Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-20-2010, 09:21 AM   #1
Senior Member
MikesChevelle's Avatar

Join Date: Jan 2010
Location: STL
Photos: Gallery
Posts: 119
What does it mean to have a "fast" lens

I see alot of people recommending a fast 50 and was wondering what fast relates to.

01-20-2010, 09:34 AM   #2
Veteran Member




Join Date: Jun 2009
Location: on the wall
Photos: Gallery
Posts: 715
Let me google that for you
01-20-2010, 09:52 AM   #3
Senior Member
MikesChevelle's Avatar

Join Date: Jan 2010
Location: STL
Photos: Gallery
Posts: 119
Original Poster


thank you and that is hilarious
01-20-2010, 12:58 PM   #4
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,838
Fast lenses look like this. You need a high shutter speed to capture one.



Yeah, I took 20 pictures to get that, and I probably should have used Photoshop.

01-21-2010, 05:27 AM   #5
Loyal Site Supporter




Join Date: Mar 2009
Location: Southern Indiana
Photos: Gallery
Posts: 15,310
A fast lens means one with a wider maximum aperture. Usually that will be a prime lens with a maximum f stop between 1.2 and 2 or a zoom with a maximum f stop of 2.8. Basically it is fast because you can shoot with a faster shutter speed wide open than you can with a slow lens.
01-21-2010, 05:42 AM   #6
Junior Member




Join Date: Jan 2010
Posts: 27
Why does not exist f1.4 zoom lens?
01-21-2010, 09:43 AM   #7
Veteran Member




Join Date: Dec 2006
Location: Outside of Philly
Posts: 1,564
QuoteOriginally posted by crossing Quote
Why does not exist f1.4 zoom lens?
Because they would be way too big and expensive to be practical. Look at the size of the 16-50mm f/2.8. To make it two stops faster, you're going to have add QUITE a bit of glass. It would probably weight ~10 pounds and cost ~$4K.

If you need faster than f/2.8, you go primes.

Olympus makes a couple of f/2 zooms, but 4/3s has a smaller sensor so the lenses can be a little smaller (although they're still REALLY big!)
01-21-2010, 09:47 AM   #8
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,838
QuoteOriginally posted by crossing Quote
Why does not exist f1.4 zoom lens?
Price, size and weight. Olympus has a couple of f2.0 zooms for their system, which has a smaller sensor than Pentax uses. One is a 14-35mm f2.0. It costs $1850, weighs 915 grams and uses a 77mm filter. The other is a 35-100mm f2.0, for $2050. It takes the same 77mm filter so you can save money when you get the pair. It weighs 1650 grams and has 21 lens elements.

For an f1.4 zoom, price might be $6000. At that level, some people start to limit their lens purchases, so they might not sell many copies.

01-21-2010, 02:07 PM   #9
Ash
Community Manager
Loyal Site Supporter
Ash's Avatar

Join Date: Mar 2007
Location: Toowoomba, Queensland
Photos: Gallery | Albums
Posts: 22,681
QuoteOriginally posted by crossing Quote
Why does not exist f1.4 zoom lens?
Here's one...


Tamron | 13VM2812AS 2.8-12 mm f/1.4 Industrial Lens | 13VM2812AS

Wouldn't bother trying to find an adapter for it to go on your cam... something tells me its IQ is not all that crash hot...
01-22-2010, 07:46 AM   #10
Veteran Member




Join Date: Dec 2006
Location: Outside of Philly
Posts: 1,564
QuoteOriginally posted by Ash Quote
Here's one...


Tamron | 13VM2812AS 2.8-12 mm f/1.4 Industrial Lens | 13VM2812AS

Wouldn't bother trying to find an adapter for it to go on your cam... something tells me its IQ is not all that crash hot...
I doubt that the image circle of that lens would be even close to covering an APS-C sensor.

They DO make fast zooms for video applications, but video cameras have MUCH smaller sensors as well.
01-22-2010, 09:17 AM   #11
Veteran Member
WMBP's Avatar

Join Date: Dec 2006
Location: Dallas, Texas
Photos: Gallery
Posts: 2,496
QuoteOriginally posted by MikesChevelle Quote
I see alot of people recommending a fast 50 and was wondering what fast relates to.
Mike,

As others have mentioned already, "fast", when applied to lenses, simply means that the lens has a large maximum aperture. When somebody says a lens is fast, I usually understand that to mean that the lens can reach at least to f/2.8 and possibly larger (f/2, f/1.8 etc). Photographers like fast lenses, for two reasons. The most important reason is that larger apertures mean shallower depth of field (other things being equal) and photographers like to have the option of shallow depth of field. Also, faster lenses make it possible to shoot in lower light without a flash.

Now, to the "fast 50."

Back in the 35mm film days, 50mm focal length was deemed to provide a "normal" focal length. (More on this below.) And back in those days, just about every lens maker had a "fast 50", that is, a 50mm prime that went to f/1.4. Because 50mm lenses produced results that were pretty close to what our eyes normally see, 50mm was a popular focal length, meaning that manufacturers sold a lot of 50mm lenses. And because sales were good, makers were able to make these lenses high quality yet keep the prices low, which just meant that they sold more. So just about every serious photographer had a fast 50 in his kit bag.

These days, you can find an f/1.4 lens at 50mm from just about every lens manufacturer, and the lenses are usually relatively affordable - and usually high quality, too. My Pentax FA 50 f/1.4 is one of my best lenses - and one of the cheapest.

Interestingly, you don't see a lot of lenses at other focal lengths that go to f/1.4. Sigma has a 30mm f/1.4 for the Pentax K-mount that appears to be a very nice lens. Perhaps there are other f/1.4 lenses out there but I'm not aware of 'em. I have a Sigma 28 f/1.8, a Pentax 35 f/2 and a Pentax 70 f/2.4. Zoom lenses seldom go faster than f/2.8, apparently for engineering reasons that I don't begin to understand.

Anyway, we Pentax users no longer have a lens for the "normal" field of view that is both really fast AND affordable. Normal field of view for an APS-C sensor like the ones in the Pentax DSLRs would be a focal length in the low 30s. Actual "normal" human field of view is represented by a lens a little wider than 50mm (on a 135-format film SLR), closer to about 45mm or even a tad less. (Experts are not unanimous about this.) Given the 1.5x "crop factor" of the Pentax DSLR cameras, a lens with a normal field of view - that is, a field of view that shows things pretty much as they appear to your unaided eyes - would be around 30mm, give or take 1-2mm. My normal lenses are my Sigma 28 f/1.8 and my Pentax 35 f/2.

If I win the Texas lottery, one of the first things I'll do is buy the Pentax 31 f/1.8. But right now at Amazon, the Pentax 31 costs almost three times as much as the Sigma 30 f/1.4 or my Sigma 28 f/1.8. I'm posting a photo

Will
01-22-2010, 10:07 AM   #12
Veteran Member




Join Date: Dec 2006
Location: Outside of Philly
Posts: 1,564
QuoteOriginally posted by WMBP Quote
Mike,


Interestingly, you don't see a lot of lenses at other focal lengths that go to f/1.4. Sigma has a 30mm f/1.4 for the Pentax K-mount that appears to be a very nice lens. Perhaps there are other f/1.4 lenses out there but I'm not aware of 'em. I have a Sigma 28 f/1.8, a Pentax 35 f/2 and a Pentax 70 f/2.4. Zoom lenses seldom go faster than f/2.8, apparently for engineering reasons that I don't begin to understand.
Not much to understand, it's just a size/complexity issue. They COULD easily make a 24-70 f/1.4 lens, it would be BIG and VERY EXPENSIVE. People wouldn't buy it. Therefore they don't make it.

Think about the size differential from a 16-50mm f/2.8 and the 18-55 f/3.5-5.6. That's a difference of two stops. Now take the 16-50 and imagine how much bigger it would have to be to get f/2 throughout the range. Then do this "mental exercise" one more time to get f/1.4. I'd guess it would be around $6K (and weigh 10 pounds) by the time you're done with it. You're much better off with a 30mm f/1.4 and 50mm f/1.4 and a second body.
01-22-2010, 10:31 AM   #13
Veteran Member
WMBP's Avatar

Join Date: Dec 2006
Location: Dallas, Texas
Photos: Gallery
Posts: 2,496
QuoteOriginally posted by egordon99 Quote
Not much to understand, it's just a size/complexity issue. They COULD easily make a 24-70 f/1.4 lens, it would be BIG and VERY EXPENSIVE. People wouldn't buy it. Therefore they don't make it.

Heh, well THAT part I do understand. I meant that I don't understand the size/complexity issues involved. For me at least, identifying them as "size/complexity" issues (or as I put it "engineering" issues) simply tags the issue for filing away. It doesn't represent understanding. :-)

I have very little understanding about how lenses are built and, candidly, not much desire to learn. I don't care how hard life is for lens makers. I do care about the image quality of my lenses. I just haven't felt that my attempts to learn about the innards of the lenses has made any difference to my ability to identify what will be a good lens and what won't be.

Let's say that the 35 f/2 is bigger than the 40 f/2.8 because the former is a stop faster, and making lenses faster requires making 'em bigger. If that's the case, then how is it that the 50 f/1.4 is actually SMALLER than the 35 f/2? But that's okay, don't tell me. As I said, I don't really care. (Note: Not caring isn't the same thing as not wanting to know. I'm vaguely curious. I just don't think that satisfying my curiosity will be easy or worth the effort.)

As for costs, those are a bit of a mystery to me, too. It's fairly intuitive that a product that's more complicated to make would be more expensive, and would therefore cost more. Except that it's not quite true, all of the time. The fast 50 (a.k.a. "nifty 50") has generally been an affordable lens. I assume the reason for that is that this lens has sold well, so the makers are willing to make a smaller profit per unit.

Will
01-22-2010, 10:36 AM   #14
Veteran Member




Join Date: Dec 2006
Location: Outside of Philly
Posts: 1,564
Fair enough Will....As for how much an extra stop could cost, check out the price (and size!) differential between the Canon 200mm f/2.8 and Canon 200mm f/2 (and those aren't even zooms )

As for the size difference between the 50/1.4 and 35/2, I believe that has to do with wide angle (and the 35 is wide angle on a film body) requiring a more complex retrofocus design (and THAT is engineering beyond my feeble brain )
01-22-2010, 11:21 PM   #15
Veteran Member
Jewelltrail's Avatar

Join Date: May 2008
Location: Rhode Island
Photos: Albums
Posts: 4,180
QuoteQuote:
Jst1moredave:One is a 14-35mm f2.0. It costs $1850, weighs 915 grams and uses a 77mm filter. The other is a 35-100mm f2.0, for $2050. It takes the same 77mm filter so you can save money when you get the pair. It weighs 1650 grams and has 21 lens elements.
Dave, now that is fuuuuuuuuuuuuuuuuuuuuuuuuuuuuunnnnnnnnnnnnnnnnnnnny. LOL
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, pentax help, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Do custom "artistic" or even "funny" lens caps evenexist? lovemehate Pentax SLR Lens Discussion 35 02-10-2016 09:10 AM
Which Zoom Lens? "Tamron AF 18-250mm", "Pentax-DA 18-250mm" or "Sigma 18-250mm" hoomanshb Pentax SLR Lens Discussion 4 07-30-2010 09:50 AM
K-mount Experts: How to convert a "KAF2" lens to "KF"? panoguy Pentax SLR Lens Discussion 24 07-08-2010 05:20 PM
"Hunger for a DA*50-135?" or "The DA*50-135 as a bird lens!" or "Iron age birds?" Douglas_of_Sweden Post Your Photos! 4 08-13-2008 06:09 AM
Wishing for a "Fast Lens" krs Pentax SLR Lens Discussion 11 12-11-2007 10:47 PM



All times are GMT -7. The time now is 11:48 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top