Barlows and Extenders

Barlows, Extenders and Effective Focal Ratio

A Barlow multiplies focal length, which also multiplies focal ratio and increases back-focus. All three effects matter, and the last one is often useful in its own right.

• 2x Barlows: The standard choice, doubling every eyepiece's magnification and effectively completing a small eyepiece set.
• 3x and higher: For planetary and lunar imaging where image scale must match the camera's small pixels. Rarely useful visually given typical seeing.
• Telecentric amplifiers: Maintain a parallel light cone rather than a diverging one, which matters for solar etalons and some binoviewer applications where the light angle affects performance.
• Focal extenders for imaging: Designed for camera use with corrected fields, unlike visual Barlows which may not perform across a sensor.
• Added back-focus: A Barlow pushes the focal plane outward, which is often the cheapest way to make a binoviewer or a deep accessory reach focus.
• Element count and coating: Multi-element apochromatic Barlows preserve contrast far better than simple two-element designs, particularly in fast telescopes.

Why Choose David Astro for Barlows and Extenders

A cheap Barlow in front of a good eyepiece wastes the eyepiece. We would rather you spent once.

• Set planning: We help you choose a Barlow that fills the gaps in your eyepiece range rather than duplicating a focal length you already have.
• Seeing realism: We will tell you when a 3x Barlow will exceed what your sky supports and simply give a larger, softer image.
• Back-focus use: If your real problem is reaching focus with a binoviewer or deep accessory, we will point out that a Barlow may solve it directly.
• Authorized dealer: Genuine products with manufacturer warranty, in stock here and shipped without customs delays for Canadian buyers.
• Ships from Canada: No duties or brokerage fees for Canadian orders.

Barlow Lenses in Canada — Frequently Asked Questions

Does a Barlow degrade the image?

A good multi-element Barlow is very nearly invisible optically. A cheap two-element one adds noticeable chromatic aberration and reduced contrast, especially in fast telescopes.

2x or 3x?

2x for general use, since it produces magnifications you can actually use on most nights. 3x is mainly a planetary imaging tool, where sensor pixel size rather than the eye sets the requirement.

What is a telecentric amplifier?

An amplifier that keeps the exit light cone parallel rather than diverging. This matters for solar etalons and some binoviewers, where a diverging cone shifts performance across the field.

Can a Barlow help me reach focus?

Yes, frequently. It moves the focal plane outward, which is often the simplest solution when a binoviewer or a long accessory train will not come to focus in a refractor.

Filling gaps in your eyepiece set?

Tell us what you own and we will recommend the right amplification. Ships from Canada.