Horst, welcome to the forum! Thanks for your information and photos, which are helpful. I'd be very interested in your results as you test this lens, though not for the vignetting issue in particular. You are the first person in this forum, so far as I know, to acquire an actual Mitutoyo tube lens. I don't know if you have anything to compare it with, but many of us would like to know if it offers any optical improvement over using a good camera lens.Horstl wrote:If there is interest, I can test the MT40 also on a 24x36mm camera - this will not work together, but it would be possible to determine the usable field. I think APS should be acceptable.
The reason I'm not especially interested in where it vignettes is that the MT-40 is not the Mitutoyo tube lens I would choose if I purchased one. It is supplied in a mount that makes it easy for "enduser integration," as Mitutoyo calls it. I don't know if it this lens optically the same as the much cheaper MT-1--which requires an additional mount, but as Enrico pointed out, has a larger image circle. The required mount is readily available from Edmund, looks easy to install, and does not add enough cost to bring it up to the price of the MT-40.
Here is the list of parts I was considering (I'm currently looking in other directions, but might come back to it). All parts listed below are from Edmund Optics, unless specifically noted otherwise. It incorporates some good suggestions made by Charlie Krebs, and information obtained from Edmund Optics via email and phone. For example, there were some things I couldn't quite grasp without dimensional drawings not available online.
A.) MT-1 tube lens: $628 (Stock number NT54-774) As Enrico said, this is the 200mm tube lens with the larger stated imaged circle. (There is also the MT-2, which is 400mm, effectively doubling the objective's magnificiation. Pity there is no 100mm version--which would permit objectives to be used at half their rated magnification and--perhaps--higher resolution than objectives intended for the reduced magnification.)
B.) MT-1/MT-2 C-mount adapter: $159 (Stock number NT58-329) This is a two-part adapter designed specifically for the MT-1 or MT-2 tube lenses—no custom parts required. The adapter clamps around the tube lens and provides standard C-mount threads on both sides.
C.) Mitutoyo to C-mount 10mm adapter: $33 (Stock number NT55-743) This allows the objective to be nicely mounted on the tube lens.
D.) Male T-Mount to Female C-mount adapter: $39 (Stock number NT58-753) This is for the camera side of the tube lens—bumps the thread size up to T-mount to permit a wider tube to avoid vignetting.
E.) T-Mount Extension tube 100mm: $33 (Stock Number NT52-296)
F.) 35-60mm T-mount Fine Focus Tube: $71.00 (Stock number NT52-300)
G.) T-mount to Nikon F-mount adapter:free to me, because I have several, but very cheap online. Not an Edmund part.
E, F, and G fill the distance between the tube lens and the sensor on my Nikon D200. Others would want the correct adapter for their camera mount—most of which should be easily available off of a T-mount. And you would want to adjust for your camera’s “register” (also called flange focal distance)—the distance between the lens mount and the sensor. For Nikons, it is 46.5mm.
For solid mechanical support, I’d add the following:
H.) Arca-Swiss plate from Chris Hejnar (not an Edmund part) Chris Hejnar makes some extra-thick Arca-Swiss style plates—iirc, ¾ or 1-inch thick. Probably overkill--and he also makes plates of normal thickness. In any event, I’d want everything mounted solidly on an Arca-Swiss plate of some kind.
I.) T-Mount 48mm Ring Mount with ¼-20 tapped hole: $65 (Stock number NT52-304) I’d probably get two of these. They would clamp around the T-Mount tubes and provide a thread for bolting them onto the Arca-Swiss plate.
J.) C-Mount 30mm Ring mount with ¼-20 tapped hole: $65 (Stock number NT52-930) Perhaps optional, but I'd like solid support on both sides of the tube lens. This would clamp around the C-adapter on the objective-end of the assemblage (might need to add a bit of C-tube to get room for the clamp) and provide a means of bolting it firmly to the Arca-Swiss plate. Due the difference in the size of parts "I" and "J," There would need to be some vertical support between the Arca-Swiss plate and this ring. I'd probably just start with a bolt, a nut, and a few washers, and then make something a bit better once I saw how this worked.
K.) Optional: Mitutoyo Filter Holder $69 (Stock number NT56-993)
This would be good for placing a polarizer (analyzer) in the light path. Alternatively, the polarizer could be placed in a simple C-tube, with retaining rings.
Additional thoughts: As experimentation with tube lenses continues, I'm leaning toward the use of a focusing helicoid rather than the fine focus tube listed above. My original thought was that focusing the tube lens would be done rarely and precisely. Now it appears that there may be good reasons to rack the tube lens farther from the sensor than 200mm, and that speed of such adjustment, rather than absolute precision, is more important. After just a quick look, it appears that most of the focusing helicoids are for M42, rather then T-mount. (These are both 42-mm, but have different thread pitches.) So some changes might be in order if that direction is undertaken.
Also, while the above approach would likely provide both mechanical and optical quality (at a price), it would not offer the ability to quickly change to tube lenses of different focal lengths. I'm increasingly seeing this capability as being very important.
Edited to correct mistake pointed out by Oskar (and various typos as I stumble across them).
Edited again 2-26-2010 to correct mis-typed Nikon register from 46mm (incorrect) to 46.5mm (correct).