lens aperture, draw a circle on a card twice this diameter, point the Barlow towards the Sun, when the image fills the circle, the spacing between the Barlow lens and the card is the focal length. works for all Barlow and negative lenses.

This might help: http://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app#MagChart http://www.televue.com/engine/TV3b_page.asp?id=52&Tab=_photo

Paul, Understood. I assume your markings on the edge of the slit holder should match the necessary orientation of the slit plate. That would remove ambiguity. Sorry if I've "muddied the waters" - my only experience is with the Custom designed plates. Ken

Paul, I assume(d) the current Jeulin reflective slit plate was a copy of the Custom design plate that OVIO manufactured for me. When viewed from the telescope side, the numbers appear correct, the chrome coating and slits are on the rear face - towards the collimator.

This may help.... https://www.celestron.com/pages/edgehd-optics

Louise, On my Custom OVIO slitplate I had 6mm holes behind the slits (6mm long) to prevent any unwanted light getting through.

Louise, A wrap of translucent paper around the bulb then the partial aluminium foil reflector would help. Bulbs generally need a diffuser to suppress the actual bright filaments.

Not that I recommend it, but the SCT threads on the FR are the same as the SCT threads on the diagonal, 2" x 24tpi

Louise, Thanks for that! I hope you had a good Hogmanay. Wishing you a safe and happy New Year.

I was just reading up on Arp's Atlas of peculiar galaxies, and he said due to the solar minimum he was able to get far deeper images from the 200" Hale telescope than previous! https://ned.ipac.caltech.edu/level5/..._contents.html I was wondering if amateurs have noticed the same during the current solar minimum????

Paul, I’d like to think all the amateurs who build a LowSpec, and any other spectrograph will put them to regular use. We need as many active spectroscopists as possible. There are more challenges and opportunities in spectroscopy than there are observers.

Louise, long before that..... It was actually a Shelyak design, hence the “non commercial use”

“Astronomical Spectroscopy for Amateurs”

Louise, No, never met her or her father. Only know they had a Spectra-L200 kit which Piper assembled and used.

Louise, p160.... I tried the battery powered neon....batteries didn’t last long!

Paul, IMHO go for one of the Chinese options....recommend a 12V 5.5/ 2.1 mm socket and a on/off switch - if this could be automated it would be a bonus!

For completeness: Coronado use the ITF (or Maier equivalent), Lunt went for a Blue Schott BG 38 filter - unfortunately they both can fail.... The Maier replacement has been used by MANY solar observers over the past seven years and I'm not aware of any failures!

Louise, No, definitely more like the Chinese one.... I mounted it in a small project box, with 12V socket and on/off switch. This sat on the outside of the housing and powered the Neon lamp fitted in a perspex block which flipped down onto the slit gap.

The ITF (Induced transmission Filter) is usually the filter element placed before the final narrowband blocking/ sort filter in an Ha set-up. These are subject to failure.....luckily we found a suitable replacement from Maier Optronics.

Louise, I manufactured the Spectra-L200 as a kit which could be easily assembled by amateurs....they sold all over the world. Piper S&T.pdf

A spectrograph definitely needs a reference lamp. As a minimum a Neon, this provides calibration around Ha which is an important wavelength for astronomers. The RELCO is also good and give a wider coverage. When I started with the Spectra-L200 "IKEA" kit, I had the same reference lamp issues..... I found at the time that the hand held fluoro "inspection" lamps had a small 12V to 110/220V inverter built in, so I used to raid the hardware shops and buy them up, and strip them for the inverter and the 12V plug. The inverter looked very similar to this one: https://www.banggood.com/150W-Inverter-Boost-Module-150W-DC12V-Step-Up-Board-Frequency-Square-Wave-p-1278570.html?rmmds=detail-left-hotproducts__3&cur_warehouse=CN This initially powered a neon lamp. I used about 100 of them (!!) with no failures, no issues, in fact I'm still using one of the early build inverter/ neon set-ups today, almost ten years later. This is shown in "Astronomical Spectroscopy for Amateurs" p160 and p202. There's also a "non commercial" circuit diagram for a suitable inverter.

Lousie, Now that Paul's on board, you should ask him when he's going to incorporate a reference lamp in the design of the LowSpec

Louise, Yes, every time... thermal effects, flexing in the housing etc etc etc can impact on the accuracy of measurements. It's not unusual to take a reference image before and after a long series of target exposures. Fitting a reference lamp - check the alignment and orientation to the slit gap. Ideally the lamp should be on the optical axis as near the slit gap as possible. On the Spectra-L200 I used a flip mirror to direct the reference lamp to the slit gap.

Paul, welcome on board! good to see you here, as you’ll see there are a few members already building your LowSpec spectrographs. Keep up the good work. Ken

Louise, I take a reference exposure every time I take a target spectrum of a star.... It quickly becomes second nature.......