Good Morning,
I'll toss in my 2 cents (or pence, since your across the pond in the UK) in. Yes, I agree that lighting is the key here. That said, the lens - not so much in terms of a focal length or macro, but how it lets you adjust it. What I mean by that is what is referred to as focus throw. So, what is focus throw?
- In general - new auto focus lenses do NOT have it, and the older manual focus lenses do have it.
That still does not tell you what it is. What focus throw is - is the following.
- The amount of rotation a lens has using the focusing ring.
- There is a ring, wrapped around the body that you turn in order to bring the object into focus. The more the amount you can turn the ring - the better. Some lenses have perhaps 20 or 30 degrees worth of travel from close focus to infinity - this is great for auto focus - less distance for the focus motor to turn, and thus the faster you can get auto focus. Bad for what you are going to be looking for, because you want a lot of travel. I have a Zeiss lens that has about 355 degrees of travel - 180 degrees of it is for 6 inches to 12 inches. Something like this will provide you with the ability to every so slightly turn the focusing ring to make small adjustments to get the focus sharp.
- A sharp focusing lens, is a product of its optics. You need to go to the lens data base to find lenses with reputations for being extremely sharp.
The reason folks immediately say "macro" is because macro lenses are built this way. Sharp optics, and large focus throw, allowing for very fine focus. There is one additional "trick", that you can also apply. You can "focus" with the lens, or you can focus with "adjusting" the distance - making very slight adjustments. This distance adjustment can be done with the object - moving it close or farther away. It can also be done with adjusting the camera position too. So in order to do this, there are two types of an attachment - one called a bellows that fits between the lens and the camera (needs to be a K mount on both ends). This provides you some additional adjustments. In particular for magnification. The other is called a rail, that allows you to percisely adjust the physical position of the camera.
So, do you need all of these? A lens yes, but the next items, the bellows and rail? It depends on the control that you can exert in terms of focus with the lens, and your overall physical setup. They are options.
I remember coming across this little video. So you set the item down - shine a light on it, take the camera and shoot the picture - right. Pretty simple and straight forward. Well, here is what another photographer went through - who does not specialize in product photography.