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Author Topic: Quick steps: how to set AF calibration on Hy6/AFi cameras - its really cool!  (Read 3389 times)

EricWHiss

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If you have a Hy6 or AFi with the latest firmware and you have always wanted to know what the AF Focus offset function in the options does, here's an explanation.   It adjusts the accuracy of the cameras focus indicators relative to what back you have fitted digital or film.  It does not change the focusing screen, only the indicators and AF accuracy.   My AFi-ii 12 focuses fairly well already and the focusing screen seems to be very well aligned for manual focusing by the eye, however I had noticed that it seemed the focus indicators were not agreeing perfectly with the focus screen.  DOF with the fast lenses like the 110/2 or the 180/2.8 is just paper thin, especially at portrait distances.   Sometimes when my eyes are tired or when I'm doing critical work, I'd rather rely on the focus indicators which are very useful.  They point the photographer which way the focus needs to be adjusted - in or out and then both come on when its perfect.   I wanted this indicator be as accurate as possible and fortunately the camera designers built in setting in the options menu to do just that.  Here's how easy it is:

1) Set up your camera on a tripod and use a target with high contrast edges on it that also has some fine details in an uncluttered area.  The larger contrast edges are for the AF in the camera and the fine detail for you to confirm focus.   I downloaded one of the black and white test charts from imatest and printed it out and taped it up on the wall across my office.
2) Position the camera such that center of the frame where the focus points are falls over the target.  
3) Set your cameras focus switch to manual, and set your camera up for tethering
4) Use live view at 100% (leaf has great Live View - YMMV) to manually focus the lens for best focus
5) Last step - be careful to not bump or move the camera - hit the options button on the grip and turn the top scroll wheel until you get to AF Offset.   Now just adjust the lower scroll wheel until the focus confirmation indicates perfect focus.  The adjustment count is very fine and the both focus indicators will stay on through a few steps so make sure to move it through a big enough range to get both near and far indicators to turn off noting the offset count on each - then set the final setting between the two.  

If you have several backs and camera bodies, you'll need to do this for each camera body and back combination.  If you change to say your film back or alternate back you will need to set the offset value to whatever that back takes - or presumably 0 for film backs.   It may be that many of you with Hy6 and AFi's do not need any offset calibration at all.  

The correction will work with all lenses.  You do not need to do this for every lens.  


Eric Hiss
« Last Edit: September 21, 2011, 02:12:53 am by EricWHiss »
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uaiomex

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Ok, that's it. It's being years now since I wanted first to ask these questions:
 
Why LV is possible while tethering to a monitor and not on the back's LCD?

I've read many times CCD's can't be used for LV, that you need a CMOS sensor. Don't P&S cameras use CCD's and they always had LV since the beginning?

And, If tethering (whatever the reasons) allow for LV from a digital MF back, how come nobody comes with a solution to use an iPad or iPhone?

Tia
Eduardo



If you have a Hy6 or AFi with the latest firmware and you have always wanted to know what the AF Focus offset function in the options does, here's an explanation.   It adjusts the accuracy of the cameras focus indicators relative to what back you have fitted.  It does not change the focusing screen, only the indicators and AF accuracy.   My AFi-ii 12 focus fairly well and the focusing screen seems to be very well aligned for manual focusing by the eye, however I had noticed that it seemed the focus indicators were not agreeing perfectly with the focus screen.  DOF with the fast lenses like the 110/2 or the 180/2.8 is just paper thin, especially at portrait distances.   Sometimes when my eyes are tired or when I'm doing critical work, I'd rather rely on the focus indicators which are very useful.  They point the photographer which way the focus needs to be adjusted - in or out and then both come on when its perfect.   I wanted this indicator be as accurate as possible and fortunately the camera designers built in setting in the options menu to do just that.  Here's how easy it is:

1) Set up your camera on a tripod and use a target with high contrast edges on it that also has some fine details in an uncluttered area.  I downloaded one of the black and white test charts from imatest and printed it out and taped it up on the wall across my office.
2) Position the camera such that center of the frame where the focus points are falls over the target.
3) Set your cameras focus switch to manual, and set your camera up for tethering
4) Use live view at 100% (leaf has great Live View - YMMV) to manually focus the lens for best focus
5) Last step - be careful to not bump or move the camera - hit the options button on the grip and turn the top scroll wheel until you get to AF Offset.   Now just adjust the lower scroll wheel until the focus confirmation indicates perfect focus.  The adjustment count is very fine and the both focus indicators will stay on through a few steps so make sure to move it through a big enough range to get both near and far indicators to turn off noting the offset count on each - then set the final setting between the two. 

If you have several backs and camera bodies, you'll need to do this for each camera body and back combination.   You do not need to do this for every lens. 


Eric Hiss
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Gigi

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Eric - thanks for this. Glad to have the step-by-step as well. Neat stuff.
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Geoff

EricWHiss

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Eduardo,
Your questions about live view and tethering have really been addressed in the forums and actually some of the newer phase backs do have live view already.   
This thread is really about focus indicator calibration. 
Eric
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ondebanks

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Don't P&S cameras use CCD's and they always had LV since the beginning?


Yes, because they always had fewer pixels in both their sensors and their LCDs. The live video you see is at low resolution, usually achieved by decimation (most pixels are discarded, to make readout much faster).

Ray
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uaiomex

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Well, I know this issue is being brought many times here but I sincerely don't understand a few specific things and I thought they could be easily answered. I didn't mean to hijack the thread. I'll post it again on a new thread. Thanks anyway Eric.
Eduardo


Eduardo,
Your questions about live view and tethering have really been addressed in the forums and actually some of the newer phase backs do have live view already.   
This thread is really about focus indicator calibration. 
Eric

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Lacunapratum

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Thanks Eric.  That's very helpful.  I was dreading it.  I have one that's already adjusted but I was always afraid of doing it for the other one. 
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baudolino

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The correction will work with all lenses.  You do not need to do this for every lens.  

Eric, you are wrong on this point - the correction will be different with different lenses. I've had my Hy6 and all three AFD lenses calibrated by Sinar in Zurich on an optical bench and my 80mm comes with recommended adjustment of +1, the 180 comes with -6 and the 50mm with -7. I got a little sheet of paper printed by them with the recommended adjustments. Subsequently, I checked the adjustments recommended by Sinar using the LensAling Pro, with - surprise, suprise - identical results as those recommended by Sinar. Regards, Martin
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EricWHiss

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Martin,
That's interesting to read, thanks for the input.   I did my test with two lenses, the AF 80mm PQS and the 180/2.8 and got that same result.   I am struggling to see how the lenses could affect this setting - any thoughts?   I mean its clear that differences between the film plane or sensor chip alignment could change the AF focus calibration as its downstream from the AF electronics and focusing screen, however the lenses are upstream - how could they change things?  Not saying it isn't true, just would like to know how.
Eric
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baudolino

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Eric, I am not strong on the theory but I suppose it is the same situation as some Leica M lenses needing adjustment for back- or front focusing, also the same as other makers' AF lenses (Canon, Nikon) focusing slightly off - after all, the top end DSLRs all have the micro focus adjustment which you also set differently for different lenses - the AF offset on the Hy6 is the same thing. Martin
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Gigi

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Re: Quick steps: how to set AF calibration on Hy6/AFi cameras - its really cool!
« Reply #10 on: September 22, 2011, 05:31:21 am »

What you are suggesting is that the adjustment is per lens, dealing with manuf. tolerances in lens:sensor plane (or film plane) alignment. Its interesting to see the range  of your lenses. Maybe its time to start testing our own. Seems like Lensalign matched up with Sinar's own results, yes?
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Geoff

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Re: Quick steps: how to set AF calibration on Hy6/AFi cameras - its really cool!
« Reply #11 on: September 22, 2011, 05:32:47 am »

Martin,
That's interesting to read, thanks for the input.   I did my test with two lenses, the AF 80mm PQS and the 180/2.8 and got that same result.   I am struggling to see how the lenses could affect this setting - any thoughts?   I mean its clear that differences between the film plane or sensor chip alignment could change the AF focus calibration as its downstream from the AF electronics and focusing screen, however the lenses are upstream - how could they change things?  Not saying it isn't true, just would like to know how.

Hi Eric,

There are several elements in the AF cycle that can (or need to) be adjusted.

First there is the mechanical tolerance of the lens(mount). We are utilising the extremely narrow DOF of a wide aperture AF sensor. The exact depth of focus (in the projected image plane) of the AF sensor is probably in the order of the thickness of a human hair (or less).

Next there is the potential discrepancy between the optical path to the AF sensor versus the optical path to the image sensor. we are again faced with construction accuracy versus several tens of microns of depth of focus. When we're unlucky, these tolerances can add instead of canceling each other out.

Next there is the mechanical drive train of the focus mechanism in a lens, with its hysteresis tolerance when changing focus direction. In addition there is the accuracy of the stepper motor(s), how small a change of focus plane is the AF mechanism capable of.

A common way of dealing with all that is an electronic 'factory' calibration which can (partly) be stored in the lens. Most likely that is implemented as a lookup table which is built from an offset and a multiplier (or more complex if a lens also uses internal focusing). The easy part of that equation is the offset, and that's one of the reasons why it has become available as a user adjustable parameter which is probably stored in the camera body. The other parameters used to build that lookup table are too complex for an average user to calibrate by hand. A computer application with knowledge of the mechanical focus properties of the specific lens is required to find an optimized solution.

Due to the differences in lenses, the offset can be different between lenses. I'm not sure how it's implemented, but one could store the offset in the camera body, and the other parameters/lookup table in the lens. One could also store a second offset in the camera body which is added to the generic offset (which cannot know the tolerances in the camera AF path) used in the lens' lookup table.

Cheers,
Bart
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baudolino

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Re: Quick steps: how to set AF calibration on Hy6/AFi cameras - its really cool!
« Reply #12 on: September 22, 2011, 07:19:32 am »

yes, LensAlign agreed with Sinar's measurements - I did not test at all distances / apertures though; tried about 2-3 meters distance at full aperture

the AF offset is only available in the latest firmware version which has to be installed by a service technician - involves not just uploading new firmware but also some hardware adjustments that are necessary. perhaps the new bodies already come with this version; my Sinar Hy6 didn't so I had it updated by Sinar for free (together with the measurements of the required offsets for my lenses). But if you have the latest FW installed then I'd suggest using the LensAlign for each lens to find what values you should dial in.

One more thing to remember (as it is easy to forget when shooting) - the Hy6 body does not remember what offset you dialed in for each lens; you need to remember the offset for each lens and re-set manually every time you swap lenses.
« Last Edit: September 22, 2011, 07:32:22 am by baudolino »
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EricWHiss

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Re: Quick steps: how to set AF calibration on Hy6/AFi cameras - its really cool!
« Reply #13 on: September 22, 2011, 10:45:16 am »

Reiner at DHW confirmed via e-mail that the offset needs to be done for every lens.    Martin, I thank you for bringing that up.    
I think the offset calibration makes a difference and worthwhile for Hy6/AFi shooters to look into especially if they rely on the focus confirmation and/or AF a lot.  

Interestingly I did the calibration on a bunch of my lenses last night, including the ones that I did previously.   If I had done just the first four, I'd still be thinking only one figure was needed!

AF 80 f/2.8 PQS    +16
80  f/2.0  PQ         +16
180  f/2.8 PQ        +16
110  f/2.0             +16

90mm APO           +  5
60-140mm                0


More observations:  
1) With the AFi-ii 12 back, it seems like the apex of the focus is readily visible and the zone is just paper thin.  But WOW!  when you get it right its just amazing.
2) The adjustments are finer than I can see on the focusing screen even with the lupe finder.
3) The focus direction - from infinity to close or close to infinity did not appear to affect the results


I'm glad most of my lenses so far have the same offset value - that way I don't have to remember as many.  Maybe I will write with pencil the value on the bottom of the lens to help remember?

RE: Firmware.  The bodies that I got this year from Leaf and DHW have the latest firmware. Actually the body from Leaf had  V 3.10 without the a3 the DHW had and I was told that this is the final version.
« Last Edit: September 22, 2011, 11:07:18 am by EricWHiss »
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