Sharp Long lenses for my K-30

Agreed, if the lens has poor resolution you are stuffed.

But if it is soft due to poor contrast you can often work wonders in PP.

And if it is an older non APO lens that has poor contrast primarily because the differential focusing of blue/UV wavelengths isn't corrected you might get big improvements just by using a UV filter - as well as whatever PP can do.

Contrast can be corrected, but you can only pretend to remove softness by increasing the micro-contrast. The image is still soft.
And don't forget, if you have to sharpen your image in post then you will be sharpening the noise, which will already be significant with the soft lenses which are also slow
Same goes for anti-aliasing filters - sharper image at source = less noise after processing (a benefit that no-one seems to have picked up on).

I had sigma 120-400 os hsm short of funds so sold it as also have pentax 300 still regret selling it but owner only lives around the corner

I think the answer to the OP's questions depends very much on 'how much to spend'? For me, there is nothing to compare to the Pentax 55-300 in IQ terms for the money, a DA L will only set you back about £200 or even less if you shop around. It is in a different league to the Sigma 70-300. The Sigma 150-500 is excellent too, but in my experience it is not quite as sharp as the Pentax 55-300 and not quite as contrasty either. Also, the Siggy is considerably more expensive and heavier. The problem with the Pentax is its reach - only 300mm max and it is so poor with a TC that it's not worth bothering to try this.

I think sharpness is really important with a long lens, it can't be simulated successfully in PP, the detail has to be there in the original shot, especially when photographing wildlife, birds in particular. I agree with the other posters about the DA*300 being the best of the bunch, but it is cost prohibitive for many.

Here are a couple of examples of images shot with the Pentax 55-300 and the Siggy 150-500:

Pentax DA L 55-300





Pentax DA L 55-300





Sigma 150-500





Sigma 150-500




Hope this is helpful.

Regards
David

I took my 55-300mm out the other day and it constantly amazes me how good it is.

I can only comment on the lenses that I have, but I can say the following:-

Sigma 100-300 F4.5-6.7. Old lens, slow and full of CA on digital.

Sigma 70-300mm F4-5.6 Macro. Cheap and budget soft, unless you work with it. After a while it does not talk to the camera properly. Does have a useful Macro ability though. CA is not bad.

Sigma 170-500mm. Can be an excellent lens, then again, it can be a pain! Needs a lot of work to get to know it and work with it. Bokeh too fussy. At the end of the day if you work hard you can get great results with it. But on the other hand, it is not as good as the next lens.

Pentax DA55-300mm. A good lens, decent quality and sharpness. You don't have to work as hard as the Siggy's, but I would not say it is the ultimate.

The Ultimate:-

Pentax DA*300mm F4
Seriously, it is a case of you get what you pay for. This lens is sharp from wide open, has stunning bokeh, and the colours are excellent. If you can afford it, then seriously this is the only lens that you will need.

As for the extra reach of the Sigmas you mentioned at 500mm? Well I would say that a cropped shot from the DA*300 will have more detail than the siggys at 500mm. It is that good.

One final thing that will (maybe) help. Pentax have the 1.4x converter that is about to hit the shops. So, I would say, if you want the ultimate on a Pentax body, get the 300mm, and save up for the converter. Then you will have superb gear for long shots, no questions asked.
But if you cannot afford it, then the 55-300mm is a good alternative. But remember, you get what you pay for.

Hope this helps.

Thanks for the help..although you didn't mention anything about the 15-500mm APO DG is it closer to the 170-500 or the 55-300 in terms of IQ and the detail it can capture at its long end..