Diagonal Optical Lenght

[Earl]

How much length does a diagonal add to a refactor? As I need to use one to get my lodestar to focus, but an extension will be better.

[JamesF]

It varies from diagonal to diagonal depending on size (1.25" vs. 2") and design.  I'd make a first estimate of 60mm for a 1.25" diagonal.

James

[Earl]

More or less for a 2 inch?

[JamesF]

More, definitely.  I think, but I'm far from certain, that you're probably looking at 90mm to 100mm for a 2" diagonal.

Could you make up a bit of cardboard tube to hold the camera to get the length as close to right as possible?

James

[Earl]

blue peter adapter awesome !! bog roll

Cheers James

[John]

I've got the measurement for the light path through a 2" William Optics diagonal - it's 156mm from the end of the 2" barrel to the top of the 1.25" - 2" adapter. Here is a little diagram that I found when I was researching how to use a Chromacor CA corrector:

[JamesF]

blue peter adapter awesome !! bog roll

Cheers James

Just don't let too much dew get at it

James

[JamesF]

I've got the measurement for the light path through a 2" William Optics diagonal - it's 156mm from the end of the 2" barrel to the top of the 1.25" - 2" adapter. Here is a little diagram that I found when I was researching how to use a Chromacor CA corrector:

I've always assumed that the bit that fits inside the focuser tube doesn't count, on the grounds that it isn't adding anything to the optical path.

James

[Earl]

I've always assumed that the bit that fits inside the focuser tube doesn't count, on the grounds that it isn't adding anything to the optical path.

James

I think in the photo something s been threaded into the filter thread on the push fit adapter.

[John]

I've always assumed that the bit that fits inside the focuser tube doesn't count, on the grounds that it isn't adding anything to the optical path.

James

I'd agree James but this diagram was to help sort out the positioning of the Chromacor which needs to be at a precise position down the optical train to work at its best. It was the only info I had quickly to hand.

[rgm]

If you want to reduce the length, use a prism diagonal.  The optical path of light through the prism is less than reflecting off of a mirror.

[earth titan]

I had a scope (Revelation) that I couldn't getc focus on with a 2" diagonal although a 1.25" was fine. Therefore to answer a question a couple of posts earlíer - the optical paths are different.