Diagonal

[Okeydokey]

I'm looking to move from 1.25" to a 2" eye piece (collection) do I really need to use a diagonal, apart from the ergonomics or is there any other reason/benefit?

Thank you

[rowan46]

It does require a 2" diagonal to fit the eyepieces. Also the diagonal is part of the optical train so without it you may be unable to reach focus. Imagers use an extension piece instead of a diagonal.

[Rainmaker]

You don't need a diagonal for visual but most people find it makes for more comfortable viewing to be looking down rather than craning your neck to see through the scope. 

Depending on the scope you may need to make up the difference in optical path length with an extension tube.

Takahashi OTAs are supplied for direct 'through the scope' viewing and to use a diagonal you leave out the extension tube.

Theoretically the view should be better without a diagonal, in practice it is difficult to see unless the diagonal is poor quality or dirty.