Two cameras, one set of lenses, matching back focus for each camera?

[Safaran Qureshi]

Hi guys,

 

I am focus pulling on a local TV commercial in a few weeks.

 

We will be shooting on an Alexa for static shots and then shooting on an FS7 on a Movi.

 

We'll be using the same lenses for both cameras.

 

As the gear is owned by the production company, I was told gear would be prepped for me and therefore no prep day.

 

My main concern is that the back focus will be off when I put the lenses on the FS7 (or vice versa) and the markings of the lenses will be off, making it difficult for me to pull focus whilst its on the movi.

 

Just wondering if this is a common issue what AC's do about this in varying budgets/levels.

 

Lovely to hear any thoughts on this, thanks!

 

 

Edited August 18, 2022 by Safaran Qureshi

[Robert Hart]

You may have answered your own question ( no prep day ). Promises to prep gear for you due to mishap, may not always be the best kept. The best you might do will be to allow time in your schedule to set up each camera in turn on a tripod. The focal plane mark on the body should be the same measured distance from a focus chart (siemens star) as your shots are likely to be from subject. Set your shutter speed or gain level or both so that you have to open the lens aperture wide, then note where the focus mark on the lens is for each camera. A good monitor will be your best friend in this instance. Please heed better advice than mine when it comes along.

Edited August 19, 2022 by Robert Hart
error

[Dom Jaeger]

I work for Panavision where we make very sure that camera flange depths are correct, so I don’t really know what procedures a production company might have in place to check their gear. But presumably the last job went ok? Can you talk to the equipment manager about their prep procedures?

Are you using zooms? Are you taping out or otherwise measuring distances and relying on the focus marks? If not, and it’s mainly monitor focussing then you don’t need to be too concerned about camera flange depth being exact. 
 

If you do want to rely on the focus marks, check a mid to wide focal length and see if it lines up wide open. Shorter focal lengths will be more out if there is a flange depth discrepancy. Or check a zoom by focussing at the long end and making sure it stays in focus at the wide end. If you find an error, check another lens to make sure it’s the camera not the lens. As mentioned, if it is the camera, the focus marks will be more out on shorter focal lengths and less on longer ones. By 100mm you won’t notice even a large flange depth error.

[Robert Hart]

Dom. Slightly off-topic. Where do you obtain precision plastic shim material in Australia these days? Cheers.

[Dom Jaeger]

1 hour ago, Robert Hart said:

Dom. Slightly off-topic. Where do you obtain precision plastic shim material in Australia these days? Cheers.

Hi Robert,

I have been using the same Artus shim stock assortment kit for ages now, as well as having a drawer full of various shim materials (plastic, brass, gold and silver leaf, etc) accumulated over the years, so I don’t know where you’d buy it nowadays sorry. A lot of companies have their own shim sets for camera and lens mounts - Arri, Zeiss, Cooke, Angenieux etc.

I think Artus will ship internationally, but lots of places sell shim stock. I find the assortment kits more useful than individual sheets. 

I have noticed it’s getting harder to find some engineering products here, since our manufacturing sector has been so decimated. 

[Robert Hart]

Dom. thanks for that. Cheers.