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First Light - Altair Astro/GSO 8" RC F8

hograt

By hograt
in Imaging - Deep Sky

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hograt

hograt

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Posted

Set up my new F8 8"RC OTA at the weekend and have been working through the setup to get things optimized since then. Switching from a widefield Apo @ F4.5 to F8 certainly presents its challenges for the mount. Saying that, I've worked through the autoguide settings empirically and have arrived at some values which give me good results.

The Altair/GSO OTA is well well built, the upgraded focuser is OK, it handles an Atik16HR+SXfilterwheel without any obvious flop and it also works well with my Lakeside motor focuser.

Tonight will be a long session; I kicked off "first light" with an easy M57. This is composed of :

RGB 30sec Bin 2x2 @ 20 frames each

L 90sec Bin 1x1 @ 20 frames

L 300sec Bin 1x1 @ 5 frames

Colour calibration was determined by imaging a G2V star with RGB filters.

Mount is EQ6 Mod, guided with an ST80 through Ascom (pulserate x30).

Aquisition through Maxim Dl, which also handled the autoguiding.

Rudimentary processing with Pixinsight, no flats, bias or darks yet. There's plenty more to bring out in the data.

I'm pleased with the performance, the optics look promising so far.

Martin

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hograt

hograt

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Thanks for the positive response everyone. In fact, I'm collecting more subs right now and have pushed the exposure up to 10 minutes without major guide issues. The moon isn't helpful tonight.

John, I'm running at prime focus. I will look into a focal reducer, my F6.3 Antares is not up to the job by a long shot. When I used that initially, I was quite worried I'd been sent a duff set of optics.

The scope arrived out of collimation, but only marginally. Ian at Altair Astro tells me they check several sets of optics from each batch with an optical expert and star test every OTA. That level of detail gives me confidence in the product. I used a trial copy of CCD Inspector to guide the collimation, it was helpful but I ended up looking at the defocused star as the atmospheric conditions were not great.

Catanonia, the principle here is that you turn the scope and camera onto a G2V star, which coincidentally matches out own sun's spectrum - don't use the sun though :). Taking a simple image of the star (I've attached a text file with suitable stars) through Red, Green and Blue filters and then measuring their individual intensities (a click in maxim dl) enables one to determine the optical train's sensitivity to each colour. In my case I measure intensities of:

R=270854

G=303051

B=237448

These are normalised as follows:

Red = Green/Red = 1.12

Green = 1.00

Blue = Green/Blue = 1.28

When combining the RGB channels to form the colour image, the colour channels are multiplied by the value to normalise their intensity. I use Maxim dl, and this is straightforward in the stack function.

It's preferable to calibrate each session, close to the point in the sky you will image. It takes only a minute, and you can automate it e.g. in CCD Autopilot (there is a 60 day demo).

I'm happy with this approach as it is empirical but always interested to hear others views and their workflow.

Hope this info is helpful

Martin

G2V.zip

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