Paul C. Buff, Inc. Technical Forum

Don't know if this has been discussed. Hopefully, it has already been solved?

I have 64" white PLM umbrella, about ten months old. Mounted on PLM speed ring with screw in shaft hole as it says. Seems only one location possibility. But it has tremendous side spill. Looking in from the side, from about 90 degrees, the flash tube is clearly visible about a foot in front of umbrella edge. Lots of wide gap for light to go out 90, and of course, it does. I don't see any advantage of that. Seems counter productive to concept of a parabolic umbrella.

Do I have it mounted correctly? Should I be able to see the flashtube so clearly standing outside the umbrella?

If that is the right umbrella position, then it seems to need a light guard, like the regular umbrella reflectors with a side wall. I always assumed the shaft should be mounted on those so the flash tube was not visible?

However PLM speedring and umbrella reflectors are the same diameter, so that speedring will not fit inside the umbrella reflector to provide a side guard. Maybe something like a narrow flexible band strapped around the speedring OD, extending forward about an inch - so that flash tube is not visible standing at the side? It would not block light hitting umbrella, only the light bypassing the umbrella. For lack of anything else, I am using masking tape around the speedring OD, standing straight and wide out in front, which is better, but pretty kludgy.

In my opinion, design needs to be different. I see no advantage of a parabolic umbrella having intense side spill. Either a side guard accessory for current speedring, or a new speedring design. Unfortunately, I already have two of the current speedrings.

Thanks for listening.

The tube should not be outside of the front edge of the PLM by more than an inch or two. The intermediate shaft, or the shaft that the speedring screws into, will have a V shaped channel. On one end of this channel, there will be a small hole, and a few inches toward the center, there will be an idtentical hole. The hole that is close to the end of the shaft will mate to the set screw at the very tip of the PLM on the outside diameter. The second hole will mate up to the screw that holds the whole umbrella open. When fully installed, only a few inches of the position shaft should remain visible on the open side of the umbrella, and it should be flush with the hardware on the outside of the umbrella.

The length of the position shaft should be about 11.5" on a 64" PLM and would have two holes. If yours is closer to 17", then that would be for an 86" PLM and would explain the discrepency. Also, if this is the case, please contact our customer service department, and we will gladly get that corrected for you.

Thank you. My shafts sound right then. Seems to fit only the one way. The smaller shaft (position tube, screwed to the speed ring) is 11.5 inches by itself. My setup has the small screw into the first hole on it, more or less at its midpoint, which is how I understood the instructions. Assembled dimensions are about 10+ inches from fabric apex to small TOP ring on speedring (where the large mounting screw is), and about 14- inches from fabric apex to front of larger speedring rim. There is only one inch of the position tube still visible. Sighting a line across the two edges of the fabric diameter, fabric extends more than 14 inches forward from apex, slightly past the speedring, maybe back to chrome face of Alienbees itself. Which sounds good, yet, due to the angle, there the flashtube is, sitting out in the open, in clear view, offering substantial side spill all around (as shown).

I am unsure of your meaning, 1 or 2 inches outside "PLM". I see quite a bit more. My flash tube extremity extends only 1/2 inch forward of the speed ring, but the problem (as I see it) is that it is clearly visible from a good six inches in front of the PLM fabric edge. That is a LOT of direct side spill. It seems not adjustable for this.



Camera lens axis here is sighting across a point five inches in front of fabric edge. That large black area at right (not in focus) is the umbrella fabric edge. Camera stands just outside the fabric diameter a foot or two. This is the side angle I refer to. This is five inches, and the flash tube is clearly visible from at 6 inches (or more) in front of the fabric edge. That just struck me as wrong (excessive spill).

Its pattern is awesomely wide. At ten feet, it only meters 1.4 stops less at 90 degrees than when rotated around so same point is in the center. That is in a 20x24 foot room. I'm trying to use it behind the camera as fill, which is why it seemed significant. The PLM umbrella was purchased 2/1/2011. Could it be misshaped? Everything else looks first class, and I'm assuming it probably is not unique. The flash tube is slightly inside it, but the flash tube is not protected against side spill, a little wider than 180.

I am overthinking it, but it would seem helpful if there could be some sort of side wall guard on the OD of the speed ring, a straight wall extending forward at least 1/2 inch - to limit it to no more than 180 degrees. I am thinking a side guard similar to the 7UR umbrella reflector. 7UR almost fits here, behind the PLM speedring, but not quite, diameters do not fit inside. Not sure how that affects fabric diameter, but it looks like 1/2 inch couldn't hurt much. The 7UR reflector could of course be the same issue with a regular umbrella, but it is deeper, and the shaft can be adjusted deeper on it.

So, is that just how it is supposed to be? Maybe it is better outdoors.

Thanks.

Side spill from the modeling lamp won't end up in the picture. Put the flashtube inside the white PLM an inch or two and you will get zero side spill in you shots.

Since focus is more critical with the extreme silver PLMs in order to achieve the collimated light, what is the proper focal distance for each of the three sizes? Measured, say from the internal apex of the fabric to the mounting plate of the Einstein or AB (rather than to the flash ring or dome, since the mounting surface is easier to measure directly)

I have noticed a lot of side spill, as well, which made me think I must not be accurately focused. But if I move the flash tube fully into the extreme silver, I suspect that I will no longer have it focused, either.

For the soft silver/white variants, I don' think this matters nearly as much, and if I had it to do over again, I think I would just order the straight shaft versions of those puppies.

I'm sorry, but zero spill is simply unbelievable. Maybe it is our definitions. I just mean out the side, very near 90 degrees from center of pattern. I am not aware that any pattern width is spec'd, to be less or otherwise, and I do know umbrellas are wide. I am aware a speedlight in an umbrella also has wide spill, not 180, but simply because it has no side guard either, so the flash lens is so easily visible from a wide angle outside, even if the fresnel lens beam is more narrow to compare to the umbrella size. I guess I was just imagining parabolic was not so wide, not 180 degrees. I really doubt the side spill is parabolic, it is direct line of sight from the flash tube, the fabric is not involved.

The modeling light is off, no issue to me, it is shut out of any pictures anyway.

The issue I see is that the flashtube is simply so clearly visible from the side of the umbrella, which is extreme spill, only down 1.4 stops at near 90 degrees (at equal distances). The small screw is in the recommended first hole as the instructions say, and it can be said the flash tube is about one inch inside the umbrella. It is just so clearly visible out the side however, which is direct spill to me. Without metal work, there is only one more inch of travel possible, if the outer tube fully retracts to sit on the top disk of the speed ring. There would still be substantial spill.



Sorry for the crummy picture, but it shows ten feet width of background (still full of wrinkles). Should have used seamless, but was preparing this one for a in a few days. The 64" PLM stand is about four feet in front of the center of background, too close, but there so it can be carefully aligned so center line of PLM aims at right side of the background, and the line through edges of fabric on both sides of diameter aim at the other left side. Purpose is to show a 90 degree view of pattern, from center to 90 degrees at side. It is of course too near and bright in the center, so I ignore the over-brightness. But in its way, it shows a rather even pattern from 0 to 90 degrees.

The camera is off center, closer in line with right edge of background, aimed in at center, distorting a bit. Camera looking in towards the left does show a narrow dark black fabric shadow around 90 degrees, so there is an edge at 90 degrees, but it is mighty bright up until there... The light is a bit closer in the center, so I'm unconcerned it is brighter there, which is false, but was not expecting that a parabolic umbrella pattern is so even from 0 degrees to 90 degrees. Mine seems to be a real good 180 degree light, but just not what I imagined parabolic would be. Frankly, bouncing a reflector from the bare wall is not nearly as wide.

Probably it is it has to be... I am not disgruntled, it is more an oddity, and was just wondering if I am using it correctly. Perhaps such a beast is supposed to be 180 degrees, I just was not expecting it from parabolic, which I imagined the concept would put most of its light out parallel with center line.

Still, IMO, the speed ring seriously needs a side guard to prevent all that open light - somewhat like the U7R umbrella reflector, at least to be 1/2 inch taller than the current speedring edges. Seems an easy fix. Some kind of strap, like a wide belt, clamped around the speedring OD ought to help considerably.

I see now that the site's PLM item ad page says the 7UR reflector can be used with the regular shaft, "to eliminate side spill" it says. That is the spill I refer to also, and this shaft and 7UR is apparently the approved fix, and the right option I guess. The problem is, the speedring needs something like that too.

There is no way to really focus white material. The beam spread of the white PLM is about 150 degrees (from center line to -1f, which is fairly standard, and how all of our reflectors are measured), as described on the product info page. Silver material can be focused better, as it provides a specular reflection equal to the angle of incidence. Since the reflection is specific and predictable, it can be controlled. White, however, has diffused reflection, and will scatter light in all directions. With the umbrella placed closer to the light, whatever side spill you will have will, in most normal use cases, fall outside the frame. If side spill is a problem, and it must be corrected, the 7UR can be used with the 7mm shaft configuration. With a white PLM, there would be no performance difference from using the offset shaft mounting vs. the speedring mounting.

Critical focusing can vary based on distance from light to subject, as the light crosses at its focus, sort of like how at least one lens element moves based on focus. Threading the screw into the drilled hole will be a good useable focus in typical situations, but the umbrella portion can be positioned along the position shaft and the screw tightened to a friction fit anywhere.

As for the white and soft silver, white cannot be focused, and soft silver can benefit some from focusing, but certainly not to the extent of the extreme silver.

Yes, I understand that it can be varied, but since the PLMs are parabolic, there should be a specific on-axis focal point based on the geometry of the PLMs. I've been assuming that the pre-drilled hole is supposed to position the flash tube at that point, but now I am not so sure.

So I would think the design for each of the sizes specifies/defines where that point is along the shaft, and that is what I am looking for.

The PLM is not a perfect parabola, as it would not be possible from a 16 sided fabric umbrella nor would you want it to be. If it were, it would cast a very strong shadow of the stand and head at all distances as well as projecting the ring of the flash tube (as it is not a perfect point source). Since the PLM is not a perfect parabola, there is a crossing of light. Where this crosses will be the most concentrated amount of light, or the focus point (as well as it can be defined). With a given light to umbrella position, there is one area that is the focus point. While there is a significant depth of field to this area, if a change is made of the light/PLM combo to subject distance, the subject can be moved out of the focused area. To reposition the focus area to the subject, the light to PLM relationship would need to change.

At about 14', the flash tube would need to rest just outside the open area of the PLM for maximum focus. This aligns with the pre drilled hole. The depth of field of the focused area in this position should be useable in normal studio shooting, but if your PLM is significantly closer or further, you may be able to tweak the focus a little better.