I'm another who would usually crop early on, just after any rotation if that's needed.
Leaving the cropping till the end can meen I end up wasting time removing dust specks etc on parts of theimage that are just going to be dumped.

There have been a few occations when I've tried multiple crops, and with those its best to get the rest done first. (Wouldn't be an issue if I had lightroom).

A wide angle adapter will let you try out compositions too. The IQ won't be up to a dedicated lens but mine are easily good enough for web use.

Unfortunately nobody seems to make an adapter to mount k bayonet lenses on m42 threads. Mounting m42 to PK is very common and has been done since the k mount first came out, so if you have some m42 lenses it's a great device for macro. M42 helicoids are cheap and easily available in a range of different lengths, K mount ones are rather rare

I'm severely tempted by the 10-20 (the one lens I'm really after) but my budgets currently blown

Whilst I'm with John/Chris/Ken/Horst on this I think it's worth adding that there are some rare occations where a filter might be a good idea.

If your likely to be getting salt/dirty water spray around (not so rare with WR cameras) add a filter (even a relatively cheap one) till clear of the spray.

I've used them to hold a Bokeh mask in place between the lens & the filter).

They may come in handy for full spectrum converted cameras.

The main arguments for UV filters comes from film days where the sensing medium was sensitive to UV. These days the sensor it coated to prevent UV sensitivity.

If on a tight budget a coupling ring is one of the cheapest options (You've already got the lenses) enabling a wide lens to be used reversed on another lens. Typically ~£5 on e-bay.

The advantage of teleconverters is they enlarge the image without reducing working distance, though this is at the cost of extra aberations which may be noticable.

It's worth a look at Nass' extreme macro website he covers all the options.

Good luck David!
If the laminated paper fits, I think you should be able to get it out eventually. It might need a lot of careful probing to get just the right bit near the middle, and as Gamka suggested make sure the battery isn't pulled up & holding the catch, so that might nedd a bit of wriggling too.

If you're wanting to use older lenses from before the A series, there is a menu option that will need changing (It's called something like shoot without lens).
The default setting is to only take photo's when the camera can comunicate with the lens, once changed the camera no longer worries if it's can't get a responce from the lens.

The ME-super comes from the time when the A series lenses were just out. Most of the lenses I used with mine were M series (no A setting on the aperture ring), yours might also be a mixture.

It seems to be a similar porblem to several 'PKA' extension tubes where the earth return is not being made.
Looking at the e-bay link it looks like the bottom of the TC is anodised so scratching the base of the TC as per JAK's photo should do the trick.

If this doesn't work it might be that there isn't a return conection between the ends of the TC or that one of the other contacts/wire has broken. Try checking each in turn with a multimeter. There should be very little resistance (no more than a few ohms) between coresponding contacts on front & back faces. My money's on the scratching.

The lens itself doesn't have the cresent of contacts but does have the only one used for a 50mm. Many lenses only have a few of the contacts, which ones varies based on the focal length.

Seems like the right approach to me (at least if you can't put in the actual focal length)
Using the mid point the system will under compensate at the telephoto end and over compensate at the wide end but both should be fairly minimal for most zooms.