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.
- 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.