First, let's get rid of some nomenclature:
EF-S means a lens in the Canon EOS system that works only with cameras with APS-C or smaller sensors (if ever smaller sensors than APS-C EOS sensors are created). They can not be used with cameras with larger "full frame" 35mm film size sensors.
55-250 mm is the focal length of the lens. For an APS-C camera, a 55-250mm lens gives the same approximate field of view / angle that an 88-400mm lens would produce for a 35mm film camera or an FF digital camera. This is only important if you are familiar with 35mm focal lengths and want to know what the "equivalent" angle looks like with cameras of a different format size.
f / 4-5,6 refers to the maximum aperture of the lens. A lower aperture is a wider aperture that allows more light to enter the lens. In this way, a shorter shutter speed or a lower ISO value can be used if necessary. Both lenses have a maximum aperture of f / 4 at 55 mm. The maximum aperture narrows gradually at focal lengths between 55 m and 250 mm. At 250 mm, the maximum aperture is f / 5.6.
IS Image stabilization is a technology that counteracts the movement of the camera / lens during the exposure time. It allows slower shutter speeds without camera shake caused by camera movement when the camera is held in the hand than would otherwise be possible. It does not help with motion blur caused by the movement of the subjects in your photos. That can only be a shorter shutter speed.
II The Roman number two. This indicates that this is a second, updated version of a previous lens with the same name (except the suffix "II"). A subsequent version would be called "III".
STM Stepper Motor Refers to the type of autofocus motor used to move the focusing elements of the lens.
There are some important differences between the EF-S 55-250mm F / 4-5.6 IS II and the EF-S 55-250mm 1: 4-5.6 IS STM:
- Two different optical formulas. Although the names are very similar, the optical formulas of the lenses are not the same. The EF-S 55-250 mm 1: 4-5.6 IS II (2011) is Optically identical to the previous EF-S 55-250 mm 1: 4-5.6 IS (2007). While this is not always the case when comparing an original version with the "II" version of a Canon lens, the differences between the "55-250 mm" and the "IS II" of 55-250 mm are purely cosmetic, except an updated IS (image stabilization)) firmware. These lenses had 12 lens elements in 10 groups. The "STM" on the other hand has 15 lenses in 12 groups.
- The way in which the focusing elements are moved in the lens. The original "IS" and "IS II" (55-250 mm) had a micromotor autofocus. This is the most basic (and cheapest) AF motor type on Canon EOS lenses. They are good enough, but they are neither as fast nor as quiet as Ultrasonic Motor (USM) AF units in higher-class Canon EOS lenses. The newer "IS STM" uses a newer stepper motor to move the focusing elements of the lenses.
Of course, differences in optical design can affect the optical performance of the lens. In this case, "IS II" and "IS STM" are very similar from 55 mm to about 100 mm. Beyond 100mm, the general consensus of most reviewers is that the newer STM lens will maintain more or less the same "sharpness" at 250mm, while the older "IS II" will soften at 135mm and more greatest performance drop at the longest focal length of 250 mm ("zoomed all the way up"), especially at the edges and in the corners of the frame.
The other major difference in the optical design is that the increased number of lens elements in the "STM" is on the back of the lens so that the lens can use the internal focus. This allows the "STM" lens to focus without rotating the front of the lens barrel forwards / backwards when the focus is adjusted. The front barrel of the "IS II" turns and moves gradually as the focus is adjusted. The front cylinder of the "STM" moves inward / outward when zooming, but the cylinder does not rotate during zooming. Using polarizers or graduated neutral density filters that are affected by lens rotation can be a distinct advantage, as the filter does not have to be readjusted each time the focus distance is changed.
The STM autofocus motors are designed to be quieter and quieter than the micromotor AF. The benefits of capturing video should be obvious: the focus can be changed from one distance to another during a smooth transition, while being quieter and less likely to be picked up by the camera's microphone. Compared to micromotor lenses, the STM lenses tend to focus faster and to be quieter and quieter. The higher resolution USM lenses are optimized for still image capture. They are usually quite quiet, but they focus on focusing as fast as possible without worrying about "jerking" between the focus positions. The focus is on getting to the desired focus position as quickly as possible so that the still image can be taken NOW.
Another major difference between most micromotor AF lenses and STM is manual focus. To manually focus a micromotor lens, set the AF / MF switch from AF (auto focus) to MF (manual focus). The lens is then focused using a mechanical connection between the focusing ring on the lens and the lens elements within the lens. When you move the focus ring with the switch to & # 39; AF & # 39; move, the focusing mechanism may be damaged. When the & # 39; AF / MF & # 39; switch is on & # 39; MF & # 39 ;, the lens can be focused even if it is not connected to a camera.
STM lenses are all focused. There is no direct mechanical connection between the focusing ring and the focusing elements of the lens. When the focus ring is rotated, it sends a signal to the camera, which sends a signal back to the lens and instructs the focus element to move. The finest focus setting that can be made with manual focusing is a single step of the AF motor. This allows you to manually focus on full time, even if the "AF / MF" switch is set to "AF". In addition, the lens must be attached to a powered-on camera to move the focusing mechanism.
(Most USM lenses have a manual manual focus via a mechanical link between the focus ring and the USM ring inside the lens, allowing the lens to be manually focused even when not attached to a camera. By-Wire USM Lenses By December 2017, all but one have been discontinued.)
So what is "better"?
It all depends on what you want to do with the lens.
- The "STM" is a slightly better optical performance.
- The "STM" has a faster, quieter autofocus, but requires the focus-by-wire connection to focus in discrete steps.
- The "IS II" can be manually focused without any camera power and can be set finer than the smallest step of stepper motors in STM lenses.
- The "IS II" is usually cheaper, so that the money saved for another lens or other lighting device or other accessories can be spent.
For most people, the newer EF-S 55-250mm 1: 4-5.6 IS STM would be the more desirable option in all aspects except the budget. However, the older "IS II" is well able to take good photos that are almost the same as the newer model.