I had a good read of the GIGAmacro site. In there equipment list I was intrigued to notice they were using a telecentric adapter. I had no idea what that is ( to be honest I probably am only slightly wiser if at all). So I did some googling I discovered a telecentric lens keeps the same magnification no matter what the distance. Important aside When I have been creating stacked photos I noticed that as the stackshot focusing rail moved between the shots the size of the image would change albeit slightly.
So I then found this: thread on the photomacrography web site:
Reading it, not always understanding everything, I realised I had every thing required to try out a Telecentric stack. I took the front mount from a spare parts minolta bellows and mounted it on my Tilt shift bellows. I then tried a variety of different lenses before finding the ideal combination ( of what was in my lens tool box) Here it is all set up:
Ideal combination was front lens Olympus zuiko 135mm F4.5 bellows lens. I set it at 4.5. The rear lens acting as the subject infinity aperture Minolta MD 100mm F4 set at F 22. I then adjust the positioning of the two lenses as was recommended by the photomacrography thread. Namely I looked through the olympus lens and adjusted the positioning of the lenses so the Minolta's aperture was in focus by my eye. I couldn't actually see the blades( in silhouette) so I adjusted to get a very sharp outline of the aperture hole. Note: all this was done over several different attempts to get it right.
During the set up trial and error experimentation it became clear the vignetting I was seeing on my FF sensor wasn't going to go away so I set the camera to APSs capture mode. After 3-4 attempts I saw the effect I was looking for with a 20 shot sequence there was absolutely no change in the magnification as the focusign rail moved between the shots: Heres the resultant picture (I used and Ancient because of the strong #d nature of the coin). Processing was by Helicon soft using the depth map method. Any suggestions comments greatly appreciated. Of course the lighting needs attention but remember this was, for me a proof of concept trial.
I am guessing that with the right knowledge and equations you could actually calculate accurately the distances so as to get a very accurate 3d rendition with this telecentric set up.
First, I want to thank you for wasting the rest of my day, because now I have to go out and learn all this stuff.
My initial question is, do non-telecentric coin imaging techniques actually introduce magnification problems? This is a wonderful solution to an optics geek () but is there really a problem to solve?
SsuperDdave I am just getting my head around it so I think you will have a better chance of understanding it before I do. telecentric lenses show objects at their true size if you have two 5mm cubes and place them so that one is closer to the lens than the other. A normal lens will see the cube that is farther away as smaller. A telecentric lens will see both cubes as the same size. You loose the distance perspective but you apparently gain a lot more. telecentric lenses as I understand it are brilliant for applications where you are measuring distances You don't need to know the distance from the telecentric lens to take measurements. My limited understanding is without the telecentric convertor the Gigamacro system would require considerably more computing power to do its job. What I read on the Photomacrography site is telecentric lenses make stacking and stitching easier. There is one problem. the object being photographed must be smaller than the diameter of the front optic. But that sounded ideal for coins to me.
I have finally found a use for that monster Schnieder Kreuznach 210 mm enlarger lens(72mm filter thread). I tried it out about 30 minutes ago and it apperars to work well in a telecentric set up( with the minolta Bellows lens behind it
I published my 2x Super Macro review over on PM forum and there is some discussion about measuring telecentricity in that thread. I initially thought the 2x may be telecentric because the stuck red pixel on my HRT2i was rendering as a single dot rather than a locus of dots that move based on the magnification changes. But measurement showed that t 2:1 there was a 14 pixel shift across 9mm FOV over 150um vertical displacement, so the lens is not really telecentric at 2:1.
AK, I'm very interested in seeing what you did in order to build a telecentric system. I tried it one time with a pair of 75ARD1's but it was not all that successful. Could you perhaps outline the process you learned from the PM thread? Or is it better to just review that thread?
Contact me for photographic equipment or visit my home page at: http://macrocoins.com
Its probably better you review that thread. To be honest I think I fluked it through ignorance. It was really hard to position the lenses to get the effect. I followed the guidelines in that thread. Positioning the front lens is the hardest thing to do. I placed the bellows rail with the two lenses mounted and sighted through the system looking from the front lens to the back( reverse of what the camera does) I then adjusted the bellows( I found fully closed worked best in the end) and the front lens until the edges of the aperture blades in that rear lens were as razor sharp as I could get them. I then remounted the bellows on the copy stand and focused on a coin. To test If I had set it up right I moved the Camera arm up and down. When I had it right the coins image would stay the same size ( of course going out of focus) If I was out by a fraction the coins image would change size as soon as I moved it. My bellows Rail is mounted by three screws to a 250mm Arca plate I have to say that mounting makes it heaps easier to adjust the lenses and bellows. I can remove the bellows with lenses from the the copy stand make the adjustments with the rail sitting horizontally. Then remount it into the arca clamp on the stand. I first tried to make the adjustments with the bellows on the copy stand and it was diabolically hard to do, in other words I couldn't. That 20 shot stack was amazing to take ( for me) as through the whole movement the coins image stayed exactly the same, the processing was noticeably faster than usual. For me that image even with the glarey bits is one of my better results. I think those with more experience could really use this technique. I tried the SK 210 after my first successful attempt I was impressed with the performance I can get 3/4 sized images of Thaler sized coins, The SK210 has such deep depth of field even in this set up stacking isn't necessary. However setting up the SK was much harder!
Edit: Earlier int he week I found one person had adapted a lens to be telecentric by removing an aperture system from a kaput lens and then mounting it in an adapter so that it was sitting at the registry distance of the lens being used. I was going to try that technique but I didn't think I had the skills to get the mounting right.
I had another go with the Schneider Kreuznach large format enlarger lens ( 210mm 5.6) as the front lens and the minolta 100mm F4 bellows lens as the rear aperture lens. Heres the set up both lenses are mounted on the bellows rail the SK is on a spare front bellows mount. You can see there is a huge gap between the two lenses:
(Yes the bellows rail isn't truly vertical I fixed that after taking the above shot) I had a medal that was 47.66 mm in diametre just smaller than the front optic of the SK. Heres a demo shot taken with the minolta at between F11-F16( SK was wide open)
It looks pretty good until you examine a 100% crop. From what rmpsrmps showed in another thread this looks like diffraction:
I then took a series of test shots at steadily wider apertures finally ending up with the Minolta Bellows lens wide open(F4) there was considerable improvement but I think diffraction is still there:
With the minolta at F4 the DOF is such that the high points of the medal are out of focus....so despite my impressions in the first post, with this lens set up stacking even for a 47.66 diametre medal is necessary.
Now I am absolutely sure I obtained the telecentric effect with the Olympus 135 mm and Minolta 100mm bellows lenses. I am not so confident with the set up in this post. On the weekend I will post some questions on the Photomacrography site to clarify.
The issue that I didn't correct in post processing is the light fall of across the field of view.
Late afternoon edit: I tried a 25 shot stack. Heres a 200% crop. I am definitely getting the telecentric effect with the SK210.
I am really pleased I kept the SK210mm the magnification is low but the resolution is phenomenal!
I had to have a few more attempts: same set up as in the last photo. A stack of 25, of a Silver dollar sized medal(this shot really recommends the technique IMHO):
I did some testing of the Venus 2x and found that it was not telecentric at 2x. The technique was to simply measure the distance on a calibration slide, then move the ref plane and measure it again. Any fixed object distance can be measured. If the scale does not change between measurements, the lens is telecentric. I verified this technique using the Nikon MM5x objective, which is known to be telecentric. I did not see even a single pixel of scale shift over a 150um Z-range. I published the results over on PM forum in my Venus 2x review thread...Ray
Contact me for photographic equipment or visit my home page at: http://macrocoins.com
Thanks I had a quick look on ebay for a calibration slide. I found there were direct types. What sort are you using? I presume I can place the calibration slide anywhere in the optical path(I was thinking immediately behind the SK( thats the easiest most secure place). I had some of my questions answered ( by my self) I was very please to get some use out of the SK but I was really wondering was it actually doing anything I had never thought of using such a set up to bring the SK,s minimum focus down. My main concern was whether I had just created a fancy set up that looked interesting but was not really performing. The 200% crop was the one piece of evidence that told me I had a truly useful optical system system( even if not telecentric). The minolta 100mm F$ bellows lens on its own can not produce such resolution, while the SK on its own has such a long lens to subject distance( around 80cm) on a single bellows that it was impractical. Putting it on two bellows did help but introduced so much vibration into the optical path as to be useless.
It will take me a couple of weeks or so to get a calibration slide( When I know which sort is best).....I will post the results when I have tested the set up.
austrokiwi just wondering have you done anymore testing on this type of photography. I have enough lens. I also have a extra bellows coming. I am going to put one of these together and try it as well. I also found some more threads on google on this topic. there is also a listing for a lens manufactured for this type of photography. I want to build my own like you did. I will do this later this fall. I will post the images when I get this built and see how it goes great thread you did a great job on your images. I find more and more I like to learn as much as I can about this stuff. have a great one
I struggled with getting repeatable results. I think it was a case of beginners luck. my problems in getting the set up correct each time lead to me looking at the Rhinocam
austrokiwi yes after watching the video s on these new lens and how they work. I can see why you would purchase the rinocam. the lense in the video they demo. they don't even connect a camera to the lens just wires and watch the computer monitor to do there focus the lens. the lens is mounted solid. everything else is done by the computer and your mouse. I like what they are doing and this lens system would be great for coin photography. have a great one
austrokiwi have you watched that video on coin photography. the lens they are using will do a coin up to 3 inches. that's a large coin if you get a chance. if you have not seen the video take some time and go watch it that lens is amazing. the image fills the monitor what a great way to check coins for error and variety. one can set back and just watch the monitor. the bigger the monitor the more you see the coin. have a great one
"Navitar designs and manufactures a wide variety of high magnification imaging optics for a broad range of applications including the biomedical, nanotechnology, semiconductor and electronic imaging industries. We provide leading equipment manufacturers with highly repeatable and automated precision optics that can be designed into new instruments with smaller footprints and lower prices than older equipment"
aardspeed great you found other links. wish I knew how to attack links here. I watched a video last night of how to mount the lens and focus the lens. there monitor was a laptop with a large screen. I think the camera was no bigger than 2 centimeters. it was inside the cable that connected the lens to the laptop. I like to get my hands on one of these and take it apart. I don't see why a person could not build one of these lens. if I can find the same site. I was on last night they had up a sketch of the construction of one of these lens. I would like to see how it made again. if you find a link please share that again thank you aardspeed.
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) but is there really a problem to solve? 
Posted 02/19/2015 11:09 am
