NIGHT FOCUS

Main concept

It is difficult and time-consuming to precisely focus on the stars when taking starry landscape photographs. The star on the screen may not be clearly visible and capturing the focus point may take time.

The Kenko NIGHT FOCUS was developed to make this process visually easier to ensure sharper focus. It is attached to the front of the lens like a normal screw-in filter*.

* For focusing only. After focusing the filter should be removed.

The idea for the NIGHT FOCUS was inspired by the Bahtinov mask invented by Russian astronomer Pavel Bahtinov to ensure reliable focus when photographing nebulae and star clusters in astronomical telescopes with focal lengths of 500mm or 1000mm or longer. Since the Bahtinov mask was designed for astronomical telescopes, it did not match the optical characteristics of the short focal length photographic lenses and did not provide effective focusing.

Technology

The pattern on the glass surface generates three stripes of light from bright stars, and by adjusting the focus so that the three stripes overlap in the center, you can focus on the stars precisely and quickly.

For the NIGHT FOCUS, we examined the optical characteristics of the 24-70mm zoom lens, which is the primary target for many people today. Unlike the Bahtinov masks, the Kenko NIGHT FOCUS has high light transmission, preventing the field of view from becoming darker.

How stars look when NIGHT FOCUS filter is attached

When looking at a first class star with the NIGHT FOCUS attached, a light stripe is generated around the star. The star is in focus when the intersection of the three stripes overlaps and appears to coincide with the center of the star (Figure 1). When the focus ring is moved, only the central stripe appears to move (Figures 2 and 3). Adjust the focus ring by moving the focus ring in small increments.

Different patterns of the light stripes

Depending on lens type and camera used, the stripes pattern can differ in following ways:

How to use

1. Attach the NIGHT FOCUS to the lens.
2. Bring a bright star into the center of the field of view.
3. Zoom in to maximum magnification in Live View.
4. Set the focus.
5. Take a test image with the Kenko NIGHT FOCUS attached.
6. Play back the image, zoom in, and check the focus.
7. Remove the NIGHT FOCUS, compose the image, and take the final shot.

SuggesteD lens and cameras

Cameras:

• Cameras with Live View function.

Lenses:

• 24-70mm f/2.8-4 zoom lens.
• Prime lenses of approximately 20mm-50mm f/2-2.8.

Suggested lens are those which have close focal length and F-value.

Some lenses with focal length up to about 18mm to 75mm can also be used.

* The filter is design to fit f/2.8 or f/4, 24-70mm zoom lens.
* The ease of focusing varies depending on the lens design.
* Some AF lenses that electronically control the focus may not have a fine pitch and may not be adjusted to the correct position.
* It may be difficult to catch the focus point when the atmosphere at high altitudes is turbulent.

Attaching to the lens

The NIGHT FOCUS is screwed on like all screw-type filters and can be attached directly to the lens. The NIGHT FOCUS filter size is 82mm only, so be sure to have a stepping ring to match the lens you have.

The Kenko Square Conversion Frame for 82mm also allows you to use the NIGHT FOCUS filter with a 100mm wide square filter holder. The Square Conversion Frame is an item that allows a round filter to be attached to a square filter holder.