John, I can't directly answer your questions, but have a couple of comments . . .
I am not sure if there is any logic or some practical reason(s) for your ordering of the components. But if it were me, I would put the fixed extension tubes on the camera, then the bellows, then the hellicoid, then the lens. This way all of the bits that can be adjusted for length/focus are at the front end. I can't see why you would reverse a 100mm macro lens. As I understand it, the lens reversal achieves a closer focus, but with everything else you have going, why expose the delicate rear end of the lens this way? If you didn't have a macro, then reversing a normal 50mm lens could make sense, but this seems unnecessary. This much extension is going to suck up every photon in the neighborhood; if the object you are imaging is too close to the surface of the lens element, that certainly complicates using flash to try to bring your exposure time within reason. Mark C. provided extensive discussions of his development of a workable system to capture his very fine snowflake images - you might want to check back in the archives, that could be helpful. As to whether more extension is ridiculous or just silly, my answer is that size per se doesn't matter. It is all in how you are going to use it and the results you are trying to achieve. If you keep going, at some point you will need extensive scaffolding to hold the system, several solar reflectors to add enough light to the system, and it will be difficult to move the system. Maybe a backpackable electron microscope would be more practical? But again, it depends on what itty bitty object you are trying to capture. stan On Jul 6, 2012, at 10:52 PM, John Celio wrote: > So I have this setup for shooting seriously close-up macro: > https://picasaweb.google.com/lh/photo/CIUtr5fsiR0rzShfFjE08NMTjNZETYmyPJy0liipFm0?feat=directlink > That is: Camera / helicoid tube at 49mm / bellows at 137mm (approx)/ > 12mm tube / 20mm tube / 36mm tube / generic reverse mount ring / D-FA > 100mm macro at 1:1 > > I've been meaning to share this for a while, because the last time I > tried using it in this configuration (sans rear cap on the lens, of > course), I was unable to focus on anything. I had a little flower > practically pressed against the glass at the end there but had to pull > the lens' focus back about halfway before I could actually focus on > it. > > So I'm hoping you guys can help me figure a couple things out: > > 1. Is it possible to have a lens so far away from the sensor plane > that focus can't be achieved? > > 2. What's the macro ratio of this setup as it is in the picture? > > 3. Does it make a difference if I have the lens reverse-mounted like > this rather than mounted normally on the last extension tube? > > 4. Would it be ridiculous or just silly to attempt to add more > extension in the future? > > > John > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
