i use DNG not PEF and they open with windows photo viewer in Windows 10

it was around the £80 mark at Johnsons a couple of years ago, give them a call.
Johnsons Photopia Ltd,
Service/Repair
Hempstalls Lane
Newcastle-under-Lyme
Staffs
ST5 0SW
tel. 01782 753344 Service
01782 753300 General
01782 753330 Technical

it is a known fault with the model and as you say plenty of evidence of this. try a call to trading standards and discuss the problem with them. my son had a fault with a VW Golf which was a common one and VW dealer said he would have to pay . a phone call to trading standards and a letter sent to VW dealer with the information given by them the repair was carried out free of charge. Pentax always seem to want to bury their heads in the sand on recurring faults until backed into a corner.

also i have read the big Sigma lenses do like a fair bit of light to get the best from them

all very good shots Nigel. could you not just set the aperture wide open to focus and then stop back down for the shot? i think with the colour and the shapes within the roses maybe go in closer for some interesting abstracts

the best black and white software seems to be Nik Silver Efex Pro, lots of presets , film types etc. very user friendly. unfortunately you have to buy the whole Nik collection, Colour Efex Pro4 , Silver Efex Pro 2,HDR Efex Pro 2(does not work with Elements) ,Dfine2, Viveza2 (film emulator), Sharpener Pro3 (RAW sharpener, Output sharpener) cost £95 from Google, who slashed the price from what it was when NIK were selling it. it installs as a plug in with photoshop, lightroom, and elements.

https://www.google.com/nikcollection/

with a converter you could lose image quality as it is another piece of glass with an extension tube you just lose a bit of light which you can compensate for also there is probably a calculation as what length tube will give you 1:1. with my Tamron Adaptall 90mm the 1:1 adaptor is a 43mm ext tube they made for it,so not a standard length but don't know what would be needed for 100mm.

have you tried Alan Marlow, he cleared a load of grit out of a lens for me . cost £48. worth an email or phone call i would think

link:- http://www.cam-rep.co.uk/

these were taken with the Pentax A70-210mm f4, using catch in focus.

have you done them without the grip using bulb?