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05-24-2011, 05:25 AM   #1
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Need help understanding flash tables in Sigma EF610-DG manual

I have two new Sigma EF-610 DG flashes, and they work great. I have mostly used p-TTL mode, but I want to learn manual.

In the past (the olden days) I read a graph on the back of my flash that told me how to set exposure for a certain distance. The difference was that my flash back then did not have variable power or zoom settings (nor could I change ISO without finishing the roll).

I see these tables in the back of my Sigma manual, but I can't seem to figure out what they mean.

Table 1: I assume the column headers are zoom settings, and the row headers are power settings. So are the table entries meters at ISO100? How do I know aperture?

Table 2: I am lost here. What is this table used for?

Table 3: I know this is for multi flash mode, but I don't have a clue how to read it.

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Last edited by klh; 05-24-2011 at 05:37 AM.
05-24-2011, 06:24 AM   #2
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You are correct, Table 1 is providing the distance in meters.

Here is the guide number (GN) equation:

GN = distance f-number

I used Excel to create f-number tables for various ISO settings (GN will change as ISO changes)

Here is a calculator that will do the same thing.

OCPA's Flash Calculator

Table 2 looks like it did the calculations for you at ISO 100. Shutter speed on the left and distance on the top = f-stop .

Tim
05-24-2011, 07:27 PM   #3
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QuoteOriginally posted by atupdate Quote
You are correct, Table 1 is providing the distance in meters.
I'm sorry, but I'm still not sure. Let's say as an example that I want the flash 2 meters from my subject with the zoom on 35mm. My camera is on ISO100, and I want to use f/8. How do I use this table to choose the flash power setting? Do I multiply 2 meters by f/8 to get GN=16? Then looking at table for 35mm, I see the closest is 18 at 1/4 power?

QuoteOriginally posted by atupdate Quote
Here is a calculator that will do the same thing.

OCPA's Flash Calculator
That's great. Now which GN do I choose the GN from this table?

QuoteOriginally posted by atupdate Quote
Table 2 looks like it did the calculations for you at ISO 100. Shutter speed on the left and distance on the top = f-stop .
Thanks, but you lost me here. Are you sure that is shutter speed on the left? Is it assuming high speed sync?
05-25-2011, 07:56 AM   #4
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I must apologize for a little bit of misinformation in my first post (Since I made my cheat sheets, I haven't looked at the math/GN tables in over a year).

Table 1 shows the Guide Number (in meters) of your flash for a given power setting (row headers) and zoom setting (column header). The GN at 35 mm and full power is 36.

So, for ISO 100, 2 meter distance and f8, the equation works like this:
2 (Distance - meters) x 8 (f Stop) = 16 (GN).

From your flash chart, to get a GN of 16 at 35mm zoom setting, you will need to set your flash power at about 1/4. The actual guide number at 1/4 power is 18 so you may need to move back a little bit to prevent over exposure.

To change your GN for different ISO's



Yes, Table 2 appears to be a high speed sync table. I do not know how to use this table.

Hope this helps.

Tim


Last edited by atupdate; 05-25-2011 at 09:03 AM.
05-25-2011, 12:01 PM   #5
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I read in one of your other threads that your are using umbrellas. What you need to understand is that using an umbrella decreases your effective guide number for the flash. The umbrella acts as a larger light source (like an extra wide flash zoom), along with light spillage to the surroundings, both decrease the amount of light that is directed at your subject.

For example, my umbrellas decreased my effective guide numbers significantly for my Sigma DG 500 Super when compared to its widest zoom (17mm). To put it in numbers for you at ISO 400:

Flash @ full power with 35mm zoom = Guide Number of 230 (ft)
Flash @ full power with 17mm zoom = Guide Number of 131 (ft)
Flash @ full power with Umbrella = Guide Number of 57.6 (ft)

I'm starting to put a tutorial together that will show how to make their own cheat sheets like the one below. The sheet isn't perfect but it normally gets me pretty close; even when using two umbrellas together.



Tim

Last edited by atupdate; 05-26-2011 at 09:39 AM.
05-25-2011, 12:32 PM   #6
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QuoteOriginally posted by atupdate Quote
...Yes, Table 2 appears to be a high speed sync table. I do not know how to use this table.
Table 2 is for HSS. Probably like my Pentax flash, the Sigma has a mode switch to select HSS separately. Then, the camera will allow shutter speed to go above 1/180. The table works the same as Table 1 except with shutter speeds, not manual power levels. So, at ISO 100, if your shutter speed is 1/500, GN=12. You can select f4 and have a range of 3m.
05-25-2011, 12:42 PM   #7
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Don't know about other models but think the max. sinc. speed on a K-X is 180.
Jake
05-25-2011, 06:29 PM   #8
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QuoteOriginally posted by atupdate Quote
I read in one of your other threads that your are using umbrellas. What you need to understand is that using an umbrella decreases your effective guide number for the flash. The umbrella acts as a larger light source (like an extra wide flash zoom), along with light spillage to the surroundings, both decrease the amount of light that is directed at your subject.

For example, my umbrellas decreased my effective guide numbers for my Sigma DG 500 Super by 1.75 when compared to its widest zoom (17mm).
To put it in numbers for you:

Flash @ full power with 35mm zoom = Guide Number of 161 (ft)
Flash @ full power with 17mm zoom = Guide Number of 92 (ft)
Flash @ full power with Umbrella = Guide Number of 51.4 (ft)

I'm starting to put a tutorial together that will show how to make their own cheat sheets like the one below. The sheet isn't perfect but it normally gets me pretty close; even when using two umbrellas together.



Tim
Tim,

Excellent. I'm beginning to understand. I was aware that shooting through an umbrella would lower the GN; I had read that it was at least a stop.

How did you determine your reduction? Did you measure it with a meter?

05-26-2011, 05:23 AM   #9
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QuoteOriginally posted by klh Quote
Tim,
How did you determine your reduction? Did you measure it with a meter?
I set the umbrella 5 feet from my test subject and manually shot at two different power levels at a 1/125 shutter speed. For each power level, I adjusted the f-stop until the exposure was correct. Then I calculated the GN using the distance and f-stop number.

For some odd reason I did mine at ISO 400. My previous post shows a heavy border box at 1/8 and 1/16 power. Those corresponded to f4 and f3.5.

5 ft x f4 = GN 20 and 5 ft x f2.9 = 14.4.

Tim

Last edited by atupdate; 05-27-2011 at 06:55 AM.
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