Lens flare with ND filter

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Riccardo259

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Richard
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Hi everyone, I'm having a small problem that I wondered if anyone could help me with. When I'm trying to do a long exposure shot (usually of a body of water) and I have an ND filter on my lens to enable the longer exposure, I tend to get a lot of lens flare in the middle of the shot, or else the outer edges of the shot are exposed correctly but the middle is completely black. Does anyone know why this is happening or have any ideas on how to prevent it? Thanks
 
Cheap variable ND filters can produce a "cross" type effect, with a dark centre.
Are you using a fixed or variable ND filter?
 
mattyg said:
Is your viewfinder covered.
Click to expand...

+1, long exposures in daylight with an SLR need the viewfinder to be covered to prevent light leaking in the back. It sounds unlikely, but it does happen. That's why Canon and Nikon provide a rubber viewfinder cap with their DSLR cameras.
 
I'm using a variable ND filter, and the viewfinder wasn't covered - I shall try that next time, thanks.
 
Alastair said:
+1, long exposures in daylight with an SLR need the viewfinder to be covered to prevent light leaking in the back. It sounds unlikely, but it does happen. That's why Canon and Nikon provide a rubber viewfinder cap with their DSLR cameras.
Click to expand...


...and why pro cameras have an eyepiece shutter.

I agree with the others though. Post an example... let us see it.
 
I found something similar yesterday when trying my Camidox 10 stop for the first time. Images were washed out with some glare. Then I remembered about covering the view finder!
 
I'm curious as to how covering the viewfinder eyepiece can reduce flare, since the light path to the sensor is completely blocked by the raised mirror when the exposure is being made.
A far as I'm aware, you block the viewfinder to prevent stray light affecting the metering, before the exposure.
Once the mirror is raised, there is no longer a light path from the viewfinder to the sensor.
Anyone care to explain this?
 
As I understand it the mirror is semi-silvered to allow the auto focus to work. This would allow some of the light through and not be a total block.
 
Bythesea said:
As I understand it the mirror is semi-silvered to allow the auto focus to work. This would allow some of the light through and not be a total block.
Click to expand...
Only if you have a Sony SLR.

If reflex mirrors are semi-silvered then it's news to me.
 
I don't know know why you'd want to cover the viewfinder while metering with the ND on unless you were using live view. Regardless, with a 10 stop ND metering goes out the window and it has to be manual.
 
Brian G said:
Only if you have a Sony SLR.

If reflex mirrors are semi-silvered then it's news to me.
Click to expand...
Not just Sony. According to Canon my 5D mkiii has a semi silvered mirror. It is how the phase detect autofocus works. I'm sure it's not the only one.
 
Well, I learned something today!
 
Is the Nd filter a screw on jobby or the square variety
 
My variable ND filter does this too. Its because you are effectively using two polarising filters in one. by rotating the filter you are changing the position o one polariser against the other. Once you get towards the two extremes, you get a dark or light 'cross' across the image.
 
I have wondered about this..... Have learnt something useful today!!
 
Brian G said:
I'm curious as to how covering the viewfinder eyepiece can reduce flare, since the light path to the sensor is completely blocked by the raised mirror when the exposure is being made.
A far as I'm aware, you block the viewfinder to prevent stray light affecting the metering, before the exposure.
Once the mirror is raised, there is no longer a light path from the viewfinder to the sensor.
Anyone care to explain this?
Click to expand...

With the mirror up, light from the viewfinder is not blocked 100%. The main problem area is around the piggy-back mirror used for AF. Normally not an issue, but with a 10-stop ND filter fitted and very long exposure times, even the tiniest chink can allow significant light through. It's a common problem.

It's true that viewfinder blinds were introduced, decades ago, to prevent light from affecting the meter, long before 10-stoppers were widely used.
 
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