Good morning.
The index Ic - z`, I have been experiencing for some time in a color CCD camera equivalent DSLR with satisfactory results.
http://www.aavso.org/fotometria-con-webcam
The response of the RGB matrix in the IR has a widespread feature in all RGB sensors, this can be seen at this link and the graph adjunt (olimpis). There are many other references to this.
http://www.astrosurf.com/buil/350d/350d.htm
The important element is not about removing the IR cut filter, but that it can be exchanged at will with one that enables the passage of IR from 700 nm. In my case I use a Opteka R72. when the RGB channels separated with this filter channel R collects light between 700 and 1000 nm, and the B 800 to 1000 nm. So these would be invested and would have to exchange. But as the R band does not have a fall at 850 nm as a Ic, would have to adjust to Ic (but this is not problem, would come to be much like ASAS, OGLE, TASS, in conformity with the due corrections). The band B would have to adjust at z` similarly using the index itself R-B bands of the camera and its relation to Ic-z`. but for the reason that B does not coincide exactly with z`, would have to do the adjust using the iterative method of Bruce L. Gary. The only limitation index from very red stars have a value which can not be distinguished even more red stars.
Beware: in the iterative method, the equivalence between R-B (infrarred) DSLR vs Ic-z`se takes only as a starting point for transformation, from the second iteration index Ic-z`obtenido DSLR transformed magnitudes is used, which is refined in each iteration.
In this sense Fotocalc RGB (software that I developed for reduction DSLR), has been designed to work with these two infrared bands DSLR using this methodology. The manual will finish soon in its first phase, explains all this in detail, although this would have to translate it into Spanish to read, but has done testing with very promising results. This has been the reason that has taken a different path citizensky approach in this paper, which completely ignores the infrared bands of the DSLR, but they have an enormous wealth of informations.
On the web you can find some work for calculating effective temperatures with indices Ic - Z.
I hope their views.
Hi Chris,
This is an interesting idea. We did something similar in graduate school, where we were using a photoelectric photometer at UBV, but the U filter had a red leak. We included a fourth "filter" which was a U filter sandwiched with a long-pass filter, so that all that was transmitted was the red leak light. You could then scale it and subtract from the U filter measurement.
What you suggest should work, as long as what is shown on the various plots is exactly what your particular camera's RGB filters are like. Note, however, your response in the far-red will be less than if you were using a monochrome system with true Ic and z' filters, tailored to give maximum throughput. You also have to remove the IR blocking filter in the DSLR, and perhaps add the longpass filter in a filter wheel in front of the DSLR if you want to also obtain RGB from the camera. It is still a neat idea.
Arne
If Arne, thank you very much. I use a filter wheel I built. The results in channel R + Opteka R72 (equivalent to the band I), are very similar in accuracy at those produced by the optical channel G (transformed to the band V) when the IR cut filter is used own camara. I have no filter on, I switch between Baader UV / IR Cut to (R, G, B) and filter Opteka R72 for (I, Z`), the latter filter only cost me 14 $. When I see several years the iterative method of Bruce Gary, I learned specifically with that intention, I y z` transform (taken from the R and B channels Opteka + filter R72). I already did the test by photometry M7, and I see me approaching end of all my experiments, I am in the process is to perform photometry (for its plethora of colors) Landolt SA98 BVRrÌcz` field using optical RGB and IR channels from camera and transforming using the camera indexes themselves (with their respective air mass corrections, etc. to what you already use a method that uses a 2 coefficients air mass to automatically generate the inermedios coefficients), and then compare the results with true values. I'm using the photometry of Peter Stetson for BVRI and Allyn Smith for r`i`z`. (Incidentally, the photometry of Peter Stetson matches to detail throughout with Arlo Landolt).
As to obtain the value of the leakage z` filter (in this case towards blue), I so far. to solve the leakage problem had thought of using the iterative method to refine the result of the transformation of z`, but a method such as that described could be done, I thought several ways to do this but still do not have anything definite at this point. but surely it is a matter of time to have it.
To get lots of curves lu band I yz`usando serious DSLR fantastic, huge gaps in this region that are irreplaceable is would fill my passion is the IR.
rRegarding the correction of atmospheric extinction coefficients using two air mass is optional Softeare I wrote a very simple but useful, it is optional to use this method.
Right now I'm aligning the optics of the telescope, why tarry a few days before taking pictures to photometry.
Oliver Christopher Lòpez
Hi Arne.
The method that mencionanste is functional to correct the leak, in this case would have to do shots with the same exposure time field calibration using a Z` filter mounted on the camera DSLR whitout internal filtrer, take the channel B (IR) to the response of z `, then the difference is established from Opteka R72 mas chanel B vs Z` mas chanel B, as this is is also a relationship loss vs color, is added to the coefficient of Transformation in slope and zero, and transforming once is correcte.
The glass used for the band a Shott z`es RG 830, this glass is the one with filters Z` costly of 200 or $ 400 as z`2 trademarks of Astrodon (not the case of having dielectric Astrodon z_s2 cutting treatment to uns 920 nm) .
http://www.astrodon.com/products/filters/astrodon_photometrics_-_sloan/
I have a B + W # 093 which has the same glass Shott RG 830 and only costs $ 54
http://www.amazon.com/40-5mm-Infrared-Filter-093-RG830/dp/B0012LUQXM/re…
for IR pass filter to use use is even cheaper
http://www.amazon.com/Opteka-720nm-Infrared-X-Ray-Filter/dp/B000MD8XKO/…
also I have a zikkor to 950 nm, such as buy that way I had to cut for mounting on the wheel, attached image.
this is not a problem for DSLR observers, because they can use their modified camera without cutting internal filter and change the filter from the outside.