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Red Dot finders with blurred dots!


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I have two Baader Planetarium Sky Surfer Red Dot finders and a third William Optics red dot finder. On each of these finders the red dots have each 'degraded' until they a indistinct (thus inaccurate) blurred 'splodges.  I can see no way of asdjusment to bring the dots 'to focus'.  Is there a remedy?

Sadly, all three are well out of warranty period thus returning them to their respective suppliers is out of the question.  Anyon eelse found this problem?

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Your sig implies you know what you're doing. For beginners, I'd ask if they were simply using the finders incorrectly. 

Three such finders have failed you? Over what kind of period? Have you been cleaning/wiping dew from them? Do you have any others which are still working ok to compare them to?

Would you be able to take a photo of the problem?

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When you focus your eye on the body of the finder, the red dot is out of focus. When you focus your eyes for infinity the red dot is sharp and the body of the finder unsharp.

Could it be that you compared the red dot to the body of the finder?

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  • 2 months later...

Another thing worth checking is the glass/plastic screen that the dot is displayed on. If there's a film, be it from oily fingers, salt air etc, it can cause the light to diffract. Just a thought :)

Also, check the batteries?

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If your eyes get worse and need glasses then you need to wear them, or get some.

I do not think an RDF "produces" a dot.

It produces a collimated light beam that when it enters the eye is focused by the eye to a dot.

So if you need glasses the beam is incorrectly focused.

In an RDF I would expect:

Red LED, Pin hole, Collimating lens, Beam splitter/combiner.

The LED illuminates the pin hole, the pin hole is used as a souce and collimated by the lens, this collimated beam hits the splitter/combiner and half is reflected back at you. When the collimated beam enters the eye the eye lens refocuses it back to a dot, that being the pin hole.

So if the eyes need compensation the dot will be out of focus = fuzzy, when observed.

Edited by ronin
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I have two Baader Planetarium Sky Surfer Red Dot finders and a third William Optics red dot finder. On each of these finders the red dots have each 'degraded' until they a indistinct (thus inaccurate) blurred 'splodges.  I can see no way of asdjusment to bring the dots 'to focus'.  Is there a remedy?

Sadly, all three are well out of warranty period thus returning them to their respective suppliers is out of the question.  Anyon eelse found this problem?

I have an observation based on my new finder. If I put the 'lens' of the finder against my hand, the dot is very out of focus. If I hold the finder at arms length and view something in the distance through the lens, the dot is perfect.

It's not the finder, it's what your eyes are doing

Richard

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