pjm1
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Ok, my pair of Kood filters arrived this morning. I bought them from Crooked Imaging for £18 each and they're Lee-compatible 100mm square resin filters, with the soft grad being 125m long.
For resin they feel pretty solid - not as heavy as the glass Big Stopper I have but that's to be expected.
I decided to do some quick testing for colour cast, EV reduction and the like. I also wanted to see how soft the grad was across the frame.
I took four images of a very boring indoor shot - a white gloss door with some ghastly interior halogen light messing with the colour balance across the frame. Not the sort of image that you're ever likely to use an ND filter for, but it served a purpose for this experiment. The images, shot on a tripod-mounted D750 with 85mm lens at f/2.8 and ISO 400 were:
1. No filter
2. ND4 plain grey filter added
3. ND4 soft grad filter added, with the filter top aligned with the top of the holder bracket (not the very top of the holder, just the bracket which takes the actual filters)
4. ND4 soft grad filter, aligned centrally within the holder
Of note for the grad, the lens diameter of the 85mm is 67mm - not a huge lens element by any stretch, but probably "average" for FX. The lens diameter affects how much of the gradient is "seen" by the sensor - as does the focal length.
I loaded the four images into LR then PS as layers. Using the colour sampler tool I set up a couple of sample points just in from the top and bottom of the image edge:
(Click on image for full size link). I underexposed to avoid lifting the ISO much further. I guess I could have slowed the shutter a bit more to expose correctly, but the underexposure showed the colour casts off a bit better to my eyes. The two sample points were set at the crossing points of the guides in the image above.
ND4 Plain Grey filter
This recorded a true 2 stop difference at both sample points, more or less (at least +2 EV gave a better fit than +1.9 or +2.1). There was a slight blue colour cast, requiring a Camera Raw Filter adjustment of Temp+4 and Tint-2 to get it back close to the original (with the +2 adjustment). Obviously correcting the slight colour cast is easy with a plain filter, but it was good to see reasonable consistency across the top and bottom of frame and confirmation it was a 2 stopper. These adjustments didn't quite nail each of the two sample points, but they were close enough in both luminosity and colour.
ND4 Soft Grad filter
With the top of the filter aligned to the top of the filter holder bracket, the top sample point required an adjustment of +1.85EV. The bottom sample point required +1EV. This means a spread of probably about 1EV across the entire frame, so this really is a very soft grad. If I'm honest, probably a bit too soft and I reckon I'll be using a hard grad more than this one, except perhaps for mountain shots. The colour cast was, again, slight - requiring an adjustment of Temp+4 and Tint+8 - noticeable if you know it's there without being unbearable if unadjusted (IMHO). Making these adjustments pretty much nailed both sample points, suggesting the cast was fairly consistent... however...
With the filter aligned in the middle of the holder, the top sample point required an adjustment of +1.15EV and (surprise, surprise) the 0.85EV differential was preserved (nice linear grad then) which meant the bottom point required +0.3EV. The colour cast, however, was different, requiring only a tiny tint adjustment (+2) - this says to me the grad is casting rather than the underlying resin, which is a shame but perhaps not that much of a surprise. Knowing this, it's perhaps a bit unexpected that a single WB adjustment corrected both sample points in the above example, but it pretty much did. In this adjusted image, the top point was slightly off in terms of hue meaning a different adjustment at the top vs bottom would probably have helped.
Soft Grad with a wide angle
I'll be honest and say I was surprised at the very shallow gradient the soft grad filter applied. This is, of course, partly due to the smaller diameter of the 85mm lens as well as the fact it's a slight telephoto rather than wide angle. So to compare the effect this grad has with a WA, I tested it on another couple of shots with my 19-35 zoom, set to 19mm. This lens has a 77m diameter, although the front element is considerably smaller than this. Being wide-angle, it will "get" more of the gradient than a telephoto, even with the WA attachment to connect the filter holder (which holds the filters very close to the front of the lens).
It turns out this did help the grad's effectiveness - an adjustment of +2.5EV was required at the top (so more than a 2-stopper in practice) and exactly +1EV required at the bottom. I placed the colour sampling points closer to the edge of the frames than in the picture above with this lens, just to check the full extent of the gradient.
Again, there was a WB (Tint and Temp both +2) adjustment required, although the slight mismatch in hue between the top point and bottom point even after this WB adjustment. Bear in mind, though, these adjustments are very minor in the grand scheme of things - this is no strong cast at all. It does suggest the tiniest cast might be coming from the resin itself (the tint) and a further slight cast from the gradient (the temperature). You could, if you really wanted to, correct this tiny cast in post fairly easily with a grad in LR, since there isn't a hard edge anywhere in this grad, save at the very bottom.
Conclusions
The plain grey ND4 filter is good - it has a very slight but easily correctable colour cast and is confirmed as a 2-stop reduction. I'd definitely recommend this filter as for £18, it's excellent value.
The soft grad with a longer lens, is just too soft with only a 1 stop effective gradient across the frame, at least at 85mm. With a wider-angle lens (19mm) it is more useful, delivering a 1.5 stop gradient across the frame. This still feels a touch too limited for me, but it's definitely better than with a longer lens.
No matter which lens you are using, I would recommend using this filter aligned to the top edge of the holder bracket to avoid hitting the bottom "edge" of the gradient at all. This means that you could, theoretically apply a gradient adjustment in LR (or PS) to counteract the slight cast from the gradient effect of this filter.
I will probably buy the ND4 hard grad to compare, which will be more useful than this for brighter skies with flat horizons. I can't find a reverse grad from Kood anywhere, which is a shame as I'd like to add one of those to my collection. The ND4 soft grad is probably just short of what I need in terms of gradient and therefore effect... I will probably invest in a soft 3-stopper which should (if consistent with this) give a 2.25-stop gradient across the frame. Although stacking grads isn't ideal, this soft grad plus a 3-stopper (ND8) soft grad will then give me everything from 1.5 to nearly 4 stops of gradient. In addition to a single ND4 hard grad, that should cover pretty much all requirements.
Again, it's worth reiterating how reasonable these filters are. Compared with Lee, you're getting a resin instead of glass filter, but it's still pretty accurate - especially the plain grey 2-stopper. I would say the soft grad is useful as part of a kit of grads, but because of its limited effect, it isn't the first grad I'd recommend anybody buy. I'll report back when I've had a play with Kood's hard grad to compare.
For resin they feel pretty solid - not as heavy as the glass Big Stopper I have but that's to be expected.
I decided to do some quick testing for colour cast, EV reduction and the like. I also wanted to see how soft the grad was across the frame.
I took four images of a very boring indoor shot - a white gloss door with some ghastly interior halogen light messing with the colour balance across the frame. Not the sort of image that you're ever likely to use an ND filter for, but it served a purpose for this experiment. The images, shot on a tripod-mounted D750 with 85mm lens at f/2.8 and ISO 400 were:
1. No filter
2. ND4 plain grey filter added
3. ND4 soft grad filter added, with the filter top aligned with the top of the holder bracket (not the very top of the holder, just the bracket which takes the actual filters)
4. ND4 soft grad filter, aligned centrally within the holder
Of note for the grad, the lens diameter of the 85mm is 67mm - not a huge lens element by any stretch, but probably "average" for FX. The lens diameter affects how much of the gradient is "seen" by the sensor - as does the focal length.
I loaded the four images into LR then PS as layers. Using the colour sampler tool I set up a couple of sample points just in from the top and bottom of the image edge:
(Click on image for full size link). I underexposed to avoid lifting the ISO much further. I guess I could have slowed the shutter a bit more to expose correctly, but the underexposure showed the colour casts off a bit better to my eyes. The two sample points were set at the crossing points of the guides in the image above.
ND4 Plain Grey filter
This recorded a true 2 stop difference at both sample points, more or less (at least +2 EV gave a better fit than +1.9 or +2.1). There was a slight blue colour cast, requiring a Camera Raw Filter adjustment of Temp+4 and Tint-2 to get it back close to the original (with the +2 adjustment). Obviously correcting the slight colour cast is easy with a plain filter, but it was good to see reasonable consistency across the top and bottom of frame and confirmation it was a 2 stopper. These adjustments didn't quite nail each of the two sample points, but they were close enough in both luminosity and colour.
ND4 Soft Grad filter
With the top of the filter aligned to the top of the filter holder bracket, the top sample point required an adjustment of +1.85EV. The bottom sample point required +1EV. This means a spread of probably about 1EV across the entire frame, so this really is a very soft grad. If I'm honest, probably a bit too soft and I reckon I'll be using a hard grad more than this one, except perhaps for mountain shots. The colour cast was, again, slight - requiring an adjustment of Temp+4 and Tint+8 - noticeable if you know it's there without being unbearable if unadjusted (IMHO). Making these adjustments pretty much nailed both sample points, suggesting the cast was fairly consistent... however...
With the filter aligned in the middle of the holder, the top sample point required an adjustment of +1.15EV and (surprise, surprise) the 0.85EV differential was preserved (nice linear grad then) which meant the bottom point required +0.3EV. The colour cast, however, was different, requiring only a tiny tint adjustment (+2) - this says to me the grad is casting rather than the underlying resin, which is a shame but perhaps not that much of a surprise. Knowing this, it's perhaps a bit unexpected that a single WB adjustment corrected both sample points in the above example, but it pretty much did. In this adjusted image, the top point was slightly off in terms of hue meaning a different adjustment at the top vs bottom would probably have helped.
Soft Grad with a wide angle
I'll be honest and say I was surprised at the very shallow gradient the soft grad filter applied. This is, of course, partly due to the smaller diameter of the 85mm lens as well as the fact it's a slight telephoto rather than wide angle. So to compare the effect this grad has with a WA, I tested it on another couple of shots with my 19-35 zoom, set to 19mm. This lens has a 77m diameter, although the front element is considerably smaller than this. Being wide-angle, it will "get" more of the gradient than a telephoto, even with the WA attachment to connect the filter holder (which holds the filters very close to the front of the lens).
It turns out this did help the grad's effectiveness - an adjustment of +2.5EV was required at the top (so more than a 2-stopper in practice) and exactly +1EV required at the bottom. I placed the colour sampling points closer to the edge of the frames than in the picture above with this lens, just to check the full extent of the gradient.
Again, there was a WB (Tint and Temp both +2) adjustment required, although the slight mismatch in hue between the top point and bottom point even after this WB adjustment. Bear in mind, though, these adjustments are very minor in the grand scheme of things - this is no strong cast at all. It does suggest the tiniest cast might be coming from the resin itself (the tint) and a further slight cast from the gradient (the temperature). You could, if you really wanted to, correct this tiny cast in post fairly easily with a grad in LR, since there isn't a hard edge anywhere in this grad, save at the very bottom.
Conclusions
The plain grey ND4 filter is good - it has a very slight but easily correctable colour cast and is confirmed as a 2-stop reduction. I'd definitely recommend this filter as for £18, it's excellent value.
The soft grad with a longer lens, is just too soft with only a 1 stop effective gradient across the frame, at least at 85mm. With a wider-angle lens (19mm) it is more useful, delivering a 1.5 stop gradient across the frame. This still feels a touch too limited for me, but it's definitely better than with a longer lens.
No matter which lens you are using, I would recommend using this filter aligned to the top edge of the holder bracket to avoid hitting the bottom "edge" of the gradient at all. This means that you could, theoretically apply a gradient adjustment in LR (or PS) to counteract the slight cast from the gradient effect of this filter.
I will probably buy the ND4 hard grad to compare, which will be more useful than this for brighter skies with flat horizons. I can't find a reverse grad from Kood anywhere, which is a shame as I'd like to add one of those to my collection. The ND4 soft grad is probably just short of what I need in terms of gradient and therefore effect... I will probably invest in a soft 3-stopper which should (if consistent with this) give a 2.25-stop gradient across the frame. Although stacking grads isn't ideal, this soft grad plus a 3-stopper (ND8) soft grad will then give me everything from 1.5 to nearly 4 stops of gradient. In addition to a single ND4 hard grad, that should cover pretty much all requirements.
Again, it's worth reiterating how reasonable these filters are. Compared with Lee, you're getting a resin instead of glass filter, but it's still pretty accurate - especially the plain grey 2-stopper. I would say the soft grad is useful as part of a kit of grads, but because of its limited effect, it isn't the first grad I'd recommend anybody buy. I'll report back when I've had a play with Kood's hard grad to compare.
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