As I always take my own advice, when its good, Ive ordered a Canon 50mm f/1.8 lens. will reverse my Praktica 50mm onto it for close up work.

Worth keeping an eye on charity shops for old lenses that still have their uses, I bought the Praktica lens, with an MTL3 body, for £12.

I love my 50mm canon lens Got it for a nice sum of £40. Not done much protrait work with it yet but its a very good lens!

Its construction feels poor and cheap. Its very "plasticy" as you described, but I just have to remind myself what images Im getting from a 40 quid lens

I found an old MTL3 in the roofspace with several lenses. If anyone is interested I can see what they are. If worthwhile and someone wants them it may help offset the price of the D40

Lets see, the following lenses are in the bag:

Tessar 2.8/50 Carl Zeiss Jena DDR
MC S 1:3.5 f=135 Carl Zeiss Jena DDR
MT Flextogon 2.4/35 Carl Zeiss Jena DDR
A 2x teleconverter
An extendery thing, presumably to increase the focal length.
Luxon 122m flash, which may or may not work on the Nikon hot shoe.

So I should be able to get a reversing ring for the Nikon and put the 50 onto it?

I have a nasty feeling the registration distance is wrong for mounting M42 glass on Nikon bodies, but the Flek 35 and the S 135 are both reasonably sought after by Canon/Pentax/Olympus users because we can mount them with an adaptor and they are very fine lenses.

In your shoes Id take some nice piccies of them and slap them on ebay. You should get a tidy sum (think in terms of £100 in total and you probably wont be disapointed).

The Tessar 50 is less popular so Id hang onto that as Serious suggested. It will work nicely reversed.

If the extendery thing has no glass in it and goes between the camera body and the lens then it is a macro extension tube. It reduces the minimum focus distance of the lens used at the cost of loosing infinity focus ability. An alternative cheap way to try macro rather than reversing a short prime.