My images from my 15028 show a definite coma. I have had a bash at refining collimation which has improved the look of my flat frames (less vignetting) but I haven't tested it on real stars yet.
I have found a review in Sky & Telescope which suggests moving the reducer 1 - 2mm closer to the sensor. My problem is that the reducer screws into the focusser and requires a tool to remove it, when I received the telescope the tool was missing. I was told that someone had been performing an adjustment and the tool had disappeared.
The tool consists of two prongs which fit into corresponding holes which can be used to turn the reducer to unscrew it. I have tried a piece of bent fencing wire but that was too flexible.
Can anyone tell me what the two pronged thing is called and where I might get hold of one? Alternatively, has anyone a suggestion for making something which will do the job?
Thanks,
John
You can get tools for removing the retaining rings for camera lenses which might do the trick e.g.
https://www.ebay.co.uk/itm/Pro-DSLR-Lens-Repair-Spanner-Wrench-Open-Tool-10-100mm-for-Canon-Nikon-Camera/124023579347?hash=item1ce061a2d3:g:ze0AAOSwBXleBIdF
(https://i.ebayimg.com/images/g/ze0AAOSwBXleBIdF/s-l1600.jpg)
Thanks,
I've immediately found and bought one.
John
A very interesting scope you have there John. Lots of chat about loose screws, flopping mirrors and difficulty getting all the bits to be concentric on the forums as well as the correct spacing. But they are talking in terms of +/- 0.3mm!:-
https://www.cloudynights.com/topic/663055-new-sharpstar-15028hnt-initial-impression-with-pics/page-5
As you suggested, collimation seems to be pretty critical with these beasts.
Interesting that the secondary position can also affect it (but logical I suppose).
Lots of luck
Noel
Quotedifficulty getting all the bits to be concentric on the forums as well as the correct spacing
Aluminium foil is your friend.
Standard household foil is typically 0.016 mm
Very very adjustable, especially for shims.
Mac.
Also you can take leaves off a feeler gauge and have known thickness shims which are much more solid - they are dirt cheap on ebay.