Flash effectiveness of 85mm on DX

[lex_jenkins]

<blockquote>

<p>"In any case you should totally ignore maker's guide numbers - they're <em>all</em> invariably at least one stop optimistic."</p>

</blockquote>

<p>A 1/3 deviation from nominal specs is possible, considering acceptable tolerance for manufacturing. A full stop deviation is unlikely. Reputable manufacturers like Nikon do not pull guide numbers out of thin air or out of magician's hats. Guide numbers are determined according to <a href="http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=43503">ISO standard 1230:2007</a>; and <a href="http://www.iso.org/iso/catalogue_detail.htm?csnumber=7824">ISO 2827:1988</a>. If Nikon deviated significantly from the ISO standard, their manual flash calculator and GN flash methods were be useless. In practical application they're actually quite accurate.</p>

<p>As with ISO determination of film speed and sensitivity of electronic recording media to light, the standards specify methodology, which manufacturers follow in order to meet the ISO standards.</p>

<p>And as with film speeds, sensor sensitivity, etc., there may be some variations from nominal specs, particularly in real world applications that don't involve lab testing methodology per ISO standards.</p>

<p>But when flash units from Nikon and other reputable manufacturers are tested with accurate flash meters or according to the ISO methodology, the nominal guide numbers are generally within acceptable tolerances. But if you're not photographing test charts it may be appropriate to adjust the flash and/or camera exposure settings to suit a given scenario.</p>

<p>I've tested every flash I own, from the oldest Canon AB-46 and Olympus PS-200, through the Nikon SB-800, and a few Vivitars and other off brands. All tested within 1/3 EV of nominal specs, both with a flash meter and in empirical evaluation of the film and raw files.</p>

<p>But the appropriate flash exposure for, say, a document on white paper may not be ideal for a gray tabby cat against a dark carpet. The guide numbers aren't incorrect. They're just reference points, starting points from which we determine the ideal or preferred flash exposure.</p>

[rodeo_joe1]

<p>Strangely Lex, I've also tested every flash I own, as well as those many that have passed through my hands. Precisely <strong>none</strong> of them came anywhere near to the maker's specified Guide Number. Tested using one of 3 flashmeters that I own - all of which agree with each other and give a proper exposure.</p>

<p>These weren't cheapo brands of flashgun either, but Canon, Nikon, Metz, Minolta, Nissin, Sunpak, Toshiba, National, Osram etc. Even the occasional Vivitar.</p>

<p>The <em>fact</em> that maker's GNs are plain wrong isn't just my opinion, but one voiced on the likes of Strobist Blogspot and any other forum dealing with speedlights (or lites).</p>

<blockquote>

<p>"But the appropriate flash exposure for, say, a document on white paper may not be ideal for a gray tabby cat against a dark carpet."</p>

</blockquote>

<p>- That's exactly why incident metering is the norm for studio flash exposures, and why a true GN should be accurate. The exposure for both those subjects should be the same to give a correct rendition. With a reflective reading you'd end up with grey paper and an 18% grey cat; whether it was that exact shade of grey or not.</p>

<p>Maybe the ISO's methodology doesn't give results that align with real-life usage. I'm not going to invest 38 Swiss Francs to find out. But if you know the actual contents of those documents, then please post them, or a precis of them.</p>

<p> </p>

[rodeo_joe1]

<p>Too late to edit the above but this thread: http://photography-on-the.net/forum/showthread.php?t=384985<br>

is typical of what people's experience with maker's GNs versus realistic measurements show.</p>

[carl_s]

<p>Richard,<br>

Can you elaborate as to why the AF-S is a better item than the AF-D? There are a fair number of reviews floating around that say the G lens isn't <em>that </em>much better than the D lens. <br>

Some even say they prefer what seems to be the better build quality of the older D lens. </p>

[richard_barron]

<p>As much as I wanted the old AF-D version to be a great lens, it just wasn't. It was noted for focus hunting, or locking on to a subject when it was slightly out of focus. At apertures larger than f/2.8, it was only adequately sharp, but I got an f/1.8 to shoot at f/1.8, so that was a disappointment. Bokeh was kinda ratty. On the other hand, it did make nice 18-point sunstars.<br>

I've only had my hands on the AF-S version a couple of times, but when I did, I was impressed. Both times I was shooting basketball action wide open. Focus was fast and dead-on, and the results were decently sharp. It's definitely not in the same class as the f/1.4, but if I were in the market for an 85mm f/1.8, the AF-S version is the only one I would consider.</p>

[lex_jenkins]

<blockquote>

<p>"Maybe the ISO's methodology doesn't give results that align with real-life usage."</p>

</blockquote>

<p>The ISO testing methodology almost certainly doesn't correspond with most real world applications. That's just the nature of ISO standards, as almost every serious b&w film photographer and darkroom practitioner has discovered at some point.</p>

<blockquote>

<p>"I'm not going to invest 38 Swiss Francs to find out. But if you know the actual contents of those documents, then please post them, or a precis of them."</p>

</blockquote>

<p>Nor I. But I've read enough ISO standards to know they're usually both very specific and not necessarily practicable for real world applications. In a former career I worked for a government agency in regulatory enforcement, and the job duties included maintaining the library's subscription service to ISO, ANSI, NFPA and other standards, as well as being thoroughly familiar with the many federal government regulations derived from those consensus standards. And I do have a copy somewhere of the ISO standard for determining true film speed. Not surprisingly, the standard calls for methodology that will consistently deliver the true speed of a given film (as usually determined for least measurable density over film base plus fog), but which will deliver results that won't necessarily please most photographers for real world applications. Hence the endless discussing and cussing how to expose and develop film for which ISO standard speeds have been determined.</p>

<blockquote>

<p>"...this thread: <a href="http://photography-on-the.net/forum/showthread.php?t=384985" rel="nofollow" target="_blank">http://photography-on-the.net/forum/showthread.php?t=384985</a><br />is typical of what people's experience with maker's GNs versus realistic measurements show."</p>

</blockquote>

<p>I'm not seeing anything in that discussion that contradicts what I've said. It's a familiar mixture of unspecified and questionable methodology, "Me too!" choruses, guesswork, misinterpretations about how to meter flash (one fellow mentioned using a spot meter to measure flash output - I'm not sure how that would work and suspect it would deliver misleading results), or how to apply the manufacturers' GN tables. And there were a few sensible observations.<br>

<br>

It's possible I've enjoyed a run of good luck, with every flash I've owned at least meeting the manufacturers' guide numbers within acceptable variations (around 1/3 EV). And I need to retest my old Olympus PS-200 when I've replaced my flash meter battery, because it appears to significantly exceed the labeled GN. And it's possible my flash meter is erroneous and overstates the actual output. But that's unlikely because my flash photos would consistently be underexposed, which they aren't when I've accurately measured the distance and set the flash appropriately.<br>

<br>

The most common brain fart I've experienced when mentally converting guide numbers is to forget the correct multiplication factor (1.4, rather than 2) when calculating the flash exposure for my digicams which have a base ISO of 200, for flash units with guide numbers calculated at ISO 100. Sure enough, this would result in significant underexposure. But it was operator error, not due to the manufacturers exaggerating the actual flash output. And I've made that same damned calculation error so often it's become a bad habit. And while I wouldn't wish my own brain farts on another photographer, I have to wonder how many other folks have made the same guide number calculation errors by using the wrong multiplication factor.</p>

[rodeo_joe1]

<p>I think this thread has got enough off-topic without diversifying into film ISO measurement methodology. However, I'll leave you this to ponder Lex.</p>

<p>Below are pictures of the LCD display of a Nikon speedlight. You can clearly see that it's set to full manual power and indicating a GN of between 32 and 33 - depending on the F number chosen and within the accuracy of the distance scale. Underneath that is a reproduction of part of the published GN table for <em>that very same flash</em>, where under those same conditions the GN is clearly stated as being 42. That's very nearly one whole stop difference!</p>

<p>A concensus of incident flashmeter readings at 2 metres from the flash consistently say f/14. That's a GN of 28, which isn't too far off the LCD indication, but a mile away from what's written in the manual. Following the flashmeter exposure readings I get a perfect exposure. One that fills the histogram nicely without showing "blinkies" on a pure white object included towards the centre of the shot. Following the LCD indication also gives an acceptable, but slightly dimmer exposure; as you'd expect. Following the table in the instruction manual would clearly underexpose by just over a stop compared to the meter readings.</p>

<p>A look at the actual output and LCD reckoner of a Canon 540EZ speedlite showed an even greater discrepancy, where the Canon's rear LCD claimed a ridiculous GN of 52 for similar settings to the above. Actual pictures taken at f/14 and 2 metres distance showed that a GN of 28 was pretty much bang on for that as well. Hardly surprising since both guns use the same value of storage capacitor and both have a theoretical power of 75 Joules.</p>

<p>Not isolated cases, since I know for a fact that the speedlights in question have the same power as the latest SB-900 and 910. A similar inflated GN figure appears in the tables of their manuals as well. So, do Nikon, Canon and the like simply pull Guide Number figures out of the air? Seems very much like it to me.</p><div></div>

[glen_h]

<p>My first electronic flash was a Vivitar 283, which I used for many years. It has a too high trigger voltage for DSLRs, though. I also have (somewhere) the lens kit which allows for 24mm, 28mm, 70mm, or (I believe) 140mm. (Without a lens kit, it matches full frame 35mm.) <br>

It isn't easy to generate a smaller flash area with such lenses, so the increase in guide number isn't so high as you might hope. The decrease with wider lenses is about what you would expect. <br>

I recently got an SB-28, my first zooming flash. I used it on both a D70s and EL2. </p>