I often start with Google for the search to begin with, by typing in the name of the lens and do an image search. I can, for example, type in "Eurynar" and in the search results I might see a landscape photo posted on this forum. Since there may be hundreds of photos posted taken with different lenses in the photo threads here it's not likely that the photo Google suggested was taken with an Eurynar lens, but that there may be one in the thread somewhere since the lens was mentioned, so I click on the link and get a printer-friendly page with no images. Then I'll have to search for the word "Eurynar" on the page, find it and look at the date the post was posted. Then click on the normal forum view and manually search for that post. Sometimes I find it with the photo still there and sometimes it's gone because it's old.
Using the "site:" trick on Google doesn't help in this case. It will find the threads but not the specific posts.
It's easy, however, to find plain discussion threads about certain topics.
Have you tried using the "search thread" feature? That is, once you've determined by whatever means that the search term of interest to you exists somewhere in a long thread, open that thread and use "search thread" to find the specific posts in which that search term occurs.
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