Im using my Tamron SP AF 300 2.8 LD [IF] with the Pentax F 1.7 AF adapter to give me 510 ƒ4.5 at 6 pounds.
The A*300 2.8 would be awesome with that. My biggest reason for wanting ƒ2.8 is you still get nice sharp crisp AF even with a TC.
That being said, I don't often carry the lens. It's a second day kind of lens in the bush. If I find something and I think I might go back, I'll carry the 300 2.8, straight there and straight back. I don't actually wander with it. Much of the time it's in the back of the car waiting for something near the road.
There are a few opinions above I'd just completely disregard.
Even with long lenses you get lots of subject isolation at ƒ5.6 in close for depth of field I usually shoot at ƒ5.6 or ƒ8. The big advantage to a faster lens is more light for the AF system. For fast subjects that can make a huge difference.
I haven't ever used a 150-450 so I'm at a loss there. For hiking, I prefer the 60-250 or 200 2.8 with a TC in the bag if needed. I honestly don't know if I'd use it much or not. My DA*60-250 gives me 350 ƒ5.6. With the 1.7x 425mm ƒ6.3.
As a general rule I use long slow combinations reluctant;y. I however do muse from time to time at the possibility of selling the 60-250 and Tamron 300 and getting a 150-450. On a full frame 150-450 is the equivalent of 100-300. That's really not that useful for birds, but should be a great wildlife lens.
Sorry, I can't be of more help.But this really is a matter of prefereence. It can be hard to find the subject with a fixed focus lens.
The Tamron 300 with a 2x TC on it.This is actually 600mm ƒ8, the Tamron TC doesn't directly record the ƒ stop and focal length in the viewfinder.
The 300 2.8s have a lot of resolution to spare for TC use.
Here's the 300 with the 1.7x
A closer look says it's a little sharper than with the 2X, but I really need Pentax to come out with the 2x TC. I'm not convinced the Tamron optical quality is anything to write home about. SO 300 2.8 isn't really a popular choice over the 150-450. But I really can't imagine having the 150-450 without the 300 2.8.
I'd like to have it as a walk around for the K-1, but the 60-250 with the 1.4 does just fine. And I don't know that I'll ever own a lens that heavy again. One beast is enough. The 18-135 and DA*60-250 with the TCs provide lots of reach for hiking in a nice lightweight package. And if it's a walk over 3 miles, I'll trade the DA*200 for the 60-250 to save weight.
Unless you have set up where you are not going to be moving much, bag lenses just aren't practical. AT 2000 grams the 150-450 is twice the weight of my 60-250, 3 times the weight of my DA*200 2.8, and I've had days when my 60-250 was causing me pain by the end of a 20 mile hike. The biggest factor is not the lens characteristics, but how you plan to use it. Imagine carrying 5 pound bag of sugar with you where ever you go. You'll start to get the idea
My Tamron 300 2.8 is 6 pounds, and it would be the first to go if I stared welling off lenses. Not because I don't like it's images, I prefer them, just because based on current use, my other two telephotos get used more.
Out on a hike with the DA*60-250 and 1.4 TC, hand held. (I should have used a tripod.) I might have a better image with the 300, but , it wasn't there so it's moot. And the 60-250 and 1.4 TC on the K-3 gives me more reach than the 150-450 on a K-1, for a fraction the weight.
Last edited by normhead; 10-16-2018 at 06:31 AM.