Paul C. Buff, Inc. Technical Forum

Hi,

I understand the difference between the 3 types of PLM's : Extreme, Soft Silver and White.

What is less clear for me, is how the size affects the beam of light, or the look of the light.

Any info, of when to choose a size 51", 64" or 86" for different usage? Single person versus group of people, etc?

And also, which size of Soft Silver, 51" or 64" would most closely "fake" the look of the 47" octabox?

Thanks in advance!

Pierre

As with any modifier, the larger the light source at a given distance, the softer the shadows will be.

The spread of light bounced or through a white PL will not be affected much by size, thought the soft wrapping of a larger modifier still applies. The soft silver and extreme silver will have a spread increase equal the the increase in size of the open face of the PLM. For example, the 51" PLM has an open face of 43.75" while the 86" PLM has an open face of 73", a difference of about 39". Assuming all else stays the same, the beam spread will be 39" wider using an 86" vs a 51".

Alternatively, you could use the larger PLM and move it back, while keeping a reasonable softness, in order to even out the fall off across a small group of people.

For example, a 51" may look nice for a single subject when positioned up close, but add three other people to the shot, and by the time the light reaches the farthest person, it will have fallen off due to the inverse square law, and the person closest to the light will still look good, but the farthest will be underexposed. Move the light back, and the fall off is not as great, evening the light across all subjects. But the shadows will become harsher due to the decrease in apparent size of the modifier. Increase the PLM to 64" or 86", and you will increase the size of the modifier, and soften the shadows.

The closest thing to an ungridded 47" octa would be a soft silver with a white front diffusion fabric. The 64" would be a tad larger face.

Thanks for the answer!

It's really useful and it helps me understand better how to choose the right PLM's!

One thing that would be great, not just for me but for all the PLM users is if you could give us some ratio for each size and type of PLM's at a given distance.

Example (not based on real numbers) :

86" Extreme Silver at 10 feet = coverage of 5 feet so a ratio of 0,5 relative to the distance
64" Extreme Silver at 10 feet = coverage of 4 feet so a ratio of 0,4 relative to the distance
51" Extreme Silver at 10 feet = coverage of 3 feet so a ratio of 0,3 relative to the distance

86" Soft Silver at 10 feet = coverage of 8 feet so a ratio of 0,8 relative to the distance
64" Soft Silver at 10 feet = coverage of 6 feet so a ratio of 0,6 relative to the distance
51" Soft Silver at 10 feet = coverage of 4 feet so a ratio of 0,4 relative to the distance

86" White at 10 feet = coverage of 20 feet so a ratio of 2,0 relative to the distance
64" White at 10 feet = coverage of 16 feet so a ratio of 1,6 relative to the distance
51" White at 10 feet = coverage of 12 feet so a ratio of 1,2 relative to the distance

This type of chart with the real numbers for the 3 sizes and 3 types of PLM's, with and without the diffusion fabric at 5 feet, 10 feet and 15 feet would be a TREMENDOUS tool for all of us!!!

Am i crazy? Maybe!!! Or just too much coffee for the day!!! :)

Regards,

Pierre

Hi again,

Concerning my previous message...

It could be the same type of charts like the ones you provide for the honeycomb grids

Regards,

Pierre

The problem is the parabolics don't follow the same spread rule like reflectors and softboxes, and grids.

This is especially true for the extreme silver; which, as it is backed off, will get narrower, then wider. The most focused point is about 14', which is why we publish specs at that distance.

The white will have a very wide spread, just like any other shoot through or bounce white umbrella, with a spread of 160-180 degrees. This would remain fairly constant at any distance, with coverage defined more from light to subject distance than from beam spread.

I will however, pass along your suggestion.