Manual focus lens front focusing results on only one of your bodies?

ChristianRock · 10-09-2019, 02:36 PM

Originally posted by stevebrot

There is a problem with either the focus screen shimming or the mirror alignment.

I would agree with you if it was happening to all lenses, but it only happens with this one... and by quite a lot. I mean, when I compare with my f/1.4 or f/1.7 lens shots, the focus is in a totally different place once the shutter is pressed.

It seems like the diopter shfts the focus point on the viewfinder so that is acceptable to me for now. Otherwise I can use live view.

pschlute · 10-09-2019, 07:10 PM

Originally posted by ChristianRock

but it only happens with this one... and by quite a lot. I mean, when I compare with my f/1.4 or f/1.7 lens shots, the focus is in a totally different place once the shutter is pressed

This indeed very odd. Your use of other lenses suggests there is nothing wrong with the camera, and your use on other bodies suggests nothing wrong with the lens. Just that this lens/camera combo has a problem.

Only other thing I can think of is that your KS1 shutter-shock is causing an element in the lens to move slightly.

08amczb · 10-09-2019, 11:39 PM

You must align correctly the ground glass in the viewfinder by shims! If the distance between the sensor and the mount doues not mach the distance from the mount to the ground glass you will see different focus plane in the viewfinder and on the final image.
I would bring the camera to the local pentax service.

pschlute · 10-10-2019, 01:46 AM - **1 Like**

Originally posted by 08amczb

You must align correctly the ground glass in the viewfinder by shims! If the distance between the sensor and the mount doues not mach the distance from the mount to the ground glass you will see different focus plane in the viewfinder and on the final image.
I would bring the camera to the local pentax service.

He has said that it is only this one lens that misfocusses on his camera.

08amczb · 10-10-2019, 02:05 AM

I assume it's the only F1.2 lens he has, so it may need more accuracy. The others may cover the error by the slower apertures. I have no better idea. Focus confirmation doesn't handels 100% perfectly lenses below F2 even with the F2.8 accurate middle focus point.

Medex · 10-10-2019, 02:46 AM

If you did focus in the center of an image (globe), then your lens BACK focuses, because things in focus are behind the prominent part of the globe.
I use manual focus projection lenses adapted to Pentax mount on K-1. They all have some back or front focus. But let say, Revuenon 55/1.2 focuses perfectly without any fine focus adjustment. So, in your case I would do some test on tripod, because focus zone is so narrow at f1.2 that any not perceptible movement of your body can influence the result.
Mount your camera on tripod, do manual focusing through the OVF until you get focus confirmation (Green hexagon in the view finder), then check your focus in the Live View mode with magnification to decide you have right or wrong focus, front or back focus. Repeat the test several times to see if the misfocus have the same tendency and make Fine focus adjustment (Apply All - for manual focus lenses), but keep information about that somewhere on you lens (sticker ar similar), because it is applicable to this lens only.

**rjbrett** · 10-10-2019, 02:55 AM

I've had similar problems with some of my old manual focus lenses, and came to the same conclusion as Othar. When I used the diopter adjustment lever on the viewfinder I was able to mostly correct this, and more tellingly, then had a similar problem a couple of days later when my eyesight returned to normal and I hadn't yet thought to return the diopter adjustment lever to it's original position. I had been doing long hours in front of a monitor and was pretty tired and run down. The lenses I was using were all considerably slower.

**Serkevan** · 10-10-2019, 03:10 AM

Originally posted by ChristianRock

I see where the focus is in the viewfinder. Then when I press the shutter, the focus is elsewhere.

Are you shooting wide open? If not, some lenses can have severe focus shift (so the lens *is* correctly focused wide open but the focus plane shifts once you stop down for the shot)

Jonathan Mac · 10-10-2019, 06:19 AM

If focus is not right when manually focusing it's because the viewfinder focusing screen is not in the right place and needs to be shimmed, or the mirror is in mis-aligned. Having said that, the default focusing screens in DSLRs can't usually be relied upon to be accurate below f/4 or so, so unless you're using a very precise split-screen or similar specialised focusing screen then I wouldn't expect to be able to accurately focus with it, especially at f/1.2.

Unregistered User · 10-10-2019, 07:30 AM

Originally posted by Jonathan Mac

If focus is not right when manually focusing it's because the viewfinder focusing screen is not in the right place and needs to be shimmed, or the mirror is in mis-aligned. Having said that, the default focusing screens in DSLRs can't usually be relied upon to be accurate below f/4 or so, so unless you're using a very precise split-screen or similar specialised focusing screen then I wouldn't expect to be able to accurately focus with it, especially at f/1.2.

When you add shims, they go between the focusing screen and the prism - i.e. they decrease the distance between the focusing screen and the mirror, which moves the plane of focus forward. If the camera is already front-focusing, adding shims will only make it worse.

I suspect that Pentax shares your view regarding precise focusing using the viewfinder - hence, they no longer refer to "focusing screen", but call it a "fresnel" (theirs has a diffraction grating that provides a little magnification, a-la a fresnel lens). Documentation about cameras on the InterNet now all talk about viewfinders in terms of being able to see what the camera's pointing at, rather than the ability to focus the lens. In fact, there is a large number of so-called external viewfinders, which couldn't possibly help at all.

So my view is that they've done to cameras what's been done to telephones - the addition of new technology apparently designed to interfere with the effective use of the tool. I don't think that people don't talk on the 'phone much anymore not because they have suddenly developed an aversion to speech, but because using a telephone has become WAAAY too complicated and inconvenient. (Part of the "deep state" conspiracy to keep the peasants from being able to inform each other about the evils of politics, no doubt.)

Even at my advanced age and failing eyesight, I can still focus visually much better than any autofocus system I've seen - not necessarily more precisely, but faster and more accurately. With a real camera (i.e., 35mm SLR), since my left hand is already on the focusing ring and my eye to the viewfinder, focusing is done before I even have the thought to do something. With the K-1 for example, I push the button and wait for the lens to respond, and by the time it's found something, it's the wrong something or the proposed subject's already gone. Even with a manual winder, I could have taken three well-focused pictures with a Canon AE-1 in the time it takes to get one picture in focus with the K-1. (Naturally, a small prime lens can be brought into focus much faster than a long telephoto zoom lens. I'm thinking "on average", here.)

One might argue that I can still use the lenses in "manual mode", I can have my hand on the focusing ring, and so forth, but that's all wasted because the viewfinder has been designed merely to show me what the camera's pointing at. Actually attempting to focus the lens using the viewfinder (the main reason I wanted an optical viewfinder, and a big reason why I've got the K-1) is pointless (by design).

**othar** · 10-10-2019, 08:03 AM

Originally posted by dlh

but that's all wasted because the viewfinder has been designed merely to show me what the camera's pointing at. Actually attempting to focus the lens using the viewfinder (the main reason I wanted an optical viewfinder, and a big reason why I've got the K-1) is pointless (by design).

While the split screen of my P30 is easier to use with manual focus lenses than the plain focus screen of my K-3, I am still able to get reliable sharp images without using focus confirmation when using manual focus lenses on my DSLR (as long as the lens doesn't get too wide, but after a certain point this is a problem on the P30 too), provided I didn't mess up the diopter settings of the OVF.
Therefore I wouldn't go as far as saying the OVF is useless for MF lenses. On the other hand does the current lens lineup (from Pentax) only include AF lenses, where no split screen is needed or even desired, so it is a quite understandable design choice.

ChristianRock · 10-10-2019, 08:39 AM

Originally posted by Jonathan Mac

If focus is not right when manually focusing it's because the viewfinder focusing screen is not in the right place and needs to be shimmed, or the mirror is in mis-aligned.

If that was the case, my f/1.4 lenses would not be focusing correctly which they are...

Originally posted by 08amczb

I assume it's the only F1.2 lens he has, so it may need more accuracy. The others may cover the error by the slower apertures. I have no better idea. Focus confirmation doesn't handels 100% perfectly lenses below F2 even with the F2.8 accurate middle focus point.

It's quite a bit off even by f/2.8. My Rikenon P 50 1.4, for example, gives me whatever I focus on even at f/1.4. So does my Sigma 30 1.4 and my 50 1.7 lenses.

I think I'll just accept that this is how things are, and compensate as much as I can with the diopter.

Originally posted by Serkevan

Are you shooting wide open? If not, some lenses can have severe focus shift (so the lens *is* correctly focused wide open but the focus plane shifts once you stop down for the shot)

It's off by a lot wide open, I don't think it's a focus shift issue.I provided examples in the original post.

Originally posted by dlh

One might argue that I can still use the lenses in "manual mode", I can have my hand on the focusing ring, and so forth, but that's all wasted because the viewfinder has been designed merely to show me what the camera's pointing at. Actually attempting to focus the lens using the viewfinder (the main reason I wanted an optical viewfinder, and a big reason why I've got the K-1) is pointless (by design).

I think in your case - correct me if I'm mistaken - where the issue is consistent and happens to all your manual focus lenses, you could use the "For All" fine focus adjustment that Medex mentioned in this thread. I've used this and it works well. Now if every lens is giving you a different result and you change lenses a lot, things might be a bit more difficult...

Qman · 10-10-2019, 09:59 AM

I still think it's the lens, otherwise something would be in focus in the photo. This isn't a case of front or back focus, it's a case of no focus. I'd like to see two identical photos, one on the KS1, one on a different body, so that we can see the difference between cameras.

pschlute · 10-10-2019, 10:03 AM - **1 Like**

Originally posted by dlh

So my view is that they've done to cameras what's been done to telephones - the addition of new technology apparently designed to interfere with the effective use of the tool. I don't think that people don't talk on the 'phone much anymore not because they have suddenly developed an aversion to speech, but because using a telephone has become WAAAY too complicated and inconvenient. (Part of the "deep state" conspiracy to keep the peasants from being able to inform each other about the evils of politics, no doubt.)

is that what the tin hat that comes in the box is for

---------- Post added 10-10-19 at 06:07 PM ----------

Originally posted by Qman

I still think it's the lens, otherwise something would be in focus in the photo. This isn't a case of front or back focus, it's a case of no focus. I'd like to see two identical photos, one on the KS1, one on a different body, so that we can see the difference between cameras.

True

Christian (OP) . This is a very, very, edge case. You really need to provide unequivocal evidence to prove your point here. It's not that folk don't believe you, but just its very unlikely.

swanlefitte · 10-10-2019, 10:39 AM

If all your lenses on the other cameras tend to need like a +1 adjustment where the ks1 needs around -5 it is what it is. The other link in the combination is the connection. The 1.2 perhaps is wider so the outside area of connection has a difference between the ks1 and other cameras like the metal slightly concave?

10-09-2019, 07:10 PM	#17
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,198	Originally posted by ChristianRock but it only happens with this one... and by quite a lot. I mean, when I compare with my f/1.4 or f/1.7 lens shots, the focus is in a totally different place once the shutter is pressed This indeed very odd. Your use of other lenses suggests there is nothing wrong with the camera, and your use on other bodies suggests nothing wrong with the lens. Just that this lens/camera combo has a problem. Only other thing I can think of is that your KS1 shutter-shock is causing an element in the lens to move slightly. Last edited by pschlute; 10-09-2019 at 08:39 PM.

10-10-2019, 07:30 AM	#25
Unregistered User Guest	Originally posted by Jonathan Mac If focus is not right when manually focusing it's because the viewfinder focusing screen is not in the right place and needs to be shimmed, or the mirror is in mis-aligned. Having said that, the default focusing screens in DSLRs can't usually be relied upon to be accurate below f/4 or so, so unless you're using a very precise split-screen or similar specialised focusing screen then I wouldn't expect to be able to accurately focus with it, especially at f/1.2. When you add shims, they go between the focusing screen and the prism - i.e. they decrease the distance between the focusing screen and the mirror, which moves the plane of focus forward. If the camera is already front-focusing, adding shims will only make it worse. I suspect that Pentax shares your view regarding precise focusing using the viewfinder - hence, they no longer refer to "focusing screen", but call it a "fresnel" (theirs has a diffraction grating that provides a little magnification, a-la a fresnel lens). Documentation about cameras on the InterNet now all talk about viewfinders in terms of being able to see what the camera's pointing at, rather than the ability to focus the lens. In fact, there is a large number of so-called external viewfinders, which couldn't possibly help at all. So my view is that they've done to cameras what's been done to telephones - the addition of new technology apparently designed to interfere with the effective use of the tool. I don't think that people don't talk on the 'phone much anymore not because they have suddenly developed an aversion to speech, but because using a telephone has become WAAAY too complicated and inconvenient. (Part of the "deep state" conspiracy to keep the peasants from being able to inform each other about the evils of politics, no doubt.) Even at my advanced age and failing eyesight, I can still focus visually much better than any autofocus system I've seen - not necessarily more precisely, but faster and more accurately. With a real camera (i.e., 35mm SLR), since my left hand is already on the focusing ring and my eye to the viewfinder, focusing is done before I even have the thought to do something. With the K-1 for example, I push the button and wait for the lens to respond, and by the time it's found something, it's the wrong something or the proposed subject's already gone. Even with a manual winder, I could have taken three well-focused pictures with a Canon AE-1 in the time it takes to get one picture in focus with the K-1. (Naturally, a small prime lens can be brought into focus much faster than a long telephoto zoom lens. I'm thinking "on average", here.) One might argue that I can still use the lenses in "manual mode", I can have my hand on the focusing ring, and so forth, but that's all wasted because the viewfinder has been designed merely to show me what the camera's pointing at. Actually attempting to focus the lens using the viewfinder (the main reason I wanted an optical viewfinder, and a big reason why I've got the K-1) is pointless (by design). Last edited by Unregistered User; 10-10-2019 at 07:58 AM.

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10-09-2019, 02:36 PM	#16
ChristianRock Pentaxian Join Date: Jul 2013 Location: People's Republic of America Photos: Gallery \| Albums Posts: 9,910 Original Poster	Originally posted by stevebrot There is a problem with either the focus screen shimming or the mirror alignment. I would agree with you if it was happening to all lenses, but it only happens with this one... and by quite a lot. I mean, when I compare with my f/1.4 or f/1.7 lens shots, the focus is in a totally different place once the shutter is pressed. It seems like the diopter shfts the focus point on the viewfinder so that is acceptable to me for now. Otherwise I can use live view.

10-09-2019, 11:39 PM	#18
08amczb Veteran Member Join Date: Dec 2013 Posts: 796	You must align correctly the ground glass in the viewfinder by shims! If the distance between the sensor and the mount doues not mach the distance from the mount to the ground glass you will see different focus plane in the viewfinder and on the final image. I would bring the camera to the local pentax service.

10-10-2019, 01:46 AM - 1 Like	#19
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,198	Originally posted by 08amczb You must align correctly the ground glass in the viewfinder by shims! If the distance between the sensor and the mount doues not mach the distance from the mount to the ground glass you will see different focus plane in the viewfinder and on the final image. I would bring the camera to the local pentax service. He has said that it is only this one lens that misfocusses on his camera.

10-10-2019, 02:05 AM	#20
08amczb Veteran Member Join Date: Dec 2013 Posts: 796	I assume it's the only F1.2 lens he has, so it may need more accuracy. The others may cover the error by the slower apertures. I have no better idea. Focus confirmation doesn't handels 100% perfectly lenses below F2 even with the F2.8 accurate middle focus point.

10-10-2019, 02:46 AM	#21
Medex Pentaxian Join Date: May 2013 Location: Vilnius Posts: 1,020	If you did focus in the center of an image (globe), then your lens BACK focuses, because things in focus are behind the prominent part of the globe. I use manual focus projection lenses adapted to Pentax mount on K-1. They all have some back or front focus. But let say, Revuenon 55/1.2 focuses perfectly without any fine focus adjustment. So, in your case I would do some test on tripod, because focus zone is so narrow at f1.2 that any not perceptible movement of your body can influence the result. Mount your camera on tripod, do manual focusing through the OVF until you get focus confirmation (Green hexagon in the view finder), then check your focus in the Live View mode with magnification to decide you have right or wrong focus, front or back focus. Repeat the test several times to see if the misfocus have the same tendency and make Fine focus adjustment (Apply All - for manual focus lenses), but keep information about that somewhere on you lens (sticker ar similar), because it is applicable to this lens only.

10-10-2019, 02:55 AM	#22
rjbrett Site Supporter Join Date: Sep 2016 Location: Brisbane Posts: 895	I've had similar problems with some of my old manual focus lenses, and came to the same conclusion as Othar. When I used the diopter adjustment lever on the viewfinder I was able to mostly correct this, and more tellingly, then had a similar problem a couple of days later when my eyesight returned to normal and I hadn't yet thought to return the diopter adjustment lever to it's original position. I had been doing long hours in front of a monitor and was pretty tired and run down. The lenses I was using were all considerably slower.

10-10-2019, 03:10 AM	#23
Serkevan Site Supporter Join Date: May 2019 Photos: Albums Posts: 5,976	Originally posted by ChristianRock I see where the focus is in the viewfinder. Then when I press the shutter, the focus is elsewhere. Are you shooting wide open? If not, some lenses can have severe focus shift (so the lens is correctly focused wide open but the focus plane shifts once you stop down for the shot)

10-10-2019, 06:19 AM	#24
Jonathan Mac Pentaxian Join Date: Apr 2009 Location: Madrid, Spain Posts: 10,897	If focus is not right when manually focusing it's because the viewfinder focusing screen is not in the right place and needs to be shimmed, or the mirror is in mis-aligned. Having said that, the default focusing screens in DSLRs can't usually be relied upon to be accurate below f/4 or so, so unless you're using a very precise split-screen or similar specialised focusing screen then I wouldn't expect to be able to accurately focus with it, especially at f/1.2.

10-10-2019, 08:03 AM	#26
othar Site Supporter Join Date: May 2014 Location: Linz Photos: Albums Posts: 3,098	Originally posted by dlh but that's all wasted because the viewfinder has been designed merely to show me what the camera's pointing at. Actually attempting to focus the lens using the viewfinder (the main reason I wanted an optical viewfinder, and a big reason why I've got the K-1) is pointless (by design). While the split screen of my P30 is easier to use with manual focus lenses than the plain focus screen of my K-3, I am still able to get reliable sharp images without using focus confirmation when using manual focus lenses on my DSLR (as long as the lens doesn't get too wide, but after a certain point this is a problem on the P30 too), provided I didn't mess up the diopter settings of the OVF. Therefore I wouldn't go as far as saying the OVF is useless for MF lenses. On the other hand does the current lens lineup (from Pentax) only include AF lenses, where no split screen is needed or even desired, so it is a quite understandable design choice.

10-10-2019, 08:39 AM	#27
ChristianRock Pentaxian Join Date: Jul 2013 Location: People's Republic of America Photos: Gallery \| Albums Posts: 9,910 Original Poster	Originally posted by Jonathan Mac If focus is not right when manually focusing it's because the viewfinder focusing screen is not in the right place and needs to be shimmed, or the mirror is in mis-aligned. If that was the case, my f/1.4 lenses would not be focusing correctly which they are... Originally posted by 08amczb I assume it's the only F1.2 lens he has, so it may need more accuracy. The others may cover the error by the slower apertures. I have no better idea. Focus confirmation doesn't handels 100% perfectly lenses below F2 even with the F2.8 accurate middle focus point. It's quite a bit off even by f/2.8. My Rikenon P 50 1.4, for example, gives me whatever I focus on even at f/1.4. So does my Sigma 30 1.4 and my 50 1.7 lenses. I think I'll just accept that this is how things are, and compensate as much as I can with the diopter. Originally posted by Serkevan Are you shooting wide open? If not, some lenses can have severe focus shift (so the lens is correctly focused wide open but the focus plane shifts once you stop down for the shot) It's off by a lot wide open, I don't think it's a focus shift issue.I provided examples in the original post. Originally posted by dlh One might argue that I can still use the lenses in "manual mode", I can have my hand on the focusing ring, and so forth, but that's all wasted because the viewfinder has been designed merely to show me what the camera's pointing at. Actually attempting to focus the lens using the viewfinder (the main reason I wanted an optical viewfinder, and a big reason why I've got the K-1) is pointless (by design). I think in your case - correct me if I'm mistaken - where the issue is consistent and happens to all your manual focus lenses, you could use the "For All" fine focus adjustment that Medex mentioned in this thread. I've used this and it works well. Now if every lens is giving you a different result and you change lenses a lot, things might be a bit more difficult...

10-10-2019, 09:59 AM	#28
Qman Senior Member Join Date: Jun 2017 Posts: 232	I still think it's the lens, otherwise something would be in focus in the photo. This isn't a case of front or back focus, it's a case of no focus. I'd like to see two identical photos, one on the KS1, one on a different body, so that we can see the difference between cameras.

10-10-2019, 10:03 AM - 1 Like	#29
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,198	Originally posted by dlh So my view is that they've done to cameras what's been done to telephones - the addition of new technology apparently designed to interfere with the effective use of the tool. I don't think that people don't talk on the 'phone much anymore not because they have suddenly developed an aversion to speech, but because using a telephone has become WAAAY too complicated and inconvenient. (Part of the "deep state" conspiracy to keep the peasants from being able to inform each other about the evils of politics, no doubt.) is that what the tin hat that comes in the box is for ---------- Post added 10-10-19 at 06:07 PM ---------- Originally posted by Qman I still think it's the lens, otherwise something would be in focus in the photo. This isn't a case of front or back focus, it's a case of no focus. I'd like to see two identical photos, one on the KS1, one on a different body, so that we can see the difference between cameras. True Christian (OP) . This is a very, very, edge case. You really need to provide unequivocal evidence to prove your point here. It's not that folk don't believe you, but just its very unlikely.

10-10-2019, 10:39 AM	#30
swanlefitte Pentaxian Join Date: May 2015 Location: Minneapolis Photos: Gallery Posts: 4,068	If all your lenses on the other cameras tend to need like a +1 adjustment where the ks1 needs around -5 it is what it is. The other link in the combination is the connection. The 1.2 perhaps is wider so the outside area of connection has a difference between the ks1 and other cameras like the metal slightly concave?