Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Handheld spectroscope for eyepiece filters

  • Please log in to reply
7 replies to this topic

#1 George9

George9

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1599
  • Joined: 11 Dec 2004

Posted 10 November 2019 - 01:51 PM

I was playing around with an $8 plastic handheld spectroscopes, one of the triangular black ones. It is graduated with a 10nm scale. It is not well calibrated in terms of absolute wavelength, but 10nm seems about the right width per line.

 

I am updating my narrow band filter collection so I have a number of filters available. I was surprised how accurately I could estimate the FWHM, within 20% (or about 2nm) on five filters. Estimating the transmission is tough; hard to tell even a 2x difference. And hard to tel if you are just making or just missing a line without a reference, but easy to go back and forth between filters and compare placement.

 

For $8, it teaches you a lot about your filters. You can easily see which ones pass red light in addition to their main wavelength. You can tell which kind of old Lumicon you have. You can tell exactly what your UHC-like filter is passing.

 

Some predictable results:

 

I got my first DGM NPB filter. In daylight it is mostly red to me. The spectroscope shows its passbands. In the telescope on M57, as related by other viewers, it seems to perform just like UHC filters. The big red passband did not brighten the sky background to my eye (due to poor red sensitivity in dim light). I look forward to testing it out on objects with H-alpha or other red emissions.

 

My Celestron OIII is very narrow, as demonstrated in the spectroscope. In the telescope, it really dims the view of not just the sky and stars, but also the OIII emissions themselves. It really is a photographic filter that should be marketed as such. It was still better than no filter on M27 and M57, but noticeably inferior to my other visual filters, OIII and UHC. Nice price though.

 

George

 

 

 


  • jeremiah2229 and j.gardavsky like this

#2 petert913

petert913

    Gemini

  • *****
  • Posts: 3456
  • Joined: 27 May 2013
  • Loc: Portland, OR

Posted 10 November 2019 - 02:24 PM

How funny that you post this.  I have been searching the internet to see if there are any spectroscopy services that could scan my filters and

give me a print out of their spectral characteristics (400nm to 750nm or so).  If anyone knows of such a service, I would appreciate the tip.

 

I never thought to just use a prism spectroscope.   I don't need anything super accurate.  This just may work !


  • George9 likes this

#3 robin_astro

robin_astro

    Viking 1

  • -----
  • Posts: 742
  • Joined: 18 Dec 2005

Posted 10 November 2019 - 02:59 PM

 If you know any amateurs with a spectrograph, it is very easy to do (Even a simple Star Analyser) You just take spectra with and without the filter in front of a light source and divide one by the other. It was one of the first things I did when I got into spectroscopy back around 2002. Here are the crude measurements I made back then.

http://www.threehill...ter_spectra.htm

A proper spectrograph will show precisely where the pass band is, even for narrow band filters eg as Christian Buil did here

http://www.astrosurf...ters/curves.htm

 

Cheers

Robin


  • George9 likes this

#4 TOMDEY

TOMDEY

    Aurora

  • *****
  • Posts: 4906
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 10 November 2019 - 04:41 PM

Yes, a pocket spectroscope is handy. We optical scientists carried this thing around (B&L, Kodak, KPNO, ITT, Harris, L3 etc.)    Tom

Attached Thumbnails

  • 300 BL Thin Film Wedged Pocket Spectroscope.jpg

  • George9 and Mike Mc like this

#5 George9

George9

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1599
  • Joined: 11 Dec 2004

Posted 10 November 2019 - 09:49 PM

Thanks, all. I forgot to mention that I did narrow the slit on the $8 one with two pieces of aluminum foil and scotch tape. The default slit is too wide to make measurements. And it's based on the a diffraction grating, not a prism, so the output is linear with wavelength and easier to estimate.

 

George


  • j.gardavsky likes this

#6 Simon B

Simon B

    Apollo

  • *****
  • Posts: 1032
  • Joined: 16 Jan 2017
  • Loc: Vancouver, BC

Posted 11 November 2019 - 02:21 AM

How funny that you post this.  I have been searching the internet to see if there are any spectroscopy services that could scan my filters and

give me a print out of their spectral characteristics (400nm to 750nm or so).  If anyone knows of such a service, I would appreciate the tip.

 

I never thought to just use a prism spectroscope.   I don't need anything super accurate.  This just may work !

 

Petert913 A cloudynights member by the username 'Lunarfox' will scan them for you for free, just send him a PM : )  He'll add it to his already quite large database:

 

https://searchlight....9d-153d7e7c0eb8


  • j.gardavsky likes this

#7 Ernest_SPB

Ernest_SPB

    Apollo

  • *****
  • Posts: 1343
  • Joined: 13 Nov 2010
  • Loc: St.-Petersburg, Russia

Posted 11 November 2019 - 03:19 AM

by the way see handheld specroscopes, like the following:

https://www.aliexpre...rchweb201603_55

https://www.aliexpre...rchweb201603_55

https://www.aliexpre...rchweb201603_55

https://www.aliexpre...rchweb201603_55



#8 j.gardavsky

j.gardavsky

    Mariner 2

  • -----
  • Posts: 218
  • Joined: 18 Sep 2019
  • Loc: Germany

Posted 11 November 2019 - 05:42 AM

I am still using the old Zeiss Handspektroskop with the straight view Amici spectral prism,

CZJ Handspektroskop.jpg

 

Best,

JG


  • Terra Nova likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics