CCDSPEC Spectrometer and PCSpectra software

Spectroscopy of Arcturus – re-analysis of spectrum from 4/8/2018 on 26/9/2018

Hi All

The following images are of my analysis of a spectrum of Arcturus I took using my CCDSPEC spectrometer. On this occasion, I used my Sky Watcher Equinox Pro 120mm OTA on EQ6 Pro (although I was hand guiding it rather than using the drives). The camera is a QHY6 and the acquisition software was EZCAP which comes with the camera. I took the spectrum in Lichfield, Staffordshire, UK on 4/8/2018 and analysed it 26/9/2018 using RSPEC software.

Attached are:

  1. Uncalibrated spectrum line graph (x-projection).
  2. Calibrated spectrum of Arcturus – I used an amateur spectrum on the internet to provide three data points for the RSPEC Calibration Wizard (linear approximation).
  3. A plot of my calibrated spectrum against the closest reference spectrum I could find in RSPEC. Arcturus is spectral type K1.5IIIFe-0.5 but closest match I could find on RSPEC was K1iv, so I have plotted against that. In spite of the slight differences, I have been able to identify almost exact matches for range of lines between the two spectra – it amazes me how amateurs can obtain incredibly precise data using spectroscopes on their very modest backyard setups!
  4. From this I have generated a calibration graph for my own future use which I have also posted here – if you have a better/alternative one you have created please do upload it in response to my post here.


Comparison of spectra of 12V Compact Fluorescent Light Bulbs

The 12V Compact Fluorescent Light Bulbs I have purchased come in two flavours – 2700K and 6400K (later is daylight). Tonight, I took spectra of both types using my CCDSPEC spectrometer to determine whether the peaks shown on the spectra were the same. It turns out that they are and hence can be readily used for calibration purposes on my spectrometers. The main difference between the two is the intensity of the peaks with the 2700K light bulb having much lower intensities than the 6400K light bulbs.

Information on different colour temperatures of compact fluorescent bulbs can be found at


2700K spectrum:

6400K spectrum:

Re-analysis using RSPEC Software of Vega spectrum from 4/8/2018

This is a re-analysis using RSPEC software of the Vega spectrum I took 4/8/2018 using my Sky Watcher Equinox 80mm Pro telescope & CCDSPEC spectroscope, hand guided on Manfrotto mount.


CCDSPEC spectrum of Vega 4/8/2018

I have now taken out a trial subscription to RSPEC amateur astronomy spectroscopy software

The following is the original spectrum taken using Nebulosity 6 software:

This is an x-projection of the above from PCSpectra software supplied with the CCDSPEC spectrometer:

The following screenshot shows the above spectrum loaded and displayed in RSPEC software (below):

In the above diagram, I calibrated the x-axis using a Vega spectrum from the internet, using two points. I have created the following Vega spectrum for calibration purposes based on this internet data. Note that I have annotated the lines using Angstroms as RSPEC uses Angstroms on its x-axis and it all gets rather confusing if one graph is in Angstroms and the other in nanometres as it is not obvious that the difference in scale exists on the x-axis and the graphs do not line up.

RSPEC allows reference spectra to be compared to user spectra. Here, I have loaded up a reference spectrum in blue at the same time as my own Vega spectrum in red (below):

Having calibrated my spectrum against two lines on the reference spectrum I created above from other internet resources, there is excellent correlation between the lines on my spectrum and the RSPEC reference spectrum (no – I did not use the RSPEC spectrum to create my calibration Vega spectrum!)

Another interesting feature in RSPEC is to use it to identify elemental lines – using this feature on my spectrum:

I think that the closest elemental match to the lines seen in my graph is found when both Star Type A is ticked (Vega is A0V) and also Hydrogen Balmer series:

Three LED lamp calibration light

I purchased the following multi-coloured LED strip light from ebay – Ed at the last RAG meeting asked whether coloured LEDs could be used as a calibration light for spectrometry – it seemed like a good idea! This one comes with a neat little remote control to allow it to be placed some distance away (ideal for focusing a telescope on it and then turning on and off and changing colours).


I made a calibration light out of the strip light above and a piece of Perspex made to diffuse light (off ebay designed for light boxes). I could then take spectra using my CCDSPEC spectrometer:

The first three spectra show that red, green, and blue are all very pure colours from the relevant LEDs in the strip:

Spectrum of LED strip light – green LED (below):

Spectrum of LED strip light – red LED (below):

Spectrum of LED strip light – blue LED (below):

Producing multiple lines on a single spectrum:

The above graphs demonstrate that the LEDs individually produce pure colours. However, for calibration purposes, it is useful to be able to have multiple lines on a single spectrum. This is where this particular colour-changing LED strip is useful – the strip uses three different coloured LEDs as above but allows you to select various combinations of LEDs to produce variety of “colours” – each of this is a mixture of LEDs switched on together in varying amounts.

The following are three examples of combinations – there are a total of 16 colours available (16 combinations):

Spectra from the three examples of colour combinations:

X-projections from spectra from the three examples of colour combinations:

White colour on the LED strip:

Probably the most useful combination is when all three LEDs are turned on together “white” – donated by a convenient “W” button. The spectrum from this produces three convenient peaks for calibration (below):


Comparing spectra from compact fluorescent lights in lounge, portable 230V desk lamp and portable 12V calibration light

In previous posts, I have discussed the various calibration lights I have tried for my spectrometers. Each time I come back ultimately to fluorescent lights – these have typical spectra and easy to identify peaks and are ideal for relatively low resolution spectrometers such as my CCDSPEC and Science Surplus DIY Spectrometers.

They are available as long bulbs or more compact portable bulbs called Compact Fluorescent Lights (CFL). The spectra are similar.

Initially I used a compact fluorescent light in my study/lounge but then realised I could do with a portable arrangement to take outside into the field. I obtained a simple desk lamp and used 230V CFL bulbs powered using an inverter on my leisure battery. This is not the safest method – 230V can cause harm – but then I found a caravan online shop selling off its last 12V CFL bulbs. I did not realise these were sold in 12V varieties so I have obtained a number of these and built myself a lamp holder than plugs into a 12V cigar-type lighter plug socket so it can be powered from any standard 12V telescope power supply.

In today’s post, I am comparing the spectra on the three sources of CFL bulbs – the ceiling lights in my lounge, 240V desk lamp and homemade 12V mobile calibration system. The question I need to answer is whether all three produce similar spectra – in which case the 12V homemade setup will be my preferred calibration light as it is mobile and safe.

I used my CCDSPEC spectrometer for today’s tests.


Taking spectrum from 240V desk lamp CFL arrangement (below):


Taking spectrum from 12V desk lamp CFL arrangement (below):


Comparing the three spectra:

Spectrum from 240V CFL ceiling light (below):

Spectrum from 240V CFL desk lamp (below):

Spectrum from 12V CFL homemade lamp (below – here I have altered the exposure to give longer and shorter exposures to show that this made minimal difference to the spectrum as long as it did not reach maximum (16000 on intensity at which point peaks broadened and became less useful for calibration as exact wavelengths difficult to read from graph)):


To assist in comparison between the three spectra, I have repeated them below but this time one after the other:

It is amazing how similar these bulbs are – from different manufacturers but still providing same peaks with slight differences only in intensity. It shows that the similar chemical makeup of their constituent gases and that the emission spectra of those gases do not vary.

My conclusion – any of these bulbs can be used for calibration of my spectroscopes and hence I can happily use the 12V outside in the field.

Spectra taken with CCDSPEC Spectrometer @ Rosliston Forestry Centre RAG meeting 14/9/2018

I demonstrated my CCDSPEC spectrometer at the mid-monthly RAG meeting at the Forestry Centre tonight.


CCDSPEC Spectrometer:

The following spectra were all taken using the CCDSPEC spectrometer during the RAG meeting. The spectra are direct from the CCDSPEC spectrometer without telescope or other optical aid.

I started by taking a spectrum of one of the long fluorescent ceiling bulbs in the building (below):

For comparison the following is a spectrum I took from a compact fluorescent bulb in our study on 3/8/2018 (below). The same lines are clearly evident:

The following is another comparison spectrum from Wikipedia – I have labelled it with the wavelengths of the main lines:

I then took a spectrum of my calibration light made from the neon bulb in a RELCO starter bulb:

We also compared the above to a spectrum from the LED projector at the forestry centre (below):

Ed Mann came up with the idea that lasers might work well as calibration lights.

He had two laser pens with him – blue and green – so we tried taking a spectrum of those laser pens reflected off a white piece of paper (below):

Does perspex effectively change solar spectrum or compact fluorescent light spectrum recorded with CCDSPEC spectrometer?

I mentioned at the RAG meeting on Friday evening that I was making a portable calibration light using a compact fluorescent bulb in a desk stand and that I was making a Perspex diffuser to go in front of it.

Lee wondered whether the Perspex would change the recorded spectrum due to its absorption characteristics. I am very grateful to Lee for pointing out this possibility as it clearly needs to be checked, especially as being able to know the exact wavelengths of the peaks on the spectrum produced by the bulb is vital to the calibration process and if these change as a result of the Perspex then this will mean that I will need to be careful using this material during the calibration process.

I have this tested this hypothesis this evening. If the Perspex does change the spectrum then I will know that it will limit the use of the lamp as a calibration device.

My test below used the solar spectrum initially, followed by use of same compact fluorescent bulb as being used in my portable calibration light.

Result of these tests = Perspex sheet reduces intensity but does not effect spectrum – therefore can be used as diffuser in front of calibration light without problems.


Solar spectrum taken by pointing CCDSPEC spectrometer out of window (not attached to a telescope) – this spectrum is without anything in front of the CCDSPEC spectrometer:

The following spectrum was taken as above but this time I placed the piece of Perspex I intend to use as the diffuser on the new portable compact fluorescent bulb calibration lamp in front of the CCDSPEC touching the 2 inch eyepiece adapter so that very little light could get into the CCDSPEC without going through the Perspex (below):

In the following image, I have compared the above two spectra and added some lines to demonstrate that absorption lines are essentially unchanged between the two:

The above spectra are not calibrated on x-axis. The following is a repeat of the image with Perspex in front of the CCDSPEC but this time calibrated to give wavelength on x-axis in nanometres (nm):

The above shows that the solar spectrum as shown on CCDSPEC stretches from essentially 400nm to 750nm – this will be limited by the instrument’s response as the solar spectrum extends either side of this.

The following graph shows typical transmission characteristics of variety of plastic materials including acrylic from 200-1200nm:

From the above spectrum, it is unlikely that plastics make little difference to the spectrum of light over the range of wavelengths covered by CCDSPEC, and this appears to be born out by my solar spectra today.

Spectrum from CCDSPEC pointed at desk lamp with compact fluorescent bulb WITHOUT Perspex between them (darkened room, below):

Repeating above but this time placing Perspex over end of CCDSPEC – compact fluorescent bulb, darkened room:

Perspex can be seen to reduce intensity but does not meaningfully change the spectrum so will not adversely affect the ability of the Perspex covered light to act as calibration instrument. The reason that I want to add perspex in front of the calibration light is to act as a diffuser and give even illumination (the Perspex has appropriate surface to act as diffuser).

Spectroscopy from Lichfield with CCDSPEC – Damian and Andy

Damian and I went outside at my house in Lichfield and manually guided the spectroscope to get a bundle of spectrums of stars tonight. Once he had got the technique there was no stopping our boy Damian!

He calibrated the spectroscope using a compact fluorescent bulb – we used linear equation for figures for calibration file tonight.

Comparing images of spectra from brighter stars with online typical spectra – we could immediately find most of main lines generally within 2nm (20A) or real values. Wow!

Sky Watcher Equinox Pro 80mm, Manfrotto alt-az manual mount, hand guided, CCDSPEC, Nebulosity 4 software, QHY6 camera.

Note spectral classes:

Deneb A2 la
Altair A7V
Arcturus K1.1IIIFe
Vega A0V



N.B. With the peak of the Perseids tomorrow night and a reasonably clear night tonight we had expected to see a number of Perseid meteors…….Damian saw one in the nearly two hours we were outside and I missed even that one!


Calibration of the CCDSPEC/QHY6/Sky Watcher Equinox Pro 80mm/Nebulosity setup:

Calculation spreadsheet for higher order polynomials Excel Andrew Thornett 100818

Damian’s calibration below (his measurements circled):

Some spectra were amazing, showing incredible lines:



Spectral type A7V



Some spectra were not so amazing:

How to use the higher order co-efficients with PCSpectra

From: Kenneth Elliott
Sent: 10 August 2018 14:15
Subject: Re: 3rd order polynomials


Hi Andrew

This is how you use the higher order co-efficients with PCSpectra

Original (linear values entered into PCSpectra calibration file):

70.255, 0.6474

How to enter higher order co-efficients, x2, x3 and x4, into PCSpectra calibration file:

70.255, 0.6474, 0.001, 0.000000013, 0.00000000000121

Alternatively, scientific format can be used for co-efficients e.g.

7.0255E1, 6.474E-1, 1E-3, 1.3E-8, 1.21E-12

Pitfalls of using higher order co-efficients in PCSpectra:

There are two pitfalls

1: You need to have lots more lines if you use higher order fits and any fits outside the wavelength range you have got calibration lines may be wildly wrong as the equation has no constraints, so its fine with the Argon lamp.

2: you need lots of precision in the coefficients to get the accuracy, otherwise if it is multiplied by X**4 it could be wildly out.

How to improve accuracy/usefulness of higher order coefficients with PCSpectra:

Three different ways you could do this:

1. Astrosurf French site which has line idents and fitting programs, but I gave up trying to use it as, although the program runs in English, if there is an error then the error messages are in French.

2. Using STARLINK (UK) software – on Linux and needs a fair level of skill to get going.

3. The HST software both on Linux – on Linux and needs a fair level of skill to get going.