A minor update to VPhot has been made.
Mostly minor tweaks, but two items of general interest:
- Throughput has been improved. VPhot will plate solve the images you submit, but will now spend no more that 25s to do so. In the past it would try for 220s. This had sever impact on the processing queue when a large batch of files was submitted that were all doomed to not be solved.
Also the Quick Upload page includes an advisory of the length the queue. So if it says there are 500 files ahead of your upload then you know to come back after dinner to see your images.
- The Single Image Photometry report has been modified:
The IM (Instrumental Magnitude) column has been replaced with Max (Maximum ADU). This creates an improved opportunity for refining your exposure time: you will have max adu, snr and the known magnitude of the comp star all in the same report. Take a shot of a calibration field like M67 and you will have the data you need to derive the exposure you need to achieve a target snr for a given magnitude.
And anyone who does this, please share your analysis!
Changes come slowly to VPhot; sorry about that. Please believe that we do listen to your suggestions and complaints and there is a team that records the issues and sets plans for making more updates to improve this flagship application.
Cheers,
George
In the CCD2 CHOICE course we use instrumental magnitudes, primarily downloaded from the VPhot single image photometry tool, to make the spreadsheets and plots for calculating transforms. This may seem old fashioned, but many people (including myself) believe that calculating transforms by the spreadsheet method, at least once, leads to a better understanding of transforms.
Will we no longer be able to use VPhot reported IM's for making the transform spreadsheets?
Phil
George:
This has broken TG procedure as well! Need to revert to previous IM field not MaxADU.
Ken
In the single image Photometry Report the Target estimate column takes up a lot of room. Could that column be made narrower so that both Max ADU and IM could appear in the report? I like George's idea of adding Max ADU in the report, just not at the cost of giving up the IM.
Phil
Hi Phil:
Unfortunately, it would not be a simple matter of using less space in the report. It would also involve "adding" a field to the underlying database. The current revision just required replacing one field name/content with another. The database structure remained the same.
Adding an extra field is a big problem in terms of needing to reformat the database and more importantly all the coding that uses the database. Ouch!
I think we both feel that the IM is necessary for the important transformation tools we use/need, thus my comment about reverting to the previous IM field.
Ken
VPhot release 4.0.7 has been withdrawn: we're back to 4.0.6
IM is needed for transforms. We missed that in testing.
Clearly there is a code (TG and spreadsheets) dependent upon the column list in the Photometry report. Even the addition of a column for Max would break TG unless it was added to the end.
So I will work to get the queue management features back in. I might try to get the Max replacement of IM availiable by special checkbox: I for one will find this very valuable information.
George
Thank you George!
Phil
Hi Everyone,
All this stuff, MaxADU, snr, IM, etc are availiable on the Measurement Details page in Vphot is it not?
Dennis
Yes, but the advantage of having the instrumental magnitudes in the VPhot report is that the IM data are in a format that is needed for TG and very easy to download, then open with a spreadsheet for use in the spreadsheet method.
Having the IM data in the VPhot report makes calculating transforms easy.
Phil
Yes, all the data is there. But that would be for one star.
I was trying create a report that would have that data for the 100+ stars of a std field like NGC7790. With that kind of volume of data one could derive a function : exp= f(target_mag, filter, target_snr). To bound this function you would want to know the maxexp you could take without saturating the image for that mag star. And then you would want to know the snr you would achieve at that maxexp.
So the goal was to get the 4 quantities, exposure, mag, snr, maxadu all in one place so they could be modelled.
If there is interest in discussing exposure settings for photometry, let's start a new thread. I'd love to hear how other people do it. I've got thousands of targets in the AAVSOnet that are moving to new equipment and will need to have their exposures reset.
George
George,
I'd be interested in that topic. Would you want to keep the discussion focused on developing an algorithm that you can use for resetting all the AAVSOnet target exposures? Another way to look at this might be to have the observers figure out the the best exposures for their targets .
Of course you have to start somewhere. For upgraded systems I think the same exposures used for the original pre-upgraded systems would be close enough to start the processes of adjusting the exposures. In this case the discussion should then be about how observers can figure out how to adjust the exposures for their targets to the upgraded systems. If the onus is on the observers I think there would also need to be a more systematic way of communicating these exposure requests than we have now.
Phil