Difference between an APO scope and an achromat

[MooEy]

aiya, no point counting all those figures la. bound to have some error here and there. the error in ur diagonal is going to be way more than your tube.

the main thing that we look at is how the optics converge the light. there's alot of factors in making a gd scope, not just whether the tube will bend under stress of the weight. spherical abberation and crossing of wavelength are more important.

usually before a tube is sold, it is being collimated, this pretty much remove most of the problem associated with the misalignment.

the rest of the accuracy of the focal plane is usually compensated by the dof of the optics. unless ur tube is going to be off so much like the focuser in my scope(although it's fixed now), there isn't alot of difference.

anyway, it would be interesting if chaosknight could machine a tube for a scope. maybe one day someone could work with him and make one. probably the first cnc machined telescope that is made in singapore.

about the question which weixing asked, i believe he can answer this question way better than me. no point for me to answer.

~MooEy~

[VinSnr]

Hi,
Since the topic had been change to Difference between an APO scope and an achromat, I would like to ask the question:
What are the advantages of an apochromatic(APO) refractor over an achromatic refractor??

We all know that the main advantage of an APO refractor over an achromatic refractor is the very small or no chromatic aberration. But does anyone know what other advantages does an APO refractor have over an achromatic refractor ???

Have a nice day.

Better spherical abberation and better figure of the lens. This is one reason why an APO could normally go to crazy high powers but an achromat could not.

The chromatic abberation of an achromat could be minor for a good achromat, but it will still show purplish stars on photos. Of course, you can colour balance to get rid of that purplish hue, but you will affect the colours of other objects as well. So if you are into astrophotos and an die-hard one, then APO is a better choice for you.

[ChaosKnight]

Waah.....Mooey, CNC isn't cheap leh. And i've only seen solid alu rods, haven't seen any hollow tubes so far.

[MooEy]

haha, can one la. get someone to invest in one of those tmb objectives
105/6.2 looks like a gd start, or maybe the 130mm objective.

~MooEy~