The CCD sensor of the average camera can detect IR light. If the manufacturers didnʼt filter out that light weʼd have reddish colored pictures that picked up more IR light than we see as humans. Because we donʼt want false color in our normal photos manufacturer's design cameras to filter out this extra reddish light, with an IR filter. These filters are so strong they mask out IR (hydrogen alpha) wavelengths that we might be able to pick up from astronomy objects. Specialized astronomy cameras come from a variety of manufacturers. Astrophotography cameras come from the manufacturers like: Orion, Meade, Stellacam, SBIG, Starlight Express, etc. The specialized cameras donʼt have IR filters to remove the hydrogen alpha IR light from the image. So they will show more red glowing emissions of gas clouds from hydrogen gas as itʼs glowing in space. You'll see more dark lanes of dust in front of these glowing lights as well, because you capture more light with a dedicated Astrophotography camera. The gas is giving off a glow that humans can't see, because we donʼt see hydrogen alpha emissions with our eyes.
Typical astronomy photographs may be taken by these specialized cameras which are used for astronomy. There are three or four major types of cameras. The stock CCD DSLR (usually with IR filters intact, but some may be removed), webcams, astronomy cameras and video cameras. Some astronomy cameras use chips from video cameras and these often provide low light video and live video and also may have only video output which requires digitization into a video card unless you're showing the video image live. This can introduce more artifacts, so these are used for live applications. We are only showing examples from Astronomy still cameras and my unmodified DSLR (IR light being blocked.) There are other specialized cameras as well. But the four in this list covers the basic cameras most amateur astronomers use.
A one shot color camera typically has a color filter matrix in front of a monochrome sensor. This matrix will actually allow a color photo by filtering out the colors and allowing only red, green or blue colors to trigger a sensor. Itʼs a little more complicated than this, but the end result is a one shot color image. The image on some cameras can actually be transferred as a RAW signal to the computer and the raw information can contain a monochrome image and color data separately. Then computer software can be used to manipulate that RAW format image and finally the colors are added through a process of merging the color data with the monochrome data and a full color picture is possible. Cameras like the Canon EOS T1i can merge that data ahead of time and merge it into JPEG formatted photos. This is a separate topic. Suffice it to say we can have one shot color cameras and also monochrome cameras, typically astronomy monochrome cameras that require filters and multiple exposures for each primary color to create a color photo. A one shot color camera will lose sensitivity to the dark object and be less sensitive. Monochrome cameras are 8 to 16 times more sensitive to low light. The “color filter matrix” diminishes the faintness a one shot color camera can see, so the one shot camera needs longer exposures.
There are many more things to say, but Iʼll try to keep the post short. Astronomy cameras basically can take much better low light photos with less noise.
M42 - Is a favorite target of astronomers
I asked Ford Amateur Astronomers if they could supply me with some good photos of M42 that show nebulosity, that is the gas detail of M42. I wanted to show what a typical photo by an astronomer could look like and compare it to the fast exposures and budget processing that Iʼm doing with a very basic image processing program, actually a $4 ipad App. My photos are shorter exposures and through my DSLR camera, so they canʼt look as good as these other photos, because they are capturing less detail to begin with. They are also being processed with a program that likely is using less bit depth and surely using less power than Photoshop which is a $700 program.
First up we have a photo that has a minor flaw, but it shows what a good astronomy camera can do.
James Lathom of the Ford Amateur Astronomy club took the above picture of M42 fairly quickly using an alt/azumuth mount.
He included the following comment: Shot this over the weekend as I was playing with the camera. Single star alignment Alt-az IOptron Mini Pro, so rotation was not good, and it was a 90sec single shot with an SBIG 8300C.
The next photo is from FAAC member, Tony Licata. Tony mentioned that this is one of many photos he has taken of M42. He said this is one that was layered. In other words, many exposures taken at different brightness levels were combined to create a composite image. The bright parts of the image were likely taken from a lower exposed photo and the fainter parts were from a higher exposure photo. The photo was merged and likely this was done inside Photoshop or some other expensive program marketed toward astronomers. Photoshop costs about $700, and there are a lot of plug-ins toward specific problems that can fix photos that astronomers are working on. Also there are other very expensive image processing programs as well that do other things to these photos, for example provide a better color balance.
There is a lot to love about the photo above. The amount of glowing gas and dust is amazing in this photo and the “running man” figure is clearly seen. The Pac Man figure is seen close to the trapezium. Iʼd really like to get more dust and glowing like these photos, but I wonʼt with short exposures with my Canon T1i. And I wonʼt get really nice processing detail using Filterstorm on the iPad. Filterstorm is fun to play with, portable and immediate. Itʼs power is far below Photoshop, but itʼs a $4 app.
I could talk on and on about Tonyʼs photo above. And I could talk a little bit about all the exotic steps that astronomers take, for example dark frame exposures, white frames and noise reduction. The use of color “curve” settings, which is one thing that Filterstorm has. There are exotic filters and plug ins as well which can be used in Photoshop to make an image more spectacular.
Letʼs get down to some really low budget and quick photos that the Canon T1i took and I toyed with in Filterstorm on the iPad.
The first one below is an image of the core of M42. You can see part of the Nebula and the pac man as well. This is a closer image and not wide field. The photo shows over saturation and noise. It also shows color shifts. Some of these due to experimentation I was pushing this trying to show more glowing gas and dust. Pushing it perhaps beyond the detail in the capture, creating noise.
There is more detail in some areas of this image, due to the high magnification, but overall there are more problems with this image. I actually did two kinds of radical manipulations of the original image and merged those two versions into this image. So this was a layer, but it wasnʼt a layer of two different original exposures. It could not show an increased dynamic range from multiple exposures, as I started with and only used one source photo. There is a lot of grain and noise in this photo as well, this due to my fast processing methods, the cheap app and limited light of that single 30 second exposure.
These are the two intermediate layers I used. Both fairly radical in their color shifting and offsets. I used curves and negative curve adjustments in some cases, meaning the RGB curves were pulled up and down at times. Imagers will often say donʼt use negative curves. Iʼve used negative curves to try to reduce sky glow or enhance the dramatic highlights and darken up parts of the image.
Next we have a pretty quick process I did using filterstorm on a wide field photos that is kind of like a 30 second exposure at 3200 iso. Rather than being a 30 second exposure itʼs a 330 second exposure at 200 iso. This means it was a long exposure but the sensitivity of the camera was set to a lower setting and that is still nearly the same basic kind of source photo as the earlier 3200 iso 30 second exposure I showed.
As you can see this photo is much darker than the earlier photos by other FAAC members. Itʼs a wide field photo, taken through the Meade F6 80mm refractor telescope at HJRO. There are problems of course with this, the gradient levels of colors are more severe, there is more vignetting, the brightness of details and dust wonʼt show up because there wasnʼt much detail captured to begin with. The image is over saturated as well.
You can barely see the “running man” in the photo below. FIlterstorm is fun app with instant gratification. Itʼs fun to play with and very portable as it runs on an iPad. It has limitations and the Canon EOS stock camera has limitations as well.
Now you can see why I'd like to get a dedicated astronomy camera like an SBIG.
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