Do I Need A LIght Meter?

[Derrel]

Different sensors and processing of the in-camera .JPG images, maybe? In the old days, 7 to 8 stops' worth of total dynamic range meant that the highlight tone placement on a color positive image was not that far above the mid-tone, and the detail-free shadows were not very far below the mid tones.

The "new" Exmor gen Sony-made sensor tech brought with it an amazing shift in how much a BLACK shadow could be "lifted" in post.Pentax was an early adopter of Sony sensors.

 

[lance70]

Yes

 

[Braineack]

The "new" Exmor gen Sony-made sensor tech brought with it an amazing shift in how much a BLACK shadow could be "lifted" in post.Pentax was an early adopter of Sony sensors.

underexpose by 4 stops?

dont even worry:

 

[Derrel]

As per Brsineack's above example photo, he shows us that today's concept of exposure is now somewhat relative. In the days of color slide film, an exposure four EV under mid-tone would be mostly useless. But now with the new Sony-made sensors, even a severely underexposed frame can be rescued, often with pretty decent quality as the final result. This is a great example of why a flash meter is no longer an absolute necessity.

 

[smoke665]

. Free app for android. Keylight Pro Keylight PRO 2.0 - Android Apps on Google Play .

Neat. I just downloaded and installed it. A very advanced numerical analysis tool for specific flash units. Not a meter, but in some ways, more useful as a "predictor" tool. Thanks!

Got a chance to try this last night with the new AB's. Wow, super fast setup once I entered the light information in the "gear bag". First test shot on the main light was within +1 stop. Fine tuned the settings and it was spot on afterwards.

 

[Derrel]

I played around a little bit with Keylight Pro 2.0 this evening. Basically the app is a very sophisticated guide number computer that works on Android. According to Keylight's data the Einstein 640 monolight at full power with a Buff foldable softbox has a guide number of about 102. According to one of my Seedotron power packs at 100 watt seconds with a 65-degree metal reflector, the guide number is 105. I combined these two data points into one setting using the app and took a couple screencaps.

 

[smoke665]

@Derrel did you have a chance to determine the accuracy of the calculated aperture, ISO, distance or fall off?

 

[Derrel]

@Derrel did you have a chance to determine the accuracy of the calculated aperture, ISO, distance or fall off?

I don't own an Einstein monolights,but I went to Buff's site and their Expected Output chart confirms by actual meter reading the 102 GN with their softboxes. The Speedotron D402 GN figures are reliable, dating back to the era before most people owned a flash meter, and actually relied on the GN method.

The falloff computing that the app offers is something I have never seen offered before: the power of Android computing.

Buff's web page, Expected Output confirms by actual meter readings the GN of the app. What I really wanted to know was the relative true power of the Einstein 640. When comparing two different flash units, the beam spread of the light is a critical factor. Buff data days the AB B1600 at Full power and their Einstein E640 at full power are
640 - 660 watt seconds,
With a Guide Number of 155 using their standard 7-inch 80 degree reflector. What the older Speedotron power pack lists as a GN of 150 is an output level of 200 Watt-seconds using the D402 power pack and that system's 65 degree beam spread reflector.

When comparing flash units, product model numbers are not very useful. For example the Alien Bee B1600 model and the Einstein 640 are both listed as an actual 640 - 660 watt seconds of output. With their standard 7 inch 80 degree reflector the Guide Number is 155, but with the Speedo D402 ( 400 W-sec, 4- outlet) pack set at 1/2 power with a 65-degree reflector the Guide Number is 150. As one can see we have flash units labeled 1600, 640, and basically 200, all creating the same Guide Number. With different beam spread angles.

The ability to choose from a list of flash units, or to enter in revised or modified guide numbers is very useful. For example switching from the 7 to the 8.5 inch, 45 degree high output reflector in the Alien Bee Line, boosts the guide number by 1 full EV.