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Archive 2011 · Dumb flash meter / light meter questions
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p.1 #1 · Dumb flash meter / light meter questions


I'm interested in getting the most out of some old Vivitar manual flashes for indoor studio/product photography. I figured (not knowing much about flash lighting) a light meter/flash meter would help. I've found a few good deals on used Sekonic L-508s and also Minolta FlashMeter IV and V models (not the less-capable "LightMeter"). I've read the manuals for the L-508, 368 and Minolta IV /V models. Except for the Minolta IV, I'm not sure how one uses a light meter to arrive at an exposure assuming the flash output power is also controllable.

From what I understand, for flash photography one typically adjusts the aperture with the shutter set to the max sync speed for the camera. The light meter is placed in the incident light, button is pushed, flashes fire and the light meter suggests an aperture which will provide a suitable exposure. But, if your flash output is controllable, it seems only the Minolta IV gives you the "guide number" to adjust the flash along with the suggest aperture.

Have I missed something here? It seems like all the other meters are "less" capable in not suggesting GN along with an exposure. If so, how do you use your Sekonics with controllable light output assuming you want depth-of-field control?


Dec 30, 2011 at 09:36 AM
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p.1 #2 · Dumb flash meter / light meter questions

I've not used a light meter with a GN reading, so I can't really share my experience with that feature on a light meter ... but since a GN is going to be your aperture x your flash to subject distance, you can easily reverse calculate it ... but you shouldn't even need to go there.

Take your reading resulting in a given aperture, i.e. f11. If you want your DOF to be @ 5.6 instead (2 stops wider), then adust your power down two stops less (1/2 power = 1 stop, 1/4 power = 2 stops) to compensate for the 2 stops more light coming in through your larger aperture.

That being said, even though your light output is "controllable" ... your flash to subject distance is remaining constant, so the the reverse calculation to achieve a GN is really unnecessary since the variable willl be your adjustment to your output, not your distance.

In either case, it really is just a matter or simply adjusting your output and taking another meter reading. Your meter reading is in "stops" given in the form of aperture readings ... and your flash output control is also in "stops" given in the form of 1/2, 1/4, 1/8 etc. ... but they are still "stops", i.e. doubling/halving so the mental correlation remains the same between the two.

My Sekonic doesn't have a GN feature to it, but it does have an EV reading feature to it that I find quite useful, e.g. an EV reading of one area might be EV13 and another area @ EV 11 which lets me know I've got a two stop difference. I find that easier to work with for falloff/dynamic range of the scene, in addition to getting regular aperture readings. I find this combination more practical than I could imagine a GN readout being.

There's a part of me that wants to say that you are making this more difficult than it really is ... but I've had tons of people tell me that over the years and I never really appreciated being told that, when all I was trying to do was better understand something. So, I'll only "hint" at it to say I wouldn't "worry" about the GN aspect as being hyper-critical. Of course, someone might say that about EV readings and I'd defend the EV significance to me.

Hopefully, others can chime in better than I @ the GN aspect of your meter decision, but consider this ... you can take a test reading of your flash and reverse calculate your flash's GN, then just place a piece of tape with the GN number on it on each flash ... but I think you'll find it much easier to just read the meter rather than work from a GN calculation. I realize that this sounds a bit "foreign" to you til you get your hands on a meter.

Recommendation ... being in San Diego there are pro stores that you can visit. I'd recommed going to one and renting a light meter for a day. Granted it probably won't be one with a GN reading feature, but I think that in a matter of a couple hours (or minutes) of playing with it and your lights, you'll find that the GN issue is no longer an issue.

Also, when you go to rent from the store, they typically can give you a "crash course" if you just ask (call ahead for a good time to go) on equipment that your are renting and are usually very understanding of up & comers that want to grow. Spending a $ or $$ with a good rental house is a great way to get both some gear and some education/experience (the education/experience being the more valuable). One outing with rented equipment can give you a learning curve that that you could spend weeks (or never) trying to "figure out" in cyber-world.

To me, a good rental house is the best kept secret/friend a photographer can have ... and George's has been around since the dinosaurs used film.
They are my "go to" when I'm in the area ... good shops understand it's a long term word of mouth/networking/solution provider relationship, not just a "quick sale".
(Sadly, I live 2,000+ miles from San Diego and 100 miles from the nearest "so-so" rental house).

Here's a link to George's Camera Store in North Park (corner of 30th & University) and a link to their rental pricing ($10 for a daily rate on the meter). Get one for a day/weekend and it'll be the best $10 you've spent in a long time ... way better than a cup of coffee from Starbucks.

GL ... HTH



Edited on Dec 30, 2011 at 04:00 PM · View previous versions

Dec 30, 2011 at 03:02 PM
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p.1 #3 · Dumb flash meter / light meter questions

See http://photo.nova.org/Ratios/ for an explanation of how meters work and the manufacturer recommended method for using one to set ratio and determine exposure.

It is possible to live without a flash meter by using the highlight clipping warning. For example if you want to set a 3:1 ratio put a white towel on a stand where the face will be and set your camera to f/4. Turn on just your fill light and adjust it until the towel is barely clipping. Turn it off and set the lens of the camera to f/5.6. Now turn on just the key light and adjust it's power until the white towel is just barely clipping. You will have set the lights one stop apart in INCIDENT strength using the clipping warning for comparison.

1:1 fill
2:0 key light 2x as bright where it hits object
3:1 reflected ratio is 3:1 when the two overlap

Turn both the lights on and then using the clipping warning adjust the aperture as needed to put the highlights below clipping in the playback. If camera was at 5.6 for setting the key light when you turn the fill back on it will put more light in the highlights also so you will find your aperture will need to be stopped down more.

The same is true if setting ratios with an incident meter. First you meter the fill at f/4 then turn it off and meter the key at 5.6. Then when both lights are on you point the dome of the meter at the lens (to average the two lights) and take the reading used to set the lens. It will wind up being similar to the one arrived at with the white towel and clipping warning.

Two different ways to the same end: 3:1 ratio with correctly exposed highlights. It will cost you nothing to try the first method and if you do you may find as I have you don't really need the meter if you understand how to interpret the camera feedback in the clipping warning relative to the RAW results you see on the computer in the highlights, which is easy once you try it a few times.

Dec 30, 2011 at 03:52 PM

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p.1 #4 · Dumb flash meter / light meter questions

What RustyBug said. If you're using a flash meter, the Guide Number (which should be listed on your flash anyway—you don't need a meter to know what it is) is of no particular use. GN exists for the benefit of shooting without a meter.

But now we've got a meter. We know exactly how much light is falling at any position. The meter tells us how to adjust the camera, the flash, or both, all from one number. Heck, assuming you don't care what your light looks like, it even tells you how to adjust the subject-to-flash distance if you like. Inverse Square Law, baby.

You meter and get f/8. You want f/4. What do you do? Adjust the flash's power down two stops. Easy peasy.
You meter and get f/16. You don't care what aperture you use. Set the camera to f/16.

If you were only skimming the Sekonic manuals for features, go back and read the beginning of them. They have a very good tutorial about flash metering.

Dec 30, 2011 at 04:16 PM
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p.1 #5 · Dumb flash meter / light meter questions


Thanks for your responses, I think they make perfect sense to me now. I was a bit confused since I was thinking of GN *as* the flash power output (i.e. like a volume knob) when in reality it's a "corrected factor" based on aperture & distance that one can use to dial a flash lacking more details. Rusty, I think you're right and I was making it more complicated than need be .

To use the light meter's reading to adjust flash output I can take its reading and I only have to think of everything in terms of stops, including flash output, and dial the camera aperture and/or the flash output up or down as desired. Just like playing with shutter vs. aperture (sans flash) assuming ISO is fixed to get a proper exposure except now it would be flash output vs. aperture (the balance of the two) with ISO and shutter fixed.

So now another question: How important (for your creative photography) is knowing ambient vs. flash contributions on your light meter? The 508 doesn't have this feature, but the Minoltas and the newer 358 does. I'm guessing this might be more important if you were trying to calculate fill-light for outdoor type shoots and I'm not there yet, but I'm considering the light meter as a long-term purchase.

Thank you again,

Dec 30, 2011 at 08:11 PM
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p.1 #6 · Dumb flash meter / light meter questions

slrl0ver wrote:
...From what I understand, for flash photography one typically adjusts the aperture with the shutter set to the max sync speed for the camera.

Setting the maximum shutter speed is one way; it will minimize the amount of ambient contribution, and will reduce the amount of "ghosting" from subject movement.

Sometimes, though, one wants ambient contribution -- for subject fill, to show distant backgrounds, etc. -- and in those cases...

slrl0ver wrote:
...So now another question: How important (for your creative photography) is knowing ambient vs. flash contributions on your light meter?

I have a Sekonic L758DR, and it can show ratios, dynamic range, the phase of Jupiter's moons...well, not quite, but it has a lot of features.

Truth be told, I don't use most of the capability of this meter. I usually just use the camera's meter to set my shutter speed for the amount of ambient I want, and then use the flash meter to dial in my flashes' power settings.

1) Set an aperture for the DoF I want.
2) Set shutter speed for that aperture, and the number of stops over or under "normal" I want my BG to be, if any.
3) Meter flashes and adjust power as needed at my chosen aperture.
4) Fire away.

Dec 30, 2011 at 08:25 PM

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