homemade optical lens adapter? at DVinfo.net

Paul Doss · November 1st, 2003, 05:44 PM

There was a site where the guys were making a short or feature. They were using a homemade optical lens adapter made out of a 35 mm SLR. Anyone have the link. I had it but lost my computer in a fire.

Thanks.

PS I know they were having trouble with dust etc. on the frosted glass but would like to know if they've done any more work on it.

Brandt Wilson · November 7th, 2003, 04:45 PM

Paul,

Was this it?
http://www.dvinfo.net/conf/showthrea...&threadid=7713

Paul Doss · November 7th, 2003, 11:18 PM

Brandt,

Thank you very much. Yes that thread led me to what I was what I was looking for.

Agus Casse · November 8th, 2003, 04:13 PM

http://www.pstechnik.de/datasheets/p...al/d_vdf_l.jpg

Check that out.. now that seems pretty awesome...

Brandt Wilson · November 10th, 2003, 12:44 PM

Agus,

This device, and ones like it, tend to run very expensive, on the order of several thousand dollars. This seems to be the primary reason people are trying to build devices that allow them to use 35mm lenses and give them the same depth of field (I think I've got that right) properties of motion picture cameras, rather than buying the existing hardware.

I designed my own box to try this, but abandoned it because I could not reduce the visible grain enough to satisfy me.

Agus Casse · November 10th, 2003, 01:40 PM

There should be a tutorial or guide for newbies like me to be able to build my box too... i can figure it in my mind of how to build it.. but still dont get a lot of things that a guide with pictures would help a lot.

Brandt Wilson · November 10th, 2003, 05:16 PM

Hm. There's really quite a bit to this. I'm not sure how P+S Technik gets their gear into such a small package, because the minimal focal length of most cameras is fairly long.

My box used mirrors to generate an artificial focal length in a unit that was 8" long, then had a standard SLR camera mounting plate on the front.

I designed in a rotating ground glass, but had difficulty in finding a fresnel of appropriate resolution...all that I looked at risked a moire effect. At that point, I ran out of "free time" to pursue it, so I abandoned it.

One other method you might look at is using an erecting lens and a condenser lens, which is a compound convex shaped lens. This would provide an image you could focus on. Sorry, I don't have any drawings, just formulas and a dense idea in my head of what needs to happen optically.

Agus Casse · November 10th, 2003, 11:56 PM

I just borrow a SLR camera, and i put my TRV18 in the viewfinder.. of course... i got the same image that you sould see in the photo camera viewfinder.. but the quality was allright....

i would love to get an old camera.. replace the ground glass.. and put the viewfinder in my video camera... and done...

let see what i can do...

in the meanwhile here is a test...

http://www.altoque.tv/jaguar35mmtest.wmv

Brandt Wilson · November 11th, 2003, 09:35 AM

Agus,

Your approach is in the right vein, but the heavy vignetting is one of the main problems with a home-built unit. The other issue is the grain from the ground glass that is visible in the image.

The manufacturers of the expensive units have overcome grain by vibrating or rotating the ground glass at high frequency.

I was able to overcome this, to a greater degree, but the problem I had was the fresnel, which is what provides even illumination when you are looking through the viewfinder.

Agus Casse · November 11th, 2003, 10:51 AM

The ground glass is the one that have the round circle tool that helps you to focus in the camera?

I didnt have too much grain really.. and the shadows or vigneting... was produce cause i just close the camera to the other camera viewfinder... in case i could remove the plastic in the SLR camera... i could close up more the DV camera to get a better image...

for sure that i didnt have too much grain... now i will try another shoots now that i have daylight

Brandt Wilson · November 11th, 2003, 04:37 PM

Agus,

The ground glass is the optical element that allows you to view the image. The circle you mention is the focusing aid...you can buy a replacement ground glass that does not have a focusing aid.

I'd be interested to see what the images look like after you've moved the camera closer to the ground glass, or zoom in tighter. I'm interested to see if you are able to get a clean image without hot spots or vignetting.

I made an attempt at converting a Pentax SLR about a year ago. I may make another go at it. You can simulate the effect by placing a piece of cellophane (envelope window) into the film guide of an empty camera, then locking open the shutter. This is the image that will hit your ground glass, unless you have some form of magnifier in place. These are often attached to the GG, but are far more often than not fresnel lenses. Fresnels cause vignetting in video.

You could try using a plano-convex lens in the place of the GG/fresnel. Put the flat side into the film plane. This will give you the proper critical distance between your lens and your resolving optical element. To make things simpler for photography, you might insert another double convex lens behind the plano-convex as an erecting lens, so your image is upright.

I need to look at all this again.

Paul Doss · November 11th, 2003, 05:10 PM

Agus,

I would be interested in seeing anything else you do on this to.

Brandt,

It sounds like you were getting close when you were at this last year. Hope you do take it up again. Keep us posted.

I assume that you must veiw the frosted glass from the side that the light strikes. I guess that is the reason for going through the veiw finder instead of out the back. You can't see (very well) through the frost can you?

Brandt Wilson · November 12th, 2003, 12:22 AM

The reason the ground glass in the viewfinder is used in these cases is that there is also a focusing lens that evens out illumination. I haven't worked out how to reproduce this in the film gate.

If you were to take a piece of frosted cellophane from a business envelope window and tape it into the film gate, you'll see that on the surface of the cellophane is the image from the lens, perfectly square (and upside down), but there is a round hotspot. It's a hard round hotspot...I'm not sure what kind of lens I need to eliminate the hotspot.

Perhaps someone has an idea?

Paul Doss · November 12th, 2003, 02:28 PM

<<you'll see that on the surface of the cellophane is the image from the lens, perfectly square (and upside down), but there is a round hotspot. It's a hard round hotspot>>

Under regular normal use of the SLR, why would the film not be affected by this?

Paul

Brandt Wilson · November 12th, 2003, 11:26 PM

Here's my idea on why the hotspot doesn't affect the film.

If you look at the projected image in the cellophane from an angle, it looks fine. There are no projected hotspots. However, if you look down the barrel, you will see the light source. Like with a film projector...looks fine on the screen, but if you look down the light stream towards the projector, there is a hotspot.

Beyond this, I'm not sure.

November 1st, 2003, 05:44 PM	#1
Paul Doss Regular Crew Join Date: Feb 2002 Location: Gulf Shores, Alabama Posts: 57	homemade optical lens adapter? There was a site where the guys were making a short or feature. They were using a homemade optical lens adapter made out of a 35 mm SLR. Anyone have the link. I had it but lost my computer in a fire. Thanks. PS I know they were having trouble with dust etc. on the frosted glass but would like to know if they've done any more work on it.

November 7th, 2003, 04:45 PM	#2
Brandt Wilson Major Player Join Date: Jan 2003 Location: Portland, OR Posts: 220	...was this it? Paul, Was this it? http://www.dvinfo.net/conf/showthrea...&threadid=7713

November 10th, 2003, 12:44 PM	#5
Brandt Wilson Major Player Join Date: Jan 2003 Location: Portland, OR Posts: 220	...same principle, but very spendy Agus, This device, and ones like it, tend to run very expensive, on the order of several thousand dollars. This seems to be the primary reason people are trying to build devices that allow them to use 35mm lenses and give them the same depth of field (I think I've got that right) properties of motion picture cameras, rather than buying the existing hardware. I designed my own box to try this, but abandoned it because I could not reduce the visible grain enough to satisfy me.

November 10th, 2003, 05:16 PM	#7
Brandt Wilson Major Player Join Date: Jan 2003 Location: Portland, OR Posts: 220	...tutorial Hm. There's really quite a bit to this. I'm not sure how P+S Technik gets their gear into such a small package, because the minimal focal length of most cameras is fairly long. My box used mirrors to generate an artificial focal length in a unit that was 8" long, then had a standard SLR camera mounting plate on the front. I designed in a rotating ground glass, but had difficulty in finding a fresnel of appropriate resolution...all that I looked at risked a moire effect. At that point, I ran out of "free time" to pursue it, so I abandoned it. One other method you might look at is using an erecting lens and a condenser lens, which is a compound convex shaped lens. This would provide an image you could focus on. Sorry, I don't have any drawings, just formulas and a dense idea in my head of what needs to happen optically.

November 11th, 2003, 04:37 PM	#11
Brandt Wilson Major Player Join Date: Jan 2003 Location: Portland, OR Posts: 220	ground glass and practical application Agus, The ground glass is the optical element that allows you to view the image. The circle you mention is the focusing aid...you can buy a replacement ground glass that does not have a focusing aid. I'd be interested to see what the images look like after you've moved the camera closer to the ground glass, or zoom in tighter. I'm interested to see if you are able to get a clean image without hot spots or vignetting. I made an attempt at converting a Pentax SLR about a year ago. I may make another go at it. You can simulate the effect by placing a piece of cellophane (envelope window) into the film guide of an empty camera, then locking open the shutter. This is the image that will hit your ground glass, unless you have some form of magnifier in place. These are often attached to the GG, but are far more often than not fresnel lenses. Fresnels cause vignetting in video. You could try using a plano-convex lens in the place of the GG/fresnel. Put the flat side into the film plane. This will give you the proper critical distance between your lens and your resolving optical element. To make things simpler for photography, you might insert another double convex lens behind the plano-convex as an erecting lens, so your image is upright. I need to look at all this again.

November 7th, 2003, 11:18 PM	#3
Paul Doss Regular Crew Join Date: Feb 2002 Location: Gulf Shores, Alabama Posts: 57	Brandt, Thank you very much. Yes that thread led me to what I was what I was looking for.

November 8th, 2003, 04:13 PM	#4
Agus Casse Major Player Join Date: Jul 2003 Location: Guatemala Posts: 322	http://www.pstechnik.de/datasheets/p...al/d_vdf_l.jpg Check that out.. now that seems pretty awesome...

November 10th, 2003, 01:40 PM	#6
Agus Casse Major Player Join Date: Jul 2003 Location: Guatemala Posts: 322	There should be a tutorial or guide for newbies like me to be able to build my box too... i can figure it in my mind of how to build it.. but still dont get a lot of things that a guide with pictures would help a lot.

November 10th, 2003, 11:56 PM	#8
Agus Casse Major Player Join Date: Jul 2003 Location: Guatemala Posts: 322	I just borrow a SLR camera, and i put my TRV18 in the viewfinder.. of course... i got the same image that you sould see in the photo camera viewfinder.. but the quality was allright.... i would love to get an old camera.. replace the ground glass.. and put the viewfinder in my video camera... and done... let see what i can do... in the meanwhile here is a test... http://www.altoque.tv/jaguar35mmtest.wmv

November 11th, 2003, 09:35 AM	#9
Brandt Wilson Major Player Join Date: Jan 2003 Location: Portland, OR Posts: 220	Agus, Your approach is in the right vein, but the heavy vignetting is one of the main problems with a home-built unit. The other issue is the grain from the ground glass that is visible in the image. The manufacturers of the expensive units have overcome grain by vibrating or rotating the ground glass at high frequency. I was able to overcome this, to a greater degree, but the problem I had was the fresnel, which is what provides even illumination when you are looking through the viewfinder.

November 11th, 2003, 10:51 AM	#10
Agus Casse Major Player Join Date: Jul 2003 Location: Guatemala Posts: 322	The ground glass is the one that have the round circle tool that helps you to focus in the camera? I didnt have too much grain really.. and the shadows or vigneting... was produce cause i just close the camera to the other camera viewfinder... in case i could remove the plastic in the SLR camera... i could close up more the DV camera to get a better image... for sure that i didnt have too much grain... now i will try another shoots now that i have daylight

November 11th, 2003, 05:10 PM	#12
Paul Doss Regular Crew Join Date: Feb 2002 Location: Gulf Shores, Alabama Posts: 57	Agus, I would be interested in seeing anything else you do on this to. Brandt, It sounds like you were getting close when you were at this last year. Hope you do take it up again. Keep us posted. I assume that you must veiw the frosted glass from the side that the light strikes. I guess that is the reason for going through the veiw finder instead of out the back. You can't see (very well) through the frost can you?

November 12th, 2003, 12:22 AM	#13
Brandt Wilson Major Player Join Date: Jan 2003 Location: Portland, OR Posts: 220	The reason the ground glass in the viewfinder is used in these cases is that there is also a focusing lens that evens out illumination. I haven't worked out how to reproduce this in the film gate. If you were to take a piece of frosted cellophane from a business envelope window and tape it into the film gate, you'll see that on the surface of the cellophane is the image from the lens, perfectly square (and upside down), but there is a round hotspot. It's a hard round hotspot...I'm not sure what kind of lens I need to eliminate the hotspot. Perhaps someone has an idea?

November 12th, 2003, 02:28 PM	#14
Paul Doss Regular Crew Join Date: Feb 2002 Location: Gulf Shores, Alabama Posts: 57	<<you'll see that on the surface of the cellophane is the image from the lens, perfectly square (and upside down), but there is a round hotspot. It's a hard round hotspot>> Under regular normal use of the SLR, why would the film not be affected by this? Paul

November 12th, 2003, 11:26 PM	#15
Brandt Wilson Major Player Join Date: Jan 2003 Location: Portland, OR Posts: 220	Here's my idea on why the hotspot doesn't affect the film. If you look at the projected image in the cellophane from an angle, it looks fine. There are no projected hotspots. However, if you look down the barrel, you will see the light source. Like with a film projector...looks fine on the screen, but if you look down the light stream towards the projector, there is a hotspot. Beyond this, I'm not sure.