Jump to content




Photo

138mm Diopters

diopters lens

  • Please log in to reply
5 replies to this topic

#1 Bradley Stearn

Bradley Stearn
  • Basic Members
  • PipPipPip
  • 117 posts
  • 2nd Assistant Camera
  • London

Posted 20 June 2015 - 01:03 PM

I'm going to be focus pulling on a short film for a couple days starting tomorrow. In terms of camera kit it's all fairly simple, we're shooting Amira with a CP.2 prime kit. We're going to be using an arri LMB-15 mattebox, with 4x5.65 filter trays. 

 

Due to being busy this week, I wasn't able to attend prep at the kit house with the DOP. Something I haven't worked with yet are Diopters, and we have a set of 138mm diopters on this shoot. I've seen them used before on a set I was 2nd ACing on, but didn't pay as much attention as I should have towards how the 1st AC placed the diopters into the mattebox. Am I right in saying that diopters sit in a tray just behind the mattebox? If anyone can offer any advice that would be great, I'm sure it's simple, but if I learn anything new now I can avoid any mess ups tomorrow morning. 


  • 0




#2 Bradley Stearn

Bradley Stearn
  • Basic Members
  • PipPipPip
  • 117 posts
  • 2nd Assistant Camera
  • London

Posted 20 June 2015 - 01:10 PM

If anyone could offer an explanation towards how Diopters actually affect the close focus of a lens that would be highly appreciated as well. 


  • 0

#3 Satsuki Murashige

Satsuki Murashige
  • Sustaining Members
  • 3081 posts
  • Cinematographer
  • San Francisco, CA

Posted 20 June 2015 - 07:55 PM

You won't be able to use 138mm diopters with an LMB-15, you'll need either a rod-based matte box with a 138mm bellows like an MB-19 or 114mm clamp-on retaining ring that can hold a 138mm filter. I'd call the rental house right away and see what they have. Otherwise, you'll have to tape the diopter to the front of the lens.

Diopters shift the infinity focus of the lens closer, so a +1 shifts infinity focus to 1 meter, +2 to 1/2 meter, +1/2 to 2 meters. One trick I learned recently from Greg Irwin is to use a wireless follow focus and re-mark the focus disks for each diopter in prep. This way you can keep using Imperial distances to tape focus, if that's your preference. If you only have one disk, you can use 1/2" camera tape, tab one end, and keep them on the lens case.
  • 0

#4 Bradley Stearn

Bradley Stearn
  • Basic Members
  • PipPipPip
  • 117 posts
  • 2nd Assistant Camera
  • London

Posted 22 June 2015 - 03:06 AM

Thanks for the response Satsuki! Turns out yesterday the rental house gave us two mate boxes anyways, the LMB-15, and an arri swing away similar to the MB-19 that you mentioned. The LMB-15 was for a rotating polariser in a 4x5.65 tray, and then the swing away mattebox with the bellows was to hold our diopters. We ended up not using the diopters yesterday, I think on our second day of shooting (wednesday) they play to do an extreme close-up of an actors face, so we will probably be using the diopters. 

 

Thanks for the explanation of how they work, I will try and make the judgement for the DOP to let her know which diopter would work best in relation to the lens we are using/shot. 

 

I had a play with the diopters during setup yesterday morning just to make sure I could get them into the mattebox, to save wasting time/looking bad when the DOP asks me to put one in during the day. I thought we had the wrong clamp on ring, but I then realised it involved screwing the ring off, and then placing the diopter in between that ring and the clamp. At least I know for next time though!


  • 0

#5 Satsuki Murashige

Satsuki Murashige
  • Sustaining Members
  • 3081 posts
  • Cinematographer
  • San Francisco, CA

Posted 22 June 2015 - 04:28 PM

Glad to hear it worked out. Usually, a good rental house will know that the matte box you ordered won't work with the filters requested and will give you a call or make a suggestion. Good to know they had your back, thank them with some nice craft beer when you get the chance!
  • 0

#6 Jake McClean

Jake McClean

    New

  • Basic Members
  • Pip
  • 1 posts
  • 1st Assistant Camera
  • London, UK

Posted 28 June 2015 - 09:50 AM

Also for anyone else reading this there are a few things to bear in mind using diopters (plenty of resources on the web & books, but useful to have here).

 

- Different strengths shift Infinity closer, as Satsuki said, however this distance is measured from the diopter lens, not the focal plane.
E.g "+1" diopter places infinity at 3'3" / 1metre from diopter lens. 

 

- Make sure they're in the correct way. I believe curved/bulged side faces subject. Becomes a little confusing when you take the mattebox ring off to put the diopter in...

 

- Careful swinging the mattebox back into place, you dont want to scratch or smash it if the mattebox is set to close to the front of the lens. 
Same goes for lenses with moving fronts.

 

- Don't assume the mattebox has the 138mm locking ring - another thing to check in prep. Has happened to me in the past... :unsure:

 

Jake


  • 1



Pro 8mm

rebotnix Technologies

Ritter Battery

Technodolly

Willys Widgets

Aerial Filmworks

Tai Audio

The Slider

Media Blackout - Custom Cables and AKS

Zylight

Glidecam

Visual Products

Abel Cine

CineTape

CineLab

Broadcast Solutions Inc

Paralinx LLC

Rig Wheels Passport

CineTape

Technodolly

Ritter Battery

Media Blackout - Custom Cables and AKS

Pro 8mm

CineLab

The Slider

Glidecam

Tai Audio

Aerial Filmworks

Paralinx LLC

Willys Widgets

Rig Wheels Passport

Visual Products

Zylight

Abel Cine

rebotnix Technologies

Broadcast Solutions Inc