B&W 10 stop ND filter vignette - help required

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woollyback

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Hello folks,

Does anyone use the B&W 10 stop filter on a 17-40 with 5D2. I am experiencing a problem of dark corners (is this called vignette??) up to about 35mm.:shrug::shrug:

Is this normal or am i doing something wrong.:thinking::thinking:

I remove the normal UV filter and use no lens hood but I still get a type of circular image @ <35(ish)mm, beyod that all is well.

Any ideas or pointers would be great and much appreciated

Cheers

Rob
 
It's perfectly normal Rob. If you think about the AOV of the lens at wide focal lengths then some of the light is passing obliquely through the filter and therefore suffering a greater loss than light approaching along the lens axis.
Trigonometry my friend.

Bob
 
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Bob,

I never understood maths - so bombed out and did chemistry instead :).

That's a bit of a bummer then if me wide angle is only 35mm - would I be better off with a crop camera (which I have) and anultra wide say 10 -20mm as you only use a middle bit of the image or is it the same cos your shorter in fl??.

Or am I being completely numb an missing the point?.

Cheers for any guidance

Rob
 
A quick bit of maths then Rob.....

The filter is Xmm thick and the density is constant.
You lens has a diagonal angle of view of 63 degrees at 35mm
That equates to 31.5 degrees per side (diagonally. that is)
The cosine of 31.5 is about 0.852
1/0.852 is 1.17 (all approximate)
That all means that the light entering the corners of your lens are travelling through 17% more dark glass than light entering on the optical axis.
(You also have to factor in the vignetting caused by the filter's frame)

Bob

Edit...
Looking at it another way....
You're crossing a busy road. You run directly across....the shortest route and have X chance of being hit by a car.
Your friend crosses too but he runs diagonally (at 31 degrees). He's on the road for longer and has a 17% more chance of being hit.

Edit again....
It's the AOV and not the sensor size that gives the problem.....no real benefit going wider (shorter FL) with a crop if you arrive at the same AOV
 
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Bpob,

Thanks for that - I wish you had been my maths teacher :).

So looks like I'm pretty much stuck with it then

Cheers

Rob
 
It's worse at lower f/numbers because of the natural vignetting of the lens. Switching on the 5D2's Peripheral Illumination Correction will help with that, in the same way that it's very easy to correct the filter thing in post production.

Personally, I quite like the effect but if you want to get rid of it in post, then make sure you are generous with the exposure (expose to the right) as it pulls a lot of noise out of the shadows when you correct.
 
I found vignetting to be worse with my Big Stopper if I forgot to to cover the viewfinder whilst taking the shot. Use the little rubber thingy on the strap or just some electrical tape.
 
Morning all!
Sorry about my piccies being removed from the linked thread.

At 24mm on full frame the vignetting is easy to correct in PP.
I don't usually bother as it often helps the image composition.

Here's a recent image straight out the camera
i-6qnNCJh-S.jpg


The same image with the colour cast corrected and tweaks to Exposure, Brightness and Contrast plus some light local adjustments.
20110827-112003-IMG1107-S.jpg
 
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Freester said:
I found vignetting to be worse with my Big Stopper if I forgot to to cover the viewfinder whilst taking the shot. Use the little rubber thingy on the strap or just some electrical tape.
Click to expand...

I must admit that I haven't tried that!
I'll give it a go next time I'm out. (y)

I know that the camera's exposure estimates are a pretty wild if the mirror is down and the viewfinder is uncovered.
But using Live View, not only can you see the image composition without removing the Big Stopper, but the exposure estimates seem spot on!
It seems the light sealing is pretty good when the mirror is up; but it's probably not perfect and your suggestion seems perfectly valid.
 
My 2p.....
With the blue colour cast I get using the Lee Big Stopper it is easy to blow the blue channel.
The highlight clipping blinkies don't always flash and the white histogram doesn't show any clipping.
The only clue is that the RGB histogram shows the blue channel getting clipped.

I find that to use the camera's in-built metering, I need to underexpose by a full stop in order to keep highlight detail in the blue channel.
 
I just got a 10 stop ND from B+W. I use a Neutral B+W for protection. I get no vignetting with the Neutral but when I remove it and use the ND on this 35mm FF fixed lens... bam.. vignetting. Based on the comments above, I guess not much I can do.

lightbox
 
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