I don't remember this being asked, and "search" isn't helping me. I apologize if this has been answered before.

What filter will most closely resemble the effects of a ground-glass 35mm adapter (for me, the Letus35A) other than the shallow DOF effect? I would like to match footage as closely as possible between shots I take with the adapter and those taken without. I expect that shots that require very low-light and shots where I want a very long lens will work best without the adapter, but I want them to have a bit of the "feel" the adapter produces.

I'm guessing it might be something like a promist or black promist, but I don't want to start shelling out money on filters if they aren't close to what I need.

Haven't tried it, but my vote would be for an Ultracon. I have one, and the milky effect on the darks and slight flare of the highlights looks very similar to the 35mm adapter frame grabs that I've seen. I was planning to use one for Steadicam shots when I get my own adapter.

I actually did this in post, with Magic Bullet - mostly for the diffusion.

I've also done it the traditional way by using a Cokin Sunsoft ($5 on eBay mint cond). It made some difference, but not as much as in the picture on this site
http://www.geocities.com/cokinfiltersystem/_sunsoft.htm

Does anyone have some side by side comparisons of e.g. the Tiffen Ultra Contrast Filters and the Letus gg? Does anyone have acces to this wide ranges of filters? They come in densities 1/8, 1/4, 1/2, 1, 2, 3, 4 and 5. So picking the right one would be nice. Personally, I prefer not too much diffusion in the highlights to compensate the surrounding shadows, as occurs with the Low Contrast.

As Marcus, I'm preparing some projects and would have to combine Letus and non-Letus footage.
Doing it in post is not a good option, since you can't adjust what you haven't got.

Thanks.

Tiffen link: http://www.tiffen.com/displayproduct.html?tablename=filters&itemnum=44UC1