Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-22-2016, 05:27 PM   #1
Junior Member




Join Date: Jul 2016
Location: Alps
Photos: Gallery
Posts: 35
77 limited : awesome, but focus past infinity ?

Hello,
So I finally got myself the infamous prime some months ago, and it's hard to put it off my k3ii since! Fantastic feeling, contrast and colours. Worst thing is that I'm now yearning for the 31 and hell is expensive (doubled its price in few years...).
Only one question : I've never had a lens with focus at infinity "out of focus". I've got to go back by quite a margin when I'd just want to manually focus until it reaches the end for infinity focus. I had to micro adjust AF to +9 also. Is that an OK behaviour? Should I return to Pentax under guarantee?
Thanks for your advice

11-22-2016, 05:57 PM   #2
Site Supporter
Site Supporter




Join Date: May 2009
Location: North Carolina
Posts: 790
If you have to dial in +9 AF adjustment and infinity focus is that far off, either something is really off kilter with that lens or your camera. I've never had to use AF adjustments on any of my cameras.

Do you have to dial in that much AF adjustment with other lenses?
11-22-2016, 06:00 PM   #3
Loyal Site Supporter
Loyal Site Supporter
clackers's Avatar

Join Date: Jul 2013
Location: Melbourne
Photos: Albums
Posts: 15,929
Going past infinity is fine, I think the idea of accurate hard stops has gone the way of the dodo, because of fluctuating temperature, etc.

+9 is still within the specifications.

Hope that's all you have to contend with.

Have you checked for decentring yet? Best to do all this within your warranty period.
11-22-2016, 06:36 PM   #4
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 42,007
QuoteOriginally posted by clackers Quote
Going past infinity is fine,
...but highly unusual for a lens built to FA 77/1.8 standards. Given that the PDAF required significant fine tune, I too suspect a centering defect or physical damage to the lens.

Edit: Pål Jensen was good enough to remind me that slight infinity overrun is intentional with many longer lenses. I checked my copy of the FA 77/1.8 and found an overrun of about 1 degree of arc at 1 mile (1.6 km) distance at 20 C ambient temperature.


Steve


Last edited by stevebrot; 11-30-2016 at 04:47 PM.
11-22-2016, 06:36 PM   #5
Site Supporter
Site Supporter




Join Date: Mar 2008
Location: Prince George, BC
Photos: Gallery | Albums
Posts: 3,460
When I bought my first M*300/4 in 1983, one of the new specs was that it was the first Pentax lens to do away with the hard infinity stop to account for temperature fluctuations. It is a benefit for those that do a lot of extreme temperature work.
11-23-2016, 02:50 AM   #6
Junior Member




Join Date: Jul 2016
Location: Alps
Photos: Gallery
Posts: 35
Original Poster
QuoteOriginally posted by brofkand Quote
I've never had to use AF adjustments on any of my cameras.

Do you have to dial in that much AF adjustment with other lenses?
It's the only lens I ever had to AF adjust, so I guess my camera is OK.
11-23-2016, 06:39 AM   #7
Site Supporter
Site Supporter




Join Date: May 2009
Location: North Carolina
Posts: 790
QuoteOriginally posted by azath Quote
It's the only lens I ever had to AF adjust, so I guess my camera is OK.
I think it's probably worthwhile to send that lens back to Pentax - needing to dial in that much micro adjustment plus the issues of infinity focus is not normal for that lens in my opinion. Others may disagree, but it doesn't take a lot of money or time to send the lens back to Pentax's repair facility.

11-23-2016, 01:59 PM   #8
Junior Member




Join Date: Jul 2016
Location: Alps
Photos: Gallery
Posts: 35
Original Poster
QuoteOriginally posted by clackers Quote
Have you checked for decentring yet? Best to do all this within your warranty period.
Nope but I will try (just been reading on the subject). It's still on guarantee for a while.

Thank you all for answers.
I think I'll have it checked by Pentax. Still within the specs indeed, but not by much and that's why I'm concerned.
11-30-2016, 03:31 PM   #9
Site Supporter
Site Supporter
Pål Jensen's Avatar

Join Date: Dec 2007
Location: Norway
Photos: Albums
Posts: 4,340
QuoteOriginally posted by stevebrot Quote
...but highly unusual for a lens built to FA 77/1.8 standards. Given that the PDAF required significant fine tune, I too suspect a centering defect or physical damage to the lens.


Steve
This lens, like almost all telephotos, are designed to focus past infinity. The 43mm do the same. It is for compensating for temperature.
11-30-2016, 04:43 PM   #10
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 42,007
QuoteOriginally posted by Pål Jensen Quote
This lens, like almost all telephotos, are designed to focus past infinity. The 43mm do the same. It is for compensating for temperature.
When I read your comment, it occurred to me that I seldom shoot wide open at infinity and have no basis from which to make a statement one way or the other. I was aware it is common practice of providing breathing room at infinity for longer lenses, but did not think it would apply to a moderate tele like the FA 77/1.8. So, I mounted up my MIJ copy (bought 2009) to the K-3 and found a couple of prominent trees at about 1 mile (1.6 km) distance. Using magnified live view, best focus was attained at about 1 degree of arc shy of the infinity hard stop. Cool, now I know for sure.

On a whim, I then mounted up an assortment of manual focus fast-50s and was surprised to find their hard stops dialed in to a fairly consistent 100m. Well, if that isn't interesting. I then checked my DA 50/1.8 and found that it focuses a full 10 degrees past infinity before hitting its stop. I guess they felt safe with that given there is no focus scale on the ring.

Finally, I tried my M42 Vivitar 135/2.8 (Komine). It was fairly gratifying that, like the FA 77/1.8, it too focuses just a smidgen past infinity despite it being a modestly priced lens when it was made in 1971.

I will amend my comment above.


Steve
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!
focus, infinity, k-mount, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Super-Takumar 1:2.5/35 on Sony E-mount Body Focus Past Infinity butangmucat Troubleshooting and Beginner Help 28 07-19-2016 11:15 PM
Pentax M lens focus past infinity? GXRUser Troubleshooting and Beginner Help 5 11-21-2013 07:18 AM
Pentax 85mm f/2 -- does yours focus past infinity? deadwolfbones Pentax SLR Lens Discussion 10 04-30-2010 10:32 PM
Why focus past infinity alehel Pentax SLR Lens Discussion 8 05-15-2009 02:41 PM
Why would you ever want to focus past infinity? Isaac314 Pentax SLR Lens Discussion 18 10-22-2008 02:02 PM



All times are GMT -7. The time now is 08:14 AM. | 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