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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Full open vignetting<><>

Rick Darge

Rick Darge

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I did a quick run&gun short film a few weeks ago with a friend.. I noticed this anomaly while processing footage earlier today,

Shot this clip fully open on the Red 18-50 zoom, I was wide @ 18mm. Using 6 stops of ND and slightly underexposed the shot by 1.5 stops. This is the RAW image, untreated. Notice the left side of the image, in the upper left corner, it is vignetting & looks like a gaussian blur was applied. I haven't tested or seen this problem come up before. Is this the nature of the Red zoom when fully open and at its widest focal point? Or could this be another issue?

4K original TIFF
http://www.theredshooter.com/vignette.tiff
 
Hi Richard,

I would send your lens back to Red, it should not do that,

Stephen
 
Can you check the lens without the NDs first.
I have seen problems on other lenses where lots of NDs caused problems with wide lenses.
 
I have seen that as well. On several different zooms when fully open.

My Nikon zoom does that as well.
 
Stephen Williams said:
Hi,

Some of my Nikon zooms do that in all 4 corners, the fact that it is just 1 corner show that there is an issue with this individual lens.

Stephen
Click to expand...

I found it too hard to tell from that image because the only detail/high contrast is in the upper left.
 
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I just shot a series of tests, f/2.8 no ND, f/2.8 6 stops of ND, f/22 no ND

I will post JPEGS as soon as Redcine is finished outputting footage..
 
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I can't tell if this softness/vignetting is only on the left or if its on the right as well. My eyes are going crazy and I can't tell what I'm looking at anymore..

Here are 3 stills, RAW, output out of Redalert.. I converted them to JPEG files with MAX quality settings


Test still #1 : http://www.theredshooter.com/tests/1.jpg

ASA 320 - 18mm - f/2.8 - 1/48 - 6 Stops of ND (1.2 & .6 stacked)


Test still #2 : http://www.theredshooter.com/tests/2.jpg

ASA 200 - 18mm - f/2.8 - 1/2000 - No ND


Test still #3 : http://www.theredshooter.com/tests/3.jpg

ASA 320 - 18mm - f/22 - 1/120 - No ND
 
Richard, it's hard to tell because the images are so soft. What kind of ND's are you using, Schneider? It just seems that all that stacking may have caused some sort of anamoly in the lens, depending on how well everything was stacked in front of the lines. Were the ND's parallel to each other? Was the mattebox a little off kilter?
 
Justin, I was using Schneider glass. NDs were parallel to eachother. I was using the ARRI LMB-5 clip-on MB and nothing was off kilter as far as I could tell. If you look at image #1 and image #2(no NDS), they look pretty similar in softness

Justin_Kirch said:
Richard, it's hard to tell because the images are so soft. What kind of ND's are you using, Schneider? It just seems that all that stacking may have caused some sort of anamoly in the lens, depending on how well everything was stacked in front of the lines. Were the ND's parallel to each other? Was the mattebox a little off kilter?
Click to expand...
 
This may be one of those occasions where a focus chart will tell us something that a landscape cannot.

If you don't have a focus chart at your place, point the camera at something with regular high-frequency detail... bricks, a rug, some ugly wallpaper, a window screen, anything.
 
try shooting a white card/wall or Grey area ( light evenly )
set Red spot approx 75-80 IRE ( use ND's for wide open and combination of ND f stop for other T stops you want to see) ... now zoom from 18-50 ... 50-18 ... you'll see perhaps the right or left side corners get a little darker ?
look very careful to see if the slight darkening is actually in the image area ( piture safe) or just in corners of the "look around" ...
i can see my right side of frame will get slightly darker but it is only in the "look around" and does not come into image safe area ...
many zooms do the same...

to check sharpness across frame - shoot test chart ..
 
I was looking at the bottom left corner of the images, note the highlights of the wheel were streaking on an angle. It's happenening in the first 2 images, but not the third, which means the NDs is no the cause of the problem.
 
rgdfilmsRED said:
I can't tell if this softness/vignetting is only on the left or if its on the right as well. My eyes are going crazy and I can't tell what I'm looking at anymore..

Here are 3 stills, RAW, output out of Redalert.. I converted them to JPEG files with MAX quality settings


Test still #1 : http://www.theredshooter.com/tests/1.jpg

ASA 320 - 18mm - f/2.8 - 1/48 - 6 Stops of ND (1.2 & .6 stacked)


Test still #2 : http://www.theredshooter.com/tests/2.jpg

ASA 200 - 18mm - f/2.8 - 1/2000 - No ND


Test still #3 : http://www.theredshooter.com/tests/3.jpg

ASA 320 - 18mm - f/22 - 1/120 - No ND
Click to expand...

I don't see any vignetting, but damn those are some ugly stills! :) 18mm is not that wide - not wide enough to be worrying about vignetting, as far as I know.
 
In case anyone is interested.. Here is a focus chart I shot.. It wasn't large enough, so i focused for the center, and moved the chart around to each corner.

13MB zip file.. 4k JPEGS, highest quality setting..

http://www.theredshooter.com/focustests/Focus_363.zip

Light was kept at an even f/2.8 with the help of 3 stops of ND in front of the lens. Lit by 2 kinos. Focus was measured by tape & adjusted slightly using the 2x focus assist.

Feedback welcome
 
While the board on the center is properly exposed the charts on the angles are over and result in a washed out image that doesn't help to judge
Maybe joust a problem in processing the raw files...

but as i can see the right side is quite ok
The left side is a lot more blurred (compared to the right).

Maybe your lens mount isn't in its place correctly. with a closer f you won't see but full open it appears evident.
 
Stephen Williams said:
Hi Richard,

I would send your lens back to Red, it should not do that,

Stephen
Click to expand...

Maybe we had better investigate all the possibilities 1st? If it is the lens, we will take it back. But since there are variables (NDs), it just might be prudent to check before jumping to conclusions?

Jim
 
Hey Jim

I've been doing a lot of my own 'garage tests' these past few days, as well as going through older footage.. The NDs don't have any noticeable effect as far as I can tell. This problem exists when the lens is fully open and wide. I would have written it off except for the fact that the anomalies are occurring on the left side of the frame, and not the right, which struck me as odd.. If I stop down to f/4-5.6, these problems become a lot less noticeable to my eye
 
Jannard said:
Maybe we had better investigate all the possibilities 1st? If it is the lens, we will take it back. But since there are variables (NDs), it just might be prudent to check before jumping to conclusions?

Jim
Click to expand...

Hi Jim,

Never seen ND's effect focus on one side and cause vignetting on a lens before.
Putting the lens on a lens projector would be interesting.

Stanley Kubrick always asked lens manufactures to send 10 examples of any lens he wanted to buy, he would then pick the best one & send 9 back!

Stephen
 
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