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Old Jan 5, 2011, 12:56 AM   #1
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Default Sigma 300/2.8

Anyone know much about this lens? Would it still AF well with a 2x TC on it? I would love to have a 600/5.6 and one that was AF would be even better even if it is lot more money. I know that my Sigma 135-400 is soft and has focus issues but it is also not really a pro grade like the 300/2.8. So any and all info would be great. I may still go with the Tamron 300/2.8 but as I get older Af becomes a lot nicer

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Old Jan 5, 2011, 3:46 AM   #2
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Hi John,

You are correct that the 135-400 is not in the same optical class as the Sigma EX 300 f2.8. The EX designation is the giveaway, and denotes Sigma's highest grade lenses, and the 300/2.8 qualifies.

I have a Tamron SP 300/2.8 Model 60B Adaptall 2, a Sigma EX 300/2.8 APO (pre DG), and a Pentax FA* 300/2.8, so I can give you a decent evaluation.

The Tamron is the softest, and shows the most CA/PF, but softer in this class of lens is still in a different class than most consumer grade lenses. The degree of difference is very slight. The Sigma has a touch of spherical aberration wide open which causes a "dreamy" look, but I've only seen this wide open from this lens. It's a bit sharper than the Tamron, but controls CA/PF considerably better, and it's almost hard to get images that show any. The Pentax is the best of the 3, slightly sharper, and even better CA/PF control.

There are prices to pay for the higher quality and AF. I bought all three used and got the Tamron for @ $700 USD in Ex condition, the Sigma in Ex condition for about $1000 more, but it's an AF lens and harder to find, and paid almost $1000 more again for the Pentax in Good condition (but the glass is flawless). Each was a pretty good deal, IMO.

I'm guessing that the Sigma EX 2x APO or APO DG TCs would be your best bet, and either these or the Tamron or Kenko 2x MC7 AF TCs would be second choice. Any of these should AF well using the Sigma 300/2.8. The rule of thumb for AF compatibility with Pentax bodies is generally you need a fast enough lens to keep the max aperture at faster than f8 for reasonable AF performance. At f5.6, this combo would qualify.

I don't have any AF 2x TCs, but I have stacked a Tamron 1.4x and the Sigma 1.4x APO (which is essentially the same as a 2x) and gotten good AF performance on the K20 and K-7. My favorite TC combo with any of these lenses is the P F 1.7x AFA on top of either of the 1.4x TCs for a total of 714mm f6.3, and this combo also will AF reliably in most any daylight. I also like the F 1.7x AFA with any of these lenses alone for 510mm f4.8.

I haven't used the Sigma nearly as much as the Pentax because I usually also carry a second body with an FA*300/4.5 + 1/7x AFA, and the Pentax lenses both manually focus in the same direction while both the Sigma and the Tamron both need to be rotated in the opposite direction to infinity -- I like less confusion when shooting birds. . . The reason that MF functionality matters is that the 1.7x AFA requires manual prefocusing since it's cannot cover the entire focusing range with a 300mm lens. I actually prefer to shoot with one because this essentially adds a focus limiter to the lens, and it's quite a bit faster to lock focus than with the lens alone once you get used to it.

I'll likely be using the Sigma more this coming season as I'll probably be more often carrying the Sigma EX 180/3.5 APO DG Macro with another 1.7x AFA on the second body, and they focus in the same direction . . .

The Pentax is the best, but probably not by enough of a margin to be worth twice as much as the Sigma on the used market. The AF capability of the Sigma is worth the premium over the MF Tamron, IMO, but the Tamron is hard to beat at close to the same price or cheaper than a used F* or FA* 300/4.5.

Handling is considerably different on each of these lenses. The Tamron, being an MF lens has the longest focus throw. The Pentax is in between, and the Sigma has the shortest. The Pentax focuses about as quickly as the Sigma though, and it has a three stage focus limiter that makes it even faster and more convenient to AF. The Tamron has the thinnest barrel, and is easiest to carry by grabbing the body. Sigma is in between, and still convenient to grab one-handed, but the Pentax body is very thick, and since it's also the heaviest, I don't really trust myself to grab it one-handed (but I've got small hands). The Tamron and Pentax tripod rings both have strap lugs, while the Sigma doesn't, but the Sigma is the only one that has a removable tripod ring, so it's the most convenient to use handheld.

I can easily recommend any of these lenses. For probably 99% of shooters, any of them would qualify as the best lens from an optical quality standpoint in their collection.

Here are some links to posts using these lenses

K-7. FA*300 + 1.7x AFA


K20, FA* 300 no TC


K20, Sigma EX 300/2.8 + 1.7x AFA


K20, Sigma + 1.7x AFA


DS, Tamron SP 300/2.8 + Tamron 1.4x TC + 1.7x AFA


K20, Tamron 300/2.8 + 1.4x TC + 1.7x AFA


Sorry I don't have more examples without TCs, but I use them most of the time. . . Most feel that any TC inevitably degrades the IQ anyway, so consider these degraded images . . . but they look pretty good to me. . .

I'd get any of these lenses again at close to the prices I paid, but set pretty strict limits for prices that I'm willing to pay for a given lens. The limits I had set for each of these were Tamron -- $800 for EX, $500 for a beat up one with good glass, Sigma $1800 for Ex condition, $1500 for VG, Pentax $2500 for any condition with good mechanical function and glass.

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Old Jan 5, 2011, 12:15 PM   #3
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Thanks for all the great info yet again Scott! I guess it's time to go looking for lenses. I like my Vivitar 120-600 especially for the money but PF is an issue as it the lack of speed, really needs to be f11 at the widest to get sharp pics.

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Old Jan 7, 2011, 7:15 PM   #4
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Scott has a great evaluation for these lenses and helped me decide this one earlier this year. I went with the tamron 300 sp because it fit my budget most and mine had brand new glass put in from factory and came bundled with the adapter and the tamron sp 2x tc all for 750, shipping was 50 bucks because of the care taken to package and sent but well worth price and if you can find one for a deal you wont regret this lens. I dont have any other 300's but I can compare the IQ to a zeiss 200mm 2.8 lens I have and can say it is quite sharp. I used to shoot a vivitar in this range and when I bought the Tamron I was blown away with how great the photos come out of the camera. I never pp shots taken with my tamron SP, sharpening the photos takes from the quality of the shots and gives them an un-natural look IMO so I tend to leave them alone. I cant tell you how bad I wanted the Pentax 300 2.8 and I have to admit that want is completely fulfilled.

again I cant really offer a fine comparison but can also share shots with the tamron 300 2.8 sp without a TC here since scott didnt post some already.


hope the info helps, any of these mentioned lenses you will be extremely happy with, so enjoy the price hunt and let us know which one you end up snagging.
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