Has anyone attended any of the third party lens mfrs.' sponsored workshops, on their equipment or on nature, landscape, sports photography, etc. ? I see a few offerings in various topics of nature and landscape and macro, by such as Tamron, Sigma, and Tokina and wondered if anyone has attended these type workshops, before I sign up, and if you recommend them? Although the ones I see are shorter in days(usually 1 day) than many workshops, I would be interested in them.