Originally posted by T_MB Yes...I know it is 3:00am--I am stuck stuffing wedding invites. On my union breaks, I am "window shopping" lenses. Getting a wider prime is temping, but I do not know if it is worth it given that I already have the 50 1.4 Hypothetically speaking, if I were to purchase another lens--the goal being fast, wide, good low-light performance, which of these would you recommend?
Pentax SMCP-FA 35mm f/2.0 AL Lens with Case and Hood - Pentax
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Tamron AF 28-75mm f/2.8 SP XR ZL Di LD Aspherical (IF) Lens for Pentax Digital SLR Cameras - Tamron
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Tamron AF 18-200mm f/3.5-6.3 XR Di II LD Aspherical (IF) Macro Zoom Lens for Pentax Digital SLR Cameras - Tamron
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Sigma 28mm f/1.8 EX DG Aspherical Macro Large Aperture Wide Angle Lens for Pentax and Samsung SLR Cameras - SIGMA
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I'm not a lens expert like some of the people here, (and I SURE don't have some of their budgets), so I'll have to give you my gut level feelings.
I rented a 18-250 from
CameraLensrentals and it drove me nuts. That experience alone would put the 18-200mm out of my mind, personally. The hanging lens creep drove me batty. People say you get used to it, but I didn't in the two weeks I played with it.
Going from f/4 to f/2.8 is a noticeable jump, but STILL may not be enough of a jump to get the perspective you want in no-flash zones. IS and a monopod may be enough to overcome some of that, but you'll need to practice. I'd also seriously recommend practicing the "self hug - T" tripod technique -- personally I find that more effective than a monopod with a heavy lens.
So that brings me, personally, to the two primes. I own the FA 35 f/2 and would personally consider it the best walk around lens I've ever had. It's not a perfectly normal view, but it's dang close. Small, comfortable, feels nice, even though it's not an limited. I'd tentatively say it's smaller a bit more comfortable than the Sigma 28mm option, and is going to give you a very similar field of view.
What I'd recommend is getting out your tripod in a relatively dark place. Maybe a candle lit dining room, or something like that. Set up your 16-45 and take a couple shots at 28mm and at 35mm and then put on your 50mm and compare.
I'd also like to point out you rent the Sigma 28mm for $70 for a month with the damage waiver. If that two lens rule is hard and fast, maybe renting the 18mm-250mm and renting the 14mm f/2.8 or 31 f/1.8 is the way to go. I've used CameraLensRentals.com once, and heard only good things about them here on the boards. The worst part of the experience was having to send them back at the end, although I understand they'll work out competitive prices if you request to buy it instead of returning it....