I managed to pick up a DOI ring flash from ebay for £50.
And this was the result ... link
Hand held, camera set on X-sync f16 and "catch in focus" enabled. Simply move very very slowly towards your subject and just before it comes into focus hold your breath, inch (mm) closer and once in focus the shutter fires automatically, a wonderful tool.
Welcome to the obsession that is macro shooting.

That can't be a nice way to go
Top pics though

What a set, awesome.
2 gets my....... oh and 4 just edge it for me.

link

I got this recently with the same lens.
The only real tips I can give are to follow your target for a good while before shooting and continue to follow after you have released the shutter.
Aperture about f5.6 - f8, shutter no lower that 1/50th, good light but most of all don't rush to get the shot, relax, and take shed loads, you are bound to get a couple right if you take enough.

That really do not know what they are talking about!!!
I'm not one for a rant usually but this idiot got the bile rising!!

link

I'm still refusing to pay for what I once had for free!!!!!!!!!!!!!!!!!!!!

I have 2 sets of Jessops tubes one is marked with PK and the other with PK/A. The reason I purchased both is because they both have the contacts so I can use my Pentax A 50mm and control it from the camera, no auto focus though, I almost always use Catch in Focus. On both occasions the advert contained photos where you could clearly see the contacts. Try contacting the vendor and ask if the contacts exist.

As for a formula I would also find this useful, I tend to guess, and add/remove segments as required depending on how close I think I can get to the subject and how much I want of it in the frame. e.g. you need less tube length to get a butterfly in the frame but to get a full face close up of an ant would require more and sometimes some of the second set.

This shot was taken with one full set - 65mm. It is surprising how quickly you get to the point of knowing which tubes and how many you will need.

I use it all the time when shooting bugs (as long as they are still). Because I use the tubes and the 50mm I have to get very close to the subject so this has to be done with a great deal of stealth. So by holding down the shutter release and very, very slowly creeping up on the bugs I can focus on getting the part of the bug I want in focus. Works a treat.
great feature.

This picture reminds me of a very old pop song circa 1979 by The Monks

I have just read this thread from the start and what a laugh it is. The more PE posts the more obvious the wind up becomes, I was fooled by his first slight at macro shooters and took the bait, but as the posts progress it is becoming more obvious that this is simply a ruse, well done PE for catching so many of us.
All, watch for the switching between being unable to spell and having astonishingly bad grammar and then in the next post perfect in all respects.
Consistency Mr PE, consistency!
I wonder when the real identity of PE will emerge.
I also think it is a PU member spicing things up.
Keep up the good work PE it's a giggle and let's have some more examples of your superb work.