Single element DOF adaptor (not 35mm) at DVinfo.net

Matt Champagne · June 16th, 2005, 06:51 PM

After doing a bit of research into pinhole cameras, single element lenses, and various other things on optics I decided to try an experiment.

I bought a cheap reading magnifier from walmart for $5 US (2in x 2in reading magnifier +1 I think but not sure). I had some mylar contact paper and an old picture frame. Put all of those into a cardboard box. I cut a whole at the front the size of the magnifier and taped it there. Then I crawled inside and held the cheapo focusing screen and moved it around by hand. To clarify what I am saying: I am not using any 35mm lens. Its just magnifier (diopter?) and focusing screen.

I have a few screen shots but my websever isn't letting me ftp them. It looked pretty terrible actually, but that I believe is primarily due to the extremly sub-par ground glass I am using. The important thing however about this experiment, and the only reason I think its worth posting is this: My image size was greater than 5in x 7in. I would say I had at least 4x4 in. of useable image, and fairly bright considering the screen I was using.

Essentially, what I am doing is creating my own single element large format lens. I also bought a large 8"x11" magnifier. My assumption from my tests (note I know very very little about optics) is I will get DOF something akin to a 135mm to 180mm lens, but I can increase (deepen) the DOF by puting an aperture in front of the front lens (thus the reasoning behind using the biggest lens possible. I think it might also be good to put a -1 diopter behind the first lens...but honestly that's just a guess. Optics experts any suggestions?

I will pursue this futher and try to keep updating my progress, but I will probably be dividing my time since Matthew Wauhkonen's post has inspired me to give wax another try.

Matt Champagne · June 16th, 2005, 06:58 PM

Here are some screen shots. Sorry for the poor quality, I held it all by hand. The ground glass is simply matte mylar paper on a picture frame glass. There is also quite a bit of problems with reflection from the inside of the box. The image is so wide it just seems to go everywhere, and also I hadn't painted the box black (though honestly that might not be enough to prevent reflections.

www.louisianaloud.com/Image0.jpg
www.louisianaloud.com/Image1.jpg

Sarena Valilis · June 16th, 2005, 08:53 PM

the pinhole IS the lens...

Matt Champagne · June 16th, 2005, 09:56 PM

Sorry I didn't mean to be unclear about that. I'm aware of how a pinhole camera works (now)...I was just saying that I had been searching all about various light techniques and why they work...not that my design is a pinhole camera. I tried a pinhole and it is way too little light. My design is a single element lens as the title states.

Aaron Shaw · June 17th, 2005, 12:44 PM

I don't think this will help with getting a shallow DOF though :). Pinhole cameras have an (effective) infinitely deep DOF!

Matt Champagne · June 17th, 2005, 02:21 PM

A pinhole would not, but each magnification level via the diopter at the front involved in simulating a pinhole of a certain size, increases the circle of confusion and therefore shallows the DOF. I think with a +5 or greater diopter you would start getting a pretty shallow image. I think the bigger problem is that the fall off rate of the focus won't look 35mm at all, it will be much more gradual. It would be a unique image...hopefully unique in the 'defining a new cinematic style' way, as opposed to the looking really cheesy and weird way.

Rune Hals · June 20th, 2005, 05:54 PM

Hey, why hasnt anyone here tried this before?.
I tried it with a my Diopter(?, its an old lens from a minolta slide projector) and the images i got was actually quite good, not that far from the images i got from the 35mm slr lenses i have tried it with.

I did have some troubble focus on things from a far distans, and things closeup.

Here are some grabs from my tests.
(note. since i used the closeup lens as the actual lens that captures it all, i wasnt able to get close enough up to the gg, so i got some vignetting and hotspots, the gg is terrible made, the camera isnt that pro either[gs120])

well well, here is the link: http://arez.vestlan.com/dof/Single_lens/index.html

Matt Champagne · June 20th, 2005, 08:59 PM

Your already getting better results than me I can see. Do you know the strength of your diopter? Also have you tried limiting the light that enters the diopter? How big of an image are you getting? Personally I think mine is a little too big (4in x5in).

Rune Hals · June 21st, 2005, 08:35 AM

Well, im not sure how strong it is. Im no optics expert, and i have no idea how to measure the strength. But what i can say about it, is that it is a very thick positive lens. a bit under "one and a half inch" long in diameter. and its offcourse used for 35mm slides, i dont know if that has something to say about the size of the projected image. but it gives you images about the same size as a standard 35mm slr lens would give you.

About the image you got... that was a bit too big. I think "that" can give a lot of light loss since you probarly only use a small area of the projected image.

Now , i really liked the idea of using just a simple glass from a magninfier or some sort. It might be a good thing for people who dont want to invest in expensive optics to try building a DOF adapter. They might be very sceptic to the whole idea, so now they can just play around a bit with it and experience the power of shallow dof, and also. I like the idea of getting a new look that we havent seen before. Cuz thats what one of the things "alternating imaging methods" is about.

You should try your experiement with a better GG. maybe something less opaque. And keep on experimenting. Cuz this is all very interesting...

Matt Champagne · June 21st, 2005, 01:39 PM

Does anyone know how I could calculate the CoC for such a single element lens? I want to see if I can use this DOF field calculator:

http://www.dofmaster.com/dofjs.html

If there is a way to calculate an at least approximate CoC for a given single element lens, then I can save alot of time and money by not using a lens that will just give me deep DOF anyway.

June 16th, 2005, 06:51 PM	#1
Matt Champagne Major Player Join Date: Nov 2004 Location: New Iberia, LA Posts: 229	Single element DOF adaptor (not 35mm) After doing a bit of research into pinhole cameras, single element lenses, and various other things on optics I decided to try an experiment. I bought a cheap reading magnifier from walmart for $5 US (2in x 2in reading magnifier +1 I think but not sure). I had some mylar contact paper and an old picture frame. Put all of those into a cardboard box. I cut a whole at the front the size of the magnifier and taped it there. Then I crawled inside and held the cheapo focusing screen and moved it around by hand. To clarify what I am saying: I am not using any 35mm lens. Its just magnifier (diopter?) and focusing screen. I have a few screen shots but my websever isn't letting me ftp them. It looked pretty terrible actually, but that I believe is primarily due to the extremly sub-par ground glass I am using. The important thing however about this experiment, and the only reason I think its worth posting is this: My image size was greater than 5in x 7in. I would say I had at least 4x4 in. of useable image, and fairly bright considering the screen I was using. Essentially, what I am doing is creating my own single element large format lens. I also bought a large 8"x11" magnifier. My assumption from my tests (note I know very very little about optics) is I will get DOF something akin to a 135mm to 180mm lens, but I can increase (deepen) the DOF by puting an aperture in front of the front lens (thus the reasoning behind using the biggest lens possible. I think it might also be good to put a -1 diopter behind the first lens...but honestly that's just a guess. Optics experts any suggestions? I will pursue this futher and try to keep updating my progress, but I will probably be dividing my time since Matthew Wauhkonen's post has inspired me to give wax another try.

June 16th, 2005, 08:53 PM	#3
Sarena Valilis Regular Crew Join Date: Aug 2003 Location: hollywood , ca USA Posts: 38	pinhole the pinhole IS the lens...

June 20th, 2005, 05:54 PM	#7
Rune Hals New Boot Join Date: Jun 2005 Location: Norway Posts: 17	Hey, why hasnt anyone here tried this before?. I tried it with a my Diopter(?, its an old lens from a minolta slide projector) and the images i got was actually quite good, not that far from the images i got from the 35mm slr lenses i have tried it with. I did have some troubble focus on things from a far distans, and things closeup. Here are some grabs from my tests. (note. since i used the closeup lens as the actual lens that captures it all, i wasnt able to get close enough up to the gg, so i got some vignetting and hotspots, the gg is terrible made, the camera isnt that pro either[gs120]) well well, here is the link: http://arez.vestlan.com/dof/Single_lens/index.html Last edited by Rune Hals; June 20th, 2005 at 06:11 PM.

June 16th, 2005, 06:58 PM	#2
Matt Champagne Major Player Join Date: Nov 2004 Location: New Iberia, LA Posts: 229	Here are some screen shots. Sorry for the poor quality, I held it all by hand. The ground glass is simply matte mylar paper on a picture frame glass. There is also quite a bit of problems with reflection from the inside of the box. The image is so wide it just seems to go everywhere, and also I hadn't painted the box black (though honestly that might not be enough to prevent reflections. www.louisianaloud.com/Image0.jpg www.louisianaloud.com/Image1.jpg

June 16th, 2005, 09:56 PM	#4
Matt Champagne Major Player Join Date: Nov 2004 Location: New Iberia, LA Posts: 229	Sorry I didn't mean to be unclear about that. I'm aware of how a pinhole camera works (now)...I was just saying that I had been searching all about various light techniques and why they work...not that my design is a pinhole camera. I tried a pinhole and it is way too little light. My design is a single element lens as the title states.

June 17th, 2005, 12:44 PM	#5
Aaron Shaw Major Player Join Date: Jul 2004 Posts: 587	I don't think this will help with getting a shallow DOF though :). Pinhole cameras have an (effective) infinitely deep DOF!

June 17th, 2005, 02:21 PM	#6
Matt Champagne Major Player Join Date: Nov 2004 Location: New Iberia, LA Posts: 229	A pinhole would not, but each magnification level via the diopter at the front involved in simulating a pinhole of a certain size, increases the circle of confusion and therefore shallows the DOF. I think with a +5 or greater diopter you would start getting a pretty shallow image. I think the bigger problem is that the fall off rate of the focus won't look 35mm at all, it will be much more gradual. It would be a unique image...hopefully unique in the 'defining a new cinematic style' way, as opposed to the looking really cheesy and weird way.

June 20th, 2005, 08:59 PM	#8
Matt Champagne Major Player Join Date: Nov 2004 Location: New Iberia, LA Posts: 229	Your already getting better results than me I can see. Do you know the strength of your diopter? Also have you tried limiting the light that enters the diopter? How big of an image are you getting? Personally I think mine is a little too big (4in x5in).

June 21st, 2005, 08:35 AM	#9
Rune Hals New Boot Join Date: Jun 2005 Location: Norway Posts: 17	Well, im not sure how strong it is. Im no optics expert, and i have no idea how to measure the strength. But what i can say about it, is that it is a very thick positive lens. a bit under "one and a half inch" long in diameter. and its offcourse used for 35mm slides, i dont know if that has something to say about the size of the projected image. but it gives you images about the same size as a standard 35mm slr lens would give you. About the image you got... that was a bit too big. I think "that" can give a lot of light loss since you probarly only use a small area of the projected image. Now , i really liked the idea of using just a simple glass from a magninfier or some sort. It might be a good thing for people who dont want to invest in expensive optics to try building a DOF adapter. They might be very sceptic to the whole idea, so now they can just play around a bit with it and experience the power of shallow dof, and also. I like the idea of getting a new look that we havent seen before. Cuz thats what one of the things "alternating imaging methods" is about. You should try your experiement with a better GG. maybe something less opaque. And keep on experimenting. Cuz this is all very interesting...

June 21st, 2005, 01:39 PM	#10
Matt Champagne Major Player Join Date: Nov 2004 Location: New Iberia, LA Posts: 229	Does anyone know how I could calculate the CoC for such a single element lens? I want to see if I can use this DOF field calculator: http://www.dofmaster.com/dofjs.html If there is a way to calculate an at least approximate CoC for a given single element lens, then I can save alot of time and money by not using a lens that will just give me deep DOF anyway.