How many SB900s to overpower sun

CreaDVty: I see that on the blog you atarted in the fall of 2009, that you are an amature photographer, who started "Road Map for Family Photographers", to leaqrn how to take better pohotos of the children and families and for other aspiring photographers to teach them or aid them on their journey through the image creating process.

Ian, of UKphotographers, is a photographer who has been in the business for a while. He has a lot more experience than you do. He is a commercial photographer. He also does portraiture, wedding and event photography, architectural photography, ad infinitum. I know this and tell you this, that I have the same experiences, in the same fields tht Ian has, only for a longer time frame.

He started off trying to share his knowledge with you, as well as others. if he tells you that there are differences using different zoom settings in an umbrella, believe him. Any photographer can say "Yeah, I use umbrellas", but that statement does not tell the whole story. A shoe mount Speedlight does not even do a good job in the typical umbrella. You have a rectangular light pattery in a round modifier. You are not even lighting up the entire surface of the umbrella. If you use a round umbrella, you should use a light source that has a parabolic reflector.

Is is a translucent umbrella and bouncing off it. If so, that in itself loses more light because you are shooting some of it through the fabric and nor reflecting all of it back toward the subject. If you are going to bounce out of an umbrella, use one with a thicker, closely knit material for more light efficency. Shooting through a translucent umbrella is transmitted light, while bouncing light off an umbrella provides you with reflected light. There is a difference in this kind of light. I am not going to teach you the difference, but rather have you learn for your seld the difference.

If you use a larger umbrella (they come 24", 32" 36" 42", 48", 60", etc. etc.) the shoe mount flash will not provide sufficient power or coverage. Again, a call for a more sophisticated light for umbrella use. Same goes for using the rectangular Speedlights with Softboxes. There are people out there trying to us large softboxes with a light that wasn't made for that purpose.

Different shapes for umbrellas also contribute to how the light is modified and directed. Different fabrics (i.e. - translucent white, solid white, matt silver, shiny silver, matte gold, shiny gold) also contribute to the color and quality of the light.

Then enters the brolly-box. This is a cross between an umbrella and a softbox and has its own set of parameters.

I could go on for a while, but I just want to give you a brief synopsis of what one tiny portion of lighting for photographers is about.

The size of the umbrella has a lot to do with the quality of light

For some reason my other reply last night didn't get posted (search term I used was "hissy fit" ). Anyway I want to set the record straight so I'm reposting.

Re the 45m GN, I made a mistake - it's not from Nikon, it's from a light meter test by gisle (dpanswers). Under that same test, the GN at 24mm is 29m. Here is a link:
http://dpanswers.com/content/rev_nissin_di866.php

The advantage to be gained from zooming from 24mm to 105mm is a factor of 1.55x or slightly more than one stop.

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.

About the calculations, I reexamined them. I made a mistake in factoring a 4-stop reduction for the 4-stop ND filter. I should have just figured out the power needed to get to f/16. The 4-stop factor was unnecessary because it was going to be compensated by a widening of the aperture to f/4.

As for the umbrella penalty, I factored in 1 stop reduction, which is wrong for a 25" shoot-through. The correct umbrella penalty is dependent on how it is measured. I tested the umbrella penalty and found it to be either 3 stops for a zoomed flash (iow bare zoomed flash vs. zoomed flash w/ umbrella) or 2 stops for a flash at 24mm (bare wide flash vs. wide flash w/ umbrella).

Thus in the calculations if a flash is zoomed, the GN to be plugged in was 45m, but and the umbrella penalty is 3 stops. With a wide flash, the GN to be plugged in is 29m, and the umbrella penalty is 2 stops.

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

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

Thank you friend for your patient and gentle advice. Just a few points:

1. I started in 2007 not 2009 though perhaps my poor pictures may make it seem like I started only a few months ago! Anyway, you are of course right that pros like Ian have exponentially more experience than I do. I said as much previously, and also said that I am open to learning. If I claim to know everything, then that is the point when I stop learning. The first step to learning is to know what I don't know.

Just to clarify also, I'm not trying to be a pro either or comparing my meager skills to pros. My goal is just to improve as much as I can given the limited time and budget I have for weekend shooting because I want to do the best I can do for my family and friends. The point of the blog I created is only to use it as a notebook so that I can push myself to learn and so that others can use whatever I've learned. I may have only little knowledge and experience, but there are many who have even less than that. (Incidentally, I have met a few pros who know less than I do, and in my opinion, produce poorer photos than I do.) I don't see a lot of information out there to bridge the gap either, and the information out there is so scattered. For example, I didn't see even a single TTL flash hands-on tutorial out there. So I created one. I didn't see explanation of lighting for amateurs like me. So I created one. etc.

I asked Ian to provide evidence for his statements because I don't usually accept things on faith. Your point though, is well understood. It is the same with any profession. No part-time hobbyist can compare with a skilled and experienced professional.

2. About umbrellas, yes speedlights are not ideal for them. Studio strobes are much better for the reasons you mentioned. I yearn to get one myself. The problem is that I take non-setup photos 90+% of the time. So, as much as I would like to lug around a monolight with portable power, it isn't practical. For the kinds of shots I take, the most practical solution for soft, directional light when bouncing is not practical or possible is to use an umbrella. If you know of a better solution, please let me know.

3. Yes I am aware that there is a difference in light quality and efficiency between reflective umbrella vs. shoot-through umbrella vs. softbrella vs. softbox vs. strip light, and how the size, shape, materials, and other factors affect its quality. But you are right that there is far more to learn about lighting. If you look at my previous messages here you will find a consistent theme that I am here to learn (from pros like you and Ian) and to share.

Best regards,
Michael

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

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

creaDVty said:

For some reason my other reply last night didn't get posted (search term I used was "hissy fit" ). Anyway I want to set the record straight so I'm reposting.

Re the 45m GN, I made a mistake

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Numero: 1

creaDVty said:

• it's not from Nikon, it's from a light meter test by gisle (dpanswers). Under that same test, the GN at 24mm is 29m. Here is a link:

http://dpanswers.com/content/rev_nissin_di866.php

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You have memory problems and flit between subjects you have no comprehension of or understanding.

The Nikon figures I quoted were quoted specifically because you cited them:

creaDVty said:

creaDVty wrote:

In theory, 4 flashes can do it at 1 meter. The GN below assumes fully zoomed flash and further assumes Nikon's numbers are accurate.

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creaDVty said:

Assuming GN of 45m at 105mm zoom and ambient of f/16, 1/125, iso 100:

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creaDVty said:

The advantage to be gained from zooming from 24mm to 105mm is a factor of 1.55x or slightly more than one stop.

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Not according to Nikon numbers you referred to.

creaDVty said:

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.

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The zoom advantage I want you to demonstrate is the difference between using a flash in an umbrella at 105mm zoom and a flash in an umbrella at 24mm zoom. You think there's a difference of 'slightly more than 1 stop' ... there isn't. Did you get that? There isn't.

Your obsession with making the umbrella pointless by using a zoomed flash is beyond belief. If I chose to use an umbrella or softbox for whatever reason, I want those two modifiers to have an even coverage across their surface and not a hotspot in the middle. You basically do not understand and will use a zoomed flash in your umbrella and get a more pronounced hotspot than ever, and have no benefit from inflicting this anomally.

creaDVty said:

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.

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FFS. The point was that you were factoring in the GN difference of a 105mm zoom when there was no factor to be included.

The difference is you have a hotspot and uneven lighting across your umbrella when you needn't have that hotspot and you could have a better quality light by using the umbrella properly with no difference to the power output that you still believe to be greater due to the GN difference.

creaDVty said:

About the calculations, I reexamined them. I made a mistake

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Numero: 2

creaDVty said:

in factoring a 4-stop reduction for the 4-stop ND filter. I should have just figured out the power needed to get to f/16. The 4-stop factor was unnecessary because it was going to be compensated by a widening of the aperture to f/4.

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I'm saying nothing.....

creaDVty said:

As for the umbrella penalty, I factored in 1 stop reduction, which is wrong for a 25" shoot-through. The correct umbrella penalty is dependent on how it is measured.

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Numero: 3

creaDVty said:

I tested the umbrella penalty and found it to be either 3 stops for a zoomed flash (iow bare zoomed flash vs. zoomed flash w/ umbrella) or 2 stops for a flash at 24mm (bare wide flash vs. wide flash w/ umbrella).

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Well tell me something I haven't been saying all along. Of course that will be the case! You cannot expect a flash used in an umbrella set to a zoom setting of 105mm to retain the flash's guide number. LOL. Hello ?? Zooming your flash is pointless. It offers no advantage. There's no need for multiple reduction factors to be applied to modifiers, if you use them correctly you only need one.

Furthermore, did you use a flashmeter or did you guess using a histogram?

creaDVty said:

Thus in the calculations if a flash is zoomed, the GN to be plugged in was 45m, but and the umbrella penalty is 3 stops. With a wide flash, the GN to be plugged in is 29m, and the umbrella penalty is 2 stops.

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Numero: 4

Whaheyyyyyy.... Based on YOUR estimate of there being 'about a stop difference' between a 105mm and 24mm zoomed flash - unmodified. Your result just proved to be the same as my example, and what I've been saying all along... NO DIFFERENCE!!!

Now you really must feel like an idiot.

QED. (quod erat demonstrandum) ...that which was to be demonstrated...

--
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 said:

creaDVty said:

...and your aspiration for providing tutorials on things you completely do not understand?

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Yawn. Wake me up when you think of a better comeback. And thanks for the plug.

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Wakey, wakey....

You know, there's often a chance that when you're confident and well informed and factually correct you can come over as being arrogant. With you Michael, you will never be called arrogant.

It most definately wasn't a plug.

--
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?

Ian,

1. I corrected the citation for my 45m gn to gisle's dpanswers. Consistent with that I used the same source to get the gn for 24mm, and that's how I calculated my figures. If you wish to insist on using nikon's numbers that's fine. However, first pls use your flashmeter to find a 2 stop advantage between bare flash 24mm and 105mm. Come back to me when you have that evidence. .

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.

3. Of course I understand that a hotspot will lead to a harsher light. But if the goal is to overpower the sun, which is the higher priority - getting adequate illumination or evenly filling the umbrella?

4. As for the umbrella penalty, I must refer you a third time to what I said way back: your point about the gn no longer being 45m when you use an umbrella is well taken. However i thought that was accounted for by the umbrella penalty. I also expressly said I didn't know if it was accurate. The other night I tested it, and found it to be higher than 1 stop. How much higher depends on whether the flash is zoomed or not. In either case, as long as the gn used is consistent with the umbrella penalty used then the result will be the same. On one hand under these conditions it shows there is no zoom advantage. On the other hand it also shows there is no perceptible difference in softness of light. I showed you test shots at 105mm and 24mm and the light quality was the same.

5. No I still don't have a flashmeter. It's not high on my priority list. I used the histogram. I can post the test shots of the umbrella penalty if you wish to double check. Or you can try it yourself.

6. your explanation for the absence of a difference in gn for a zoomed flash or wide flash when an umbrella is used is that the umbrella is a modifier and therefore any light that gets there is irrelevant. You only consider the modifier. Did I paraphrase that well enough for you? Assuming so, I believe your explanation is incorrect. I believe the real reason there is no apparent difference in the umbrella output in your test (and mine) was that whether the flash was zoomed or wide, they both had almost the same coverage (and of course same total output) thus the same gn. If the umbrella is large enough such that there is a material difference in coverage between the two, I believe that's the point where a material gn advantage (as well as quality difference) will be observable. What do you think?

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

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

UKphotographers said:

creaDVty said:

UKphotographers said:

...and your aspiration for providing tutorials on things you completely do not understand?

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Yawn. Wake me up when you think of a better comeback. And thanks for the plug.

Click to expand...

Wakey, wakey....

You know, there's often a chance that when you're confident and well informed and factually correct you can come over as being arrogant. With you Michael, you will never be called arrogant.

It most definately wasn't a plug

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Ian, you missed it. Pls. note which of your statements I quoted. And while I would love to explain that would be so crass.

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

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

creaDVty said:

Ian,

3. Of course I understand that a hotspot will lead to a harsher light. But if the goal is to overpower the sun, which is the higher priority - getting adequate illumination or evenly filling the umbrella?

Click to expand...

creaDVty said:

What do you think?

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I think that you STILL DO NOT HAVE A CLUE WHAT YOU'RE TALKING ABOUT. Since filling the umbrella or zooming the flash give EXACTLY the same result - what is to pick between them and how can there be any other answer to a question like this other than hello again !! There's no difference !!

You quite plainly don't understand as that point 3 fully illustrates.

You have illustrated that there is NO advantage to using 105mm zoom in an umbrella to obtain any more light on the subject. Whether that be in a coal mine or in bright sunlight the difference is ZERO. You even stated this yourself in the results you found doing it yourself with whatever you used - as I pointed out to you in your last misguided post.

This is plainly a lost cause and you really have no hope of understanding.

When people like you provide information by the way of 'tutorials' when you can't understand this simple fact - whether you're being told it, or you even do it yourself and publish the results, then it's hardly surprising that there is so much misinformation around propagated by, and passed on by equally dumb people who don't have a clue.

You misquoted Nikon data, you calculated the relative losses of both 105mm and 24mm zoom through an umbrella based on your own equipment, you arrived at the conclusion that the sum difference of the two settings is ZERO yet you still you think there's some advantage to using a zoom of 105mm and want me to check whether Nikon's figures are correct - which in your instance is totally irrelevant !!!

UNBELIEVABLE !!

--
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?

Sir, it is you who do not understand my point.

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.

Why would you get so worked up with using a zoomed flash when it is equally true that there is no material difference in quality (at least under these circumstances), which is the harm that you believe would result therefrom??? There is no inaccuracy in plugging in the 105mm gn either because the umbrella penalty varies with the zoom. To quote: "???????"

P.s. Please answer the question about your "modifier" explanation.
--
http://betterfamilyphotos.blogspot.com/

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

Further clarification: point 3 was in response to your earlier question that "rather than filling the umbrella evenly, you'd prefer to zoom the flash to get a 0.1 stop advantage."

Point 3 should therfore be prefaced with: "to the extent you claim that a zoomed flash will result in a hotspot"

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

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

creaDVty said:

Further clarification: point 3 was in response to your earlier question that "rather than filling the umbrella evenly, you'd prefer to zoom the flash to get a 0.1 stop advantage."

Point 3 should therfore be prefaced with: "to the extent you claim that a zoomed flash will result in a hotspot"

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Do I need to be a clairvoyant to answer your questions now? Truly this is getting ridiculous.

creaDVty said:

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.

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What are you going on about? I have never insisted anything of the sort.

I have made no claims to any change in quality of light being harder or softer - this is entirely your own obsession.

POINTLESS... here is where you bring it up:

creaDVty said:

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.

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And your point is STILL wrong.. you can't use the GN of a 105mm zoomed flash as the basis of your calculations.

This is your post I replied to where you stated to use the 105mm GN:

creaDVty said:

In theory, 4 flashes can do it at 1 meter. The GN below assumes fully zoomed flash and further assumes Nikon's numbers are accurate.

Assuming GN of 45m at 105mm zoom and ambient of f/16, 1/125, iso 100:

Ambient is equivalent to f/11 at 1/250. To get one stop underexposure, aperture would be at f/16. To shoot at f/4 you need a 4-stop ND filter.

At distance of 1m, the flash can get an aperture of f/45. With a 4-stop ND filter, that drops to f/11. To get that to equivalent of f/16, you need to increase power by 1 stop (iow, 2 flashes). If the umbrella causes a 1-stop light loss, you need to double the flash again to 4.

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All that ASSUMES you can use the GUIDE NUMBER of a zoomed flash..

AAAARRRRRGGGGGGHHHHHHHH !!! You can't !!!

--
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 said:

Why would you get so worked up with using a zoomed flash when it is equally true that there is no material difference in quality (at least under these circumstances), which is the harm that you believe would result therefrom???

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What are you talking about now? You are changing your tack faster than the actions of a fiddlers elbow.

Your statement there cites 'that there is no material difference in quality' yet your previous post states:

creaDVty said:

3. Of course I understand that a hotspot will lead to a harsher light.

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What ??? You are one crazy mixed up kid.

creaDVty said:

P.s. Please answer the question about your "modifier" explanation.

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No.

You have got to be joking right? If I did, we'd still be here next month STILL getting you to understand that using a flash at 24mm zoom GN (small) and 105mm zoom GN (MASSIVE) has very little difference on the resulting GN value after them being modified.

--
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?

UKphotographers said:

Do I need to be a clairvoyant to answer your questions now? Truly this is getting ridiculous.

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(Clairvoyance is remote viewing. You mean "telepath.")
The almighty Ian is supposed to be omniscient is he not?

The reason you failed to understand my point is that it's stuck in your head that I'm wrong (or perhaps the world is wrong) and rather than viewing my statements objectively, you are viewing them in a way to fit your perception. I invite you to read my statements anew, with a fresh set of eyes, and consider in what way I may be correct, because perhaps - just perhaps - a light bulb may go off "Oh, so that is what he meant." This is how I endeavor to read your statements despite your acrimonious tone and ad hominem attacks, and it's how I'm able to remain objective and able to understand your points, regardless of whether we agree or disagree. Please think about that before giving in to your instinct to retaliate.

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? 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.

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What are you going on about? I have never insisted anything of the sort.

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OK, this is the 2nd time I'm referencing your statement:

"So rather than having an umbrella which is fully illuminated to provide a soft light with your flash set to it's widest setting you instead set it to it's maximum zoom and have a hotspot right in the middle??? What's the point in that ? "

In any case, if you did not mean to argue that zooming the flash will make it harder then why did you have such a hostile response about that suggestion in the first place? Never mind. I don't care as long as you're not arguing that zooming the flash will make the light harder under circumstances when there's no GN difference, which was my point from the beginning. I kept asking you that saying pointless, harder, softer, etc. and until now you either ignored it, or gave me an irrelevant response such as about watt seconds or stating that everyone else other than you bodges their shots.

UKphotographers said:

And your point is STILL wrong.. you can't use the GN of a 105mm zoomed flash as the basis of your calculations.

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Ian, I already explained to you previously, as early as 5 days ago:

"However, your point about whether the GN would still be 45m is well taken. That I thought was taken into account by the 1-stop loss for umbrella use (I don't know if it's 1 stop but I assumed you were correct)."

If you insist that the GN for 105mm is wrong, what makes you so convinced that 24mm is the only correct GN? Is 24mm written in stone somewhere? What if someone were to criticize you for using 24mm instead of 35mm or 17mm or 14mm? I tried to tell you previously and for the last time -- using 105mm GN is ok as long as you use the umbrella penalty for 105mm, and likewise using 24mm gn is ok as long as you use the umbrella penalty for 24mm. Differences will cancel each other out. Regardless of whether you agree or disagree, do you understand what I'm saying? Please make a sincere effort to do so before dismissing it as false and insulting me or anyone else again.

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

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

creaDVty said:

If you insist that the GN for 105mm is wrong, what makes you so convinced that 24mm is the only correct GN? Is 24mm written in stone somewhere? What if someone were to criticize you for using 24mm instead of 35mm or 17mm or 14mm? I tried to tell you previously and for the last time -- using 105mm GN is ok as long as you use the umbrella penalty for 105mm, and likewise using 24mm gn is ok as long as you use the umbrella penalty for 24mm. Differences will cancel each other out. Regardless of whether you agree or disagree, do you understand what I'm saying? Please make a sincere effort to do so before dismissing it as false and insulting me or anyone else again.

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I chose 24mm as it was the least contentious wide setting and which most people would have as a benchmark without WA adapters. These would improve matters, but the resulting output would be the same. (I intentionally left out diffusers).

The modifier is a simple piece of fabric... it does one thing... not different things for different flash settings.

The result of that ONE thing it does is the same... All the time...

The ONE thing it does is... you point a light at it, it disperses the light all over. You only have a FIXED quantity of light... Therefore the result of using a wide or zoomed flash is the same exposure on the subject.

Using a wide zoom spreads the light as much as possible in the modifier giving a wide and even as possible coverage. This utilises the modifier in the way it was designed and the intention with which it was used. Shadows are softer as the perimeter of the modifier is contributing an equivalent share of light and utilising the modifiers maximum potential.

Using a zoom of 105mm doesn't do this, as it is the wrong setting to use in a modifier which is intended to soften shadows by increasing the surface area of the light.

Zooming your flash artificially increases the guide number, doesn't evenly fill the modifier, creates a hotspot, and the net result on your subject exposure is NOTHING.

Unless you adhere to the rules you cannot apply any sort of factoring to your calculations (as you found out).

A simple piece of modifier fabric does ONE thing it spreads light ALL over. There need NOT be any more than ONE factor to calculate this action. If you need more than ONE - you're doing it wrong.

--
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?

UKphotographers said:

The modifier is a simple piece of fabric... it does one thing... not different things for different flash settings.

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Yes. I understand your modifier explanation.

This is my question for you. (It's an honest one, not rhetorical.) What if you had a very large umbrella, so large that it could not be filled either with a 24mm, much less 105mm zoom. If you use 24mm zoom with that large umbrella, wouldn't the area covered by the flash be larger than the area covered by the 105mm zoom? If so, and if the total light output from the flash is constant, would there be any difference in light intensity reaching the umbrella surface?

I haven't tested so I don't know for certain. However, to the best of my limited knowledge and experience, I believe the intensity would be brighter for 105mm zoom. At the same time, due to the smaller area covered, the light would be harder compared to the 24mm zoom.

But then wouldn't the umbrella act as an equalizer. I think it is precisely because it does only one thing that if the light intensity reaching it is higher, then the umbrella's output would be higher as well. Otherwise, you could adjust the power on the flash up and down and nothing would change, which of course is not true.

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.

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

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

Let us talk a little about a rule of physics - the angle of reflectance is equal to the angle of incidence. This means that based on how the light is hitting an object, flat or curved, it reacts in a certain manner. If you instance, you shine a flash light straight against a mirror, the light comes straight back. This is the same as zooming to 105mm. The light goes into the center of the umbrella where there is minimum curvature and it come straight back (some of which will be blocked by the actual flash unit in it path. If you aim the light to the right or left of center, it will reflect in a different angle, there fore the light is going in a different angle. With a wide angle on the flash, the lights hits more of the curved surface of the umbrella and therefor reflects back at the subject with more coverage. Wide gives better coverage and light quality, period.

Look at profession grade portable lights or studio lights. They all use a parabolic (round) reflector, especially made for use with umbrellas. Shorter and shallower angle. This covers the entire surface of the umbrella, giving a more pleasing light to begin with, but with even coverage also.

On my way to take the kid to school, so let me think about that a bit.

In the meantime, suppose we're bouncing off a flat reflector or shooting through a flat scrim, would the foregoing analysis be correct?

Thanks in advance.
--
http://betterfamilyphotos.blogspot.com/

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

Bouncing off a flat reflector would work under the same principal. For instance, you are pointing at an angle of 30 degrees, the light would reflect off at 30 degrees of the opposite angle.

With the scrim, the light bouncing off the back surface would behave the same way. The light passing thru the fabric would basically go straight thru with some scattering due to reflecting off the internal surfaces of the threads of the scrim.

Shooting on an angle also changes the dynamics of the light, as the light that is farther from the light source will be weaker when reflected. In other words, the light striking the surface will be stronger closer to the light. The light striking the reflector farther from the light source will be weaker because of the added distance.

Sorry, I wasn't clear with my question. I didn't mean to ask about the law of reflection. What I meant to ask was, suppose you have a flat reflector or a flat scrim. And let's suppose it's quite large. What is the effect of using 24mm as opposed to 105mm? Is it:

a) no difference - the reflector (or the scrim as the case may be) is a modifier, and does only one thing to all light sources, therefore the flash zoom is irrelevant, as long as the total light is the same.

b) there is a difference. The 24mm would have larger coverage at the modifier's surface than the 105mm. Given the same total output, the light intensity would be lower than with a 105mm zoomed flash. The 24mm would also be softer because of the larger coverage.
c) some other answer.

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

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

creaDVty said:

creaDVty said:

The modifier is a simple piece of fabric... it does one thing... not different things for different flash settings.

Click to expand...

Yes. I understand your modifier explanation.

This is my question for you. (It's an honest one, not rhetorical.) What if you had a very large umbrella, so large that it could not be filled either with a 24mm, much less 105mm zoom. If you use 24mm zoom with that large umbrella, wouldn't the area covered by the flash be larger than the area covered by the 105mm zoom?

Click to expand...

Of course it would. This is what causes your hotspot. This is evident on smaller umbrellas too.

creaDVty said:

If so, and if the total light output from the flash is constant, would there be any difference in light intensity reaching the umbrella surface?

Click to expand...

Well, yes. Isn't that obvious? That's what causes the greater hotspot with a 105mm zoom.

If you had a VERY large umbrella - shoot through - you would never need to buy a smaller umbrella again.

You could set your flash close, far, wide or zoomed and the effect of these actions would effectively be an umbrella of variable sizes resulting in varying degrees of shadow softness and contrast.

The action of choosing a 105mm zoom over a 24mm zoom is one which will result in obtaining characteristics of a smaller sized umbrella, defeating the point in you using an umbrella of the size you have already chosen.

Over a specific size, and even with barebulb type flash a single flash in an umbrella will not be able to provide enough even coverage to be totally effective. This is why brolly boxes, softboxes, diffusion scrims, parabolics and linear tubes exist, along with the power packs to drive them.

--
Ian.

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