Z7/FTZ AF fine-tuning

Started Nov 9, 2018 | Discussions
JimKasson
JimKasson Forum Pro • Posts: 27,458
Z7/FTZ AF fine-tuning
5

In another thread, I started out testing the Z7 for autofocusing accuracy in various focusing modes, but discovered -- thanks, Marianne and Horshack! -- that my testing wasn't valid because I was assuming that there was a CDAF trim step after the cameras PDAF focusing, and it appeared that either that wasn't happening at all, or it wasn't very effective.

That caused me to think about the PDAF fine-tuning function in the Z7. I'd figured that it wouldn't affect accuracy, just speed, in that it would allow the hare-like PDAF phase of the autofocusing to get closer to the correct location so that the tortoise-equivalent CDAF phase would go faster.

But what if there isn't a CDAF phase, at least with adapted lenses? Then the PDAF fine tuning would affect accuracy, not speed.

I put the 105 mm f/1.4 lens on a Z7, set it up a bit under three meters from my checkerboard ramp, and made 16 exposures in AF-S Single mode with AF fine tuning set to -20, -10, 0, +10, and +20. I racked the lens towards the far on the odd exposures, and in the near direction on the odd ones. I analyzed all the data, and here's what I saw:

AF fine-tuning does affect accuracy. It affects it in just about the same way as in the D850, with each step changing the image-field focal plane by about 4 micrometers.

It's going to take a while to digest the implications of this and to find out if it applies to native lenses.

Jim

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Horshack Veteran Member • Posts: 8,184
Re: Z7/FTZ AF fine-tuning
1

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only). In other words, since AFMA adjusts what the camera considers "in focus" it will naturally affect the focus plane in the direction it's tuned to.

What remains to be seen is if there any lenses which actually need AFMA on the Z7 for optimal accuracy. For example your 105mm results above indicate that it's most accurate without AFMA. All the AFMA is doing for this lens is shifting the focal plane away from its optimal position. The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

JimKasson
OP JimKasson Forum Pro • Posts: 27,458
Re: Z7/FTZ AF fine-tuning
2

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

it will naturally affect the focus plane in the direction it's tuned to.

What remains to be seen is if there any lenses which actually need AFMA on the Z7 for optimal accuracy. For example your 105mm results above indicate that it's most accurate without AFMA.

For pinpoint, but not for the other modes.

All the AFMA is doing for this lens is shifting the focal plane away from its optimal position. The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

I hope you're right, but I'm going to keep nosing around this issue. The first thing I'm going to do, unless you've already done it, is see how -- quantitatively -- AF fine tuning affects accuracy.

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Lance B Forum Pro • Posts: 32,297
Re: Z7/FTZ AF fine-tuning

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only). In other words, since AFMA adjusts what the camera considers "in focus" it will naturally affect the focus plane in the direction it's tuned to.

Makes sense.

What remains to be seen is if there any lenses which actually need AFMA on the Z7 for optimal accuracy. For example your 105mm results above indicate that it's most accurate without AFMA. All the AFMA is doing for this lens is shifting the focal plane away from its optimal position. The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

I'm thinking this last paragraph makes sense to me as far as actually utilising the AF fine tune adjustment on the Z7.

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Lance B Forum Pro • Posts: 32,297
Re: Z7/FTZ AF fine-tuning
1

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

it will naturally affect the focus plane in the direction it's tuned to.

What remains to be seen is if there any lenses which actually need AFMA on the Z7 for optimal accuracy. For example your 105mm results above indicate that it's most accurate without AFMA.

For pinpoint, but not for the other modes.

All the AFMA is doing for this lens is shifting the focal plane away from its optimal position. The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

I hope you're right, but I'm going to keep nosing around this issue. The first thing I'm going to do, unless you've already done it, is see how -- quantitatively -- AF fine tuning affects accuracy.

It would be good to know what exactly is going on. Thanks for your continuing efforts, Jim.

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Horshack Veteran Member • Posts: 8,184
Re: Z7/FTZ AF fine-tuning

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

it will naturally affect the focus plane in the direction it's tuned to.

What remains to be seen is if there any lenses which actually need AFMA on the Z7 for optimal accuracy. For example your 105mm results above indicate that it's most accurate without AFMA.

For pinpoint, but not for the other modes.

Are the results you posted above for pinpoint? I didn't see any mention of that so assumed it was regular AF-S.

All the AFMA is doing for this lens is shifting the focal plane away from its optimal position. The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

I hope you're right, but I'm going to keep nosing around this issue. The first thing I'm going to do, unless you've already done it, is see how -- quantitatively -- AF fine tuning affects accuracy.

AFMA by definition has to affect accuracy since again it moves the focus plane. If you instead mean precision then it shouldn't affect it, outside of non-optimal tuned scenarios, as I described here: https://www.dpreview.com/forums/post/50781856

JimKasson
OP JimKasson Forum Pro • Posts: 27,458
Re: Z7/FTZ AF fine-tuning

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

it will naturally affect the focus plane in the direction it's tuned to.

What remains to be seen is if there any lenses which actually need AFMA on the Z7 for optimal accuracy. For example your 105mm results above indicate that it's most accurate without AFMA.

For pinpoint, but not for the other modes.

Are the results you posted above for pinpoint?

No, for Single.

I didn't see any mention of that so assumed it was regular AF-S.

Single is the second AF-S mode from the left.

All the AFMA is doing for this lens is shifting the focal plane away from its optimal position. The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

I hope you're right, but I'm going to keep nosing around this issue. The first thing I'm going to do, unless you've already done it, is see how -- quantitatively -- AF fine tuning affects accuracy.

AFMA by definition has to affect accuracy since again it moves the focus plane. If you instead mean precision then it shouldn't affect it, outside of non-optimal tuned scenarios, as I described here: https://www.dpreview.com/forums/post/50781856

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Horshack Veteran Member • Posts: 8,184
Re: Z7/FTZ AF fine-tuning

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

Take a contrast detection function, which usually arrives at ideal AF by finding the point of maximum detected contrast, then adjust what's considered maximum contrast by introducing a bias to the calculation, so that instead of contrast 'x' being considered the maximum point of contrast it's contrast x-y or x+y (for both AFMA directions). The camera will then focus to x-y or x+y rather than x. The same way it works for PDAF, but with the bias affecting the contrast evaluation of focus rather than the phase evaluation.

JimKasson
OP JimKasson Forum Pro • Posts: 27,458
Re: Z7/FTZ AF fine-tuning

Horshack wrote:

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

Take a contrast detection function, which usually arrives at ideal AF by finding the point of maximum detected contrast, then adjust what's considered maximum contrast by introducing a bias to the calculation, so that instead of contrast 'x' being considered the maximum point of contrast it's contrast x-y or x+y (for both AFMA directions). The camera will then focus to x-y or x+y rather than x.

So the camera would have to find the in-focus point, then deliberately move the focal plane away from it. Possible, but definitely odd.

The same way it works for PDAF, but with the bias affecting the contrast evaluation of focus rather than the phase evaluation.

PD is different in that you have two signals to weigh.

Jim

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jfriend00 Forum Pro • Posts: 12,712
Re: Z7/FTZ AF fine-tuning

Horshack wrote:

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

Take a contrast detection function, which usually arrives at ideal AF by finding the point of maximum detected contrast, then adjust what's considered maximum contrast by introducing a bias to the calculation, so that instead of contrast 'x' being considered the maximum point of contrast it's contrast x-y or x+y (for both AFMA directions). The camera will then focus to x-y or x+y rather than x. The same way it works for PDAF, but with the bias affecting the contrast evaluation of focus rather than the phase evaluation.

Except with contrast measurement, you don't get a positive or negative reading.  The only way you could introduce a bias is to find the point of maximum contrast and then drive a specific direction until that was reduced by a certain amount to bias the focus in that direction.  I would think PDAF could do this quite differently.

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John

Horshack Veteran Member • Posts: 8,184
Re: Z7/FTZ AF fine-tuning

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

Take a contrast detection function, which usually arrives at ideal AF by finding the point of maximum detected contrast, then adjust what's considered maximum contrast by introducing a bias to the calculation, so that instead of contrast 'x' being considered the maximum point of contrast it's contrast x-y or x+y (for both AFMA directions). The camera will then focus to x-y or x+y rather than x.

So the camera would have to find the in-focus point, then deliberately move the focal plane away from it. Possible, but definitely odd.

Thats it. I agree it's odd - the whole notion of implementing AFMA for CDMA is strange. I suspect Nikon did so for people who use AFMA for intentional adjustment of focus rather than for AFMA, to keep the adjustment consistent across the focusing modes.

The same way it works for PDAF, but with the bias affecting the contrast evaluation of focus rather than the phase evaluation.

PD is different in that you have two signals to weigh.

Naturally it's different since it's a phase system that requires two signals. What I meant as the same is how the bias is introduced into the calculated result.

Horshack Veteran Member • Posts: 8,184
Re: Z7/FTZ AF fine-tuning

jfriend00 wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

Take a contrast detection function, which usually arrives at ideal AF by finding the point of maximum detected contrast, then adjust what's considered maximum contrast by introducing a bias to the calculation, so that instead of contrast 'x' being considered the maximum point of contrast it's contrast x-y or x+y (for both AFMA directions). The camera will then focus to x-y or x+y rather than x. The same way it works for PDAF, but with the bias affecting the contrast evaluation of focus rather than the phase evaluation.

Except with contrast measurement, you don't get a positive or negative reading. The only way you could introduce a bias is to find the point of maximum contrast and then drive a specific direction until that was reduced by a certain amount to bias the focus in that direction. I would think PDAF could do this quite differently.

You do get a positive and negative result for CDAF because to find the maximum point of contrast you have to first focus past that point (overshoot), so the direction toward that point and back can be formulated into positive and negative values, the polarity of which can be determined by whether the initial focus movement was toward MFD or infinity.

jfriend00 Forum Pro • Posts: 12,712
Re: Z7/FTZ AF fine-tuning

Horshack wrote:

jfriend00 wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

Take a contrast detection function, which usually arrives at ideal AF by finding the point of maximum detected contrast, then adjust what's considered maximum contrast by introducing a bias to the calculation, so that instead of contrast 'x' being considered the maximum point of contrast it's contrast x-y or x+y (for both AFMA directions). The camera will then focus to x-y or x+y rather than x. The same way it works for PDAF, but with the bias affecting the contrast evaluation of focus rather than the phase evaluation.

Except with contrast measurement, you don't get a positive or negative reading. The only way you could introduce a bias is to find the point of maximum contrast and then drive a specific direction until that was reduced by a certain amount to bias the focus in that direction. I would think PDAF could do this quite differently.

You do get a positive and negative result for CDAF because to find the maximum point of contrast you have to first focus past that point (overshoot), so the direction toward that point and back can be formulated into positive and negative values, the polarity of which can be determined by whether the initial focus movement was toward MFD or infinity.

My point is that CDAF doesn't have positive or negative signals.  You don't even know which direction you're off until you go one direction and find out whether the contrast is rising or falling.  It's definitely harder with CDAF and thus why it's so much slower than PDAF.  Yes, you could find where the max contrast is and then bias a particular direction from there.

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John

Horshack Veteran Member • Posts: 8,184
Re: Z7/FTZ AF fine-tuning

jfriend00 wrote:

Horshack wrote:

jfriend00 wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Jim, thanks again for the ongoing testing. I think it's been assumed AFMA would affect the accuracy of AF, esp since it's been established that Nikon decided to implement AFMA for their CDMA as well on the Z7 (based on the fact it affects pinpoint AF as well, which appears to be CDAF only).

Do you know for a fact that Pinpoint is affected by AF fine tuning?

Yep, I verified it myself when someone else on this forum mentioned it does.

In other words, since AFMA adjusts what the camera considers "in focus"

How's it going to do that for CDAF?

The same as it does for PDAF, by introducing a bias to the in-focus focus evaluation, but for contrast rather than phase.

I’m having a hard time imagining exactly how that’s going to work.

Take a contrast detection function, which usually arrives at ideal AF by finding the point of maximum detected contrast, then adjust what's considered maximum contrast by introducing a bias to the calculation, so that instead of contrast 'x' being considered the maximum point of contrast it's contrast x-y or x+y (for both AFMA directions). The camera will then focus to x-y or x+y rather than x. The same way it works for PDAF, but with the bias affecting the contrast evaluation of focus rather than the phase evaluation.

Except with contrast measurement, you don't get a positive or negative reading. The only way you could introduce a bias is to find the point of maximum contrast and then drive a specific direction until that was reduced by a certain amount to bias the focus in that direction. I would think PDAF could do this quite differently.

You do get a positive and negative result for CDAF because to find the maximum point of contrast you have to first focus past that point (overshoot), so the direction toward that point and back can be formulated into positive and negative values, the polarity of which can be determined by whether the initial focus movement was toward MFD or infinity.

My point is that CDAF doesn't have positive or negative signals. You don't even know which direction you're off until you go one direction and find out whether the contrast is rising or falling. It's definitely harder with CDAF and thus why it's so much slower than PDAF. Yes, you could find where the max contrast is and then bias a particular direction from there.

You're describing the inherent shortcomings and complications of CDAF vs PDAF. The CDAF-based AFMA algorithm I described would use the existing information already gathered by a CDAF invocation, which includes directional information, so I'm not sure what disctintion you're making other than pointing out that CDAF is an inferior focusing mechanism.

And yes, the process of AFMA bias application for PDAF is much simpler, since the calculation for phase evaluation is performed instantaneously based on the comparison of the phase signal pair.

incoherent1 Regular Member • Posts: 463
Re: Z7/FTZ AF fine-tuning

Thank you. This directly addresses the question I raised here:

https://www.dpreview.com/forums/post/61677466

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tommiejeep
tommiejeep Veteran Member • Posts: 7,043
Re: Z7/FTZ AF fine-tuning

Following closely. Through my own experiences in shooting the Sony 7 series with the Techart Pro adapter I am convinced that it uses PDAF only and is that touch faster and more dependable for pin point accuracy when shooting small targets than my native lenses with the CDAF micro adjust.  It appears, in my use, is that on sensor PDAF without a CDAF adjustment is more accurate than seperate AF sensor with lenses which have not been fine tuned.  There is always MF .

Interesting to see if the FTZ operates the same way and if Fine tune is needed. From my brief, one hour, experience with the Z7, Z6, FTZ, 70-200 2.8 E, 105 1.4E and 300 f4 E, they seemed fine but no take away card for home computer and not shooting my normal subjects.

From a financial view point, shifting from Sony to Nikon only works if I can use all of my Nikon lenses without constant fine tuning for FL and distance.

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jfw Contributing Member • Posts: 515
Re: Z7/FTZ AF fine-tuning
1

Any chance of you brain surgeons boiling all this down into some pragmatic AF-tun advice for us lowly laymen??   ... Don't bother with new Z lenses?  Might need with F lenses?  Too early to tell & need more testing/ thinking?  Other? Thanks guys!

Jerry

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JimKasson
OP JimKasson Forum Pro • Posts: 27,458
Re: Z7/FTZ AF fine-tuning
  • jfw wrote:

Any chance of you brain surgeons boiling all this down into some pragmatic AF-tun advice for us lowly laymen?? ... Don't bother with new Z lenses? Might need with F lenses? Too early to tell & need more testing/ thinking? Other? Thanks guys!

Jerry

Too early to tell and need more testing.

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Livio Spallone Regular Member • Posts: 359
Re: Z7/FTZ AF fine-tuning

Horshack wrote:

The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

Decentered elements are not the only possible cause of error, chromatic and spherical aberrations still  play a role , a lesser one now that we focus at the working aperture.

Going back to practical user experience : all my Nikkor and Sigma lenses did not require finetuning but I had to finetune my 300 f2.8 VR + TCs and 500 F4 VR + TCs , in my experience ( YMMV ) adding a TC always bring some frontfocus (still does) and an increase of focus shift (now mainly solved).

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Lisperit

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Horshack Veteran Member • Posts: 8,184
Re: Z7/FTZ AF fine-tuning
1

Livio Spallone wrote:

Horshack wrote:

The only lenses which should require AFMA on an MIlC are those with decentered elements as there isn't anything else in the path to affect the phase balance like in DSLRs.

Decentered elements are not the only possible cause of error, chromatic and spherical aberrations still play a role , a lesser one now that we focus at the working aperture.

SA only plays a role if one wants to incorporate focus-shift correction in their AFMA, which as you indicated is not necessary on the Z since it focuses stopped down, at least up to f/5.6, beyond which focus-shift isn't an issue for nearly all lenses.

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