This post is the result of a query about how to use the Spiratone 0.15X Fish-eye adapter on another post (link). I started to answer the question there, but hated to intrude into someone's post with a lengthy marginal discussion. I have put coverage of the Spiratone Fish Eye Auxiliary here on the Classic Manual forum because this auxiliary lens was designed, made, and sold in the days of classic manual film cameras. There are some more modest modern equivalents that will pop up in maddening frequency if you try to search for "fisheye" on Google or eBay, but the finish and character of the Spiratone adapter is on another level in my opinion. This was an item developed for and used on film cameras in its day, although it is adaptable, of course, to modern digital cameras as well. A longer review of the Kenko version of the auxiliary is to be found at (link). I caution also that the following account is entirely arrived at pragmatically by trial and error. I have no manual for these lenses, nor could I find one at Butkus or on Google. The Spiratone 0.15X and its Samigon and Kenko kin were fitted onto the front filter screws of whatever lens it was mounted on. How much and what kind of fisheye it was depended on the focal length of the lens it was mounted on, as well as the format of the film/sensor. Here is the text of an original ad for the device: With it you can cover a full 180º;aImost three times the angle of a 35mm wideangle, four times the angle of a normal lens (it's equivalent to an 8mm focal length)! There's even more: the very same lens works with most cameras - 35mm (rangefinder and single lens), twinlens, 4X5', even 8x10" view cameras! - by means of different fittings. And with normal and telephoto lenses; and when used on 35mm SLR's - you can view through your finder in the usual manner: the mirror need not be locked out of the way. Nine element design. Quality: Thousands of these tenses are already in use by professional, industrial, advertising, TV and motion picture photographers -- pictures taken with the Spiratone aux. Fish-eye have appeared in every major news, business, photography magazine. Weighs only 10 oz. Sharpness range (at maximum opening) from 3' to infinity; closest subject to-fish-eye distance 1/2 (HALF) inch!Aside from a special domed cap necessary to protect the protruding front lens element, the device comes in two parts: the nine-element adapter itself and, just as critically, the adapter unit needed to actually mount it on a lens (the "fittings" referred to in the ad text). Without one of the "fittings" (the YELLOW arrow in the picture) it is very difficult to impossible to actually use the lens. Unfortunately, the fittings and the lens proper have often been separated by people who had no idea what this was. I do not recommend buying the lens without one of the fittings. The base of the lens proper has a screw mount that is 26mm -- aside from the fittings actually made for this item, it is extremely difficult to find 26 to 52mm (for example) step down rings, or any 26mm to anything rings, for that matter. It might be possible to get one made, but the price for this would be very high, more than the price of the fish eye even at its highest selling price. In my case I did buy the Spiratone 0.15X without a fitting, but already had a fitting for the Samigon unit. Later, I was lucky enough to find an eBay seller who offered a few of these from some old stock he had found. OK, so you've got the lens with an adapter. The one shown in the picture is a 52mm adapter. Step-down adapters can be used to fit the auxiliary lens to larger (than the fitting) lenses. While it's not ideal, step-UP rings can be used to adapt to smaller diameter filter threads. Here, the auxiliary lens is the equivalent of the "camera" in the "camera>filter" order in step-up/down rings. The next step in using the auxiliary lens after mounting it on the filter threads of a lens on a camera, is to set the focal length of the lens on the auxiliary (the GREEN arrow). For a 35mm lens, set the dial to 35. The focal length range is from 30mm to 200mm. Presumably the higher settings are for those large format cameras that this auxiliary can be used on. In general the optimum effect of 180º; coverage (more or less) is obtained at the 'normal' focal length for the image size (e.g., 28 or 35mm on an APS-C format, 50mm on a 35mm format, and so on.) I have always set the fish-eye auxiliary to the actual focal length of the lens, not the "equivalent" on a format. Otherwise, you'd have to set the auxiliary lens at 50mm for a 80mm on a 6x6cm format, and that's not likely to be how it operates. Before digital, conversion factors between different formats were seldom spoken of. I've always used the widest aperture available for the primary lens on the camera proper. Setting the focal length on the auxiliary will alter the display of the f/stops on the auxiliary lens itself. For example, on a 35mm lens, the adapter can be set to apertures of f/4 to f/16. At 200mm setting, the auxiliary will allow f/stops from f/22 to f/90. (!). I confess I have no idea how you would calculate exposure on a camera without through-the-lens metering. Perhaps that is already calculated in the f/stops that display so that you would just set your film speed and see what shutter speed you would need at f/5.6, f/90, or whatever. In any case, I have only used these lenses with TTL metering set to Aperture Priority. There are times, after all, when totally manual is harder. The first picture is of the Spiratone ad from Modern Photography of February, 1970, and a picture of the lenses with color coded arrows for different functions as referred to above.