I've noticed that for the past few months, the photos released by NASA from the James Webb Space Telescope seem less sharp than before. Was there a technical problem? Or is it just my impression looking at the images on my phone?
The James Webb is still functioning correctly, so there hasn't really been a major malfunction that would explain a general loss of sharpness. It's probably a matter of what you're looking at and how. NASA publishes images processed in very different ways depending on the observations - some are mosaics assembled from multiple exposures, others are heavily compressed when they go online to save bandwidth. If you're viewing them on your phone, JPEG file compression can really degrade fine details. The actual raw telescope data remains available in public archives, but it can be a bit disappointing to the naked eye precisely because the telescope captures in infrared and they need to be reprocessed for them to make sense.
Another thing to consider is that the targets being observed vary enormously. Webb doesn't just observe distant, sharp galaxies - it also looks at dust clouds, exoplanet atmospheres, things where the details are by definition blurry or diffuse. If you've noticed that across several different images, there's a good chance it's simply because the latest published observations were of objects that are less visually "sharp." NASA also continuously adjusts its processing procedures based on what works best, so image styles can change from one month to the next without anything being wrong.
You might have that impression because you're looking at it on your phone - small screens make everything look less detailed. JWST hasn't had any major technical issues since its launch, well nothing that would've seriously degraded its capabilities. Plus you gotta keep in mind that NASA doesn't just publish super high-res shots of their best observations - sometimes they release composite images or less processed data. If you actually compare the raw images from before and now, they should be at the same level.
Don't assume it's necessarily a technical problem with the telescope itself. What could explain what you're seeing is that NASA sometimes publishes raw or less processed images than others, and it also depends on what the instrument is observing (cosmic dust, very distant sources). Since you're looking at them on your phone, you're naturally going to perceive fewer details than in full resolution on a screen, but honestly, the images that have been published over the last few months are still at the level we've had since the start of the mission.
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