LISA vs Alpy600

[James Foster]

I'm trying to decide what low-resolution spectroscope might be better to acquire,

1.) LISA with calibration module (and maybe IR kit) R=1000
2.) Alpy 600 with guider & calibration module (Cheaper option) R=600

I want to expand into full visual and/or IR spectroscopy because I'm interested in variable stars and the the brighter SN.

I'm mostly using my present L-200 spectroscope for medium resolution (R=8000Ha to 3500CaK) projects like Gam Cas, VV Cep, Solar Analogs, etc, but want to
get full spectrum images with high fidelity; my particular spectroscope has severe chromatic aberration at the far blue and red ends when using a low resolution
(150 l/mm) grating.

I'm going to be using this mostly with a CDK17 @ F/6.8 (430mm aperture) or (when in the mountains at 2500 meters) a 33cm aperture classical cassegrain @ F/7.5.
I also have a C-11 with a F/6.3 reducer, but use this mostly for photometry. I understand that the LISA is much more massive than the Alpy 600, but with my Hendricks
focuser, see: http://planewave.com/products-page/gene ... I27d_Kb4Uo, I don't think this will be a problem for my system
to handle.

I'm just looking to acquire the "best" performance low-medium resolution spectroscope to give me high fidelity spectra in the 3800-7500 A region and ability to
get at least as faint as 16th magnitude with a 1 hour exposure with SNR of 10; before suggesting, I have a SA200 grating, but that resolution is too low for my needs.

If I have to sacrifice the higher resolution LISA to get fainter objects with the ALPY 600 so be it! I've read a lot about both systems, but the number of LISA users and their published data seems to be declining relative to ALPY users; I know this can be because of the of cost between both systems.

I want to purchase either of these very soon, before the political situations in Europe/US/Russia drive up the value of the Euro. Thanks for any input!

Sincerely Yours,

James

[Robin Leadbeater]

Hi James,

LISA has a clearly higher resolution but in any case your star image size might be the deciding factor as the ALPY has a fixed slit width of 23um which might be a bit narrow for the big scope depending on your seeing. The ALPY focus is reported better than the LISA at the UV end but drifts off at the IR end. LISA has a separate kit of components specially for the IR.
An efficiency comparison between the two would be interesting but I have not seen a head to head (On the face of it the reflection grating in the LISA could potentially be more efficient but there might be more losses in the multi-element lenses)

Robin

[James Foster]

Thanks for the reply Robin!
I read Christian Buil's review on the Alpy600 and how he tried to differentiate the
two spectroscopes. Clearly the LISA has better resolution on bright targets, seen at
spitting the Na lines clearly while the Alpy600 is barely at the task (R1000 vs R600).

As you suggested, no tests have been made at the "efficiency" between the two to make
useful spectra of dim targets. This is probably easier with LISA and it large slit options,
as C. Buil points out, on scope whose aperture is larger than 300mm. Just so happens
the two system I plan to use it on are 330 and 430mm aperture; just barely over.

On the other hand, Alpy600 has superior (non-distorted) performance shortward of
410nm, where LISA's inherent F/6 reducer compromises performance in the blue-UV end.

James

[Robin Leadbeater]

Hi James,

I run my ALPY with a C11 at about f6 (280mm aperture 1680mm FL). That means the slit is 2.8 arcscec on the sky which is a reasonable match to my typical 3 arcsec seeing. With your 430mm f6.8, the 23um slit would be 1.6 arcsec so I would definitely lose efficiency using the ALPY with my seeing and your scope.

Cheers
Robin

[James Foster]

To: Robin,

RE:" your 430mm f6.8, the 23um slit would be 1.6 arcsec so I would definitely lose efficiency using the ALPY with my seeing and your scope"
I totally agree! My seeing varies btw 3.8"-2.1" FWHM at home. Of course I also have another set-up exactly like yours, C-11 with F/6.3
reducer so the Alpy600 would have a good place there. At Mt. Pinos the seeing is usually better at 2.5"-1.6" and sometimes at little at 1.1"
(the advantage from shooting at a high 2500 meter mountain top!)
I want to make a purchase decision before I go to class next week in Texas, so I have a few more days pouring over C. Buil and others reviews
on the two systems.

James

[Ken Harrison]

James,
My 2c....
I think the LISA is a more capable long term solution.
Terry B out here in Australia uses his LISA to great effect.

[Francois Teyssier]

Hello James,

This is an interestion question

Here's a comparison of [OIII] 5007 range for symbiotic CI Cygni at R = 600 (Alpy) and R = 1000 (Lisa)
The grey spectrum obtained at R = 11000 gives the "real" profiles

This region is interesting because of three main lines [OIII] 5007, He I 5016 and Fe II 5018 (He I and Fe II according to the orbital phase)

CICyg_Comp.png (14.49 KiB) Viewed 8166 times

The two lines OIII and Fe II are obvious and well separated with Lisa, not with Alpy.
Even when the lines are stronger, the intensity of the two lines can be measured for Lisa with a gaussian adjustment. This is not possible with Alpy.
This point is important because it allows the measure of electronic temperature with the spectrum obtained by Lisa

Other lines for a diagnostic :
H gamma and [OIII] 4363,
or in NP : [SII] 6716 6731 (electronic density), well resolved with Lisa

I recommend Lisa

Best regards,

François

[Christian Buil]

I agree with François comment's. The LISA is also potentialy more adapted to your relatively large telescopes (slit wide vs seeing).
But it is exact, the chromatic aberration of LISA is less corrected down to 4000 A. A compromise question... !

Christian

[James Foster]

Thanks Francois & Christian!

I'll probably follow your kind advice and pursue the LISA option.
One more question. Is it time consuming to switch from Visual to IR mode?

(i.e. Can you switch from Vis-IR quick enough to catch your target on the same night?)

I'm intrigued by C. Buil's wide Vis-IR spectrum with the LISA, but it looks like 2 LISA units
(1 Vis, 1 IR) were used to produce these results; see: http://www.astrosurf.com/buil/lisa6/obs.htm

James Foster
Los Angeles, CA

[Olivier GARDE]

One more question. Is it time consuming to switch from Visual to IR mode?

(i.e. Can you switch from Vis-IR quick enough to catch your target on the same night?)

I'm intrigued by C. Buil's wide Vis-IR spectrum with the LISA, but it looks like 2 LISA units
(1 Vis, 1 IR) were used to produce these results; see: http://www.astrosurf.com/buil/lisa6/obs.htm

James Foster
Los Angeles, CA

Hi james,

It's very difficult to add or remove the IR kit in a LISA during a night, so that why is better to have 2 LISA (but for a double price !!!!)