CTO Filter

[lunaticitizen]

I bought this color filter from B&H because I wanted to bring down the temperature of my Nissin i60A flash to 2900K for our Christmas picture.
https://www.bhphotovideo.com/c/produ..._RoscoSun.html

However, I just found out that my i60A's color temperature is 6850K.


And when I applied the filter, it only brought down the color temperature to 3400K.


Should I have applied another piece of filter on the flash head? Ideally it should be 2700K.

[revi]

Unless you have other relevant light sources in the picture or use camera jpegs,
is there any particular reason to worry about the exact colour temperature?
Your flash may "drown" any ambient lamps.

If you really need to get that temp down to 2700K, perhaps add another 1/4 CTO?
If that 2700K comes from the ambient bulbs, I'm not sure how reliable that value is.
(for starters, LED light is not black body radiation)

[lunaticitizen]

Unless you have other relevant light sources in the picture or use camera jpegs,
is there any particular reason to worry about the exact colour temperature?
Your flash may "drown" any ambient lamps.

If you really need to get that temp down to 2700K, perhaps add another 1/4 CTO?
If that 2700K comes from the ambient bulbs, I'm not sure how reliable that value is.
(for starters, LED light is not black body radiation)

Sorry, not enough information from my part.

Yes I did have other relevant light sources that I included such as my floor lamp, table lamp, and the LED lights of the Christmas tree. I purposely chose high-CRI LED bulbs for the lamps and they're 2700K according to their spec sheet . I just looked up "black-body radiation" on Wikipedia! Interesting.

My flash was, I guess, not the main light; it meant to illuminate our faces, only.

When we took the picture, I had the feeling that the flash light on our faces was too white, hence my little test above.

Btw when I took the picture, I fixed the WB on the camera to 2700K. Not sure if that was the right way.

[DanK]

Leo,

I'm not an expert on flash photography, but I think I can confidently say that yes, setting WB to a fixed 2700 was a mistake, guaranteeing that WB would be too cold on the faces.

My own flash work is mostly candids, where I have no control over lighting. Occasional events as well, but I have no control there either. I haven't used gels in so long that I realized today that I don't know whether I still have any.

My most common starting settings are AWB, ETTL, manual at 1/60 or a little more, f/4 or a little narrower, ISO 400. In most indoor settings, the exposure set via E-TTL will create a reasonable balance between flash and ambient light, avoiding harsh fall-off. of course, you can adjust if the mix is wrong.

When I have control, the ambient light is 3000K. In my own home, I use Soraa bulbs in some rooms, which are as far as I can tell the among most color-accurate LEDs available to consumers in the US, so I'm confident that the ambient lighting is at least close to 3000K. (I did test it, long ago.) If I'm not mistaken, my flash is 6000K at full power, but like most, it changes somewhat if the power level is dropped.

With these settings, as Remco says, flash dominates. Yes, there can be some variation within an image in white balance, but usually not that I can see. There will be shots where the overall WB is off (usually, too warm, not to cold), but since I shoot raw, it's usually simple to fix that with the eyedropper tool in LR.

So my guess is that with the filter you bought, you might just need a slight warming of WB in post.

I hope this helps. Someone with more expertise with flash can correct me if I went off the rails anywhere.

Dan

[Manfred M]

It sounds like you are shooting in a mixed light environment and that can be very challenging as each light source can have a completely different colour temperature. To complicate things even more, the colour temperature of the light source may not even be the factor that drive the colour cast. For every light source, we have two main sources of light; the source itself and the colour of the surrounding room which reflects the light from the various sources.

If you shoot in a room that has warm-toned walls, floor and ceiling, etc., then the overall colour temperature in the images will drop and if you have cool toned walls, floor, etc, then the colour temperature of the light in the room will have a higher Kelvin value.

In any flash picture, one "trick" is to take a shot with the camera set to the ISO, shutter speed and aperture and to then take the shot without using flash. Higher shutter speeds will reduce the influence of the other light sources. The camera's sync speed is the limiting factor, unless you are switching over to high speed sync (HSS) mode. That will record the contribution that the ambient light makes to the image. If the shot is entirely black, then the ambient contribution is negligible. Anything that does show, will be in the image taken with flash.

When I use CTO filtering, I start with 1/4 cut and will test the various strengths until I get an image that is visually pleasing and will go with that setup.

Mixed lighting is a reality, even in daylight settings. If you take a shot with your subject under a tree, you will get a green colour cast on your subjects.

The attached image is one taken at evening Golden Hour on a clear and cold day. The areas illuminated by the setting sun (i.e. the highlights) are quite warm and the areas in shadow, where show the clear, blue colour from the winter sky (I was pointing the camera toward the north, so the colour temperature is likely in the 10 000K - 20 000K range. The sunlight just above the horizon is likely to be in the 2 500K - 3 200K range. Classic impact of mixed light.

[lunaticitizen]

Leo,

I'm not an expert on flash photography, but I think I can confidently say that yes, setting WB to a fixed 2700 was a mistake, guaranteeing that WB would be too cold on the faces.

My own flash work is mostly candids, where I have no control over lighting. Occasional events as well, but I have no control there either. I haven't used gels in so long that I realized today that I don't know whether I still have any.

My most common starting settings are AWB, ETTL, manual at 1/60 or a little more, f/4 or a little narrower, ISO 400. In most indoor settings, the exposure set via E-TTL will create a reasonable balance between flash and ambient light, avoiding harsh fall-off. of course, you can adjust if the mix is wrong.

When I have control, the ambient light is 3000K. In my own home, I use Soraa bulbs in some rooms, which are as far as I can tell the among most color-accurate LEDs available to consumers in the US, so I'm confident that the ambient lighting is at least close to 3000K. (I did test it, long ago.) If I'm not mistaken, my flash is 6000K at full power, but like most, it changes somewhat if the power level is dropped.

With these settings, as Remco says, flash dominates. Yes, there can be some variation within an image in white balance, but usually not that I can see. There will be shots where the overall WB is off (usually, too warm, not to cold), but since I shoot raw, it's usually simple to fix that with the eyedropper tool in LR.

So my guess is that with the filter you bought, you might just need a slight warming of WB in post.

I hope this helps. Someone with more expertise with flash can correct me if I went off the rails anywhere.

Dan

Thanks, Dan.

I again forgot to mention that I shoot raw, so I guess setting WB on camera doesn't really matter because I then process the file with LR.

The thing is that when I changed the Temp on LR, the faces look okay but the the floor lamp etc. didn't look quite right anymore

Btw, 3000K bulbs are quite rare here. I've never found one unless you're okay with bulbs like Philips Hue whose temperature can be adjusted. I prefer 2700K at night in mostly, except in the half-baths which use 2200K bulbs

Now I remember that flash' color temp also depends on the power. I was puzzled because the spec for the i60A says 5600K.

[lunaticitizen]

Thanks, Manfred.

I think you got it right; it was mixed lighting that got me confused.

If you shoot in a room that has warm-toned walls, floor and ceiling, etc., then the overall colour temperature in the images will drop and if you have cool toned walls, floor, etc, then the colour temperature of the light in the room will have a higher Kelvin value.

Mixed lighting is a reality, even in daylight settings. If you take a shot with your subject under a tree, you will get a green colour cast on your subjects.

Yes, and I guess the (fake) Christmas tree was the one that made the picture look a bit green-ish.

I didn't want to reduce the contribution of ambience because as I mentioned above, I wanted to include the floor lamps etc. in the picture.

I thought since I knew the color temperature of the lamps, I could just color-correct my flash and the result will look okay.

It didn't look quite right to me...

I don't have another CTO filter with me now; I'll look for 1/2 and 1/4 CTO filters from local stores first...

[Manfred M]

Leo, it would be helpful if you posted one of your images so that we can see what they look like.

[lunaticitizen]

Leo, it would be helpful if you posted one of your images so that we can see what they look like.

Of course, Manfred.

However, I've deleted most of them because they didn't look right, and in this one I also didn't include my floor lamp etc. as I had intended to.

This is a WhatsApp pic shared with my parents and re-downloaded again to share with you guys; heaven knows what kind of compression WhatsApp did to it.



The layout:

[Manfred M]

While this is far from perfect, I think it is more in the direction you were looking for.

I adjusted the colour, contrast and exposure on the main subjects and the background separately.

[lunaticitizen]

Much better, Manfred! Thanks.

[lunaticitizen]

But how if I want to include 2700K light sources in the picture? Will I have to process them in layers, separately?

[Manfred M]

My usual strategy is to use my lights for the scene, which lets me forego the use of any other light sources in the room. For me it's easy as I own 6 studio flashes and 5 speedlights. If I plan to use an existing lamp as part of the scene, I will put one of the speedlights in the lamp and use its light output, rather than the lamps.

Another thing that I do, is to shoot everything using a tripod. That way I can separately light some of the elements in the shot (if I have to), shoot them separately and then blend them in post.

In my processing of your image, I noticed that your floor and ceiling lamp were the main light source for the sides and the back of the room, while the softbox primarily lit you two and the cats. I selected the people and pets and worked them on one layer and the room on another. I tried for a fairly neutral colour for the room (I assumed that the mats on the framed pictures were white) and I also assume that the white areas of the sweaters were white, so I worked to make those areas neutral.

For the background, I just removed most of the yellow. I did the same thing for the subject, but found that the skin tones were a bit too cool and I added some magenta to warm up those areas on the hands and faces.

I tend to like my backgrounds to be a bit subdued, so I darkened that part of the shot slightly, to simulate the light falling off. As the softbox light was a bit brighter in the area closest to the light source (jeans and pants) I burned those down a bit to downplay them a bit.

That sums up my thoughts and edits.

[lunaticitizen]

Thanks, Manfred.

I'll need to work on my processing skills if I were to do even a subset of what you did.

And more lights, too 👍