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''There is nothing like seeing an original. They are such a beautiful object,'' she said.
She oversees the photography collection, including the climate-controlled vaults where film negatives and glass plates, and at-risk film and slides, are stored at 12degC and 2degC respectively.
As well as depicting New Zealand over time, the collection also shows the development of photographic technology including daguerreotypes, prints, albums, postcards, panoramas, 35mm slides, lantern slides, glass and film negatives and digital files.
Part of the collection is albums - there are 600 of them - including one by Dr T. M. Hocken, which has the earliest documented photo of Otago, taken in 1864 or 1865.
Much of Petersen's job involves helping people with research inquiries.
The photographs show so much of the country's early days.
''If people wonder about what the original foliage looked like around Lake Wanaka, then one of the best sources of information is photographs.''
Petersen has an art history background and used a lot of historical photographs for her PhD thesis.
''That is how I became familiar with the public collection.''
She says it is not only important to store photographs from a historical point of view. they are also beautiful in their own right.
''Despite what you can do with a high-resolution scan, there is nothing like seeing the original.''
So being able to display works in their original form is special, she says.