Alex Nelson

Baltars generally didn't leave the factory in any kind of mount, or with any kind of focusing mechanism. Because of the variety of mounts and camera systems available at the time, it wouldn't have been worth it to Bausch and Lomb. Instead, rental houses and camera manufacturers installed the optical blocks (like yours) into some rudimentary thread-based focusing mount that suited their inventory. You'll need to find the infinity position first, since that will be the closest the lens sits to the film plane and can usually offer a pretty quick answer as to whether or not a particular lens can be adapted to a particular camera system. In your case, 75mm is a pretty safe focal length, since longer lenses traditionally sit further from the film plane or sensor than do wide primes and are therefore less likely to interfere with mirrors or other internal obstructions. You can work out which helical you need with a simple formula: d=f^2/(a-f) where d is the distance the lens travels from its infinity position in inches, f is the foca length in inches, and a is the close focus distance in inches. Say you want close focus at three feet, you would need to move your 75mm Baltar .27" from its infinity position. I actually have a set of Baltars at home. If I can find my notes, I can tell you where infinity is on the 75mm.

I had a couple of minutes today to spend with a 14mm Ultra Prime and a cheap set of digital calipers. My readings, on the whole, seem to line up pretty well with Dom's. It does seem that certain dimensions are more open to interpretation than others. Below is a rendering of the mount I quickly drafted from today's measurments.

I did consider retrofitting an adapter (specifically those on eBay), but they would interfere with the design. In the interest of control, I'm going to have a new one machined to the measurements I pull from a sample of lenses. It does seem silly, though, that so simple and ubiquitous a mount design would be so difficult to reproduce independently.

Hey Ben, I've been printing camera accessories with Shapeways as well. There's a firm in Maryland that can nickel-coat 3D printed parts to give them a little more strength: http://www.repliforminc.com/home.htm By the way, what CAD package are you using? I've had enough of AutoCAD and I'm looking for a replacement.

I actually found the ARRI patent earlier (it's got some nebulous name like "Device for Securing Motion Picture Lenses to Cinema Cameras"). Unfortunately, it's got frustratingly few details. It mainly describes the general operating concept of the PL mount.

Sounds like a plan. This is primarily intended for digital motion picture cameras, so shutter clearance isn't an enormous concern (although, given that the Alexa Studio and F65 will have mechanical shutters, maybe I should re-evaluate that idea). Thanks again, everyone, for your help and responses.

Hahaha, I know, this project is more involved than it probably needs to be. What complicates everything is that the pinhole is created by a mechanical iris rather than a drilled hole. The other complication is that I need the focal length to be shorter than the flange focal depth of a PL camera. I'm aiming for around 25mm. I've done tests with a Nikon D7000, so I know the concept is sound. My goal is also to make this a more finished and robust piece of gear than most DIY pinhole lenses. I'm 3D printing the barrel and most of the moving parts, but the mount needs to be able to handle the pressure of a PL locking ring. It's true, I don't need to work within the same tolerances that Zeiss requires, but I do need a snug fit. My hope is that, once I have dimensions to work with, it really will be as straightforward to CNC as you've said, Dan. I've actually held Clairmont's pinhole lens and it works using pre-drilled swappable plates. It's a nice system, and very well designed (of course), but more cumbersome than what I've designed.

That's quite helpful, actually. I wasn't aware of Les.

Thank you, everyone, for your responses. I am, thankfully, only designing a pinhole lens, so back-focus isn't very critical. My biggest concern, at this point, is that the mount fit securely in any camera body. Also, the machining will all be CNC. I have no illusions about my ability to mill something like this by hand. OEM reps haven't been very forthcoming with information, so my best bet appears to be what Hal has suggested. I also considered photographing the rear of a lens (or a sample of lenses), straight on, using a copy stand and a long lens. Since the external diameter of 54mm is a certainty, it stands to reason that the rest of the dimensions can be extrapolated from there.

Hey everybody, I know this is an odd and probably naive question, but I'm looking for the dimensions to fabricate a PL mount for a lens. I know the diameter is 54mm, but the more critical specs are maddeningly difficult to find. I'm trying to produce a one-off lens for an upcoming project, so I doubt I qualify to license the mount design from ARRI. I suppose if it comes down to it, I'll just have to take my calipers to an Ultra Prime or something. If anyone can offer some direction, though, I would greatly appreciate it. Best, Alex Nelson

Hey everybody, I know this section gets bloated with requests for reel critiques and such, but if you'd be so kind as to give my website, www.ahnelson.com, a quick look and review, I would really appreciate it. And hey, if you happen to check out my reel and want to leave feedback on that as well, I would certainly welcome it. And please, be brutal.

What was the recording medium on "Grey"? Until Arri actually enables the SxS recorder, it seems like your options are limited to the SRW-1 deck, a P2 deck, or a Nano Flash. I know the Weisscam DM-2 will also work, but virtually nobody has access to that. Anyway, the compression resulting from any one of these would certainly have an effect on the post process.

Besides providing a reel, what do you guys think is the most important or desirable function of a cinematographer's site?

Thanks for the input! I meant for visitors to download the PDF of my resume, but I forgot that many browsers don't give you an option. They just open it in the tab or window you're using. I'll probably post a fix for that tonight. Is there any other information, besides project descriptions, that you think is missing?

My last website was done entirely in Flash. It was buggy, unreliable, and impossible to update. Basically, everything I wanted in a professional site. So, after about a year of that, I've completely overhauled the design (all HTML now). In an effort to make the site easy-to-use as well as reflect my personal philosophy, I've taken a minimalistic approach. I'd love to hear any comments and suggestions (particularly honest, constructive input). You can view it at www.ahnelson.com. Thanks guys! -Alex

I think the most important thing is to light with more subtlety and nuance. The lighting tended to look a little "sourcey", but you had nice placement of shadows and compelling shot design. What year are you?

Hey everybody, I'm pretty happy with my current reel, but I get the feeling that it doesn't grab people the way it ought to. I'd appreciate and an all feedback you can give me (the more honest and frank, the better). You can watch it on Vimeo: http://www.vimeo.com/5370319 Any suggestions for improvement would be very helpful. Thanks!