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05-27-2012, 05:08 AM   #1
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SMC Pentax 4/75-150mm vs. Tamron 3.8-4/80-210mm

I recently bought a lot off of eBay and as part of it came a Tamron Adaptall-2 3.8-4/80-210mm lens. I have made a quick comparison at 150mm to my SMC Pentax-M 4/75-150mm.
Shot with a Pentax K100D. All crops are 100%, not modified in any way.
1. Pentax @ 150mm f4
2. Tamron @ 150mm f4
3. Pentax @150mm f8
4. Tamron @150mm f8

The Tamron seems to be softer even at f8. No further conclusions, just for everyones' benefit who consider buying any of these lenses.

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05-27-2012, 06:41 AM   #2
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Moved to the normal lens forum for discussion.

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05-27-2012, 07:14 AM   #3
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The Tamron has lower contrast, which is often equated with softness - it might look better with a contrast boost. I had a Quantaray 100-300 that needed PP for contrast and it was a fine lens. My lens in this range is a Rikenon 70-150/4 XR; if I didn't like it so much I'd send it to you, to see how it fares - so I suppose you had better send your two to me
05-27-2012, 10:19 AM   #4
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I could get into a "my lenses in that range are..." rant but that would be thread-jacking, eh?

But without naming names, I can say that my zooms of 2.5x and under are all quite sharp and contrasty. Those 2x and under are even better. Some 3x+ zooms are also good; and some aren't.

Which of course leads to: if your zoom seems low-contrast (and thus soft) and you don't like PP, just boost contrast (and maybe saturation and/or sharpness) in-camera. Assumption: If you shoot RAW, your JPG settings carry-over as defaults in RAW development.


Last edited by RioRico; 05-28-2012 at 05:47 AM.
05-27-2012, 10:53 PM   #5
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I have the Pentax 75-150/4, and it's certainly an excellent performer. I remember seeing a resolution test in a respected magazine of that era, and it measured pretty much identically to its counterparts from Olympus and Nikon (unlike the Kiron in this test). My recollection is that it performed equally as well as primes in that focal length range.

RioRico's right of course - most of the 2x zooms of that era were good to excellent, and the larger the zoom ratio the worse you can expect them to perform (though some were pretty good too). Also, I reckon the tele zooms were rather better than the wide zooms.

Since the 2x tele zooms work so well, why don't I tend to use my 75-150 very much nowadays? Well, it's bigger and heavier than a prime, and its focus action is a little stiffer. Also, you won't in general get full SR, unless you match the FL to the value you input to the camera.
05-28-2012, 06:21 AM   #6
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QuoteOriginally posted by m42man Quote
Also, you won't in general get full SR, unless you match the FL to the value you input to the camera.
And that's my main quibble with MF zooms. SR is an immensely useful tool|crutch. MF zooms and SR are not congenial partners. SR is only effective if the actual and input focal lengths are fairly close. Averages suck. If picking an average value, each end can be far away, their images actually degraded by SR. So put a 70-210 on your cam, tell the SR'bot it's 120 or 150, then pixel-peep your 70 and 210 shots. Bummer.

I have a very few rather good MF zooms: Cosina, Kiron (x2), Komine, Pentax (x2), Samyang (x2), Schneider, Tamron, Tokina. Two-thirds are A-type, so I can and do use them with flash, usually with SR on, even macro. Without flash, I only use SR if I know I won't zoom. Mostly I shoot in bright light with a fast shutter, or on a tripod, both types better without SR. I sold half my MF zooms because of these limitations; only the best (and worst) remain.

Zoom design really has improved greatly over the decades. Like Earth girls, AF zooms are easy.

Last edited by RioRico; 05-28-2012 at 06:26 AM.
05-28-2012, 12:29 PM   #7
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The shake reduction on my K100D tricked me as well. First I took these test shots hand held. I managed absolutely ok with the Pentax zoom, but for some reason whichever focal lenghts I set for the Tamron (tries 150mm and 200mm as well) I ended up with blurred images. Finally I put away my lazyness and set up a tripod.
My guess is that the Tamron is heavier in the nose so the slightest movement caused much more blurr on the final images. Or might have been the 1-2 shots before I took the shots that caused my hands shaking
05-30-2012, 01:27 AM   #8
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QuoteOriginally posted by RioRico Quote
And that's my main quibble with MF zooms. SR is an immensely useful tool|crutch. MF zooms and SR are not congenial partners. SR is only effective if the actual and input focal lengths are fairly close. Averages suck. If picking an average value, each end can be far away, their images actually degraded by SR. So put a 70-210 on your cam, tell the SR'bot it's 120 or 150, then pixel-peep your 70 and 210 shots. Bummer.
I'm surprised you're setting values of 120mm and 150mm. If you use the formula: 2*max*min/(max+min), the value you end up with is 105mm. You aren't allowed this value, but 100mm is a good available alternative. This should give you slightly better than 2x blur reduction at 70mm and slightly worse than 2x at 210mm.

You'll definitely have problems at the 70mm end if you set the value to 150mm (you'll magnify any blur), and you'll be sailing close to the wind if you set it to 120mm. At the 210mm end, all you'll end up with is reduced SR effect, whether you set 100mm, 120mm or 150mm. You won't be doing any harm by having SR switched on (all that happens is that the camera will move the sensor to counter the shake, but not as much as it should).

I took some shots with my 75-150mm at 75mm (the end most sensitive to SR problems) at 1/20 sec shutter, with and without SR. I'd set the value to 100mm, so I'd be expecting something like 3x blur reduction. I've not uploaded images here before, so we'll see what happens...

The first crops were with SR off, the second with SR on. I wasn't trying particularly hard to avoid shake. I think this shows that there's a great deal of variability in the blur you get from shot to shot, but, on average there's less blur with the SR switched on. Ironically, the sharpest shot is probably the second crop in the SR-off set, but I'm sure this is just a happy accident!

Edit: I've just remembered, I refocused after the first 4 shots, for some reason, so it's quite possible the second crop is sharpest because it's more accurately focused than those following.

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Last edited by m42man; 05-30-2012 at 01:39 AM.
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