Sun, 04/17/2016 - 16:29
In the new version (1.4) of “"AAVSO DSLR Observing Manual” I didn’t find any information about modified DSLR: in the version 1.2 there was one paraghaph (2.5 “Filters and spectral response”) about these DSLR ones.
I have got a Canon 700D modified with a Baader filter (IR cut 420nm/680 nm) so the DSLR is very sensitive in Halpha. I bought an OWB EOS clip Astronomik filter in order to use my modified DSLR for terrestrial photography.
Can I use my modified DSLR to make photometry? Or do I have to use the OWB EOS clip filter?
Thank you very much and clear skies.
Gianni Galli
Hi Gianni,
I don't see any problem using a modified DSLR for photometry. It needs only a good enough UV-IR cut filter as the RGB pigments on the pixels are transparent to the IR. Using modified DSLR + UV-IR cut simply just means your transformation coefficient will be different (smaller, better) from such of a regular DSLR. The regular G band-pass is too short on the red roll-off side, using a DSLR with the IR dye being removed should compensate for that missing red.
The G remaining difference against a Bessell photonic "V" will be the too wide roll-off on the blue side. It can be compensated by subtracting some of the blue channel from the G signal as done in my VSF technique.
https://www.aavso.org/apps/jaavso/article/2880/
Another possibility is to use an additional yellow filter like the Hoya Y50 to cut that extra-blue and get a very good Bessell's V.
I didn't realize the filter section of the manual has been removed, I don't understand why, I will have a look at it.
Clear Skies !
Roger
Hi Gianni,
As Roger mentioned, the modified DSLR should be fine for photometry so long as the UV and IR are blocked. One or two people taking the AAVSO DSLR Photometry course over the last couple of years have owned modified DSLR cameras but I have not had any feedback regarding how well they have worked.
Roger, good to hear from you. I decided to take the section on modified cameras out of the latest version of the DLSR Manual because students in the three courses I've run found it a bit overwhelming. We spent a lot of time discussing pros and cons of modified cameras but the vast majority of them had unmodified cameras.
A future edition of the DSLR Manual could have an appendix on modified cameras once they have been properly tested for photometry. Unfortunately I don't have access to a modified DSLR myself, if there is enough demand then I could investigate borrowing one for a few weeks to do the necessary experimentation. Cheers,
Mark
Good afternoon mates.
At this time I perform photometry DSLR with a color ccd filtered with a Baader IR / UV cut. But I also filtered with a Opteka R72, and the answer is very very close to Ic band, with the difference that does not cut beyond 900 nm. Attached a graph done with the landolt sa98 field. my question is: as there is no label for IR channels as there are for the optical (tri-colored green) or (tri-color red), etc., ¿I can simply pick (Cousins I) to report photometry on chanel R (IR)?
But can I use a modified DSLR camera without a uv-ir cut filter or is it mandatory? During the modification, I only removed the LPF2 filter on my Canon T3i. And what about white balance? Do I need to do manual WB or daylight?