Valerio

I had this new attempt with planet Uranus

Image taken with Celestron C6 with Lowspec v.3 at 600 l/mm, 40 minutes total (5min x 8subs) with dark frames. Camera ASI 294 MC pro. I had a pretty bad noise ... but anyway I think that the spectrum is not so bad

Yes I am pretty happy with the results. Fun and science, a perfect match 🙂

I must say that sometimes the program does some strange things, above all with labels, and I have to reload everything and start again.

You are right the Telluric bands are not perfectly matched, it's strange because I had many good lines in the RELCO reference and I think I have put them correctly in the calibration

I made some more experiments with calibration and acquisition of Sun spectra and Mars spectra. I think that I am getting a pretty good calibration, which I got with a halogen lamp (Flat) and the RELCO lamp.

Valerio

Hello,

still struggling a little bit on calibration. I was trying to obtain a "final" instrumental response for my telescope+spectroscope. I have read this web page that seems to be pretty clear http://spectro-uvex.tech/?p=1585&lang=en, and also something similar here https://www.horiba.com/fileadmin/uploads/Scientific/Documents/OSD/203_Instrument_Response_Corrections.pdf

So I have created with an halogen tungsten lamp (2950K) this spectrum

that gives me this 1D profile

that I compared with a planck curve at 2950K (green). Dividing one by the other I should obtain the Instrument_response = lamp_signal / black body profile - blue line

that "should" be pretty universal for my setup (telescope C6 f/10+spectroscope). Of course this is not valid for the atmospheric corrections, I know, I should follow the second "long" part of the process to add that calibration, too.

What I am not yet sure is the curve of the halogen lamp. In the examples in those websites they show a "mountain-like" curve, that goes almost to zero on the right part of the spectrum, but with my setup all the spectra I get are getting more and more bright toward the red part of the spectrum, even if they should go to black I think. Is this due to the IR part of the spectrum that my camera (ASI 294MC PRO) is too sensible to? Should I use an IR-Cut filter to obtain the right spectra (in general)?

Also, not still sure which slit to use... it depends on the brightness of the source? Less bright... thicker slit?

thanks!

Valerio

Very bad weather these past days so I couldn't get more spectra. I hope soon... and I hed no time to look deeply into your great explanation. Next week end I think I will try something

Thanks!!!

Hi

I tried to get the spectrum of 2 bright stars and analyze them with BASS project. Still learning but improving
First one Capella: I was able to calibrate it and try a response correction. Not sure if I went through the best steps for the response correction. After the calibration with the RELCO lampI used a G5III ref spectrum and divided my spectrum bt this one, then I used that curve as the correction response curve.

This seems pretty similar to the spectra I found online. I couldn't find a way to add elements lines with the Element name as Ken did in a previous post... just the lines

I then tried with Aldebaran. I thought that I could use the same response file, but it doesn't seem to work, it transforms my spectrum too much I think...

This is the original spectrum, only with calibration

the purple one is with Capella response curve

So I tried with a reference spectrum K5III (the same as aldebaran) and I got this curve, that seem more similar to the reference K5 spectrum but it seems it has less "resolution"

A lot to learn but something nice is happening 🙂

Valerio

Ken,

First of all thank you for your great help. I know, now I have to study BASS project and replicate your graphs. If I understood well you just imported a Sun (G2V) spectrum as a reference to see the absorpion lines in my spectra, correct? Are these spectra available in BASS project?

I will improve the calibration with RELCO lamp using 4/5 lamps and install them in fromt of my scope.

I see now that the spectrum #1 is not overexposed, but is there some kind of rule of thumb to determine the best exposure of the spectrum to avoid overexposing? I think that it must be more some kind of "visual" rule, but (considering my 4 spectra) lighter spectra in general are better ones?

To ceate the Instrument response curve I can use a known star spectrum and divide my spectrum of that star by that one, to obtain the Instrument response ... but once I get it is it always valid with any other object  and in every weather condition?

thanks

Valerio

I finally had an almost clear sky and i tried to get my first "real" spectrum. I used my Celestron Nexstar evolution C6 f/10 with Lowspec version 3.

The only visible bright body tonight was Mars (with clouds everywhere) and after a few trial and errors to focus everything I think I got a pretty good result. I'm not sure which is the best spectrum in terms of brightness (exposure time). I tried 4 versions, all with 30um slit:

Probably the first one is overexposed... which one is usually the best to use in Bass project to have the best analysis?

After that I captured the RELCO calibration lamp, with the same exact positions in the spectrograph, except I had to detach it from the telescope because the lamp was to faint to capture though the telescope lens.

Best

Valerio

9 hours ago, Merlin66 said:

Ken,

I am happy my spectrum are improving! :-)))

Now I am studying the BASS project and I hope to be able to analyse my own spectra soon.
It's possible that something moved in the assembly with these two spectra because I didn't completely close the screws of the cover. I will test with stars and close everything perfectly next time!

Camera and grating data are ok but the imaging lens is 100 mm. probably this is the error in your calculations?

When sky gets clear I will try with a star. I hope I will not have issues with focus and guiding...

Thank you again for your great help

Valerio

Ken,

thanks for your great analysis. I flipped the grating and tried again with Relco lamp and a blue day sky. The slit is 30um. I tried to keep the central part in focus. What's the better way to obtain a full spectrum in focus? Should I take more images rotating the grating with the micrometer and then compose them together?

Are the dark horizontal lines a problem?

Valerio

Hi,

this is a second test with the inverted grating and full resolution capture.  I used a RELCO SC480 lamp

What do you think about collimation and focus?

I still have to start using BASS Project and of course try to connect the telescope (Celestron C6 f/10) with some real tests

Thank you for any feedback

Valerio

5 hours ago, Merlin66 said:

Valerio,

The spectrograph is designed to use the blazed 1st order spectrum.

(The angle of rotation for the 2nd order is twice as great....just use the bright 1st order.)

If you want a higher resolution use a grating with more l/mm.

 

Thank you Ken, always very kind and precise!

Thanks Ken, very helpful. I have not yet installed BASS Project and will do soon. I must say that the image I posted was a screen grab with cel phone so probably I will have a better resolution with the camera image (ASI294MC PRO) :-))
I will also flip my grating to have the spectrum with blue on left as you say. I will check again the slit disk but since I had difficulties in assembling it in the plastic holder I don't know if I can remove it now --- hahaha --- without breaking it or bending it, but if you say that this probably is not a problem I will try this way.

I will post soon another test with full resolution after these changes

Question: is it better to use the 1st order spectrum (brighter) or a 2nd order (darker but more spread out?). It depends on the source?

Thanks

Valerio

the disk I bought is perfectly the same in both sides. Mirror on boh surfaces

Hi

I finally finished my lowspec assembly and tested it. First light seems promising. I tried with a normal lamp in front of the opening where the telescope should be.

This is the first order spectrum with a 600 lines grating.

After that I searched for the central maximum and I found it to the right (micrometer completely pushed in)

but when I try to use a longer exposure time the result is this

As you can see besides the slit I see around it a strange image, that seems the border of the hole in the plastic of the piece holding the slit disk

this is the piece photographed in normal light

this is the piece photographed with a light that reflects on the inside of the hole, that shows the orange part around the slit

Is this normal? I understand that I was using a very bright light and probably with a star I cannot see this border, but I wanted to know if this happens to you too...

Thank you!

Valerio

I have now all the printed parts, all the hardware and I just received all the optics form thor Labs... looking forward now to assemble it and fine tune everything. I hope this part is not too complex...

Best,

Valerio

Hi Paul,

thanks for your reply! And what's the use of the T2-cap_int_thread piece? I cannot see its place in the project... because it seems that both the telescope and camera holes need the T2-cap_ext_thread, correct?

thanks!

Valerio

Hi Paul,

is the thread in the upper hole of the lid (and the thread of the grating holder cap) the same as the other threads (T2 telescope and camera holes)?
If they are all T2 I could use the same metal ring also for the lid hole that contains the grating holder cap, because otherwise I have problems with printing the plastic threads with my printer.

thanks!

Valerio

Hello,

Update of my Lowspec: this is a really slow process, many hardware parts are hard to find and still waiting for them. I just ordered the THORLABS optical pieces and waiting for them (I ordered the 600 lines/mm grating).

I had some problems with the threads in some pieces, above all the two 04_T2_thread_camera and 04_T2_thread_telescope. I cannot print with enough precision to make them thread with the telescope and camera adapters. So I decided to buy a couple of threaded metal pieces, link this one
https://www.telescopi-artesky.it/it/artesky/adattatori-m48/3756-riduttore-da-m48-a-t2-artesky-8055517132036.html
and it fits perfecty into the 2 side holes of the main body (you probably need to glue it to be perfectly sure)

This way I have metal threads that can be more precise and will not degrade with time. I advice you all to do so.
I didn't print the red cap yet, I hope I will not have problems with those threads as well. Is that a M42 thread? In that case I could use another threaded metal ring as the other holes...

I have a question: I don't need the illuminator (or... is it important or can be avoided?) so what should I do with piece 16_jeulin_slit_illuminator? 
I don't print it at all (leaving the hole) or I have to print it anyway with a black material?

Thank you!

Valerio

Hi Paul. I already received the micrometer from the link you provided. Very fast and serious! ...and cheap :-)))

Thanks

Valerio

Thanks Paul,

wow it's really waaay cheaper! I will try to order it tomorrow and let you know if it works, thanks! As a meatter of fact Thorlabs is not a cheap website...
Anyway, I will work with a f/10 Celestron C6, so will this 600 l/mm grating be fine?

https://www.thorlabs.com/thorproduct.cfm?partnumber=GR25-0605

Thanks again!

Valerio
 

Hi Paul,

I almost finished to print all the smaller pieces. I see from your last post there is an upgrade for the guide lens holder: is it already on thingiverse or do you plan to update it soon?
Found almost all the hardware parts, can you tell me if this Micrometer is ok ? https://www.thorlabs.com/thorproduct.cfm?partnumber=148-801ST

I will now order the optical parts from Thorlabs. Question: for a starter, is it ok to order just the 300 l/mm grating? You list also the 1800 l/mm, but will this spec work also with 600 l/mm? Is it a good compromise between the two (in terms of low res spectra and cost/usability)? I think they all work with the lenses you list in the Optical parts, right?

Thank you!

Valerio
 

Wow it's a great project! But I think I will stick to your design and maybe one day build the calibation unit as well 🙂

Hi Paul and Ken, thanks for your kind words I hope to be able to build it! I know it's not the best material but I am using PLA on an ENDER 3 printer. Never used other materials and not sure if this printer is suitable for this kind of project but I hope so! I hear there are heat expansion possible problems and IR transparency issues: how are they bad with this material?

Yes for a start I will use the cameras I presently use for my astrophotography, later, if everything works fine I will think of a mono camera

Valerio

Trento, Italy

Hello Paul and everybody, first of all thanks for the great LOWSPEC 3 project I am starting to build. I am new to this forum but I read all the conversation and hope to be able to print everything and then add the optics (that seems pretty complex reading all the chat threads). Anyway, I just printed the lid and the main box (printer ENDER 3), and I see Paul has just updated the lid. Is it important to reprint it? If it's so I will of course print it again 🙂

Now I need to print all the other pieces... and then I will think to buy the optics
I am going to use this spectroscope with this setup:

Celestron C6 f/10 or f/6.3 (with reducer)

Main Camera ZWO ASI 294MC pro color

guide camera ZWO ASI 120 MM Mini mono

Do you think it is a good working setup ? Is it ok without changing anything in the original project (to have correct focus on both cameras?)
Thank you!

Valerio