I have recently purchased Nikon D7200 with an 18-140mm f/3.5-5.6 lens. But I am confused whether to buy a slim or regular filter — which will be appropriate for my lens?
The other answers discuss the linear/circular and how it plays with AF systems nicely. I wanted to chime in to talk about future proofing.
Having to rebuy the same equipment to fit your newer equipment is pointless. For example, if you did buy a 67mm filter to fit your 67mm lens, you'd be up a creek if you bought a fancy new wide angle lens that uses 72mm filters. (You would end up needing to buy another filter).
In order to future-proof, you'll want to take a look at your current lens line-up and any future lenses you might acquire (let's be realistic, yea?) and get the filter that will fit the largest one. Use Step Up rings for smaller lenses so that, ultimately, you only have to buy a single filter.
As for slim filters - I do believe they warrant consideration. Personally, I use the Formatt Hitech 100mm system on a Canon 16-35 f/4 for most of my landscapes. I get heavy vignetting at 16mm (full frame). Given it's a system, there's not much that I can do about it. But, you may run into a situation where a super wide lens vignettes a bit more with a Step Up Ring + Reg. Filter vs a Step Up Ring + Slim Filter. I'm not recommending you get a 100mm system - more so that, since you'll likely use step up rings, a slim filter may vignette less in this configuration - thus you have less work to do in post.
Also, keep in mind how often you'll put on and remove components. This additional wear-and-tear will be better combat by brass threaded rings and filters.
A slim filter is just a filter that is slim.
You can use either one. On an ultra-wide angle lens, the regular filter may cause vignetting which is why they make slim filters. By buying a slim filter, you will have more chances of it being usable on another lens in the future.
The only loss from not buying a regular one is that the slim one is hard to get a grip on. If you shoot a lot while wearing gloves, you may find the slim filter frustrating. As @scottbb said, slim filters do not have front filter threads, so they have to be the front-most when used in a stack.
So you seem to be asking a couple of questions:
- Should you buy a slim or regular filters
- What bonus will an HD filter add
- Will the 77mm hoya filter work for your lens
- What is the difference between CPL and CIR-PL
To answer these:
- Buy a regular filter. See this question for a better explanation: Circular polarizing filter - slim or regular?
- What "HD" filter are you talking about?
- I assume that your lens is the Nikon AF-S DX NIKKOR 18-140mm f/3.5-5.6G ED VR. It takes a 67mm filter so either buy a 67mm one or get a 67-77mm adapter to use a 77mm hoya. You don't specify what kind of filter it is so I can't comment on it further.
- 'CPL' and 'CIR-PL' are both shorthand for circular polarizer. There is no difference.