ALPY/Lisa: 460Ex+414ex?

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Rainer Ehlert
Posts: 135
Joined: Thu Sep 29, 2011 9:36 pm

Re: ALPY/Lisa: 460Ex+414ex?

Post by Rainer Ehlert »

Hi Simon,

I just made a series of 120 seconds exposures using my ASI 174MM (No cooling) @ an ambient temperature of 23.5°C.

The star in the center is 37 Tau

Here the wetransfer link for download

https://wetransfer.com/downloads/cbbfd5 ... 400/6772c7

regards Rainer
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
Simon de Visscher
Posts: 48
Joined: Sun Dec 29, 2019 5:48 pm

Re: ALPY/Lisa: 460Ex+414ex?

Post by Simon de Visscher »

Hi Rainer,

Thanks a lot for sharing this, And sorry for my late reply, it’s a very busy week :)
I’ll have a look at your data asap!

Thanks again and clear skies,

Simon
--
Simon
LISA/Alpy600/LHIRES N400f5, AP130EDT
Robin Leadbeater
Posts: 1926
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: ALPY/Lisa: 460Ex+414ex?

Post by Robin Leadbeater »

Simon de Visscher wrote: The thing is: for extra-faint targets (Mv=17 or even 18+), their positioning on the slit requires to see them with the guiding cam, which means exposures of 1 or 2 min maybe. On short exposures the 178mm that I use has roughly the same SNR as the 174mm (smaller pixels but smaller RON as well) but clearly the dark current becomes problematic if the exposure gets longer than a couple of tens of seconds. Hence my move to a cooled camera.
Yes this exactly what I am doing using my old cooled ATIK16IC-S (similar to the Titan) and the ALPY. For the faintest I stack perhaps 20x20sec guide camera exposures then measure the position of the target, a brighter guide star and the slit so I can offset the guide position by the right amount. (The target is invisible during guiding) This is my faintest spectrum using the ALPY200 (a quasar at z=4.5 and g mag 20)
https://britastro.org/observations/obse ... ebf4faaefe

I agree you have to use a low noise cooled camera. I bought what everyone at the time said was the best uncooled guide camera (A Lodestar II I think) but it was nowhere near as good as the old ATIK16IC-S so I sent it back. It will fail eventually and then I will have the same problem as you :( It is a shame they discontinued the Titan.

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Simon de Visscher
Posts: 48
Joined: Sun Dec 29, 2019 5:48 pm

Re: ALPY/Lisa: 460Ex+414ex?

Post by Simon de Visscher »

Hello Robin,

Thanks for sharing your thoughts.
Robin Leadbeater wrote:Yes this exactly what I am doing using my old cooled ATIK16IC-S (similar to the Titan) and the ALPY. For the faintest I stack perhaps 20x20sec guide camera exposures then measure the position of the target, a brighter guide star and the slit so I can offset the guide position by the right amount. (The target is invisible during guiding) This is my faintest spectrum using the ALPY200 (a quasar at z=4.5 and g mag 20)
https://britastro.org/observations/obse ... ebf4faaefe
Truly amazing measurement! BTW I read some slides concerning your "Alpy200", that's also a very interesting achievement, which - to some extent - is a good alternative to the LISA for ALPY owners interested in recording very faint targets. I might try that at one point :D One question, did you think trying the ALPY200 with the ALPY/Sol'Ex/Uvex 35um slit? That would mean going down to R~100 but on the other hand would improve the slit transfer efficiency for instruments with a long FL.
Robin Leadbeater wrote: I agree you have to use a low noise cooled camera. I bought what everyone at the time said was the best uncooled guide camera (A Lodestar II I think) but it was nowhere near as good as the old ATIK16IC-S so I sent it back. It will fail eventually and then I will have the same problem as you It is a shame they discontinued the Titan.
Yes indeed, it is a pity. But on the other hand it is kind of expected: spectroscopists are a small fraction of observers and nowadays with the advent of super low-noise-and-small-pixels CMOS, the Titan is basically only useful in that case. So from the point of view of Atik it somehow makes sense to have stopped producing them (benefit/cost ratio way too low).

Best,

Simon
--
Simon
LISA/Alpy600/LHIRES N400f5, AP130EDT
Robin Leadbeater
Posts: 1926
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Re: ALPY/Lisa: 460Ex+414ex?

Post by Robin Leadbeater »

Hello Simon,
Simon de Visscher wrote: One question, did you think trying the ALPY200 with the ALPY/Sol'Ex/Uvex 35um slit? That would mean going down to R~100 but on the other hand would improve the slit transfer efficiency for instruments with a long FL.
Yes I have wondered if a wider slit might be better but have not tried it. A wider slit also lets more sky in so it is a balance. (With the faintest objects the sky is brighter than the target, even in my reasonably dark rural skies). With my setup (CII with focal reducer at f5.5) a 23um slit is 3 arcsec which is my typical seeing FWHM. If the seeing is poor the faintest targets would be more difficult in any case even with a wider slit. For a longer focal lengths a wider slit (perhaps with a 300l/mm grating) could definitely be a better solution. The lowest possible focal ratio should be used, especially for extended objects. ALPY allows focal ratios down to f4 without vignetting I think. There are some tests and ray diagrams by Christian Buil on here somewhere

My ALPY200 grism was specially made for me by Paton Hawksley but if you are interested in an ALPY200 setup, let Shelyak know. It has been on their list to develop it as an option for a long time but more interest might raise the priority.

I only based my setup on the ALPY because I had one and it was easy to do. Lower dispersion versions of other spectrographs might also be possible and might work even better. (reflective gratings tend to be more efficient than transmission gratings, even at low line densities)

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Simon de Visscher
Posts: 48
Joined: Sun Dec 29, 2019 5:48 pm

Re: ALPY/Lisa: 460Ex+414ex?

Post by Simon de Visscher »

Robin Leadbeater wrote:Yes I have wondered if a wider slit might be better but have not tried it. A wider slit also lets more sky in so it is a balance. (With the faintest objects the sky is brighter than the target, even in my reasonably dark rural skies). With my setup (CII with focal reducer at f5.5) a 23um slit is 3 arcsec which is my typical seeing FWHM. If the seeing is poor the faintest targets would be more difficult in any case even with a wider slit. For a longer focal lengths a wider slit (perhaps with a 300l/mm grating) could definitely be a better solution. The lowest possible focal ratio should be used, especially for extended objects. ALPY allows focal ratios down to f4 without vignetting I think. There are some tests and ray diagrams by Christian Buil on here somewhere
Right I was especially thinking to targets with a linear size at focus larger than the slit, i.e. for which the sky SNR is not affected by the slit width. But yes for small m~20 galaxies, the problem is more subtle. In my case this could be quite appropriate because my newton (f5) has a FL of 2m, and my seeing is usually between 2 and 3 arcsec. I was considering the LISA, but given the price and the fact I have the ALPY already, an ALPY*00 could be an cheaper and yet excellent alternative. I'll get in touch with Shelyak to know a bit more on this.

Thanks for sharing on this!

Simon
--
Simon
LISA/Alpy600/LHIRES N400f5, AP130EDT
Simon de Visscher
Posts: 48
Joined: Sun Dec 29, 2019 5:48 pm

Re: ALPY/Lisa: 460Ex+414ex?

Post by Simon de Visscher »

Robin Leadbeater wrote:but if you are interested in an ALPY200 setup, let Shelyak know. It has been on their list to develop it as an option for a long time but more interest might raise the priority.
Got the answer from Shelyak, indeed there is apparently no plan to produce such an ALPY200 any time soon, but they take note of interest.
So I'll continue with my current setup for now, and if one day I want to go deeper in mag, the easiest (yet more expensive) solution will be the LISA, with its 35um slit.

Cheers,

Simon
--
Simon
LISA/Alpy600/LHIRES N400f5, AP130EDT
Rainer Ehlert
Posts: 135
Joined: Thu Sep 29, 2011 9:36 pm

Re: ALPY/Lisa: 460Ex+414ex?

Post by Rainer Ehlert »

Simon de Visscher wrote:Hi Rainer,

Thanks a lot for sharing this, And sorry for my late reply, it’s a very busy week :)
I’ll have a look at your data asap!

Thanks again and clear skies,

Simon
Hi Simon,

What do you think about the capabilities of the uncooled ASI 174MM ? I think it is quite a noiseless camera.

As I wrote somewhere my skies are not that clear in order to get lower them maybe mag ~15.
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
Simon de Visscher
Posts: 48
Joined: Sun Dec 29, 2019 5:48 pm

Re: ALPY/Lisa: 460Ex+414ex?

Post by Simon de Visscher »

Hello Rainer,

I will have some time this w-e to do some tests, and in particular I'll compare to an Atik Titan I just bought to someone who had no use of it anymore. I'll let you know!

Cheers,

Simon
--
Simon
LISA/Alpy600/LHIRES N400f5, AP130EDT
Robin Leadbeater
Posts: 1926
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: ALPY/Lisa: 460Ex+414ex?

Post by Robin Leadbeater »

Simon de Visscher wrote:Hello Rainer,

I will have some time this w-e to do some tests, and in particular I'll compare to an Atik Titan I just bought to someone who had no use of it anymore. I'll let you know!

Cheers,

Simon
That will be interesting. The old Sony CCDs like the ICX424 used in the Titan (and in Steve Chambers' original SC3 modified webcam design which was my first astro camera) gives a pretty clean image even when not cooled and excellent when cooled so it will be interesting to see where it stands compared with modern CMOS. I once considered buying a Titan to replace my old USB1 16IC-S but thought it was too expensive new. I think I will keep a look out for a second hand one

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
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