How many SB900s to overpower sun

Quantum Help · Aug 7, 2010

No, I was not interperting it as that. I think you mistakenly mis-read my response. Those are three different ways of using the Speedlight ( or any light fo that matter ). Since the question was involving what would happen if the light was bounced off a surface on an angle, I was basically making reference, similar to the inverse law of light, that bouncing light on an angle to a surface, the light striking closer to the light source is stronger and that the light striking farther away from the light source is weaker. This totally changes the light pattern that the reflected light will illuminate the subject matter.

Bouncing a light on a surface (umbrella, wall, thru a diffuser panel) in best utilized keeping it a 90 degrees to that surface (i.e. - aim at the center of the umbrella). The trick is to manipulate the angle of the surface that is relative to the subject. Example, the umbrella you are using is aimed at the subject on an angle when it several feet off the subject / camera plane, like in being used as the main light. Another umbrella, is used on the other side of the camera, closer to the subject / camera plane, therefore being on a shallower angle and is used with less power as a fill light.

Now, I did not also say that you couldn't use a light light you had proposed. It could be used with say one person, to cast a dramatic light on that person. It would not be appropiate to use it on a large group because of light fall off.

creaDVty · Aug 7, 2010

Took a while to respond to you because I had to wait for night time .

UKphotographers said:
UKphotographers said:

Take a bare bulb studio strobe, fire at full power. The strobe will illuminate a very wide part of the 1km umbrella but not all of it. Right?

Click to expand...

Wrong.

Hmm. I have to admit I have zero experience with studio strobes. Please tell me what's wrong with that statement. Thanks.

UKphotographers said:
You're a crazy mixed up kid. The actual light on us would be the same. Your statement above is opposite to your infered claim about me finding some magic energy saving system and your claim below.

huh? how's it opposite? anyway pls don't answer that. it doesn't matter.

UKphotographers said:
UKphotographers said:

Again: If the zoomed flash will hardly make a difference in gn , are you claiming that the light quality will be significantly harder? ....I keep showing you test shots showing no difference in hardness yet you insist that the umbrella will become pointless .

Click to expand...

Geez take a look at the part I put in bold. I kept saying that with a small or medium umbrella there won't be a difference either in GN or in softness because with a small or medium umbrella the coverage is almost the same. I said the difference in GN and softness would be observable when the coverage is significantly different. No contradiction. You just missed a point that I thought wasn't subtle at all.

UKphotographers said:
In the instance where an exact match to the perimeter of the canopy and even coverage by a 24mm zoom is made, and the zoom is then changed to 105mm - despite the intensity on the umbrella canopy increasing over a smaller surface area, the resulting light EV on the subject will be exactly the same. The surface area which that light covers on the canopy of the umbrella is smaller. The light is more intense over that smaller surface area. The resulting light from that reduced size of coverage area on the canopy will cause the light to be harder (compared to the 24mm coverage with full even coverage) - yet the light EV on the subject is unchanged.

OK. Glad you put it that way (hope you don't mind the extra emphasis on the last phrase). To summarize your argument, you believe that with 24mm you will have softer light AND the same amount of EV on the subject compared to 105mm. 105mm is going to have harder light but same EV on the subject compared to 24mm, so there's no advantage whatsoever from zooming. The EV on the subject will be the same because the umbrella is a modifier, which does only one thing to all light sources, therefore zooming won't increase the EV. Given that zooming just makes the light harder without any advantage in higher EV, zooming the flash w/ an umbrella is just plain stupid. You offered as proof the test you did on a westcott umbrella (is it 43") and the results I myself got with a 25" shoot-through. There were other points you made, but I think I mentioned all your major points. (So I think I do understand you.)

Very well then. I figured no matter how much I explain, you wouldn't believe me. Well, I don't have a 1km umbrella but I do have a wall. So please see this:

http://betterfamilyphotos.blogspot.com/2010/08/bouncing-tip-zooming-flash-basic.html

UKphotographers said:
You have Mensa membership longer than I have been in the business for (31 years). Do the Math.

I didn't say longer. I said "almost as long" (about 18 yrs), which I based off your website statement where you said 20 yrs+ ( http://www.accoladephotography.co.uk/info.htm ). If you've been in biz for 31 yrs. then good for you.

--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

UKphotographers · Aug 8, 2010

creaDVty said:
creaDVty said:

In the instance where an exact match to the perimeter of the canopy and even coverage by a 24mm zoom is made, and the zoom is then changed to 105mm - despite the intensity on the umbrella canopy increasing over a smaller surface area, the resulting light EV on the subject will be exactly the same. The surface area which that light covers on the canopy of the umbrella is smaller. The light is more intense over that smaller surface area. The resulting light from that reduced size of coverage area on the canopy will cause the light to be harder (compared to the 24mm coverage with full even coverage) - yet the light EV on the subject is unchanged.

Click to expand...

OK. Glad you put it that way (hope you don't mind the extra emphasis on the last phrase). To summarize your argument, you believe that with 24mm you will have softer light AND the same amount of EV on the subject compared to 105mm.

Exactly the same as I said in the beginning.

--
Ian.

Samples of work: http://www.AccoladePhotography.co.uk
Weddings: http://www.AccoladeWeddings.com
Events: http://www.OfficialPhotographer.com

Theres only one sun. Why do I need more than one light to get a natural result?

creaDVty · Aug 8, 2010

UKphotographers said:
UKphotographers said:

OK. Glad you put it that way (hope you don't mind the extra emphasis on the last phrase). To summarize your argument, you believe that with 24mm you will have softer light AND the same amount of EV on the subject compared to 105mm.

Click to expand...

Exactly the same as I said in the beginning.

What? I summarized your argument but I'm saying I disagree with you. Please check out my test shots where 105mm is harder but brighter (on the subject).

--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

creaDVty · Aug 8, 2010

Quantum Help said:
No, I was not interperting it as that. I think you mistakenly mis-read my response.

Whew. My bad.

Quantum Help said:
Bouncing a light on a surface (umbrella, wall, thru a diffuser panel) in best utilized keeping it a 90 degrees to that surface (i.e. - aim at the center of the umbrella).

So, Quantum Help, if I understand you correctly, you said previously that the umbrella has minimum curvature in the middle (around the axis of the umbrella shaft). If the flash is zoomed to 105mm, it seems that more of the flash would be utilized at 90 degrees to the surface. So does that mean that using the above principle, flash at 105mm is more efficient than flash at 24mm? (Not to say anything about the light quality.)

--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

UKphotographers · Aug 8, 2010

creaDVty said:
UKphotographers said:

creaDVty said:

OK. Glad you put it that way (hope you don't mind the extra emphasis on the last phrase). To summarize your argument, you believe that with 24mm you will have softer light AND the same amount of EV on the subject compared to 105mm.

Click to expand...

Exactly the same as I said in the beginning.

Click to expand...

What? I summarized your argument but I'm saying I disagree with you. Please check out my test shots where 105mm is harder but brighter (on the subject).

You also stated that the guide numbers and umbrella factors resulted in no change, which is what was being discussed. Now, you're using a wall 7 feet away.

Which are you saying? 105mm is brighter or there's no change? Again, you're flitting around changing circumstances and fitting any convenient results to your undrestanding.

You can't have it both ways - even though, in your mind you managed to 'prove' both ways. Even at your recent wall tests - if you can't see that theres an obvious difference in the shadows of the 24mm and 105mm samples - even bounced off a wall - you must have eyesight problems. You're making comparisons based on a 14 foot modifier there, and here you keep banging on about a medium to small umbrella!!! I don't recall the OP ever mentioning a wall !

Should I expect you to say 'I should have said...' prior to those results as well as the instances where you left out other pertinent information previously?

This is getting ridiculous to the extreme.

--
Ian.

Samples of work: http://www.AccoladePhotography.co.uk
Weddings: http://www.AccoladeWeddings.com
Events: http://www.OfficialPhotographer.com

Theres only one sun. Why do I need more than one light to get a natural result?

creaDVty · Aug 8, 2010

UKphotographers said:
Which are you saying? 105mm is brighter or there's no change?

I will refer you to these quotes:

1. 1 week ago: 3. The OP never said what size umbrella he is using or what kind of bracket he is using. If the umbrella is very large and the flashes are in a very tight group you're right that the full umbrella won't be used. However if the umbrella is medium sized or the bracket doesn't group the flashes so tightly, zooming will be ok.

2. 1 week ago: Also, you made two statements that seem to be mutually incompatible. 1. You said that using a flash with full zoom in an umbrella would create a hotspot. (True) 2. But you also said that with an umbrella zooming a flash doesn't make a difference in terms of guide number. --> wouldn't the hotspot result in a higher GN?

3. 4 days ago: Ian, you asked me to demonstrate to you the zoom advantage. My answer is: sure, under the same conditions that you can demonstrate to me that zooming the flash makes the umbrella pointless. Also, if your tests show no difference in GN between zoomed and wide flash, then there's no need for an outburst for zooming the flash - in either case, the result is the same. Again, my point about your statements being mutually inconclusive.

4. 4 days ago: 2. I understand what you mean about proving a zoom advantage. My point however is that you cannot claim that zooming an umbrella will create a hotspot that makes the umbrella pointless while simulataneously arguing that there is no gn advantage to be gained from zooming. This is the nth time I've said that - whether you agree or disagree, do you understand what I'm saying? (Not a sarcastic question. ) if you insist that I demonstrate a zoom advantage then I likewise insist that you show me that zooming the flash will make the umbrella pointless. I'm not being testy. The two are correlated. Under the same circumstances that you demonstrate one, you demonstrate the other. That is why I asked if you can show me a test shot proving that zooming a flash makes the umbrella useless. You have yet to do that despite repeated requests. Fwiw I suspect you will need a very large umbrella or maybe a wall instead.

5. 4 days ago: To put it simply: prove that using a zoomed flash will make an umbrella pointless and I will show you a difference in GN. Under circumstances when there is no material GN advantage (eg small umbrellas), using a zoomed flash will not result in a material change in quality of light either. If you disagree, please prove it.

6. 4 days ago: Again: If the zoomed flash will hardly make a difference in gn, are you claiming that the light quality will be significantly harder? If you insist on that, PROVE IT almighty ian. I keep showing you test shots showing no difference in hardness yet you insist that the umbrella will become pointless . The yet-unproven statement you made that started this all.

7. 3 days ago: My explanation for the equal brightness of the umbrella in our testing is not that the umbrella is an equalizer of some sort but rather that it so happens the coverage of 24mm and 105mm is almost the same in a small or medium umbrella. This is also why I think that when the umbrella is large enough that zooming makes a difference in terms of coverage of the umbrella, we would also observe a difference in GN, and vice-versa.

8. 2 days ago: "Finally caught up?" Dude, I have been saying that from the beginning. You either misinterpreted or didn't get it. Even the fact that there is no diff in umbrella output w a small umbrella is something I mentioned with my first response to you. I also said that with a very large umbrella there would be a difference, just as you said that with a large modifier, you can vary the zoom and get different effects.

9. 2 days ago: So after all, we're back to the old point. You said then as you are again saying now:. You can have softer light without reduction in power. Softer light I presume comes from the larger coverage. But somehow you are claiming to get more coverage without reducing light intensity.

10. 2 days ago: Yes of course zooming cannot increase the power. I never said such a thing. What I'm saying is that you get more light intensity by decreasing coverage. Decreasing coverage is possible by zooming but if a small or medium umbrella is used there will not be a material change in coverage and thus not a material change in light intensity. Is that wrong?

(continued...)

--
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creaDVty · Aug 8, 2010

(continued from Part 1)

11. 2 days ago: And just so I'm absolutely clear I'm again saying that in THIS case with a small umbrella no material difference exists - either w GN or with softness.

12. 2 days ago: Ian, please - I said with a small or medium umbrella the difference is immaterial (and neither is the softness). ... But if we use a very large modifier you agreed zooming would make a diff. (Let's leave out small umbrellas for now pls). In that case even applying a diff umbrella penalty, you will end up withhigher gn just bec the modifier is acting like a smaller modifier if you zoom. If you have the same power but smaller coverage why wouldn't intensity increase? If we use a small umbrella we don't see much of a diff just bec the coverage is not that diff either. Not bec umbrella is some equalizer.

13. 1 day ago: My explanation is: there is no difference because the coverage is almost the same for a small umbrella. (And just to be very clear, i'm talking about the coverage of the umbrella surface.) If the coverage is different, then there will be an observable difference in GN.

14. 1 day ago: I say 'no'. I say that there is a difference in umbrella coverage between the two. Given the same power from the strobe, you will find higher intensity with the 105mm both at umbrella surface and with the umbrella as well (it will function as a smaller, brighter umbrella). I say you will find that the umbrella will produce brighter but harder light with the strobe w/ reflector than with the umbrella + bare bulb strobe combo. Do you disagree?

After all those statements you still do not understand me? FOR THE (AT LEAST) FIFTEENTH TIME: IF THERE IS A CHANGE IN UMBRELLA COVERAGE THEN YES THERE WILL BE A CHANGE IN SOFTNESS AS WELL AS GN. IF THERE IS NO CHANGE IN UMBRELLA COVERAGE, AS IN THE CASE OF A SMALL OR MEDIUM UMBRELLA, THEN THE CHANGE IN SOFTNESS WILL NOT BE OBSERVABLE AND NEITHER WILL THE CHANGE IN GN.

creaDVty said:
Even at your recent wall tests - if you can't see that theres an obvious difference in the shadows of the 24mm and 105mm samples - even bounced off a wall - you must have eyesight problems.

WTF? I SAID in the foregoing statements AND in my blog that IF there is a material change in softness there will be a material change in GN and if there is no material change in GN there will be no material change in softness. I was PRECISELY demonstrating the fact that if you use a zoom THE LIGHT WILL BECOME HARDER as well as BRIGHTER (YES - on the SUBJECT!!!!). YES! BELIEVE IT OR NOT I SAID 105MM WAS ALSO HARDER! YES I WROTE IT!!!!!! REREAD IT.

creaDVty said:
You're making comparisons based on a 14 foot modifier there, and here you keep banging on about a medium to small umbrella!!! I don't recall the OP ever mentioning a wall !

You've got to be kidding. Do you not understand that the purpose of the experiment was to test your modifier theory and your truly remarkable statement that the intensity will be higher at the umbrella surface but the EV on the subject will be the same? I said I don't have a 1km-wide umbrella (or a large umbrella) but I have a wall. Are you saying your modifier theory applies to umbrellas but not to walls? Is your amazing modifier theory something you learned from your experience, from your analysis, some $$$$ seminar, or direct communication from heaven?

creaDVty said:
This is getting ridiculous to the extreme.

Do you know why, Ian? Because I am committed to seeking the truth and am capable of admitting mistakes if it serves the truth. You, on the other hand, are committed to being right and proving others wrong. Consequently you only see where you are right and where you think others are wrong. If it's something where you are wrong and others are right, you cannot see it -- it's in your blindspot. That's why you keep misinterpreting my statements. (BTW, was your kneejerk response about the barebulb yet another misinterpretation?)

We keep going around and around because if there are two sides of the same coin, and I point to one, you point to the other. When I accept the other, you point to the first one. You fail to understand that they are related. You are incapable of understanding it because it just may mean that you are wrong, which is something you cannot accept.

P.S. On that last point, please prove me wrong by accepting your error. Don't worry, I won't rub it in ... too much.

--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

Quantum Help · Aug 8, 2010

You are asking me the same questions that got you and UK into doing hissy-fits back and forth. This is going to be my final reply as I will not lower myself:

1. There are a variety of umbrella shapes and sizes. Some are flatter in the center area than others. Traditionally, most photo umbrellas, especially the larger sizes have a flatter center area. Some umbrellas, like the Brolly-box are deeper and longer than they are flat and wide. They are traditionally used with a difusser material, like a soft box. There was even a reflector, brom Larson Industries, called the Larson Reflectasol. It worked like an umbrella, was was a pryamid shape -- no flat center surface.

2. If you want to get more light (power) out of the umbrella, you have to put more power into it. (Remember my statement about using your 3 flashes on the bracket instead of one to get more light?)

3. Zooming to the max zoom and aiming at the center will not produce more light. As I had mentioned several times previously, you may even lose light because the flash unit itself as well as the bracket holder, may block the light reflecting back towards the subject.

4. There have been a multitude of answers to your questions over the last 10 days on the same repetitive line of questions. I think that the time has come for you to actually experiment with different shape umbrellas, brolly-boxes, soft boxes and studio lights other that the Canon Speedlights. You will gain knowledge and actually see and learn how the different components give you different quality of light.

5. Goodbye.

creaDVty · Aug 8, 2010

Quantum Help, rest assured I have no quarrel with you. There is nothing you have said with which I disagree (though with some I would ask if a qualification is needed). If I asked questions, it is in the name of inquiry. Thank you for all the info you have patiently provided.

--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

jean bernier · Aug 8, 2010

Wow, what an exchange! Quite entertaining at first. That being said, I have not had the patience to read all of the posts.

Fact is, in real life, the zoom setting does have an effect on the reading (disregarding the quality of light and the coverage). I flash metered a SB-800 speedlight installed on a white umbrella. I measured with zoom head at 17mm, 24mm and 105mm. There was a difference in measurements: the 17mm gave the weakest reading, as the diffusing lens does absorb a little light, and more light is wasted outside the umbrella perimeter. Best umbrella coverage of course (the white dome is even better at this).

24mm gave a perfectly acceptable coverage of the umbrella, and .2 stops extra was measured.

105mm produced the expected hotspot, and .2 to .3 stops extra output was measured.

There was a total of .4 to .5 extra stop compared to 17mm available due to the (inappropriate) use of the zoom head. Almost no light is lost out of the umbrella perimeter at the 105mm zoom setting, and this is probably the main reason for the difference, plus the somewhat reduced coverage favours a higher reading on-axis.
I would choose the 24mm setting for my own use.

Now back to the OP. IMO, using a high power battery flash, or a battery monolight, or a regular studio monolight powered by a square wave inverter is the better option, no matter what Joe uses. The speedlight solution is for those occasions when you're doing action shots with flash in bright daylight: nothing can replace a high shutter speed for those, so FP sync is the way to go. And TTL is available if you like it.

But for everything else, with 800ws of flash power (wich seems to be a reasonable amount), manual exposure at max sync speed, the sun can be tamed, and for wide apertures, max sync and ND filters are used. It is much cheaper than shelling for 4 SB-900 plus radio links. Think about the hassle of maintaining the batteries, installing the numerous speedlights, the radio links, the unreliable optical triggering of remotes if you want to save a few radio receivers, the overheating problems, the recycling time and the duty cycle, the not-so-sturdy installation (you will need some kind of counterweight too)...just does not look the best approach IMO. You total 320 ws of power with the speedlights, in manual at full power. With an average 2,5 stop drop because of FP, it becomes the equivalent of less than a single normal sync SB-900 : and you must still carry four around. Four loaded SB-900 plus bracket are not small and light anymore anyway...
--
Jean Bernier

All photographs are only more or less credible illusions

UKphotographers · Aug 9, 2010

jean bernier said:
(compared to 17mm)..

24mm gave a perfectly acceptable coverage of the umbrella, and .2 stops extra was measured.

105mm produced the expected hotspot, and .2 to .3 stops extra output was measured.

0.1 of a stop difference and a hotspot. Pretty much the same as I said.

--
Ian.

Samples of work: http://www.AccoladePhotography.co.uk
Weddings: http://www.AccoladeWeddings.com
Events: http://www.OfficialPhotographer.com

Theres only one sun. Why do I need more than one light to get a natural result?

jean bernier · Aug 9, 2010

I'm with you, UKPhotographer, the difference is negligible between 24mm and 105mm, certainly not worth altering the umbrella's function wich is to enlarge the light source (aka softening the light).
The umbrella is a 42 inch white model.

I reversed the umbrella this morning and did a few measurements. As expected, the difference is this time worth mentioning, you've got to admit:
Shoot through umbrella 24mm: f:4
Shoot through umbrella 105mm: f:4,4

Now, if the aim is to maximize the speedlight's fixed output (full manual), a 0,4 stop extra light may or may not save the day, but it is still worth considering. Nevertheless, I would never use 105mm for umbrella as I don't want to defeat the umbrella's function: if I bring a 42 in umbrella to the shoot, I want 42 in type of light, otherwise I would install a smaller umbrella that is more compact and safer to use in windy conditions. The difference in output is due to loss of light around the umbrella perimeter but more importantly, the spread (coverage) is altered: an umbrella is somewhat parabolic in shape and is supposed to redirect all light forward. If you reverse it and shoot through, it becomes something similar to a giant bare bulb, emitting light in a very broad pattern. The 105mm position reduces this power-reducing spread. In fact, it surprises me that there is not more difference between normal and shoot through: that will depend mainly on the tickness of the fabric.
--
Jean Bernier

All photographs are only more or less credible illusions

creaDVty · Aug 9, 2010

Thanks for taking these measurements, Jean. You, Ian and others here are pros while I am not. Your choices are informed by knowledge, experience and skills much greater than I possess. I understand why you would not use 105mm in any case. A smaller umbrella in lieu of zooming to 105 in order to limit the risk of wind is not something I had considered. One would think I wouldve learned my lesson by now, having not one but two umbrellas with broken ribs

Meanwhile, I wanted to close the loop on a couple of things and was wondering:

1. Is it the case that when the gn difference from zooming is small, the difference in quality is also small? I think yes but I haven't tested this though I might, using an umbrella version of the wall experiment. I

2. Is the zoom "advantage" proportionate with the size of the modifier (understanding that using a speedlight to light up a huge modifier is not very effective)? Comparing my results with a 25" shoot through vs a wall it appears the answer seemed to be yes but I don't have a flashmeter to check.

Anyhow, I'm glad I learned a few things, among which was that the zoom advantage isn't as large as I supposed.

Best regards,
Michael
--
http://betterfamilyphotos.blogspot.com/

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UKphotographers · Aug 9, 2010

jean bernier said:
The umbrella is a 42 inch white model.

I reversed the umbrella this morning and did a few measurements. As expected, the difference is this time worth mentioning, you've got to admit:
Shoot through umbrella 24mm: f:4
Shoot through umbrella 105mm: f:4,4

Just to confuse matters - my results were for a shoot through at 0.1 difference. I only did it this way to match the way Michael was shooting. The soft silver was used normally. (no difference, reflective). Like all modifiers - they have their own characteristics - which is why I specified the size and make in my results. Michaels results matched mine - he didn't say which way round the umbrella was pointing, but I assume shoot through as that was mentioned a few times and samples were shown in that orientation.

If the canopy material is really thin, then more of a hotspot will be created and the light won't be diffused as well. If it's not diffused as well it won't spread to the same degree. If it doesn't spread to the same degree you will get a different EV on your subject.

Good thing or bad thing? Bad thing for both I guess. If you use 24mm then light will pass (almost) directly through yet little will be directed towards your subject - you will still get a wide canopy of light, but it would only be softened a small amount. At 105mm you'll get a higher EV and an even harder light. The same occurs in direct facing softboxes where the interior is not lit by a speedlight yet a barebulb will adequately light it. The speedlight result is crap with a hard hotspot, whereas the barebulb does what it's supposed to, giving a more even spread.

--
Ian.

Samples of work: http://www.AccoladePhotography.co.uk
Weddings: http://www.AccoladeWeddings.com
Events: http://www.OfficialPhotographer.com

Theres only one sun. Why do I need more than one light to get a natural result?

creaDVty · Aug 9, 2010

Ian and Jean, my initial tests were with a 25" shoot-through. I don't have a flashmeter so I used histogram voodoo

to estimate that there's no ev diff on the subject.

Ian, if I understand you correctly, if we use a transparent plastic umbrella (for the sake of discussion), there would be virtually no softening effect, hence a large diff in EV. If the umbrella material is thin enough then it begins to resemble the hypothetical plastic umbrella, thus a noticeable diff in gn as well as hardness? Conversely if we had a thick umbrella, the light would be diffused sufficiently that there ought to be no diff in ev because the light will splash around like water resulting in the same light intensity on the shooting side of the shoot-through? I hope I understood you correctly? If so, this modified version of the modifier theory may account for why the difference isn't 1 stop, which would happen only with a totally transparent plastic umbrella. Is it also the case that the coverage of the 105mm wouldn't be as narrow as would be predicted from the angle of a 105mm lens - because the theoretically narrow beam gets scattered when it splashes around the umbrella surface, in effect increasing the coverage?

And with a reflective umbrella, the umbrella acts like a hall of mirrors: whether we shine a wide light or a narrow light, the light will likely bounce around the entire umbrella surface - resulting in almost the same coverage whether it's 24 or 105, thus accounting for the minimal (0) difference you found for a reflective umbrella?

I'm just trying to reconcile all of the results so far.
--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

jean bernier · Aug 9, 2010

creaDVty said:
Ian and Jean, my initial tests were with a 25" shoot-through. I don't have a flashmeter so I used histogram voodoo to estimate that there's no ev diff on the subject.

Ian, if I understand you correctly, if we use a transparent plastic umbrella (for the sake of discussion), there would be virtually no softening effect, hence a large diff in EV.

Indeed

creaDVty said:
If the umbrella material is thin enough then it begins to resemble the hypothetical plastic umbrella, thus a noticeable diff in gn as well as hardness?

Agreed

creaDVty said:
Conversely if we had a thick umbrella, the light would be diffused sufficiently that there ought to be no diff in ev because the light will splash around like water resulting in the same light intensity on the shooting side of the shoot-through?

This splashing around is there, but is very ineffective: the hotspot makes the exposure

creaDVty said:
I hope I understood you correctly? If so, this modified version of the modifier theory may account for why the difference isn't 1 stop, which would happen only with a totally transparent plastic umbrella. Is it also the case that the coverage of the 105mm wouldn't be as narrow as would be predicted from the angle of a 105mm lens - because the theoretically narrow beam gets scattered when it splashes around the umbrella surface, in effect increasing the coverage?

Well, look at the shoot through umbrella that was photographed at the link previously mentioned: the hotspot is really hot, and the rest of the umbrella surface is very dimly lit, hence not contributing much light. The large shoot through has effectively become a much smaller source. A little more light passes through the fabric due to the direction of light rays (direct to subject, no angle), there is reduced coverage (less scattering)because of the reduced circumference, all contributing a little more efficiency.

creaDVty said:
And with a reflective umbrella, the umbrella acts like a hall of mirrors: whether we shine a wide light or a narrow light, the light will likely bounce around the entire umbrella surface - resulting in almost the same coverage whether it's 24 or 105, thus accounting for the minimal (0) difference you found for a reflective umbrella?

Yes it bounces around, but it is not distributed the same: at 105mm, you have an umbrella with a strong, smaller bright area surrounded by a dimly lit surface: it is still soft, but not as much as an evenly lit umbrella.

I'm just trying to reconcile all of the results so far.

creaDVty said:
--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

--
Jean Bernier

All photographs are only more or less credible illusions

UKphotographers · Aug 10, 2010

creaDVty said:
Ian, if I understand you correctly, if we use a transparent plastic umbrella (for the sake of discussion), there would be virtually no softening effect, hence a large diff in EV.

The same difference as the GN difference between 105mm zoom and 24mm zoom, because you're doing nothing to it.

creaDVty said:
If the umbrella material is thin enough then it begins to resemble the hypothetical plastic umbrella, thus a noticeable diff in gn as well as hardness?

yes.

creaDVty said:
Conversely if we had a thick umbrella, the light would be diffused sufficiently that there ought to be no diff in ev because the light will splash around like water resulting in the same light intensity on the shooting side of the shoot-through?

No. (How does splashing around like water work?). If the duffusion surface diffuses the light properly, both a 24mm zoom and 105mm zoom will be diffused 180 degrees. The EV on the subject will be the same, yet the hotspot will still be there at just over 5" wide for the 105mm zoom compared to the 24" of the 24mm zoom. The 5" hotspot will be harder than the 24".

creaDVty said:
I hope I understood you correctly? If so, this modified version of the modifier theory may account for why the difference isn't 1 stop,

Nothing has changed. Even your test illustrated the same.

--
Ian.

Samples of work: http://www.AccoladePhotography.co.uk
Weddings: http://www.AccoladeWeddings.com
Events: http://www.OfficialPhotographer.com

Theres only one sun. Why do I need more than one light to get a natural result?

creaDVty · Aug 10, 2010

I think everyone agrees the small hotspot will definitely be harder because it's smaller. But all those photons that would have been dancing in that 24" inch space are now sardined into a (theoretically) 5" space - that's why I thought there ought to be an EV difference.

At the same time, I've looked at the hotspot for 105mm and compared it to the 24mm and strangely, the 105mm isn't that much smaller than the 24mm. Certainly not by a factor of 23x (the ratio of a 24" diameter circle to a 5" diameter circle). I can upload shots later if that forwards the discussion. My guess is that modifiers attenuate (but not eliminate) the difference between the two zoom settings in terms of coverage, EV and softness (that's what I meant by the modified version of the modifier theory).

--
http://betterfamilyphotos.blogspot.com/

TTL Flash Tutorial and other resources for taking better candid and family photos.

UKphotographers · Aug 11, 2010

creaDVty said:
I think everyone agrees the small hotspot will definitely be harder because it's smaller. But all those photons that would have been dancing in that 24" inch space are now sardined into a (theoretically) 5" space - that's why I thought there ought to be an EV difference.

Everyone agrees but...

There is no 'but'. There is no 'dancing in'. Quite simply, the projected light from the flash is modified by the umbrella surface - whatever the characteristics of that umbrella surface is. A 24mm zoom covers 84° and a 105mm zoom covers 23°. These figures are as acurate as I could find since there was no spec on the zoom coverage angle of the SB800.

creaDVty said:
At the same time, I've looked at the hotspot for 105mm and compared it to the 24mm and strangely, the 105mm isn't that much smaller than the 24mm. Certainly not by a factor of 23x (the ratio of a 24" diameter circle to a 5" diameter circle). I can upload shots later if that forwards the discussion. My guess is that modifiers attenuate (but not eliminate) the difference between the two zoom settings in terms of coverage, EV and softness (that's what I meant by the modified version of the modifier theory).

I think you're guessing on the false results you obtained (judging on the basis of the other tests you've done), and in this case too, I think your tests will be wrong.

By all means upload those shots you've done.

--
Ian.

Samples of work: http://www.AccoladePhotography.co.uk
Weddings: http://www.AccoladeWeddings.com
Events: http://www.OfficialPhotographer.com

Theres only one sun. Why do I need more than one light to get a natural result?

How many SB900s to overpower sun

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