Thanks for the advice everyone.

I think I'll stick with my 55-300mm unless I get a windfall between now and August and then I'd be tempted to go for a Sigma 70-200mm f/2.8 (non OS if I can find one) because I'm looking to get into sports photography (football specifically). Rainsleeve may come in handy there as well!

Roy

Thanks. I'll look into that. I never joined as a member there because I felt more comfortable here but I would like to sell this lens....

Price drop: £250 inc. UK RMSD

Thanks for the suggestions so far. I feel more comfortable that the 55-300mm range will cover most eventualities and I might change to the wider zoom if I'm feeling brave and/or in calmer waters. I'll definitely consider a rainsleeve / rain protector (they seem quite cheap on Amazon so I'll consider stretching my finances, Gwyn) and a UV filter for spray protection.

Bernard - I'll attach my camera to my wife with a length of nylon cord; she looks quite buoyant and it will save me from temptation if she starts complaining about the trip. I wouldn't want to lose a perfectly good camera.

Roy

Lens is now on ebay and Amazon (thanks for the tip Gareth) but still available here cheaper!

Thanks John. I have a Sigma 18-50mm f2.8 EX DC. Good IQ but not it's not WR. I wondered if a Sigma 70-200mm f2.8 (enabling faster shutter speeds to stop movement on the dolphins and the motion of the boat) or a Pentax 60-250mm f/4 (slower but weather sealed)would be recommended?

I have a trip planned to the South-West of Ireland in early August and have booked a trip on a small boat, 12 passengers, with a marine biologist captain. The intention is to see dolphin, porpoise, fin whales and minke whales if we're lucky. Also chance to see Atlantic seals on rocks by the water's edge.

My first question is for advice on technique and resources. Is there a good book, internet site or advice from the learned members here that could help me increase my chances of getting some good shots?

Secondly, what about equipment? Probably the best images would be dolphins leaping from the water and I understand that if you're fortunate they can actually come quite close. I have a K20D, 100mm Macro f2.8 WR and DA 55-300mm but there are faster zooms (Pentax and Sigma) and I assume WR would be a good idea. Where, if anywhere, should I look to upgrade?

Any experienced marine wildlife Pentaxians than can help me?

I have an "as new" DFA 100mm WR that I'd be prepared to swap.
Regards,
Roy

It was a pleasure dealing with you also. I hope you enjoy the lens.

Thank you all for the advice. I'll post it on ebay but as a parting shot I'll drop the price here to £260 including UK postage (RMSD). Will also post to the EU if buyer pays postage.