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I took images of T UMa with a DSLR. Went through VPHOT steps all of the way until it was time to submit a report. But did not use Transform Generator, instead derived coefficients via Excel plots. The report says a CCD was used yet it was actually a DSLR. How do I get the report to indicate DSLR? The report also said the filters were B and V. SInce the images were taken with a DSLR and transformed should the Filters be Johnson B and Johnson G instead of B and V? BTW, I did map the telescope settings for TG and TB.

Here is the report:

#SOFTWARE=VPhot 4.0.6
T UMa,2458979.62396,8.506,0.003,B,YES,STD,ENSEMBLE,na,98,10.227,1.100,na,X25366HI,na
T UMa,2458979.62396,8.218,0.011,V,YES,STD,ENSEMBLE,na,98,9.857,1.100,na,X25366HI,na



Eric Dose
Eric Dose's picture
There are some problems here.

There are some problems here. Solving some of these will probably answer your questions:

(1) First, one doesn't transform images, one transforms magnitudes.

(2) Your transformed results will be in the passband that you transformed to. If you transformed to V, your results are in V. If you transformed to TG, your results are in TG, etc. Either is reportable.

(3) I've never heard of "Johnson G", either as a filter or as a passband. It's certainly not in the AAVSO filter/passband list.

Hi Eric, my mistake, meant

Hi Eric, my mistake, meant Johnson V not G.


MZK's picture
Not really!

Hi Gary:

1. Do not map TB and TG to B and V. If you decide not to transform, they should be reported as TB and TG.

2. If you decide to transform, I recommend "renaming" the filters to B and V just before the transformation so that they get reported as (Johnson) B and (Johnson) V.

3. There is no such thing as Johnson G (or Johnson B in the sense that you mean it).

4. What you are doing is using the transform coefficients that you generated with a spreadsheet by plotting your TG and TB magnitudes vs. the known B and V comp magnitudes, to calculate the transformed B and V magnitudes. That works fine. They should be reported as transformed B and V in the AAVSO report as they are. That is correct.

5. WRT CCD, this is an interesting issue. ALL reports from VPhot report things as CCD. CMOS does the same thing and based on your report DSLR does the same. VPhot, when created, just wanted to indicate an "electronic" magnitude as opposed to a Visual magnitude. In the future, it might be nice to know BUT based on the fits headers I normally see, there is no indication whether the detector is a ccd, or cmos, or dslr or other. The instrume header usually reports the specific model number and not the type. So, VPhot could not figure that out.  Hmmmm! You could edit the report but I'm not sure it is worth it.

6. So the bottom line is that your report is correct/okay as shown.


Hi, Ken,

Hi, Ken,

2. For this report do I need to go back into the telescope setting to rename the filters and then re-run the  transformation?   In doing so does it change the previous magnitude results or just the report info?

3. I meant Johnson V not G. My mistake.

This is my first time at using VPHOT to report transformed data Fantastic program. Took me awhile to get it right. Would be great if the Transform Generator program could run within VPHOT without having it as a seperate program requiring Phython/Anaconda since I'm having trouble getting it to work.

Thanks for your help. Much appreciated.


MZK's picture
Report OK


2. Your report is correct. Nothing more to do. EITHER mapping filters or renaming filters will help accomplish what you need to do, i.e., transform TB; TG to B; V.

However, IF you ever want/need to generate untransformed TB/TG magnitudes due to the lack of both filters (not likely with your DSLR bayer array but possible?), it is safer to avoid the mapping and just "rename" as necessary.

IF you ALWAYS transform, mapping is appropriate.  It saves a manual step. I hope this makes sense? Just a caution not a requirement.

4. TG will almost certainly remain separate for the near future. If you are having problems with it, send me a separate email ( with a description. There should be a detailed installation problem solver on the TG page. It works 95% of the time but not always.


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