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Thanks for responding. If I’d produced those spectra in isolation I’d have doubted my technique, sanity, etc. (which was my reason for asking) but they’re pretty close to what’s in BeSS already so these are replicable observations. I’m very curious. I’ll post a separate thread asking if anyone (BAA) is posting to BeSS… Andy, David, etc may be able to comment/help.
Kevin,
It’s not a typo.
My Atik460 needs 4.43um in ISIS. It was explained at the workshop as fine tuning needed to exactly match the FL but my memory might be failing.
Regards
Tony
John,
I find the freehand drawing of the response curve can produce markedly different results with different attempts.
Also, the placing of the star on/in the slot (and what portion is recorded) also plays it’s part.
Don’t get paranoid about your setup – yet.
Keep on swimming.
Regards
Tony
Some great discussion on frame calibration.
Quick questions:
Does a Dark not contain Bias, by definition?
As in, we already use flat-darks in ISIS Masters and indeed have that option for photometry in AIP4WIN?
The latter allows a fixed offset/Bias value.
Regards
T
I followed Robin’s method of capturing a series of Miles stars just for practice and instrument response/calibration.
It works well. (Unless, like i did on one occasion, you misidentify a comparison Miles star. That leads to some head scratching! But reinforces Kevin’s point).
i particularly like the Miles database excel spreadsheet for finding suitable Miles stars. Very useful.
Kevin, I don’t know if I understand your description above correctly but are you guiding through a guide-scope/camera separate to the Alpy guide module?
If so, I managed to do this down to (above) mag 12 target but only with a fixed setup and considerable patience. It was also prone to wind, bumps, etc. A QHY5LII through a 50mm finder/guider would plate solve in SG Pro. But I then had to manually point to the target for the last few pixels. I couldn’t get SG Pro to be that accurate.
I now follow accepted practice. A Lodestar or G3 on the Alpy module. Can’t plate solve but the field is big and bright enough to find a star. Actually, I’m at the point where I can find/see far fainter than I can capture usable spectra. I use the QHY/Finder as a rough ‘first-pass’.
Regards
T
Interesting thread. (And as Andy says, an excellent Spectrum John).
I’m not sure what the relationship is between ISIS and Demetra code (that is, whether ISIS code/logic has been reused) but just out of interest I’m still having a little tussle with higher order polys in Demetra calibration. Lower orders are fine and produce excellent results. Anything above three and I sometimes get very strange results.
Rgds
T
Hi Steve, Did you set the Session date in the first sign on screen under “Session Parameters (top-left)? That is, set the Context before you open an item from the Observation list?
Some of my reduction frames wouldn’t load either. I have to save them as .fts files.
And finally, the Yahoo Groups page has to be accessed through the French Yahoo site. Don’t know what I’m, doing wrong but it won’t show in my list without doing that.
Regtards
T
Steve, Kate,
I find that the diffuser (or simply a sheet of artists quality tracing paper taped to the end of the tube) works well for twilight flats. A mate of mine uses a clean white thin t-shirt!
For more formal flats I constructed a lightbox out of white (artists) foam mounting board from Hobbycraft. A couple of A2 boards was enough for me.
It’s very light (no pun) and can be cut with a craft knife or Stanley but is really rigid and can be glued with PVA. I constructed mine in two halves. The first contained a (tracing paper) screen which fits the end of the scope with an outer ring of LEDs powered by a common switchable 12v adapter supply. The LEDs face outward and do not directly illuminate the screen..
The LEDs work down to 5V so by switching the adapter you can change the brightness.
Skyflats need just this unit.
If no ‘sky’ than I put another foam box over the end and turn the LEDs on. The box internally reflects the light so as not to produce any direct light or shadows onto the paper. Evenly illuminated without any interference patterns.
Works a treat.
Regards
T
Thanks Robin. I’ve been playing around with the instrument response and the ‘art’ of defining the response curve.
I’d spotted the two anomalies you mention but there’s no bump/dip in my curve at those wavelengths so I’m at a loss.
I’ve now tried the division of curves and I get the idea of highlighting the discrepancies but I lack the practiced eye to diagnose the causes.
Onward and upward!
Gents,
Slightly confused… Given the discussion at the workshop i was left with the distinct impression that I need a focal reducer for my f10 SCT to get the best Aply match. I have both Meade and Celestron reducers. I’ve copied the following from an old community discussion and there appears to be a big difference in the respective focal lengths.
Which one is the best match for mating the f10 SCT to the Alpy? Am I right in assuming the longer FL will produce less chromatic aberration? but if so what does that do to the SCT/Alpy focal length match?
“I recently measured the focal length of a Meade 0.63x and a Celestron 0.63x focal reducer – the Meade had a focal length around 145mm and the Celestron around 235mm. So the “optimal” distance between lens and focal plane is greater for the Celestron; about 50-55mm for the Meade and around 85mm for the Celestron. The focal length measurements were pretty crude (+/- 5mm?) but clearly a difference.”
Regards
Tony
Great plotting tool. Simple, elegant.
V useful. Thanks Robin.
Silly, I know, but just plying with it…
