frosted cd, london? will 600 sandpaper do?

Jonathon Wilson · February 15th, 2005, 09:13 PM

Forgive me if some of this comes off as brain-dead stupid and it sounds like I'm patronizing or talking below you... I'm not, I just want to explain myself clearly, and perhaps this will help. You probably already know _all_ of this, but...

Yes, using any kind of magnifier on the regular LCD screen of your camcorder won't help much - you'll just see very big pixels. This is the real advantage of removing the camcorder and looking directly at the ground glass with your eye... your eye has much higher 'resolution' than your LCD monitor :) and once you can magnify that ground glass image with a loupe or even a plain old magnifying glass, you'll really be able to see whether the image is in focus or not.

If it were me, I would take the following approach:

Zoom your SLR lens to 105mm (it's longest setting?) and leave it there.

Base your focus adjustments on the marks on the lens. Here's where I'm most fuzzy... I also have a zoom lens for my SLR - it's a cheap 80-200, but it may shed some light. I have two different rotating rings:

Ring 1 is the aperture, with numbers 3.9, 5.6, 8, 11, 16, 22 - which represent the F-Stops for the size of the aperture opening. It's the ring closes to the mount.

2) is a big barrel combination focus/zoom. The entire barrel slides up and down the lens and can rotate as well. Sliding it up and back changes the zoom, (which is marked down on the barrel which gets exposed as I shorten the zoom). Rotating it adjusts focus. I have _two_ sets of numbers on the ring itself, as it sounds like you do too. In my case, the two sets of numbers (one in white, one in red) represent the focal distances in meters and feet, respectively. I wouldn't be surprised if yours were similar. There will be an infinity sign at one end. Turn the lens to the farthest point opposite inifinity and find the number. This represents the nearest point your lens can focus. In my case, this is 1.3 meters.

3) Put your star chart on some kind of stand, perpendicular to the camera _EXACTLY_ this distance away. For my zoom lens, this distance would be 1.3 meters.

Now... Leave everything exactly the way it is, and move _only_ the adjustment on your focal flange distance (in my case, this is the nuts between the two pieces of plywood) until the star is _most_ in focus like this:

Theoretically, you won't be able to resolve all the way to the exact center of the star. This means that at some point outside of the center of the star, there is a blurred circle. As you adjust your focal flange depth, this circle will grow and shrink. The goal is to make this center blurred circle as small as possible. Once you're reached that point, then you should be pretty close to having your focal flange depth correct.

In reality, this measurement is measured in tenths of millimeters (For my Canon FD mount, the spec'd focal flange depth is 42.1 mm) (!). It's awfully hard to adjust 20 thread-per-inch nuts at a tenth of a millimeter precision. So just get as close as you can.

Now -- if you get all that right, then theoretically, you should be able to simply turn the lens to a number, say 5 meters... put the target at exactly 5 meters and it should be in perfect focus. If you're really good, then you should be able to get in focus, and then pull your zoom to any point (without twisting it) and it will stay in focus.

Much of the focusing that happens in larger movie productions is done by tape measure... not by eye. (Eye is used to check of course, but generally, it's the numbers on the AC's/Focus Puller's tape measure that determine the position of the dial). This is why the focus marks matter.

Leo Mandy · February 15th, 2005, 09:23 PM

See my new post on infinity - but I think you have solved it.

Thanks Jonathon, I am going to try that next. No, it did not sound patronizing and I appreciate the time and effort your put into it. What you say makes sense 1.3 meters - focus, should focus on everything. My barrel and zoom lens sounds exactly the same as yours and works in the same way - thanks for clarifying what the marks on the ring mean.
I am going to have to try and lock down my GG for this and get a decent tape measure because I do want to get as exact as possible.

Also, I just finished watching your 'rain' video - and I have to say it looks soooo much like film that I cannot believe you are disappointed with your device!! The colours are great and the movement, DOF and grain look amazing. A great job.

Mark Kubat · February 16th, 2005, 01:13 AM

Wow, first time I saw your site - amazing stuff!

Great stuff on your site too about avisynth and virtualdub - I'm using other means for this part (Magic Bullet and deinterlacing in Premiere Pro) - wow, your depth of field stuff is unreal...

Whoa!

Okay, okay, I am definitely building this thing.

Mandy/Jonathon - thanks for sharing your findings! Amazing!

Jonathon Wilson · February 16th, 2005, 10:40 AM

Thanks for the nice words --

Mandy, I'm not at all unhappy with the current adapter... particularly for my VHS-C cam, I just have certain things that I wish were better. It's the curse of these things... there's always something that would be 'a bit better if I only...'

Mark, be careful! Once you get hooked, you'll find yourself perusing weird optical/hardware web sites at 3am the night before a big 8am meeting at work... neglecting your significant others... breaking your piggy bank to buy some aluminum angle iron... and noticing things that other people are throwing out as garbage, thinking, "Hey... I could use that for..."... you know -- all the classic symptoms of an addiction (like Crack, just more constructive). Regardless, it's certainly fun!!

How do you like Magic Bullet? I've never actually used it, but their demo videos certainly look nice. I've always been happy 'enough' with my avisynth tricks to not shell out any $$ for a more commercial solution, but I always worry that there's some magic in the commercial approaches that I can't replicate... (way off topic now... this thread is about the frosted ground glass, is it not) :)

Leo Mandy · February 16th, 2005, 11:22 AM

I will have to jump in with the addiction thing. Hey, this thing gets out of hand on the quest to make the perfect DOF machine or whatever. That is why I ask question after question, even if there are silly simple stupid questions!

Working on the Focal length today and getting tracing paper and maybe, if I can find it - architectural paper as well!

(OT - I have used Magic Bullet in the past - waaaaay too slow for rendering times). Most NLE's have enough plugin that come with the program that you don't need it - colour curves, colour correction, grain etc)

Mark Kubat · February 16th, 2005, 06:56 PM

Okay, you two have seduced me to cross over to the "dark side." Finally got my SLR off my kid sister because it has a nice 28-105mm zoom lens I'm going to test with... tomorrow, it's the macro/c.u. (close-up) adaptor - I'm gonna test with the DVX100 I own but want to really build this for the new Sony HDV cam I've rented - the FX1/Z1... Amazing low light so with this system, it should be a real hit!

Guys, what macro size is the best? +2?

Also have to buy some cheapo CD player at Walmart. Jon, great pics on your site - the architectural paper looks like a hit.

Mandy's right - rendering slow on Magic Bullet. Your stuff is tremendous - really, I'm an expert at watching all this stuff on the web and I can tell - you've nailed the filmlook stuff perfectly with your avisynth solution.

VHS-C? Amazing!

So I'll be starting tomorrow, folks... Will keep you posted!

Mark

Mark Kubat · February 16th, 2005, 07:20 PM

Guys, because I have it here at home and it's almost self-adhesive, I'm gonna test out with GLAD "Press'n'Seal" wax-paper like film to make my clear CD into a "GG."

Just thought you might want to try this - there is logo etc. on roll of stuff but you can get an area large enough without logo to place over CD...

will know more once I actually get it spinning - but it's diffuse and just looking through lens at it in dark room, upside down reverse image appears nicely on the CD....

More later.

Cheers.

Leo Mandy · February 16th, 2005, 07:34 PM

Mark keep me posted on the Press and Seal stuff. I went out tonight and hit all the computers stores looking for packing CD that were clear without the green tint. Came up with a few. I will check into the Glad Press and Seal material if it looks good for you!

February 16th, 2005, 01:13 AM	#33
Mark Kubat Major Player Join Date: Jan 2003 Location: Toronto, Canada Posts: 375	Kudos, Jonathon! Wow, first time I saw your site - amazing stuff! Great stuff on your site too about avisynth and virtualdub - I'm using other means for this part (Magic Bullet and deinterlacing in Premiere Pro) - wow, your depth of field stuff is unreal... Whoa! Okay, okay, I am definitely building this thing. Mandy/Jonathon - thanks for sharing your findings! Amazing!

February 16th, 2005, 06:56 PM	#36
Mark Kubat Major Player Join Date: Jan 2003 Location: Toronto, Canada Posts: 375	Jon and Mandy - we're addicts Okay, you two have seduced me to cross over to the "dark side." Finally got my SLR off my kid sister because it has a nice 28-105mm zoom lens I'm going to test with... tomorrow, it's the macro/c.u. (close-up) adaptor - I'm gonna test with the DVX100 I own but want to really build this for the new Sony HDV cam I've rented - the FX1/Z1... Amazing low light so with this system, it should be a real hit! Guys, what macro size is the best? +2? Also have to buy some cheapo CD player at Walmart. Jon, great pics on your site - the architectural paper looks like a hit. Mandy's right - rendering slow on Magic Bullet. Your stuff is tremendous - really, I'm an expert at watching all this stuff on the web and I can tell - you've nailed the filmlook stuff perfectly with your avisynth solution. VHS-C? Amazing! So I'll be starting tomorrow, folks... Will keep you posted! Mark

February 16th, 2005, 07:20 PM	#37
Mark Kubat Major Player Join Date: Jan 2003 Location: Toronto, Canada Posts: 375	Just to be different - GLAD press'n'seal Guys, because I have it here at home and it's almost self-adhesive, I'm gonna test out with GLAD "Press'n'Seal" wax-paper like film to make my clear CD into a "GG." Just thought you might want to try this - there is logo etc. on roll of stuff but you can get an area large enough without logo to place over CD... will know more once I actually get it spinning - but it's diffuse and just looking through lens at it in dark room, upside down reverse image appears nicely on the CD.... More later. Cheers.

February 15th, 2005, 09:13 PM	#31
Jonathon Wilson Regular Crew Join Date: Feb 2004 Location: Austin, TX Posts: 182	Forgive me if some of this comes off as brain-dead stupid and it sounds like I'm patronizing or talking below you... I'm not, I just want to explain myself clearly, and perhaps this will help. You probably already know _all_ of this, but... Yes, using any kind of magnifier on the regular LCD screen of your camcorder won't help much - you'll just see very big pixels. This is the real advantage of removing the camcorder and looking directly at the ground glass with your eye... your eye has much higher 'resolution' than your LCD monitor :) and once you can magnify that ground glass image with a loupe or even a plain old magnifying glass, you'll really be able to see whether the image is in focus or not. If it were me, I would take the following approach: Zoom your SLR lens to 105mm (it's longest setting?) and leave it there. Base your focus adjustments on the marks on the lens. Here's where I'm most fuzzy... I also have a zoom lens for my SLR - it's a cheap 80-200, but it may shed some light. I have two different rotating rings: Ring 1 is the aperture, with numbers 3.9, 5.6, 8, 11, 16, 22 - which represent the F-Stops for the size of the aperture opening. It's the ring closes to the mount. 2) is a big barrel combination focus/zoom. The entire barrel slides up and down the lens and can rotate as well. Sliding it up and back changes the zoom, (which is marked down on the barrel which gets exposed as I shorten the zoom). Rotating it adjusts focus. I have _two_ sets of numbers on the ring itself, as it sounds like you do too. In my case, the two sets of numbers (one in white, one in red) represent the focal distances in meters and feet, respectively. I wouldn't be surprised if yours were similar. There will be an infinity sign at one end. Turn the lens to the farthest point opposite inifinity and find the number. This represents the nearest point your lens can focus. In my case, this is 1.3 meters. 3) Put your star chart on some kind of stand, perpendicular to the camera _EXACTLY_ this distance away. For my zoom lens, this distance would be 1.3 meters. Now... Leave everything exactly the way it is, and move _only_ the adjustment on your focal flange distance (in my case, this is the nuts between the two pieces of plywood) until the star is _most_ in focus like this: Theoretically, you won't be able to resolve all the way to the exact center of the star. This means that at some point outside of the center of the star, there is a blurred circle. As you adjust your focal flange depth, this circle will grow and shrink. The goal is to make this center blurred circle as small as possible. Once you're reached that point, then you should be pretty close to having your focal flange depth correct. In reality, this measurement is measured in tenths of millimeters (For my Canon FD mount, the spec'd focal flange depth is 42.1 mm) (!). It's awfully hard to adjust 20 thread-per-inch nuts at a tenth of a millimeter precision. So just get as close as you can. Now -- if you get all that right, then theoretically, you should be able to simply turn the lens to a number, say 5 meters... put the target at exactly 5 meters and it should be in perfect focus. If you're really good, then you should be able to get in focus, and then pull your zoom to any point (without twisting it) and it will stay in focus. Much of the focusing that happens in larger movie productions is done by tape measure... not by eye. (Eye is used to check of course, but generally, it's the numbers on the AC's/Focus Puller's tape measure that determine the position of the dial). This is why the focus marks matter.

February 15th, 2005, 09:23 PM	#32
Leo Mandy Major Player Join Date: Dec 2004 Posts: 749	See my new post on infinity - but I think you have solved it. Thanks Jonathon, I am going to try that next. No, it did not sound patronizing and I appreciate the time and effort your put into it. What you say makes sense 1.3 meters - focus, should focus on everything. My barrel and zoom lens sounds exactly the same as yours and works in the same way - thanks for clarifying what the marks on the ring mean. I am going to have to try and lock down my GG for this and get a decent tape measure because I do want to get as exact as possible. Also, I just finished watching your 'rain' video - and I have to say it looks soooo much like film that I cannot believe you are disappointed with your device!! The colours are great and the movement, DOF and grain look amazing. A great job.

February 16th, 2005, 10:40 AM	#34
Jonathon Wilson Regular Crew Join Date: Feb 2004 Location: Austin, TX Posts: 182	Thanks for the nice words -- Mandy, I'm not at all unhappy with the current adapter... particularly for my VHS-C cam, I just have certain things that I wish were better. It's the curse of these things... there's always something that would be 'a bit better if I only...' Mark, be careful! Once you get hooked, you'll find yourself perusing weird optical/hardware web sites at 3am the night before a big 8am meeting at work... neglecting your significant others... breaking your piggy bank to buy some aluminum angle iron... and noticing things that other people are throwing out as garbage, thinking, "Hey... I could use that for..."... you know -- all the classic symptoms of an addiction (like Crack, just more constructive). Regardless, it's certainly fun!! How do you like Magic Bullet? I've never actually used it, but their demo videos certainly look nice. I've always been happy 'enough' with my avisynth tricks to not shell out any $$ for a more commercial solution, but I always worry that there's some magic in the commercial approaches that I can't replicate... (way off topic now... this thread is about the frosted ground glass, is it not) :)

February 16th, 2005, 11:22 AM	#35
Leo Mandy Major Player Join Date: Dec 2004 Posts: 749	I will have to jump in with the addiction thing. Hey, this thing gets out of hand on the quest to make the perfect DOF machine or whatever. That is why I ask question after question, even if there are silly simple stupid questions! Working on the Focal length today and getting tracing paper and maybe, if I can find it - architectural paper as well! (OT - I have used Magic Bullet in the past - waaaaay too slow for rendering times). Most NLE's have enough plugin that come with the program that you don't need it - colour curves, colour correction, grain etc)

February 16th, 2005, 07:34 PM	#38
Leo Mandy Major Player Join Date: Dec 2004 Posts: 749	Mark keep me posted on the Press and Seal stuff. I went out tonight and hit all the computers stores looking for packing CD that were clear without the green tint. Came up with a few. I will check into the Glad Press and Seal material if it looks good for you!