Diagonal Woes

[Billy Boy]

Hi

I'm really new to this so Apologies if this is an epecially dense question...I'm using a Skywatcher 6" newtonian on an EQ5 mount. To save on neck-craning I bought a cheap diagonal. Last night I popped it into the end of the focuser, then placed the plossl in the other end. All I could see was an "over exposed" image - including the spider. The scope is collimated as far as I can make out, same thing happended with my other eyepiece, and without the diagonal all is fine. The only thing that comes more-or-less into focus using the diagonal is the tree at the bottom of the garden...I assume I'm missing something really obvious? Any help very much appreciated!!

[Merlin66]

Diagonals add about 50mm to the "back focus" - from the sound of it you don't have enough space to fit a diagonal between the focuser and the eyepiece. This is not unusual for a newtonian

Can you rotate the telescope tube in the mounting rings to bring the eyepiece to a better location....

Ken

[SteveP]

Billy

Unfortunately what you're doing probably won't be possible. The design of a Newtonian prevents there being a lot of 'inward' focusing which is what you'd need with a diagonal fitted. You might be able to focus on near distance but not those things at infinity. There might be the possibility of fitting a low profile focuser but even then I'm sceptical. The only alternative I can suggest would be a regular neck massage.

Steve

[ottUp]

Hi

I assume I'm missing something

Yup. You don't use a diagonal with a Newtonian reflector.

• First, you don't need one. Diagonals are designed so that the eyepiece points upward at the bottom end of refractors or SCTs, for more comfortable viewing. On a Newtonian, the eyepiece already points upward. (If it doesn't, rotate the tube in the tube rings).
  
• Second, it won't work. Because the Newt's dimensions are calculated without a diagonal, if you add a diagonal, making the light path 20 to 30 cm longer, you won't be able to bring it to focus - which is what you're seeing.
  

- Richard

[Billy Boy]

Richard, Steve and Ken

Thanks for the replies, guys. That makes sense - and has me looking up "back focus".

The obvious solution of rotating in the tube rings also occured to me for the first time last night: what a strange mix of theory and messing about in the dark with cold hands this pursuit is...

What a great discovery this site is! Thanks Again.

[ottUp]

Richard, Steve and Ken

what a strange mix of theory and messing about in the dark with cold hands this pursuit is...

Wait 'til you add swarming mosquitoes into the mix! You'll be wishing for the cold to come back.

Keep plugging away - It's a constant learning exercise, this hobby, and there is always some new stage to conquer.

- Richard

[The Warthog]

You have an excellent combination of scope and mount there, so you have a good start into the hobby. Keep coming back with your questions. Remember the only stupid question is the one you don't ask.

[brantuk]

Ditto on all the diagonal comments. I'd also suggest a pair of fingerless gloves and a red light torch to help with fumbling around in the cold dark nights (which tend to be the best for viewing). Reusable hand warmers are great too.

[yeti monster]

Wait 'til you add swarming mosquitoes into the mix! You'll be wishing for the cold to come back.

The best repellant for mozzies (and all other wee beasties) is Avon skin so soft. Better than any insect repellant, I used to use it when I worked in India and only got bitted once when I forgot to put it on it time.

[Billy Boy]

I'm looking forward to the mozzies. Fingerless gloves is a damn good tip though ! I'm armed with a red LED headlight and wolly hat, and have no qualms at all about looking a right plonker. I do find I'm spending most of my time looking at the nightime weather forecast...Thanks for all the encouragment !