flip up or ttl I think is a personal preference.
The quality of optics in loupes should be the first consideration while purchasing a loupe as this may have direct bearing on our eyes.
Being more experienced, What do you think on this subject, Dr. Jeff?
This should sum up my opinion on this topic.
I own 3 pairs of loupes. A flip up pair of 2.5x Heine's that I bought in d-school because they were the most competitively priced and hardly ever used because of their weight. I ended up preferring to just use regular, non magnified safety glasses for years rather than the Heine's
A pair of 2.5x TTL rigid framed orascoptic's that I use for most of my day to day work (and have used for the last 5+ years now)
And a recently purchased pair or 3.8x rigid framed orascoptics that I use for endo, most crown and bridge, and some select anterior esthetic direct composite cases.
As for quality of optics and its importance, I strongly feel that BOTH the quality of optics AND the comfort of the fit are essentially equal in importance. If the optics quality is great, but overall the loupes are uncomfortable while you're wearing them, then what's the point as your likely to start bending your neck/back in ways that can cause muscle issues/pain long term - hence why more than often clinicians don't use flip ups as no if's and's or but's about it, they're heavier than TTL's and cause more neck muscle issues. Secondly, if they fit great, but have optics issues - such as variations in the intrapupillary distance due to frame flexibility or an improper original fitting, then you're more than likely to have eye strain/fatigue which can lead to headaches, etc.
Bottomline, is when you put your loupes on, the less variables involved, and the closer they are to the weight of just a regular pair of eye glasses the better longterm performance you'll be getting everyday, which will allow you to function better, longer at your job.
