Camera Labs

Hi folks,

Modern DSLRs can be used for astrophotography with varying degrees of success. One issue which affects them all, however, is the fact that the camera sensors are sensitive to infra-red and this is a problem for normal photography. To counter this the manufacturers typically include a filter in front of the sensor which cuts out infra-red and the very deep red end of the visible spectrum. These filters have the dual benefit of protecting the sensor and, in recent models, it is this filter which is shaken ultrasonically to help remove dust.

The trouble is that for deep sky astrophotography that filter also cuts out very useful light including hydrogen alpha emission lines in nebulae. Here are two shots (courtesy of Hutech) which illustrate the issue (standard filter on the left and modified filter on the right).

No dark frames or flat field frames applied

As implied by the source of the images above, one company that has addressed the problem and offers modified DSLRs is Hutech. They have just released an EOS 40D with a with Type Ib astronomical filter and are due to release an EOS 40D with a clear wideband multi-coated filter in the next few weeks. The product announcement page is here. The price is around $1800 which isn't too much of a premium to pay if you need the functionality. In my view a modified 40D with it's remote live view and focus capabilities is the best of the DSLR pick for astrophotography. Such a camera can also be used for normal photography provided you add a specially designed filter between the lens and body but doing so prevents use of EF-S lenses.

Sorry if this sounds like an advert. In a way it is but I am not aware of another company which modifies cameras in this way so it isn't as though this post is putting other companies at a disadvantage. However, if anyone else does know of such a firm please let us all know and I'll don the sackcloth and ashes!

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

Thanks for the info Bob. I wonder if Canon will do a model like the 20Da...

More importantly, will you be swithcing your 40D for an astro model?!

Interesting info Bob,
It does raised some question why the filter is necessary , I believe the film days does not have this problem.

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Nikon D7000 and a bunch of Nikkors

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Gordon. I imagine that with the low volumes Canon are probably happy to leave this to firms like Hutech. No, I won't be trading in my 40D for a modified model. Of course, if I win the lottery...

DavidL Without that filter the sensitivity of the camera's sensor to infra-red would induce some artefacts into the pictures which wouldn't be correctable with post processing. As an example, consider a picture of the family around the fire!

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

Hi folks,

There is an article over at Christian Buil's site where he examines how the anti-aliasing and bandpass filters immediately in front of Canon's EOS 40D sensor affect the light striking that sensor. For anyone contemplating astrophotography with a DSLR (especially the 40D and 350D/Rebel XT) it is, in my opinion, well worth a careful read.

The original article is in French (here) but for those who, like myself, are linguistically challenged there is a reasonably intelligible version in Googlish.

Even if the results of the tests are of no interest there is a nice sequence showing the sensor assembly in various stages of disassembly.

Bob.

_________________
OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.