reservists

As I recall from comments at the image below, the helmet with a ball on top is Artillery. There was an Artillery Barracks in Waterford (now gone) and in this 25" map, I see a passage with steps which matches, at the NE side of the Eastern corner of the barracks buildings, at the spot now occupied by St. Carthage's Avenue.

This has to before 1922, and probably before 1914, too.

Stripped button down collar shirt, very cool.

Could they belong to the Royal Munster Fusiliers? The ball-and-flame collar badge on both uniforms is very like that of the RMF (and also like that of the Royal Inniskilling Fusiliers and that of the Grenadier Guards)... They're like the one used by the Royal Artillery too, but they lack the 'UBIQUE' banner at the base.

No... having looked at the buttons and helmet more closely, they clearly belong to the Royal Artillery

Opposite: Etablissement Duval, to the right Hotel de Lorraine, to the left possibly Restaurant a Coeur Doux. This seems to be in the vicinity of the Brasserie Bougeneaux (see the comment to the picture below) but if so this looks very different today.

Looks like the right edge of the Bougeneaux's awning at the left side of this photo.

This is the Brasserie Bougeneaux in the Boulevard de Strasbourg, 10th Arrondissement of Paris: Baedeker: Paris and Environs, 1913: Gare de l'Est (PI. B, 24; p. 217) : Brass. Bougeneaux, 9 Rue de Strasbourg, corner of the boulevard ; No. 11, Rest. Schaeffer, good ; No. 13, Rest. de l'Hot. Français (Barbotte); No. 8, Coeurdoux plain, but good; No. 6, corner of Rue d'Alsace, Bouillon Duval; No. 5, Terminus Est, at the hotel (p. 10). — Drouant, 79 Boul. de Strasbourg, corner of Rue St-Laurent, a large and very popular establishment (oysters). Today's view: maps.google.com/maps?q=9,+bd+de+strasbourg,+paris The Bd de Strasbourg does in fact lead directly to the Gare de l'Est (note correct capitalization).

The presence of a flag of known colors clearly visible in the image gives us a rare opportunity to reasonably determine what filter was used over the camera's lens. Assuming that the color pattern is correctly oriented towards us, the stripes would be blue-white-red. From the relative shades of these colors on the flag, and based on my limited filter experience, it seems reasonable this photo was taken with a green filter, which is normally reserved for portraits. But please correct me if I'm wrong!

Interesting idea! I see two problems: 1. the flag might be hoisted on the wrong (red) side – even though the bearer looks like a gendarme, so he should know what he is doing, and 2. the colors might not be standardized as today, in particular the blue might be lighter. I did a little crude test with digital filters off today's standardized tricolore, and in all cases the blue came out darker than the red.