Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-23-2009, 06:29 PM   #1
Veteran Member
raymeedc's Avatar

Join Date: Nov 2007
Location: Brooklyn, New York
Posts: 951
50mm lens comparison myth?

I've heard experts, who seem to have been knowledgeable in such matters, state that Pentax 50mm f:2 lenses have always been a marketing tool to sell as kit lenses on new bodies that were in actuality f:1.8 or f:1.7 lenses with a block on the aperture path to limit it's maximum aperture being used, & yet I see users comparing one to the other, often attesting to the superiority of the faster lenses. Is this true, or are they really identical lenses?

05-23-2009, 06:32 PM   #2
Damn Brit
Guest




Trust a New Yorker to be a conspiracy theorist.
I'm sure that if it was true, it would be common knowledge now...
but you never know.
05-23-2009, 06:55 PM   #3
Senior Member




Join Date: May 2007
Location: Philadelphia, PA
Posts: 167
Busted!

I just compared an A 50/1.7 to an A 50/2 and a M 50/2. They are clearly different, although the size is the same the front element of the 2s is more recessed and a bit smaller.

See picture and more descriptions here:
Pentax Normal Prime Lenses
05-23-2009, 10:00 PM   #4
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,814
QuoteOriginally posted by raymeedc Quote
I've heard experts, who seem to have been knowledgeable in such matters, state that Pentax 50mm f:2 lenses have always been a marketing tool to sell as kit lenses on new bodies that were in actuality f:1.8 or f:1.7 lenses with a block on the aperture path to limit it's maximum aperture being used, & yet I see users comparing one to the other, often attesting to the superiority of the faster lenses. Is this true, or are they really identical lenses?
Not true for 50mm lenses. See this chart, and note the f2 lenses are 5 elements and 5 groups, optically different than the other 50mm lenses.

Pentax Normal Prime Lenses

However, I think it is true for the older 55mm lenses, SMC Pentax 55mm f1.8 and SMC Pentax f2. If you have the two lenses side by side, you can see the ring that limits the aperture opening on the f2 lens. They also have the same optical formula. The Takumar versions are also like this. I don't have any proof to show you, but I have owned lots of these particular 55mm lenses and I am convinced myself.

I think as a marketing concept it sounds kind of dumb. I know Canon sells some cameras with disabled features in firmware, and more expensive models simply enable the features. But here they have built an f1.8 lens, then modified it with extra parts (including a different aperture ring) and labor, to sell it for less. Maybe the f1.8 lenses were overpriced instead, but I don't see the payoff from the perspective of today's manufacturing perspective.

05-23-2009, 10:54 PM   #5
Veteran Member




Join Date: Jan 2009
Location: Canada
Posts: 1,255
QuoteOriginally posted by raymeedc Quote
I've heard experts, who seem to have been knowledgeable in such matters, state that Pentax 50mm f:2 lenses have always been a marketing tool to sell as kit lenses on new bodies that were in actuality f:1.8 or f:1.7 lenses with a block on the aperture path to limit it's maximum aperture being used, & yet I see users comparing one to the other, often attesting to the superiority of the faster lenses. Is this true, or are they really identical lenses?
You're talking about the 55's, not 50's:
The following is the optical formula for 55 f/1.8 and f/2.0:


There wasn't a K mount 50 f/1.8.
05-24-2009, 05:57 AM   #6
Veteran Member
raymeedc's Avatar

Join Date: Nov 2007
Location: Brooklyn, New York
Posts: 951
Original Poster
QuoteOriginally posted by Just1MoreDave Quote

However, I think it is true for the older 55mm lenses, SMC Pentax 55mm f1.8 and SMC Pentax f2. If you have the two lenses side by side, you can see the ring that limits the aperture opening on the f2 lens. They also have the same optical formula. The Takumar versions are also like this. I don't have any proof to show you, but I have owned lots of these particular 55mm lenses and I am convinced myself.
Yes, it must be the older 55s they were referring to. I can see that the current 50s are clearly different lenses.
05-24-2009, 08:15 AM   #7
Forum Member




Join Date: Feb 2007
Location: Los Angeles
Posts: 77
Pentax also "crippled" some their early lower end camera bodies so that the selected shutter speed could only go as fast as 1/500, although the actual shutter mechanism was identical for all their early cameras.

On one camera (the Pentax S1) you could actually turn the shutter speed dial to an unmarked detent past 1/500 to get the 1/1000 speed. Pentax had simply removed the 1/1000 indicator from the shutter speed dial, although they had left the actually 1/1000 speed!

This was all done because retailers wanted both high-end and low-end cameras to sell. Because Pentax was manufacturing essentially one camera they need to employ these "tricks" to broaden their line.

These practices seemed to have stopped after the release of the SP500 in the early 1970s, the last of the "crippled" shutter speed models.

Last edited by jimby; 05-24-2009 at 08:20 AM.
05-25-2009, 10:02 PM   #8
Senior Member




Join Date: Dec 2008
Location: Grand Rapids, MI. USA. Earth.
Posts: 139
I can't imagine the rage that went down when Pentax announced the crippled K-mount...

05-25-2009, 10:29 PM   #9
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,166
QuoteOriginally posted by asdf Quote
You're talking about the 55's, not 50's:
The following is the optical formula for 55 f/1.8 and f/2.0:


There wasn't a K mount 50 f/1.8.
It is interesting that the M, A, F, and FA 50mm f1.7 had the 6/5 optical formula of the K 55mm f1.8 and f2.



Could it be that the 50mm f1.7 lenses evolved from the K55mm lenses?
05-31-2009, 05:44 PM   #10
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,814
Proof!

I have an SMC Takumar 55mm f2 lens, so I took it apart to find the ring that limits it to f2. Disassembly is typical Asahi/Pentax: remove name ring, filter ring and unscrew front lens group to see this:



The ring is the part just above the aperture. It would have been nice to just pop it out but it doesn't do that. I then removed the rear lens group - no glass to scratch. Then unscrew the three common screws in front and the whole central barrel can slide out the front. Here is the barrel:



On the side you'll see three tiny common grub screws that hold in the evil part. But this part also helps hold the aperture blades in. It's hard to remove without having a few blades fall out too. Reinstalling them is a bit fussy but not impossible. Here's the part:



And with it removed. You can see I got fingerprints all over the blades but they're all in place.



To convert this lens to an f1.8 lens, I can file the opening in the evil part so it is larger. The aperture ring does allow the lens to open to f1.8 when it's set at f2. Therefore, Asahi/Pentax only had to have three parts that were different between f1.8 and f2 lenses: the part with the f2-size hole, an aperture ring labeled f2, and a name ring labeled 1:2/55. The Takumar versions often had the "1:2/55" text in yellow, so a bit of different paint too.

I got this lens as an extra in a package deal and I meant to test it against the 1.8/55. I don't need to do that now, but I haven't decided if filing a bigger hole will help or hurt its resale value.
06-01-2009, 10:32 AM   #11
Veteran Member




Join Date: Aug 2007
Location: England
Posts: 309
QuoteOriginally posted by Just1MoreDave Quote
I think as a marketing concept it sounds kind of dumb. I know Canon sells some cameras with disabled features in firmware, and more expensive models simply enable the features. But here they have built an f1.8 lens, then modified it with extra parts (including a different aperture ring) and labor, to sell it for less. Maybe the f1.8 lenses were overpriced instead, but I don't see the payoff from the perspective of today's manufacturing perspective.
Intel did this with 386's. They sold two, called (IIRC) SX and DX. The DX had a floating point processor, the SX didn't. SX motherboards had an empty socket in which you could add a floating point processor. However, it turns out that SX's *did* have a FP processor, but Intel had disabled it.

Richard
06-01-2009, 11:40 AM   #12
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,166
QuoteOriginally posted by Just1MoreDave Quote



. . .

I got this lens as an extra in a package deal and I meant to test it against the 1.8/55. I don't need to do that now, but I haven't decided if filing a bigger hole will help or hurt its resale value.
IMHO, it would hurt its resale value. However, its may not hurt it much due to the f2's not being that sought after.
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!
50mm, aperture, k-mount, lenses, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
lens comparison- fa50mm / tamron 17-50mm / tamron 28-75mm bimjo Pentax SLR Lens Discussion 11 03-16-2010 01:10 AM
Sharpness comparison between Pentax 18-55 and Tamron 17-50mm Rafalas Pentax SLR Lens Discussion 93 02-08-2010 07:23 AM
DA* 16-50mm Myth Burgerbrater Pentax SLR Lens Discussion 18 09-30-2009 08:38 AM
pentax lens Myth ljfitz Pentax SLR Lens Discussion 10 12-29-2008 03:47 PM
Lens Comparison siric Pentax SLR Lens Discussion 10 07-10-2008 07:08 AM



All times are GMT -7. The time now is 11:09 AM. | See also: NikonForums.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