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12-19-2012, 07:27 AM   #1
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Front focus in manual lens

All

I have a K-r and recently acquired a Pentax A 50mm 1.4 manual lens. I noticed that I could never get it to focus correctly and after researching a bit I printed off a focus chart and used catch in focus to ensure it's not my eyes that are the problem. My test shows that I have front focus which is what I was seeing in my pictures. I don't have an online account for anywhere to post an image but I took a photo from around 0.5m away at around 40 degree angle at 1.4 and it had front focus of around 10mm.

I have researched on here and found various threads saying that this is a general issue when you try to use fast manual lenses as the system is optimised for AF on slower lenses (or something to that effect). Lots of people seem to recommend getting a new focusing screen, with KatzEye being mentioned a lot. However, I can't find anywhere selling these in the UK, only really cheap versions on Amazon.

So, does anyone have any other advice on things I could do, or is it just something I need to accept and try to adjust for? Has anyone from the UK had a similar issue and found anyone supplying a focusing screen that has fixed your issue?

Cheers

12-19-2012, 07:52 AM   #2
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Did you rely strictly on the green light (and/or beep sound) or strictly on your eyes in deciding when to press the shutter button?
12-19-2012, 08:03 AM   #3
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Yes, your K-r viewfinder (and most other APS DLSRs) is optimised for being as bright as possible for the typical slow lenses which have AF rather than accuracy of focussing manually with fast lenses.

You can manual focus very accurately using the Live View function especiallyif you can magnify the image to the part of the subject you want to focus on. I asumme the K-r can do this function.


For using the OVF The best thing for manual focus of fast fast lenses definitely is a new focus screen. I bought and installed kit from fucusingscreen.com For my K-7 I have an S-type (which is cut from a Canon5D precision matte screen).
With fast lenses like f1.2 - f2.8 the image snaps into focus accurately.

The trade off is that the viewfinder is slightly darker with slower lenses. I noticed at first but I'm used to it now. I've had no problems using my slower zoom lenses even in less than ideal lighting.

A split screen type is apparently brighter but it is reported to have a compromise with metering accuracy using spot metering. I havent tried this type.


The K-r page is here.
Focusing Screen

Last edited by steve1307; 12-19-2012 at 08:10 AM.
12-19-2012, 09:22 AM   #4
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QuoteOriginally posted by steve1307 Quote
Yes, your K-r viewfinder (and most other APS DLSRs) is optimised for being as bright as possible for the typical slow lenses which have AF rather than accuracy of focussing manually with fast lenses.

You can manual focus very accurately using the Live View function especiallyif you can magnify the image to the part of the subject you want to focus on. I asumme the K-r can do this function.


For using the OVF The best thing for manual focus of fast fast lenses definitely is a new focus screen. I bought and installed kit from fucusingscreen.com For my K-7 I have an S-type (which is cut from a Canon5D precision matte screen).
With fast lenses like f1.2 - f2.8 the image snaps into focus accurately.

The trade off is that the viewfinder is slightly darker with slower lenses. I noticed at first but I'm used to it now. I've had no problems using my slower zoom lenses even in less than ideal lighting.

A split screen type is apparently brighter but it is reported to have a compromise with metering accuracy using spot metering. I havent tried this type.


The K-r page is here.
Focusing Screen
Hi cuasey - before I did my test it was all a learning process. I was using my eye as thought that was the only way to do it with manual lenses. Then I realised the beep and the hexagon in the viewfinder still function. Images were always out of focus where I wanted it though. It was then that I tried catch in focus as I figured that rules out my eyes being an issue.

Steve - Sounds like live view will help when I am doing more planned stuff. However, will keep looking into where I can get a new screen from in the UK as I prefer to use the viewfinder when doing more ad-hoc stuff like photos of family etc.

12-19-2012, 09:25 AM   #5
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QuoteOriginally posted by thechumpen Quote
Hi cuasey - before I did my test it was all a learning process. I was using my eye as thought that was the only way to do it with manual lenses. Then I realised the beep and the hexagon in the viewfinder still function. Images were always out of focus where I wanted it though. It was then that I tried catch in focus as I figured that rules out my eyes being an issue.
The reason I asked the question is that the luminous hexagon and the beep are actually part of the auto-focus mechanism, and if you relied on them, the camera, not the lens, might be the problem.
12-19-2012, 09:29 AM   #6
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My experience of the green hexagon as a focus indicator for mf is that it's pretty hopeless - you usually do indeed get front or back focusing, dependenting on which particular lens you have mounted. You should realise that mf is difficult, particularly with the standard focusing screen (which is designed to maximise DOF), so, as others have pointed out, Live View would be the way forward.
12-19-2012, 09:40 AM   #7
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I just tried with live view and it is indeed much easier, especially when you zoom in. Thanks for the tip.

I will keep an eye out for a new focusing screen as well. I'm loving using the prime but can't stretch to the new AF ones so will be picking up older ones instead so definitely want to improve manual focus through the view finder. I actually quite enjoy using manual focus as well, makes it a bit more fun somehow.

causey - I see what you're saying. I tried doing the test with some AF lenses as well but only have the 18-55 kit and the 55-300 so couldn't get the aperture large enough to be able to tell whether it was spot on or not i.e. most of the test page looked in focus.
12-19-2012, 09:48 AM   #8
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There are several different focusing screens available for Pentax cameras. I use the Katz Eye. They aren't cheap. On Ebay, a seller named Jinfinance sells focusing screens very cheap. Quality is hit and miss. I bought one and tossed it but others have had good luck. There is also focusingscreens.com at a price point between the Katz Eye and Ebay cheapos.

A quick question. Is your diopter adjusted properly? That can affect your manual focusing. I grew up in the film era and all our old manual cameras had a focusing aid viewfinder of some sort, usually a split prism. They work very well on a fast 50. If you want to use your MF lenses a lot, I consider a split prism viewfinder an essential.

12-19-2012, 10:01 AM   #9
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QuoteOriginally posted by thechumpen Quote
All

I have a K-r and recently acquired a Pentax A 50mm 1.4 manual lens. I noticed that I could never get it to focus correctly and after researching a bit I printed off a focus chart and used catch in focus to ensure it's not my eyes that are the problem. My test shows that I have front focus which is what I was seeing in my pictures. I don't have an online account for anywhere to post an image but I took a photo from around 0.5m away at around 40 degree angle at 1.4 and it had front focus of around 10mm.

I have researched on here and found various threads saying that this is a general issue when you try to use fast manual lenses as the system is optimised for AF on slower lenses (or something to that effect). Lots of people seem to recommend getting a new focusing screen, with KatzEye being mentioned a lot. However, I can't find anywhere selling these in the UK, only really cheap versions on Amazon.

So, does anyone have any other advice on things I could do, or is it just something I need to accept and try to adjust for? Has anyone from the UK had a similar issue and found anyone supplying a focusing screen that has fixed your issue?

Cheers
FF/BF is generally only an AF issue. You can't expect viewfinder AF confirmation to be perfect w/ manual lenses because it has quite a bit of tolerance.

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12-19-2012, 10:25 AM   #10
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QuoteOriginally posted by thechumpen Quote
My test shows that I have front focus which is what I was seeing in my pictures.
The only way to get front focus when focusing manually is if the focusing screen is not shimmed properly. Assuming you are focusing by eye and not using the green hex, which is part of the AF system. The green hex and AF system are useful but not extremely accurate with fast glass, as Adam noted there is too much 'slop' in the system. One thing that helps is start at a distance and move into focus, check the result. Then start close and move away into focus and check the result. Is one of those better than the other? If so, then you know how to focus with that lens. But a different lens might work the other way around. This gets you to use the 'edge' of the AF lock rather than the center. Sometimes it helps, sometimes not.

You should also check that your diopter is set correctly, if that is off then things will appear in focus on the screen but will not be in focus.

A new focusing screen will NOT automatically make focusing any more accurate, it will allow you to see more accurately when the lens is wide open. As noted above current focusing screens are not optimized for fast glass or manual focusing. You still need to be able focus by eye accurately. And the diopter has to be correct and the shims of the focus screen have to be correct.

The best test is to set up on a tripod, focus as best you can by eye then go into liveview and zoom in, check how you did by eye. If it is not right on then something needs adjusted.

I would check the diopter first, then try the start away/start close test and see where the green hex lights up.

And no test you do is useful unless the camera is on a tripod. At f/1.4 you are dealing with such a narrow depth of field that just breathing will change it.
12-19-2012, 10:47 AM   #11
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Using the Live View and the zoom function on a TRIPOD with it focus on something close at f1.4 use a battery or something like that, forget the focus chart trick. Get the focus perfect THEN without changing anything shut off live view and look through the viewfinder, it should be in focus. If not carefully adjust the diopter to get
it there if you cannot then the screen is not right. You can't go wrong with this as the live view does not use any AF and is exactly what the sensor sees and how
the pic turns out. Using an AA battery is the best focus aid as it has very clear contrasty letters and colors and is round so it will show if the focus point is at
the center or away from you on the sides.
You can do the same with the AF, except mark the lens where the LV focus point is then focus with the Green dot beep thing. Check the lens mark it should align if not the AF is off.
My Kx was OK, My K10 Screen was off and I found after shimming the focus screen the AF was OK ? a friends K10 was OK but his K100 was not !
Don't quit you will get it...
12-19-2012, 10:52 AM   #12
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As others have suggested, make sure the diopter is set correctly for your eye. Move the slider until the grid lines in the VF are razor sharp. I was also having trouble using MF lenses using my K100D's smallish viewfinder. I purchased a Pentax eyepiece magnifier O-ME53, and it made all the difference for me. It's probably not as effective as a new focusing screen, but it worked well enough to allow me to achieve good focus using MF lenses.
12-19-2012, 10:55 AM   #13
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QuoteOriginally posted by Adam Quote
FF/BF is generally only an AF issue. You can't expect viewfinder AF confirmation to be perfect w/ manual lenses because it has quite a bit of tolerance.
That is not true IF you are using either focus confirmation or catch-in-focus with your manual lenses.
12-19-2012, 11:52 AM   #14
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QuoteOriginally posted by vrrattko Quote
That is not true IF you are using either focus confirmation or catch-in-focus with your manual lenses.
Thanks for the extra comments. As doing it by eye wasn't working I tried using focus confirmation and catch in focus but got the same results as by eye. I am now in the situation where what I see as in focus through the VF and what the camera sees as in focus using catch in focus etc are both slightly out when it comes to the Actual image generated. Using live view and zooming in seems to get it right though. I don't know enough about this stuff to understand why or how this happens.

I will do what you suggest bobpur as I may be able to get it more accurate by changing it so that my eye sees it the same as live view I.e. tricking my eye slightly.
12-19-2012, 03:46 PM   #15
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QuoteOriginally posted by vrrattko Quote
That is not true IF you are using either focus confirmation or catch-in-focus with your manual lenses.
I don't agree with this. The focus confirmation with MF lenses will get you very close, but it's not exact in my experience. Try it yourself and see. Focus on your target until the focus confirmation lights up in your VF. Now fine-tune your focus slowly, and notice how the indicator remains lit as you slowly adjust back and forth. As Adam mentioned, there's a small range of tolerance for the camera's focus confirmation mechanism.
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