I'm running into a strange problem, there seems to be a dark spot in the middle of my model, as if the camera was casting a shadow? I can't find any information on this, I attached a render with a completely blank/white environment. As far as I understand the band in the middle of the model should be uniformly silver/grey since the light coming from all directions is the same, so where is this shadow coming from?
Can you share the scene?
Are you looking at the bottom view and seeing the ground shadow possibly?
I can not share the 3D model sorry.
No it is a side view, however I tried to rotate the model and the effect persists. I have noticed that it only appears with a metal material type, if I change it to plastic I get the expected behaviour of a uniform colour.
The HDRI is all white you said?
I may be wrong, but I blame the fresnel effect:
I added a sphere to a KeyShot session, applied all white HDRI and then applied anodized black material to it and you'll see the results in the first image attached.
I then changed it to plastic and you see the results in the 2nd image attached. Same as your results, right?
The reason for this behavior is called fresnel. Metal is highly specular and therefore is going to reflect your environment. As the sphere's surface becomes less and less perpendicular to the camera in KeyShot, the amount of reflectance you see on the sphere increases. Theoretically, this is happening in the plastic one too, but just not to the same degree. If you increase the IoR (to more closely simulate a metal and change the specular value to white, you'll see the same effect start to take place.
I hope this helps to clarify. I studied industrial design in school and when we had to create marker renderings, that dark reflection in the center of an object was called the 'core shadow' even though, it's a reflection to help explain the form of the object. What you're seeing is 100% correct.