You are not allowed to push your camera lens onto the glass or plastic display case. Also, the photo should not have reflection. So, how do one take photos of items inside display case?
So, how do one take photos of items inside display case?
A circular polarizing filter will help you reduce reflections.
You don't necessarily have to push your lens up against the glass -- just getting closer will help to reduce the reflections.
Avoid having a strong light source in line with the camera, either behind you or on the camera. Don't use on-camera flash.
Remote strobes and careful lens choice are your friend.
I dealt with this effect at the Sydney Aquarium. They don't have any particular rules about photography there, but many of the exhibits are protected by two layers: a glass layer to hold the fish in and a plastic layer outside of it to protect the fish from kids banging on the glass. The result is that there is always a gap between your camera and the glass which made it really difficult to get pictures. Most people would try to take 1 or 2 pictures, realize the strobe flash reflects off the glass really badly, and give up taking pictures.
I had a strobe I could trigger remotely, so I would light up the scene from one angle and take the picture from another. I was the only person in the aquarium who could take pictures of the fish (and there were some serious envious stares from some of the other would-be photographers).
To take your pictures, you would have to get close to the glass (I can understand why they don't want you to touch it), pick a lens which lets you take the picture you want from this range, and then hit the scene with a strobe from another angle.
A few generic tips, I don't want to repeat what others have said. Some of these are more generic and can be used in the future elsewhere.
- Get as close as you can to minimise you/your camera/other reflections.
- You want the angle between the camera and the light source with the object being the pivot point over 90 degress to avoid reflection of any light. If you can't do that, turn the flash off.
- A polariser helps reduce reflections
- If you can touch the glass, get some disposable glass wipes, clean up any fingerprints left by other people.
- Again if you can touch the glass; rubber lens hoods are ideal, use that to make contact with the glass and form a seal. Voila. No more reflections!