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Archive 2016 · Hard Stop Infinity Focus Question

  
 
mysh
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p.1 #1 · p.1 #1 · Hard Stop Infinity Focus Question


I was wondering why lens designer don't always put hard stop infinity focus on their lenses.

I don't know all the tech issues that go into lens design but it seems like it wouldn't be that challenging to do this. Is there a logical reason why lens designers don't make all lenses with hard stop focus?




Sep 24, 2016 at 02:18 PM
naturephoto1
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p.1 #2 · p.1 #2 · Hard Stop Infinity Focus Question


mysh wrote:
I was wondering why lens designer don't always put hard stop infinity focus on their lenses.

I don't know all the tech issues that go into lens design but it seems like it wouldn't be that challenging to do this. Is there a logical reason why lens designers don't make all lenses with hard stop focus?



Are you talking about Manual Focus lenses or AF lenses? I do not know of any MF lenses that do not have a hard stop inifinity focus, but AF lenses usually do or always? do not have a hard stop for infinity if they are focus by wire.

Rich



Sep 24, 2016 at 02:22 PM
mysh
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p.1 #3 · p.1 #3 · Hard Stop Infinity Focus Question


I meant either one. I just wonder why all lenses don't have this. I would think customers would welcome it on all lenses AF and MF.


Sep 24, 2016 at 02:29 PM
freaklikeme
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p.1 #4 · p.1 #4 · Hard Stop Infinity Focus Question


Because MF is engaged either by wire (as with mirrorless) or via an automatic clutch (as with most Canon lenses, for example) so the position of the elements (the focus distance set) has nothing to do with the position of the manual focus ring. If the manual focus ring moved while the lens AF'd, keeping it's position relative to the focus distance, like some old Minolta lenses, then you could have hard stops.


Sep 24, 2016 at 02:42 PM
cputeq
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p.1 #5 · p.1 #5 · Hard Stop Infinity Focus Question


mysh wrote:
I was wondering why lens designer don't always put hard stop infinity focus on their lenses.

I don't know all the tech issues that go into lens design but it seems like it wouldn't be that challenging to do this. Is there a logical reason why lens designers don't make all lenses with hard stop focus?



Tolerances.

Just a fraction of a millimeter can be the difference between a sharp infinity-focus shot and one that comes just short of sharp infinity.

There are slight tolerances in camera bodies (distance from sensor to flange), flange/mount thickness itself, and then tolerances in lenses from rear element / point of focus to the sensor plane.

Summed up, they could pose serious problems if a 'hard stop' was created on the lens -- and then the lens and/or camera tolerances meant this hard stop was a bit too short or too long.

That's not even considering temperatures, which could also slightly skew tolerances one way or another.

And why do tolerances exist? Cost. Mechanical devices made to very tight tolerances would be unaffordable for most people.






Sep 24, 2016 at 02:49 PM
gyoung143
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p.1 #6 · p.1 #6 · Hard Stop Infinity Focus Question


Before the advent of fly by wire, 'manual focus' lenses had a hard stop infinity, even my old Nikon AF lenses have hard infinity stops. All my Leica,Nikon and 'alt' manual focus lenses have accurate hard infinity stops, and very useful they are too.
The tolerances in registration distance should be less than will give problems with lens tolerances, or the camera is so poorly made as to not be worthy of consideration for serious use.
For more than 50 years I have used precision 35mm cameras, Leica and Nikon especially, for landscape photography using the hard infinity stop and never had a problem until I stated adapting lenses to Sonys, and have shimmed the adapters so I can carry on that way.
No excuse IMHO for a manual focus lens to have an innaccurate focussing scale and infinity stop, but its impossible to achieve with a fly by wire focus system.

Gerry



Sep 24, 2016 at 05:00 PM
DocsPics
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p.1 #7 · p.1 #7 · Hard Stop Infinity Focus Question


Kind of a head scratcher....before going out to shoot the Northern Lights, I have to take $2000 lenses and focus them at infinity during daytime, then tape the focus ring in position before going into the night. I guess I should be glad tape was invented (second in importance only to the wheel).





© DocsPics 2016




Sep 24, 2016 at 05:27 PM
cputeq
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p.1 #8 · p.1 #8 · Hard Stop Infinity Focus Question


gyoung143 wrote:
Before the advent of fly by wire, 'manual focus' lenses had a hard stop infinity, even my old Nikon AF lenses have hard infinity stops. All my Leica,Nikon and 'alt' manual focus lenses have accurate hard infinity stops, and very useful they are too.

Gerry


I haven't been shooting for 50 years (much less been alive that long! ) but I'd say you've been blessed or perhaps film 'hides' certain flaws (just like low-MP cameras can hide lens or AF flaws).

I say this because I've also used MF lenses on their native mounts and so far only one infinity hard-stop has ever been accurate - I think it was an adapted Canon FD 20mm on a Sony A7, of all things.

Nikon 105/2.5 AIS, Zeiss 35/2 (ZE), multiple Pentax AF lenses using MF (all native mounted), etc. have all been off at infinity (the ZE 35/2 was close, but required about a 1mm 'back off' after hitting the hard stop). I think my late grandmother's film Canon (something) with her 50/1.8 FD was even off, but I'm going off really fuzzy memory on that one.


I really dislike it, because I really like hard-stops for things like astrophotography, but they've been very elusive to me!

Even with Fuji's AF/MF lenses with the MF clutch and hard-stops on the lens....the lens will electronically focus past infinity slightly after hitting the lens hard-stop. I have to believe this is to account for 'slop' in manufacturing or environmental concerns.

And I have to wonder if such 'slop' is accounted for because some are in the habit of zooming in to 100% on high-MP images, looking for problems

Most of my hard-stop concerns have been very slight, in that had I taken the photo past infinity and had it printed, the problem may or may not have been noticeable.





Sep 24, 2016 at 05:57 PM
mysh
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p.1 #9 · p.1 #9 · Hard Stop Infinity Focus Question


I have had the opposite experience. I have used about 25 manual focus nikon lenses and all but two were spot on.
I also have a Zeiss 15mm and that one is correct as well. odd you have had so many issues with it.

By the way I use a Nikon D810

cputeq wrote:
I haven't been shooting for 50 years (much less been alive that long! ) but I'd say you've been blessed or perhaps film 'hides' certain flaws (just like low-MP cameras can hide lens or AF flaws).

I say this because I've also used MF lenses on their native mounts and so far only one infinity hard-stop has ever been accurate - I think it was an adapted Canon FD 20mm on a Sony A7, of all things.

Nikon 105/2.5 AIS, Zeiss 35/2 (ZE), multiple Pentax AF lenses using MF (all native mounted), etc. have all been off at infinity (the ZE
...Show more




Sep 24, 2016 at 06:08 PM
arduluth
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p.1 #10 · p.1 #10 · Hard Stop Infinity Focus Question




DocsPics wrote:
Kind of a head scratcher....before going out to shoot the Northern Lights, I have to take $2000 lenses and focus them at infinity during daytime, then tape the focus ring in position before going into the night. I guess I should be glad tape was invented (second in importance only to the wheel).



No reason you should have to do that. Unless D810 live view is that bad, that should be plenty if light to focus. Even with a well calibrated hard stop at infinity, I still would confirm focus.



Sep 24, 2016 at 09:19 PM
akclimber
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p.1 #11 · p.1 #11 · Hard Stop Infinity Focus Question




DocsPics wrote:
Kind of a head scratcher....before going out to shoot the Northern Lights, I have to take $2000 lenses and focus them at infinity during daytime, then tape the focus ring in position before going into the night. I guess I should be glad tape was invented (second in importance only to the wheel).



My trick is to use live view. Find a star, zoom in all the way, manually focus, then tape. It's easy and any temp variations from day to night that might affect things are not a factor.



Sep 24, 2016 at 09:32 PM
mysh
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p.1 #12 · p.1 #12 · Hard Stop Infinity Focus Question


thanks everyone for the comments. It gave me a better idea why its not done more in modern lenses.


Sep 25, 2016 at 01:45 AM
gyoung143
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p.1 #13 · p.1 #13 · Hard Stop Infinity Focus Question




akclimber wrote:
My trick is to use live view. Find a star, zoom in all the way, manually focus, then tape. It's easy and any temp variations from day to night that might affect things are not a factor.


Do I understand that you zoom in to the longest focal length to focus, and then zoom out afterwards to frame the shot?
Apologies if I have misunderstood but if you do that you are asking for trouble, few if any zoom lenses will hold focus as you zoom, many are not even designed to do so.

Gerry



Sep 25, 2016 at 02:38 AM
jcolwell
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p.1 #14 · p.1 #14 · Hard Stop Infinity Focus Question


gyoung143 wrote:
Do I understand that you zoom in to the longest focal length to focus, and then zoom out afterwards to frame the shot?
Apologies if I have misunderstood but if you do that you are asking for trouble, few if any zoom lenses will hold focus as you zoom, many are not even designed to do so.

Gerry


Yes, most zoom lenses are not "parfocal".



Sep 25, 2016 at 06:03 AM
jhinkey
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p.1 #15 · p.1 #15 · Hard Stop Infinity Focus Question


DocsPics wrote:
Kind of a head scratcher....before going out to shoot the Northern Lights, I have to take $2000 lenses and focus them at infinity during daytime, then tape the focus ring in position before going into the night. I guess I should be glad tape was invented (second in importance only to the wheel).



Unfortunately it has nothing to do with the $2000 lens - it's just plain physics (finite manufacturing tolerances, thermal expansion of materials, etc.) and the advent of AF with MF override. To get what you want your $2000 lens would cost an order of magnitude or so more.

Not a head scratcher at all.



Sep 25, 2016 at 07:49 AM





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