300d, CLS, OIII characteristics graph and light spectrum

[rikyuu]

hi,

I thought I'd combine the information I have on the characteristics of the 300d, Sky Watcher OIII filter and Astronomik CLS filter into one graph and include the light spectrum and main emission lines for information.

I hope this is useful to someone.

Cheers

[Merlin66]

Neat graphical display, but I disagree with your resonce curve for the 300D.

The curves I find for the std and modded ( clear filter) 300D do not peak in the Ha.( I use this regularly for spectroscopy)

Buil on his website has a collection of filter spectra and comparisons for the Canon cameras

http://astrosurf.com/buil/50d/test.htm

EOS 350D versus EOS 400D

Astronomical filter curves

If it's modded (Baader) there's a clean cut off at 400nm and 700nm.

[rikyuu]

Thanks for the feedback Merlin. I should have more specifically said 300d filter removed, rather than modified. I keep calling it modified as I modified it, but the standard convention is to call it filter removed.

Just a little background into the 'filter removed' estimation I made:

There's precious little information on this that I can find, most are fitted with the baader filter which cuts off cleanly at 700nm as you say. I just wanted to provide an indication of the continuation of the response of the camera into the IR region with the filter removed and estimated that as the red peak is so narrow compared to the blue and green responses, coupled with the standard filter which cuts off around 550nm sloping down to 700nm which roughly corresponds to the unmodified red response, that without the standard filter, the red response would continue broadly into the IR band up to 700nm, but maybe not as flat as I have shown in the gross estimation. In the absence of more accurate info, it's just an estimation of this. I've also presumed it still has some significant response in IR due to the need of a sharp IR cut filter at 700nm. I was considering the value of putting this line on there due to the lack of info, but thought it would still be a useful indication.

[Merlin66]

Coincidentally I have a 300D with filter removed!

I've already generated ( under Vspec) a full camera response curve that goes from about 360nm all the way through to 800nm.

If it would be of interest, I can upload a .bmp copy of the file.

There's a VERY significant drop around 560nm between the green and blue pixels.

[narrowbandpaul]

i would love to see this graph merlin......

I have the 300D and I love sciency thingymabobs...simples

PM or email if you wish...

rikyuu how do you estimate QE........

Paul

[Merlin66]

I'll copy to .bmp and upload....

I can use a std star spectrum to generate the camera response from the actual shape of the image.

The difference in "shape" and intensities across the whole spectrum give you a first approx. of the overall curve.....

[narrowbandpaul]

yep...thats a scientific method. as is using a calibrated Si diode.

Estimation is very subjective.

Vega was your standard?

Interestingly perhaps it is best to use a star with very few absorption lines. A B star would satisfy this.......try and get as near to a planck blackbody curve as possible.

look forward to the results....

paul

[rikyuu]

oh how I wish I didn't put that little red line on the graph. It was just meant to be an indication.

Really, I was just going to post the scan of the Skywatcher OIII characteristics as they aren't available on the net and I bought one, so I had the little paper thingy with a graph on it so thouhgt it might be useful to someone looking at these filters. After scanning it, I though it might be useful to newbies to add a little extra info so spent some time adding the graphs together for the other bits I have. Nothing scientific, I don't have a spectothingy or a QE calculator I'm afraid. I just did it in my lunch break and I found it a useful visualisaiton.

Someone please delete my graph and post before I get calls from NASA!!

[narrowbandpaul]

it is good information for noobs.

and filter comparisons really are useful.....

[Merlin66]

OK

First image shows the actual spectrum of Vega as recorded by the modified Canon 300D (Blue curve). Superimposed is a reference spectrum of Vega.(Purple) you can see the difference in shape.

This is basically caused by the responce curve/ QE of the 300D.

Using these two curves you can "extract" a camera responce curve, second image, which can then be used to "correct" any future spectra taken with the same set-up.

vega_01_820.bmp

responce_300d.bmp