High speed synch mode photography and guide numbers

[skip_wilson]

<p>I have a Nikon D7100 and have questions about shooting in high speed synch mode with my SB 600. The Nikon SB 600 speed light manual gives tables for variable flash shooting distances ranges based on various f stops, ISO and zoom-head positions ( I assume focal length lens you are using) using TTL mode without any mention of flash guide number. It also gives tables giving various guide numbers for the SB 600 flash based on, again, zoom-head position in mm, ISO and flash output in Manual mode. eg 1/1, 1/2 etc. The flash manual states that halving the shutter speed eg going from 1/500 to 1/1000 decreases the guide number by 1 EV which I believe is 1 stop of light. Bryan Peterson in his book on Proper Exposure talks about quadrupling shutter speed decreases the guide number by 1/2. My question is: if I want to calculate distance I have to be from subject (a face in bright light with flash exposure, large lens opening and very fast shutter speed eg high speed synch or using hi shutter speed with flash to catch a hummingbirds wings) to get a proper flash exposure of the subject knowing my f stop and ISO -- how do I get my guide number to calculate that distance? Do I even need to use the guide number when I shoot with TTL in high speed synch mode? Please walk me through the steps I would do to find the shooting distance I need, knowing the f stop and ISO setting and focal length setting of lens. I suspect I would usually be shooting in manual mode for my camera and TTL mode with the flash.<br>

I appreciate any help and hopefully, relatively simple explanation if there is one. :) Skip Wilson</p>

[glasslakesphotography]

<p>Hi Skip,<br>

That is a lot of math which made my head hurt just reading it. I work with flash now and again and I operate on the basic principles of trusting TTL, and adjusting the flash compensator +/- to get what I am looking for. It is less exact, but running the numbers is a real pain in the arse. But when working with flash in a controlled setting like a portrait, a flash light meter is your best friend. If you do not have or use one then you can work by these rules:peeds<br>

ISO controls all the light in the image<br>

Shutter Speed controls the ambient light<br>

Aperture controls the amount of flash in the image. <br>

Remember that it is all about balance. Identify the overpowered or underpowered light and modify it. Shade, diffusers, ect are your friend. If the flash is maxed out then move it closer. The inverse square law applies, where doubling the distance is 1/4 the light. If you are having to use super high shutter speeds then your light source is probably too bright. Maybe lowering the ISO and toning it down will work? Like a flashlight at high noon, how useful is it? <br>

Sorry that I cannot directly answer your question, but possibly changing your methodology may yield the desired results. Also I found this link. http://dpanswers.com/content/genrc_flash_calc.php<br>

Hope this helps!</p>

[Alan Marcus]

<p>What I know about guide numbers:<br>

A guide number (GN) is just that, a guide. Mostly they are published by the manufacturer of the flash unit. The values are usually based on an indoor setting with 10 feet light ceiling. The good news is; it is easy to test and derive a reasonably valid guide number. Choose a typical situation. Set the flash to subject distance at 10 feet (3 meters). Shoot a series f/16 – f/11 – f/8 etc. Choose the best exposed frame. Suppose f/11 is best, then GN is 11 X 10 = 110. For metric folks its 3 X 11 = GN 33.<br>

<br>

To use: Estimate lamp to subject distance and divide guide number by distance. Thus if lamp to subject is 20 feet and the GN is 110 then 110 ÷ 20 = 5.5 then round to f/5.6.<br>

<br>

Some nuances’ :<br>

I believe the camera’s shutter speed setting is moot as to GN. This is because we set the shutter to synchronize with the flash and the flash duration is a blitz is far faster than the shutter. Exceptions are supper fast flash to freeze hummingbird wings. A super-fast blitz will cause ISO to plummet as film and imaging chips accumulate light. Under super-fast conditions you must test for a revised guide number.<br>

<br>

For fill-flash in outdoor situations, use sunlight exposure choosing a shutter speed will synchronize. Say 1/125 @ f/16. Now suppose the guide number is 110. Divide GN by f/# thus 110 ÷ 16 = 6.8. This math tells us that if the lamp is 6.8 feet from the subject, the intensity of the flash will be the same intensity as the sunlight. Now this will be flat lighting. Best if the fill is subordinate by 1 f/stop. To accomplish; multiply flash distance by 1.4.This calculates a revised flash to subject distance, it is 10 X 1.4 = 14 feet. The 1.4 factor causes you to increase subject to flash distance and the 1.4 factor computes a 1 f/stop drop in flash intensity at the subject plane.<br>

1,4 factor = 1 f/stop<br>

2 factor = 2 f/stops<br>

2.8 factor = 3 f/stops<br>

4 factor = 4 f/stops.<br>

The factor is based on the square root of 2 and follows the law of the inverse square (used to calculate light fall off with distance. <br>

<br>

How do I get my guide number to calculate that distance?</p>

<p>Guide # 200<br>

Use f/11 then distance flash to subject is 200 ÷ 11 = 18 feet<br>

Use f/16 then distance flash to subject is 200 ÷ 16 = 12 ½ feet.</p>

<p>Using existing light with flash:<br>

Because flash is usually harsh, use slower shutter to allow ambulant light to register along with flash.<br>

No advise as to TTL, this gray hair never used but my guess is, the TTL system automatically sets everything. If my lash-up had TTL I probably would leave my slide rule home. </p>

[Wouter Willemse]

<p>Not really an answer, but if it is really for distant shots with a telelens, something like a <a href="http://www.speedgraphic.co.uk/diffusers_filters_etc/better_beamer/12837_p.html">Better Beamer</a> may be useful.</p>

<blockquote>

<p>Do I even need to use the guide number when I shoot with TTL in high speed synch mode?</p>

</blockquote>

<p>The problem is that the flash output drops fast in high speed sync mode. The SB700 shows the range of the flash (at least as long as the head isn't under any other angle than 90 degrees), and the range drops quickly when the shutter speed exceeds the flash sync speed. I never saw a good calculation for it, but considering you talk about a 1/1000th speed, the loss of flash power is going to be very considerable.</p>

[lex_jenkins]

High sync speed shoe mount TTL flash is mainly

useful for fill flash in daylight and a few

limited situations. It's not useful for freezing

motion, such as hummingbirds in flight. There are

some good illustrated articles online

demonstrating the uses and limitations of high

sync speed flash.

[William Michael]

<blockquote>

<p>1. My question is: if I want to calculate distance I have to be from subject, <strong>large lens opening</strong> and very fast shutter speed eg <strong>high speed synch .</strong> . . I suspect I would usually be shooting in manual mode for my camera and TTL mode with the flash . . . <strong>how do I get my guide number to calculate that distance</strong>?</p>

</blockquote>

<p>The Guide Number is only "a guide" - not an absolute.</p>

<p>The Guide Number (when using the Camera up to and at its Maximum Flash Sync Speed) will allow you to calculate the Flash’s MAXIMUM WORKING DISTANCE for any APERTURE. This, I think, is actually what your question is about.</p>

<p>When you move your camera and flash to HSS the Guide Numbers change. Some Flash User Manuals will provide a table for these guide numbers. However, even if your Flash User Manual has a such a table, I suggest that you run some tests yourself, because, the use of HSS is mainly always for <strong>FLASH AS FILL. </strong><br /> <br /> The AMOUNT of OVERLAY of the Flash, for Flash as Fill, on top of the AMBIENT Exposure does have a Technical Component based upon the Guide Number (which remember is also only AN INDICATIVE and not ‘Gospel’) but additionally there is a SUBJECTIVE element to it. <br /> i.e. If you ask <em>“How much “Touch of Flash as Fill’ is the minimum to be 'adequate'?”</em> you will get different answers from different Photographers – so each of us will have a different MWD for any Flash Unit when used for fill.</p>

<p>*</p>

<p>In this shooting scenario that you describe above, I don’t worry about retro-calculating the Guide Number, but I think in <em>'how much “loss” I get when moving to HSS'.</em> Importantly I reckon and think in MWD (a distance) and not in Guide Numbers. The application of what distance I will lose make shooting really simple with no need for any calculation on the run. It is easy to experiment and then interrogate a few sets of sample of the images to get a feel for how much Flash as Fill you deem necessary and how much Maximum Working distance you will lose when you move your gear to HSS - and I suggest that is the best way for you to move forward.</p>

<p>But I can give you some starting positions and the explanations for them by way of examples. I trust you will find these useful.</p>

<p>Here Specs for your Flash:<br /> <em>“SB 600 . . . a guide number of 30/98 (ISO 100, m/ft.) or 42/138 (ISO 200, m/ft.) (at the 35mm zoom-head position, 20°C/68°F.)”</em><br /> Ref: (extract) Nikon User Manual pdf file</p>

<p>First we need to establish you base MWD. I will assume that your camera have a MAX SYNC SPEED of around 1/200s. Your question describes the shooting scenario as “<em>a face in bright light with flash exposure</em>” then, assuming you are in sunlight and using the 'f/16 Rule' for your AMBIENT EXPOSURE of the Scene you’ll be pulling about: F/11 @ 1/200s @ ISO100.</p>

<p>With those exposure parameters, your MWD for the Flash as Fill is about 9 feet. i.e. GN(ft)/APERTURE - that is – 98ft/11 ≈ 9ft</p>

<p>I have CANON DSLR’s and I use CANON Speedlites for High Speed Sync with those cameras, (typically 580 and 580MkII).</p>

<p>Based upon trial and analysis, my Rule of Thumb when moving to HSS is: <strong>I will lose about 40% of the MWD once HSS is engaged.</strong><br /> And further, (based upon Max Flash Sync Speed of camera = 1/200s) my Rules of Thumb are:<br /> Shutter speed shorter one stops - 1/400s – will lose about 35%~40% MWD<br /> Shutter speed shorter two stops -1/800s – will lose about 45% MWD<br /> Shutter speed shorter three stops -1/1600s – will lose about 50% MWD</p>

<p>The above Rules of Thumb are based on CANON Speedlites and my SUBJECTIVE analysis of the minimum flash overlay that I require for Flash as Fill. But I expect that Nikon Cameras and Flash gear will be VERY similar, if I used Nikon.</p>

<p>So, for you to open to F/4 your FLASH, I expect that will need to be at about 4.5ft (OR CLOSER) to have an effective FLASH as FILL over the AMBIENT Exposure.</p>

<p>Also note that, the base GN that was quoted in the Nikon User Manual was for the Flash Zoom Head set for a 35mm FL lens: the use of the Zoom Head on the Flash (to accommodate the FL of the lens that you use) and any ‘focusing’ or ‘diffusing’ LIGHT MODIFIER will change that base MWD.</p>

<p>Also note that you can use HSS and Flash as Fill with the Flash Head <strong>OFF the Camera</strong>, for example using an OFF CAMERA CORD and note that the <strong>MWD refers to the DISTANCE of the FLASH to the SUBJECT.</strong> So you can work the camera at a farther distance and still get the Flash in close to use effectively as fill, even the extension of one arm's length can be useful and I do use this technique, but it takes practice especially regarding aiming the flash correctly.</p>

<p>*</p>

<p><strong>The choice of ISO:</strong></p>

<p>In the above example you could bump the ISO, for example you could bump to ISO200. In this case the guide number will increase by a factor of 1.414 (square root of 2), this is referenced in the Nikon Data Sheet extract which I quoted above.</p>

<p>Let’s follow the example using ISO200 - for the AMBIENT exposure you will be pulling about: F/16 @ 1/200s @ ISO200 and you are already at (or close to) the Camera’s Maximum Flash Sync Speed, now to get to F/4 - from - f/16 you will have to open up the APERTURE FOUR STOPS and also to compensate for the correct AMBIENT EXPOSURE you will need to increase the SHUTTER SPEED FOUR STOPS – that is you will be pulling: F/4 @ 1/3200s @ ISO200.</p>

<p>Now the kicker is, (using my Rules of Thumb), Shortening the SHUTTER SPEED by FOUR STOPS and using HSS, the <strong>Flash’s MWD is shortened by MORE THAN 50%</strong>, so in this case you will need the Flash Head at or closer than 4.5ft from the SUBJECT. And this is now becoming quite problematic</p>

<p>***</p>

<blockquote>

<p>2. My question is: using hi shutter speed with flash to catch a hummingbirds wings) - I suspect I would usually be shooting in manual mode for my camera and TTL mode with the flash . . . how to get a proper flash exposure of the subject knowing my f stop and ISO.</p>

</blockquote>

<p>As already mentioned by Lex, HSS of itself is <strong>NOT suitable for freezing <em>very fast</em> motion</strong> like the wings of an Hummingbird. In daylight a very, very fast shutter speed will get better results. In a dark shooting scenario then a VERY FAST FLASH PULSE with the FLASH AS THE KEY LIGHT will also be effective. Note the latter is NOT HSS.</p>

<p>What HSS can do, when used as FLASH as FILL, is “FILL” the shadows of a moving subject which has already had their Subject Movement “frozen” by virtue of the fast SHUTTER SPEED.</p>

<p>For example the typical “jumping in the air shot of the Bride and Bridesmaids” For this shooting scenario we would typically use Tv ≈ 1/1000s~1/1600s and we might also choose use HSS Flash <strong><em>to Fill</em></strong>. Also it is best to use open shade and a shaded BACKGROUND for this type of shot so that one can maximize the MWD of the Flash, by virtue of having a lower EV of the overall Scene for the AMBIENT EXPOSURE, (as opposed to shooting the shot in Direct or Open Sunlight).</p>

<p>***</p>

<p><strong>Summary:</strong></p>

<p>If you choose to use HSS for Flash as Fill for Portraiture in Daylight, whether the reason is to use a large aperture to gain a Shallow Depth of Field or to use Flash as Fill for a moving Subject:</p>

<p>1. in both cases you will have more Flash Working Distance available to use if you situate the Subject(s) in Open Shade and with a Background where there is little or no Direct Sunlight</p>

<p>2. it is best to use the camera’s lowest ISO so that you can use the fewest number of aperture stops / shutter speeds changes from the Maximum Flash Sync position to achieve the desired Aperture</p>

<p>3. it is worthwhile mentioning that if the desire is simply for SHALLOW DEPTH of FIELD and one must shoot in direct sunlight then it is nearly ALWAYS better to use an ND filter and if Fill Light is absolutely necessary, then use a REFLECTOR, rather than even trying to use a single Speedlte</p>

<p>4. even when well past the MWD, a single Speedlite might still provide a <strong><em>Catch Light</em></strong> in the eyes of the Subject and although not providing “Flash as Fill” the use of Flash (and HSS) might be useful</p>

<p>5.To effectively or more easily use Speedlites for Flash as Fill, in bright sunlight with HSS - one needs to use an array of MULTIPLE SPEEDLITE FLASH HEADS</p>

<p>WW</p>

[William Michael]

<blockquote>

<p>I believe the camera’s shutter speed setting is moot as to GN.</p>

 

</blockquote>

<p>Hi Alan – if you use “<em>moot</em>” to mean “<em>not relevant</em>” – then - for most general and typical shooting scenarios, this is so.</p>

<p>However, the Opening Post <strong>specifically asks about using High Speed Sync with a Speedlite</strong>.</p>

<p>In such shooting scenarios, using HSS and Speedlite - the choice of the Camera’s Shutter Speed definitely has an impact on the effective power of the Flash, <strong>i.e. the Shutter speed choice has a definite affect on the Guide Number, in these cases.</strong><br>

<strong> </strong><br>

WW</p>

[skip_wilson]

<p>Thank you so much for that detailed, yet understandable explanation, William W. I appreciated the work you put into choosing the examples for me. That is a great way to put a point across that, in itself, is difficult to grasp at the start. One point I had difficulty fully understanding, however, was your comment about " HHS of itself not being suitable for freezing very fast motion, eg hummingbird wings." You mentioned " in a dark shooting scenario a very fast flash pulse with the flash as the key light would also be effective. Note the latter is NOT HSS" If I needed light on the flying hummingbird eg it was in shade, wouldn't I need HHS along with a very fast camera shutter speed so that I wouldn't get the band of light across my photo as I was trying to freeze the wings with the fast shutter speed when I am shooting in normal flash speed sync mode? As I understand, the flash becomes a constant pulsed light source when on HSS in order to avoid that problem. How then would I go about getting the proper set up for photographing a flying hummingbird in shade where I want to fill it with some fill flash and yet nearly freeze its moving wings? I see I would probably have to have a flash fairly close to the bird because of the falling power output of the flash in HSS and me, with the camera, further away so as not to dissuade the bird to come within "range" for the picture. Your thoughts, please. Thanks. Skip</p>

[William Michael]

<p>OK. I understand the confusion. I'll only address the "Hummingbird Photo" and I will address it as if you just asked me 'how would you go about stopping Hummingbird wings?'</p>

<p>1. What I do know is Hummingbirds' wings flap at a very fast rate. I have no idea how fast and I have not photographed Hummingbirds, but I'll bet a Mars Bars that if I were to shoot an Hummingbird in AVAILABLE LIGHT a Shutter Speed of 1/1000s I would capture BLUR. Maybe even 1/2000s will not be fast enough to negate Subject Motion Blur.</p>

<p>2. My next thought then is;<br /> <em>'suppose I assume that 1/4000s is fast enough to stop the wings'</em><br /> and then I think; <em>'Crikey, I'd be pulling F/11 @ 1/4000s @ ISO2000 if the bird were in front-lit sunlight between 10am and 3pm'</em> (REF: F/16 Rule / based on EV = 15)<br /> and then I'd think; <em>'that's getting to an extreme ISO'</em><br /> and then I'd think; <em>'What if the bird were in shade (EV = 12) . . . I am pulling F/5.6 @ 1/4000s @ ISO 4000'</em><br /> <br /> 3. So, after all that thinking I concluded that FLASH is necessary to FREEZE the wings on an Hummingbird.</p>

<p>***</p>

<p>OK we are now up to where your question begins . . .</p>

<p>Disclaimer - I might be totally wrong regarding the best technique to freeze Hummingbirds' wings! Frankly, I neither have much interest in photographing birds nor much experience - and no experience at stopping their wings. So my commentary is based solely on theory and my EXPERIENCE using Flash to stop other (very) fast moving things, but not birds' wings.</p>

<p><strong>I think that we need a very short duration flash to freeze those little flapping wings</strong></p>

<p>So let's look at the TOTAL DURATION of the FLASH when it is used in different modes (i.e. how much time the flash is active). A simple and quick example is one I've often referred my students - <a href="http://www.bobatkins.com/photography/technical/canon_speedite_high_speed_sync.html">HERE - BOB ATKINS on HSS and (normal) FLASH. </a></p>

<p>Read down to near the end and under the para heading - <em>"What does all this mean?"</em><br /> <strong> <br /></strong>Note that a SHORT FLASH DURATION is established NOT by using the Flash in HSS, but using the FLASH at 1/2 power, or less.</p>

<p>The exact FLASH DURATIONS relative to POWER OUTPUT for your gear you might research yourself, but at a guess, I expect that using you flash somewhere about 1/8 to 1/16 power you'll get the FLASH DURATION fast enough to freeze wings - you'll need to find out how fast the little wings flap too - that can be your mathematics assignment instead of worrying about Guide Numbers.</p>

<p>So let's assume that I am correct and we do need to use the flash at 1/8th power to get the FLASH DURATION fast enough to freeze the wings - the it stands to reason, depending upon the level of the ambient light and the distance (closeness) we can get the flash to the bird - we might need more than one flash to get enough Flash Light to overpower the Ambient Light.</p>

<p>When I wrote that it would be better if the bird were in a dark place - I didn't mean a black room, I meant tree shade would make the shot easier. My <strong><em>guess</em></strong> is that you'd need the FLASH to be about 3~4 Stops stronger (maybe less), than the Ambient to get a very good result. But that's the best part about the Journey in learning The Craft - just try it - and see what happens.</p>

<p>Obviously using the Flash outside of HSS, you will be limited to a Shutter Speed at the FLASH SYNC SPEED of your Camera - but that is a good thing, because you can use low ISO and a reasonable Aperture. (e.g. F/11 @ 1/200s @ ISO 400 for a bird situated in EV = 13, for example "Open Shade").</p>

<p>I trust that is a more focused and specific explanation regarding the "Hummingbird" question, of why I wrote what I wrote.<br /> <br /> WW</p>

<p><strong>Addendum:</strong> I just re-read my original commentary, and the <em>'error'</em> in my original commentary was an error of omission and that was not to mention "FLASH DURATION" and link that topic to why HSS is not suitable for freezing very fast Subject Motion.</p>

<p>I am sorry that I missed making that (important and significant) comment in my initial response.</p>

[skip_wilson]

<p>Again, thank you William W. Just to be the contrarion here; doesn't the flash set in HSS mode act as a continuous pulsed flash with a "continuous" duration during the brief time the shutter is fully open using a very fast shutter speed, so that I could or would need to use that mode, HSS, to freeze that hummingbird's wings while using fill flash in a shady setting with fast shutter speed and with a low f stop eg f2.8 or 4 to get a nice background and not have that partial band of exposure that I would get without using HSS? Skip</p>

[William Michael]

<blockquote>

<p>The flash set in HSS mode acts as a continuous pulsed flash with a "continuous" duration during the brief time the shutter is fully open using a very fast shutter speed - so I could . . . <em><strong>[note edited out the word “need”]</strong></em> . . . use that mode, HSS, <strong>to freeze that hummingbird's wings while using fill flash</strong> in a shady setting <strong>with fast shutter speed</strong> and with a low f stop e.g. f2.8 or 4 to get a nice background <strong>and not have that partial band of exposure that I would get without using HSS?</strong></p>

</blockquote>

<p><strong>YES</strong> – I agree that you <em><strong>could</strong></em> choose to use HSS to illuminate the Subject - to - as you wrote “<strong><em>use fill flash in a shady setting</em></strong>” - IF - you initially choose to use a very fast shutter speed.</p>

<p><strong>NO</strong> – <strong>Definitively NO</strong> - the (HSS) FLASH is NOT freezing the Subject Motion Blur. <br /> It is the very fast shutter speed that will (might, maybe, possibly) freeze the Subject Motion Blur.<br /> All the Flash is doing in that situation, <em><strong>is adding a set of continuous pulses of light for the duration of the Shutter Opening</strong></em>. Your CHOICE of the DURATION of the SHUTTER OPENING - i.e. The "Shutter Speed" will be the defining factor as to whether or not the bird's wings will be frozen.</p>

<p>***</p>

<p>Aside from an hypothetical scenario, why would you consider this arrangement? I think that you might not be recalling the ISO factor that I mentioned previously.</p>

<p>Let’s think this through. You mention that the HSS FLASH will be active as a continuous pulse for the duration of the very fast shutter speed that you select. Let’s choose a very fast shutter speed <em><strong>that we assume will freeze the wings.</strong></em> Let’s choose 1/2000s. Let’s also choose a shady area and shady background. Let’s say under trees on a lightly cloudy day. About EV = 12.<br /> Let’s choose F/4.0 > F/4 @ 1/2000s for EV12 ≡ ISO 1000 <br /> Let’s choose F/2.8 > F/2.8 @ 1/2000s for EV12 ≡ ISO 500</p>

<p>Let’s suppose we actually need 1/4000s to freeze the wings, and still the scene is EV = 12<br /> Let’s choose F/4.0 > F/4 @ 1/4000s for EV12 ≡ ISO 2000 <br /> Let’s choose F/2.8 > F/2.8 @ 1/4000s for EV12 ≡ ISO 1000</p>

<p>Let’s suppose the scene is only one stop darker, let’s assume EV = 11 and 1/2000s.<br /> Let’s choose F/4.0 > F/4 @ 1/2000s for EV11 ≡ ISO 2000 <br /> Let’s choose F/2.8 > F/2.8 @ 1/2000s for EV11 ≡ ISO 1000</p>

<p>And now let’s assume we need 1/4000s with a scene EV = 11<br /> Let’s choose F/4.0 > F/4 @ 1/4000s for EV11 ≡ ISO 4000 <br /> Let’s choose F/2.8 > F/2.8 @ 1/4000s for EV11 ≡ ISO 2000</p>

<p>I would prefer to shoot at a lower ISO than any of those, if I could.</p>

<p>***</p>

<p>Regarding this bit –</p>

<blockquote>

<p>“<strong>and not have that partial band of exposure that I would get without using HSS?”</strong></p>

</blockquote>

<p>The point is, you wouldn’t have a partial band of exposure if you did not employ HSS for that particular shooting scenario.</p>

<p>Let’s assume <strong>the scene’s background is EV = 12.</strong> (you mentioned that you want a “nice background”) Let’s assume you initially select 1/200s shutter speed and you do NOT engage HSS. You then choose a partial Flash Power ‘x’ to provide a fast enough FLASH DURATION to FREEZE the Subject Motion Blur.</p>

<p>For the “nice background” that you want, you can choose F/2.8 and using a shutter of 1/200s (for background scene EV = 12) and you will need ISO 50. If your camera cannot make ISO 50, then you would need to close the aperture to F/4 and use ISO 100.</p>

<p>If the background scene is darker than EV = 12, the you’ll have little difficulty overlaying the flash to fill the foreground subject (Hummingbird) by choosing an appropriate Flash Power to ensure a Flash Duration which is short enough to Freeze the Hummingbird’s wings whilst selecting a large aperture (and corresponding Shutter Speed to correctly expose the background and attain that nice background blur (Bokeh) that you desire.</p>

<p>***<br /> <br /> <strong>In any case, I suggest that you try all methods: and see what works best.</strong></p>

<p>As I mentioned previously I have never stopped Hummingbird’ wings – I am just working from first principles, theory and experience (and lots of fun) bursting balloons, filled with water and other fast moving things.</p>

<p>I am a tad surprised that a specialist birdologist photographer hasn’t weighed in yet as there are many talented ones here at Photo.net.<br /> <br /> WW</p>

[q.g._de_bakker]

In fewer words:<br>- when the flash lasts longer than the shutter is open, the shutter determines exposure.<br>- when the flash lasts shorter than the shutter is open, the flash determines exposure.<br>That includes motion stopping capabilities and such.<br><br>Guide numbers are only valid when the flash determines exposure.

[skip_wilson]

<p>Thanks again for your responses. So... I guess my best bet when needing very fast shutter speed (eg. freeze hummingbird wings) in low ambient light (eg. shade) and shooting with a low f stop (eg. f2.8-4) is to use HSS; but realize since guide numbers aren't fully accurate here what with the fall off in guide number (ie flash distance) as the shutter speed increases, that I may very well may have to set up a remote slave flash CLOSER to the subject, with distance determined by trial and error, and be able to have my camera with its built-in flash set as a commander in -- or flash off mode further away from the subject. I would leave my slave flash on TTL and shoot with my camera in Manual mode as I usually do at a fairly low ISO. I would have my slave flash power at 1:1 power since in TTL. I don't think I would want to set my flash on any less power (eg 1:4) as then my necessary distance for good fill flash would be less than desired forcing me to have to be even closer to my hummingbird which isn't good . Do I have this right? Also, does shorter flash duration equate to less power output and if so, should I be making my flash output less than 1:1 on my slave rather than TTL? I didn't know if that made any difference if it is a continuous pulse in HSS? Thanks Skip</p>

[William Michael]

<blockquote>

<p>I guess my best bet when needing very fast shutter speed (eg. freeze hummingbird wings) in low ambient light (eg. shade) and shooting with a low f stop (eg. f2.8-4) <strong><em>is to use HSS. . . </em></strong>I don't think I would want to set my flash on any less power (eg 1:4) as then my necessary distance for good fill flash would be less than desired forcing me to have to be even closer to my hummingbird which isn't good . <strong><em>Do I have this right?</em></strong></p>

</blockquote>

<p>I again suggest that you try all the methods and compare the results for yourself. It won’t cost you anything more than a bit of time and effort.</p>

<p>That stated - In that shooting scenario I would NOT use HSS, yet I would use a LOWER Power Flash output to ensure a very short FLASH DURATION to freeze the wings of the Hummingbird, that is to say I would NOT use the Shutter Speed to freeze the wings of the Hummingbird.</p>

<p>This is based on my guess that I would need a very VERY fast shutter speed to freeze those wings and it is easier to use the Flash Duration to do that.</p>

<p>Again I don’t know the SPEED at which the Hummingbird wings flap at . . . but my guess is you’ll need 1/2000s <strong>at least</strong> and that means you will be at a very high ISO which is not (IMO) a good idea.</p>

<p>Also, reiterating, to get enough FLASH POWER, one might need more than only one Flash unit.</p>

<p>Please let us know the results of your tests.</p>

<p>WW</p>

 

[James G. Dainis]

This from the interenet:

 

"Estimates of hummingbird wing tips maximum speeds range from 300 to 500 inches per second, or a little more than 28 miles per hour. They only appear to be so fast because they're so small."

 

Hummingbirds also move their wings in a circular motion so the speed is continual. There is no momentary stop of the wing motion as it changes from going up to going down.

 

 

At 1/500 sec shutter speed the wings will have moved one inch. Something to think about.

[skip_wilson]

<p>I'll let you know my results when the hummingbirds make their way here this summer. It will be interesting to see how close my off camera flash will need to be to get good lighting on the bird at a fraction of full power . Thanks again. Skip</p>