Some things you should know before you start this project. Because there is no prism in this adapter images will appear upside down on the screen. This is expected with astronomical telescopes but it makes action or near action photography pretty difficult. It also take a little bit of getting used to for terrestrial subjects. There is a good deal of trial and error in getting the proper focal distances with this adapter system. This is particularly true if you are using telephoto extenders. I have found that I really did much better with telescopes than 35mm camera lenses in this because of the greater focusing range of most telescopes. I have included a setup and the picture I took to demonstrate some problems. |
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Adding a telephoto lens to the Agfa 1680 is a matter of creating a telescope that is an optical match for the camera. The primary lens of the camera is large enough that when you try to use the camera with a standard spotting scope or telescope you only get a small image in the center of the frame. |
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A telescope is the combination of a larger primary lens and an eyepiece that produces a visual image formatted for the human eye. Because the primary lens of the Agfa is larger than a persons pupil the eyepieces of most telescopes and binoculars are not adequate. It was my idea to use a larger lens for an eyepiece. |
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I used the normal lens of a 35 millimeter camera which has a large primary and secondary aperture and is able to fill the image on the Agfa screen. I still own a number of universal screw mount lenses and with experimentation the one that worked best is a Chinon 55mm f 1.2 lens. This is the heart of the adapter. The critical element in getting full coverage of the CCD is getting this 55mm lens as close as possible to the front element of the Agfa lens when you make the adapter. |
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Connecting the 55mm lens to the system requires a front and a rear adapter. I made the front adapter by combining the universal screw thread female adapter ring from a Vivitar tele converter with two step up filter adapter rings. I used a 49-52 and a 52-52. The 49 mm was for a Takemar lens which I originally used. I have added step down rings to use the Chinon lens which has a 55 mm filter thread. These created a housing that enclosed the universal screw thread adapter and it has held effectively securing the screw thread adapter with crazy glue. The crazy glue is very brittle and will break if the housing is not very snug fitting on the adapter. The rear adapter is made using the female thread end of a short extension tube and a 46-52 millimeter step up filter adapter. The fit on these was not as tight as the front adapter and I have connected them using epoxy. This is the choice when there is not a snug fit between the adapter rings. I cut the extension tube off to make the adapter as short as possible. I have two sets of extension tubes that I use to adjust the distance of the primary lens from the 55mm lens. |
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| When you use a telephoto extender the size of the image is reduced. This means you won't get full screen high edge quality images with most telephoto lenses. In the example of the 400 millimeter lens in the photo above the coverage of the frame is poor quality on the edges. I have included the photo taken with that setup to illustrate what I mean. I have left the image upside down and I ask you to note the drop off in quality at the edges. This is a reduced full frame. If you look at the photo of the camera above, this image is displayed on the LCD. |  |
| The importance of getting the eyepiece lens close to the front lens of the camera is something I cannot stress enough. I have included a couple of examples to illustrate. I originally used a Super-Takemar 1.8 55 mm lens as the eyepiece lens for the adapter. Here are a center and upper right corner of an image taken of a window screen at about 15 feet through a 500 mm Soligar Mirror lens. Note the fall off of quality in the corner. These are unretouched pieces of the original image. |   |
| Now here is the center and upper right corner taken with the Chinon lens. The difference between these two lenses is that the rear lens of the Chinon is about 1/8" closer to the Agfa lens than the Takemar lens. I tested this theory by putting a Haze filter on the camera and comparing pictures and the Chinon quality dropped when the thickness of the filter was added between the lenses. Note also the difference in magnification. |   |
| It is important that you keep the aperture of your 55 mm lens fully open and set to the infinity focus position to get the largest possible image into the camera. The up side is that you can do some powerful telephoto photographs with this camera. This image was taken using the Celestron 8 telescope (2000 mm) at a distance where I was not able to see what the bird was doing with my naked eye. |  |
