Quick Tips: What filter size should you buy?

Here's a quick tip on purchasing filters.  This doesn't concern UV or clear filters but for other photographic filters such as neutral density or CPL.  For UV filters buy the size of your lens thread.

Tip:

Buy the largest filter size, commonly a 77mm thread, and use a step up ring.

What are Step Up Rings?

Step up rings are like adapters from a smaller sized thread to a larger thread.  Say you are using an Nikkor 18-55mm lens, which has a 52mm thread.  Go buy a 52-77mm step up ring so you can attach a 77mm filter on your 18-55mm lens.

Why buy a 77mm and step up ring?

The answer: economical.  If you are serious in photography and love landscapes, eventually you'll be buying an ultra wide angle (UWA) lens.  And common UWA's have 77mm threads.  

Here's the idea.  

Say your current lens is a Nikkor 18-55mm and you want to try CPL filter for landscapes.  So you go buy a 52mm CPL filter, which costs around say $50.  You enjoy your 52mm CPL and soon you decide to buy a Sigma 10-20mm f4-5.6.  Now if you do purchase the Sigma, then your $50 CPL would be junk because it won't fit on the Sigma, which has a 77mm thread.  So you'll have to buy a 77mm CPL which would cost around say $80.  Your 52mm CPL is now a $50 paper weight.

But if you buy a 77mm CPL, for $80, and a step up ring, commonly at $12, then you've only spent $92, economical no?  and once you do buy an UWA, you don't have to buy a new filter.

Also,

"This saves a lot of fiddling when you are out shooting and trying to swap filters around." ~Ken Rockwell