August 2014

EF-M55-200mm f/4.5-6.3 IS STM

Photo 1: EF-M55-200mm f/4.5-6.3 IS STM

Photo 1: EF-M55-200mm f/4.5-6.3 IS STM

This month's technical report introduces the EF-M55-200mm f/4.5-6.3 IS STM (Photo 1), a zoom lens designed specifically for our EOS M and EOS M2 mirrorless cameras.

Development objectives

This is our fourth EF-M interchangeable lens, following a standard zoom,[*1] a thin pancake lens,[*2] and an ultra-wide-angle zoom,[*3] which are already on the market. We designed this telephoto zoom lens to be light and compact for easy telephoto shooting enjoyment without compromising portability. This lens, together with the standard zoom lens, can cover a broad array of shooting situations. Moreover, we completed this telephoto zoom lens to strike the right balance between image quality, usability, and price.

*1 EF-M18-55mm f/3.5-5.6 IS STM
*2 EF-M22mm f/2 STM
*3 EF-M11-22mm f/4-5.6 IS STM

The main features of the lens are listed below.

A new five-group optical zoom design achieves compactness and outstanding image quality
Aspherical lens and UD lens elements deliver outstanding image quality at all zoom settings
The focusing mechanism uses a stepping motor and a lead screw for quiet, smooth Movie Servo AF performance while recording movies
Image stabilizer gives a stabilization gain of 3.5 f-stops in shutter speed [*4]
Circular diaphragm provides beautiful bokeh out-of-focus effects
Full-time manual focus function [*5]

*4 Using CIPA measurement standards at a focal length of 200 mm (35mm-equivalent 320 mm) on an EOS M camera.
*5 The focus can be adjusted manually after autofocusing when the camera's focus mode is set to [AF + MF].

The following sections detail the lens's technologies.

Feature 1 - High-grade, stylish exterior finish

The lens has been made significantly more compact and lightweight. It has a maximum external diameter of 60.9 mm, an overall length of 86.5 mm, and a weight of about 260 grams.

The exterior design maintains consistency with the designs of the other EF-M interchangeable lenses (Photo 2), and the highly textured, metal-toned lens chassis, with a high-grade coating, matches with any camera body color.

The twill knurling [*6] on the focusing ring and zoom ring provides a comfortable fit in the hand and makes the rings easier to operate.

*6 Twill knurling is a diamond-shaped, anti-slip pattern formed in metal.

Photo 2: The EF-M lens series

Photo 2: The EF-M lens series

Feature 2 - Outstanding image quality from a compact, lightweight form

For this lens, we came up with a new design for a five-group zoom mechanism that benefits from short-back focus. Image stabilization and support for AF shooting for movies were also added. The lens delivers sharp, high-contrast resolution all the way to the frame edges while remaining compact enough for excellent portability.

The lens's construction consists of 17 elements in 11 groups (Figure 1). The tenth element just after the diaphragm is a GMo aspherical element, which keeps the optics compact while maintaining excellent image quality. And the additional chromatic aberration correction with a UD element ensures top image quality at all zoom positions (Figure 2).

The lens placement and optimized coatings both control flaring and ghosting and achieve excellent color balance.

The rear-focusing method using the fourth lens group assists the quiet, smooth Movie Servo AF while recording movies. The minimum focusing distance is 1.0 meters at all focal lengths.

The seven-blade aperture produces stunning bokeh out-of-focus backgrounds with nearly circular blur patterns and the deep blurring inherent to telephoto lenses.

Figure 1: Cross-section view of the EF-M55-200mm f/4.5-6.3 IS STM optics

Figure 1: Cross-section view of the EF-M55-200mm f/4.5-6.3 IS STM optics

Figure 2: MTF characteristics of the EF-M55-200mm f/4.5-6.3 IS STM

Figure 2: MTF characteristics of the EF-M55-200mm f/4.5-6.3 IS STM

Feature 3 - Fast, comfortable autofocusing

This lens features the same lead-screw focusing mechanism with a stepping motor as found on past EF-M zoom lenses. The fast CPU and optimized AF algorithm realize fast, precise AF during still-image shooting and also enable AF subject-tracking while recording movies with the quiet, smooth movement of the focusing lens element. [*7]

*7 When the Movie Servo AF setting is turned on at the camera.

Feature 4 - Image stabilizer

The focal length at the telephoto end is 200 mm, 35mm-equivalent 320 mm, which is a telephoto focal length. The most common mistake in telephoto photography is probably camera shake that spoils the quality of images. The image stabilizer is what alleviates this bane of photography.

The lens's image stabilizer achieves a stabilization gain of 3.5 f-stops in shutter speed. [*8] It also has a function that automatically distinguishes between normal shooting and panning and then selects the optimal image stabilization mode for the shooting situation.

Photo 3: ET-54B

Photo 3: ET-54B

Accessories sold separately are the ET-54B lens hood (Photo 3), with a satin finish on the hood's inner surface to improve its anti-reflective performance, and the LP816 drawstring soft case.

This single lens can be used in a wide range of situations, from photos that draw distant objects into the shot to portraits that sharply render each strand of hair. Add this lens to your collection so you can discover the real pleasure of an interchangeable-lens camera and experience the fun of choosing lenses for different subjects and situations.

*8 Using CIPA measurement standards at a focal length of 200 mm (35mm-equivalent 320 mm) on an EOS M camera.

Mode EF-M55-200mm f/4.5-6.3 IS STM EF-S55-250mm f/4-5.6 IS STM
Lens construction 17 elements in 11 groups 15 elements in 12 groups
Aspherical lens elements 1 No
UD elements 1
Aperture blades 7 (circular aperture)
Image stabilizer Yes
Min. focusing distance 1.0m 0.85m
Max. magnification 0.21 x 0.29 x
Filter size 52mm 58mm
Max. diameter 60.9mm 70mm
Length 86.5mm 111.2mm
Weight Approx. 260g Approx. 375g

Table 1: Specification comparison between the EF-M55-200mm f/4.5-6.3 IS STM and the EF-S55-250mm f/4-5.6 IS STM