The "real" values for the FA 77mm f/1.8 Ltd. Just out of curiosity.

bc_the_path · 06-02-2008, 11:01 AM

I faintly remember seeing somewhere that the measured focal length and the true aperture value of this legendary lens were slighltly different than specified. However, my searches did not help me find that piece of information again.
The focal length was closer to 80mm and the maximum aperture was to 2.

Is my memory playing tricks on me or what?

(I adore this lens, no matter what the numbers say).

Gooshin · 06-02-2008, 11:07 AM

maybe the one made in Burma?

bc_the_path · 06-02-2008, 11:59 AM

In the Popular Photography review of DA* 200mm f/2.8 they have measured the focal length as "198.33mm", for example. For the FA 50mm f/1.4 they report "51.93mm, f/1.45".
They did not tell whether those were made in Burma. :=)

Shashinki · 06-02-2008, 12:53 PM

Whats the point of making the lens 77mm if its not 77mm?

I can see the 70mm not being exactly 70mm, but why decide on crazy numbers like 31mm, 43mm and 77mm if they were not that focal length?

TomInJax · 06-02-2008, 02:42 PM

Part of the issue is that the focal length is measured at infinity. As you focus closer the actual focal length becomes longer and the effective f stop changes to let less light hit the sensor. So, perhaps Pentax designed the lens to be 77mm at infinity and test labs measure at... ummm... let's say 50 feet. That may account for the difference. Just a guess.

lbam · 06-02-2008, 03:51 PM

(77mm is approx half way between 70mm and 85mm... )

k100d · 06-02-2008, 05:34 PM

Originally posted by bc_the_path

I faintly remember seeing somewhere that the measured focal length and the true aperture value of this legendary lens were slighltly different than specified. However, my searches did not help me find that piece of information again.
The focal length was closer to 80mm and the maximum aperture was to 2.

Is my memory playing tricks on me or what?

(I adore this lens, no matter what the numbers say).

your mind is not playing tricks with you. i've read many many posts on these lenses to make my decision.

Godfrey says here that the lens is longer than 77mm
Should I get 77mm or 70mm? - Photo.net Pentax Forum

the f2 remark, i haven't heard, but this post does mention the DA70 is closer to 2.8
Digital SLR and Lens Review: By popular demand: Pentax DA 70mm Limited compared to FA 77mm

now if i could only take as good photos as i am at scrounging around and reading

06-02-2008, 11:01 AM	#1
bc_the_path Veteran Member Join Date: Mar 2007 Location: Ankara, Turkey Photos: Gallery Posts: 401	The "real" values for the FA 77mm f/1.8 Ltd. Just out of curiosity. I faintly remember seeing somewhere that the measured focal length and the true aperture value of this legendary lens were slighltly different than specified. However, my searches did not help me find that piece of information again. The focal length was closer to 80mm and the maximum aperture was to 2. Is my memory playing tricks on me or what? (I adore this lens, no matter what the numbers say).

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Debug Mode Question about "AF Test Area" values	brecklundin	Pentax DSLR Discussion	1	06-16-2010 04:46 PM
A real prob"lens" with my items	tcerveny	Pentax SLR Lens Discussion	7	09-28-2009 02:19 AM
"Real Life" Rusty Farm Stuff - bokeh content	mikeSF	Post Your Photos!	17	04-21-2009 10:43 AM
"Real-life stuff" — with birds! HAHA!	gawan	Post Your Photos!	24	04-20-2009 06:39 AM
Buying First "Real" Camera and Need Opinion On ZX-5 w/Accesories	brandontowey	Troubleshooting and Beginner Help	2	02-15-2009 07:13 AM

06-02-2008, 11:07 AM	#2
Gooshin Veteran Member Join Date: Sep 2007 Location: Toronto, the one in Canada. Posts: 5,610	maybe the one made in Burma?

06-02-2008, 11:59 AM	#3
bc_the_path Veteran Member Join Date: Mar 2007 Location: Ankara, Turkey Photos: Gallery Posts: 401 Original Poster	In the Popular Photography review of DA* 200mm f/2.8 they have measured the focal length as "198.33mm", for example. For the FA 50mm f/1.4 they report "51.93mm, f/1.45". They did not tell whether those were made in Burma. :=)

06-02-2008, 12:53 PM	#4
Shashinki Veteran Member Join Date: Jan 2008 Location: Norway Posts: 355	Whats the point of making the lens 77mm if its not 77mm? I can see the 70mm not being exactly 70mm, but why decide on crazy numbers like 31mm, 43mm and 77mm if they were not that focal length?

06-02-2008, 02:42 PM	#5
TomInJax Veteran Member Join Date: Dec 2007 Location: Jacksonville, FL Photos: Gallery Posts: 531	Part of the issue is that the focal length is measured at infinity. As you focus closer the actual focal length becomes longer and the effective f stop changes to let less light hit the sensor. So, perhaps Pentax designed the lens to be 77mm at infinity and test labs measure at... ummm... let's say 50 feet. That may account for the difference. Just a guess.

06-02-2008, 03:51 PM	#6
lbam Veteran Member Join Date: May 2008 Location: Toronto Photos: Gallery Posts: 442	(77mm is approx half way between 70mm and 85mm... )

06-02-2008, 05:34 PM	#7
k100d Veteran Member Join Date: Feb 2008 Location: Toronto Posts: 3,911	Originally posted by bc_the_path I faintly remember seeing somewhere that the measured focal length and the true aperture value of this legendary lens were slighltly different than specified. However, my searches did not help me find that piece of information again. The focal length was closer to 80mm and the maximum aperture was to 2. Is my memory playing tricks on me or what? (I adore this lens, no matter what the numbers say). your mind is not playing tricks with you. i've read many many posts on these lenses to make my decision. Godfrey says here that the lens is longer than 77mm Should I get 77mm or 70mm? - Photo.net Pentax Forum the f2 remark, i haven't heard, but this post does mention the DA70 is closer to 2.8 Digital SLR and Lens Review: By popular demand: Pentax DA 70mm Limited compared to FA 77mm now if i could only take as good photos as i am at scrounging around and reading