Special-Effects Filters: Diffusion Filters

Diffusion filters are used to create soften images. The keywords are enchanting, romantic and dreamy. Basically, a diffusion filter diffuses strong light without affecting the sharpness and contrast of the image. Thus, it is different from the effect of out of focus. Diffusion filters are mainly used in portrait work. In general, small skin defects can be eliminated almost completely, and facial contrast and wrinkles are soften. To create a better result, aperture should be opened up so that the subject can stand out well against the background. Unfortunately, for a 950/990/995 it is difficult to achieve this large-aperture effect we normally enjoy with a 35mm or 120 camera except in the close-up mode. This is partly because the largest aperture of 950/990/995 is not large enough. However, we still can achieve reasonably good results. Your subject should be well lighted; otherwise, diffusion effect will not be so great. Also avoid very harsh mid day light because diffusion could wash out all the details.

Top Row: Hoya Duto, Tiffen FX, Cokin Sunsoft, Cokin Diffuser Bottom Row: B+W Soft Focus 1, B+W Soft Focus 2, B+W Soft Image

Click on the icon to see a larger image

The above shows a number of diffusion filters, each of which is either named as a soft-focus or as a diffuser filter. In general, diffusion filters contain some mechanism built into the filter for dispersing the incoming light. Filters like Hoya's Duto and B+W's Soft-focus 1 and 2 have concentric circles etched into the filter surfaces (i.e., the Duto construction method). The density of these circles determines the softness of the resulting image. Others, such as B+W's Soft Image, Cokin's Diffuser and Tiffen's Soft/FX, have different etched patterns. These patterns may contribute their own patterns to the formation of foreground and background. See the last section on this page for some details.

The right image below was taken with a Tiffen's Soft/FX #3 filter. Compared with the left one it shows clearly that the use of a diffusion filter produces a much better skin texture than the one without. Also note the the "glowing" effect of the highlight and bright areas, and the diffused background.

Without diffusion filter	With diffusion filter
Click on the icon to see a larger image

The following are more examples of different diffusion filters. The Cokin Sunsoft adds a touch of sunset gold, B+W Soft Focus 1 is of Duto type and creates a soften background with a very weak touch of the Cokin Radial Zoom effect, and B+W Soft Image produces a soften image weaker than that of B+W Soft Focus 1.

Cokin Sunsoft	B+W Soft Focus 1	B+W Soft Image
Click on the icon to see a larger image

Effects of Diffusion Filters

Not all diffusion filters deliver the same result. Filter manufacturers make a number of diffusion filters of various degree. For example. Tiffen has Soft/FX filter #1 to #5; but, only #3 is available for 37mm thread size. B+W has Soft-focus 1 and 2, and Soft Image. Cokin has Diffuser 1, 2 and 3, and a Sunsoft which produces diffused images with a touch of sunset gold color. The following images show the effects of using different diffusion filters under a uniform illumination environment. Compared with the one that did not use any filter, all other images have slightly lighter tone due to the spreading of light. Hoya's Duto has the lightest effect. This is followed by Tiffen's Soft/FX and B+W's Soft Focus 2. In terms of the strength of the diffusion effect, B+W's Soft Image is slightly stronger than B+W's Soft Focus 2, and is weaker than B+W's Soft Focus 1. I would say these are of the soft-focus type that does not degrade the sharpness of an image. On the other hand, Cokin's Diffuse 2 is a diffusion filter that spread the light into the darker areas, creating a very soft and diffused image. Cokin's Sunsoft is similar to that of Diffuser 2, and adds a sunset golden touch.

No filter	B+W Soft Focus 1	B+W Soft Focus 2
B+W Soft Image	Cokin Diffuser 2	Cokin Sunsoft
Hoya Duto	Tiffen Soft/FX 3
Click on the icon to see a larger image

The next few images show the effect of diffusion filters under sunlight. Compared with the image taken without a filter, we immediately notice that the images taken with B+W's filters reduce contrast to some degree. Hoya's Duto also reduces contrast a little which is comparable to that of B+W's Soft Image. It is clear that of the three B+W filters, the strongest is Soft Focus 1 and the weakest is Soft Focus 2 with Soft Image in the middle. Hoya's is similar to that of B+W's Soft Focus 2. Cokin's Diffuser 2 and Tiffen's Soft/FX #3 both show a nice "glowing" effect which does not appear in all images taken with the Duto type filters (i.e., B+W's Soft Focus 1 and 2, and Hoya's Duto). In terms of the diffusion effect, Cokin's Diffuser is the strongest, and Sunsoft produces a beautiful touch of sunset gold. Which one is the best? This depends on the situation and your need. But, if you are careful, you will notice the background in all of these images are different! So, you might want to take this into consideration when choosing a diffusion filter. Please continue with the next section to see more details about background.

No filter	B+W Soft Focus 1	B+W Soft Focus 2	B+W Soft Image
Cokin Diffuser 2	Cokin Sunsoft	Hoya Duto	Tiffen Soft/FX 3
Click on the icon to see a larger image

But, Not All Diffusion Filters Are Created Equal

While all diffusion filters soften the subject to various degree, background is another story. In fact, the construction of a filter dictates the impact on the background. The following is an image without using a filter. The portion of the background that will be examined carefully is marked with a yellow rectangle.

The following images are the original, untouched portion of the same scene taken with various combinations of diffusion filters. The first impression when looking at these images is that Hoya's Duto and B+W's Soft Focus 1 and 2 filters reduce the contrast and tonality of the original. When filters are combined, this becomes even more obvious. See the images taken with both B+W's Soft Focus 1 and 2, and the one with B+W's Soft Focus 2 and Soft Image. B+W's Soft Image and Tiffen's Soft/FX #3 maintain the contrast and tonality very well, and Cokin's Diffuser also does a good job. So, it appears that Duto type filters do lower the contrast and change tonality a little because the concentric circles spread the light into the shadows.

No filter	Hoya's Duto
B+W's Soft Focus 1 (Duto)	B+W's Soft Focus 2 (Duto)
B+W's Soft Image	B+W's Soft Focus 1 and 2
B+W's Soft Focus 2 and Soft Image	Cokin's Diffuser
Tiffen's Soft/FX #3	Two Tiffen's Soft/FX #3
Click on the icon to see a larger image

The etched patterns of a diffusion filter also contributes to the formation of the background. For the Duto type filters, the Hoya Duto has a background similar to the original; the B+W Soft Focus 2 blurs the background; and B+W Soft Focus 1 produces a regular pattern which is even more visible in the image using both Soft Focus 1 and 2. I suspect this pattern is actually the image of those concentric circles, and the offset of these circles of the Soft Focus 1 makes them very visible.

B+W's Soft Image filter has many circular patterns scattering in the filter. These circular patterns produce a not very pleasant background as can be seen above and in the full images in the previous section. This pattern is softened a little when Soft Image and Soft Focus 2 are combined. Tiffen's Soft/FX has many randomly etched short arc patterns. As a result, the background shows a quite regular interweaving line pattern. This situation improves when two Soft/FX filters are used. Finally, Cokin's Diffuser 2 has a very densely etched pattern. Perhaps because the pattern is so dense, this filter does not produce any particular pattern in the background. Hence, it appears that only Cokin's Diffuse 2 produces a patternless background.