About your scopes?

[swamp thing]

Hi

Just two scopes for me at the present.

One is a 10" Dob for general everyday observing from local sites.

The other larger 16" Dob is for dark skies only.

I would like to add a RFT at some point, but a bigger dark sky scope is the priority at the moment.

Regards Steve

[ronin]

Pitbull: An APO is a refractor.

To be APO the focal plane for all the visible wavelengths has to be very narrow. Think (but not sure) that it is all within +- 1/4 wavelength (probably the green wavelength). Try google and Wikipedia.

This means no discernable colour aberation.

The term APO also includes spherical aberation limitation, just not sure what the specification is for that aspect.

It used to be that to make an APO you had to use 3 len's, however with the maufacturer of new glass tyoes, fpl-51 and fpl-53, you can make an APO from 2 glass types. Not sure about the spherical aspect - that seems to get forgotten.

One thing to remember is that the glass types allow you to make an APO, the design and grinding are the bits that actually make the APO.

[Pitbull]

Ronin,

Thanks for that explanation, it helps us newbies clear the fog in this huge hobby

[brantuk]

"Excuse my ignorance but what is APO?"

Apochromatic or colour corrected, as opposed to achromatic wich isn't. Achro's only bring two wavelengths to focus (usually red and blue) - appo's focus red/green and blue. Both are corrected for sherical abberation.

You'll see this manifested as a coloured tinge around an object using an achro - the full moon is a good example where you'll see a yellow or blue tinge on the limb - in an appo I'm hoping this doesn't happen cos I just got a triplet and still waiting for chance to "first light" it lol

[Wardd2]

i have a skywatcher 130 and i went for it as it was the largest telescope i could afford at the time. i couldnt get a dob as i have a storage issue especially with the base. i am planning on keeping mine for a while and then maybe thinking about a serious upgrade, to what i dont know yet