Quote:
Originally Posted by robin_astro
Hi Steven,
Sorry for the thread revival but unfortunately you cannot obtain the instrument response this way as the camera response is only part of it. The grating response is just as significant and the atmospheric extinction also makes a contribution. (Even the telescope optics make a small contribution) The only practical way to include all these is to measure a standard star with a known spectrum under the same conditions as the target. When done correctly, it does work though as these examples of using a Star Analyser and ALPY spectrograph show.
http://www.threehillsobservatory.co....roscopy_21.htm
Cheers
Robin |
Robin,
No issues at all about reviving the thread.
I am still very much a beginner and the feed back provided is part of the learning process.
I agree that relying purely on camera response as an instrument correction isn't foolproof, the major problem is the Planck curves are not accurate.
The problem I have is the Rspec video method (which I assume is a universal method) where one uses an instrument response calibrated professional spectrum as a starting point for determining the response of one's own setup.
I find using this method that details which are muted and insignificant in the uncorrected spectra below 400nm in particular, become magnified and unrealistically detailed when instrument correction is applied.
This problem seems to be due to the much higher sensitivity of professional CCDs in the shorter wavelength range.
This characteristic seems to have been "carried over" into the instrument correction of my own setup.
No such problem exists when the instrument correction is based only on the QE properties of one's own CCD.
Of course I may be doing something wrong that deviates from the video but it isn't obvious.
The other issue that arises is the effects of atmospheric extinction when long exposures are required.
Being relatively faint 3C-273 required lengthy exposures in which the elevation of the object changed markedly during the imaging session.
Is there a limit defined for the elevation change when one requires a different star to produce a new instrument response curve?
If so this will define the maximum time for a subexposure.
Regards
Steven