ISO & studio strobes

ok, testing is done. I used 1 light with a 24x36" soft box. I powered up to about half. i was set 6-7 feet back at roughly a 40-45 degree angle. I used my spydercal since it is all black and white so I would have something I know is white to measure off of. I did 2 separate ISO's with F/stop ranges. I first did ISO 100 with a shutter speed of 250. just to see if my lights and camera would sync that fast. "they do" I shot a series from the metered reading of f/5 down to f/2.8. I only will show the first 3. next I did the same at ISO 400. Shutter speed 250. again, same F/stop range. only needed 2 to sow this. I imported all of them into CS5 and used the eyedropper tool to measure white. I chose the center of the left top square. 1 or 2 I think are marked where I took it from. again, each test was set to the sekonic meter reading . The ISO 100 was metered at f/5 and the ISO 400 was at f/4.5 all of these reading were with the dome in, facing the light source.
images are as Followed.
ISO 400 f/4.5

1947 x 1023

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1913 x 1022

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1901 x 978

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1908 x 1029

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1957 x 1026

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There is something strange going on here.. If you metered at 100 ISO and got a reading of f/5 you should have got a reading of f/10 at 400 ISO.

I adjusted the power to reach f/4.5. I wanted to remeter and check my wb at a higher iso

momoe wrote in post #12167464
ok, testing is done. I used 1 light with a 24x36" soft box. I powered up to about half. i was set 6-7 feet back at roughly a 40-45 degree angle. I used my spydercal since it is all black and white so I would have something I know is white to measure off of. I did 2 separate ISO's with F/stop ranges. I first did ISO 100 with a shutter speed of 250. just to see if my lights and camera would sync that fast. "they do" I shot a series from the metered reading of f/5 down to f/2.8. I only will show the first 3. next I did the same at ISO 400. Shutter speed 250. again, same F/stop range. only needed 2 to sow this. I imported all of them into CS5 and used the eyedropper tool to measure white. I chose the center of the left top square. 1 or 2 I think are marked where I took it from. again, each test was set to the sekonic meter reading . The ISO 100 was metered at f/5 and the ISO 400 was at f/4.5 all of these reading were with the dome in, facing the light source.
images are as Followed.
As you can see on the top right, there is the number value of my spot I picked to be white. I selected the same spot in all of the images. when I added all of the 3 numbers and divided by 3, I had my average. it appears that I am metering 1/3 stop off. my 4.5 should be a 4.0 and my 5.0 should be a 4.5

if I am wrong as to how I went about this, Please speak up because I want to get this right.

i'm going to ask you to put your camera at 125 shutter speed and 100 ISO to do this test

re read this https://photography-on-the.net …hp?p=12146982&p​ostcount=5

re read this https://photography-on-the.net …p?p=12148410&po​stcount=13

open up your images in photoshop

go to levels (only) and do a screen shot

and report back

I will do this but I was told before that when you measure each light to do it facing the light with the dome down. is this wrong?

momoe wrote in post #12169576
I will do this but I was told before that when you measure each light to do it facing the light with the dome down. is this wrong?

I didn't read those links, but I thought everything should be metered facing the camera, what matters?

momoe wrote in post #12169576
I will do this but I was told before that when you measure each light to do it facing the light with the dome down. is this wrong?

the idea of the dome in is to get a reading of one light at a time

you can turn on one light and meter if you like, then turn it off and do the same for the other light

when both lights have equal output, turn them both on and meter them together with the dome up

Kechar wrote in post #12169691
I didn't read those links, but I thought everything should be metered facing the camera, what matters?

for your final reading you would be correct

for setting up 2 or more lights you need to meter each light individually to get your ratios

FJ LOVE wrote in post #12169727
for your final reading you would be correct

for setting up 2 or more lights you need to meter each light individually to get your ratios

Rgr that, thanx!

yes, I understand that, I did the test above with only 1 light. so I measured it with the dome down facing the light, would I get a different reading with it up facing the camera?

momoe wrote in post #12169753
yes, I understand that, I did the test above with only 1 light. so I measured it with the dome down facing the light, would I get a different reading with it up facing the camera?

using only one light, metering with the dome up it won't be different

the problem with dome up is trying to measure one light when two are firing

your reading will be contaminated from the output of the second strobe

momoe wrote in post #12169753
yes, I understand that, I did the test above with only 1 light. so I measured it with the dome down facing the light, would I get a different reading with it up facing the camera?

Depends on the angle of the light sourse to the subject.