Now I'm looking at standard starfields and transforms I see advantages in using VPhot. I've uploaded and stacked tri-color images (indicating to VPhot these are B, V and R) for three standard starfields. I've run photometry to get a photometry report for each of the starfield, deselected poor candidates and downloaded the revised photometry reports. These have then been imported into the TG to get the transform equations, which have been averaged, and the averaged transform equations loaded into my Telescope Profile. So, this is where I'm a little stuck. How do I apply the transform equations in VPhot to the standard starfield IM's to get a transformed set of Standard Starfield IM's, which should show a lower error? Or do I need to do this in a spreadsheet?
Thanks, in appreciation,
Gary
Sounds like you are almost there!
now
- From TG export the coefficients as a INI file.
- In VPhot import that INI file into your telescope profile
- Take an image of a Standard field and specify targets and a comp and check star
- Create an AAVSO report, just as if you were going to submit to WebObs
- Take that report and load it into the VPhot Transform Applier tool.
- Process the file and then examine the output reports.
Cheers,
George
Thanks for the feedback, George.
So I can get through the first four steps without problems. I have a couple of clarifications:
1) Even though my telescope profile contains transform coefficients, the initial photometry report and generated WebObs file are untransformed values? I thought I'd read in another forum post that if your telescope profile included transformation equations, then the transform was automatically applied?
2) If I want to measure all (or most of the stars) in the standard starfield, I have to change their designation from comp (blue) to target? If this is the case, is it probably not quicker to export the file and apply the transformation equations in Excel, particularly if dealing with a big standard starfield
3) The TA only seems to work with one comp star; can it handle ensembles?
After I generate the AAVSO report for a couple of targets, one comp and one check (all four standard stars) and load it into the first box in the TA and 'Create Transformed AAVSO Report' I get two errors, target not in VSX (not surprising since it's not a variable) and Missing information; Need Tv-Bv and BVcolor.
Here is what is reported for my telescope. Do these look about right for an OSC camera?
Best regards,
Gary
Gary stated:
1) Even though my telescope profile contains transform coefficients, the initial photometry report and generated WebObs file are untransformed values? I thought I'd read in another forum post that if your telescope profile included transformation equations, then the transform was automatically applied?
Transformation is not automatically applied in VPhot or other software without selecting the proper tool and images within that software. Vphot uses the '2-color transform' or TransfromApplier link/tools to transform magnitudes during or after image photometry. Your transform coeffs obviously need to be available in order for transformation to occur, when selected.
2) If I want to measure all (or most of the stars) in the standard starfield, I have to change their designation from comp (blue) to target? If this is the case, is it probably not quicker to export the file and apply the transformation equations in Excel, particularly if dealing with a big standard starfield
Why do you want to measure 'all' of the comps in the std field? Do you just want to run a test/confirmation of a few known stars to confirm how good your coeffs are? You do not need to 'transform' the standard star IMs to get better coeffs. That is not how coeff generation is done. Confused?
3) The TA only seems to work with one comp star; can it handle ensembles?
At this moment, TA only works with one comp. There are logical reasons for doing this related to reporting appropriate comp information.
In the next VPhot version (already written and tested), an ensemble will be possible in TA. We are asking additional questions about it first!
Ken
Happy New Year, and…
Hi Ken,
Happy New Year, and thanks for replying.
Transformation is not automatically applied in VPhot or other software without selecting the proper tool and images within that software. Vphot uses the '2-color transform' or TransfromApplier link/tools to transform magnitudes during or after image photometry. Your transform coeffs obviously need to be available in order for transformation to occur, when selected.
Thanks for confirming this - perhaps I'm not selecting the images needed. Certainly, the transform coefficients are in my telescope profile.
Why do you want to measure 'all' of the comps in the std field? Do you just want to run a test/confirmation of a few known stars to confirm how good your coeffs are? You do not need to 'transform' the standard star IMs to get better coeffs. That is not how coeff generation is done. Confused?
I'm not sure if you remember, but a year or more ago, we talked about a paper I was writing on transforming tri-color data to BRV. Well, I recently submitted a modified form of this paper to the JAAVSO, and the reviewer said a fundamental issue with my paper was my reported results were considerably worse than the expected range state in the DSLR Observing Manual. So I thought I'd run the data through VPhot is see what I got, since the first time around I used spreadsheets. Further, some of the folks I mentor have asked about VPhot, so I thought it was about time I learned how to use the package. So, therefore, having derived and averaged the transformation equations for a number of standard starfields, I want to see how much better the magnitude estimates are for known stars. So why not use the same standard starfield data? I was not planning to recalculate the coefficients.
At this moment, TA only works with one comp. There are logical reasons for doing this related to reporting appropriate comp information.
In the next VPhot version (already written and tested), an ensemble will be possible in TA. We are asking additional questions about it first!
That will be a good improvement.
Best regards,
Gary
Gary:
Ed Wiley and I have investigated exactly what you are trying to do, but with ccd/cmos images.
It will be interesting to see the same data reported for a OSC/DSLR images.
We do have a little trick (still tedious) in VPhot that may help you get your results. It would be easiest to talk/zoom/skype to describe.
Ken
A zoom call would…
Hi Ken,
A zoom call would be very helpful. It will help me resolve any outstanding issues with VPhot and allow you to go through the trick. Also, most of my students have RGB-based systems, so perhaps a couple can help with testing their system and start doing some science. Weekends are a little tricky as I have an 8-old-year, but I'm free this Sunday afternoon, and available throughout a lot of the week during the day. Perhaps, you could give me a couple of dates/time options. Please contact me at ghawkinsall@gmail.com for scheduling.
Best regards,
Gary