I have been to 22 different countries with my camera gear, DO NOT declare any of it! You are not importing or exporting goods so it is not declarable. If you do you are asking for a whooping.
And the reason why you would generally take that approach is that your camera gear is classed as "personal effects" - most countries aren't too concerned about goods you take in for re-export. Most countries also don't like to develop a reputation for making things difficult for tourists.
I think the exception is, for some countries, registration of equipment you take with you when leaving your country of residence, especially when you live in a "rip off" country (e.g. South Africa) where electronics and cameras are very expensive, and residents tend to buy new "toys" when overseas.
When I used to live in South Africa, I always diligently registered my camera gear for re-importation, but was never once asked for any documentation when returning.
When entering Australia I have always found that customs are more concerned about whether or not your shoes are clean than about whether you have commercial amounts of camera gear with you. - I guess, do not admit to Australian customs that you have had your camera on a farm in South America - they might want to wash it for you! *grin* - More seriously - if Australian customs think you have had your camera bag in the bush and it looks dirty, they might insist on washing/decontaminating it!
Of course there is always the warning that someone will find a country where these general rules do not apply...