Brevis Vignetting Issues

S

sk8orinda

Active member
So, I have a DVX100b, and I recently got me a Brevis 35 with a Canon and a Nikon mount. everything is perfect, does exactly as it should, but the vignetting is pretty bad. in the right lighting conditions, you might not notice it, but it's always there to some extent.

NOW, granted, I have yet to buy a super nice lens (working with a Canon 28-135 f3.5-5.6 that serves as a good indoor lens, and a crappy Nikon 100mm 2.8 which I use for outdoor stuff) it showed up on my friend's cheap 50mm 1.8 Nikon lens too, so I'm ruling out the lens speed.

so, like I said, my lenses aren't that good, but I have a feeling it's not just the glass that's causing it.

Can anyone share techniques they have used to eliminate vig on their adapters???

My idea involves cutting a tiny bit off the bottom of the carbon fiber housing, making the lens closer to the GG... thoughts?
 
It's very important that your unit is using the correct imaging element for the camera in use to get best edge to edge illumination. The DVX100b is a bit of a transition camera and with your lens choices, we find CF1, (not CF1le) will provide potentially better performance if you lean towards wider angle lenses. Do you know which imaging element is installed?

Your f3.5 zoom would actually be unusable on many adapters, so there, you're actually ahead. Keep in mind that the lens is only at f3.5 when you're at 28mm, and the effective aperture is at f.5.6 at 135mm.

Either way, I can pretty much guarantee that an imaging element change will address the issue...and they drop in with about 3 minutes of effort :-)
 
Dennis, you really do have a good hold on the various imaging elements that correct problems depending on the camera and lens used. Have you addressed HV30 issues? I still see poor footage coming from the HV20/30 and most adapters. Maybe it's user error or the type of lens used (small format DSLR) who knows. What do other adapter makers do to correct these problems since they pretty much stick to one imaging element?
 
I think the brevis is THE adapter for HV20/30's I would really like to see what footage you are talking about
 
Okay, I will admit when I am wrong. I may have only seen very limited footage that had vingetting from the HV30 and Brevis. On vimeo and youtube, folks often tag their videos with other adapter names to get them viewed. But there are vids out there with the SGPro and the Letus and HV30 and doesn't look so good:

http://www.vimeo.com/1457615
http://www.vimeo.com/736166
http://www.vimeo.com/757052
http://www.vimeo.com/1265893
http://www.vimeo.com/627983
http://www.vimeo.com/1154024

Maybe thatlast one was intentional but it seemed to have vignetting and hotsoptting.

Not trying to bash adapters, I was just simply wondering if the HV30 has problems with adapters accross the board.
 
I agree, other adapters do have problems with vignetting, I dont know what brevis does to their GG but no one else has figured it out yet
 
The difference is that we extensively test with both small cameras and larger cameras..and we're the only ones who deal with the rather obvious differences in the optics. It's extremely expensive to do R&D this way, but our customers are happy with an adapter that works with their entire camera collection :-)

This one by Carlos B using an HV20 is pretty special: http://www.carlosbaena.com/live/live_SF.html

And this one is eye-popping sharp with the HV20 and CFX:
http://www.vimeo.com/1659093

Enjoy :-)
 
oh im glad you didnt reference my vids on vimeo regarding the hv20 +brevis CFX. they're horrible. just bought the brevis 2 weeks ago and the vids are mostly tests on an old minolta series 1. wheew. :) i wouldnt want ppl to think the brevis had many problems. i changed lenses on a school vid and its beautiful!
 
Well, here I go. I've recently acquired a Brevis CF1 and the following Nikon Ai Lenses for my HV30:

50mm f2
28mm f2.8
70-200mm f4-f5.6

I do get sharp footage- but even when zoomed in to the max I see vignetting- even outdoors in broad daylight- it's not very dark- but it is there. This is even when my lenses are wide open- it is completely impossible to close them down because the vignetting would literally distort my image. Is it because of my lenses? Or what could I possibly be doing wrong? And what would you suggest doing in post (in FCP) to reduce vignetting as much as possible?
 
It would be nice to get Jon or Dennis on here and tell us which lens models to stay away from. I know that a lot of the cheaper lenses of Nikon are made for a smaller screen so that would mean they project a smaller image and would create vignetting on a 35mm format.
 
Sometimes you just got to buckle down and spend good money on fast lenses.

With my canon lenses, 28mm will vignette at f2.8. you'll have better luck with a faster lens at 2.0 or better.

f4 - 5.6 for a zoom just sounds too slow.

I would think 2.0 on a 50mm would be fine though. However 50mms are cheap so I would try to find a f1.4 for faster lens.
 
My guess also is that the 70-200 might vignette no matter what. It may have to do with the rear element size. Don't know about the 28mm 2.8 but the 50 should be fine.

I have an old Tameron 35-135 f3.5 that vignettes like crazy on my adapters but none of my other lenses do including Tokina f2.8 zooms.
 
The key phrase here is zoomed in fully, you're seeing vignetting. The bare HV20 (no adapter affixed) goes from a nice flat waveform response at full wide, to easily 1 full stop of loss at full zoom. So the camera's fall-off adds to the lens fall-off...and then you can have a fair bit of vignette.

Step 1 is to make sure your lenses are designed for full format.

Step 2 is to check out the still photogs comments on edge falloff for a lens you're considering. For example the Nikon 17-35mm f2.8d lens has been commented on by Ken Rockwell as having very low edge fall-off. Sure enough, on our adpater, it's nearly perfect. Every lens (even given the same f-stop and focal length will vary in this regard and it's 100% a design issue.

Step 3 is to reduce HV20 or HV30 zoom-in as much as possible. The bare camera goes from a nice flat waveform to losing nearly a full stop at the edges when fully zoomed. For this reason, using our flip with it's extra XY adjust is important. The HV20/30s are well known for imaging block alignment issues...meaning if your adapter won't adjust for this, you end up zooming in way more than you should. For the Brevis MP.1 flip, there is a large range of adjustment...and it's a one-time setup issue for each camera used :-) Less zoom-in is definitely better.
 
All lenses have a certain amount of vignetting around the edges. If you're comparing to what you get with a still camera using the same lenses then you have to remember that unless you have a full frame camera (like a Nikon D3, D700, Canon 5D, etc.) then you are dealing with a crop factor and are only capturing the center area of the lens which (usually) shows very little fall off even on cheap lenses.
 
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