Pinched Optics?

Make sure your dew heater isn’t on full blast, wait for the scope temperature to settle.

I see them on occasion on my frac but usually only early in the night when temps drop, once it’s acclimated they go away.

Yes its pinched, but let’s rule out heat and acclimation first.

I agree with Brian. You would be surprised how common it is that they overtighten the elements in the factory.. one of the guys i know had to email their tech support and get an actual diagram on how to loosen the element. A simple way to test this is to make an artificial star from a flashlight and a pinhole in a piece of aluminium foil, and try to focus on it while you are inside with the telescope at room temperature and outside while it is acclimated. If it also gets worse in the colder months it is very likely that the element is overtightened and you might have to contact technical support for further diagrams. If you wish so i could also include the diagram they sent to him if you want to take it apart and do it at home yourself quicky, the systems are not gonna be far off from each other, there can Either be a compression ring that is more common on higher quality refractors or a very common grub screw.

Tony Gondola · Jan 26, 2026 at 09:50 PM

Jan Hlavačka · Jan 26, 2026, 09:34 PM

I agree with Brian. You would be surprised how common it is that they overtighten the elements in the factory.. one of the guys i know had to email their tech support and get an actual diagram on how to loosen the element. A simple way to test this is to make an artificial star from a flashlight and a pinhole in a piece of aluminium foil, and try to focus on it while you are inside with the telescope at room temperature and outside while it is acclimated. If it also gets worse in the colder months it is very likely that the element is overtightened and you might have to contact technical support for further diagrams. If you wish so i could also include the diagram they sent to him if you want to take it apart and do it at home yourself quicky, the systems are not gonna be far off from each other, there can Either be a compression ring that is more common on higher quality refractors or a very common grub screw.

Jerry is running remote…

That is way worse in that case.. if its a problem that happens just in the cold i guess its not that terrible, but if its pinched bad i think he is going to have to pay a visit

Jerry Gerber · Jan 27, 2026 at 01:32 AM

I am not sure the optics are pinched due to a mechanical issue.  I've been imaging remotely for 2 years with this scope and do not see this problem 90% of the time.   It may have to do with the cold weather, I don't run the dew heaters on high, I let the Pegasus powerbox automate the dew heating based on the dew/temperature sensor and it never gets near the highest setting. 

I'll have to experiment and also see if there's any way I can minimize the impact with processing..

Thanks guys!

You see, from my experience dew heaters wont help you in cold weather like this, people i know who had this issue had it pinched because the dew heaters do not have the capacity to keep the whole tube warmer, just the element. So the aluminium tube tends to contract and pinch the elements. It is really Hard to confirm this for me though, because of the resolution of the image. You can usually tell This is happening my seeing multiple distinct “cut” lines through the star, not just one. You can solve this by getting silver bubble insulation and wrapping the tube up, so its going to radiate all the heat out more slowly

lunohodov · Jan 27, 2026 at 08:11 AM

Jerry, is the dew heater strap wrapped around the objective lens?

During winter, I often image with temperature drops around the 0°F (-17°C) mark and have noticed something similar a couple of times. I haven’t seen anything after moving the strap away from the lens, closer to the edge of the dew shield.

I’m not sure how it works on refractors but that sounds like it would only delay the issue, I am 90% sure that would heat the air and cause local turbulence inside the dew shield

Jerry Gerber · Jan 27, 2026, 01:32 AM

I am not sure the optics are pinched due to a mechanical issue.  I've been imaging remotely for 2 years with this scope and do not see this problem 90% of the time.   It may have to do with the cold weather, I don't run the dew heaters on high, I let the Pegasus powerbox automate the dew heating based on the dew/temperature sensor and it never gets near the highest setting. 

I'll have to experiment and also see if there's any way I can minimize the impact with processing..

Thanks guys!

The think is Jerry, pinched optics are a mechanical issue. The dew heater is putting in just enough energy to warm the glass above the dew point. That can still be pretty cold and you can still get mechanical pinching of the optics by the cold tube and cell. The only real fix for this is resetting the objective so that it has a little more clearance in the cell. It doesn’t take much to make a difference.

Jan Hlavačka · Jan 27, 2026, 08:48 AM

lunohodov · Jan 27, 2026 at 08:11 AM

Jerry, is the dew heater strap wrapped around the objective lens?

During winter, I often image with temperature drops around the 0°F (-17°C) mark and have noticed something similar a couple of times. I haven’t seen anything after moving the strap away from the lens, closer to the edge of the dew shield.

I’m not sure how it works on refractors but that sounds like it would only delay the issue, I am 90% sure that would heat the air and cause local turbulence inside the dew shield

But I doubt that turbulence is the issue… John did an entire study of dew formation and prevention. The thread is on the bin.

lunohodov · Jan 27, 2026 at 02:23 PM

Jan, I don’t see what you’re describing.

John Hayes gave a great talk recently – The Physics of Dew Prevention, which I enjoyed very much. I highly recommend it.

Warm regards

Thank you for this guide!! This is very well Explained in detail

Jerry, is the dew heater strap wrapped around the objective lens?

During winter, I often image with temperature drops around the 0°F (-17°C) mark and have noticed something similar a couple of times. I haven’t seen anything after moving the strap away from the lens, closer to the edge of the dew shield.

Jerry Gerber:
Yes, it's wrapped around at the point where the actual lens is.