Alp 600 flats

[Peter Somogyi]

Hello Forum,

For documentation purpose, let me share my experiments - for others not having to repeat this effort.

In the zip I attach here - all with Alpy 600 (except one) + 250/1000 newton + ATIK 414:

flats.zip

(158.25 KiB) Downloaded 295 times

Files content:
res_banknote_blb.fit: "BLB" lamp (https://en.wikipedia.org/wiki/Blacklight) from banknote checker; nontransmitting plastics (multiple layer) as a diffuser
res_lhires_gr600_35u.fit: LHires + 35 micron slit + 600/mm grating; with the "BLB" I mentioned
res_flat_int.fit: regular Alpy 600 calib.module flat lamp
res_halo_hobbyplastic.fit: halogen lamp + "hobby glass" (in fact it's a shiny fully transmitting plastic, dedicated for DIY)
res_halo_plastic.fit: halogen lamp + papre-holder semi-transmitting thin plastic, 1 layer
res_halo_tshirt.fit: regular t-shirt (avoiding any nonwite region)
res_led_flatbox.fit: my earlier made flatbox solution from LED stripes (used for high resolution ext.flat; very compact and avoids leak light with the LHires)
res_sun.fit: uncovered scope with background rainy sun; to check calibration (there's a shift in H-alpha, but other regions seems OK)

Used a calibration in UV with a 1-week ago made ref.star (G Per), with a recent Ar/Ne shot.
Location of flat materials always in front of scope, a bit careless - so that seeing unusual humps might come from that, and I did not address that one problem so ignored it fully.

The most relevant comparisons I'd recommend:

flat_internal_vs_halo_plastic.png (4.71 KiB) Viewed 2435 times

This is a global view how the internal vs halogen lamps work.
But the main reason I've put up all of this experiment, is the following:

flat_internal_vs_halo_plastic_UV.png (3.81 KiB) Viewed 2435 times

Which tells me that the Alpy internal lamp has a settle curve ending around 3700-3800A - the straight line below is mapped to the overall background level.
Also be aware that in 2D, the internal lamp has reflections < 3500A but it's less important- mentioning in contrast to the external Halogen which is free of reflections (so it's not the reflecting image what is mapped below 3700A).

I estimate the external halogen could be used till perhaps 3550A if done many or via noise filter.
Let me also point out that my T-Shirt + halogen seem to have a hard cut somewhere between 4000-4100A.

Just for fullness, efficiency comparison in UV with my earlier made LHires + 600/mm grating:

res_blb_alpy_vs_lhires600.png (5.09 KiB) Viewed 2435 times

As you see, the the "BLB" lamp still produces well captured signal down to like 3500-3550A, with a similar efficiency curve in case of both instruments.

Hope this helps others working with the Alpy when considering a good extraction of the IR curve to the UV extent.

Cheers,
Peter

[Francois Teyssier]

Thank you for sharing, Peter
François