Q: Best method of alignment to correct for seeing variations

[chiltonstar]

Q for the experts: how best can I correct for the changes in seeing that occur while capturing a spectrum with an SA 100, using a DSLR?

The scope (5" Mak) with a DSLR is not tracked in RA, so the star produces a vertical spectrum on the frame, but small changes in the seeing produce "wiggles" in this line and in the spectral features. If I use eg VSpec, this is not allowed for (I assume) and the spectral features are accordingly broadened. I can correct manually in PShop, bit by bit, but it's hard work.....

Clearly, I could wait for nights with perfect seeing, but this is the UK!

Any ideas?

eg Alnitak:-

Chris

[Merlin66]

That's about as good as it gets, unless you start using a slit etc etc etc.

If the image is well aligned across the chip, VSpec etc can do the vertical binning to capture as much as possible - as you say the seeing will impact on the resolution.

( Your grating is sitting a little off - the dark "horizontal lines" (caused by the seeing) should be as close to horizontal as you can get..a little more practise and you'll be good to go!)

[chiltonstar]

Many thanks Ken. No magic software then...........

Chris

[Merlin66]

No, nothing I've found so far...

The target star seems to be in focus? For best spectral resolution the spectrum, not the star, should be focused....

Notwithstanding that, I'm sure you'll be impressed when you start to process the image....

Onwards and Upwards

[chiltonstar]

No, nothing I've found so far...

The target star seems to be in focus? For best spectral resolution the spectrum, not the star, should be focused....

Notwithstanding that, I'm sure you'll be impressed when you start to process the image....

Onwards and Upwards

I focused on the spectrum, although the star is in reasonable focus as well - maybe because I used the 5" Mak, which has a long fl, high f number, and therefore an extended depth of field, I imagine??

I've had some tries with this image and others in VSpec, and the results are indeed excellent...... I like VSpec now I've played with it a bit more; RSpec was easier at first, but of course was not free....

"Plus ultra!"

Chris

[nytecam]

Hi - my drift-scan spectro page @ http://home.freeuk.com/m.gavin/driftsp.htm