Paradox.db.3

There's a part of the story I didn't share, but in short, I ordered a second copy of the lens with the intent of either returning it if it had the same "defect" as my original copy, or keeping it and selling my original. As it turns out, I'll be returning the new lens. Looks like the lens was not meant for taking Moon photos in my climate. At 600mm, the lens will not focus to infinity in colder than freezing weather. I noticed the strange behaviour in my original lens a couple of Winters ago, but didn't do anything about it at the time. After all, I don't like to shoot often in -35°C weather. But the lens also exhibits the same behaviour even at -10°C. Last night, I took both lenses out side by side in -10° weather and they both, at the same rate, began to lose the ability to manually focus on the Moon. The focus went as far as it could, and stopped just short of getting the Moon in sharp focus. I'm going to test one more lens, just to be sure, but I'm thinking this lens wasn't designed to be used in sub zero weather. At least not for astrophotography.

I have two lenses, both with slightly different coatings, as it appears. What does this indicate? I seem to get similar image quality from both, but haven't done a real world side by side test.

I realize that being new to the forum, I'm late in the thread. I sold my 55-210 and now use Tamron's 18-300. Yes, people say it's soft at 300mm but I don't see it so much. (I also don't do wildlife.) Plus it doubles as a great macro lens. As for price, it's comparable to the 70-350. It's the ultimate walk around lens, in my opinion. The attached image was taken with my Sony a6500 and Tamron 18-300mm at 180mm, f/20, ISO 6400, 8s shutter. I was about a foot from the tree.

Has anyone found a solution? My lens will stop focusing to infinity after being out in the cold for an extended period of time. Not sure it's the same issue.

I'm no expert in this camera (or even in this mode as I don't use it at all) but have you tried a factory reset?

As I understand it, the sensor has a filter placed overtop, so the sensor itself doesn't actually get touched when cleaned. I've cleaned the sensor in the past with cleaning mode first, and then resorted to a rocket blower next. If the dust is still present, I'll use a clean, soft lens brush to gently sweep away any dust, and then use the rocker blower again. When all else fails, I resort to the cleaning solution in the sensor cleaning kit. The last time I did this, it left streaks all over the sensor, so I performed the clean again to take care of any residue left behind. It all looks fine, and I don't see any scratches, but how often can this be done before it starts showing up in images (if ever)?

I saw another thread describing how the lens doesn't focus consistently at 300mm beyond a certain distance. My issue is temperature related, where once the lens is out in the cold night air for an extended period of time, it will no longer reach focus to infinity. These are nights where the temperature is below freezing. Anyone else noticed this phenomenon?