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Thread: New Two-Part Tutorial Added: Camera Flash

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    New Two-Part Tutorial Added: Camera Flash

    Just added a two-part tutorial to the main page:

    Camera Flash, Part 1: Light Quality & Appearance
    Camera Flash, Part 2: Flash Ratios & Exposure

    These will likely be updated and modified with time. Is there anything you think I've left out? Something you feel differently about? Spot any typos? Let me know your thoughts.

    Many thanks!

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    Moderator Donald's Avatar
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    Re: New Two-Part Tutorial Added: Camera Flash

    Sean

    As one who was completely ignorant (until I just read these) about the use of flash, I:-
    a) don't know enough to comment on whether there's anything missing
    b) think both parts comprise a clear, straightforward and accessible tutorial on the subject.

    Made an awful lot clear that previously was mysterious. Thank you.

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    Re: New Two-Part Tutorial Added: Camera Flash

    Thanks for the feedback Donald. Flash is a pretty complicated photo topic, so a big concern was not making it too dense...or too long. There's several guides out there that are thorough and accurate, but they are also tens of pages or more in length.

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    Moderator Dave Humphries's Avatar
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    Re: New Two-Part Tutorial Added: Camera Flash

    Hi Sean,

    That's an excellent starter on the topic.

    One thing I half expected to see, but never did, was the timeline diagram with a spike towards the right for rear curtain flash sync. But maybe that's going too far in these two pages, there is probably already enough to absorb there, as you can see, I haven't got the hang of it yet

    I am still a little unclear on why with the 1X going to 2X, we need to increase FEC by one stop AND decrease EC by 1/2 to 2/3 stops, it feels like a double compensation.

    Let me write it out and the penny may drop;
    Taking EC down would under expose the image, both ambient and flash, by the 1/2 to 2/3 stop, so putting in +1 FEC brings that up element up again and gives the desired ratio, hmmm. I think I get it The key (I think) is it did this maintaining the same exposure for the brightest element.

    However, when I started thinking about it, taking the table at face value, it seemed that just increasing FEC by +1 would do it, but I guess this would over-expose the flash lit elements.
    Not withstanding that, the ratio still felt right at 2X what it was.

    I think I'm being a silly billy - it may just be me being thick , or maybe this rambling will help you understand my mis-understanding and clarify it for all (I hope).

    Or maybe this is the difference in the two methods of expressing the ratios you were talking about.

    I'll be having another read 'later' and let you know if anything else ocurs to me.

    Thanks,
    Last edited by Dave Humphries; 22nd September 2009 at 01:19 PM. Reason: clarify my thoughts

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    Re: New Two-Part Tutorial Added: Camera Flash

    Quote Originally Posted by Dave Humphries View Post
    One thing I half expected to see, but never did, was the timeline diagram with a spike towards the right for rear curtain flash sync. But maybe that's going too far in these two pages, there is probably already enough to absorb there, as you can see, I haven't got the hang of it yet
    Yes, I intend to add a portion on second curtain sync. There's just one thing holding me up: I just haven't found a good example of it from my own collection yet!

    I also intend to add other sections to it with time, but thought that these two pages encapsulated most of the key topics already, so I thought it made sense to just make them public and include more later.

    Quote Originally Posted by Dave Humphries View Post
    I am still a little unclear on why with the 1X going to 2X, we need to increase FEC by one stop AND decrease EC by 1/2 to 2/3 stops, it feels like a double compensation.

    Let me write it out and the penny may drop;
    Taking EC down would under expose the image, both ambient and flash, by the 1/2 to 2/3 stop, so putting in +1 FEC brings that up element up again and gives the desired ratio, hmmm. I think I get it The key (I think) is it did this maintaining the same exposure for the brightest element.

    However, when I started thinking about it, taking the table at face value, it seemed that just increasing FEC by +1 would do it, but I guess this would over-expose the flash lit elements.
    Not withstanding that, the ratio still felt right at 2X what it was.

    I think I'm being a silly billy - it may just be me being thick , or maybe this rambling will help you understand my mis-understanding and clarify it for all (I hope).

    Or maybe this is the difference in the two methods of expressing the ratios you were talking about.
    Not silly at all. This part was the most confusing to me as well, so it's good you brought this up. It clearly needs updating so that it's easier to follow. I think that section might be better served by walking through the process of what happens as you adjust EC and FEC at the same time in each of the INCREASE/DECREASE paragraphs.

    Yes, changing the ratio AND maintaining the same exposure as before is the tricky part. It's also something that the majority of other websites gets wrong. Many say that if you decrease EC by 1, you need to balance FEC by an increase of 1, etc. The problem is that EC and FEC are not independent -- the former influences the latter.

    However, I had recently changed the chart to use the flash:ambient convention for the flash ratio instead of the (flash + ambient):flash or total:flash convention. In the process, a few of the values in that chart did not reflect the new convention. That has been fixed. Further, the FEC/EC values are not independent of the original flash ratio, so a generic chart for shift up or down one stop in the flash ratio is not possible -- it needs to be based on the original flash ratio your camera would have otherwise used. The chart is therefore now shown assuming a default 1:1 flash ratio.

    However, I need to include an interactive chart or a flash ratio calculator, which shows the FEC/EC values needed to change the flash ratio from one value to another. I have to think about the best way to go about this though since it could easily over complicate things.

    In your case, increasing FEC may have looked just fine depending on what the original flash ratio was. If it was 1:1 or 2:1, then it would lead to a noticeable exposure increase. If it was just 1:2 or 1:4, as your camera would do in fill flash mode, then you were likely only increasing the exposure by a fraction of a stop and increasing the flash ratio by one stop -- so the overall exposure looked pretty much the same.
    Last edited by McQ; 22nd September 2009 at 08:00 PM.

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    Re: New Two-Part Tutorial Added: Camera Flash

    Hi Sean,

    I think that section might be better served by walking through the process of what happens as you adjust EC and FEC at the same time in each of the INCREASE/DECREASE paragraphs.
    Agreed.

    The problem is that EC and FEC are not independent -- the former influences the latter.
    Yep, that much I knew, but I had not thought at this level before

    That last paragraph helped me realise why you were talking about needing an interactive calculator. However, as you say, it could get awfully complicated and confusing.

    How about three rows at the top for the flash:ambient ratio - where the centre column is say 4:1 on top, 1:1 in middle and 1:4 beneath it. Then have just one row each for EC and FEC as now, and use your mouse over trick (css?) to change the values in unison on the EC and FEC rows depending which of the flash:ambient ratio is hovered over?

    I find it more helpful to think like this; in the example I gave of increasing from 1X to 2X, what you are actually doing is reducing the ambient by 1 stop, even though the most obvious thing you appear to be doing is increasing the FEC. i.e. encourage us to think 'take ambient down', not 'bring flash up' and the opposite where you want more ambient; think 'take flash down'.

    It might help, but I haven't thought it through, so I could just be creating another problem.

    By odd coincidence, I was, for almost the first time, using FEC that very afternoon on the spider shots, but only in a trial and error sort of way, take a pic and assess balance between ambient and flash, but at least I knew enough to turn the dial the right direction to get the expected result.

    Thanks,
    Last edited by McQ; 22nd September 2009 at 08:00 PM.

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    Re: New Two-Part Tutorial Added: Camera Flash

    OK, the FEC section has been completely overhauled. It's longer, but hopefully clearer.

    I like your idea of a javascript mouseover table that shows the EC/FEC settings for different starting flash ratios. However, the problem is that I only saw your post just now -- after I completed the section updates and included a calculator! Oh well. Take a look and let me know if it all makes sense.

    ------------------------------------------------
    FYI, the formulas are as follows:

    FR0 == original flash ratio
    FR == new (desired) flash ratio

    FEC = log2[FR/FR0]
    EC = log2[(1+FR0)/(1+FR)]


    (log2 is a base 2 logarithm)
    ------------------------------------------------

    It is the EC equation that's not as straightforward. To my knowledge, these formulas are nowhere else on the web, so I had to derive them for the tutorial. As stated before, most sites/books get the EC value wrong. I had always wondered why my exposures were a little off when using FEC and EC to change the flash ratio a little...
    Last edited by McQ; 22nd September 2009 at 08:15 PM.

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    Re: New Two-Part Tutorial Added: Camera Flash

    Update: Just added a section on red-eye reduction in the first part of this tutorial.

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    Re: New Two-Part Tutorial Added: Camera Flash

    Quote Originally Posted by Dave Humphries View Post
    One thing I half expected to see, but never did, was the timeline diagram with a spike towards the right for rear curtain flash sync. But maybe that's going too far in these two pages, there is probably already enough to absorb there, as you can see, I haven't got the hang of it yet
    Update2: Now there's also a section on first and second curtain sync in the second part of the tutorial.

  10. #10

    Re: New Two-Part Tutorial Added: Camera Flash

    I feel there are some things that could have been added in the first tutorial. But feel free to ignore what I say.


    Two ways to achieve this are by using either a flash diffuser or a bounced flash.

    bounced flash is diffuse but loses intensity

    While it may at first sound counterintuitive, aiming your flash *away* from your subject can actually enhance their appearance. This causes the incident light from your flash to originate from a greater area, and is why portraits are usually taken with a flash that first bounces off a large umbrella.
    However, bouncing a flash greatly reduces its intensity, so you will need to have a much stronger flash in order to achieve the same exposure. Additionally, bouncing a flash is often unrealistic for outdoor photographs of people since they are no longer in a contained environment.

    • A colour cast may be introduced when bounching espeicially if the walls are not white in colour.
    • This is with reference to the part in bold. More often than not, I don't find myself needing a more powerful flash, like the SB800 or SB900 when I'm using the SB700. And I believe most flash units have adequate power to bounce flash indoors, so won't a nikon SB700 or Canon speedlite 430 surfice? The downsides of increasing the flash intensity are obvious - longer recycling time, thus fewer FPS, as well as fewer shots.

    Alternatively, the flash's white balance can be intentionally modified to achieve a given effect. Some flash diffusers have a subtle warming effect, for example, in order to better match indoor incandescent lighting, or to give the appearance of light from a sunset.

    • You might want to elaborate more on the use of colour gels, warming filters and other filters.


    You might also wish to include a part on using flash for macro photography, and the reasons for using more than 1 flash unit to light a given subject. You may also consider writing a tutorial on studo flash (as Colin has kindly done) and wireless (off-camera) flash.


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