Forums / The Science / Photometry / DSLR Photometry Procedures
DSLR Photometry Procedures
I have been working for months now trying to obtain reasonable photometry results with my Canon 20D DSLR and AIP4WIN. Imaging:
I think I may finally be closing in on an acceptable procedure. I haven't done a computation yet, but I estimate my results are now in the +/- 0.02 mag range.
Listed below is my current procedure. I would appreciate hearing any comments you might have about this method.
Thanks, Tom
Processing:
- Download and save star images, darks, flats and flat-darks.
- Set DSLR conversion settings.
After opening AIP4WIN, go to "preferences/ DSLR Conversion Settings" and select "DeBayer, white balance using scale factors."
Set the red and blue parameters to zero and save the result. Richard Berry recommended this setting in a comment above.
- Convert images to gray scale.
I have tried stacking the images first and then doing a single conversion but this method does not work for me. When using this approach, I get very poor results computing a Transformation Coefficient. So, I go through the drudgery of opening each of my 60 images (star and calibration) and converting each to gray scale individually.
- Set up calibration using the "Standard Calibration" method in AIP4WIN.
- Stack the images.
Select "multi-image/auto-process/deep-sky". Click on "Select files" and open the 30 star image files. On the "pre-process" tab, check "calibrate".
On the "alignment" tab, check "2-star alignment", and follow the standard procedures for stacking the 30 star images.
- Obtain Instrument Magnitudes for epsilon, lambda and additional stars (rho, mu, omega, sigma and 58 Per) used to determine a Transformation Coefficient.
Select "Measure/Photometry/Single Image". On the "settings" tab select a "zero point" that produces a realistic instrument magnitude. Also, adjust the "radii" so that the stars fit comfortably in the annulus.
Click on each star and record the Instrument magnitudes.
- Use Excel to process the Instrument Magnitudes (see attached spread sheet)
Obtain a Transformation Coefficient using the graphical method described by Arne Hendon in this forum.
Using lambda Auriga as the comparison star, obtain a "computed magnitude" for epsilon.
Apply a "Transformation Addend" to obtain the final magnitude.
- Compute Standard Deviation.
Repeat the above process three times using stacks of 10 images. Use the results compute a mean and standard deviation for the observation.
Thanks Brian. Yes, I would like to participate in your documentation efforts. I'll send you an email.Tom
Hi every body On the “Settings” tab, adjust the “radii” so that the aperture size is slightly larger than the star image. Adjust the annulus size as appropriate for the aperture. Also on the “Settings” tab, enter a “zero point” that gives a reasonable value for the instrument magnitude. Click the “save” button. Now, click on the “Results” tab. Shifting to your image, click on the variable star, calibration star and selected TC stars in turn. Record the Instrument Magnitudes of each for later use in the spreadsheet program. 1-Radii has 3 parameters which of them should be changed? 2-What is "zero point"? Is it different for each observation place? 3- Is differential magnitude mean instrument magnitude?
Some body can help me for these steps???(on AIP4WIN tutorial)
Tom,The procedure looks good. I have an undergraduate at DU working on tutorials for various reduction software packages. The MaximDL tutorial is done and will be posted online soon. BrianP.S. If you are interested in helping build documentation for the CS website, especially expanding upon your documentation above send me an email.