New Optical configuration...It will work?

Ask your questions, show your results

New Optical configuration...It will work?

Postby Nacho Novalbos » Mon Mar 15, 2021 1:03 pm

Good Morning.

Finally, after a few weeks, I have the equipment ready to start taking spectra of bright stars. :D

As I have disassembled the LX200 10 "until I finish with the construction of the observatory, I equipped an EQ6 with a 152/760 refractor adapting a Barlow Siebert Optics x3 ... and a Calibrex V2.
ImageImage

I would greatly appreciate your opinion about the suitability of this optical configuration for spectrography.

Kind regards
Nacho Novalbos
O.A.N.L. Barcelona
https://oanlbcn.blogspot.com/
Nacho Novalbos
 
Posts: 5
Joined: Mon Mar 08, 2021 8:57 pm

Re: New Optical configuration...It will work?

Postby Joan Guarro Flo » Mon Mar 15, 2021 9:26 pm

Bona nit Nacho,

I think first you could show some results..

Cordialment, Joan.
Joan Guarro Flo
 
Posts: 443
Joined: Thu Nov 03, 2011 8:50 pm

Re: New Optical configuration...It will work?

Postby Robin Leadbeater » Tue Mar 16, 2021 2:46 pm

It should work ok. f15 is slower than the focal ratio of the spectrograph optics so you will not lose any light there. The focal length will be similar to your 10 inch LX200 so the slit width you will need to match the star image size will be similar (Check this using your typical seeing). The biggest issue could be chromatic aberrations with all that glass in the telescope optics which could be worse compared with using the LX200 at f10 if it is not well corrected. This can give problems in low resolution spectra
http://www.astrosurf.com/buil/dispersion/atmo.htm

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
Posts: 1702
Joined: Mon Sep 26, 2011 4:41 pm

Re: New Optical configuration...It will work?

Postby Nacho Novalbos » Sat Mar 20, 2021 10:10 pm

Good evening!!

You're right Joan...
In order to verify its validity, it will be better to test the equipment and see the results.
I hope to have good weather to observe some nights and to be able to show you some spectra taken with this configuration.

Robin...
Thank you very much for your comments as well as for the link to Christian's article.
The refractor I use is a "neoachromatic" (Petzval Type), with a second group of lenses that reduce the focal length to f/5, flattens the field and minimizes chromatic aberration ... so I hope I don't have many problems with chromatic aberrations. :D

Best regards.
Nacho Novalbos
O.A.N.L. Barcelona
https://oanlbcn.blogspot.com/
Nacho Novalbos
 
Posts: 5
Joined: Mon Mar 08, 2021 8:57 pm

Re: New Optical configuration...It will work?

Postby Robin Leadbeater » Sun Mar 21, 2021 12:19 pm

Nacho Novalbos wrote:
I hope I don't have many problems with chromatic aberrations. :D

Best regards.


Hi Nacho

That is a nice instrument. Spectroscopy can be a severe test though. The correction is usually optimised for the visible range and the correction outside this range is not always good, particularly at the blue end. See the comparison of the Takahashi FSQ85 and FSQ106 by Christian Buil for example
http://www.astrosurf.com/buil/refractor/test.htm

"The spectrum delivered by the FSQ-85ED is extremely fine from the ultraviolet (3650 A) to at least 7300 A in the near infrared. The spectral resolution is almost constant in this interval. The chromatic correction in such a wide spectral range of this small bezel is simply breathtaking! I would qualify this instrument as an optical masterpiece. "

"The level of secondary chromatism of the first version FSQ-106 could in its time satisfy the astrophotographer, but poses a problem for broadband spectrography (note the impossibility of finding a correct focal point for the entire visible spectrum, even excluding the untraviolet part)"



Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
Posts: 1702
Joined: Mon Sep 26, 2011 4:41 pm

Re: New Optical configuration...It will work?

Postby Nacho Novalbos » Fri May 07, 2021 4:57 pm

Hello!!

Last night I was testing the DADOS and I took some spectra of HD96325, a G0 star with a 8.97 V magnitude.
They are 300s integration shots with the atik 16HR at the primary focus of an 152mm f/6 achromatic refractor.
My objective was to evaluate the performance of this optical configuration, which in principle is the more comfortable to work but not the most suitable for this spectrograph... :mrgreen:
Reviewing the images, it can be seen that a fairly pronounced chromatic coma appears at both ends of the spectrum. :cry:

Image

I imagine that it is the logical consequence of using an achromatic telescope with a low focal ratio...and that it will possibly improve and even disappear if a focal extender, that narrows the cone of light, is inserted between the telescope and the spectrograph.

I would appreciate any comments and/or suggestions about this topic.

Greetings.
Nacho Novalbos
O.A.N.L. Barcelona
https://oanlbcn.blogspot.com/
Nacho Novalbos
 
Posts: 5
Joined: Mon Mar 08, 2021 8:57 pm

Re: New Optical configuration...It will work?

Postby Robin Leadbeater » Fri May 07, 2021 11:55 pm

Nacho Novalbos wrote:Hello!!

I imagine that it is the logical consequence of using an achromatic telescope with a low focal ratio...and that it will possibly improve and even disappear if a focal extender, that narrows the cone of light, is inserted between the telescope and the spectrograph.


It is as I expected. Achromatic refractors do not work well for spectroscopy. the chromatism might be less at the longer focal length but it will not disappear. (f6 is too fast for the DADOS in any case. The beam will not fit in the spectrograph so you are losing light)

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
Posts: 1702
Joined: Mon Sep 26, 2011 4:41 pm


Return to Beginners corner

Who is online

Users browsing this forum: No registered users and 2 guests

cron

x