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01-18-2011, 11:47 PM   #1
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SMC Pentax-A 28mm f/2.8 to complement DA 18-250 for travel kit?

Hey all, so I picked up a K-7 last year off the forum when prices dropped after the K-5 introduction. Recently picked up a DA 18-250 from a forum member as well. Besides the lack of weather sealing, this should be a go-to lens for me for my fly fishing trips when max versatility and minimum lens changing plus being compact is key. The one glaring hole sounds like it will be low-light shooting, as I don't have a very fast setup. I will be doing 100% outdoors shooting, but don't want to be out of the game at dawn and dusk. So in a perfect world without college tuition to pay I'd get the DA* 55 for it's F1.4 for the low light times, but a good friend told me he has an A 28mm F2.8 from the 80s when he shot pentax film. Of course it would be manual focus, but should this lens' F2.8 be fast enough on the K-7 to get me by for low light situations or do I really need an F1.4 or 1.8 to be able to get sharp shots hand-held in low light?

Thanks for any advice! -LE

01-19-2011, 12:01 AM   #2
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An F2.8 won't be that much faster unfortunately. An F2 or larger aperture lens would be better.
01-19-2011, 12:05 AM   #3
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Maybe I should hold off on buying a new lens seeing as I will upgrade to the K-5 as soon as it is replaced in a year or two? Would it make the 18-250 at 18mm and F3.5 perform a hell of a lot better than on the K-7 with that new ISO ability? I don't really want to spend the money on a used DA* 55 just because I feel like that fixed focal range for me as an outdoors shooter would likely be very limiting....
01-19-2011, 12:09 AM   #4
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Try the 50mm 1.7 or 55mm 1.8, good low light performance for cheap.

01-19-2011, 12:35 AM   #5
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QuoteOriginally posted by paperbag846 Quote
Try the 50mm 1.7 or 55mm 1.8, good low light performance for cheap.
The A28/2.8 is a pretty nice lens and might be worth trying, especially if your friend will let you. It would certainly be better than the 18-250. But I agree, if you haven't used a lens faster than f/2 you need to try one or you won't know what you're missing. Getting a K-5 sure helps, but it's really no substitute for a fast lens, and I wouldn't recommend waiting a year or two when you should try a fast lens now for under $100.

I find that, with any lens, shutter speed generally needs to be faster than 1/10s (for example, 1/13 to 1/25s) for SR to work effectively on my Pentax DSLRs.

Personally, I was quite happy with my K-x and fast lenses before I got my K-5. The lenses make the difference. Going from the K-x to the K-5 was almost like only making a slight upgrade to my kit (although the K-5 does have many features I love).
01-19-2011, 12:49 AM   #6
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Sounds like a fast lens is worth it then for my dawn and dusk shooting, and I bet it would be great for really dreary days as well.

QuoteOriginally posted by paperbag846 Quote
Try the 50mm 1.7 or 55mm 1.8, good low light performance for cheap.
I looked through the current pentax lineup and didn't see any lenses with these specs....what series are these lenses? (I assume discontinued) And how much do they go for used? I am almost tempted to start saving up for a used DA* 55 though....would it be worth the extra couple hundred bucks?

Thank you! -Loren
01-19-2011, 01:29 AM   #7
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The 50/1.7 and 55/1.8 cited are manual. Newer F or FA or DA (whether * or Ltd or whatever) are AF and much more expensive. As mentioned, a 28/2.8 isn't terribly faster than a DA18-250 @28mm. Even f/2.5 doesn't make that much difference. (I have Vivitar and Tamron 28/2.5's and don't use them much.) I supplement my 18-250 with manual glass like a 24/2, some cheap 50-55/1.4's,and an 85/2. IMHO the main reason to use slower 24-28-35-40mm lenses is for discipline, and challenge, and maybe a bit of sharpness. Faster glass of 50mm and longer *is* significantly better in lower light.
01-19-2011, 02:09 AM   #8
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thank rico.....would you mind explaining to me why this faster glass for low light, as you mentioned, is usually 50mm and longer? Why no 14mm 1.4 or something along those lines ever? For me the shot to get at dawn and dusk would likely be of someone holding up a big fish and UWA is great for this, but I am concerned 55 might be too long....

Also, if I could get a used DA* 55 for a price I could afford some time in the next couple months.....any thoughts on the travel kit of the DA 18-250, DA* 55, and possibly the DA 10-17 thrown in as well?

01-19-2011, 08:10 AM   #9
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QuoteOriginally posted by RioRico Quote
maybe a bit of sharpness
This is the reason I like my 28mm f2.8 - at f4, it is miles sharper than the kit lens, and at f2.8 it has a nice out-of-focus rendering.

I think the 28mm is a good lens for IQ, but not for low light.
01-19-2011, 08:16 AM   #10
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I'd look for a 28mm F2 or one of the fast 50mm lenses, though I find 28mm more useful on APS-c. The Kiron/Vivitar 28mm/2 are nice. Not to repeat too much, but I don't find I get really significant focus isolation on a 28mm until F2, and with those lenses, you usually have good resolution at F2.8 which will improve the sharpness of your rig.
01-19-2011, 08:55 AM   #11
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QuoteOriginally posted by Loren E Quote
would you mind explaining to me why this faster glass for low light, as you mentioned, is usually 50mm and longer? Why no 14mm 1.4 or something along those lines ever?
That's one of those optics mysteries to me, but for some reason, 50-58mm is the sweet spot for fast glass, topping (or bottoming?) out at f/0.95. There are some in the f/1.4 range around 35mm and 85mm, but longer faster glass would be prohibitively bulky and expensive. The Helios-40 85/1.5 is rather monstrous, much larger than the 85/2's I've seen. A long fast lens just needs a huge objective.

Short fast lenses don't happen for a different reason -- in order for their rear elements to fit within an SLR's mirror-box space, they need a reverse-telephoto optical group called a retrofocus group. With a large (fast) objective, that RFG would need to be huge also.

Now I'm just talking here about lenses for FF and HF / APS-C cameras. Numerous fast, short lenses exist, cheap too. But they're for much smaller image frames (film or sensors). I have a Filmova 15-25/1.2 lens (cost: TWO BUCKS!) that I'm dying to try out, but I'll have to mod an old P&S to fit it. Its image circle and flange-focal distance (register) are much too small for my K20D. It *might* work on an m4/3 body, but will still probably vignette images.
01-19-2011, 09:05 AM   #12
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You might want to consider the Sigma 30mm 1:1.4 (might be a bit bulky, though).
01-19-2011, 05:26 PM   #13
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QuoteOriginally posted by RioRico Quote
That's one of those optics mysteries to me, but for some reason, 50-58mm is the sweet spot for fast glass,...Now I'm just talking here about lenses for FF and HF / APS-C cameras.
Given that APS-sized sensors are smaller than FF, and a 30mm lens in APS gives a similar field of view as a 50mm in FF, shouldn't it be possible to build a 30mm F1.4 or F1.2 that is no bigger than an old fast fifty? If not, why not?
01-19-2011, 11:33 PM   #14
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I think I am going to get a used DA* 55 to get not only a low-light lens but also a lens for poor weather to complement the K-7 so I don't have to resort to the optio. This with the 18-250 and the FE 10-17 will be my kit I am pretty sure......thanks for the advice all!
01-20-2011, 01:32 AM   #15
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QuoteOriginally posted by Spock Quote
Given that APS-sized sensors are smaller than FF, and a 30mm lens in APS gives a similar field of view as a 50mm in FF, shouldn't it be possible to build a 30mm F1.4 or F1.2 that is no bigger than an old fast fifty? If not, why not?
You've obviously mistaken me for an optical engineer. #8-) But here's my guess: Even though HF / APS-C frames are smaller than FF, with only half the area, the SLR mirror box has the same depth because Pentax kept the same lens register (flange focal distance) of 45.46mm. Any lens mounted on a Pentax body (also Nikon, Canon, Sony-Minolta, and similar SLRs) must still have its rear elements clear the swinging mirror. For shorter focal lengths, that requires a retrofocus group (RFG), which limits lens speed.

A mirrorless camera body, whether MILC/EVIL or rangefinder or whatever, allows rear elements to protrude much further into the body, almost to the image frame, so no RFG is needed. Some such protruding lenses *can* be used on SLRs, but only with MLU (mirror lock-up). This is one reason non-dSLR cameras are exciting: the prospect of FAST wide lenses.

QuoteOriginally posted by Loren E Quote
I think I am going to get a used DA* 55 to get not only a low-light lens but also a lens for poor weather to complement the K-7 so I don't have to resort to the optio. This with the 18-250 and the FE 10-17 will be my kit I am pretty sure......thanks for the advice all!
You have chosen wisely, grasshopper. That differs from my first kit only in that I got a K20D and FA50/1.4 (cheaper then). The 10-17, 18-250, and Fast Fifty, will see you through many many situations.

Last edited by RioRico; 01-20-2011 at 01:37 AM.
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