On 12/15/2020 11:38 AM, Mark Christensen wrote:
Regarding your experience, Paul of Rochester Hills (Livonia was my old stomping grounds) , I received one of these 60mm guiders (direct from China on Ebay) when they first came out a few years ago.
When looking thru it with an eyepiece I noticed similar problems.
I suspected that the objective had been installed backwards. So all I had to do was unscrew the front and flip the (cemented) lens. Problem solved.
I notified the factory in case they had an assembler/fitter who needed a bit of training.
The images are generally fine now. Never worried about HFD, FWHM or any other parameter. But having to had a filter (beyond the cut filter in the camera) should not be necessary.
By the way, you don't want absolutely perfect focus on a guider - if the centroid algorithms are anything like the norm, the more pixels the better, assuming the image doesn't become too dim.
But you don't want coma.
Cheers,
Mark Christensen
St. Charles, IL
Thanks for that! When I first got the scope I wanted to remove the dew shield to make the overall length shorter. That is when I discovered that the dew shield also holds the objective in place. when the objective fell out, I lost track of which was was front so I tried it both ways and backwards from what it currently is... is much worse. I am aware that single pixel stars are not good but without the minus violet filter they are VERY blobby. With the minus violet they are quite a bit better which says to me there is purple fringing sufficient to degrade a monochrome image.
There is also coma in a good part of the FOV. All of which I have to assume will degrade the accurate determination of a stable centroid in anything less than perfect seeing?
FWIW, with a 30mm eyepiece it looks great. But put in a 4.5mm Lanthanum eyepiece for a view similar to the FOV with the guide camera and the image is not at all sharp and very low contrast.
Funny.... I grew up in Glenview (NW of Chicago) and lived many years in Evanston before I moved to SE Michigan ;)
Paul
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Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com
