Need help with variable ND filter!!

[josephjx]

Hi all,
Just want to find out more abt VND. As we know that those calibration marking on the ring is just a guideline from min to max. But when you adjust the ring and found the appropriate exposure, how I should know what shutter speed to select or time as I do not know what F-stop am I at. Somebody pls guide me. Will appreciate it. Thanks

 

[thoongeng]

You need to understand the exposure triangle, the basics are still the same...
What do you mean by 'found the appropriate exposure'? Is that the exposure (in terms of aperture, shutter speed and ISO) that the camera suggests? Isn't that the settings you should try first, before making adjustments to each of the variables to get the effect you want?
Adding VND or any neutral density filter doesn't change the basics, they just allow less light to reach the camera sensor so that you achieve the effect you want

 

[josephjx]

Example I’m taking landscape of sunset or sunrise. I was in manual mode with F11 and iso 100, so what I left to adjust are the VND density and shutter speed? Since I don’t have the specific fixed ND to fit on, I only can adjust the ring so that my image won’t over exposed. But after adjusting, I have no idea what’s f stop am I at and not sure how long should I slow down my shutter speed? Am I at the wrong direction?

 

[Octarine]

Don't you have a meter in your camera? Just because you use manual exposure settings doesn't mean you can ignore the camera exposure meter.
In case you use some old camera without any meter, you can use your phone: download a metering up, point to target, get the reading. The unscrew your VND, keep the settings, put in front of the handphone camera, meter again. The difference should tell you how many stops light reduction the VND gives.

 

[thoongeng]

I only can adjust the ring so that my image won’t over exposed. But after adjusting, I have no idea what’s f stop am I at and not sure how long should I slow down my shutter speed? Am I at the wrong direction?

Don't confuse yourself Exposure triangle only has 3 variables, shutter speed, aperture and ISO

I was in manual mode with F11 and iso 100

You answered your own question that's the f-stop. And ISO here.

What do you mean by "I only can adjust the ring so that my image won’t over exposed"? Since you are in Manual mode, you have 'manually' selected the Shutter Speed already. I'm guessing you are adjusting the ring of the VND till the metering of the camera is at '0' exposure.

Hmm, unless you are just thinking aloud and not tried it out in the field? You would have solved the equation when tinkering with the camera

 

[josephjx]

ive been trying out in the field but just cant get the correct setting or perhaps not the best image i want. haha i think im confusing myself. im using hoya variable nd filter. so what i am referring is the stop for ND filter, not the aperture f stop. this hoya VND ranging from 1.5 to 9 stops. lets say i want 6 stops, but i do not know cos those calibration mark is just a guide. so what should i do? pardon me if im asking stupid qn. im just learning

 

[thoongeng]

No worries, no stupid questions, just phrasing not that correct so confused us as well haha...

Ok so back to basics of the exposure triangle, to the camera meter it only can see how much light it receives, it doesn't know whether there's a ND filter or not.
You're using Manual exposure mode, without the ND filter and at at setting of 1/30s, F11, ISO100 the meter reads correctly exposed or '0'. If you want 6 stops darker, what is the shutter speed?
Calculating by a stop each: 1/15s > 1/8s > 1/4s > 1/2s > 1s > 2s (or easier with math 2^6 (2 to the power of 6) will give you 64, 64 x 1/30s = 2s)
(this is a longer example to what mod Octarine suggested)

So the short answer is that if you change the shutter speed to 2s, keeping F11 and ISO100, and turning the VND till the meter reads correctly exposed, then the VND is roughly at the 6 stops setting.

The longer answer is that there are probably other factors at play eg there is probably more vignetting and colour cast at darker settings of the variable ND, affecting the exposure and artistic effect. However I will suggest not to be too concerned about what the setting of the VND is, more important is getting the "best image you want". If you used the VND to achieve the effect that you wanted, people looking at the image will probably not be faulting you if you do not know the exact setting

 

[josephjx]

Thanks a lot. I somehow get what u mean. Will try out in field soon

 

[thoongeng]

Yup practice makes perfect. Let us know your findings or other problems, have fun!

 

[Kermitfm]

@josephjx. The VND is quite versatile as you can 'dial' in the 'stops' of ND you want. However, as you already found out, the 'stops' are indicative only and you may face issues getting the settings correct because your camera exposure meter may not be able to read the light level when you cut off a lot of light.

What you need to do is to measure the 'stops' at each of your calibration marking. With a notebook and pen, record down the readings of the camera settings and using the indicative marker on the filter as a guide. You may be surprise that the indicative marks may be quite close as there would be some exposure leeway. Once you have done this, you will be more confident when you next use the VND.