Using Canon EOS lenses on the Brevis

Abaddon

Abaddon

Well-known member
I'm interested in getting a Brevis and using Canon EOS lenses. I heard the one downside to that is that the EOS lenses don't have f-stop control on them.

But how important is that? Can't I just control that on the camera?
 
You want manual lenses for use with any of the 35mm adapters. Lenses designed for digital cameras rely on signals from the camera, which will be absent with a 35mm adapter.
 
THoff said:
You want manual lenses for use with any of the 35mm adapters. Lenses designed for digital cameras rely on signals from the camera, which will be absent with a 35mm adapter.
Click to expand...


Okay, but if I switch the lenses to manual focus, what problems would I run into at that point?
 
You will need a series of ND filters on the front of the Canon lens to compensate for lack of aperture control, however, I am not sure if this method would yield the same results as stopping down with the aperture blades (if you had manual control)?
 
But what about adjusting the iris on the camera?

Wouldn't that give me all the control I need?
 
You need to maintain your camera at the optimal level, say on HVX around F2.8. Compensating the HVX iris will not avoid overexposing the Brevis diffuser/ground glass, resulting in overexposure and/or burned out highlights.
 
Christopher Barry said:
You need to maintain your camera at the optimal level, say on HVX around F2.8. Compensating the HVX iris will not avoid overexposing the Brevis diffuser/ground glass, resulting in overexposure and/or burned out highlights.
Click to expand...

Not following you here. How can you overexpose a piece of glass??? As long as it does not melt or something. Why would not the ground glass behave in a linear fashion no matter how much light is dumped on it? If it does there can be no overexposure and the brightness can be adjusted with camera iris.

Another matter is of course the fact that there might be some ideal F-stop for the camera as not to get too much DOF on the ground glass. But that is not exposure related, more like optical problem with these contraptions.
 
Think of the diffuser/imaging element as a piece of film. You will have issues (regardless of the 35mm adapter) if you blast the GG with light. Many of the units out there lose 1 to 2 stops at the diffuser, so it itself acts as an ND filter. This is not the case with the Brevis as light loss at the diffuser is extremely low. The best settings (optically speaking) are usually f4 to f8 on the 35mm lens, and similar on the video cam. Ideally the cam would not vary from f4 to f8, and exposure would be controlled using a combination of ND filters and aperture on the 35mm lens. Because adapter users are typically looking for shallow DOF, they are shooting with the 35mm lens wide open, something you would not normally do with a 50mm f1.4 outside in bright sunlight. This means that ND filters and/or polarizer filters must be used to bring the light levels down. The cam's built in ND filters should not be used, as these are after the imaging element...and will fool you into thinking the GG is exposed correctly. I've just started using 4x4 filters in a mattebox, and this is definitely the easiest way to go (but not the cheapest). If you get a 72mm ND .6, .9 and circular polarizer you will be able to use these with step up rings, on just about any 35mm lens. These filters will also work with any video camera, although if your cam is 82mm, you may want to standardize on 82mm.

The disadvantage to shooting wide open all the time is that you cannot dial in deeper DOF, to suit your shots with the same lens. Switching to a slower wide angle EOS lens, and moving the cam closer will get you deeper DOF and correct framing if you're using a set of EOS lenses.

The best thing to do (with any adapter) is mount it up and deliberately force these conditions, checking for sharpness, edge softness etc. with the 35mm lens/video cam lens at different apertures. You'll get an idea of where max sharpness, contrast, etc. lay. Many cams/lens suffer from softness when used with wide open apertures.
 
Last edited:
So in other words, the EOS lenses aren't really the way to go.

I was hoping to get them because I shoot stills with the Canon, but better to save myself the headache I guess.
 
I still refuse to understand how you could "overexpose" a piece of ground glass. Overexposure is caused in both film and digital sensors when the amount of light gets over the linear portion of the gamma curve and detail is lost. Glass does not behave this way, it is totally linear until it melts from the heat.

The other thing is that the camera used to shoot the ground glass behaves like any video camera shooting close-up. Of course the in-camera ND can be used to control the light and aperture like always without any ill effects. As long as the image in the viewfinder/scope/DVRack looks correctly exposed you are fine. The only difference is that you can control the exposure in two stages, 35mm adapter and camera. I would control it with the camera (iris & built-in ND) and use the best aperture for the DOF effect on the adapter lens.

If I am mistaken, exact physical reasons, please.

Somebody here missunderstands basic physics.
 
Petrus, let's say you have a overexposed photograph on your desk. Do you think you can get the detail back by taking a picture of that with a camera that has a ND on it?
 
Abaddon said:
So in other words, the EOS lenses aren't really the way to go.

I was hoping to get them because I shoot stills with the Canon, but better to save myself the headache I guess.
Click to expand...

Exept that you need a minute or two for adjusting the desired aperture, Canon EOS lenses are a great way to go, specialy if your still camera is Canon and even more if you alwready own a few like I do. Nikon are great also.

best
Andreas
 
Andreas said:
Exept that you need a minute or two for adjusting the desired aperture, Canon EOS lenses are a great way to go, specialy if your still camera is Canon and even more if you alwready own a few like I do. Nikon are great also.

best
Andreas
Click to expand...


So what's your take on what these guys are saying?
 
I really don't uderstand what you are asking me here. The statement some member did that you will have always you aperture wide open is false, I did give you a link that I explain how the trick works so you can try for your self. As for the ND filters, I thing I uderstand Dennis suggestion not to use the internal filters, but this is something I have to investigate further. When I will buy my adapter that is. Anyhow 72mm ND filters are cheap and you are going to use them anyway at some point.

best
Andreas
 
Regarding the overexposing issue, there is really no question about what is happening.

The GG / diffuser is the equivalent of a projection screen, and if it is overexposed, you can't film the projection screen with a ND filter or a smaller aperture and get a correctly exposed, detailed version of what was projected -- all you'll get is a dark, featureless mess.
 
THoff said:
Regarding the overexposing issue, there is really no question about what is happening.

The GG / diffuser is the equivalent of a projection screen, and if it is overexposed, you can't film the projection screen with a ND filter or a smaller aperture and get a correctly exposed, detailed version of what was projected -- all you'll get is a dark, featureless mess.
Click to expand...


Yeah, my bad, its not a matter of investigating realy then dealing when the time comes. ND filters before GG/ diffuser is the anwser. Case closed. I was trying to find a way to say: "don't bother with that its not a big deal, just have your external ND filters ready, or close the aperture" Writing directly in English makes me laisy some time and I end up writing the closest of what I actual want to say ! But realy, I wait to see with my eyes how the GG behaves using internal ND, I uderstand the theory, just want to see with my eyes.

best
Andreas
 
When a diffuser of any type is "bathed" in excessive light, you will end up with hazing and other image degradation. Our three diffuser options will behave differnently of course in terms of what constitutes overexposure.
 
You must log in or register to reply here.
Back
Top