DSLR Camera Modifications for Astrophotgraphy

[mikeg64]

There is some excellent advice and guidelines for modifying the canon EOS400-1100 DSLR cameras
for digital photography. Services are offered for performing such camera modifications.

http://www.astronomiser.co.uk/moddeddslrs.htm#1100d
http://ghonis2.ho8.com/rebelmod450d1.html

How effective are unmodified versions of these cameras for deep sky imaging?
My understanding is that the filter provided with the Canon EOS-1100D, for example
filters a significant proportion of the Halpha line.
Are there any images that exist to provide a comparison of cameras with/without this modification?


thanks

[Hornblower]

Sky and Telescope, June 2012, p. 69 has side by side images of Orion illustrating the difference. The magazine should be available in many public libraries.

[RickJ]

The Canon EOS 60Da is the current production model with designed to pass H alpha and NII emission lines. These are pretty well blocked by other models currently in production. Several years ago they also put out one designed with a correct filter for astro work but apparently it wasn't all that great as I never saw many using it. Most went with other models of the time that were modified. I don't recall the model number. Try asking in a DSLR imaging forum. Some likely are available in the used market.

If the object you are after doesn't rely on NII or H alpha for their main emission lines or are broad spectrum (like stars, galaxies and reflection nebulae) then there's no need for a modified camera. If the object does have substantial emission at H alpha and NII frequencies but also has substantial emission within its passband then you can capture the object, its color will be "wrong" however. M42 is such a nebula. It is pink in color photos that pass those red frequencies but a teal color when those frequencies are mostly blocked. But here's the odd thing. Our eyes are also very insensitive to the red of Ha and NII so we see M42 about the same blue green color with our eye in a scope large enough to show color to the eye. So is the color really wrong?

Some objects however emit almost entirely in Ha (red planetaries mostly NII) that is blocked. So those are petty well invisible or very different in detail when imaged with a standard DSLR. You'll not get very good images of these without modification. There are large areas of Ha in areas of the Milky Way that just aren't picked up by these unmodified DSLRs. But there are hundreds of good objects that can be imaged with unmodified cameras. Just that some of the show pieces aren't well suited for an unmodified camera. If H alpha objects are high on your list you'd be much better off with a real mono CCD camera. In a DSLR or OSC ccd only one in four pixels picks up these emission lines. The other 75% see only noise degrading the image quality unless the object has emission in other colors as well.

For an on line example see:
http://www.hapg.org/camera%20mods.htm

Rick

[mikeg64]

Thanks for your excellent advice, I think I know what to do now.

If I go for the unmodified version presumably I would n't be able to image emission nebula such as the North american and Pelican nebula.

At this stage I'd be quite content to image clusters such as M13, the Pleiades and a galaxy such as Andromeda.

I would also be very happy to observe some holes in the clouds!

Our eyes are also very insensitive to the red of Ha and NII so we see M42 about the same blue green color with our eye in a scope large enough to show color to the eye. So is the color really wrong?

When you say a large enough scope, I guess what mean here is the light gathering power we need enough photons for each colour.

[Hornblower]

Thanks for your excellent advice, I think I know what to do now.

If I go for the unmodified version presumably I would n't be able to image emission nebula such as the North american and Pelican nebula.

At this stage I'd be quite content to image clusters such as M13, the Pleiades and a galaxy such as Andromeda.

I would also be very happy to observe some holes in the clouds!




When you say a large enough scope, I guess what mean here is the light gathering power we need enough photons for each colour.

That is correct. If the light coming out of the scope is too dim, our cones stop working and the rods just give us shades of gray.

[RickJ]

You can always modify the camera later if you wish though by then you'll likely want to move to a real mono CCD. But you will have to unlearn some techniques that are used by DSLR imagers that don't apply to CCD work. I've considered a DSLR for comets, aurora and to replace my old film SLR cameras which are pretty well obsolete as the films I prefer for snapshots are rapidly vanishing. But I'll stick with my mono CCD cameras for most of my deep sky imaging as most of what I do is pretty well beyond the capabilities of either a DSLR or color CCD.

One issue not mentioned yet is noise. DSLR cameras are not cooled and have a lot more noise than cooled CCD cameras. If you live in a warm climate this noise will be a major headache. So if you live in say a climate like in Florida a DSLR will not work very well, modified or not. Even here in northern Minnesota where I live the noise would be a problem in summer, one reason I'm still using my film cameras. In winter they'd work fine. You may need several well charged batteries an evening however as they don't last long in very cold conditions. An external power source is best to avoid lost data if a battery goes 4 minutes into a 5 minute exposure.

Rick