Forum der Vereinigung der Sternfreunde

I am posting this because I know there are many spectrograph design experts here
Do you think this new instrument from Starlight Xpress is a good design for an astronomical spectrograph ?
http://www.sxccd.com/82-about-us/116-latest-news
https://www.youtube.com/watch?v=LiEugmhZ4SY
It seems very simple and the reflective optics mean there will not be any chromatic aberration. Maurice Gavin (who made the video) has one on loan and reports significant astigmatism. Are there any other advantages/disadvantages?

Cheers
Robin

Hi Robin,

interesting! looks nice. So one can watch weeker objects. On the spectra as shown in YouTube I don't see and optical aberrations!?.

Would it be possible using any CCD or must one use the loadstar? Do you know, how much is this spectrograph?

kindly regards
Berthold

Hi Robin, at a first glance the instrument looks quite solid and well manufactured including a Relco comparison lamp. Astigmatism is normal at Rowland circles but can be eliminated by choosing the correct focal plane with respect to the dispersion direction. I suspect, Maurice Gavins device is not correctly focused.

Cheers, Thomasd

Hello Berthold,

The Lodestar guiding camera is built into the spectrograph but I think any camera should work for imaging. You will need a very large CCD to record the full spectrum in one image though. (The spectrum from 340-900nm is 32mm long) No price yet. Perhaps next month?

The things I like less are:-

The astigmatism which will give more sky and read noise in the spectrum and will limit it when used as an imaging spectrograph (for details in extended objects)
I would prefer a mirror slit guider instead of the beam splitter which are difficult to set up properly and keep aligned. They cannot guide on as faint field stars either,

Thomas - Maurice says the astigmatism is acknowledged by the manufacturers so I think it is a characteristic of the design. (They tried to turn it into an advantage by claiming it reduces the risk of saturation

Fully corrected gratings are available but perhaps are very expensive as here for example
http://www.horiba.com/uk/scientific/pro ... -gratings/

Cheers
Robin

Hello Berthold,

The spectrum lines are in good focus but the astigmatism means the spectrum is out of focus in the direction perpendicular to the dispersion. This makes the spectrum of a star very wide, covering many rows. You can see this the star spectra in the video 1:49-2:04

Cheers
Robin

As you know, Robin, astigmatism can always be corrected by chosing the correct focal position. In our book we describe it in very detail and on page 98 you can find the attached figure for better understanding. For vertical dispersion direction in this image the focal point 'T' should be chosen. Then the focal image is only distorted perpendicular to the dispersion direction. I do not know what the manufacturer exactly acnowledges but if they use a good Rowland grating there should be no astigmatism at the correct focal position.
Cheers, Thomas

Yes, one can even see the field curvature. The strip has different widths for different wavelengths. That is one of the prices you pay for the compact lightweight design of a curved grating spaectrograph.

Hallo Robin,

yes, now I see the aberration. With a smaller CCD it would be not possible to take the full range of the spectra. But that is not so bad , I think! Do you see any problems caused by the astigmatism?

best greetings
Berthold

Hello Berthold
Well there would be some loss of signal/noise because of the extra sky and camera noise from binning the wider spectrum and you would not be able to make
good spectrum images like this for example.
http://www.astrosurf.com/buil/scan/demo.htm
but if it can really produce a well focused R~2000 spectrum across the full wavelength range in one exposure (with a large enough camera) that would be something that no other amateur (non echelle) spectrograph on the market can do now I think.

Robin

Hi Robin
Well, due to the astigmatism, it is not in focus! If you use the position of least astigmatism (as Thomas has described) you will loose resolution by at least a factor of 2! There are better spectrographs on the market and the statement "with a large enough camera" is applicable to every spectrograph. The MiniSpec, e.g., has no astigmatism and can achieve R>2000 and "with a large enough camera" you can have the whole visible and more. And there are more spectrographs on the market... And I do not understand, why you explicitly exclude Echelles (e.g. EShel is able to do that)???

ciao,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

BTW,

some years ago I did some tests with an concave grating not the Rowland mounting, but the better Wadsworth mounting for a really flat field!!

http://hobbysternwarte-plosen-eng.de.tl/MiniSpecC.htm

I did not made any further work on that, because this was always and will be a mounting for laboratory work, due to the aberrations and the loss of SNR for faint stars. That's also the reason, why they only showed spectra of bright stars... and only raw data.

Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Thanks Daniel,

That is useful information. I wondered why this design has not been used previously for amateur astronomical spectrographs and you have confirmed my suspicions. (From the published spectra, I assume they were recorded with the focus optimised for the dispersion direction)
There are also some other practical things I am not sure I like about the design. The use of a beam splitter guider, the rigidity of the sliding plate holding the camera and the potential for movement in the camera focusser for example.

As far as I know this is the only design that the manufacturers actually claim to be able to record the full spectrum 340-900nm without loss of resolution at the ends of the spectrum eg due to field curvature or chromatic aberrations. It is only a claim though at the moment. We would need proper measurements to confirm this. Are the minispec optics good enough to do this over such a wide field and spectral range? Of the spectrographs I am most familiar with, the LISA starts to loose resolution below ~4000A and the LHIRES of course with its simple doublet needs refocussing for each wavelength. The ALPY is good over this range but only produces a short spectrum at R~600. Echelles are of course designed for a wide spectrum range but I expect you are right. The designs available to the amateur today would probably all struggle to stay sharp over the full 340-900nm spectral range.

Cheers
Robin

The efficiency is another important question of course but unfortunately no manufacturers seem to publish that sort of data and you never see any good critical side by side reviews of spectrograph performance published. Perhaps we should design a series of tests for any spectrograph so we can measure the important parameters and compare performance in an objective way?

Robin

Hi Robin

You may know this:

http://spektroskopieforum.vdsastro.de/v ... f=2&t=4266

This line-ccd has a length of around 29 mm and would be really large enough to get R~2000 for the visible with an 830 l/mm grating in the MiniSpec.

Starlight wrote: "The spectral length is 340 - 900nM over a distance of 31mm and the resolution factor is in excess of 2000."
Who has a cooled CCD with 31 mm - this spectrograph will not solve that old problem...nor does any other, that is true.
However, 340 nm is not accessible due to CCD efficiency and the earth atmosphere - not for faint stars at least. And also this is an "old problem". There is no spectrograph, earth based, which can look through earth's atmosphere

Of course, that spectrograph has the advantage, that no refractive material is used and wavelength dependent aberrations are reduced. However, coma and astigmatism are in general wavelength dependent. You can see some angle dependent aberration in the YouTube video at 1:58 in the spectrum of alpha Corona Borealis.

Sure, testing would be nice. This is only possible in the lab, where one can assure constant and controlled conditions for efficiency measurements.

cheers,
Daniel

_________________
Daniel P. Sablowski

https://www.kunstmann.de/buch/axel_hack ... 42000/t-2/
https://dpsablowski.wordpress.com
https://github.com/DPSablowski
https://www.aip.de/mitglieder/dsablowski/

Hi Daniel,
There are some cameras based on the KAF11002 CCD which is 37x25mm so would do the job. For example
http://www.atik-cameras.com/product/atik-11000
https://www.sbig.com/products/cameras/stxl/stxl-11002/
but the QE of this CCD is not very high and it is rather noisy. They cost around 5000 euros too

Cheers
Robin

Hi Robin! Somewhat off-topic, but from my point of view this is not the crucial parameter but the bias quality including the internal amplifier. The QE is important if we deal with excellent cameras as in the professional domain. The QE in the manufacturers lists are probably mentioned for historical and PR reasons. Today with off-the-shelf instruments and amplifiers the bias is most important. In chapter 10.4 of our book we illuminate the situation by comparing two different cameras.

Cheers, Thomas

Hi Thomas,

Camera noise (both read and thermal) is important of course but SNR for a given exposure time depends on both QE and noise and the variation in QE between sensors used in amateur cameras is real and large. See here between Kodak CCD for example
https://www.sbig.com/site/assets/files/ ... _all-1.gif
The KAF 11002 sensor is not a good one for spectroscopy. It has ~1/3 of the sensitivity of the KAF 3200 at H alpha so would need ~3x the exposure for the same e counts. For my faint object observations I limit my exposure time to a practical maximum of ~2 hours. With this camera I would need 6 hours for the same counts that a KAF 3200 would give in 2 hrs ! This would perhaps be ok if the camera noise was much lower but it is not very good either (SBig for example quote 11e read noise and a very high 0.5e/sec for thermal noise for their camera) so even after an impractical 6 hours exposure the SNR would still be poor because of the high thermal noise. Fortunately with the latest generation of Sony CCD we can have both good QE and very low noise at low cost. (and no residual image problems or ripples in the spectral response like the Kodak CCD) They do not come in very large sizes though

Robin

Buil publishes measured parameters (QE, noise, gain etc) for many of the cameras typically used for amateur spectroscopy which he updates from time to time as new ones come out.
http://www.astrosurf.com/buil/isis/noise/result.htm
This is useful for predicting performance as here for example
http://www.astrosurf.com/buil/eshel4/eval_en.htm

Cheers
Robin

Hello Robin,

I have a question:

my english is not good enough to understand completely what Buil will tell us:

Take one star, the same exposure time, once KAF3200, without binning mode, then this atik 460 or so with binning 2x2:

what are the advantages from the atik please:

Is the S/N better?
The FWHM is not better, or?
Ok, the readout time is faster, ok!

Are there any other advantages I did not realized?

What is your opinion? Do you think it would be usefull to change the KAF 3200 to the atik 460?

All the best and greetings to your wife too
Berthold

Hello Berthold,

If you already had a KAF3200 camera I would keep it but if I was buying a new camera I think I would chose the ATIK460 with the Sony CCD
The final performance is similar for the two cameras (The ATIK460 has a limiting magnitude 0.5 fainter for the same SNR) but the big difference is the price (~2000 euros for the ATIK460EX compared with ~6000 for the QSI 532).
The KAF 3200 CCD also has the residual image problem (Buil calls it lag) Do you remember it on the camera used for the MONS campaign ? The first image after the bright calibration image had a ghost image.
Here is another camera comparison by Buil which shows the residual image effect for the KAF 3200 CCD but not for the KAF 8300 CCD
http://www.astrosurf.com/buil/qsi/comparison.htm

Cheers
Robin

Hi Robin,

thank you for the clear answer!

I was not sure to understand all completely correct, but now I am sure.

I never realized those " lags" on my KAF 3200. Even if some lines are saturated at all my ThAr spectra. But I'll test it once more in the next time. My camera is not a QSI or MORAVIAN. I have one from Fischer. Not more in production!

Another question:
Exits any possibility to find out a KAF 1603 is with microlensing or without?

cheers
Berthold

Hi Robin! That's correct. But from my experience and according to our comparison of a Sigma/KAF and Megatek/Tektronix camera, the QE is by far not the dominant parameter. Imagine, the Tektronix was a 20.000 $US chip (only the chip!) with a QE of up to 90%. But the amplifier killed the whole performance. The Sigma KAF 1602, however, was much cheaper with inferior QE but an excellent bias. In any case, the bias delivers the ultimate answer about the quality of the whole system.

Cheers, Thomas

Hi Thomas,

Yes but these are old cameras with high noise values. Cameras are now available at low cost which have noise levels so low that the camera noise does not contribute significantly to the SNR and the most efficient way to get further improvement is to increase the signal by increasing QE.

As an example my current camera is an ATK314L+ with a Sony ICX285AL CCD. This has a QE of 53% at H alpha, bias noise of 5e- and a thermal signal of 1e-/hour
With this camera a signal of 900 e- in 2 hours will give a SNR of 29.5. (all values per pixel) Even if the camera noise could be reduced to 0, the SNR would only improve to 30. The only way to improve the SNR significantly in a 2 hr exposure is to increase the signal by increasing the QE. I could do this for example by upgrading to the latest version of this camera with an ICX825AL CCD which has the same noise figures but a higher QE. I could then reach the same SNR in a shorter exposure time or measure fainter objects at the same SNR in 2hrs

Cheers
Robin

Hi Robin, if the average modern CCD camera has a negligible noise level you are right, of course (I should check it out in more detail). Then a QE difference of some ten percent is indeed important, especially because the S/N goes with the telescope aperture.

Cheers, Thomas

Hi Thomas,

Thinking more about this I see something I had neglected. In spectroscopy you always have to bin several rows of pixels so that perhaps makes the effect of read noise a bit more more important than I first thought. This could be avoided by binning vertically in camera though (effectively making long thin pixels) Does anyone do this ?

Which is most important, QE or camera noise depends very strongly on the SNR you are working at though. If you are just looking to detect something in an image at very low SNR then ultimately the camera (or sky background) noise will always limit you, but this is not usually the case with spectroscopy. The higher the SNR the more important the photon noise becomes and then QE is important.

Cheers
Robin

Hi Robin! Well, maximum binning is usually 2x2 (noise increases by ). Otherwise your spectral range might become too short. In any case, that is what I did not consider as important in my argumentation. Not as far as I know. I even wonder which software can do that. On the other hand, old Reticons had been designed like this. I once worked with such detector on Hawaii having a tremendous sensitivity range. But they do not exist anymore because of the very good professional and cheaper CCD. Watch out, amateurs might well work at the detection limit. Not everybody works on bright stars.

Cheers, Thomas

Hi Robin, Thomas,
While virtually all CCDs have various square array on-chip binning modes I'm
sure I've seen asymmetric binning options (e.g. 1x2 -> 1x4) available on
some chips, such as EEV, but I've not been able to find any info on this.

Cheers,
Bernard




---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_________________
Quicquid Nitet Notandum

Hi Berrnard! Maybe you have seen it at the E2V CMOS detectors where such binning is possible. They are a bit expensive, though.
Cheers, Thomas

With my software asymmetric binning is possible using KAF3200.

Berthold

Yes, but that asymmetric binning is not on-chip so does not have the
advantage of reduced readout noise. It appears that few modern sensors now
have on-chip binning.

Bernard

-----Original Message-----
From: Berthold Stober
Sent: Thursday, September 10, 2015 3:48 AM
To: fg-spek-admin@vdsastro.de
Subject: [fg spektroskopie] Re: New spectrograph from Starlight Xpress

Link zum neuen Beitrag:
http://spektroskopieforum.vdsastro.de/v ... 361#p27143

With my software asymmetric binning is possible using KAF3200.

Berthold


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_________________
Quicquid Nitet Notandum

Hi all, I just found two cameras with asysmmetric binning possibility:
http://www.hofoo.com.cn/uploadfiles/FD2114KNU-011.pdf
http://www.azooptics.com/optics-equipme ... quipID=704

So, it seems a more or less possible CCD technique, although not too common. Cheers, Thomas

Hi Thomas,

Good detective work, but I think the binning is 'on-camera', not 'on-chip'
so I would assume the SNR improvements would not be so great ... but still
better than would be achieved by post-download software binning.

Cheers,
Bernard


-----Original Message-----
From: Thomas Eversberg
Sent: Thursday, September 10, 2015 5:42 PM
To: fg-spek-admin@vdsastro.de
Subject: [fg spektroskopie] Re: New spectrograph from Starlight Xpress

Link zum neuen Beitrag:
http://spektroskopieforum.vdsastro.de/v ... 361#p27145

Hi all, I just found two cameras with asysmmetric binning possibility:
http://www.hofoo.com.cn/uploadfiles/FD2114KNU-011.pdf
http://www.azooptics.com/optics-equipme ... quipID=704

So, it seems a more or less possible CCD technique, although not too
common. Cheers, Thomas


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_________________
Quicquid Nitet Notandum

That might be, Bernard. I wonder if asymmetric binning is possible at all for CCDs. I mean, readout is done line-by-line via a register and I have no simple idea how to get it from the chip. Easy for CMOS with amplifiers for all single pixel, buit for CCD...?
Thomas

Hi all,

It seems asymmetric binning on chip is possible at least for some CCD. Here is a description of the process
http://www.photometrics.com/resources/l ... inning.php
but I do not know if this can be done for any CCD

Robin

EDIT: I see it even mentions the application of asymmetric binning to spectroscopy down the page

I see though that Sony are getting out of the CCD business
http://www.imveurope.com/features/featu ... ure_id=284

Robin

Hi all,
My SBIG STF 8300 has this functionality and I tested it March this year.
Enclosed the intensity of one column in a Tungsten flatfield image (1000s) with 1x and 4x binning. The peak/background ratio is clear increased, but the standard deviation for the background too. At the end it needs a little bit phantasy to see the improvement in a final spectrum (3000s, 2. image).

Regards,

Ulrich

[img][/img]
[img][/img]

Hi Ulrich,
maybe you can test it by using the S/N feature of your reduction software.
Cheers
Christian

How wide is the slit (configurable ?) and for which F/ number is the design ?
I do not see how the star can be placed accurately on the slit. For bright stars this may be done using trial and error and if the design is rigid enough one may then mark the position of the star on the guider camera and place a faint star there. But I doubt that this will work with slit widths below 50-100 micron.
In view of the short focal length, the slit cannot be that wide in order to get R=2000. So the only way to get a faint star on the slit is to defocus it. But then a lot of light is lost.
For this resolution and a C8 you need pretty bright stars for the trial and error method, otherwise you'll need ages to get the star accurately on the slit.

As far as I see it now, this spectrograph could only be a competition to Dados (with 900 l/mm grating) if the price is substantially less. Unless perhaps one needs the UV, but consumer cameras don't have any QE left in that region anyway (the Dados does need a flip-mirror which may not be necessary here).
I personally would only consider it
- for educational purposes
- if the price is right
- to form character (meaning that I expect a lot of frustrations: finding the slit, difficult focussing, low efficiency, spectral smile - but after that you do know what to look for in your next spectrograph)
But perhaps I'm missing something.

Cheers, Sander

PS if the intention of this post is to give some constructive feedback to SX: I think some sort of slit viewing is mandatory. Even if it were just an eyepiece port with restricted field of view, which might be made fairly simple by using a reflection from the slit back to the beamsplitter, with a small flip mirror to switch between eyepiece and lamp - or something like that.
Of course a true reflective slit towards the guider would be better, but this would need an additional full-field flip mirror in front of the spectrograph [or an accurate electonic finder a the french use].

Hello Sander,

I have no connection with SX so cannot really offer any feedback to them. I was just asking for opinions as I often get asked what spectrograph people should buy and I only have direct experience of Shelyak instruments (and the Star Analyser of course).

I expect there will be more information soon when it is formally launched but the design shown has a beam splitter plate which diverts 10% of the light to a guide camera to acquire the target, place it on the slit and focus it. This has been used before, with the L200 for example but it was abandoned in this case in favour of the reflective slit which all other amateur commercial spectrogaphs use (eg Shelyak, Baader, SBig, CCDspec, minispec etc) I agree with you that a big potential problem with the beam splitter design is you have to keep it parfocal with the slit and also in exact register. If there is any relative movement, the star misses the slit or is out of focus and it is difficult to realign it. I personally prefer the reflective slit because you always see exactly what is happening at the slit

Cheers
Robin

From my experience with the LHIRES, I also worry about the stiffness of the sliding plate that the camera is mounted on and any movement in the camera focusing mechanism. This is a critical area and does it not look as rigid as the rest of the machined spectrograph case. It could be a weak point in the design but we would need to see some stability measurements to see if this is a problem area (unfortunately manufacturers never publish this sort of data)

Robin

Well, Robin, from my point of view the lack of experience with different spectrographs is a lasting issue in all instrumental discussions. There is no existing comparison of all or at least some instruments. Only single considerations are possible so far. And I believe, every different instrument has its deficits. Eshel has problems with its fibers, LHIRES leaks light and the mechanical design is somewhat problematic, the DADOS anamorphic magnification (grating tilt) is very high, BACHES has a stability problem and its interior is not accessible, and, and, and...

Single tests appear as if the owners only want to confirm the very expensive acquisition. The only way to circumnavigate this issue is a self design. But that requires some additional work.

Cheers, Thomas

Thomas,
The Spectra-L200 from JTW Astronomy, a 200mm Littrow, can be fitted with 30mm x 30mm gratings from 150 to 1800 l/mm. It has complete pressure sealing on all the CNC/ laser cut component joints and the interior is fully fitted with non- reflective black velour. It has as standard, a 12 position rotary index reflective multi slit/ pinholes (20 to 100 micron) entrance slit plate with reflective guiding optics (the latest slit plate versions are AR coated to reduce ghosting and improve throughput). Also fitted with a Neon reference lamp.
http://www.jtwastronomy.com/products/sp ... ymain.html

_________________
" Astronomical Spectroscopy for Amateurs" - Springer

Sander,
If the slit assembly is rigid then a beamsplitter acquisition/ guider can be made to work very well.
Over the years I used various beamsplitters on the original Spectra-L200 with slit gaps down to 20 micron.
The "trick" was to precalibrate Al's Reticule to provide a virtual slit in the guide camera. The latest version V3 worked 100%.
Al's file is available in the files area of the astronomical spectroscopy group.
https://groups.yahoo.com/neo/groups/ast ... copy/files
But, yes, in the end I did convert the Spectra-L200 over to the "traditional" reflective slit guiding (using my proprietary multi-slit gap design, custom manufactured by OVIO in France)

_________________
" Astronomical Spectroscopy for Amateurs" - Springer

Hi Thomas,
Are you saying there are fibre cable problems specific to the eShel ... if
so, which ... or just that is suffers from the usual limitations of fibre
fed systems? If the latter then I don't think that is a very fair criticism
of the eShel.

Cheers,
Bernard


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

_________________
Quicquid Nitet Notandum

Hi Thomas,
yes, the Lhires leaks some light but it is negligible in a dark environment and I could not find any mechanical problems by now. I would appreciate it when you specify the problems.
Cheers, Christian

Hi Bernard, I can not judge in necessary detail because I never performed such extensive tests. I only realized some single problems for different instruments. For the Eshel I know that there are some discrepancies in the fiber efficience. Shelyak claims very high throughput and some users estimate only about 50%. And I presume that the off-the-shelf camera optics is not perfect for the instrument. So, you can take my general input as a matter of concern considering the instrument prices and company PR. In general, do not believe in perfect instruments and be skeptic. And again, a self-design or only self-construction (Dong Li just used the puplic-domain draft of the LHIRES) might be an interesting and money saving option.
Cheers, Thomas

Christian, when working with the LHIRES at Teide we discovered a flip-mirror spring which was bend over an axis without any guidance. And instrumental torsion might become a problem for high-accuracy velocity measurements. Not to speak about leaking light during flat fielding at an instrument of 3500 Euro.
Cheers, Thomas

Hi Thomas,
I don't know what a flip mirror spring is. I assume you mean the build-in light source for calibration in the old version. Shelyak offers now an upgrade kit which means a substantial improvement. The light source is now moved by an electronically controlled stepper. Included is also a tungsten lamp for flat fields. Both works very well. You can also make darks.
Cheers, Christian

P.S.
The upgrade kit involves a new guiding unit.With the old version the guiding camera could not be focused exactly which is now possible. This results in a much better guiding quality. I can now work with 1x3 binning instead of 2x2 which means in combination with a slit width of 23 my and a pixel size of 5.4 my a substantially improved resolving power.
The new calibration unit gives you the choice between a Ne lamp or a NeAr lamp. The last one covers the nearly the whole visible spectrum. However Shelyak does not provide a suitable line table. The NeAr tables which came with IRAF have not enough lines and a table constructed with the NIST tables has too many lines. So it takes some work to get a suitable line table.
Cheers, Christian

Hi Christian,

 

The NeAr lamp used in the new Lhires kit is the RELCO, same as that in the
ALPY, and Richard Walker has made an excellent table/chart of the RELCO's
spectrum at
http://www.ursusmajor.ch/astrospektrosk ... index.html
(SQUES RELCO SC480 Calibration Lines/Eichlinien 3.0) and also included as
Appendix E.2 in the Eversberg & Vollmann book.

 

Cheers,

Bernard

 

 

-----Original Message-----

From: Christian Netzel

Sent: Tuesday, September 22, 2015 4:22 AM

To: fg-spek-admin@vdsastro.de

Subject: [fg spektroskopie] Re: New spectrograph from Starlight Xpress

 

Link zum neuen Beitrag:
http://spektroskopieforum.vdsastro.de/v ... 361#p27178

 

P.S.

The upgrade kit involves a new guiding unit.With the old version the

guiding camera could not be focused exactly which is now possible. This

results in a much better guiding quality. I can now work with 1x3

binning instead of 2x2 which means in combination with a slit width of

23 my and a pixel size of 5.4 my  a substantially improved resolving

power.

The new calibration unit gives you the choice between a Ne lamp or a

NeAr lamp. The last one covers the nearly the whole visible spectrum.

However Shelyak does not provide a suitable line table. The NeAr tables

which came with IRAF have not enough lines and a table constructed with

the NIST tables has too many lines. So it takes some work to get a

suitable line table.

Cheers, Christian




https://www.avast.com/antivirus






This email has been checked for viruses by Avast antivirus software.

www.avast.com

_________________
Quicquid Nitet Notandum