Question about Matte boxes

[Leo Mandy]

I am curious about matte boxes, never having had one - how do they work with rails? When you focus a lens, extends and contracts, so therefore the matte box would have to move in and out along with the lens. How does it therefore, attach to a rail system? It would have to move along the rail system while focusing, right?

[Leo Mandy]

Was this a dumb question? I have a plastic matte box that I have attached to my SLR lens, it moves when the lens is focused - so how does that work if the matte box is attached to the rails? Or is the matte box not attached to the rails?

[Ben Winter]

Magic. Video magic. Actually from my understanding SLR lenses are the only ones that "breathe"--that is, they extend and contract, and obviously they aren't meant to be used with a video matte box, so there's simply an incompatibility. The ones you use with SLR lenses are bellows matte boxes that specifically extend and contract (they're bellows, they do that), and the setups you see with fixed matte boxes have the SLR lens in a hole in the matte box that is much bigger than the lens itself, meaning the SLR lens sort of just pokes through the matte box hole and doesn't actually attach.

Basically, any matte box that is attached to the rails shouldn't be attached to the SLR lens unless it's a bellows matte box.

[Robert Double]

Originally Posted by Ben Winter

Basically, any matte box that is attached to the rails shouldn't be attached to the SLR lens unless it's a bellows matte box.

This is not true! You can get SLR lens that don't breathe. I have a Nikon 80-200 2.8 (latest edition), and also a Nikon 28-70 2.8 - both which dont breather. I use these lenses with a CAVision 16:9 matte box and they work great together!

[Richard Alvarez]

For lenses with 'internal focus' optics... there is little to no 'breathing' of the barrel. For lenses that DO have a movement when focusing, there is a 'doughnut' that encircles the lens, allowing for the mattebox/lens to flex, or to slip while the lens moves... depending on the mattebox design.

Follow that?

[John Colette]

Tru enough - but the focal shift on SLR lenses varies a lot - and if you use a hard mattebox - like a Chrosziel - the inner diamater of the "Donut" like a stepdown ring from the box itself - varies to about 80mm. Cine primes - like Zeiss - have fixed 80mm fronts across the whole range - and they slip neatly into the matebox.

Some SLR lenses focus internally - like the Nikon 80-200 2.8 zoom - and so there is no issue. Some move a few mm in focussing - mostly wide angle lenses, and so they are not too much of an issue - except they have front diamaters of between 50-60mm - meaning that they let light in the back of the matte box - which ruins the idea entirely!

I often use a donut of thick closed cell foam - cut to size - that slips between the front of the lens and the mattebox. Many DOPs I have worked with do the same - on a Panavision Millenium for instance....

You can also use soft "lens hoods" that collapse - in the collapsed position - they screw onto the front of the lens - and form a seal with the donut. Not as nice as a cine prime - but costs about four bucks.

The worst lens I have for expanding is a Sigma 24-70mm 2.8 zoom - but it also breathes the least of almost any lens I use - and so it's a good choice for outddor work. Changing focal length on this lens changes the length of the lens - but so does swinging a prime - so you just re-adjust the mattebox on rails between shots. If you are careful - the longer focal lengths expand more during focus - but they can be distanced back from the glass filter in the mattebox with a foam donut. Shorter, wide angles usually sit well into the mattebox, with enough room to focus without pressing into the filter.

[Ben Winter]

I don't know what the @%)* I'm talking about. Forgive me :)

[Leo Mandy]

The plastic matte box I have is large enough to let the SLR slide in and out. It also has a small adpater for 52mm, but this won't work because of the breathing. No problem though, I will attach the matte box to the rails and have it slide through the large opening. thanks for the comments.

[Bill Porter]

Also we shouldn't get started using the term "breathe" when we talk about lenses that extend. The term "breathing" is already assigned to a change in field of view during focusing.

Anyway Mandy Leo, how the hell did you get your screenname changed to Leo Mandy? I need to do the same thing; my first name is Porter and my last name is William. Bill for short!

[Richard Alvarez]

Absolutely correct John, I've custom cut a number of 'foam donuts' to fit around lens barrels to match up with cine matteboxes!

[Leo Mandy]

Interesting about the foam donuts, care to share pics with the group?

[Richard Alvarez]

Leo,

None handy right now. Basically, I measure the diameter of the lens barrel, the diameter of the matte opening, scribe them onto a piece of foam, break out the electric carving knife and carve away. NOt rocket science after all.

[Ben Winter]

I remember asking before, but I forget the answer...what's the name of the mount that's on the front of Canon FD lenses? (Maybe it's the same with all SLR's, I don't know, but I have FD's...) I need to mount a Cavision matte box to the front (it doesn't mount on rails, its the smaller kind)

[John Colette]

Sorry - double post.

[John Colette]

We're talking campimg matt foam here - the kind you take hiking. You can get black closed cell foam from a .... foam place .... and then a circle cutter from an art supply store [like a cross between a compass and a scalpel].

Couple of swishes and you have a donut!

If you *don't* seal the back of the box, and especially if you ise a polariser - light forms a ring on the glass which is VERY visible on the image.

The cheaper "DV" matteboxes from century optics use very thin foam donuts which are screwed in to adjust the box to the particular camera - the idea is the same.

-j