How do I know what size ND filters I will need ?

[BADGER.BRAD]

Yes I know its a stupid question but how to I know what size ND filters I will need to fit my cameras lens (Praktica b and Jenaflex) ? I intend to experiment with long exposure day time Photography. Many thanks all.

 

[Prest_400]

Many lenses specify the thread size needed, the cameras themselves are not important, just the thread size of the barrerl. A good tip is to buy the largest thread that may be needed (77mm) and purchase step up filters. Most normal lenses tend to be in the 49-55mm range however.
I think you can get some nice filters used, a Hoya, Tiffen or B+W ND is supposed to be excellent, maybe a polariser as well. Depending on the stops needed, there are some denser filters.

 

[Ian Grant]

Get yourself a Cokin filter holder, they take different adapters to fit varying filter threads. I can probably dig some out for you and I'm not that far from you, I've a lot surplus to requirements. Many Praktica lenses take 49mm filters & I've definitely got a few adapters as well as filters that size.

Ian

 

[AgX]

A caliper is ideal for measuring male threads, you can add a thread gauge. Both available for a few pounds.

Also many listings of lenses contain the filter thread.
Another approach is to buy some cheap filters just as a gauge.

 

[Soeren]

In full sun its hard to achieve long exposures even using a bigstopper (10 stops) with an 100 iso film though really bad reprocity failure will help. A 3 stop, 6 stop and 10 stop will take you a long way though and in more subdued ligting situations like overcast etc yould have all you need in those.

 

[Rudolf Karachun]

If you cat measure. You can go t to the store with you lenses and salesperson wold tell you what you need. Wright it somewhere for the future reference.

 

[AgX]

Rudolf, keep in mind that camera stores are on a decline.

 

[Huub]

Three things to consider. First is the thread size of the lenses you intend to use the filter on. It could be marked on the lens itself or on the inside of th lens scap, and could be something like 49mm, 52mm, 55mm or even bigger. A search on the net for the lens could also give you the information. You could also measure it yourself and compare it the list of the standard filter sizes. When you consider it to use it on more lenses: get the biggest size and use step up rings as Prest suggested.
Second thing to consider is how long you want to expose. For fast moving water you will need shutter speeds somewhere in the range of 1/4 sec to 1 sec to get those white washed water paterns. For moving waves on lakes and the sea 10 sec and up is necessary. In the first situation a 3 or 5 stop filter will do the job, for the second one you will need a 8 or 10 stop filter, depending on aperture, filmspeed and weather.
The third thing to keep in mind is that film loses speed when the shutter speed increases above 1 sec. This is called reciprocity failure and the effect differs from film to film. For HP5+ for instance, when you measure 2 sec, you should expose for 5 seconds. It gets worse with longer expores and you might find yourself doing exposures of minutes while measuring a time of 20 sec. Do research on the film of choice and make yourself a table because the effect is very noticable and there are huge differences between films.