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02-12-2015, 04:36 PM   #1
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USe of ND FIlters (Pt 2)

Following on from previous thread, I have attached three images using this brand of Variable ND filter on a wide angle lens. Sigma 10-20mm.. The uneven shading is quite evident and increasing a the ND Filter is darkened.

Camera: K-7
Lens: Sigma 10-20mm at 10mm
Mode: AV
ISO: 100
Aperture: f5.6
Shutter speed: set by camera

Clearest setting on ND Filter. Note some darkening in the sky to top right.




ND Filter darkened slightly. Note dark patch expanding on right and becoming visible in left bottom corner.



ND filter darkened further. Image peaks for itself.




Conclusion: These Variable ND Filters are completely unusable on wide angle lenses. These are branded "K&F Concept" and purchased on ebay. I advise any potential purchaser to steer clear of them.

02-12-2015, 06:48 PM   #2
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Further reading suggests B+W have a filter that operates down to 10mm on APS-C and 17mm on FF but at RRP of $645, I am not in a position to be trying it out.

https://www.schneideroptics.com/Ecommerce/CatalogItemDetail.aspx?CID=1882&IID=9491
02-12-2015, 09:19 PM   #3
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QuoteOriginally posted by Bruce Clark Quote
Following on from previous thread, I have attached three images using this brand of Variable ND filter on a wide angle lens. Sigma 10-20mm.. The uneven shading is quite evident and increasing a the ND Filter is darkened.

Camera: K-7
Lens: Sigma 10-20mm at 10mm
Mode: AV
ISO: 100
Aperture: f5.6
Shutter speed: set by camera

Clearest setting on ND Filter. Note some darkening in the sky to top right.




ND Filter darkened slightly. Note dark patch expanding on right and becoming visible in left bottom corner.



ND filter darkened further. Image peaks for itself.




Conclusion: These Variable ND Filters are completely unusable on wide angle lenses. These are branded "K&F Concept" and purchased on ebay. I advise any potential purchaser to steer clear of them.
My Canon friend has had bad, similar experiences with Promaster brand Variable ND filters.

I don't own one, makes me wonder about them. I assume it is safer to get fixed ND filters..
02-13-2015, 12:15 AM   #4
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that "high end" schneider one give's the same results. solids are the best. and with digital they should be combined with IR when over three stops of corrections.

02-13-2015, 01:02 AM   #5
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I suspect that part of the issue is that variable ND filters are really two polarizing filters.

You should note that polarizing filters are also not recommended for ultra wide angle lenses, because the effect of a polarizing filter is relative to the location of the sun in the photo and at 10mm it results in a very uneven sky darkening

You would be better with a graduated ND filter for the shot you have and the shooting angles
02-14-2015, 03:00 AM   #6
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Agree with the post above that this is a result of the filter being really a polarising filter. Still think Cokin-style filters are the way to go for quality of result, though they can be fiddly to use.
02-14-2015, 08:12 PM   #7
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A big thank you to all who have commented. It has been a great help. Taking the advise that the filter is in fact a linear polariser, I set up to the ND ring to the brightest position and by unscrewing the filter slightly was able to find a position where the polarising effect was minimal. By increasing the ND effect while keeping the body of the filter in its position. I was able to achieve far superior results. It was not perfect but by three simple brush strokes in Lightroom I was able to clean up most of the issues.

End result in broad daylight an exposure time of 1.3 seconds (0.1 Sec without filter).

Camera: K-7
Lens: Sigma 10-20mm
Filter: K&F Concept Slim Fader ND
ISO: 100
Aperture: f29
Shutter: 1.3 Sec



While, I can not give these filters a ringing endorsement, I can now say within limitations especially on wide angle lenses useful results can be achieved with patience, much attention to detail and some post processing. I am a much happier camper.
02-15-2015, 02:27 AM   #8
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I'm struggling to see what the long shutter speed achieve in that image!

02-15-2015, 04:02 AM   #9
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QuoteOriginally posted by cats_five Quote
I'm struggling to see what the long shutter speed achieve in that image!
Nothing, It is merely an experiment in order to work out how to get these filters to work as best as possible under comfortable conditions.
02-16-2015, 06:45 AM   #10
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QuoteOriginally posted by Bruce Clark Quote
Nothing, It is merely an experiment in order to work out how to get these filters to work as best as possible under comfortable conditions.


Oh good, was worrying I had missed something obvious!
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