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cf1l, vignetting?

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cf1l, vignetting?

New postby Johnny Tsang on Wed May 16, 2007 3:53 am

Why is some of the lens getting more vignetting than others?

setup: hvx200 Zoom - 71 Focus - 11

My 50mm 1.8 AF has vignetting
my 50mm 1.4 NonAF doesnt
my 85mm 1.8 AF doesnt
my 24mm 2.8 AF has it..
my 70-210mm 2.8 @ 70mm there is vignetting.. at the middle there isnt.

im confused.. why is there vignetting? anything i have to try?

I installed the cf1L dull side towards the lens..

thoughts?
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New postby Gene Crucean on Wed May 16, 2007 9:43 am

Dull side towards which lens? :)
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New postby Dennis Wood on Wed May 16, 2007 9:51 am

Johnny, three questions:

1. This is with the HVX correct?
2. Have you checked your focus at infinity? You may need to adjust the Nikon mount slightly fore or aft.
3. Are you using a spacer, or not?
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New postby Johnny Tsang on Wed May 16, 2007 12:28 pm

1 its the hvx
2 no spacer
3 adjust the nikon mount, let me try that..
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New postby Johnny Tsang on Wed May 16, 2007 12:28 pm

dull side toward nikon lens
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New postby Andreas Ursin Hellebust on Wed May 16, 2007 1:24 pm

Also: zoom 71 is quite low. I tried on an overscanned monitor, and found out that you need 72 for the entire frame to be covered by the Brevis cinescreen. On the latest shoot, we used zoom 75 to be sure everything was in order... Also: lenses are not at their best at the edges.

good luck :)
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New postby Johnny Tsang on Wed May 16, 2007 1:38 pm

another brevis owner told me that Z71 and MF 11 is the sharpest. Is this false?

so I adjusted the nikon mount, and sure enough I fixed one thing.. which is my infinity focus.. it was originally not correct.. now it is..

however some lenses have vignetting.. so I need a spacer now?
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New postby Johnny Tsang on Wed May 16, 2007 1:50 pm

vignetting:

50mm - Image

24mm - Image

70-210mm - Image
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New postby Gene Crucean on Wed May 16, 2007 3:20 pm

71 is pushing it for an HVX. Try 75ish.

Either way I would have thought that CF1L would have fixed most vignetting problems.
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New postby Dennis Wood on Wed May 16, 2007 3:52 pm

It does, but it cannot compensate for edge fall-off variations on some lenses, or vignetting that comes from stopping a lens down where adequate lighting is not present. Stopping the camera itself down a great deal can also introduce vignetting, regardless of the adapter, being used. The other thing we cannot fix is the fact that the SLR image cone is finite...meaning even though our imaging elements often allow exceeding SLR film frame widths, not every lense will be happy like this. In other words, for some lenses you will have to zoom into a 36mm wide frame.
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New postby Jon Wolding on Wed May 16, 2007 4:01 pm

I zoom in to at least 77.
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New postby Johnny Tsang on Wed May 16, 2007 5:23 pm

so regardless if its 71 or 77, it will be the same?

my friend has an HD monitor to monitor the sharpness of the back focus. That's why he told me 71 and 11 is the best.

When you zoom to 77, what is the focus? i tried and it seems to stay at 11..

dennis.. if i get a spacer will that fix it up?
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New postby Ash Greyson on Wed May 16, 2007 9:44 pm

There is no best, it will vary by machine. Every HVX is NOT the same. You are likely dealing with an off center element or lens on the HVX end. I have 2 HVXs and one requires more zooming in because the CF is more off center. Your problem looks to be on the right side and this is an HVX issue, not a Brevis issue.




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New postby Gene Crucean on Wed May 16, 2007 11:10 pm

Jon Wolding wrote:I zoom in to at least 77.

Me too, I'm usually in the 75-78 range.

Johnny, the focus is so critical that there is even play within each number. Set it to whatever focus number you think is closest and then play with it back and forth while keeping it at that number. You should see a difference. If it gave a readout of 11.8 or whatever, then that might work but whole numbers are just too coarse to judge by.

If you have a mac, check it with a free program called FlipFlop http://web.mac.com/mark.burton/iWeb/Site/FlipFlop.html

In my opinion this is one of the most important parts in making an image sharp with an adapter.
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New postby Dennis Wood on Sat May 26, 2007 11:41 am

Gene, I agree 100% that backfocus is the most critical component of every adapter shoot as getting this even slightly off will affect every shot. At very close distances with an achromat (macro) attached focus is super, super critical. Johnny, if you can access one of the Dell 24" LCDs with HD component inputs, just plug in your cam and play a bit.

Try focussing on an object at 5cm from the lens using just the HVX and achromat (no adapter) and you'll see right away what I mean. Macro shooting a flat object without a macro stand would be near-impossible as even a tiny bit of variance on parallelism between lens and subjectg will show up as a soft edge. DOF is the shallowest I've ever seen in this configuration.

Some reports we just got back from a two adapter shoot (testing our micro-collimation front rings/and new PL mounts) indicate that even camera temperature may affect back focus on the 2/3" chip cams.

We always recommend checking back focus every time you attach the adapter using the largest HD monitor you can find, or at least using both peaking and focus assist on the onboard LCD. Lock the video camera lens at f4 or so to get max sharpness from the video camera too. I'll admit that I do this myself every time I shoot...and ignore settings entirely. With cams like the XH-A1, re-set the focus/zoom preset switch you attach the adapter.
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New postby wayne granzin on Mon May 28, 2007 8:37 pm

ok so if a person has an "off center hvx" does that just mean that every adapter shoot is just going to be vignetted to one side - period?
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New postby Jon Wolding on Mon May 28, 2007 10:28 pm

wayne granzin wrote:ok so if a person has an "off center hvx" does that just mean that every adapter shoot is just going to be vignetted to one side - period?

Nope. Just zoom in past the vignette.
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New postby Dennis Wood on Mon May 28, 2007 11:06 pm

Also, make sure you've done the rear XY adjustment (page 2 of the quickstart guide). There's enough adjustment there to take care of most camera's lens-centric issues. For cameras like our HV20, which is ridiculously off-center, we'll be bringing out a special interface (cheap) part very shortly.
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Re: cf1l, vignetting?

New postby Andrew Swihart on Sun Dec 05, 2010 6:50 am

I have an HV20 , has this part been made? I have a good deal of Y axis offset that would be nice to correct.
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