[Cliff (Clifford)]

I am a little unsure of what is happening,

I have a 76mm x 570mm refractor a total of approximately 100mm ext tubes , a 4X Powermate then 40mm plossil (or other eyepiece) to reach focus without a diagonal.

Now experimenting as the weather is lousy, I tried putting a diagonal into the powermate and then the eyepiece in the diagonal and only see about 3mm difference in focus position with a 1.25" prism or 6mm with a 2" mirror diagonal?

My understanding was the diagonals took up 50-100mm of the focus distance.

Anyone like to enlighten me ? Not used extension tubes with barlows or powermates before. I did discover the powermate needs to go at the end of the extension tubes not at the telescope end to get any focus at all.

thanks
Cliff