Focusing on the Ultimate GG question

[Gogu]

Hello,

I own a Letus Ultimate with an EX1. I'm confused about the fact that after setting up the adapter on the camera and focusing on the GG I used the peaking function of the camera to check the area that is in focus and the Peaking pattern was not filling the entire image. Shouldn't the peaking pattern fill the screen almost completely if the image has edge to edge sharpness. The pattern that i'm getting is that the peaking pattern if mostly concentrated in the center of the images and starts to fade at the edges. The pattern also starts to fade completely when I start closing the iris on the camera. At about 5.6 it fades pretty hard.
The adapter GG fills my screen at about Z69 setting on the camera. Probably the peaking would fill my entire screen area at longer zoom settings (almost fully zoomed) but this would not be normal working condition. I usually set my zoom to about Z75-80 to avoid corner vignneting.

Another effect that I observed while using it is that with wider Zeiss PL mounts lenses (lower than 35mm) I cannot see the rectangular shape of the adapter window, instead it is rounded at the edges. As a consequence I have to zoom in even further to avoid vignetting (Z85) . Is this normal ?

Thanks! I'll post some photos to illsutrate what i'm talking about. ( I usually get a bigger peaking pattern now as this was an old photo and I don't remeber the camera settings, I guess the iris was stopped down a bit).

[Dennis Wood]

Obviously I'm not on expert on the Letus products, but your questions would apply to any adapter.

1. The EX1 has edge softness at macro focussing distances, like when using a 35mm adapter. We've ameliorated this to a great extent with our CFXL imaging elements, but the fact remains that the EX1 is a challenge in this regard. In our tests, the camera was sharpest edge to edge at f8, so at f8 and adequate lighting, the peaking pattern should be pretty even.

2. Using a PL mount would suggest that your lenses are projecting an S35 cinema frame gate at 18x22mm or so. Edge falloff is exacerbated typically on wide angle lenses, however once you've framed 18x22mm, your image should be filling that frame. If not, then you've got an adapter design issue that you cannot fix at your end. Wide angle lens performance varies wildly amongst adapters..certainly we've worked very hard on this.

3. Your peaking pattern might suggest that you've got an Z axis issue there to deal with in addition to the focus issue. If the adapter optics and diffusion screen are properly aligned, the peaking pattern should be centered. In this case, the peaking pattern is skewed downwards suggesting that something is not aligned...as if the adpater was drooping forward. This issue must be addressed first as you'll have edge softness top to bottom on every lens and camera you use.

Hope that helps.
Dennis.

[Dino]

Are you using the new Letus achromat, the one included in the HVX200 or EX1 Optimization kit? I found edge to edge with my Ultimate and EX1 to be very good,
just a small amount of CA at the edges, but focus was impressive in all zones.