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Old June 1st, 2007, 06:11 AM   #1
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A simple solution for removing vignetting from 35mm adapter footage

I've only briefly tested this, although not properly, but it appears to work alright. A way of dealing with the slight vignetting that may appear in some shots, normally due to wider lenses being used.

1) With your camera & 35mm adapter set up, attach your problem lens and then grab a piece completely flat white paper or anything else with a perfectly even flat white surface.

2) Place the paper so that it covers the entire view. Make sure your lighting is evenly lit too. Ensure your exposure is correct with no blown out areas using the zebras on your camera and shoot a few seconds of the white paper. You should easily see the dark vignetted edges.

3) Shoot your footage as normal with the same lens, vignetting and all.

4) Now, the editing stage. I use Vegas myself, but I'm sure this can be done with almost any editing app. Grab a still of the white paper with the vignetted edges. Place this on the very top track. Turn the track off for the time being.

5) Next load in your footage, edit as normal.

6) Alright, grab your white clip from the top track, activate the track again and place it directly above any vignetted footage you've edited that was shot with the same lens. Stretch it out to fit the width of the clip whilst making sure the edges line up.

7) Then next go to the white paper track's level slider and set the compositing mode of the track to 'Burn'. Now, you should no longer see the vignetting on the track below!

8) Of course some finer adjustments can be made. It might help to add a slight bit of blur to the white paper clip. Also reduce it's saturation to 0. Finally, you can also adjust the track's level slider depending on how much vignetting reduction you require.

The final result may end up looking slightly noisy, but should still be an improvement. A couple of further suggestions: Store the white paper images on your computer for each problem lens. Rather than having to shoot the white paper before each set up. Lastly, it may speed up your work flow by doing this to all your footage before editng and then saving out all these fixed clips that you can then edit. Rather than placing the white paper clip over every edited slice whilst you're editng.

Hope some of you find this useful.
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Old June 1st, 2007, 06:59 AM   #2
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Glenn, that's a really creative solution. Nice job.

I've been waiting to ask this question, and now you[ve given me the opportunity...

How do I know how far to zoom in on the GG? It seems that if I just use my camera to zoom in a bit further, any vignetting will be gone. Is there a reason not to do this?

How far does everyone else zoom in? BTW, I have an SG35.
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Old June 1st, 2007, 07:20 AM   #3
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Hi Paul, and thanks for your interest.

I'm using an SGPro(Rev1) and I'll normally try and zoom in as far as possible. But with the HV20 it will only go so far. Meaning that with my Nikon 28mm lens, I'll always end up with vignetting and a big hot spot in the middle. My 50mm f1.4 is the only lens totally free of problems. My other two, the 100mm and 135mm are good too.

So if you can still zoom in really far without losing focus, that'd probably be your best option.
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Old June 1st, 2007, 07:57 AM   #4
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I'm thinking that if I zoom in too much, I've reduced the field of view of the 35mm lens; not enough and it vignettes slightly.
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Old June 1st, 2007, 09:30 AM   #5
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Apparently you still have quite a lot to play with. Here's an idea, if you have an SLR camera, put the same lens, or at least a lens with the same focal length, check what it's field of view is and compare that to what you're seeing on the camera. It should give you an idea of what you should be seeing.
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Old June 1st, 2007, 10:41 AM   #6
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Funny, I just did something similar. I just pulled my camera back and looked at the image on the GG.
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Old June 1st, 2007, 11:21 AM   #7
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I tried direct comparison with my stills camera's field of view and it's a little too approximate for my taste.

Since my camcorder has no zoom numbers in its display (only a thermometer thingie), I'm toying with the idea of making (out of plastic card) a hard mask that's slightly larger than 24x36mm and mounting it just behind my spinning GG.

This would give a fixed reference point, at least, as to where the original 35mm stills coverage area would be.
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Old June 1st, 2007, 02:38 PM   #8
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Yea, if there was a way to know or measure accurately how much to zoom on the GG by using the FOV of the widest lens you think you will use, that'll be good. Maybe markings on the GG like an optical viewfinder of a film camera? How is a PSTechnik set up?

I dont know if this works since I dont have an adapter, but I'm thinking another way would be to put on your widest lens and have its aperture closed all the way and zoom your stock lens past its corners. If you have a monitor with underscan, check on it to make sure.

Another thing, with adapters having options for SLR lens mounts or cine lens mounts, cine lenses have slightly narrower FOV than SLR lenses although I'm not sure if I'm making any point with that info lol.
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Old June 1st, 2007, 02:47 PM   #9
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Quote:
Originally Posted by Zulkifli Yusof View Post
Another thing, with adapters having options for SLR lens mounts or cine lens mounts, cine lenses have slightly narrower FOV than SLR lenses although I'm not sure if I'm making any point with that info lol.
Certainly. It means you have to zoom in farther if you're using cine lenses.
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Old June 1st, 2007, 03:05 PM   #10
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if your camcorder side optics setup allows for it.

Oversimplified, the 35mm movie frame is a "half frame" format, 18x24mm 4-perf frame instead of a "full frame" 24x36mm 8-perf frame, so your cine lenses would have slightly better than half the FOV coverage of your stills lenses.

However, the cine lenses are designed to be much, much sharper, since they're built for a much larger degree of image magnification (think cinema screen magnification from a half frame negative vs. a 16x20 print from a full frame negative) and the lens designs are to different circle of confusion (image resolution) standards.

Also, the cine lenses are, of course, designed to follow focus whereas the stills lenses aren't, and the cine lenses don't have iris aperture click stops in them, and sometimes stop down to full closed, whereas stills lenses have different focusing barrels, iris stops, don't go down to full closed aperture, and typically don't have internal focusing either (i.e. the image "breathes" when you work the focusing ring)

Adding those things naturally makes the manufacturing more expensive, and the lenses are priced accordingly.
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