Astro-Terrestrial Cameras (New)
Now as well as owning arguably the best DSLR for astrophotography, you can also have a camera which can be used for both astro and day time photography / family shots without having to create a custom white balance for every terrestrial picture you take. These astro-terrestrial cameras will allow you to take daylight photos using the automatic features of the camera (auto WB and Auto ISO) without having to worry about taking a custom white balance. You can have two cameras in one.
This image was taken by one of my dual astro-terrestrial cameras. No custom WB was used. Camera settings: P Mode, Autofocus, ISO Speed Auto and White Balance Auto. Notice the natural colour rendition. Autofocus is retained and accurate. Click on the image for a full resolution version.
How does it work?
These are cameras which have been astromodified with a Baader BCF corrector filter replacement to allow sensitivity to hydrogen alpha radiation. However, the camera will produce adequate colour-corrected daylight pictures out of the box without the need to correct the image in post processing. It is not necessary to create a custom balance or add an external corrector filter either. You can use this facility with any of the following camera modes: A-Dep, M, AV, TV and P. Thus, you can, for instance, select the 'program' mode in your camera (P), as well as Auto WB and Auto ISO and every photo you take will come up with correct terrestrial colours.
Because these cameras have had their original IR colour correction stock filter replaced by a Baader BCF corrector filter, they are transparent to hydrogen alpha radiation from emission nebulae and, as a result, they are perfect cameras for astrophotography.
Another important feature in these cameras is that the anti aliasing filter has been removed in order to obtain sharper images and more captured fine detail in those images. Also, because there is less glass in the optical train, the camera's sensitivity is increased in astronomical targets.
During the modification, the camera is re-shimmed in order to maintain its autofocus capability as well as the ability to achieve infinity focus with any lens. I believe all these characteristics make the canon Rebel T3 (1100D) the best astro DSLR cameras.
What's the theory behind it?
When a DSLR is modified with a Baader filter replacement, the software installed in the camera hasn't been programmed to work with the new filter and, as a result, the pictures will come up with unnatural colours; typically with a red tinge. This can be easily corrected in post processing with software for image processing. Also, there is the possibility to take a picture of a 'grey card' to tell the camera what the real colours are so it can correct them through a custom white balance.
Left: astro modified camera without colour correction. Right: atro modified camera with colour correction.Click on pictures for full resolution images
The problem is that, typically, a custom white balance must be created for each different lighting condition. The other solution is to correct the colour in post processing. For the serious photographer this is not an inconvenience as a custom white balance is always going to produce the best results for any particular lighting conditions. However, most of us are quite happy with the work the camera does for us in selecting the different parameters. Thus, post processing, using grey cards and creating a custom white balance for each particular condition is a real inconvenience.
This is the reason why these cameras have been tweaked so that they can compensate for the different white balance parameters brought about by the Baader replacement filter.
This is a picture of a colour/grey card taken by a stock, unmodified Canon EOS 1100D. The settings used were: P (program mode), Auto WB and Auto ISO.
The same picture taken by one of my astromodified cameras using the same settings.
This picture has been taken by a camera modified for astrophotography without the changes in the firmware applied. This colour can still be corrected but it can only be done in post processing now.
Why removing the anti aliasing filter?
Some camera manufacturers are releasing high end models without the anti aliasing filter. As an example, Nikon has released a special edition D800E
version of its super high 36 megapixel resolution D800 camera body.
Essentially the two cameras are identical in every way except the lack
of the AA filter or anti aliasing filter in the D800E along with a higher price tag.
Why the missing AA filter you ask? Well, two
reasons, sharper images and more
fine detail in those images.
This is a great feature for photographers who
may not mind the occasional occurrence of moire in SOME images while
getting more sharpness and detail in EVERY image.
The bellow images and original ePHOTOzine article can be viewed by clicking the images bellow. Notice the finer detail captured in the camera without anti aliasing filter (D800E).
Gary Honis has been testing the effect of the anti aliasing properties of canon's original filters in front of the CMOS imaging sensors of recent model cameras. He has found that the removal of the anti aliasing filter produces significantly sharper images as we can see in the example bellow.
The dual astroterrestrial canon EOS Rebel T3 (1100D) has the added bonus that it has been re-shimmed to retain autofocus.
In these pictures bellow you can see how one of my Canon 1100D (Rebel T3) Baader astromodified cameras (with 12.2 megapixel) and with the anti aliasing filter removed compares to a stock Canon 500D (Rebel T1i) with 15 megapixel. Notice the increase in picture sharpness when the LP1 filter is removed (click on the images for a full resolution version).
For a further discussion on the the advantages of removing the anti aliasing filter please visit:
Value for Money
As you can see these brand new modified DSLR are arguably the best cameras for astrophotography because of their great sensitivity, low noise and ability to focus to infinity with any lens. Not only that, they can be used for normal daylight photography without using a colour correction filter or having to worry about creating a custom white balance. The competitive price of the EOS Rebel T3 (1100D) makes it possible to acquire a brand new camera with these characteristics for just over £350; an astonishing price.
Do I need a Telescope?
I can install on request a copy of the freeware software Magic Lantern which will allow greater control of the camera functionality making possible the creation of time lapses and extreme wide field astrophotography simply with the camera and a tripod. No need for a telescope; not even a timer or remote shutter as this software comes with an internal intervalometer in the camera. This is an example of what it can be achieved; a wonderful time lapse by the talented Randy Halverson:
You can find more of his work at:
What models are there available?
All the 600D (Rebel T3i), 700D and 100D models sold with a Baader filter modification have been tweaked to function as astro-terrestrial cameras.