Affiliation
Svensk Amator Astronomisk Forening, variabelsektionen (Sweden) (SAAF)
Tue, 12/05/2017 - 18:47
Hi!
I'm new to observing variable stars with a DSLR. My situation is that I use a Celestron C8 with a DSLR for deep-sky imaging, and my idea was to use the same setup for observations of variable stars. So I run into the question of appropriate software. Now, I use PixInsight for all my image processing (calibrating, stacking, post-processing) - so that is a piece of software quite well known to me. I also know that there are some photometry capabilities there - but not how useful they could be for this purpose.
So my question: is there anyone who knows if PixInsight is useful at all for this, and if so, how do I go about using it for this purpose?
Best,
Magnus Larsson
According to http://pixinsight.com/performance/ the capability to do CCD photometry is being added; there is no mention of DSLR photometry. That would imply that the software is presently incapable of being used for photometry.
You might bear in mind that the processing protocol for photometry is very different from that used for ordinary imaging, so your prior experience needs to be augmented considerably. For that reason, it would probably be a mistake to weight your knowledge of PixInsight too heavily if you want to do photometry.
Hi!
Can I suggest to read this manual?
https://www.aavso.org/dslr-observing-manual
The base is in the treatment, it's necessary to do a "de-bayerisation" in order to be able to use the spectrum "V" exclusively. PixInsight also allows this function, like AIP4Win but mainly with MaximDL.
But for the treatment of photometry, however, I believe that PixInsight does not have functions compatible with AAVSO either reference stars and compatible reports. Nothing is mentioned in PixInsight forums... But you can ask it! (https://pixinsight.com/contact/index.html)
Normaly, for photometry treatement compatible with AAVSO, you must use MaximDL or AIP4Win.
These are paid programs, but I've heard rumors that AsroimageJ software may soon also have these AAVSO-compatible features and the AAVSO's report.
But maybe I'm wrong!
JBD
Hello,
IMHO there are two separate topics to discuss - debayering of DSLR images and correct measurement procedure for e.g. aperture photometry. There are numerous tools that can debayer RAW files and several free/open source programs to do high-quality photometry. For example:
http://c-munipack.sourceforge.net
http://www.aperturephotometry.org
I have used AstroImageJ, too, but it seems to me to be a bit too specialized for exoplanet measurements. Of course, there are plenty of cases when the same procedure fits perfectly for stars as well (but not always).
Now, for me, creating a report for AAVSO is plain spreadsheet business - if you have all the data measured and in CSV or similar format, it is easy to convert it into AAVSO format.
By the way, it seems, that there are aperture photometry scripts for Pixinsight, too.
Tõnis
Hi!
Yes, Im asking about the aperture photometry, not the debayering or calibration of the images. I know there is some tools in PI, but I can't easily get my head around it - so wondered here, of someone here knew about it. All since it is a tool that I already have, rathern than needing to get to know another one. But if it is not used, I guess that answers my question...:) as a newbie, my interest is not to do something new, but to familarize myself with the process.
Magnus
PixInsight is designed to enhance astrophotographs, and the math it employs to do that is quite beautiful.
But it presents problems for photometry. Its toolset for handling linear-domain transforms (as are strictly needed for photometry) is shallow. It forces pixel responses to a 0-1 scale on loading FITS files, and you can't easily undo that. It has (or had) catalog precision problems, and the version I used 1.5 years ago was quite hopeless in handling and using plate solution data.
In short, I worked very hard on using it for photometry for about a month but then gave up. I think we're just not their market.
A a long time CCD observer with AAVSO, I suggest VPHOT, which is supported by AAVSO and is free with membership. It has so many features that make it the best for doing photometry in my opinion. It gives lots of diagnostic plots and values that can be used to optimize your results. Give it a look. There is nothing better in my optinion.
Gary
I completely agree with Gary. Once you try VPhot you will like it, . But... you still need software to calibrate the images and hopefully stamp the RA and Dec into the Fits header. I have used a variety of different programs to do that, just avoid non-linear processing.
Question: Does VPhot do DSLR images (once properly reduced)? I am a CCD observer and not a DSLR observer.
Ed
I completely agree with both Gary and Ed. In my opinion Vphot is probably the best software for photometry. It plates solves your images and can transform your magnitudes into the standard system automatically, even with ensemble photometry (providing you have previously determined your transformation coefficients). I generally calibrate my images with Maxim DL, then upload them into Vphot and use this software for the photometry.
Gianluca
I am just starting at getting my feet wet with variable star photometry. Does Vphot work well with DSLR images.
Thanks,Mike
VPhot can handle DSLR images and it will get better in the future.
I believe the steps now are:
- You need to calibrate and de-bayer the images first and upload the single channel fits files.
These images can be big. Convert them to 16bit integer instead of leaving them as floats.
- The filter names are TG, TB and TR.
- In the telescope profile establish the mapping of TB->B, TG->V and TR->R. This tells VPhot what reference data should be used. Yes, I know, it should know automatically that TG is defined as DSLR green referenced to V; working on it.
- You can report to webobs TB, TG and TR values. But better you establish transform coefficients for your camera so that you can transform the data and be able to report it as B, V. R is a little problematic to transform.
I hope to improve VPhots handling of color imagery this year.
George
I do DSLR photometry and usually use MaximDL for photometry. Since I do some mentoring for DSLR photometry, I try exporting as many software packages as possible. I have been exploring VPhot for my calibrated, debayered images. So far, VPhot has worked well. The one issue that I ran into compared to CCD images is difficulty plate solving because DSLR images are defocused. If the image can't be plate solved then you can not go any further in VPhot but at least in Maxim you can manually select your variable, check, and comp stars.