Re: My super-duper macro setup... that doesn't appear to work as hoped?
On 9 July 2012 03:25, Mark C wrote: > I have never found a good explanation of what is going on when you reverse > mount a lens. After using reverse mounted lenses quite a bit, I can say that > reversing the lens allows you to focus closer. It also seems like the > subject to lens distance does not change as much as you'd expect when you > reverse mount and change extension. But I've never learned the theory. If the lens is a symmetrical design without any floating or FREE groups of elements then the formula works equally whether the lens is mounted normally or reversed. The purpose of reverse mounting in this case is not to gain magnification, because it won't. The theory behind it is that a lens in regular, non-macro use is closer to the focal plane than the subject plane and is best corrected for that circumstance. When you exceed 1:1 magnification the lens becomes closer to the subject plane than the focal plane, and gets out of the range for which it is best corrected. Reverse mounting it goes some way towards restoring its balance. That is, it makes the plane of focus on the rear element side nearer than the plane of focus on the front element side, as it should be. There's no cover-all formula for reverse-mounted non-symmetrical lenses. A telephoto lens is almost useless reversed. Imagine putting a negative dioptre filter in front of your lens. It defeats the purpose of photomacrography and is often impossible because the subject plane falls inside the lens. But reverse mounted wide-angle lenses are famously effective. Keep in mind that, at least in SLR mounts, they were originally known as inverted telephoto lenses and are best corrected for large reductions. Reverse mount one of those and you have a true telephoto (but still of short focal length) that's best corrected for large magnifications. regards, Anthony -- 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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
On Sun, Jul 8, 2012 at 10:25 AM, Mark C wrote: > ... I have never found a good explanation of what is going on when you reverse > mount a lens. After using reverse mounted lenses quite a bit, I can say that > reversing the lens allows you to focus closer. It also seems like the > subject to lens distance does not change as much as you'd expect when you > reverse mount and change extension. But I've never learned the theory. It's a matter of how reversing a multi-element lens re-positions the lens' primary nodal point for light passing through the lens in the reversed direction. Perfectly symmetrical designs will reposition the primary nodal point symmetrically when the lens is reversed, but very very few SLR lenses are perfectly symmetrical. Reversing the lens in most cases not only reversed the lens elements but adds some extension due to migration of the primary nodal point. It's hard to calculate the shift ... -- Godfrey godfreydigiorgi.posterous.com -- 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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
Glad that I could help. There are two basic formulas that can help with macro work. You probably know them but if not - the first is that when you put a lens on extension the magnification equals the extension divided by the lens's focal length. So a 100mm lens on 200mm of extension = 2x lifesize magnification. There is a somewhat complicated formula to estimate the working distance, but you can approximate working distance by dividing the lens focal length by magnification. SO a 100mm lens on 200mm of extension would have a working distance of 50mm. A 50mm lens on 200mm of extension would have a magnification of 4x and a working distance of 12.5mm (50 /4). The formulas are approximate - they would work for a single element lens but that obviously not the case with a regular camera lens. But they would get you to a good approximation. I have never found a good explanation of what is going on when you reverse mount a lens. After using reverse mounted lenses quite a bit, I can say that reversing the lens allows you to focus closer. It also seems like the subject to lens distance does not change as much as you'd expect when you reverse mount and change extension. But I've never learned the theory. Apparently the D-FA is not using simple extension to help it focus more closely which is why it does not focus once the internal focusing mechanism is set beyond a certain point. I'm not sure what is going on there. Mark On 7/8/2012 12:09 AM, John Celio wrote: Mark, this is exactly the response I was hoping for. Thank you *very* much. I never would have thought the lens would be the part causing the problem, nor that wider angle lenses would produce greater magnification (though that kinda makes sense now that I think about it). I will try it with my FA 50 (my only other small prime with an aperture ring) right now. Thanks, John On Sat, Jul 7, 2012 at 6:57 PM, wrote: That is basically the same setup that I use for my snow crystal shots, except I use a 50mm lens reverse mounted. In fact, it is so simlar I just now pulled it out of the closet, set it up and put my D-FA 100mm macro on it. I have 300mm of extension (tubes and bellows) with the lens reverse mounted at the end. Your focusing problem lies in how how the D-FA 100 close focuses. I had no problem getting a shot in focus when the lens was set to infinity, and actually had ample working room. As I adjusted the lens's focusing mechanism I quickly was unable to get anything into focus. Obviously, something about the internal focusing on the D-FA causes a problem with it reverse mounted. Focusing on a ruler, with the D-FA 100 at infinity, and using a full frame 35mm film camera (also pulled from the closet), I saw 8 to 9 mm in the view finder. SO I reckon it to be about 4x life sized. With the 50mm I routinely use on this setup, the finder on the full frame camera shows about 4 mm, so about 8x. If you really want to get extreme get a short and fast lens and use it on all that extension. A 24mm on 300mm of extension would result in 16x or so magnification. Set the lens to infinity or use one that does not use internal focusing. Regarding protecting the delicate rear element of the lens - put a short extension tube on the rear lens mount. It will serve as a hood and also offer some protection to the rear element. To help with focusing - set up your rig in a dark place. Put a bright flashlight on the finder (where your eye would go). It will project a little rectangle of light that you can use to align your subject and get a sense of focusing distance with (when the rectangle is sharp, you are in focus.) Have fun - Mark -- 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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
Mark, this is exactly the response I was hoping for. Thank you *very* much. I never would have thought the lens would be the part causing the problem, nor that wider angle lenses would produce greater magnification (though that kinda makes sense now that I think about it). I will try it with my FA 50 (my only other small prime with an aperture ring) right now. Thanks, John On Sat, Jul 7, 2012 at 6:57 PM, wrote: > That is basically the same setup that I use for my snow crystal shots, > except I use a 50mm lens reverse mounted. In fact, it is so simlar I > just now pulled it out of the closet, set it up and put my D-FA 100mm > macro on it. I have 300mm of extension (tubes and bellows) with the lens > reverse mounted at the end. > > Your focusing problem lies in how how the D-FA 100 close focuses. I had > no problem getting a shot in focus when the lens was set to infinity, > and actually had ample working room. As I adjusted the lens's focusing > mechanism I quickly was unable to get anything into focus. Obviously, > something about the internal focusing on the D-FA causes a problem with > it reverse mounted. > > Focusing on a ruler, with the D-FA 100 at infinity, and using a full > frame 35mm film camera (also pulled from the closet), I saw 8 to 9 mm in > the view finder. SO I reckon it to be about 4x life sized. With the 50mm > I routinely use on this setup, the finder on the full frame camera shows > about 4 mm, so about 8x. > > If you really want to get extreme get a short and fast lens and use it > on all that extension. A 24mm on 300mm of extension would result in 16x > or so magnification. Set the lens to infinity or use one that does not > use internal focusing. > > Regarding protecting the delicate rear element of the lens - put a short > extension tube on the rear lens mount. It will serve as a hood and also > offer some protection to the rear element. To help with focusing - set > up your rig in a dark place. Put a bright flashlight on the finder > (where your eye would go). It will project a little rectangle of light > that you can use to align your subject and get a sense of focusing > distance with (when the rectangle is sharp, you are in focus.) > > Have fun - > > Mark -- 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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
On 8 July 2012 02:40, Stan Halpin wrote: > I would put the fixed extension tubes on the camera, then the bellows, then > the hellicoid, then the lens. For a moment I had the same thought, but then I remembered that in extreme lens extension, especially for macro work, the first preference is to focus by moving the whole rig back and forth so you don't disturb the reproduction ratio. The second preference is to move the focal plane, which in this case means the camera body ,which the helicoid tube behind the bellows achieves. Only if all other options are impossible should you rack the lens out, as doing so often means having to make gross corrections to the camera position, as well as risking contact between the lens and the subject. Personally, I think John's rig is probably exceeding best practice for this lens. He's got the lens at about 3.5x focal length extension (231.5mm ~ 251.5mm of tube & bellows plus the 1x focal length inherent in the lens itself) Extending the lens helicoid itself is doing some unknown thing, but it's not adding extension to the main focusing group of the lens, just extending the FREE element, which in reverse position may or may not serve any purpose. For big magnifications an enlarging lens often does a better job because of it's conventional symmetrical design. Modern camera lenses with floating elements and such can quickly get out of their design/performance envelope when they're put into non-standard configurations. That said, a wide angle lens reversed can give good results at spectacular magnifications, although YMMV. regards, Anthony -- 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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
On 7/6/2012 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 That is basically the same setup that I use for my snow crystal shots, except I use a 50mm lens reverse mounted. In fact, it is so simlar I just now pulled it out of the closet, set it up and put my D-FA 100mm macro on it. I have 300mm of extension (tubes and bellows) with the lens reverse mounted at the end. Your focusing problem lies in how how the D-FA 100 close focuses. I had no problem getting a shot in focus when the lens was set to infinity, and actually had ample working room. As I adjusted the lens's focusing mechanism I quickly was unable to get anything into focus. Obviously, something about the internal focusing on the D-FA causes a problem with it reverse mounted. Focusing on a ruler, with the D-FA 100 at infinity, and using a full frame 35mm film camera (also pulled from the closet), I saw 8 to 9 mm in the view finder. SO I reckon it to be about 4x life sized. With the 50mm I routinely use on this setup, the finder on the full frame camera shows about 4 mm, so about 8x. If you really want to get extreme get a short and fast lens and use it on all that extension. A 24mm on 300mm of extension would result in 16x or so magnification. Set the lens to infinity or use one that does not use internal focusing. Regarding protecting the delicate rear element of the lens - put a short extension tube on the rear lens mount. It will serve as a hood and also offer some protection to the rear element. To help with focusing - set up your rig in a dark place. Put a bright flashlight on the finder (where your eye would go). It will project a little rectangle of light that you can use to align your subject and get a sense of focusing distance with (when the rectangle is sharp, you are in focus.) Have fun - Mark -- 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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
When you reverse a lens the focus point is very close to the rear element. With your setup the focus point is somewhere inside the lens if not inside the bellows, (yes I know that's not technically true but the hyperbole expresses the problem), use a longer lens and don't reverse it if you want to use that setup. If it were me I'd just use the 12mm extension and the bellows, with the 100mm the focus point will be just a few millimeters from the front of the lens. On 7/6/2012 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 -- Don't lose heart, they might want to cut it out, and they'll want to avoid a lengthly search. -- 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.
Re: My super-duper macro setup... that doesn't appear to work as hoped?
> 1. Is it possible to have a lens so far away from the sensor plane > that focus can't be achieved? yes. > 2. What's the macro ratio of this setup as it is in the picture? no idea. only way to know for sure is to focus an image and then shoot a fine ruler to calculate it. > 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? I'd back off on the setup until you can focus on something first. Then see where you can go from there. The setup looks overly complicated to me. -- Godfrey godfreydigiorgi.posterous.com -- 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.
My super-duper macro setup... that doesn't appear to work as hoped?
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.
