Working with Manual flash powers

Discussion in 'Beyond the Basics' started by Overread, Nov 27, 2009.

  1. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Ok so I recently got a new little toy - a bigger softbox! Not one of those massive kinds used on stands, but one which is large enough to now cover over all the AF assit and other flash auto controls on the front of my 580EX2 - so its time for me to start learning more about manually controlling my flash power.

    However I have no idea where to start with this. I know that idealy one would use a ilghtmeter and take testshots to gague the power output needed for the flash - however my typical working conditions will not be studio based but outside based (and most likley hunting after bugs). So I need a way to start knowing how much to set the flash power output to so that I can ensure that I will get a good exposure.
     
  2. Village Idiot

    Village Idiot No longer a newbie, moving up!

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    Guide Numbers plus finding out how much power the soft box absorbs.

    Why not try TTL and adjusting the FEC as needed?
     
  3. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    It's actually not that hard to just use the trial & error (or guess & test) method. Especially when only using one light. Just shoot, check the exposure, make adjustments and shoot again.

    You can adjust the exposure from the flash by;
    a) changing the lens aperture
    b) changing the flash power setting
    c) moving the flash closer or farther from the subject.

    Once you do it a few times...you get a feeling for it and can estimate the settings needed for the situation. After that, it should only take a small adjustment or two.

    Now, if you are using more than one light and you want to get your ratios under control, a flash meter is really handy.
     
  4. kundalini

    kundalini Been spending a lot of time on here!

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    For me, it's a matter of experimentation *read: plenty of images to fill the dust bin*. I started off strictly TTL and have recently been "playing around" with manual flash settings. For your macro work, start off with something like 1/4 power and make adjustments as needed. Pretty much, I'm just regurgitating what Big Mike suggests.
     
  5. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    E-TTL can be nice, but the one problem (besides needing the expensive tools to make it work) is that it's still an 'auto mode' and can thus be inconsistent, depending on the reflectivity of the subject.

    In manual, the flash output is consistent (unless you change it) and it's not hard to work with something when you know it's consistent.
     
  6. Derrel

    Derrel Mr. Rain Cloud

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    Dude--thus is the PERFECT excuse to purchase a 150mm or 180mm macro lens! Your macro lens's reproduction scale is your exposure guide...start with either 1/8 or 1/4 power and a lowish ISO like 200 ISO....at 1:5 reproduction ratio the exposure will be probably your largest macro aperture, which might be f/6.3....at 1:4 reproduction ratio, you'll need to stop down...at 1:3 reproduction ratio stop down even more, and at 1:2 ratio you'll be about two and a half f/stops down from where you were at 1:5, and at 1:1 reproduction ratio you'll be stopped down to your minimum working f/stop for that particular flash power. This will work actually with any macro lens that has a reproduction scale, and it will also work with any fixed focal length lens used with a particular, say 25mm, extension tube.

    Since the reproduction ratio is always the same at say 1:3, the needed lens f/stop will always be the same at that f/stop. If you want to, tape a piece of tape and place it on the lens barrel,and make some markings as you conduct a test. With my flash and mini-softbox and Sigma 180mm f/3.5 EX Macro, I get about f/5.6 at 3 feet at 1/8 power at ISO 200.

    If you need a smaller lens f/stop, just click the sensor's ISO upward one f/stop, or boost the flash power upward from one value, like 1/8 power, to the higher value like 1/4, and presto! Pretty soon you'll be guesstimating your exposures like a pro--and with the true macro lens and say the reproduction ratio set to say 1:2, you can pre-set the flash, pre-set the focus, and just lean over toward a butterfly and as soon as the camera-to-subject distance gives good focus, press the shutter and you'll have the right exposure and the right focus; THIS IS ONE REASON macro lenses have such carefully-calibrated reproduction ratio scales, and this is how macro work was done before TTL flash was even a concept in Maitani's eye.
     
  7. IgsEMT

    IgsEMT No longer a newbie, moving up!

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    On small speedlites, shooting through anything other then stofens, I start out at 1/2 power iso 400 1/125 f8. more often, optimum exposure shooting home made foampaper/softbox under @ 10feet i get is at f/6.3
     
  8. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Ahh I already found the excuse for a 150mm macro - and even a 70mm macro as well :) (I like the 70mm for offcamera flash whilst working handheld - shorter working distance and lighter lens work far better than the 150mm which is a little heavy I find for onehanded shooting - and the longer working distance means less chance to rest it on something).

    As for the flash powers - I think I get what your saying Derral (late night and my batteries dieing on me are not helping matters ;)) And is it essentaily that magnifcation factor is a (more) major contributing factor than ambient light changes in the shooting environment?
     
  9. usayit

    usayit No longer a newbie, moving up!

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    Why not use a flash meter? There is absolutely nothing about the meter that limits its use in the studio. I use a flash meter outside all the time. Meter ambient and exposure is with shutter and aperture. Meter with flash and exposure is with flash power and aperture. I like to keep the two exposures within 2-3 stops of each other.

    Example... Set to ISO 200 at 1/4th power and let the meter report the aperture value. Set the camera to aperture priority, dial in the aperture value, and allow the camera decide the shutter value for ambient. You can "place" ambient exposure above or below the subject's flash exposure with the camera's exposure compensation.

    A macro shot should be slightly easier as the subject (flash + ambient) will determine the most important exposure.
     
  10. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Hmm its not so much that I view flash meters unusable outside, but more that I don't want the insect flying off whilst I'm metering ;) Interesting that as I read your description its similar to a video (youtube) that I saw where they were again balancing things on the aperture based on the flash output - for myshooting chances are though that I would prefer to work the other way around. Partially because aperture and depth of field are key in macro work and also because if I let the camera meter the shutter speed I know I will get slow speeds which will be far too slow for handheld most of the time - so fixed shutter and aperture are what I tend to work with at present - letting the flash autometer the settings (and adjusting as needed).
    I guess my work now will probably end up following a similar line - just with some testing thrown in to find a happy medium for the flash power output to start from.

    edit - my other aversion to flash meters is a lack of funds for one - though I do do indoor macro work with cold bugs, when I get the chance - and I like gear - so I suspect one will worm its way into my gear at some point ;)
     
  11. Buckster

    Buckster Been spending a lot of time on here!

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    I'm trying to picture the scenario in my mind. You're shooting bugs, so I'm guessing you're moving around, at least in a small area, and you mentioned shooting with one hand. So your light is - - where? In your other hand?

    All things being equal then, you should be able to dial in your settings on a blade of grass or anything at all, and then just go to town on the bugs as fast as you can get them in focus, assuming they're all in the same basic range as the blade of grass (or whatever) that you dialed in on. If they're not (meaning you're hitting the re-focus from a few inches to a few feet shot to shot, depending on where the bug is in relation to you), you're not going to be able to manually dial in different flash exposures on the meter AND catch the bugs all on the fly anyway. No way.

    At such short working distances, the inverse square law is not so forgiving as it is over long distances. Doubling or halving the distance of a foot or two is easy if you're not dialed in to a working distance already, and that makes a real difference in how much light hits the subject. I guess if you're REALLY good, as you move in on a bug with your camera hand, you could compensate by moving your flash hand further away, but MAN, what a workout that sounds like, not to mention a total headache in instant calculations or resorting to using the force like a Jedi Knight in a blindfold to get it right with any consistency!

    On the other hand, if you ARE dialed in on a working distance, then you want your flash to stay at the same relative distance from shot to shot as well. That said...

    Are you planning to use a flash bracket at least? (I ask because of the one-handed shooting reference). I think that will help you immensely. I built a bracket rig for under $10 to hold two 580EX II flashes for running around shooting bugs, and it gives me total freedom and consistency, whether I'm shooting TTL or manual - the light is always at the same relative distance to the bug, as long as my working focal length is the same. It also allows me to have both hands on the camera/lens for stability and operational control. My focal distance is predetermined within a small range, my strobes are set to work that range, and I'm off and running.

    Then it's just a matter of moving the camera into position untill the bug's in focus, and SNAP - it's mine.

    [​IMG]
     
  12. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Neat grasshopper (least it looks grasshoppery). On the subject of brackets Ideally I would use one, but I have found the 580EX2 to be quite a heavy flash for many brackets and the bracket I did get (only a cheap ebayone) had significant wabble when using it. I hope to get that bracket back soon (sent if off to an uncle to weld some more metal on) and give it another try. Idealy I want to get the flash located above the end of the lens, whilst tilting down toward the subject.

    DIY wise I am limited in that I have very few (read pretty much no) tools to hand to craft much (plus limited experience too). I have seen your 2 flash setup, but I think it would be way too heavy for handheld for long (I recall seeing yours on a tripod mount) at least for me. Plus I don't really want to sink too much more money into a dedicated setup since the canon twinlights (as overpriced as they are) are on my to get list.
     

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