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Which Refractors Pinch?

Astro-Tech AT115EDT Astro-Tech AT60ED Equipment Refractors Buying Advice
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Phil Creed avatar
Phil Creed avatar
I currently have an NP101 and an AT60ED.  Prior to that, my imaging scopes have been an AT115EDT, a Stellarvue SV70T and an AT92.

My NP101 has no pinching even in brutally cold conditions, and I've had no issues with any for pinching in cold weather except for the AT115EDT.  With the AT115EDT I had (and I'm not sure how prevalent this was), 40°F seemed to be the cutoff between round stars and stars with artifacts.

This was from a scope acquired several years ago.  I've heard similar complaints about pinched optics with imported refractors in cold weather, but I don't know if anything's been done to remedy this in recent years.

If I decided to go for more focal length than my NP101's 540mm, there's plenty of options.  But living in NE Ohio = lots of cold nights.  What other scopes are great in cold conditions, and which ones are pinching these days?

What about current Stellarvue offerings like their SVX130T and SVX140T?  Taks?  TECs?

Clear Skies,
Phil
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Nick Grundy avatar
Nick Grundy avatar
just to clarify, Is pinching an issue with design? (being exacerbated by cold weather) or is it more of a quality control issue with cheaper scopes and some samples exhibiting issues?

and by "pinching", you mean astigmatisms or other issues showing up in edges/corners?
Engaging
Phil Creed avatar
Phil Creed avatar
Nick Grundy:
just to clarify, Is pinching an issue with design? (being exacerbated by cold weather) or is it more of a quality control issue with cheaper scopes and some samples exhibiting issues?

and by "pinching", you mean astigmatisms or other issues showing up in edges/corners?

Something like what's described here:

https://www.cloudynights.com/topic/815804-pinched-optics/

Clear Skies,
Phil
Nick Grundy avatar
Nick Grundy avatar
Phil Creed:
Something like what's described here:


that actually looks like the diffraction spikes I get from a stopped down camera lens
Sean Mc avatar
Sean Mc avatar
The image above doesn’t look like pinched optics to me. (Aside from the spikes). I’d send that scope back if it was a refractor.

edit: it looks like the CN op actually get a replacement lens cell.
Nick Grundy avatar
Nick Grundy avatar
Sean Mc:
The image above doesn’t look like pinched optics to me. (Aside from the spikes). I’d send that scope back if it was a refractor.


if you mean the image I posted above, it's from a camera lens I had almost wide open at F2 (the sigma 105). I did end up sending it back though