rdenney
25-Jun-2009, 11:25
Edmund Scientific sells a number of fresnel lenses of various sizes and focal lengths.
I have a Sinar fresnel (actually, a couple of them) that seems to work well with "normal" lenses in the 150-180mm range on my 4x5 camera. With 47 and 65mm lenses, however, the angles are too shallow and the fresnel is not effective for viewing the corners (which is the whole point of using a fresnel in the first place). Clearly, the focal length for the stock fresnel is too long for those ultra-short lenses.
One possibility is to call Bill Maxwell and see if he will make a fresnel to fit the Sinar fresnel frame that has a much shorter focal length than the stock fresnel. What I know of his prices has held me back, though I know his product will be superior in every way.
But in another thread, someone pointed to Edmund Scientific's page of fresnels, and I see a 5x5" fresnel lens with a focal length of 2.8 inches, here (http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=2040). This is still a little long for the 47, but should be right in the ballpark for the 65 (and still an improvement over the stock fresnel for the 47). Am I understanding the focal length of these things properly? Has anyone tried one of these? The pop-out fresnel approach used by Sinar makes it easy to use one for composition, but then remove it if necessary for critical focusing with a loupe, so the 100-ridge/inch spec of the ES fresnel should not be a problem (even assuming the stock lens is better, which I doubt). If it worked, I would cut it down to fit my second Sinar holder. Yes, the Maxwell would be better, but if this could work I could be using it while waiting to spend the money on on the Maxwell.
For $42, it seems worth a try, but if someone has already done it, then they'll likely know something I don't.
Rick "seeking comment" Denney
I have a Sinar fresnel (actually, a couple of them) that seems to work well with "normal" lenses in the 150-180mm range on my 4x5 camera. With 47 and 65mm lenses, however, the angles are too shallow and the fresnel is not effective for viewing the corners (which is the whole point of using a fresnel in the first place). Clearly, the focal length for the stock fresnel is too long for those ultra-short lenses.
One possibility is to call Bill Maxwell and see if he will make a fresnel to fit the Sinar fresnel frame that has a much shorter focal length than the stock fresnel. What I know of his prices has held me back, though I know his product will be superior in every way.
But in another thread, someone pointed to Edmund Scientific's page of fresnels, and I see a 5x5" fresnel lens with a focal length of 2.8 inches, here (http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=2040). This is still a little long for the 47, but should be right in the ballpark for the 65 (and still an improvement over the stock fresnel for the 47). Am I understanding the focal length of these things properly? Has anyone tried one of these? The pop-out fresnel approach used by Sinar makes it easy to use one for composition, but then remove it if necessary for critical focusing with a loupe, so the 100-ridge/inch spec of the ES fresnel should not be a problem (even assuming the stock lens is better, which I doubt). If it worked, I would cut it down to fit my second Sinar holder. Yes, the Maxwell would be better, but if this could work I could be using it while waiting to spend the money on on the Maxwell.
For $42, it seems worth a try, but if someone has already done it, then they'll likely know something I don't.
Rick "seeking comment" Denney