Astrophotography by Rob


WO Fluorostar 110 (FLT110) Lens Cell Problems

I had an issue with my WO FLT where right across the field the stars appeared to be suffering the effects of coma. This effect is usually seen at the corners and edges comaof an image due the the focal plane not being flat. Usually with coma the resultant deformation of the stars is oriented away from the centre of the field. In my case the deformation was identical right across every image. To the right is a diagramatic representation of the deformation of stars due to coma.

What I found was that the lens cell had become loose. I guess this introduce a bit of slop that resulted in the deforned stars. Once I tightened the cell the problem disappeared for some time. However, I regularly checked and tightened it.

Some months later the problem reappeared. I could not tighten the cell and have the problem dissapear. I also noticed that the cell got tight quick but could still be tightened further with more effort. Things did not appear to be normal. I removed the lens cell to investigate the problem. What I found was that there are two rings that are used to hold the glass in place. The outermost one had unscrewed quite a lot. I guess this had gradually unscrewed and I have been only tighening the telescope body against this ring. After screwing in the ring as far as I could and replacing the lens cell the problem was resolved.

If you have had this problem please let William Optics know. This is an engineering problem that they should fix. I read on a forum that a member almost dropped his lens cell because it had worked its way completely loose.



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