Barlow Lens

₹ 1,776 / Piece

Supply TypeManufacturer, Exporter, Supplier, Retailer
Preferred Buyer Location All over the world

A Barlow is a negative (diverging) lens that is placed between the objective lens (or primary mirror – from now on these words will be used interchangeably) and the eyepiece of a telescope. It....

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Member Since 18 Years
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Year of Establishment 2006

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A Barlow is a negative (diverging) lens that is placed between the objective lens (or primary mirror – from now on these words will be used interchangeably) and the eyepiece of a telescope. It increases the effective focal length of an objective lens, thereby increasing the magnification. The idea is that 2 eyepieces and a Barlow will give you the flexibility of magnification of 4 eyepieces, and will give higher magnifications with less powerful eyepieces.

What are its Advantages and Disadvantages
Assuming that the Barlow is a good one, the only disadvantage is a slight loss of light throughput – this is of the order of 3%. The advantages are numerous:

Higher magnifications can be attained with longer focal-length eyepieces than would be possible without the Barlow. Short focal length eyepieces necessarily have optical surfaces that are more curved and therefore are likely to introduce more aberrations.
A Barlow increases the effective focal ratio of the objective. This gives a more acute light cone, which is less demanding of eyepiece quality because:

Rays at the periphery of the cone are closer to being paraxial and thus are less subject to aberration.
A smaller area of the field lens is used.

Many eyepieces have an eye relief (distance of exit pupil from eye lens) that is directly related to its focal length. For example, the eye relief of a Plössl is 0.73 × its focal length. Thus, with these eyepieces, for a given magnification there will be greater eye relief with a barlow than without.
Many eyepiece types do not work well with short focal-ratio objectives. The Barlow effectively increases the focal ratio, allowing the eyepiece to work well.

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