El que es necessita és una lent que per una banda reculli rajos de llum provinents d'un punt i els emeti paral·lels. Bàsicament això és una lent convexa. NT49-780-INK Adaptador i lent Adaptador, lent, camera i projector
Una de les fites bàsiques per poder fer la digitalització és tenir un sistema de captura adequat, en quant a qualitat però també en quant a cost.
L'aposta seria intentar usar, tant com sigui possible, components d'electrònica de consum que, potser ja tenim a casa o tenim pensat tenir.
Una càmera de vídeo HD domèstica, i una tarjeta capturadora per PC, és el mínim necessari.
Una videocàmera bàsica tindria un zoom de x10 amb una distància d'enfoc mínima d'entre 500mm i 1000mm. Un zoom com aquest és insuficient per ampliar el fotograma de la pel.licula de 8mm i el sistema no seria gens compacte.
Per tant, és necessaria una ampliació major i enfocar de més a prop, i com les videocàmeres domèstiques no tenen òptiques intercanviables, caldrà fer algun tipus modificació per adaptar-les al que necessitem.
Existeixen lents accessòries que permeten guanyar en ampliació i reduir en distancia d'enfoc: són les lents de macro o "close-up".
Aquestes lents s'acoblen com un filtre, i permeten obtenir una imatge virtual ampliada quan ens acostem al subjecte a la distancia focal de la lent.
Usant l'Eumig Mark 8 com a projector, no podrem posicionar la càmera a menys de 100mm de distancia del fotograma, ni tampoc col·locar cap component òptic més aprop de 60mm. Així, necessitem una lent d'entre 60mm i 100mm, suposant que tenim una ampliació suficient amb el zoom de x10 de la càmera.
Es diu que un sistema com aquest funciona de forma afocal, ja que no focalitza la imatge en un punt, si no que proporciona un feix de llum que posteriorment ha de ser enfocat.
Deixo tres imatges: la lent acromàtica, l'adaptador per muntar la lent, i tot el conjunt.
I també un fotograma capturat:
dijous, 11 de febrer del 2010
Òptica
Com a regla general: com més petita és la distancia focal més gran és l'ampliació. Així, caldria buscar una lent de 60mm aproximadament però, com no hi ha lents fotogràfiques al mercat amb aquesta distancia focal, s'han de buscar alternatives.
Hi ha diversos tipus de lents convexes: planoconvexes, biconvexes, doblets acromàtics, triplets... Les lents de més "qualitat" són normalment doblets o triplets acromàtics, així que ens centrarem en aquest dos tipus.
La solució: un doblet acromàtic de 63,5mm (~ +16 dioptries) i un diàmetre de 25,4mm d'Edmund òptics. Altres opcions, a preus molt més econòmics, es poden trobar a surplusshed, però amb menys garanties en quan a la qualitat òptica.
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7 comentaris:
Hi ,
Congratulation for your Blog. I have had a lot of fun reading it, but as I’m a newbie I have had a hard time understanding a few details. I see the image “lens adapter” and I have to find out if my Panasonic model PV-GS80 can use the same lens adapter 52mm spacer ring. I also see that you use an extra part (light blue top ring) to incorporate the achromatic lens, is this a piece that you made or you bought it? If so, what material did you use? How did you fit the lens on it? I would really appreciate any help to my questions. Thank you very much.
Hi eddy1948,
Your PV-GS80 is a 32X optical zoom camera. My setup is intended to work with an at least 10X camera, so yes, it would work, but probably this is not the best cost/quality solution in your case.
Your camera is able to zoom a lot more, so you could choose a less powerful achromatic lens, and this will result in a cheaper solution.
Those lenses could also be found mounted in different thread sizes, so you won't need to make any adapter by yourself. Also, you won't probably need that spacer ring because its only purpose is to mount the lens, and has no other optical effect.
Take a look at: "Opteka 10x" +10 dipoter (http://opteka.com/10x.aspx) and "Raynox 250" +8 diopter (http://raynox.co.jp/english/dcr/dcr250/indexdcr250eg.htm)
And finally, that extra part (light blue top ring) is made in silicone rubber for molds.
Hope you find it useful!
Hi
Thank you very much for your prompt reply.
Taking in consideration your comments we are about to order these two items:
-52mm 10x macro lens (as you suggested)
-37mm to 52mm step-up ring (our Panasonic has a 37mm thread)
Basically what I need is a lens that can get my camcorder as close as possible to the projector's lens (like on the demo video you have). That way will eliminate the hassle of trying to adjust the image at full camera zoom and gain a bit of image quality.
I will really appreciate any help as I do not understand much about how combined lenses work.
Thank you again,
eddy
Hi Eddy,
Focusing distance will be around 100mm from the film plane, and camera focus should be set to infinity. You should remove the projector lens.
Don't know how much zoom you will need to apply, but it is expected to be in your 32X range. Choosing the right lens was a matter of trial and error in my case (I had to try with four different lenses).
Good luck!
Hello Jaume,
Thanks for your help and time. Finally we received the ring and the macro lens. We removed the projector’s lens and placed the camera with the macro lens as close as possible to the projector. The results are very encouraging but the image is not big enough as we cannot zoom more than 7x without getting a blurred image. At this point we do not know what else to do to overcome the physical design of the projector which is preventing us from getting the camera closer to the film. We tested the macro lens on a piece of paper with very fine print and we believe we have to get the camera closer to the projector just one more cm to get an image double the size than the one we are getting right now. Any advice will be greatly appreciated.
Eddy
Hi Eddy,
I would try the following:
- The best place for the macro lens will be around its effective focal distance. In this case it should be at around 100mm. This optimal distance is modified in some degree by the camera optics. So, If you can't place the macro lens between 90mm and 110mm from the film plane, probably it won't work.
- Be sure to manual focus your camera to infinite. Also disable the camera macro capabilities.
- If nothing works, try reversing the macro lens.
Jaume
Eddy,
I forgot to say that you will need to move the camera forward / backward to get it focused.
Jaume
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