CCDSPEC Spectrometer and PCSpectra software

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).

Andy

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.

Andy

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.

Andy

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.

Andy

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

Andy

 

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:

Vega:

Altair:

Spectral type A7V

 

Altair:

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.

http://www.astrosurf.com/buil/isis-software.html

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

http://starlink.eao.hawaii.edu/starlink

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

http://iraf.noao.edu/

Ken

Why different image acquisition software programmes result in need to recalibrate CCDSPEC/QHY6

This follows on from Andrew’s post about needing to recalibrate his CCDSPEC/QHY6 when he changed image acquisition software from Nebulosity 4 to EZCAP:

Re-calibrating CCDSPEC/QHY6 combination for photos taken with EZCAP Image Acquisition software rather than Nebulosity software 4/8/2018

Regarding why recalibration is necessary when image acquisition software is changed:

Hi Andrew

It’s quite simple really.

Although the spectrum appears in exactly the same location on the chip, what comes out depends on how he data is clocked out and that depends on the software. Some chips have non sensitive pixels which are clicked out first and disregarded whilst other programs read out the whole chip which may be bigger than the imaging part.

So the pixel number in both X and Y can be different. Hence, it is essential to do the calibration and observations with the same readout program

Hope this helps.

Ken

PS I designed and built a CCD camera Electronics and software 30 years ago

Reflection on experience of doing spectroscopy so far

I have now been the proud and excited possessor of a spectroscope for about a month. If you have been following my posts, you will see they clearly demonstrate my intense interest and excitement in this new area (for me at least).

Statting with the fortunatel purchase of a competitively priced and very well designed system thayvallowed me to generste spectrums virtually immediately, it also allowed me to obtain star slwctra quickly and so i did not become put off by a significant learning curve.

Thay learning, i have found, does exist and can be frustrating but rewarding too when i get something to work.

I have discovered:

I can get spectra of daytime objects eaaily and quickly by just pointing the instrument at the ibject in question. This is rally easy to do and will work well for outreach. Unlike other astronomy branches, this one can be done in the day!

I can obtain spectra of bright stars with my 80mm Equinox Pro on alt-az mount also easily and it is not too much if an issue tk hand guide the telelscope to obtain these spectra. This is not mentioned in the manual and very little about it on the internet where guided exposures are the thing but my experience shows it is effective for bright objects which can easily be seen in the 10mm eyepiece in the guiding port.

The eyepiece in the guiding port simply needs to be focused on the slit – do this in the day. Then at night focus the star to a small round dot – as small as possible. When it is over the slit the star divides in two and spectrum evident in the guiding eyepiece. This is only when over the slit. The eyepiece in the guiding port has small field of view. It is really important to ensure the finder is aligned on the scope. I might add illuminated cross hairs to help here. Not on that yet.

The situation becomes more complocayed once i start to calibrate the spectrometer. Calibration helps as it enables accurate determination of the wavelength of peaks on the spectrum amd i can consistently obtain accuracy of calibration, it appears, within 1nm. Compact fluorescent bulbs seen to be good source of light for this exercise. They come with diffuser as part of the design (the glass cover is milky). They are small and portable. I could do with making a portable rig including such a bulb to take into the field as i have found that calonration needs to be done each time I change the telescope or even the image acquisition software! Basically I suspect it is best done every night the spectrometer is used. Comparison spectrum of fluorescent lights are available from Wikipedia together with information on the wavelengths of peaks on the spectrum. Although calibration is tine intensive, it ks rewarding and leads to exciting results when you can identify peaks correspnding to specific molecules or elements.

Although using the spectrometer hand guided with 80mm Equinox Pro was relatively easy, I have found that changing to the 120mm Equinox on EQ6 Pro mount is a lot more complex and time consuming and frustrating although potentially a lot more rewarding. Changing to this set up opens up the possibility of taking spectra of much fainter and difficult to find objects and taking much longer exposures including planetary nebulae and faint stars. I have only used this set up once to date (last night), and this experience demonstrated to me that the driven moint does allow me to take significantly longer exposures without having to keep moving the scope with fine control on handset even when mount is poorly aligned. I found that using the spectrometer eyepiece to align the mount was quite difficult as the eyepiece uses light from the reflection on the highly polished metal around the slit. This is a lot less efficient than a high quality mirror with costing ps and so the image is much fainter than I would normally see in an eyepiece in a diagonal. Two possible solutions to this problem for the future are:

1. Next time I could align the mount without the CCDSPEC in the scope and then insert the CCDSPEC. As the CCDSPEC will need to be calibrated and its weight needs to be taken into consideration when balancing the scope on the mount, in practice this will mean that I need to mount the telescope on the mount together with CCDSPEC in the focuser, calibrate the CCDSPEC/QHY6 whilst attached to the scope, take the CCDSPEC out, then align the mount without rhe CCDSPEC in situ, then reinsert the CCDSPEC and do observations. This leads to quite a lengthy and complex set up process and hence I can see the advantage of having an observatory with fixed and permanently aligned telescope for spectroscopy. In addition, I am worried that the mount will have difficulty being aligned without the weight of the CCDSPEC in the focuser due to balance having been achieved with the CCDSPEC in place.

2. A better suggestion has been made by Damian. He has suggested that rather than taking the CCDSPEC on and off to align the telescope, a preferable option would be to use the excellent new laser pointer made for us by Ed as part of the three star alignment of the mount. Great idea! In addition, changing the eyepiece on both the CCDSPEC and finder scopes to illuminated reticule versions will help.

Andy

CCDSPEC spectrum of Vega 4/8/2018

Taken just before midnight 4-5/8/2018, I tried using EZCAP software but then found that Nebulosity 4 gave better images. There was no interlacing effect with images of Vega through the Skywatcher 120mm DS Pro refractor up to 6 seconds in length (I presume because camera is not receiving > maximum tolerated amount of light). Even though the scope (on EQ6 Pro) was not properly aligned, it tracked sufficiently to keep the star in the slit for 6 seconds or longer.

The EZCAP-based calibration file gave incorrect wavelengths on the graph so I resorted to using the Nebulosity-based calibration file from 29/7/2018.

My spectrum clearly shows the Hydrogen Balmer series of lines.

Andy

Compare to this typical spectrum of Vega from http://ksu-astro.nckas.org/spectroscopy.html

Or this one from http://www.astrosurf.com/buil/us/vatlas/vatlas.htm