ND Filters.

[Mr. Doyle]

Heres a quick question:
If I place a 3 stop Neutral Density filter and a 2 stop Neutral Density filter in front of my lens, will it give me five stops? For those of you that know it may seem like a daft question but I am not so sure as I never really use them...Also will it effect anything else, like sharpness etc...
Thankyou.

[Emmanuel BIGLER]

In principle; yes, ND values simply add.
Expressed in terms of f-stops you can add the values as well, i.e. a filter given for 2 f-stops plus another given for 3 f-stops yields the equivalent of 5 f-stops.
Stacking several filters however increases the risk of diffuse/scattered light due to the additional glass surfaces where spurious reflections and scattering by dust can take place.
Again in principle for a perfectly plane and parallel piece of good optical glass you should fear no image degradation for distant objects, even at wide angles. Now the question is : how flat and parallel your filter glass is !
The other issue is the limitation of the actual field of view with stacked filters, it might not be easy to look from the back through the dark filters to check if the first filter mount actually restricts the effective angle or not.

[Mr. Doyle]

Emmanuel,
Thankyou very much!
I am lucky to have a super duper filtar system so I shouldn't have any trouble with flatness of the filters. Now wheres that waterfall....

[roteague]

I don't think you will have any problem with stacking filters. In principle yes, but in practice, no. Look to the work of Joe Cornish, to see what can be done using multiple grad filters (mostly split grads).

[SteveL]

A minor tip.....

You may need to 'stagger' them. If the transition on both filters takes place in the same area of the film, it may be very apparent. I usually fit the stonger grad (0.9 say) on first, getting the transition where I want it, then fit the weaker one, starting its transition where the first filter's transition stops (or is complete). Hope that makes sense :confused:

[Bob Salomon]

A minor tip.....

You may need to 'stagger' them. If the transition on both filters takes place in the same area of the film, it may be very apparent. I usually fit the stonger grad (0.9 say) on first, getting the transition where I want it, then fit the weaker one, starting its transition where the first filter's transition stops (or is complete). Hope that makes sense :confused:

Is he asking about a graduated ND or a normal ND? Your answer only makes sense with a graduated ND. His question could be either ND.

[john borrelli]

I've heard some ND grad filters may not be exactly the maximum stated value, not sure if that's important to you. Also,if these filters are new to you then I would definitely urge you to read a little about some of the technique involved in using them. They are a little tricky but definitely very useful!