Paul C. Buff, Inc. Technical Forum

Technical Discussion Forum for all Paul C. Buff, Inc. Products

Login

Post a reply
 [ 24 posts ] 

Fri Apr 15, 2011 5:41 pm

Joined: Mon Feb 21, 2011 8:25 am
Posts: 11

Joseph S. Wisniewski wrote:
It's cheap, and big, and that makes a great "foundation". That's why Paul has a sock for it, so you can switch it from the original 18 degree (more or less) collimation to 150 degree. It's also why he (like all soft box makers) has grids for his soft boxes and octas, so they can go from that 150 degree collimation to 40 degrees.


So the equations involving softboxes/octaboxes and a PLM umbrella are:

PLM with diffusion sock = softbox + grid + 3-4 f-stops of light
PLM without diffusion sock = softbox + 2-3 f-stops of light

Is this, not including the different in cost, an essentially correct assessment? Sure, the catch light is not quite as nice, but civilians (non-photogs) never seem to be aware of the catchlights in photos.

I am planning on using PLMs when I buy my first set of studio equipment, but I had some questions about them:

1. The PLM cannot direct the light upward much, while a softbox suffers the opposite limitation, correct? While a baby boomer will solve this issue, in what situation would one need to direct their lights upwards?

2. Are PLMs useful for evenly lighting backgrounds? If so, what sizes and configuration would be the best for, say, a 9' wide backdrop?

3. If one is using the optical slaves on the lights and triggers the first light, does the PLM - particularly the 86" - obstruct the sensor of another light enough to cause it not to fire? Remotes are on my shopping list, but I was just curious about this.




Top Top
Profile
 

#

Fri Apr 15, 2011 8:04 pm

Joined: Fri Feb 05, 2010 3:09 am
Posts: 73

Joseph S. Wisniewski wrote:

I tried doing a goniometer scan on PLM fabric, and got about a 17 degree spread. So, it's pattern is a lot like light that's collimated, then spread an additional 17 degrees. A gridded box produces the same effect, except it starts with light coming from every point at a huge 100-160 degree spread, then "choked" to a whatever the grid's spread is. The PLM 72 inch PLM is virtually identical to a 7 foot octa with a 6 foot round mask and a 20 degree grid. (which you can set up using Chimera stuff, for about $1000, LOL).

If there were some way (hint, hint, Buff people) to increase the spread of the PLM fabric to 40 degrees, it would be identical to a box choked to 40 degrees. Increasing the "bumpiness" of the silver reflector would do it, but that would be a permanent fix.


frugivore wrote:

So the equations involving softboxes/octaboxes and a PLM umbrella are:

PLM with diffusion sock = softbox + grid + 3-4 f-stops of light
PLM without diffusion sock = softbox + 2-3 f-stops of light


Worth noting is that a white PLM with the silver/black cover and no diffuser is sort of "in between", and I find it a very useful compromise... soft but somewhat controllable, and no need for a diffuser. It's an amazingly flexible system for not much money.

BTW, the web site should indicate that the black cover has a silver interior, I wasn't sure what to expect when I ordered mine.

One caveat about using bare silver PLM's up close... relevant to Joseph's observations... the light is hard no matter how close you place 'em. To the extent that the light is focused in a "beam", say 20 degrees... well if the PLM is close enough to cover 90 degrees of the subject's FOV, the light will still hit them at 20 degrees... light won't reach the subject from some parts of the PLM because the angle is too steep. That's what prompted me to try the white one + backing cover, and I like it much better for studio use. Outdoors, silver is almost always preferable.... as you move the light back, the surface specularity becomes insignificant.

frugivore -I use reflectors on backgrounds... usually you want a wide spread and sharp falloff (plus compactness) for that usage. I use the Lightmod mainframes on my BG lights so I can slap on gels or grids quickly.




Top Top
Profile
 
Website
 

#

Fri Apr 15, 2011 9:23 pm

Joined: Mon Feb 21, 2011 8:25 am
Posts: 11

bobk wrote:
One caveat about using bare silver PLM's up close... relevant to Joseph's observations... the light is hard no matter how close you place 'em. To the extent that the light is focused in a "beam", say 20 degrees... well if the PLM is close enough to cover 90 degrees of the subject's FOV, the light will still hit them at 20 degrees... light won't reach the subject from some parts of the PLM because the angle is too steep.

Could you not just use a fill light?

bobk wrote:
frugivore -I use reflectors on backgrounds... usually you want a wide spread and sharp falloff (plus compactness) for that usage. I use the Lightmod mainframes on my BG lights so I can slap on gels or grids quickly.

So you use the 7" reflectors? Do you use the diffusion filters on them? Or colors gels? I'm guessing you'd need two sets to have two of the same color right?




Top Top
Profile
 

#

Sat Apr 16, 2011 11:11 am

Joined: Fri Feb 05, 2010 3:09 am
Posts: 73

The Lightmod is basically just a 7" reflector with attachment. If I want all white, I use it bare; if I want a colored background, I attach a gel; If I want a bright spot in the middle, I attach a grid.

frugivore wrote:
Could you not just use a fill light?

You pretty much have to, but it's still not the same. A silver with the diffuser would be a better choice of you want softer light, or the white one.

Hardness/softness of a light source is determined by two main factors, the size of the source and the directionality (specularity) of the source. A highly focused beam will make sharp shadow lines and high contrast no matter how big it is.... I find the Silver PLM's can make skin texture pretty harsh, or at least harsher than you'd expect given how close it is. It never gets a chance to "wrap" around sharp details. Fill light will reduce the contrast, but it's not the same as using a softer main light source; no amount of fill will make a silver PLM look the same as a white one.

Basically, just keep in mind that when using a bare silver PLM close to the subject, the directionality of the light makes it act like it's smaller than it really is. As you move away, the effect disappears.

I don't have samples online, but these were shot in my studio:

Silver: http://www.flickr.com/photos/brittannyt ... 6234248058

White: http://www.flickr.com/photos/brittannyt ... 6234248058

If you browse the set, there are a couple more examples of each. Older models with less makeup would illustrate the skin texture effects better, but you can see how the shadow lines and contrast differ.




Top Top
Profile
 
Website
 
Display posts from previous:  Sort by  
Post a reply
 [ 24 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 88 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum


cron