DSLR mount help

[G4YVM]

I am trying to put my 20D onto the 16" Dob, wot I ave made.

The problem is, I cannot get the mounting tube to be short enough (not enough IN travel on the Revelation focusser).

By holding the camera, and focusing on a church spire about a mile away I can eventually bring the image to focus, which leads me to thionk that a shorter T mount tube will be the solution.

A second thought opcurres to me: the image is dark, much darker than my Mk ! eyeball perceives it to be, so I should ditch the ten-bob 1.25 inch tube altogether and get a 2" T mount tube.

Thus, I am about (but after SGL5, grrr) to order a 2" T mount from FLO. Question: is my thinking right or am I missing something here. A short 2" tube T Mount will allow me to get focus and make the image brighter.

I know I am not going to get great images off a Dob, but I need something to take to work to say, look, I made it and this is what I see!

David

[themos]

I reckon you're about 2.5mm away from infinity-focus when you focus on something a mile away in a scope of 2 meter focal length.

That's 2-1/(1/2 - 1/1600)

[G4YVM]

Thanks for that, but I dont understand what the significance is.

David