How to get star on slit in spectposcope in phd

[p1taylor]

Hi All, Hope sum one can help, I have seen a plug in for PHD that puts a set of parallel of lines in a cross to help setting star on slit you can adjust with of space between lines.

peter

[Terry B]

When I use phd for guiding on the slit I use the bulls eye overlay. Aim the scope at something bright like an illuminated wall so that you can easily see where the slit is. Then take note of where it is in relation to the overlay. I tried the grid overlay but there were too many lines and it is easy to get them mixed up. Using my L200 the slit is just beside one of the bullseye circles.
When you know where the slit is you can aim at your target star. I take quick exposures and move the target star towards the slit. When it mostly disappears it is on the slit. You then have to decide whether to guide on the slit or a field star. I find for a bright star that I guide on the secondary reflection that is just near the slit. If the star is dimmer then the secondary reflection isn't bright enough so I will use a field star.

Good luck.

[Merlin66]

Peter,
When I used non reflective slits I had Al's Reticule great freeware to produce a "virtual slit" gap and then just dropped the target star onto the double cross wire.
I assume you have a reflective slit? Use the reference lamp to illuminate the slit ( same as you would do to focus the guide camera on the slit) and note the X/Y of the slit centre and the Y value to the slit length.
You can then use these coordinates with the "lock-on" function of PHD (or with the spectro guide function of Astroart) to accurately position the star image on the slit gap.
Once the star is on or very close to the slit the slight change in the star shape guides you to the slit centreline - a nudge of +/- one pixel usually does the job.
As terry says just check the max ADU of the spectrum to confirm you're getting best signal.
Hope this helps.
(Over on the Astronomical spectroscopy forum, there's a write up in the files area detailing the "Al's reticule" method - Setting up Al's.pdf)
https://groups.yahoo.com/neo/groups/astronomical_spectroscopy/files

[p1taylor]

Thanks Terry and Ken, Al's reticule is exactly what I was after.

peter

[Merlin66]

Peter,
Like many things, it gets easier with practise.

[robin_astro]

With PHD 2 you can store the coordinates of the guiding position (found with the slit illuminated) and it will pull the star to that location automatically.
With objects that are too faint to see in a 1-2 sec guider image (I am currently down at mag 17.5 with a modified ALPY) you can work out the offset of the target from a field star from a longer exposure image, dial in the needed guide position and land the target on the slit without even seeing it - brilliant!

Robin