How to measure number of stops in a ND filter?

[satz24]

Hi all

I have a graduated ND filter (for Cokin P holder) which I bought off Ebay.

The specs on the ad did not say the filter factor or how many stops it would do...eg 1 stop,2 stop or 3 stop

HOw could I measure this?

I've tried setting my D50 to spot meter and then on Shutter priority (1/200) with ISO fixed at 400.

I then took a reading through the darkest part of the filter. This gave f7.1

I then took off the filter and the camera meter gave the reading of f22

Does that mean that the filter is almost 10 stops??? Or am I calculating something wrongly with the number of stops?

Please help

many thanks in advance

Satz

[calebk]

Originally Posted by satz24 Hi all I have a graduated ND filter (for Cokin P holder) which I bought off Ebay. The specs on the ad did not say the filter factor or how many stops it would do...eg 1 stop,2 stop or 3 stop HOw could I measure this? I've tried setting my D50 to spot meter and then on Shutter priority (1/200) with ISO fixed at 400. I then took a reading through the darkest part of the filter. This gave f7.1 I then took off the filter and the camera meter gave the reading of f22 Does that mean that the filter is almost 10 stops??? Or am I calculating something wrongly with the number of stops? Please help many thanks in advance Satz

Hmm. Try and get a reading of f/5.6 with the filter on. Helps to calculate. Here is a list of complete f/stops

f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22

[JLee]

Originally Posted by satz24 Hi all I then took a reading through the darkest part of the filter. This gave f7.1 I then took off the filter and the camera meter gave the reading of f22 Does that mean that the filter is almost 10 stops??? Or am I calculating something wrongly with the number of stops? Satz

f7.1 to f22 = 10 stops??? How did u come up with that? So I reckon what u have is a 3 stop ND Grad.

[catchlights]

how do you get 10 stops wan??
let say fr f8 to f22( f8=>f11=>f16=>f22), is only 3 stops or 8X

you measure only the darkest part of the filter, than without the filter

[satz24]

thanks guys

I knew I had something wrong with my calculation of f stops!!

camera fstops went from 22, 20, 18, 16, 14, 13, ....etc

so I assumed it was 10!!

Thanks calebk for the list of f stops. Now I understand!!!

I remember those figures from the 'old' days when my lens had aperture markings!! Maybe I can blame Nikon for my forgetting the f stop numbering!!

:-)


Satz

[Artosoft]

Originally Posted by satz24 I remember those figures from the 'old' days when my lens had aperture markings!! Maybe I can blame Nikon for my forgetting the f stop numbering!!

No. Your own mistake. Don't put a blame on others .

Regards,
Arto.

[catchlights]

Originally Posted by satz24 thanks guys I knew I had something wrong with my calculation of f stops!! camera fstops went from 22, 20, 18, 16, 14, 13, ....etc so I assumed it was 10!! Thanks calebk for the list of f stops. Now I understand!!! I remember those figures from the 'old' days when my lens had aperture markings!! Maybe I can blame Nikon for my forgetting the f stop numbering!! :-) Satz

If you would read your camera manual, you will know this is in a one third steps increment.

[ExplorerZ]

Originally Posted by satz24 thanks guys I knew I had something wrong with my calculation of f stops!! camera fstops went from 22, 20, 18, 16, 14, 13, ....etc so I assumed it was 10!! Thanks calebk for the list of f stops. Now I understand!!! I remember those figures from the 'old' days when my lens had aperture markings!! Maybe I can blame Nikon for my forgetting the f stop numbering!! :-) Satz

even if you lens have those marking, they are going at full stop (f2.8 > 4 > 5.6... )

[satz24]

If you keep the aperture fixed, say at f8, but the filter says "2 stops reduction", what happens to Shutter speed?

does it drop from say 1/200 (without filter) to 1/50 with filter?

Is that 2 stops?

thanks again

satz

[calebk]

Originally Posted by satz24 If you keep the aperture fixed, say at f8, but the filter says "2 stops reduction", what happens to Shutter speed? does it drop from say 1/200 (without filter) to 1/50 with filter? Is that 2 stops? thanks again satz

Yes that is two stops worth of shutter speed.