138mm VS 4 1/2" Round Filters?
 

Why would you choose one of these round filters over another in a matte box? I notice some matte box systems will accept either size, the 138mm round or 4 1/2. Does it matter which one you use?

138mm is 5.5 inches,

It depends on the size of your...

matte box.

And whether or not it can take rounds. These are for larger cine lenses and telephoto still lenses used for cinematography.

Thanks, Mark. Let's say you have a matte box that can use both kinds of filters, the 138mm or 4 1/2 - does it matter which one to use?

Also, is there any benefit to having more than two filter stages in a matte box?

Charles, if you can use both that's great. Two main factors determine which size: the lens with the largest front diameter and how much money you have. It's best if you can standardize all of your filters to whatever the largest diameter lens you have. Standardization saves time and money. If all your filters are the same size, you can use just one tray and switch it between filters. Otherwise you end up spending your money buying different sized trays. I think that most matte boxes only let you use one or two round filters, but a lot of square filters. Go to Arri, or Chrosziel and look at their matteboxes.

All this stuff-matte boxes, brackets, rods, donuts, etc are expensive and building a collection of even 4x4 filters is costly. That's why so many people rent part or all of their camera package for video and film. Any decent rental house will have a good selection of filters to choose from.

The main thing is the quality and condition of the filters. Tiffen, B+W/Schneider, Harrison& Harrison, Pancro, are all excellent. I'm sure I'm forgetting some. The main thing is to put the least amount of material in front of your lens. Though, sometimes you may find that the lens is too sharp and you can use all manner of things to soften the lens-stockings, cellophane wrappers, bottles... In the old days the DP would diffuse the lens for close ups on the leading lady. That isn't always the case nowadays, people go for a more subtle, natural look. When tryng out effects like vaseline, put it on a glass blank, not on the front element of your lens!

More than two filter stages can be helpful. I generally don't use more than two filters at a time, but it's always nice to be able to have an extra slot or two for more filters. Having stages that can rotate is beneficial. If you have a polarizer, or graduated filter, you can move them so you can achieve the desired effect.