Homemade 35mm Adapter

[Bob Hart]

Just a bit of an update on things AGUS. Recently I have been involved in a bit of aviation videography. I have been using the erecting prism version to enable attachment of my Nikon mount long lenses including 500mm and 1084mm mirrors. This was one of the objectives of building my AGUS35.

These are things the PD150 was never intended to see through, however provided your lenses are centred with the cam via the prisms you can get a good result.

I spent a few hours at the local airport today getting the method right.

A heavy fluid-head tripod like a Miller is essential once you start trying to aquire and pan in full frame, aircraft in flight or closer on the cabin windows or moving control surfaces.

A simple ringsight is also needed for aquisition, the right eye in the cam viewfinder, the left eye looking at the image au-natural, keeping your head level, getting the subject centred then it pops into the cam viewfinder and you track it from there.

My thinking on the AGUS is to perhaps use the smaller diameter disk in the larger housing and arrange the motor and disk in a swing-down arrangement so I can have 35mm emulation when I want it or shoot the aerial image when I want the telephotos, all in the one piece of sewer pipe.

[Shawn Murphy]

Do you have any stills?

[Bob Hart]

Shawn.

I haven't taken any captures of my test footage but stills can be arranged in about 24 hours. There is a .jpg of a comparable image shot through the 500mm Nikon, the very last before the AGUS fell to earth and broke my glass disk. IT was through the groundglass. The direct aerial images improve a little in sharpness and much more in contrast because the 500mm mirror is a f8 only lens and the MTO 1084mm is a f11 only lens. These apertures are tighter than the no more than f5.6 recommended in the Mini35 operating instructions for minimising the effect of grain effects from the groundglass (my recollection of them??)

That image is titled "0038b.JPG" and there are some images from recollection titled "agusmto.JPG" or similar which were shot through the MTO also with the groundglass. Those images are softer because it was a warm day.

As well as my particular need right now of ability to get to aircraft performing at safe height, long lenses are a seriously practical option for sports videography, which can be a difficulty with the PD150 zoom cutting out at about 70mm. You can use zooms but there is no reliable means of establishing a notional backfocus for the zoom lens when using the aerial image, so the focus will creep when zooming and you have to chase the focus with the front lens.

However, the beauty is that once you have framed and focussed and are following the action, you can use the camcorder's own focus for fine adjustment on the run. Aufocus on the PD150 also works in this mode with one small caveat. The achromat (close-up, macro or relay lens) and the rear glass element in your front lens can have no speck of dust on them. Best practice is to manually focus the camcorder to sharpness with the front lens set to infinity focus, then work your front lens to focus on the subject, then use the camcorder focus for fine adjustment on the fly with occasional switching to auto but switching mostly to manual to stop any drift to extreme close up of the rear glass of the front lens.

You will find those .jpg images at www.dvinfo.net/media/hart

[Bob Hart]

Shawn.

I have emailed some images to Chris Hurd for his assistance in posting at www.dvinfo.net/media/hart

The images will have filenames something like "aerdem03.JPG" or similar.

The MTO 1084mm images are not as sharp as the 500mm but this is as much to do with heat shimmer, trying to pan and pull focus at the same time and a more critical depth of field as of any optical deficiency.

I am investigating the Sigma 50 - 500mm f4-6.3 zoom lens plus 1.4x converter as an option with this setup. Other than the reviews found on the web, does anyone here have experience with that lens.

[Matthew Kent]

Well, after weeks of drooling and lurking on this forum, I finally had some time to put one of these DOF boxes together. It's all come around pretty easily, but now I'm of course dealing with the optics and ground glass issues... you can view my first attempt today at the link below:

DOF Test 1

It's not completely untouched (Ran it through avisynth), but it's dark qualities is pretty much what I was seeing before treating it. I have a frosted CD, which I initially used, but it doesn't seem to work right. I get a very pleasent/unpleasent bright circle in the middle, and it's really small (the size of the 35mm lens opening), while the outside is VERY dark... I'm guessing my frosted CD is too transparent.

So I've been experimenting with a half CD disc (a dvd split in half), that I've sanded down on one side with fine sand paper, and then smoothed with comet. So far with my limited resources (No car), this yeilds the best results, but as seen in the video is also unacceptably very dark.

I tried using a fresnel like the one here that I bought from OfficeMax today, but it didn't seem to do anything. I should be receiving a PCX lens soon from Anchor Optics that I'm hoping will help.

As per Jonathon, I'll probably also be buying some single-ply architectural blueprint mylar film for the ground glass... I'm hoping it will help.

Once I get this thing the way I like (I'm on my first prototype), I'll post some pictures of it... My current lens is a no-name f1.9 49mm. I'm hoping the Canon AE-1 50mm 1.4 lens I purchased on eBay this weekend will help.

Thanks for all the great discussion and suggestions (in particular Jonathon Wilson), hopefully some student films will be made with this stuff in the near future.

[Jonathon Wilson]

Heh - funny how these things go. I'm just starting in on my third adapter :) Best of luck, Matthew! The footage looks pretty good, especially for the first stuff! I'll bet you see a big difference with the Canon lens. I have that same 1.4 50mm and it just seems to do much better in terms of hotspot than other lenses I've tried.

[Matthew Kent]

Hey Jonathon, thanks for the encouragement... I've posted my second test just about 10 minutes ago using similar shots.

I received my macro lenses and bought some drafting film today. Both seem to help quite a bit, but it's still a little dark, and I've also noticed some barrel distortion in the leaves when they go out of focus. Will the condenser help with this? Currently I'm only running through the macro, so it's pretty much exactly what's seen on the disc.

Check it out:
DOF Test 2

P.S. For those of you with Macs (Like me), you'll have to wait for the 2mb file to load completely before it plays

[Matthew Kent]

Just got my PCX lens today and it seems to be working perfectly. There might be some barrel distortion here and there (or it could be my imagination), but overal, the light quality and and vignetting is improved dramatically... I don't even need to use macro lenses now.

You guys can go to the same link again for the added videos. I did one on campus before I was able to install the condenser lens, and then did one more video after I got home... it follows the same shots as the previous two... enjoy

DOF Test videos

[Dan Diaconu]

Looks good Matthew,
What camera did you use?

[Matthew Kent]

Thanks... on the first 2 DOF tests, I used a Panasonic GS120. Because I really wanted to be able to do widescreen, I upgraded to the GS150, which is the camera I used for the campus video, and the DOF test 3.

So far I'm really happy with the GS150. Both it and the GS120 seem to be excellent cameras, and for the price they're absolute steals!

In the next week I'm going to plan out a shooting session with a friend and use her as a guinea pig to really work this thing out (I'll post the results)... I want to get some practice with it before I do my first short. (^^)

[Dan Diaconu]

Keep it up, you are doing good.

[Leo Mandy]

Mathew, I also had to deal with the barrel distortion that I found using different glass in front of the camera, most probably the PCX lens because it is concave. I found this especially annoying with poles and straight objects because they bend and make the image look rather fish-eyed. I am thinking that there is another way to get rid of this - maybe the photo-enlarger condenser lens?

BTW, good job, but I don't know what codec you used for the video and when I viewed it is was pixelated for the most part.

[Matthew Kent]

Thanks for the encouragement. You said you also had this problem with the barrel distortion... did you find a lens that fixed it? My PCX lens I think is too concave, and even though the distortion is minimal, it's very noticeable.

I'm not sure about the pixilation issue, but I think I'm going to switch codecs and start using the Sorenson codec for my later videos.

[Leo Mandy]

I have to switch to an achromat (ala Bob Hart's advice). I found a great one in a 100mm slide projector - broke it open and took it and it is nice - no barrel distortion at all.
I found a codec to walk the videos, they look great! The PCX is concave and that is why you are getting the barrel distortion - you need to find something else - try

www. surplusshed.com for achromats.

[Jonathon Wilson]

A PCX lens is not concave. It is flat on one side and curves out on the other. http://www.anchoroptics.com/images/p...a_L_pcx_a1.jpg.

A PCV (Plano-Concave) lens is the opposite -- flat on one side and curves in on the other. http://www.anchoroptics.com/images/p.../a_L_pcv_a.jpg

Any concave lens will have the opposite effect that you want. You definitely want a lens with an outward curve for the proper correction.

If the focal length of the PCX lens is too short (bigger curve) it can certainly cause spherical distortion, at the expense of less correction to hotspot/corner darkening. The balance is difficult to find.

What was the F.L. and Diameter of the PCX lens you have, Matthew?

An achromat (a lens formed from two different types of glass, cemented together) will only solve chromatic abberation -- that's what they're designed for. The spherical distortion is only a factor of the focal length of the lens. (Which isn't saying you don't have chromatic distortion that an achromatic condensor would help. But generally, the condensor isn't that picky about achromats -- it's the macro, if you need one, where this is important).