The Pierro Astro T2 Barlow adapter is a very useful accessory. It has male and female T2 threads. In addition it has an internal thread to allow for the direct connection of a Televue Powermate (2.5x and 5x). For 1.25" lens cells there is a 1.25" space which allows for the internal fitting of a 1.25" cell which is then secured with two plastic grub screws.
The T2 Barlow adapter was designed to compliment the Pierro Astro ADC. Using it permits easy connection of Barlows or Powermates to the ADC while allowing the whole assembley to be connected via T2 instead of a 1.25" eyepiece clamp. Some examples of how the adapter can be used are shown above.
A consideration when using some Barlows or a Powermate with the ADC is the effect adding in the length of the ADC (approx 30mm) has on the magnification of the Barlow / Powermate. Powermates have quite a narrow range at which they work at the quoted magnification. Outside of this they will over magnify. This is a particular issue with the 5x. For some Barlows like the APM 2.7x ED Barlow, the barlow has a specific back focus distance at which point it provides a corrected image field and optimum performance. Baing able to mount the barlow very close to the ADC is therefore useful to allow back focus to be adjusted as needed.
