TS Optics APO 2.5x Barlow Lens 2″

TS Optics APO 2.5x Barlow Lens 2″

The TS Optics TSB225 Barlow lens extends the focal length of any telescope by a factor of 2.5x and delivers exceptional optical quality for both visual observation and astrophotography. The four-element APO design with telecentric configuration places it among the best Barlow lenses in its class - not only for on-axis sharpness, but across the entire image field, where simpler two-element Barlows typically fall noticeably short.

Optical Construction and Build Quality

The four optical elements are housed in a solid aluminium barrel. All lenses carry full multi-layer anti-reflection coatings for maximum light transmission, high contrast, and natural color rendition. The edges of all lens elements are blackened to eliminate unwanted reflections - particularly important when photographing the Moon and Sun (with a suitable solar filter only), where stray reflections would visibly reduce image contrast. The interior of the barrel is also matte-blackened throughout.

The four-element design allows use even with fast telescopes at f/4, such as Newtonian reflectors - where simpler Barlow lenses would show noticeable degradation in image quality toward the edges of the field.

Advantages of the Telecentric Design

The telecentric optical design offers two significant practical advantages over conventional Barlow lenses:

First, the magnification factor is independent of eyepiece insertion depth. With a conventional Barlow, the amplification changes depending on how far the eyepiece is inserted into the barrel. With the telecentric design, the 2.5x factor remains constant at all times - regardless of whether a dual polarizing filter, filter drawer, or any other accessory is placed between the lens and the eyepiece. The magnification will always be exactly 2.5x.

Second, the telecentric design does not extend the eye relief of the connected eyepiece. Long focal length eyepieces, which are commonly used in combination with a Barlow, already have a generous eye relief by nature. If this were extended further, maintaining the correct eye position would become difficult and could lead to the uncomfortable "kidney beaning" effect. The telecentric design eliminates this problem entirely.

Accessory Connections and Fitting

The Barlow lens is equipped with compression ring clamps for both 2″ and 1.25″ accessories. Compression ring clamping leaves no marks on the barrel of the inserted accessory and ensures precise centering on the optical axis. A 1.25″ adapter is included in the box.

On the telescope side, a standard 2″ filter thread is provided, accepting all common 2″ filters - for example nebula filters for increased contrast during astrophotography or visual deep-sky observation.

Astrophotography Use

The TSB225 doubles as a high-quality photographic teleconverter, multiplying the focal length of the telescope by 2.5x. The four-element APO design ensures excellent sharpness not only on axis but across the entire image field - a significant advantage over simple two-element Barlows, where the corners of the frame typically suffer in photographic use. The lens delivers good illumination and sharpness even with full-frame sensors, making it suitable for the full range of modern photographic and astronomical cameras without any concern about quality drop-off at the edges of the frame.

Technical Specifications