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PostPosted: Thu Jan 17, 2008 8:56 pm 
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Hi everyone,

This is a new one for me, and it's a direct result of terrestrial imaging (i.e. standard photography). Looking at accessories for my Canon 40D I spotted some interesting filters which are obviously standard for photographers wanting to do infrared photography - namely R72 filters. Now these have some useful applications in deep-sky imaging as well!

R72 filters only let through light of wavelength longer than 720nm, and the Silicon CCD sensor has a cut-off around 1,000 nm so the filter allows through a relatively broad band of near infrared radiation. Unfortunately it is just beyond H-alpha radiation, so you don't get the main radiation source from emission nebulae, but it is useful to work at longer wavelengths as you will be able to see stars "through" dust and nebulosity.

The image here:
http://img85.imageshack.us/my.php?image ... alfvq0.jpg
shows the familiar M42, the Great Nebula in Orion imaged in the near infrared through an R72 filter. There are a lot more stars clearly visible in the nebula itself than are apparent in visible images.

The one-shot colour camera I use (SXVF-M25C) has a very poor quantum efficiency in the near infrared, so a mono camera with higher QE would give a better result. If anyone out there has a good mono CCD, try some deep-sky imaging with an R72 filter, this work doesn't seem to have been done much before.

Greg

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Nexstar 11 GPS, 2 x Sky 90, M25C, MaximDL, Photshop CS3, Noel Carboni's Photoshop actions, 7 foot Pulsar fibreglass dome, Canon 40D, 100mm macro lens, 28-200mm zoom lens, 17-55mm f#2.8 zoom lens, 100-400mm zoom lens, 1.4x converter, 2x converter.
http://www.newforestobservatory.com/
http://www.flickr.com/photos/12801949@N02/


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PostPosted: Thu Jan 17, 2008 9:32 pm 
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Posts: 9805
Location: UK
Hi Greg,

Another keeper. 8)

If you think you have problems with IR sensitivity check out Christian Buil's analysis of the EOS 40D DSLR (original here).

Even with the bandpass filter removed the sensitivity at 700nm and longer is almost nil. Which begs the question about who
is selling R72 filters for use with a 40D and why? :shock:

Bob.

P.S. I'm enjoying your book. 8) 8) 8)

EDIT: Graphic removed (it's on the site I referred to) as it was a bit w i d e :oops:

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


Last edited by Bob Andersson on Fri Jan 18, 2008 10:39 am, edited 1 time in total.

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PostPosted: Thu Jan 17, 2008 10:30 pm 
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Hi Greg, another lovely shot! Are you considering modifying your 40D into an astro camera - like the 20Da?

On another note, I appreciate the social and bandwidth aspect of you posting links rather than images, but feel free to post images if you like up to about 700 pixels wide...


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PostPosted: Fri Jan 18, 2008 10:31 am 
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Well Bob - I see I have very little to complain about :)
No, I won't modify the 40D, that's for terrestrial use only, and maybe some very wide field shots of the Milky Way on a little EQ1 mount I have tucked away.
Thank you for the tip Gordon - I have found on other forums that the little images I can post just look terrible, that's the main reason for the links. I hope the links work quickly and efficiently though - that's the thing that can annoy me with links - when they're slow.
Greg

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Nexstar 11 GPS, 2 x Sky 90, M25C, MaximDL, Photshop CS3, Noel Carboni's Photoshop actions, 7 foot Pulsar fibreglass dome, Canon 40D, 100mm macro lens, 28-200mm zoom lens, 17-55mm f#2.8 zoom lens, 100-400mm zoom lens, 1.4x converter, 2x converter.
http://www.newforestobservatory.com/
http://www.flickr.com/photos/12801949@N02/


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