Equatorial mount for view cameragreenspun.com : LUSENET : Large format photography : One Thread
Hi, I'm using a Toyo field camera and I think that I'd like to try to do some astronomy photographs with 4X5. There are equatorial mounts available for telescopes, this is the "clock mechanism" that turns the telescope to offset the Earth's motion, necessary if the exposure is to be more than a few seconds long.
So I've been wondering if there are any equatorial mounts that attach to a camera in the same way a tripod does? I also plan on using medium format and 35 mm cameras as well - although not at the same time!
-- David Grandy (email@example.com), December 18, 1999
I'm guessing that just about any equitorial mount made for a telescope could be fitted with a threaded tripod thingy (can't remember the name of it) to screw into the bottom of any camera. Probably some of the manufacturers already make such an accessory. I've personally seen such an item but don't know what brand it was or if it was custom made. I doubt that anyone makes an entire equitorial mount specifically for cameras since there's really no need.
-- J.L. Kennedy (firstname.lastname@example.org), December 18, 1999.
I've not seen equatorial mounts made specifically for cameras. You may want to look into a device call a "barn door star tracker". This is a very simple device that can even be made at home. It is basically made of 2 one-by-fours (or sixes), about 12" in length that are attatched on one end by a hinge. About 3/4 the length away from the hinge it has a 1/4 by 20 bolt that is run through the bottom board and butts into the top board. When the bolt turns the "barn door" swings open. When the axis of the hinge is aligned with the polar axis and the bolt is turned at the proper rate, the barn door tracks the stars. Mount the device to a tripod, align the axis of the hinge to the pole, mount your camera on top and away you go! I've seen plans for this device in Sky and Telescope magazine (few years back). I was lucky enough to get one as a gift. It has the bolt powered by a small battery operated motor - pretty slick. It is not accurate with high magnification, but does fine with lenses up to 200mm (with 35mm film format). I've never tried putting my 4x5 on it. You should be able to find ads for purchasing such a device in the back of most astronomy magazines. Last I remember they ran about $120 (?).
-- Scott Bacon (email@example.com), December 18, 1999.
Not really an answer, but a related question: what is the longest exposure time of for example the moon that will not cause motion blur on the film? I figure there might be a formula (such as "handheld 35mm not longer than 1/fl seconds") based on the focal length.
-- Andreas Wickberg (firstname.lastname@example.org), December 19, 1999.
You might be better off talking to an astronomy forum. Many astronomers also use cameras. You might pick up an astronomy magazine in a local shop.
Many telescope mounts can also take a 35mm camera, often as a piggy- back on the telescope.
For hand-holding a camera, the moon moves so slowly you can regard it as stationary, and just use whatever rules you normally use for hand- holding speeds. It's a bright object anyway, and doesn't need long exposures.
To be more technical:
The moon moves about 15 degrees in one hour. It is about 0.5 degrees wide, so it shifts by its own width in 2 minutes, ie 120 seconds. If you used a very long lens (about 1000mm) to capture the whole moon in the full frame, you might want the blur to be no more than 1/1000 of the width, so the exposure should be no longer than 120/1000 seconds, ie about 1/10s.
-- Alan Gibson (Alan.Gibson@technologist.com), December 19, 1999.
It may not be the best choice for a large format camera, but I encourage you to do a web search on "barn door mount" and find instructions on building one yourself. It's quite fun and very satisfying. I made one from two pieces of 1x4 lumber. a hinge and a couple of screws. With the addition of a cheap ball head, I used this rig to take some very good pictures of comet Hale-Bopp a few years ago. The camera, BTW, was a Mamiya 220 with an 80mm f2.8 shot wide open.
A LF camera may not be your best choice for astro work. Most LF lenses are SLOW (f5.6 or slower), and slower lenses mean longer tracking times. The Hale-Bopp pics, were, as I recall, on TMAX 400 pushed two stops, with about 1 minute exposures. Anything I shot at 4.5 or slower was never satisfying.
Kodak used to make a LF Aero-Ektar, which I think was 180mm f2.5. You see them on eBay from time to time.
Don't mean to discourage you from trying.....quite the contrary! I just want to to offer some pointers to success. Clear skies!
-- Kevin Bourque (email@example.com), December 19, 1999.
I do amateur astronomy and astrophotograghy with 35mm and medium format equipment, but not yet large format (saving the $$$$ until I can). There are a large number of equatorial mounts available and almost all of them have the ability to mount a threaded adapter (usually 1/4-20). The cheapest mount I know of (I am considering getting one for a small telescope I have) that will (probably) hold a 4x5 camera is the Orion SkyView EQ Deluxe (~$250 plus some for a few accesssories, plus more if you want the motors, http://www.telescope.com). Above that price there are plenty of mounts available, and you can easily spend as much as or more that a the cost of a new, high quality large format lens. Note that because equatorial mounts must move, they have to be heavier/stronger to support the same weight compared to a normal tripod, plus you are usually (for telescopes) working are high magnification so any shaking is magnified.
A barn door type mount could also work, although the issue of how much weight you can put on one becomes an issue. They are a pain if you don't have a motor (mine does not) because you have to stand there and turn the bolt the whole time, but they are very cheap. Complete plans and usage instructions for one can be found at (they call it a "scotch mount") http://ourworld.compuserve.com/homepages/pharrington/scotch.htm
Another issue to be aware of is that polar alignment, guiding, and focus (ever tried to focus on ground glass in the dark?) are critical issues for successful astrophotography. I don't see lens speed as crtical as most telescopes are relatively slow. It just means longer exposures, again bringing up the issues of polar alignment and guiding and focus, plus reciprocity failure.
The field of amateur astronomy is much larger than the large format photography field, and there are tons of on-line sites with information about astrophotography technique. I suggest doing some more research on those sites and/or a book on the subject. The only people I have run across on-line using 4x5 film for astrophotgraphy are Brad Wallis and Robert Provin (http://voltaire.csun.edu/wallis_provin.html), but they do not use a view camera but rather a $7000 telescope (i.e. lens) on a $10000 mount. Most people stop at medium format since there are more films suitable for astrophotography (without resorting to special techniques like hypersensitizing) in that size. My favorite is Kodak PPF 400 color negative film.
Astrophotography is a difficult art, but the results can be spectaular when you do succeed. Good luck.
-- Brendan Fisher (firstname.lastname@example.org), December 20, 1999.