Blue Fireball Eyepiece Holder / Visual Back (1.25") with M42x0.75 Male/Female Threads # E-13

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In Stock (7 Available)
Ships by Next Business Day
Our Product ID: PAAR-BF-E-13
Manufacturer SKU: E-13
Item Can Ship: Worldwide
Blue Fireball Eyepiece Holder / Visual Back (1.25") with M42x0.75 Male/Female Threads # E-13

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Product Details

This Blue Fireball adapter/visual back # E-13 has a T/T2 female thread (M42x0.75) on one end and a 1.25" eyepiece barrel as well as a T male thread (M42x0.75) on the other side.

It thus acts as a T threaded visual back, allowing you to attach 1.25" eyepieces and accessories to any equipment/adapter that has a male T thread (T2 mount). Common examples are some telephoto lenses (which can be converted into excellent finder telescope with the use of this adapter, spacers, and an eyepiece), T thread adapters, off axis guiders, etc. Some Maksutov-Cassegrain telescopes use a male T thread on their rear cell, so you can use this adapter as a 1.25" visual back for such scopes. Note that most SCT telescopes use a larger 2" 'SCT' thread which is not the same as the T thread on this adapter.

This adapter is essentially identical to the Blue Fireball # E-10 adapter, except that this features an extra male T thread on the eyepiece side of the adapter. This allows users to attach other T threaded accessories directly to this adapter for a secure connection.

Since this adapter has a female T thread on one side and a male T thread on the other, it can also be used as a T thread spacer ring. When used in this mode, it will provide a spacing of approx. 25-26mm depending on the lengths of the T threads of the other items you attach to this adapter.

The eyepiece barrel features brass compression ring. Made of black anodized aluminum.


  • Total length = 31.9mm (1.26")
  • Length of female T thread = 5mm (0.20")
  • Lenght of male T thread (including unthreaded undercut) = 5.2mm (0.20")
  • Weight = 2.6oz

Blue Fireball part number: E-13