K20 D - Best Zoom lens to 300mm

I had three sigma 100-300 zooms, two with metal mounts and one with a plastic mount. I was wondering why I wasnt getting really sharp photos. I assumed that it was because of the high zoom, as I take mostly surf photos. Note that I havent had the K20d for very long. The *ist DS I had performed quite well with the sigma lenses. Mind you I didnt use the metal mounts very much at all. After reading some of the posts here, I see that not all sigma lenses are really compatible with the K20D.

I did a tripod test, and it would seem the metal mounts (I presume older models) did not really give sharp auto focus photos) The plastic mount gave much better ones.

My questions to someone more knowledgeable are:

1. Will the sigma lenses also have problems with exposure on the K20D as well.

2. Will newer sigma lenses be better for autofocus capabilities than the older ones. Some of the new D lenses perhaps may be good.

3. In the Zoom range to 300mm is there a Sigma Lens model which anyone else is using that will give really sharp photos, as well a good exposure.

4. I realise that to get the best photos you need the best equipment, but is there a cheaper Pentax zoom which will give really good performance as regards sharpness and exposure.

You may realise that I really dont want to spend a lot more money, than I need to.

I have looked at three on E-Bay.

SIGMA 70-300 f/4.5-5.6 APO DG Macro
SIGMA 28-300 f 3.5-8.3 DG Macro
PENTAX DA L 55-300 F 4.5-5.8 ED

I really want good sharp photos, and would rather not be too disappointed with a lens and then lose money by onselling it on.

Cheers from New Zealand.

Hello Andrew.

You didn;t say what the lenses are,

1) There should be no exposure issues with any lens fitted to a DSLR. Unless the lenses are full manual. In which case you can "determine" the correct exposure.

2) Newer Sigma lenses should be no better at AF than older AF Sigma's. Some difference may occur due to lens speed as more light helps the camera AF system.

3) Although I don't have a specific 300mm length Sigma, I do use the 70-200 f/2.8 Mk1 and a 50-500mm Bigma. Both are sharp. You may have a front/back focus problem.The K20 can compensate for this, Try a few manual focus test shots for comparison against AF shots.

4)Not true. Agreed, there are some expensive lenses out there that if used properly can provide excellent images but don't fool yourself into thinking that buy what is perceived to be "better" kit will do anything for you that you can't already do.

You will get plenty of advise from other forum members here on these points.

Regards

From what you say I assume you are mainly using these lenses at the long end 300mm mark.

You will struggle to get good sharp results from any of the lenses you have mentioned, the Sigma 100-300mm are just cheap budget lenses and anything taken over 200mm will doubtful look sharp, Unless you get the Sigma EX 100-300, f4 which will set you back over $1000

The other 2 Sigmas you seen on E-bay will be much the same, The best of the bunch would be the Pentax 55-300mm, but even that will have limitations,

Your best bet would be to do away with the zooms and get yourself a 300mm prime lens, but again prepare to spend well over $1000 for a good quality one.

You could try for an older manual focus 300mm prime lens which you can pickup fairly cheap for a few hundred dollars and pick up a good quality TC for it too increase focal length if you need it.

Are you using a tripod with the Sigma lenses you currently have, Post a few pics, maybe we can help with some different camera settings,

Thanks for that. I generally use them at the higher 300mm, but it depends how far out the waves are, or how close I can get. But I really need the lower focal length without a change of lens so a prime is really not an option for me.

The lenses I have sigma 100-300 are all KAF mounts, but the ones with the metal mounts just dont seem to work the camera autofocus as well as the plastic mount one. Is this the way it should be, or might it be issues such as dirty contacts or just damaged lenses.

As the surfers move fast and each individual is usually all over the place, I cant use a tripod. So all are handheld photos. I use 400 ISO and aim to get over 1/1000 as a shutter speed. I would not think that the unsharp images would be due so much to camera shake. I do see that some are, these seem to be obvious.

I did read in a previous post that sigma doesnt get the autofocus perfect, and I thought perhaps in older models that was even worse. I did read somewhere that the new penatx lenses have very fast autofocus to meet the standards of the new digital cameras.

Are the new digital lenses (d etc) better than the older lenses made for such as the MZ 30/50/60 etc, when used on the DSLR. Or are they perfectly the same standards. By trying to save some cash here, I could end up spending quite a bit if I dont get it right.

The simplest and arguably best solution is the SMC Pentax-DA 55-300mm, or the lighter made but optically identical DAL version. These are excellent performers but not overly expensive.

Modern zooms designed for digital cameras will pereform better than many film-era lenses, but don't dismiss the latter as there are plenty of lenses that are up to it. The Pentax AF lenses in general will perform best, but there are good examples from other manufacturers such as Tokina, Tamron and Sigma. Personally I rank them in that order.

Don't forget that the dgigital lenses will be generally smaller, lighter, better performers and focus closer than their film counterparts.

One question I'm surprised no one has asked yet is, have you done any tests with these lenses to determine if they are simply back or front focusing? if that is all the problem is, the K20D can be adhusted to compensate.

Have you also considered it may be another problem, you say your trying to maintain shutter speeds of 1/1000, my guess is your having to shoot wide open to do this in which case your depth of field is going to be very shallow at 300mm in which case is the focus locking on where you want it to?

Johns advice for a 55-300 is good but you really need to determine what the problem is before buying new kit. why not post some of the images here to give us a better idea of whats going wrong.

Might be worth having a gander at this thread too (might help for lens ideas).

Why not set up a static Lens Test Target, at say 10 metres and see if the lenses which you currently have will focus correctly and give sharp pictures.
Budget zooms often need to be used at f8 or f11 to get the best sharpness out of them. F8 and F11 will also give you some depth of field. To get your shutter speed up try using ISO 800.

As a relatively low cost zoom the Pentax 55-300 is pretty good and again performs best around f8 to f11.
I have borrowed a Sigma 70-300 f4.5 f5.6 APO and found that to be quite good.
Another budget lens to look out for is the Pentax 80-320, which gives a reasonable performance.

I have a Sigma 70-300 that I sometimes use with my K20D and while it's basically OK (definitely not up to the standard of my two 'main' lenses below), it is slightly soft at the long end. I've not noticed any problems focusing, but I mainly use it for landscape shots with a tripod, usually f8+ and focussing manually.

Bought the Sigma 70-300. Here I go again. If its no good I will resell it at a loss, and buy something else.

Gosh, I put a CPL filter on the lens, and none were coming out sharp and exposure was not consistent. I thought another dud. Took the filter off, and now much improved. Next question. What filter will least effect the Autofocus of the lens on the camera? Is this normal, for filters to have this effect.