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| Re: 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 may not 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