[OrenMc]

As much as I love my Sigma 300/2.8 I have been thinking of replacing it with the Pentax DA*. I wouldn't even think about it if I still had the K7 or an earlier model but the K5 does so well with ISO I feel I can maintain the speed.
Sadly, there is a bit of a difference in subject isolation and DOF between F2.8 and F4 so I would lose that but I would also be losing half the weight.

I'm also a bit concerned about the use of teleconverters. The Sigma AF works great with my Tamron MC7 on static objects, a little slow. ( on moving objects its way to slow ). The Sigma and Tamron 2X MC7 is wonderfully sharp on closer objects so I love this combination when I need to fill the frame.
So this is one of my biggest concerns is losing 600mm 5.6, and as you may know, wildlife is a big part of my photography.

I know I can manual focus the DA* with the 2X but I haven't really seen this combination used much or at alll for that matter.
So if anyone has these I would request please some photo examples.

My decision to switch is mainly portabliity. My health isn't the greatest so its a little difficult to tote this lens around for an extented period of time. I have and I can hike steep canyon walls with this lens mounted and in hand but I would rather only be carrying half the weight. Having the weather seal of the DA* here in Seattle is a factor also ( RAINY ) and I like to get down to the beaches ( wind and sand ).

So there it is. I just wanted to throw my thoughts out there and see if I could get some example of the DA* 300 with a 2x teleconverter and the Tamron MC4 X1.4.
Thanks for the help in advance.

[Skog]

I use the da* with the afa 1,7 at times. And it works ok. AF with the 1.7afa is quicker then the da* itself, but you have to make some rough manual focus adjustments before the tc bites on to it. Image quality is hard to give a objective answer.. Because it's entirely subjective I pixel peep, and I feel the tc degrade image quality quite a bit. However, under good lighting situations I have managed to get some very good results. It's inconsistent for me though.. partly because I don't use a tripod.

If you have the possibility, I'd say get both. Da* for the longer hikes, and sigma for the shorter photo trips. I suspect you'd miss the sigma..

[Clinton]

I think you're going to miss the 600/5.6. If you are mostly shooting at 300, the DA* may even be sharper @300mm (however I own neither of these lenses, so I don't know).

I just don't think the DA* was built with TCs in mind.

That said, I've seen some impressive shots in the 300mm thread with the DA* and the 1.7x AFA.

The K-5 will help make it up the loss of light on the shutter speed, but I suspect you may loose something else in quality, in contrast, and in color vibrancy. I'd suggest buying from a seller that will let you return the lens in 30 days, and then trying it out to make sure you can really get what you're looking for out of the DA* 300. You'll probably keep the DA* anyway, but I suspect you wont sell the Sigma.

[OrenMc]

Thanks for the responses, they are much appreciated.

I think one of my issues is I try to handhold all the time with the 300/2.8 and I get a little lazy setting up a tripod so my keeper rate isn't where I would like to be and what I know the Sigma is capable of.
Cliton, your are right, I will miss the 600 5.6. I wish I could find a Sigma 100-300 f4 again and I could justify that a lot more but having 2 300mm primes its not so easy.
Its just the K5 abiltiies with high ISO makes the DA 300 much better but the teleconverter compatablity is a must. Even if I do have to maual focus.
I wish I had unlimited funds but I still may end up with both. Maybe I could rent the DA 300 so I know for sure what I am getting myself into.