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Old Saturday 7th October 2017, 18:59   #1
hr21
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Join Date: Aug 2016
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Pentax SP 12x50 WP collimation

Dear All,

I have recently purchased these and they arrived today.

I have a query about collimation (they were used but in 'very good' condition - inspection suggests brand new just missing their box)

At range (say looking at something about 1km away) the image is good, no signs of double image at all - very central. Very clear too.

However, looking at something say, 20ft away, the image does show signs of more double image, not a single circle but rather more a double image showing. It is clear still but not quite right. I have tested my daughters RSPB puffin and they do not do this but of course their close focus is much closer than 20ft whereas these is about 20ft.

I'm wondering...

Is this normal from such a high powered pair?
How can I test definitely the collimation?
Should I keep them or send them back?

Thanks.
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Old Saturday 7th October 2017, 19:10   #2
Binastro
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The Pentax 12x50 SP is I think a Porroprism binocular with wider objectives.
Close up the effect you describe can occur.
Try altering the IPD, see if it helps.

The Puffin may be a roofprism with narrower spacing.

So long as at middle and far distance you have no eyestrain at all it should be O.K.
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Old Saturday 7th October 2017, 19:35   #3
hr21
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Quote:
Originally Posted by Binastro View Post
The Pentax 12x50 SP is I think a Porroprism binocular with wider objectives.
Close up the effect you describe can occur.
Try altering the IPD, see if it helps.

The Puffin may be a roofprism with narrower spacing.

So long as at middle and far distance you have no eyestrain at all it should be O.K.

Thanks - what is the IPD?
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Old Saturday 7th October 2017, 22:48   #4
Binastro
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Interpupillary distance. The distance between your eyes pupils.
This varies without optical aid as one looks closer.
But varying the eyepiece separation with binoculars can help with nearer views.
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