60x resolution problem follow up (1 Viewer)

Po'ouli · Dec 30, 2006

Well, my Diascope 85 made it safely back to Eagle Optics, but when I spoke to the rep there, he said it looked as good to him as their other Diascope 85's. I don't see how that can be, but that was his assessment. I explained the problem I had and how the scope performed on a simple star test. He responded that star tests aren't valid on scopes with prisms, but if I wanted to do one, I would need to do it repeatedly over a month to account for atmospheric effects. To their credit, they were very nice and even paid for return shipping, so I certainly have no complaint with EO. But after my experience with the scope and then talking to them for awhile, it sucked all the enthusiasm for spotting scopes right out of me. The vacation I had planned around the scope was already shot, so I'm afraid I've given up. I've been a loyal Zeiss user for many years (3 pairs of Zeiss binoculars), but now I'm feeling a bit wary of their quality control. For now I'll just be sticking to the binoculars I have. Thanks to all who responded to my original thread. I appreciate the help.

Bruce

henry link · Dec 30, 2006

Bruce,

What you were told by Eagle Optics is rubbish, plain and simple. I can well understand why birding scope dealers and manufacturers don't want people to star test the scopes they sell. In my experience an alarming percentage of birding scopes are at least mildly defective. Returns would skyrocket if every scope with a little astigmatism or slight misalignment were sent back.

A few years ago a friend of mine bought a Zeiss Diascope. He was not experienced with scopes and was perfectly happy with it. When I saw the scope I was appalled by its poor image even at 30x. I star tested it and found very serious defects. When it was returned to Zeiss my friend was told exactly what you were told by Eagle Optics; the scope is performing just as it should. I phoned Zeiss repair service and talked to the tech about it. To make a long story short I found their evaluation had been at best cursory and when I described the problems in detail they agreed to replace the scope. The replacement was defect free and is still the best specimen of a Diascope I've seen. It not only star tested well (even with prisms!), but the image quality and measured resolution were much improved, just as you would expect.

Let me say it once again. Don't assume that expensive scopes are made with such care that defects are rare. If the image looks soft and refuses to snap into a decent focus at 60x there is almost certainly something wrong. A star test is the best tool we consumers have to tell us exactly what is wrong and how bad it is.

Henry

scampo · Dec 30, 2006

I'm certain that Zeiss' quality control is as good as the best in the industry. I really wouldn't take much notice of what you were told by EO, as good as their service turned out to be. The Zeiss 85 is a top model from a top maker - you've probably had one that has been dropped in transit or something like.

Henry B · Dec 30, 2006

How do you star test a scope ? sorry for being a nuisance.

Po'ouli · Dec 30, 2006

henry link said:
Bruce,

What you were told by Eagle Optics is rubbish, plain and simple. I can well understand why birding scope dealers and manufacturers don't want people to star test the scopes they sell. In my experience an alarming percentage of birding scopes are at least mildly defective. Returns would skyrocket if every scope with a little astigmatism or slight misalignment were sent back.

A few years ago a friend of mine bought a Zeiss Diascope. He was not experienced with scopes and was perfectly happy with it. When I saw the scope I was appalled by its poor image even at 30x. I star tested it and found very serious defects. When it was returned to Zeiss my friend was told exactly what you were told by Eagle Optics; the scope is performing just as it should. I phoned Zeiss repair service and talked to the tech about it. To make a long story short I found their evaluation had been at best cursory and when I described the problems in detail they agreed to replace the scope. The replacement was defect free and is still the best specimen of a Diascope I've seen. It not only star tested well (even with prisms!), but the image quality and measured resolution were much improved, just as you would expect.

Let me say it once again. Don't assume that expensive scopes are made with such care that defects are rare. If the image looks soft and refuses to snap into a decent focus at 60x there is almost certainly something wrong. A star test is the best tool we consumers have to tell us exactly what is wrong and how bad it is.

Henry

Henry: Thanks for the thoughtful reply. Your many posts on Birdforum have been a real education for me. I hope you don't mind a quick question about star tests. At what point in the de-focusing would you expect to see the pinching or elliptical shape that indicates astigmatism? On the Diascope I had, as soon as I began to de-focus, the spiky star image would go through a tiny bowling pin shape before becoming a circle. But it only occured when the image was tiny, so I discounted it. For future reference, would that be a concern?

Thanks,

Bruce

Swissboy · Dec 30, 2006

Henry B said:
How do you star test a scope ? sorry for being a nuisance.

You should find plenty of info if you use the search function!

Paul Jarvis · Dec 31, 2006

What does a star test prove? if the image from the scope is pin sharp at every mag (zoom) that should be all that matters. If not you may have a bad body or eyepiece and can be resolved by taking it back and working out what is faulty.

Pileatus · Dec 31, 2006

Po'ouli said:
Well, my Diascope 85 made it safely back to Eagle Optics, but when I spoke to the rep there, he said it looked as good to him as their other Diascope 85's. I don't see how that can be, but that was his assessment. I explained the problem I had and how the scope performed on a simple star test. He responded that star tests aren't valid on scopes with prisms, but if I wanted to do one, I would need to do it repeatedly over a month to account for atmospheric effects. To their credit, they were very nice and even paid for return shipping, so I certainly have no complaint with EO. But after my experience with the scope and then talking to them for awhile, it sucked all the enthusiasm for spotting scopes right out of me. The vacation I had planned around the scope was already shot, so I'm afraid I've given up. I've been a loyal Zeiss user for many years (3 pairs of Zeiss binoculars), but now I'm feeling a bit wary of their quality control. For now I'll just be sticking to the binoculars I have. Thanks to all who responded to my original thread. I appreciate the help.

Bruce

Bruce,
Get a Nikon ED82 with a 30X DS eyepiece. If it isn't stunningly sharp to your eye, send it back. It will cost you $1320 and you'll never bird without a scope again.

John

Henry B · Dec 31, 2006

Swissboy said:
You should find plenty of info if you use the search function!

Thanks Robert. :hippy:

henry link · Dec 31, 2006

Po'ouli said:
At what point in the de-focusing would you expect to see the pinching or elliptical shape that indicates astigmatism? On the Diascope I had, as soon as I began to de-focus, the spiky star image would go through a tiny bowling pin shape before becoming a circle. But it only occured when the image was tiny, so I discounted it. For future reference, would that be a concern?

Thanks,

Bruce

Bruce,

The oval shape of astigmatism would show immediately with slight defocusing. The appearance of the "star" at best focus and close to best focus (2-3 rings out of focus) is really the most important area. Problems tend to become less visible and the pattern more circular as you move very far out of focus (beyond 6-8 rings). 60x is really pretty low magnification for a thorough star test of an 85mm scope. The tiny diffraction pattern close to focus at 60x would be easier to see above 100x, but 60x is usually all we have to work with in birding scopes and it's usually enough to show the common defects. I've never actually seen the roof prism defect you encountered. I think Kimmo Absetz has seen it in a few scopes.

Henry

60x resolution problem follow up (1 Viewer)

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Po'ouli

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scampo

Steve Campsall

Henry B

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Swissboy

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Paul Jarvis

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Pileatus

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