# Metering question

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##### New Member
I got a dc and an slr that cant meter. so i use the dc to meter on behalf. i got velvia 50 in the slr. if my dc reads f2.8 1/100 at iso100. what should i set on my slr? and if i go down to f1.4 on my slr what is the setting? any formula?

#### mpenza

##### Senior Member
1/200.

ISO 50 is one stop slower than ISO 100, while F1.4 is two stops faster than F2.8 (~1.4x for every stop difference). So overall, the SLR is one stop faster. For every stop, shutter speed changes by a factor of 2, so the correct shutter speed will be faster by 2 times (i.e. 1/200).

Let me know if I'm wrong...

##### New Member
Originally posted by mpenza
1/200.

ISO 50 is one stop slower than ISO 100, while F1.4 is two stops faster than F2.8 (~1.4x for every stop difference). So overall, the SLR is one stop faster. For every stop, shutter speed changes by a factor of 2, so the correct shutter speed will be faster by 2 times (i.e. 1/200).

Let me know if I'm wrong...
according to ckiang, its 1-1.

##### New Member
Originally posted by mpenza

as in 1/100s?
so if my dc reads 1/125, f2.8, iso100
the slr is at f1.4 so shutter should be 2 stops up at 1/500.
but film speed is slower so bring down one step to 1/250. Is this right?

#### mpenza

##### Senior Member
yup, that's how I understand it.

#### ckiang

##### Senior Member

according to ckiang, its 1-1.
Different situation lar.

aperture scale goes : 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32.
shutter speed goes : 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000

f/2.8 is 2 stops slower than f/1.4. So if your DC reads 1/125 at f/2.8 ISO 100, the SLR at f/1.4, ISO 100 would be 1/500s. But you are using ISO 50 there, that's 1 stop slower, so your shutter speedshould be 1/250.

Regards
CK

#### denizenx

##### Senior Member
heh aperture is area-based, so if u do f-squared u get the values of
1.4 = 2, ref
2 = 4, 1 stop less
2.8 = 8, 2 sops
4 = 16, 3
5.6 = 32, 4
etc and inbetweeners too...

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