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11-23-2011, 01:59 PM   #1
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Can you adjust for FF/BF with manual focus non-Pentax lenses?

As I was typing this thread title, as few older "Here are the similar threads we found:" came up, but none really could provide answers to my query.
Maybe someone can point one to me?

The only thread on PF that I found and being close to explaining what to do is this:
https://www.pentaxforums.com/forums/pentax-k-5-forum/166164-prediction-requir...thickness.html and if that is the case...

The question is: can one adjust for BF/FF on a non-Pentax manual focusing lens other than having to fiddle with internal parts of the camera?

Thanks!

JP


Last edited by jpzk; 11-23-2011 at 02:11 PM.
11-23-2011, 02:11 PM   #2
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AFAIK the "Apply All" under custom menu / AF Fine Adjustment does this. The same setting is applied to all lenses which do not have an individual adjustment set by "Apply One" (which only modern lenses with a data pin can have).
11-23-2011, 02:16 PM   #3
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QuoteOriginally posted by jolepp Quote
AFAIK the "Apply All" under custom menu / AF Fine Adjustment does this. The same setting is applied to all lenses which do not have an individual adjustment set by "Apply One" (which only modern lenses with a data pin can have).
Well, that is confusing then: why/how would this setting in the custom menu effect a non-AF lens?
I though this was strictly for AF lenses, no?

JP
11-23-2011, 02:22 PM   #4
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Oh ... it affects focus confirmation (the green hexgon / viewfinder red dots) only which depends of the AF sensor. To adjust what you see on the viewfinder you'd need to change the shim under the focus screen (and/or replace the screen).

11-23-2011, 02:35 PM   #5
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QuoteOriginally posted by jolepp Quote
Oh ... it affects focus confirmation (the green hexgon / viewfinder red dots) only which depends of the AF sensor. To adjust what you see on the viewfinder you'd need to change the shim under the focus screen (and/or replace the screen).
I am not really concerned with what is shown in the viewfinder for this particular lens (85/1.4 manual lens) but I need to know when the lens is in focus.
If there is a discrepancy between what shows and what the result (acurate focusing) is ... that's fine.

But now, if I choose "apply all", won't it affect all lenses fitted on that camera from then on? Even the ones showing no BF/FF ?

Maybe this should be in the "Beginner's Section" ... !

JP
11-23-2011, 02:45 PM   #6
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QuoteOriginally posted by jpzk Quote
But now, if I choose "apply all", won't it affect all lenses fitted on that camera from then on? Even the ones showing no BF/FF ?
Yes, but it's easy to work around. Which camera are you using? If you have the K-5, you could simply devote one (or more) of your five user modes to "apply all." In fact, you could have a different "apply all" setting in each user mode if you wanted. You could do the same with the K-7, but limited to one custom user mode.
11-23-2011, 03:07 PM - 1 Like   #7
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QuoteOriginally posted by jpzk Quote
...
But now, if I choose "apply all", won't it affect all lenses fitted on that camera from then on? Even the ones showing no BF/FF ?
...
Yes (and no ). "Apply all" affects all lenses except those for which "Apply One" has been set . That is, all MF lenses would share the same setting (with those more modern lenses for which "Apply All" had been chosen). "Apply All" and "Apply One" are not cumulative, also with modern lenses the body can tell them apart as it gets a lens id through the data pin (whether the lens id is copy or type specific I don't know ). I suppose "Apply All" could be set to compensate for any misaligment of the AF vs. image sensor which would affect all lenses. If lenses the body can't tell apart would require a different setting that would need to be set through the menu when changing lenses.

Last edited by jolepp; 11-23-2011 at 03:36 PM. Reason: typo
11-23-2011, 04:16 PM   #8
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OK, I'm confused. I thought FF/BF only applied to auto-focus lenses and the auto-focus system. If you are manually focusing how can you have a FF/BF issue? I thought any FF/BF issues with manual focus had to be adjusted by shimming the focusing screen. Unless you are talking about the focus confirmation green hex....

11-23-2011, 04:16 PM - 1 Like   #9
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It's a different approach to the issue, but, if your camera has LIve View mode and you can use it, then there is no need to worry about front/back focus, focus trim, etc. On the K-r, and I assume many other cameras, Live View lets you zoom the image so that very precise focusing is possible.

I have used this technique (on a tripod) in some situations where focus was critically important and have been quite pleased with the results. For me it is faster and more sure than trying to use the viewfinder.

Hope it's not off-topic. The OP indicated that "correct focusing" was more important than "shown in the viewfinder."
11-23-2011, 05:20 PM   #10
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QuoteOriginally posted by jatrax Quote
... Unless you are talking about the focus confirmation green hex....
Indeed, this is about focus confirmation which uses the AF sensor. As you say with the viewfinder image itself the fix for FF/BF is shimming.

Last edited by jolepp; 11-23-2011 at 05:27 PM.
11-23-2011, 07:17 PM   #11
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QuoteOriginally posted by jolepp Quote
Yes (and no ). "Apply all" affects all lenses except those for which "Apply One" has been set . That is, all MF lenses would share the same setting (with those more modern lenses for which "Apply All" had been chosen). "Apply All" and "Apply One" are not cumulative, also with modern lenses the body can tell them apart as it gets a lens id through the data pin (whether the lens id is copy or type specific I don't know ). I suppose "Apply All" could be set to compensate for any misaligment of the AF vs. image sensor which would affect all lenses. If lenses the body can't tell apart would require a different setting that would need to be set through the menu when changing lenses
Gosh this is very confusing ... sorry Jolepp.
QuoteOriginally posted by jdbosma Quote
It's a different approach to the issue, but, if your camera has LIve View mode and you can use it, then there is no need to worry about front/back focus, focus trim, etc. On the K-r, and I assume many other cameras, Live View lets you zoom the image so that very precise focusing is possible.
I have used this technique (on a tripod) in some situations where focus was critically important and have been quite pleased with the results. For me it is faster and more sure than trying to use the viewfinder.
Hope it's not off-topic. The OP indicated that "correct focusing" was more important than "shown in the viewfinder."
That is one good idea and I never thought about it.
I will try this out and see what focusing results I get with this method.


QuoteOriginally posted by pentup Quote
Yes, but it's easy to work around. Which camera are you using? If you have the K-5, you could simply devote one (or more) of your five user modes to "apply all." In fact, you could have a different "apply all" setting in each user mode if you wanted. You could do the same with the K-7, but limited to one custom user mode.
Yes, I have the K5.
Your suggestion to use the "User Modes" would make a lot of sense so that all MF lenses would be "clumped" in one single group; but other members below mention that BF/FF doesn't exist for MF lenses ... ??
Do I make sense ... not sure?



So, what exactly should I do with this manual-focus 85/1.4 lens in order to get proper focus results?
As I mentioned earlier, I am not so concerned about what would show through the viewfinder as much as what would show as a final image.

I will definitely test that focusing issue via the Live View method, but I'm not sure if I'd want to use this all the time with this particular lens. There are times that Live View would be OK to use, while most of the time it would be better to use the viewfinder.

Can anyone suggest some sort of detailed procedure to take, step by step?

Thank you all so very much for the time you take trying to explain this to me.

Cheers.
JP
11-23-2011, 08:18 PM   #12
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QuoteOriginally posted by jpzk Quote
Your suggestion to use the "User Modes" would make a lot of sense so that all MF lenses would be "clumped" in one single group; but other members below mention that BF/FF doesn't exist for MF lenses ... ??
You'd only want them in one group if they each needed exactly the same adjustment; I think someone already pointed out that the adjustment would only affect at what point the green hexagon showed up, to aid you in manual focusing. Personally I wouldn't bother. I ignore the hexagon and try my best to rely on my eyes. Even if all BF/FF is eliminated, the AF could still simply disagree with you about what the exact target should be.

QuoteOriginally posted by jpzk Quote
So, what exactly should I do with this manual-focus 85/1.4 lens in order to get proper focus results?
Stop down, for one thing -- the DOF will be a sliver wide open at that length. And you should search for the several threads about focusing screens; there's a lot of information on here about modifying your camera to improve manual focusing.
11-23-2011, 08:22 PM   #13
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I think this may have strayed a bit mostly because the OP mentioned FF/BF which has a specific meaning to many people. It appears the OP is looking for advice on how to get better focusing results and really does not have a FF/BF issue.

1) When FF/BF is mentioned this almost always is because a particular lens does not auto-focus precisely on a particular camera. The K-5 and other higher end cameras provide the means to tune the auto-focus for each lens to be more precise. Other camera's (k-x & k-r) have an adjustment but it is all or nothing.

2) There are four ways to manually focus on Pentax DSLR's. First is using the viewfinder and the focusing screen. This was perhaps more accurate on older full frame film cameras because the view finder was optimized for manual focus. Modern DSLRs have view finders optimized for auto-focus lenses which may not be good enough with a very fast lens like the 85 f/1.4, where the depth of field wide open is extremely small. The second is use the green hexagon to indicate that something is in focus. I find this works fine if the depth of field is large (lens stopped down) but not accurate enough with a fast lens. The third is to use catch in focus (CIF) which uses the auto-focus sensor to trip the shutter when a focus lock is obtained while using a manual focus lens. Some report this works very well, but I have not used it that much. Fourth is to use the live view either as is or by zooming in. This has the advantage of not using either the auto-focus sensor or the focusing screen. I find it works very well if the camera is on a tripod and I have the time, but it is too slow for many shots.

3) There are a few things that can be done to help with manual focusing. I have changed out the focusing screen for one better suited to manual focus lenses. Search for katz-eye or focusingscreen.com. I have also added a Pentax O-ME53 magnifying eye piece which zooms in a bit although you lose some view of the indicator lights in the camera. With these changes I find my accuracy with manual focus has improved a good bit.

4) No matter which method you use for manual focusing, a good bit of practice is involved. Remember the view finder is not as good as they used to be so you have to be better. There are some manual focusing exercises out there, do a search for 'manual focusing tips'. But for me the best way is to gradually move the focus back and forth until the image 'pops' in the view finder. It takes lots of practice to start seeing when that happens. Also keep in mind that the 85mm f/1.4 has a depth of field at 8 feet of less than 2 inches. That means you can easily get the nose in focus and the eyes blurry. With a slow lens, like the 18-55 kit lens, 2 inches is close enough. With something like the 85mm f/1.4 is just isn't, you have to be exactly precise.
11-23-2011, 09:44 PM   #14
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QuoteOriginally posted by jpzk Quote
I am not really concerned with what is shown in the viewfinder for this particular lens (85/1.4 manual lens) but I need to know when the lens is in focus.
There may be another issue at stake here, depending on the particular 85/1.4 lens: focus shift.
However accurately the lens may be focused at f/1.4, it could move off when stopped down to f/2 or further.
For static shots from a tripod you could try stopping down with the green button and using live view,
but for hand-held shots I suppose you just have to know your lens
and focus accordingly (probably a little bit in front of the subject).

The web page
Zeiss 85mm f/1.4 ZE Planar T* Lens Review
has a good discussion of this.
11-23-2011, 10:18 PM   #15
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QuoteOriginally posted by lytrytyr Quote
The web page Zeiss 85mm f/1.4 ZE Planar T* Lens Review has a good discussion of this.
Thanks for that link. This part is especially illuminating to me:
"While using the lens wide open, the correct focus lies usually a little bit in front of the point that has been expected. Beside this, the focus confirmation function of any AF-camera is a relative improper tool for accurate focusing of an f/1.4 lens on closer distances. Also, a standard focusing screen and viewfinder of an SLR camera shows the limitations of accurate manual focusing with an 85mm lens at f/1.4. For instance, it is not possible in practical use to focus more accurately than about +/- 2 cm at an object distance of 1m without additional magnification systems. For accurate focusing at full aperture or stopped down a little bit, we strongly recommend:
-use a tripod if possible
-use zoom-in function in live-view mode while the lens has been stopped down to the designated f-stop.
-focus bracketing exposures (with small steps of rotating the focusing ring)"


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