Old photos and smiling.
The best 'smiling' photos are those taken outside at this time. Why? Exposure times. HOLDING a smile is difficult for many. Outside, on a good sunny day, the exposure times were a matter of seconds - two or three for the best cameras or rather the mose sensitive emulsions. Emulsions were made on the spot and often developed immediately afterwards. Studio photo exposures were a matter of minutes - hence the need for stance props for practically all standing portraits, and head props for seated portraits.. Many smiles that do appear look faint or blurred because the pose could not be held for the full length of the exposure.
This applies to any movement, hence the blurred horses tails and legs or the blurred faces and heads in group photos and the rather wide bayonets. It also applies to the flags and standards - the wind does it's own thing! The instructions to the subject were 'stand as still as you can' or 'relax and stay that way' which is why the group photos all show troops at 'parade rest' - the easiest position to hold for a length of time.
As always - remember that photos like Brady's were negative prints and usually the right way around but tintype and Amro were direct mirror images (flip vertically). Coat fastening and rifle locks are a good indicator, but buttons, buckles and insignia were often 'tinted' or 'guilded' to hide the mirrored lettering and numbers.
View attachment 531395
c 1861 An infantry company at 'Parade Rest' (Brady)