Pentax 85mm f/2 -- does yours focus past infinity?

deadwolfbones · 04-30-2010, 01:05 PM

I recently bought an M85/2 here on the forums, and while it's in pristine condition, it focuses past infinity at the infinity range marker. What seems odd to me about this is that the MFD does not seem to be affected. Has anyone experienced a similar issue with their 85/2?

SOldBear · 04-30-2010, 01:10 PM

Originally posted by deadwolfbones

it focuses past infinity at the infinity range marker.

It is normal for any lens to have the focus ring a bit past infinity. It is part of the tolerance.

**germar** · 04-30-2010, 02:10 PM

I seem to recall that same deal with my 85 f2. I no longer have it, so I can't absolutely confirm, but I think there WAS a little wiggle past infinity, no issues with the lens.

Enjoy it!

germar

deadwolfbones · 04-30-2010, 02:18 PM

Originally posted by SOldBear

It is normal for any lens to have the focus ring a bit past infinity. It is part of the tolerance.

When the focus ring is turned all the way toward infinity, the marker is lined up perfectly with the infinity symbol.

At this point, when looking through the viewfinder, the lens is focused past infinity by a decent chunk. To get true infinity focus, I have to turn the focusing ring back toward the MFD by a bit.

This seems like some kind of alignment flaw to me. None of my other lenses behave this way.

But as I said, the fact that the MFD seems correct is baffling. But maybe I'm just measuring the MFD incorrectly?

jsherman999 · 04-30-2010, 02:24 PM

I'll check my 85 this weekend. FWIW, my Voigtlander 180 f4 Lanthar used to do the exact same thing...

axl · 04-30-2010, 02:25 PM

what is the lens focused on if it's past infinity?
I don't mean to come across as sarcastic or what... just don't get it... never thought there is something past infinity

deadwolfbones · 04-30-2010, 02:39 PM

Originally posted by axl

what is the lens focused on if it's past infinity?
I don't mean to come across as sarcastic or what... just don't get it... never thought there is something past infinity

Yeah, the concept is kind of

to me as well, but basically it means that you have to focus it back toward the MFD to get infinity focus. If you point the lens at a cloud, say (or a mountain), and focus it all the way to infinity it's just blurry. Gotta pull it back a bit to get the cloud sharp.

I've heard of focusing rings turning past the infinity marker, but I've never heard of one that stops precisely at the infinity marker, but is focused beyond infinity at that point.

krb · 04-30-2010, 02:45 PM

Originally posted by axl

what is the lens focused on if it's past infinity?

Nothing. That's the problem.

I have to say that having a focus ring that goes too far is better than one that doesn't go far enough.

SOldBear · 04-30-2010, 02:56 PM

Originally posted by deadwolfbones

When the focus ring is turned all the way toward infinity, the marker is lined up perfectly with the infinity symbol.
....
This seems like some kind of alignment flaw to me. None of my other lenses behave this way.

Now I know what you mean.

Yup. It is an alignment problem. The lens has a "stopper" screw; over time, the ring just gradually slips pass the stopper. If you are handy and brave, you can open up the lens and adjust the marker. I've done so to several lenses.

**pentaxman** · 04-30-2010, 10:16 PM

Many lenses will focus past infinity a slight amount by design. I have heard that this is to accomodate infrared film. The infinity focus can be easily adjusted. Having a split prism focusing screen makes it a cinch. You just loosen the screws holding the barrel with the distance markings to the focusing helix and turn it to line up with infinity when the lens is focused at infinity. Then just retighten the screws.

**Just1MoreDave** · 04-30-2010, 10:32 PM

Originally posted by deadwolfbones

When the focus ring is turned all the way toward infinity, the marker is lined up perfectly with the infinity symbol.

At this point, when looking through the viewfinder, the lens is focused past infinity by a decent chunk. To get true infinity focus, I have to turn the focusing ring back toward the MFD by a bit.

This seems like some kind of alignment flaw to me. None of my other lenses behave this way.

But as I said, the fact that the MFD seems correct is baffling. But maybe I'm just measuring the MFD incorrectly?

The typical Pentax prime can be adjusted so that the infinity stop is right at infinity. If someone reassembled the lens so the focus helix was screwed in as far as it will go, then attached the focus ring with the orange diamond pointed at infinity, the lens would work like yours. If the focus ring isn't loose, it's most likely just adjustmment.

I have experimented with one lens (M50/1.7) to see if the MFD could be extended or shortened by a meaningful amount. I couldn't consistently measure any worthwhile difference - it might have been 12mm/0.5 inch at the most.

It's not a big deal to fix it. I can explain how with photos if you want. It's also not a big deal to leave it as is.

04-30-2010, 01:05 PM	#1
deadwolfbones Veteran Member Join Date: Sep 2007 Location: La Crescenta, CA Posts: 7,450	Pentax 85mm f/2 -- does yours focus past infinity? I recently bought an M85/2 here on the forums, and while it's in pristine condition, it focuses past infinity at the infinity range marker. What seems odd to me about this is that the MFD does not seem to be affected. Has anyone experienced a similar issue with their 85/2?

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04-30-2010, 01:10 PM	#2
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	Originally posted by deadwolfbones it focuses past infinity at the infinity range marker. It is normal for any lens to have the focus ring a bit past infinity. It is part of the tolerance.

04-30-2010, 02:10 PM	#3
germar Site Supporter Join Date: Apr 2007 Location: North Palm Beach, Florida Photos: Gallery Posts: 728	I seem to recall that same deal with my 85 f2. I no longer have it, so I can't absolutely confirm, but I think there WAS a little wiggle past infinity, no issues with the lens. Enjoy it! germar

04-30-2010, 02:18 PM	#4
deadwolfbones Veteran Member Join Date: Sep 2007 Location: La Crescenta, CA Posts: 7,450 Original Poster	Originally posted by SOldBear It is normal for any lens to have the focus ring a bit past infinity. It is part of the tolerance. When the focus ring is turned all the way toward infinity, the marker is lined up perfectly with the infinity symbol. At this point, when looking through the viewfinder, the lens is focused past infinity by a decent chunk. To get true infinity focus, I have to turn the focusing ring back toward the MFD by a bit. This seems like some kind of alignment flaw to me. None of my other lenses behave this way. But as I said, the fact that the MFD seems correct is baffling. But maybe I'm just measuring the MFD incorrectly?

04-30-2010, 02:24 PM	#5
jsherman999 Veteran Member Join Date: Dec 2007 Photos: Gallery Posts: 8,237	I'll check my 85 this weekend. FWIW, my Voigtlander 180 f4 Lanthar used to do the exact same thing...

04-30-2010, 02:25 PM	#6
axl Veteran Member Join Date: Mar 2007 Location: Nove Zamky, Slovakia Photos: Gallery \| Albums Posts: 7,183	what is the lens focused on if it's past infinity? I don't mean to come across as sarcastic or what... just don't get it... never thought there is something past infinity

04-30-2010, 02:39 PM	#7
deadwolfbones Veteran Member Join Date: Sep 2007 Location: La Crescenta, CA Posts: 7,450 Original Poster	Originally posted by axl what is the lens focused on if it's past infinity? I don't mean to come across as sarcastic or what... just don't get it... never thought there is something past infinity Yeah, the concept is kind of to me as well, but basically it means that you have to focus it back toward the MFD to get infinity focus. If you point the lens at a cloud, say (or a mountain), and focus it all the way to infinity it's just blurry. Gotta pull it back a bit to get the cloud sharp. I've heard of focusing rings turning past the infinity marker, but I've never heard of one that stops precisely at the infinity marker, but is focused beyond infinity at that point.

04-30-2010, 02:45 PM	#8
krb Junior Member Join Date: Feb 2010 Location: N. Virginia Posts: 29	Originally posted by axl what is the lens focused on if it's past infinity? Nothing. That's the problem. I have to say that having a focus ring that goes too far is better than one that doesn't go far enough.

04-30-2010, 02:56 PM	#9
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	Originally posted by deadwolfbones When the focus ring is turned all the way toward infinity, the marker is lined up perfectly with the infinity symbol. .... This seems like some kind of alignment flaw to me. None of my other lenses behave this way. Now I know what you mean. Yup. It is an alignment problem. The lens has a "stopper" screw; over time, the ring just gradually slips pass the stopper. If you are handy and brave, you can open up the lens and adjust the marker. I've done so to several lenses.

04-30-2010, 10:16 PM	#10
pentaxman Site Supporter Join Date: Oct 2007 Location: Washington Photos: Gallery Posts: 250	Many lenses will focus past infinity a slight amount by design. I have heard that this is to accomodate infrared film. The infinity focus can be easily adjusted. Having a split prism focusing screen makes it a cinch. You just loosen the screws holding the barrel with the distance markings to the focusing helix and turn it to line up with infinity when the lens is focused at infinity. Then just retighten the screws.

04-30-2010, 10:32 PM	#11
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	Originally posted by deadwolfbones When the focus ring is turned all the way toward infinity, the marker is lined up perfectly with the infinity symbol. At this point, when looking through the viewfinder, the lens is focused past infinity by a decent chunk. To get true infinity focus, I have to turn the focusing ring back toward the MFD by a bit. This seems like some kind of alignment flaw to me. None of my other lenses behave this way. But as I said, the fact that the MFD seems correct is baffling. But maybe I'm just measuring the MFD incorrectly? The typical Pentax prime can be adjusted so that the infinity stop is right at infinity. If someone reassembled the lens so the focus helix was screwed in as far as it will go, then attached the focus ring with the orange diamond pointed at infinity, the lens would work like yours. If the focus ring isn't loose, it's most likely just adjustmment. I have experimented with one lens (M50/1.7) to see if the MFD could be extended or shortened by a meaningful amount. I couldn't consistently measure any worthwhile difference - it might have been 12mm/0.5 inch at the most. It's not a big deal to fix it. I can explain how with photos if you want. It's also not a big deal to leave it as is.

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