APO Guidescope and Centroid Determination

[André Vilhena]

Hello,

There are some guidescopes available on the market which are APO doublets. Do they make any significant improvement on guiding? I am thinking that maybe they can allow a better star centoid determination but I am not sure - the centroid on each wavelenght should be the same, shouldn't it?

Thanks,

André

[Bryan]

Andre

An APO guidescope is overkill.  Too many other factors, esp seeing and flexure, will limit guiding, regardless of the optics of the guidescope.  Personally, if you are willing to spend money on an APO guidescope, even a small aperture APO, I think the better value is an OAG, particularly if your imaging scope is longer focal length.

Bryan

[André Vilhena]

Hi Bryan,

Thanks. That confirms my thought. I was reading some papers from Craig Stark and from them I did not have the impression it would be a key factor. But them I saw a couple of people recommending them and doubt arose.

I don't image above 800mm FL - I have a 50mm f/3.8 scope which should be enough. I'll rather invest in brackets to replace the flimsy support.

Cheers,

André

[Bryan]

Andre

See attached for what I did with the ST-80 (8-0 mm f/5) before going with an OAG.  A third set of rings...inexpensive!  The farther out on the focuser/guider camera moment arm you can put it, the better.

That said, you do not need the same level of flexure mitigation at 800 mm that I need at 2500 mm...hence, my switch to an OAG.

You also should review this thread, as a check on your particular setup.

https://groups.google.com/g/open-phd-guiding/c/xE5SDi5S_1I/m/6EpDtPa7BgAJ

Bryan