Why do depth of field adapters vibrate?

[Gillvane]

Ok, i did some googling but couldnt' readily find the answer. I know sorta kinda how a DoF adapter works. You focus with a 35mm lens, the image is projected on a piece of glass or something, and then the video camera records the image from the glass. Also, there's something that flips the image from upsiide down and backwards to normal.

But what vibrates? It sounds wierd, obvously you want a camera still, not vibrating, but I see some DoF adapters are of the vibrating kind.

[Alex H.]

The focusing screen can introduce an excessively grainy look due to the matte finish on one side. The vibrations minimize the appearance. The vibrations also help to keep dust and dirt off the screen.

[Gillvane]

The focusing screen can introduce an excessively grainy look due to the matte finish on one side. The vibrations minimize the appearance. The vibrations also help to keep dust and dirt off the screen.

So the image is actually projected onto a vibrating piece of glass, and that makes the image better? Wow, I never would have figured that out.

[Jason Ramsey]

adapters either vibrate or spin. The motion of the imaging screen (as said above) is to mask the grain. The imaging screen has to have some grain structure to it, or the light would just pass straight through and you wouldn't have an image for your camera's lens to film.

but, if the grain pattern is fixed, you would see that in your recorded image as well. By spinning, or vibrating it, you keep it in motion so that it does not show as easily in the recorded image.

Three main types of adapters, each with their own potential benefits and side effects:
Static (non moving screen)
Vibrating
Spinning.

later,
jason

[Gillvane]

adapters either vibrate or spin. The motion of the imaging screen (as said above) is to mask the grain. The imaging screen has to have some grain structure to it, or the light would just pass straight through and you wouldn't have an image for your camera's lens to film.

but, if the grain pattern is fixed, you would see that in your recorded image as well. By spinning, or vibrating it, you keep it in motion so that it does not show as easily in the recorded image.

Three main types of adapters, each with their own potential benefits and side effects:
Static (non moving screen)
Vibrating
Spinning.

later,
jason

Thanks for the info. I saw some of the home made DoF adapters on ebay. They all mention that you have to flip the picture in post, but of course none of them vibrate or spin, and none of them mention the downside of that.

[Jason Ramsey]

the 4 main adapter companies (brevis, redrock, sgpro, and letus) all either flip natively or offer a flip add-on now.

Well, there is also the Cinemek G35, which is a static adapter (non-moving screen)... Probably the main option for those looking for a static adapter. Don't think it's a flip though.

Search around here in the 35mm adapter section on this forum for starters and learn the differences between the 3 different types of adapters listed above.

later,
jason

[ZazaCast]

...because they are excited...

[Jockomo]

So the image is actually projected onto a vibrating piece of glass, and that makes the image better? Wow, I never would have figured that out.

Technically it makes the image worse, but it allows you to have a shallow depth of field, which can be used to focus the viewers attention on what you want them to be looking at. A storytelling tool that is important enough to stick a ridiculous vibrating monster on the front of your camera.

[andythefilmer]

instead of a 35mm adapter, i just use a macro close up set of screw on filters. they shorten the focal length of the lens, but if you get close enough with a +1 or +2, you get a much shallower depth of field for around $25 (ebay)