3-stop ND filter reduces saturation

[Scott Whaley]

However shutter speed is often used with strobes to control background luminance & ND filters will allow that, in just the same way as aperture. A

The ND Filter reduces the ambient light "equally" across the frame. When you add a strobe you're changing the EV on selective portions of the frame. I use an ND outside to lower the overal EV of the scene so that I can balance aperture and shutter for the intended shot. Using an ND with strobe is somewhat counterproductive, because switching to HSS negates the need for an ND.

I completely agree

 

[weepete]

I'm not well versed in the ins and outs of flash photography, but could you up the power of the flash (or adjust the aperture) to counteract the effect of the ND filter on the subject, then if the background is lit by ambient there's the potential to underexpose the background by more using the ND filter?

 

[sfogel2]

To clarify, I bought the 3-stop ND filter for situations where I'm using flash outdoors, and where and I want to reduce the brightness of a very bright background compared to the brightness of my subject. I use flash to give dimension (some light and shadow) to the faces. To accomplish this, I could use a faster shutter speed, above the sync speed of my camera, and use high-speed sync flash to expose my subject. However, I've found that using high-speed sync reduces the output of the flash by 2 to 3 stops, so sometimes the flash (I use the Interfit S3 strobe) is not powerful enough. The alternative is to set the shutter speed at or below the sync speed, use an ND filter to reduce brightness of the whole scene, and then use high power on the flash, without high-speed sync, to expose my subject properly.

But with ND filter approach, I'm noticing a reduction in saturation compared to the high-speed sync approach. If others are seeing the same effect, I'm going to return the B+W filter and try a different one. Thanks.

 

[smoke665]

I'm not well versed in the ins and outs of flash photography, but could you up the power of the flash (or adjust the aperture) to counteract the effect of the ND filter on the subject, then if the background is lit by ambient there's the potential to underexpose the background by more using the ND filter?

You can but why? Managing backgrounds in relation to the subject is nothing more than the "reflective" reading (not incident) of the background in relation to the "reflective reading on the subject. A difference of 4-1/3 stops under is pure black, a difference of 2-1/3 stops over is pure white. Altering that reading will allow you to produce anything in between.

Prior to the advent of HSS you used a ND filter to lower the ambient light so you could get below the camera flash sync speed, but there are limitations with under powered speed lights. By comparison, this was a HSS, shot mid day on a very bright sunny day, ISO 640, f/5.6, 1/2500 handheld.

 

[smoke665]

use high-speed sync flash to expose my subject. However, I've found that using high-speed sync reduces the output of the flash by 2 to 3 stops, so sometimes the flash (I use the Interfit S3 strobe) is not powerful enough. The alternative is to set the shutter speed at or below the sync speed, use an ND filter to reduce brightness of the whole scene, and then use high power on the flash, without high-speed sync, to expose my subject properly.

Could you be noticing a difference in color temperature instead of saturation? I didn't find the spec on the S3 but other models were showing +/- 200 across the power range, which could be noticeable.

Have you tried shots without flash both with and without the ND? Just adjusting the exposure?

I've used the same approach stacking ND gradients to overcome difficult lighting situations but I was using more powerful studio lights or multiple speedlights. I'm not a fan of pushing any light to max power.

 

[photoflyer]

Could you be noticing a difference in color temperature instead of saturation?

The same thought crossed my mind.

 

[weepete]

You can but why?

Thanks mate, I was more curious if it was possible, than anything else. I rarely use supplimental lighting, so another tool in the box so to speak.

To the OP: I agree with the guys that have mentioned a colour shift. Many of the ND filters have a blue shift, even the more expensive ones. I wonder if this is what you are seeing as well. You could always try some test shots with a white card and see what effect it has.