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02-05-2010, 08:41 AM   #1
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The real world difference f/1.4 -vs- f/2

I've been looking at some "A" series lens on e-bay. There a lots of f/2's, a number of f/1.7's and a few f/1.4's.

Other than the 1 stop of light, what are the other benefits of using the f/1.4 over the f/2? Is the DOF that much better? The IQ? Is an f/1.4 really worth $100+ more than the f/2?

I'd like your real world opinions.





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02-05-2010, 08:50 AM   #2
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Everyone should have a f/1.4 in their arsenal; and an f/1.7.

The f/2 will take pretty much as nice pictures as the previous two; from my understanding from others on the forum, there's just a bit more "pixie dust" sprinkled on the pictures with the former two. Only having the f/1.7 and 1.4, can't say 1st hand. But I'll believe their opinions. Does it use a different formula for the glass, or the elements? I've never cared that much to research. But from overwhelming sources, I've read there's a noticeable (if still subtle) step up with the 1.7 and 1.4.

Having taken numerous pictures of friends in a dark restaurant sans flash, the extra stop of light should not be discounted as being un-important. Getting a shot with very narrow DOF is better than getting a blur.

p.s. I love using either w/the Pentax AF 1.7x TC. This is generally looked down on by many on this forum, saying the TC isn't made for that focal length. Well I've had nothing but fabulous success with that combo and I love the results.
02-05-2010, 09:01 AM   #3
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Can you post some pics of yours taken with 50mm on a 1.7x AF TC ?
02-05-2010, 09:09 AM   #4
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I have some great samples taken before Christmas with the f/1.4, with and without the TC focusing on a few buildings in NYC, but have not gotten around to PP'ing those, hosting, and sharing. That'll be a while as there's a lot to do before that.

Otherwise, this outing was taken w/the f/1.7 and 1.7X TC. It's when I decided I loved the combo:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/35674-told-not...u-tell-me.html

02-05-2010, 09:21 AM   #5
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Here's some center sharpness MTF data for the A50:1.2 & A50:1.7


Not much difference I'd say. I find 1.7 to be OK DOF-wise for portraits.

Dave
02-05-2010, 09:48 AM   #6
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QuoteOriginally posted by newarts Quote
Here's some center sharpness MTF data for the A50:1.2 & A50:1.7


Not much difference I'd say. I find 1.7 to be OK DOF-wise for portraits.

Dave
sorry but are you confusing 1.2 with 2? i think he was asking about f2
02-05-2010, 09:52 AM   #7
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I think you have to decide how much you're willing to budget for your artistic needs, and whether you feel like you need to take a lot of pics in low light.
02-05-2010, 10:43 AM   #8
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In my opinion, the difference between f/1.4 and f/2 is *not* worth the difference in price most of the time. But the difference between f/1.7 and f/2 is - only an additional $10-$20 gets you a much better lens.

02-05-2010, 11:37 AM   #9
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Well, I asked this because I see of lot of really great stuff posted using the 16-50 f/2.8 and the 16-45 f/4.

It would seem to me that a 50mm f/2 would be more than adequate if someone has been using an f/2.8 or f/4 zoom lens.

Most of what I seem to do is either outdoors or flash assisted. I don't do weddings or have a 2 year old to chase around after.

Seems that the A 50mm f/2 can be picked up for around $30 - 40. So, that should be a pretty good cost for a "comparatively" fast lens.

thanks for the information
02-05-2010, 10:55 PM   #10
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QuoteOriginally posted by Oscar1 Quote
Well, I asked this because I see of lot of really great stuff posted using the 16-50 f/2.8 and the 16-45 f/4.

It would seem to me that a 50mm f/2 would be more than adequate if someone has been using an f/2.8 or f/4 zoom lens.

Most of what I seem to do is either outdoors or flash assisted. I don't do weddings or have a 2 year old to chase around after.

Seems that the A 50mm f/2 can be picked up for around $30 - 40. So, that should be a pretty good cost for a "comparatively" fast lens.

thanks for the information
The A50 f/2 is plenty fast, you are right. The point people are trying to make is that the F/1.7 and F/1.4 are more usable at F/2 (well, sharper that is). Really, nothing you can do wrong with an A50 f/2, they will perform very well for the money. But be on the lookout for an F/1.7
02-06-2010, 01:34 PM   #11
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Right - no one is saying f/2 is not good enough for most purposes. Just that the image quality of the f/1.4 and f/1.7 lenses is quite a bit a better. Maybe not enough better to be worth selling out an additional $100 or more for an f/1.4 version, but enough better to be worth shelling out an additional $20 for an f/1.7 version.
02-06-2010, 06:10 PM   #12
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Don't be afraid of picking up an M42 Takumar 50/1.4 if you find a deal, of course an adapter might be as much as the lens (make sure it's an Asahi Pentax or Pentax adapter) I had an A 50/2 that I liked, but then I got a Super Tak and it's better.
02-06-2010, 09:54 PM   #13
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I still have the 55/f2 Takumar lens that came with my SP 1000 over 30 years ago. It is very sharp, even wide open. These lenses can be picked up for $15-20 on Ebay and are a steal. Most of us spend that in the coffee shop every week. Is an F 1.4 worth $100 more? To some it is but with patience you will find one for less. Often you can find them with a camera for much less.
02-06-2010, 10:33 PM   #14
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QuoteOriginally posted by Oscar1 Quote
I've been looking at some "A" series lens on e-bay. There a lots of f/2's, a number of f/1.7's and a few f/1.4's.

Other than the 1 stop of light, what are the other benefits of using the f/1.4 over the f/2? Is the DOF that much better? The IQ? Is an f/1.4 really worth $100+ more than the f/2?

I'd like your real world opinions.
The build quality is a bit better for the faster lenses, but the f2 lenses are good enough. There is a difference in coatings, which is very obvious when the lenses are side by side. I don't think this creates a large difference either; I've never seen it show up in images as excess flare or different colors.

Sharpness is measurably better for the faster lenses. Lenses are always better stopped down a bit from their maximum aperture, and starting with a larger maximum aperture gives the faster lenses an advantage. I know I don't have any images where this sharpness advantage makes or breaks the photo, but it is easy to demonstrate. Everyone likes sharpness. Any 50mm Pentax is a pretty good lens already, so better is a small step.

You have a greater range of depth of field options with the faster lenses. It comes with less chance to screw up the focus point, but if you have the ability, it's there to use. I think this is a clear real-world advantage. I'm going to skip "bokeh"; maybe the most important difference to some but it's subjective.

The one-stop advantage is not so easy to overlook. That can make or break an image. Also, gaining an extra stop of light usually means a hefty price hike, and it's not linear. Going from an A50/1.4 to an A50/1.2 can mean paying four times as much for only an extra half-stop, some advantages similar to the above, and bragging rights.

It's nice to have choices, so you can decide for yourself.
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