Do you need to remove sensor window to shoot UV?

[Stonius]

I was thinking of getting a Bader Venus filter to play with, but I know that sensor windows sometimes have UV blocking built in.



I'm using an ASI 290 Mono, and as far as I can see, the response at those wavelengths (350nm) is only around 25% of it's maximum sensitivity, which seems to peak more in the red.


Is this just a natural effect of the sensor or is the sensor window coated to reject these wavelengths?


I guess Venus is a pretty bright target (!) but still...



Cheers


Markus

[sunslayr]

That would match up with the chart on this (https://astronomy-imaging-camera.com/product/zwo-protective-window-asi-cameras) page for the ar window. I'd say you would need to remove it for 350nm and below.

[Stonius]

Hmm, might make more sense to try and capture it with my 1600 then. No need for modifications!

[Merlin66]

I use an ATIK 314L, ASI 1600MM and ASI 174MM for spectroscopy the QE curves just give some signal down around 370nm, below that the atmospheric transmission starts to kick in - the combo work against imaging in the far UV.
Most objectives (and obviously mirrors) will allow some imaging in the UV.
This spectrum of Sirius was taken with the Genesis and ATiK 314.

[Stonius]

So you're saying even without the sensor window cutting the UV the CMOS sensitivity just drops off regardless?


Looking at the graph for the 1600MM, it would still only get me to around 30% of peak efficiency, so that would make sense.


I don't know much about spectroscopy so I'm not sure how to read the image you posted. The bottom scale is tenths of a nM/? It looks like the amplitude drops off as the wavelengths get shorter, but I don't know enough to guess if this is attenuation from the imaging train, or just black body radiation curves?


Cheers


Markus

[Merlin66]

Markus,
On the spectral graph the X axis is in wavelength Angstrom.
Sirius is a A type star with prominent H Balmer series absorption lines - that's what you see. The curve (intensity values) drop off towards the left partly due the spectrum of Sirius (Back body) but also the camera sensitivity.
The ability to record much below 3700A is compromised.

[Stonius]

Ah, interesting - thank you for explaining :-)


Markus

[JA]

Hi M,

Not only will the sensor design and any coverglass potentially limit performance in to the UV, but the scope or lens will also limit UV performance
below about 350nm. There are some optics that can reach down to about 300nm and some very expensive specialist UV lenses that approach 200nm.

Best
JA

[Stonius]

So ...I understand that the response is attenuated in that part of the spectrum.


Yet Venus is bright.


The question is 'will the response be so attenuated as to make it a foolish quest with current equipment?'.


Best,


Markus