Hoya 77mm Pro ND 1000
The Neutral Density Filter is used to uniformly reduce the amount of light that reaches the Camera Sensor. In the case of the Hoya 77mm Pro ND 1000 that's ten stops of light (NOTE: en stops, 3.0 density, 1000x and #110 all refer to the same extreme density)
Each Stop of light reduction is equal to a doubling of exposure time which equates to an unfiltered shutter speed of 1/100th being increased to 10 seconds.
The Fuji X-T2 does a pretty good job of focusing when an ND filter is attached. I have found that with exposures up to around the 30 second mark the camera can 'see' enough to lock.
It is however generally a good idea to compose and focus before attaching the Filter. This is perfectly practical with a screw on filter on a prime lens but care needs to be taken with Zooms as the focus can be effected easily as you attach the filter. It may be safer to check focus with manual focus and focus peaking after screwing on an ND filter in this case.
You might find a filter system to be a better choice as it is easier to add and remove the filter from the filter holder (see the Lee Filter System later in this article)
Screw on Vs Square Filters
There are a couple of options to consider when choosing an ND filter. Screw on type such as the Hoya 77mm Pro ND 1000 or 'Square' Filters such as the 100mx100m Lee filters.
The Advantage with the Screw on Type is size. I have an iGadgitz case which can hold up to three 77mm sized filters. I tend to use this for the Hoya 77mm Pro ND 1000 and a selection of step-up rings.
Square Filter Systems
The Advantage of a Square System such as the 100mm filter system by Lee Filters is that it is easy to add and remove filters. The Filter Holders have spaces for 3 square filters. It is possible to stack ND filters and/or add graduated Filters.
It is sometimes helpful when taking very long exposures to 'balance' the scene with a Graduated ND filter. This means that you can capture the scene in one shot rather than having to bracket for foreground and sky. Not much of an issue for a 30 second exposure but painful if you are exposing for 5 minutes.
It is an idea to buy your ND filter in a size to fit your largest lens. This way you can save money by buying Step-Up Rings to adapt the 77mm thread to various lens sizes.
The Camera can't calculate correct exposures above 30 seconds so you will need to do some math (or utilise a handy phone App such as NDTimer (https://itunes.apple.com/gb/app/ndtimer/id390568001?mt=8)
- The ND filters can add some color casts to the photograph. These are fairly easy to remove in Post Processing but should be taken into account.
- Internal reflections of light can cause some un-wanted effects. This is more common with the square systems where there is a space between the filter and the lens
- Vignetting can sometime occur when using wide angle lenses. The only answer in this case is to zoom in slightly or edit in post.
Here are two example JPGs taken with the Fuji X-T2 showing the difference in color cast between the Hoya ND filter and the Lee 'Big Stopper'
You can check out the products mentioned on Amazon