Mon, 11/09/2020 - 00:20
I am new to AAVSO and exploring my ways.
I use my DSLR camera to capture the images (no telescope).
Can I use VPHOT/Photometrica software for my RAW images?
I came across a tutorial and found that it has all the bells and whistles that I need.
I am AAVSO member. How do I access the software?
Thanks in advance for your help.
I checked VPHOT user's manual and I noticed the access details.
Once I entered VPhot it is asking me for the telescope details to upload my image.
As I mentioned earlier, I do NOT have a telescope. I simply point my DSLR camera to the sky and capture my image in RAW (.CR2 file for Canon) format. I am able to use this file in Muniwin software to do photometry but I would like to use VPhot, if possible.
So to reiterate my questions:
1) Can DSLR image (without use of a telescope) be upoaded?
2) Can Camera's RAW image be uploaded in VPhot (and not the FITS fileit is used to)
My quick answers:
<<So to reiterate my questions:>>
1) Can DSLR image (without use of a telescope) be uploaded? YES your lens is your telescope BUT see below.
2) Can Camera's RAW image be uploaded in VPhot (and not the FITS fileit is used to) NO
PS: Take a look at the AAVSO DSLR Guide.
Thanks, Ken, for your clear response to my querry.
I will surely look into the details of DSLR guide.
This brings up another question that can Canon RAW files be converted into FITS format?
There is software available to convert RAW to FITS for your DSLR. Download the DSLR Guide from the AAVSO web site and give it a review. Most of your questions will be answered in some detail.
I just started about a month ago with AAVSO and I am using VPHOT to process my dslr data. Like Ken stated above, you will have to create a entrty that describes your lense under the telescope section. You will also have to make sure that your image is in the .fits format and that it has the proper .fits header information for VPHOT to process the image. It works well if you provide the right information. What software are you using to preprocess the image.
Mike_F and Ken:
Per Ken's suggestion, I created a telescope for my Canon Camera 35 mm lens.
I am currently using MUNIWIN software to do my photometry.
However, I would like to use VPhot due to multiple reasons.
Please guide me in the process and I will follow.
I have a .CR2 (RAW) file from my canon camera for EPS AUR variable star.
My next step is to convert it into .FITS file.
(I tried AstroImageJ software route to convert to .FITS file. But its header is incompatible with VPhot)
Ken, also I am reviewing DSLR guide.
Thanks for your help.
Mike and Ken,
I checked DSLR guide and it recommends FITSWORK to convert the files which I am working on.
Great! FITSWORK converted my file to FITS format.
Now I am uploading my file to VPhot. VPhot is asking me for RA/DEC for the center of my image and Filter. How do I find RA/DEC of center of my image? Can I use V for Filter? I have heard that for DSLR photometry TG is equivalent to Johnson V filter.
Please have patience with me as I am fairly new to VPhot. I realize you are one of the co-authors of the VPhot guide. I have gone through VPhot guide as well as your Youtube tutorials (Photomatrica).
One of the most attractive features of VPhot that I liked is the plate solving capability and available catalogs. Like I can use GCVS for Variable stars and AAVSO Comp stars database. This is so helpful for crowded images.
When I uploaded one of my images to VPhot, the software asked me for RA/DEC of the center of the image. I used Stellarium to find out the center of AURIGA constellation and entered RA/DEC values.
However, when I was processing my image in VPhot, it was showing all RA/DEC values as 0.0/0.0.
And subsequently, it did not plate solve. When I tried to load catalog data, it complained that my image is not plate solved. Finally, I noticed that WCS box was red.
What did I do wrong?
Also, I will appreciate your guidance regarding the calibration process. What software I should use for stacking and calibration? I have 10 light images, 30 Darks, Flats and Bias, each.
Vinay Bhatt, Austin, Texas.
You can upload your image to nova.astrometry.net. There it will plate solve your image. You can save the fits file from there that will have the center coordinates and upload this image to VPHOT
I use Pixinsight for the calibration of my images. There are many other software packages that can also do the calibration for you. You will also have to extract the green channel for upload in VPHOT. Make sure that your fits header that VPHOT is requiring in the upload.
Consider AstroimageJ. It's designed for scientific imaging, and it's free.
Be aware that some image processing software intended for astrophotography can be problematic for photometry.
Thanks, Dr. Barbara Harris.
I got the coordinates from the nova.astrometry.net but the pleasant surprise was to find the FITS files there.
I tried to upload my fits file to VPhot and it gave me a Fits header error message saying DATE-OBS header field invalid or missing!
Can we have this discussion off the line? I do have a few more questions about the VPhot workflow.
Thanks for your response.
Mike, appreciate your update.
I assume you are stacking a bunch of light images and calibrating them in PixInsight. Does it give you a fits file with proper headers that VPhot will accept? Does it come out with proper coordinate systems that it can be plate solved in VPhot and it will recognize variable and Comp stars?
Thanks, Phil. I will keep your advice in my mind as I do both Astrophotography as well as Photometry.
I use my telescope to do a precise pointing at the target of interest. This will place the target star at the center of the frame. I use Backyard eos for the image capture. Since this does not place the correct information in the fits header I need to add the information that VPHOT is looking for in the header information.
I add the following information to the header.
Also may sure that your time is correct in the fits header.
I use the RA and DEC coordinates from the variable star plot for the particular star. That works well since I have my star centered.
Mike, Typo is no big deal (it should be Vinay) but I do appreciate your detailed response and willingness to help others!
As you know when one embarks on a new journey, there is so much to learn. If we help each other out with the technical details then we can focus more on the task at hand...observing those beautiful variable stars! Also, one thing I am very concerned is the quality of results! Like you, I am also very new to variable star photometry. I transitioned from Astrophotography to Astro Photometry. Currently I am doing lots of experiments to understand the quality of my results like a) amount of De-Focus, b) FWHM value, c) choice of Aperture, d) choice of comp stars, etc. I have found that my results are very sensitive to those parameters and they are almost statistical based and not fully analytical or driven by a mathematical formula! Also, your work-flow and choice of software is also important. One thing I am assuming here is that the images are of high quality (good seeing conditions) and calibrated. I have not entered into the realm of air mass and transformation coefficients yet.
In short, there is a high amount of variability in variable star photometry observations.
What are your thoughts?
-Vinay Bhatt from Austin, Texas.
Sorry about the typo on the name. One thing that I did when I started is I contacted AAVSO and asked to work with a mentor. I worked with Barbara Harris and she was a hugh help to point me in the right direction and review my first few observations before I submitted. You may want to consider this as a option. I will also be willing to help, with whatever I am able to share. I can share a couple of my images to see what I am doing. If you prefer, you can contact me by my email.