Eta Carina in infrared

[cometcatcher (Kevin)]

Yeah well, Ha is already infrared, but... I have an infrared filter with "650nm" written on it so thought it would be interesting to put it in the optical path and see what happens since Ha is 656nm or so. Most Ha filters have IR cut, this one has IR pass. It's meant for daylight IR scenes.

I'm not quite sure what to make of the result, other than it might make a good topic of conversation on the infrared forums.

I'm also getting a 720nm IR filter so that will be interesting to see what it looks like.

GSO 10" F4 Newtonian, modified Canon 1100D, 650nm IR filter, 258 x 30 seconds unguided on a HEQ5 Pro. From Rigel Observatory.

First semi-clear night in a month! 90% Moon present.

[Andy01 (Andy)]

Colours are great Kevin - worth the investment in time methinks

[cometcatcher (Kevin)]

Thanks Andy! I was a little surprised to get more than monochrome out of it, but I know that these filters produce some colour in daylight also.

[traveller (Bo)]

Nice to be able to see behind the bubble. Thanks for sharing Kev.
Bo

[Camelopardalis (Dunk)]

That's a great result Kevin

My suspicion - from my own experiments recently - is that the colour cells of the Bayer array can be somewhat transparent outside of the visual spectrum, since the visual spectrum is all a DSLR is designed to care about and they've usually got a UV/IR cut in front of the sensor.

Once it's modded to remove the UV/IR cut, the passband of the colour cells becomes more apparent, and since the pixels of the sensor still have some response to IR wavelengths, when the cut out is removed we end up with photons striking the pixels and we get signal.

From that, I'm guessing the red pixels are responding to Ha + IR, whereas the green and blue just IR. It's possible they could be responding to Ha too, it just depends on where the colour cells start letting photons through again. Does this mean it's "false colour" though

[Stevec35 (Steve)]

An interesting result for sure. FWIW here's what I got some years back using Astrodon IR filters and the 12.5" RCOS. In case you're wondering these filters produce funny artefacts on bright stars apparently due to reflections from the CCD cover plate according to Don Goldman.

Cheers

Steve

[RickS (Rick)]

Certainly a worthwhile experiment, Kevin

[cometcatcher (Kevin)]

Originally Posted by traveller

Nice to be able to see behind the bubble. Thanks for sharing Kev.
Bo

Thanks Bo!

Originally Posted by Camelopardalis

That's a great result Kevin

My suspicion - from my own experiments recently - is that the colour cells of the Bayer array can be somewhat transparent outside of the visual spectrum, since the visual spectrum is all a DSLR is designed to care about and they've usually got a UV/IR cut in front of the sensor.

Once it's modded to remove the UV/IR cut, the passband of the colour cells becomes more apparent, and since the pixels of the sensor still have some response to IR wavelengths, when the cut out is removed we end up with photons striking the pixels and we get signal.

From that, I'm guessing the red pixels are responding to Ha + IR, whereas the green and blue just IR. It's possible they could be responding to Ha too, it just depends on where the colour cells start letting photons through again. Does this mean it's "false colour" though

Thanks Dunk. I'm not sure how the camera assigns various wavelengths to certain colour channels in this case. There's not much difference in the blue and green channels but a big difference in the red channel.

Originally Posted by Stevec35

An interesting result for sure. FWIW here's what I got some years back using Astrodon IR filters and the 12.5" RCOS. In case you're wondering these filters produce funny artefacts on bright stars apparently due to reflections from the CCD cover plate according to Don Goldman.

Cheers

Steve

Thanks Steve. Do you remember the wavelength of your IR filter?

Originally Posted by RickS

Certainly a worthwhile experiment, Kevin

Thanks Rick! It was a fun experiment.

[Stevec35 (Steve)]

Thanks Steve. Do you remember the wavelength of your IR filter?

There were actually several filters so it's really an infrared LRGB. Unfortunately I don't think Don manufactures these filters any more. Probably not a lot of demand for them.

The Luminance filter blocks everything shorter than 700nm.
Red is assigned to a band peaking at 850nm, green peaking at 830nm and blue peaking at 750nm.

Cheers

Steve

[Placidus (Mike and Trish)]

Just thinking about what we'd expect to happen. Not absolutely sure of my ground and I might be wrong on the fine detail.

Space telescopes can see far infrared, in order to see straight though thick dust, and see T-Tauri stars, protostars and proto-planetary discs, but need to be cooled with liquid nitrogen or helium, and need very special detectors. That's not relevant to us.

A near infrared filter with a cut-off at say 700 nM will let through near infrared from stars, while blocking emission from Ha, OIII, SII, NII, CN, etc.

Consequently, if our camera is sufficiently sensitive to near infrared, we might hope to see ordinary stars while blocking out emission nebulosity.

If we're seeing nebulosity with a near infrared filter with a gentle cut-off so it is 50% down at 650, it is probably H-alpha or NII which has just snuck past the IR filter.

[cometcatcher (Kevin)]

Thanks for your thoughts M&T. I don't know how sharp the cutoff the 720nm will be, but I also suspect it will be soft.

Are there any other nebula lines at 720nm or longer?