Letus Extreme vignette

[notdjp]

Hi all,

I have a JVC GY-HM100 with a Letus Extreme. When setting up the adapter (as per instructions) I zoom in all the way to focus on the ground glass, set the focus to manual, then zoom back out a little. But as soon as I do zoom out, even the smallest amount, a vignette creeps in. And the more I zoom out the worse it gets. So I have to keep the camera zoomed in all the way, which really restricts framing. Any ideas why I can't pull back on the zoom?
PS: I have a 50mm prime, 28mm prime, and a zoom lens (all Canon FD), and the problem is the same with all lenses -- there's no vignetting with the lenses off.
Thanks for your help,
D

 

[Egg Born Son]

Some fast lenses can be prone vignetting slightly at their widest apertures (even without the adapter). If your lens is a f1.8 or 2 you might want to try stopping down to f2.8 or 4 and adding lighting to compensate. But it might also just be the nature of the beast. I've only had my M2 for a few weeks (which has far worse light issues) and I've found eliminating vignetting entirely usually comes at some other cost. I get pretty good results at f4 but with an old M2 it's pretty dark (gotta get the cinescreen upgrade). Also I've found low-light will make it the vignetting worse in general. If it's not too bad you can make it less noticeable just by cluttering up your set, lighting unevenly and/or avoiding solid colours to the edges of your frame when you're dressing your set or composing your shot.

 

[notdjp]

THanks for that. Looks like I'll have to put up with it, or experiment with set and uneven light -- godd ideas. I think stopping it down would close up the iris, so make the vignetting worse.

 

[Egg Born Son]

It seems counter intuitive to me too but it seems to work. I was reading up on my Nikon lenses on kenrockwell.com and a lot of his tests seem to indicate vignetting (light fall off he calls it) in the corners of the photos as well as distortion in some of the fast lenses with fully open apertures. That is the basis on which he makes some of his more controversial recommendations. He picks some slower and cheaper lenses such as the 135/3.5 over the faster 2.8 because it underperforms at f2.8. Assuming it's not all in my head, I'm guessing it works because a smaller iris reduces the amount of stray light coming through the lens. Which would presumably concentrate in the centre of the image due to the function of a lens. Perhaps a mattebox would achieve the same effect. I was planning on mocking one up out of foam card over the weekend to see if I can improve things.