Measure equipment in its carrying arrangement
Decide whether the camera will travel with a lens attached or as separate components. That changes the compartment shape required. Measure the whole assembly, including a projecting viewfinder, grip and lens hood where those will be packed. The camera body's specification sheet alone does not describe the space occupied by your actual setup.
Arrange the equipment you genuinely intend to bring on a soft surface. A second lens, charger and spare battery need places, but not every item must be inside the same insert. Consider which objects need to be accessible while out and which are only required in the evening. A clear distinction reduces how much you have to move whenever you want to take a photograph.
Test the insert and backpack together
Compare the outside dimensions of the filled insert with the backpack's usable interior. The opening can be narrower than the compartment behind it. You should be able to remove the insert without forcing it. Check that enough space remains for a jacket and personal belongings and that hard objects do not press into your back.
Adjustable dividers only help when they remain securely attached. The camera should not knock loosely against other components, but should not be wedged tightly into place either. Check that padding covers the intended contact points. A soft pouch does not protect against every load and cannot turn an unsuitable backpack into an impact-resistant transport case.
Set the backpack down carefully and open it in the position you will use to retrieve the camera. Does the insert tilt, or does a compartment suddenly face sideways? Quick side access is only useful when it works safely with the actual arrangement. Practise removal on a calm, stable surface before attempting it in a crowd.
Consider weather and other contents
Keep drinks and potentially leaking products separate from the camera insert. Water-resistant fabric is not a general guarantee of protection in heavy rain. Read the manufacturer's information and plan suitable additional weather protection where needed. It should be accessible before equipment gets wet, rather than buried beneath everything else.
Weigh the loaded combination and carry it on a longer walk. If it becomes uncomfortably heavy, reconsider the equipment selection first. Extra inserts and padding add weight too. A limited setup can be more comfortable for a city visit when it still suits the photographs you plan to make. The transport system should make the equipment easier to use, not encourage you to fill every remaining gap with another accessory.
