First check the filter thread size for your lens (Probably 49mm) and then order a lens cap. The body cap is to put on the camera body if no lens is fitted. A rear lens cap would be to protect the back of a lens that is not fitted to a body.

You can order a lens cap from this website!

Can you post a picture so we can try to analyse the problem?

I tend to buy on eBay as well - you get a better choice anyway, from all over the world....

Just to expand on Matt's comments, the Rolleiflex is a fixed lens camera (75mm or 80mm), although Mutar lenses that bayonet into the filter rings can be used to alter the focal length. These are rare and very, very expensive. There is a Wide Angle Rollei with 55mm lenses (£3000 new, maybe £1500 used if you can find one!) and a Tele-Rolleiflex with 135mm lenses. These are the sort of things Bailey used in the 1960s!

The Seagull is fairly good but a bit crudely made. The Yashica 124G is the one of choice from that range, look for around £150 mint.

Don't forget the Mamiyaflex TLRs, which do have a range of interchangeable lenses, but which are bulky.

Well, on a Pentax site I shouldn't mention it, but....

The Lubitel is very cheaply made, horrible to use and will not deliver results any better than 35mm. In fact, it will probably be worse.

Why do you need to get into medium format? I ask because this will be relevant to your choice of camera. Unlike 35mm, medium format cameras are not necessarily general purpose models and some will be better suited to some uses than others.

As a general point, TLR cameras are simple and reliable and a good Rolleiflex or Rolleicord will deliver excellent results at reasonable prices. The Yashicamat is cheaper and also excellent, even if not engineered to Rollei standards.

If you can afford it, the Pentax 67 is superb, but second hand ones are often very well used and abused by prodessional use.

The original Pentax 645 is relatively low priced now, and a very fine camera. But does 645 offer a big enough jump in quality from 35mm?

If you use 35mm as well and move to a medium format SLR I suggest you choose one where the lenses operate the same way rounf for focusing and aperture, to avoid confusion. So Pentax users usefully move to Pentax or Bronica. Nikon users the same. All other makes operate the reverse way.

I think its fair to say that there is more compatibility with Pentax lenses and cameras than with most other marques. Being loyal to Pentax for many years has proved to be a good move!

I ordered an instruction book once, which arrived by return of post.

I think Matt has given a very extensive and extremely good summary - excellent stuff.

In the days of the Spotmatic Pentax made a "Ghostless" filter, only as a UV I think, and this has a curved construction of the same angle as the front element of the 50mm lens. The idea was to reduce any deviation in the light path and eliminate ghosting. An interesting idea, but I don't think it ever caught on.

I think it's a pity to have a Super-Multi-Coated Pentax lens and then add an uncoated piece of optical grade plastic on the front. As a consequence, I only use Multi-coated glass filters, always a lens hood, and if at all possible even the filters are either Pentax, B&W or Heliopan.