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11-02-2007, 11:42 AM   #1
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Lookin' 4 a AF K-Mount 70,75-300mm Lens

Hi all, I am looking for a 70,75-300mm Autofocus auto Aperture K mount lens around $140-$150. I am looking for a sharp lens, decent contrast and low distortion and need it for basic tripod/monopod zoom shots of wildlife. I am not professional, just looking for something to use with my K100d....thanks

11-02-2007, 12:13 PM   #2
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If I was you I'd boost my budget a little and get one of these
Sigma 70-300mm F4-5.6 DG MACRO

From what your saying you really shouldn't need the APO, which is around $100.00 more.
11-06-2007, 07:45 AM   #3
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QuoteOriginally posted by little laker Quote
If I was you I'd boost my budget a little and get one of these
Sigma 70-300mm F4-5.6 DG MACRO

......
PMFBI, but I am thinking of getting a 300mm lens for bird photography. A prime is fine and I though it would be less expensive, but it seems the zooms are less expensive. I can't figure that one out!

I have a K100d. I looked at the Sigma 70-300mm f4-5.6 Macro Pentax AF here and the price is stunning: $130! And the page claims the lens is autofocusing with my K100d. Is that true?

I have a Pentax FA 80-200mm f5.6 I use for photographing sports and people, and I think it's a great lens. I paid less than $65 for it when I bought the K100d. But if I can find a zoom in the 80-300 range (gotta have the 300 over the 200), I would probably sell the 80-300 Pentax.

I don't understand why there is such a HUGE price difference in lenses; especially that zooms cost much less than primes. How can that be?
11-06-2007, 08:38 AM   #4
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If you are wondering why a 300mm f/2.8 prime is more expensive than a 70-300mm f/4-5.6 zoom, time to read up on f-stop/aperture! Bryan Peterson's "Understanding Exposure" is a good read.
A 300mm f/2.8 prime needs a front element of AT LEAST 107mm! A 300mm f/5.6 only needs to be 54mm in diameter. More glass=more $$$$$.

11-06-2007, 12:37 PM   #5
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QuoteOriginally posted by egordon99 Quote
If you are wondering why a 300mm f/2.8 prime is more expensive than a 70-300mm f/4-5.6 zoom, time to read up on f-stop/aperture! Bryan Peterson's "Understanding Exposure" is a good read.
A 300mm f/2.8 prime needs a front element of AT LEAST 107mm! A 300mm f/5.6 only needs to be 54mm in diameter. More glass=more $$$$$.
So it's pretty much a function of lens speed then. Makes sense. So if I can live with the slower lens 3.5 - 4+ I'm pretty much okay, correct.

Thanks.
11-06-2007, 01:14 PM   #6
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I own 4 primes and 3 zooms, I have found primes have by far the better picture to my eyes, even the cheaper primes. Thing about Pentax's older primes, you have the "beep & square light" in viewfinder of a K100d k10d Super, to verfy focus even on a cheaper manual focus lens if you have bad vision. :ugh:
11-06-2007, 02:27 PM   #7
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Just be aware that the inexpensive lenses are usually f/5.6 at 300mm, so two stops slower than f/2.8.

QuoteOriginally posted by Papersniper Quote
So it's pretty much a function of lens speed then. Makes sense. So if I can live with the slower lens 3.5 - 4+ I'm pretty much okay, correct.

Thanks.
11-06-2007, 05:14 PM   #8
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QuoteOriginally posted by egordon99 Quote
Just be aware that the inexpensive lenses are usually f/5.6 at 300mm, so two stops slower than f/2.8.
Roger that, thanks. And am I correct that using a TeleConverter, say a 1.5 with my 80-200 F4.7 - 5.6 would probably be a lot slower? Doesn't the 1.5 converter change that to 4.7*1.5 and 5.6*1.5?.

After doing some additional reading it seems I would be better served by a 400mm lens, but man, the prices go very high quickly!

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