Mimi napiga picha shambani.

napiga breaks down into three pieces:

• ni-: 1st person singular subject marker (“I”)
• -na-: present tense/aspect marker
• piga: verb root “to hit/shoot,” extended to “take (a photograph)”

So ni-na-piga contracts to napiga, meaning “I (am) take-ing.”

• napiga (ni + na + piga): present/progressive—“I am taking,” or “I take” (right now or in this context).
• hupiga (hu + piga): habitual—“I usually take.”

Use napiga for actions happening now or in the current situation; use hupiga for regular/habitual actions.

Swahili marks location by adding the -ni suffix to a noun:

• shamba = “farm/field”
• shambani = “at/in/on the farm”

This suffix replaces English prepositions like “in” or “on.”

Yes.

• katika shamba = “inside the farm,” using the preposition katika
  • noun.
• shambani = “at/in/on the farm,” using the locative suffix -ni.

Both are understood, but shambani is generally more idiomatic for “on/in the farm.”

picha is in noun class 9/10, which means the singular and plural forms look identical:

• picha = “picture” or “pictures”

Swahili has no articles (“the” or “a”). Definiteness or number is inferred from context or added with demonstratives (e.g. picha hizi = “these pictures”).

Use the present negative pattern:

• si-: 1st person negative subject marker
• verb root piga with final -a changed to -i

Result: Sipigi picha shambani.
Optionally add Mimi for emphasis: Mimi sipigi picha shambani.

To ask “Are you taking pictures on the farm?”:
Je, unapiga picha shambani?
(You can drop Je, in casual speech: Unapiga picha shambani?)

To say “I took pictures on the farm” (past):
Nilipiga picha shambani.
(breakdown: ni- + -li- past marker + piga)

To say “I will take pictures on the farm” (future):
Nitapiga picha shambani.
(breakdown: ni- + -ta- future marker + piga)