The site search function can be limited. However, as @Archie explains Goggle is useful to search the forum, particularly by images, plus @Archie's tip can be used to search threads by topic, such as 2DOF: http://www.xsimulator.net/community/threads/forum-searching-tips-for-images.7507/

Open up Google, and type:

site:xsimulator.net/community

Followed by the search query. You can use the "+" symbol to looks for all your words (search a phrase)

I searched for: best+angle+for+a+shoulder+mount
(so full text is: site:xsimulator.net/community best+angle+for+a+shoulder+mount)

Let Google do it' search and then click on Image in the Google search results.

You can see the results here:


Then click a picture that looks like it's what you need:


Then click the "Visit Page" button to go to the post that talks about shoulder mount angles: