A CFW8 cover plate adapted for the MWFIA. A Nikon lens on the MWFIA.
The Adapter plate replaces the standard plate, on the CFW8, for wide field imaging.
The MWFIA will be available around the end of May.For ordering informaiton, click on this link.
A CFW8 cover plate adapted for the MWFIA. A Nikon lens on the MWFIA.
The Adapter plate replaces the standard plate, on the CFW8, for wide field imaging.
The MWFIA will be available around the end of May.For ordering informaiton, click on this link.
Barnard's Loop (Click on
image to see larger version)
Image published in Sky&Telescope Magazine,
May, 2001
New: Vela Supernova Remnant image by John Gleason using the MWFIA: http://www.celestialimage.com/page119.html
(More images at bottom of page)
Wide Field Imaging with CCD Cameras
Article By Steve Mandel
As an astrophotographer using film for many years, I loved to do wide field imaging. It was less demanding than high resolution work and gave good results quickly. I started by doing piggyback astrophotography and my first published image in Sky&Telescope was in 1984. It was shot with a 50mm lens, using a 35mm camera mounted on top of a C8. It showed the summer Milky Way, with the top of pines in the foreground, from Yosemite.
I purchased a used 8” Celestron Schmidt camera and pursued wide field imaging. with it. The excellent resolution, fast speed (f/1.5) and wide field (4.5 x 6.5 degrees) made it a wonderful instrument to capture large objects with short exposures. As better films, notably Kodak Technical Pan for b&w and then Kodak Pro 400 in color, became available the limitation of resolution by film grain with the Schmidt disappeared and I was now limited by resolution and seeing. I had a ball shooting with the Schmidt that culminated with Comet Hale-Bopp images-the resolution was so good that I have a 16x20 color print in my office, with no visible grain.
In addition, I purchased some used medium format equipment, Pentax 67, and did quite a bit of wide-field imaging from the US, and on two trips to Australia. The large size of the film and big lenses gave very wide and well-resolved pictures. This allowed for even bigger fields, with the Pentax I was able to get a whopping 24 x 31 degree field.
About this time, CCD cameras started to gain popularity. I was intrigued and got an ST6 from SBIG. As I quickly learned, the small size of the chip and the large size of the pixels didn't make for good wide field imaging.
With the release of the ST7 and then ST8E chips, the size of the chip stayed almost the same but the pixels shrank from 24 microns to 9 microns, and with the E chips the sensitivity increased. This made for much higher resolution images that could be shot with much shorter focal lengths. I began using my CCD camera with smaller and smaller focal lengths but was frustrated because I was still getting nowhere near the wide fields available with film.
I acquired another CCD camera, the FLI 1024 “Dream Machine”. Although it has 24 micron pixels, the large size of the chip (24 mm square) would make for a much bigger field. I was able to eliminate most of the square pixel look by upscaling in Photoshop. I got acceptable results but I couldn't push it too much more with those large pixels. I really wanted to take advantage of the small pixels and still get a wide field image, especially since SBIG announced that they were coming out with a camera that would have 6-micron pixels, upping the resolution once again. The arc second to pixel ratio is still quite high but this is very fun anyway.
The other issue in shooting wide field with a CCD camera is that if you want to produce a color image you must shoot images with red, green and blue filters and combine them digitally. The filters must be between the camera lens and the chip so as not to alter the light path as it comes through the lens elements. Also, I enjoy using a Hydrogen-alpha filter because of its ability to greatly resolve nebulas and related objects. However, introducing a filter holder, like the CFW8, supplied by SBIG, would put the chip out of the focus range of a 35mm camera lens.
To solve this problem I designed a low profile adapter for a C-mount that would hold a Nikon lens. I chose Nikon because their lenses, even the newest, can be used on full manual mode (and my wife had a couple for her camera). I then mounted it with countersunk 4x40 screws through the back of the CFW8 front plate. This brought the lens close enough to focus on the chip and use the SBIG filter wheel.
I turned the wide-angle CCD camera towards the sky and I was astounded by the views it presented, especially those done with the Hydrogen-alpha filter. I had never seen some of the objects I was imaging. For the first time I saw the full extent of Barnard’s Loop in Orion and an image of Sh2-264, the supernova remnant between Betelgeuse and Bellatrix, it looks like an alien face from a sci-fi movie. With a 50mm lens I got a field of 10 degrees x 15 degrees! The resolution begins to really drop off after this but the potential is great and a new field, no pun intended, has opened to CCD imagers.
The next leap will come shortly as the price of bigger chips drops.
You can get chips that are 36mm square and have 9-micron pixels but the
cost is in excess of $25,000. As the price of these chips comes down,
the number of wide-field CCD images is certainly going to rise. I’m looking
forward to that.
Steve Mandel operates Hidden Valley Observatory
in the hills above Santa Cruz, California. He can be
reached via his web site at www.galaxyimages.com.
The adapter is currently undergoing final design and testing. It will be initially available only for Nikon lenses and sold through RC Optical Systems in the near future.
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