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JimBuchanan
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p.11 #1 · p.11 #1 · Techart PRO FAQ


genji wrote:
I can't help thinking that this depends upon the lens design but the furthest I could move the focus point away from infinity and still have the TAP find focus on a very distant subject is shown by the red arrow in the picture below.


After rereading the last several posts, I think I'm getting it.

If the TAP has an infinity focus position, otherwise known as the infinity park position where the adapter is at it's thinnest, and the lens is at its infinity hardstop position where infinity subjects are in focus, why would one expect the TAP to achieve infinity focus when the lens is backed off infinity and extended forward? This would mean the TAP would have to go negative infinity park to compensate for the extended/off infinity lens position. Irrespective of any lens design, this would be the case for any lens, if I'm understanding the issues here.




Nov 18, 2016 at 02:00 AM
nehemiahphoto
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p.11 #2 · p.11 #2 · Techart PRO FAQ


JimBuchanan wrote:
After rereading the last several posts, I think I'm getting it.

If the TAP has an infinity focus position, otherwise known as the infinity park position where the adapter is at it's thinnest, and the lens is at its infinity hardstop position where infinity subjects are in focus, why would one expect the TAP to achieve infinity focus when the lens is backed off infinity and extended forward? This would mean the TAP would have to go negative infinity park to compensate for the extended/off infinity lens position. Irrespective of any lens design, this would be the case for any lens,
...Show more

Interesting Jim--I don't doubt you're correct. You're saying that both the lens and the adapter must be at infinite positions to acquire infinite focus, correct? That would make sense.

I am wondering if the AF usability (not as an AF confirm device) is related to the lens design and MFD. For instance, when I owened the Zeiss 100 ZF that extends a great deal...but what about a lens that has internal focusing (like my N85), or minimal physical extension when focusing? (Like a CY 85 2.8)

I would love the TAP to work with an 85...that would really open things up for me...I wonder with the success of this if Techart is considering making a more robust (faster AF motor with more physical extension and able to hold upto 1,200g) to seemlessly focus longer lenses, 50-135mm. I would fork over dough for that.



Nov 18, 2016 at 02:55 AM
artur5
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p.11 #3 · p.11 #3 · Techart PRO FAQ


Like Jim said, with disregard to lens focal length or design, if you move the focus ring of the lens from infinity to, let's say 1.5 mtr., the Techart will provide usable AF range from 1.5mt. downwards, never above.
As a general rule for optics with regular focusing (i.e. non internal ) an adapter with helicoid provides normal focus range for lenses with a focal =10x the helicoid extension. In the Techart case, if I'm not mistaken, this is 4mm. So. any lens up to10x4 = 40mm. or below will get AF range from infinity to the usual MFD of the lens, or less. To fulfill this task with a 85mm. we'd need 8.5mm of helicoid; 13,5mm for a 135 mm. etc.. I doubt that it's technically doable to reach more than 5 or 6mm of extension with a short adapter like Leica M to Sony-E, unless we employ a sophisticated system of telescopic tubes which fit one inside the other. It would be much easier with adapters from Sony to SLR mounts, which are 3 times longer than the Leica M



Nov 18, 2016 at 09:25 AM
genji
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p.11 #4 · p.11 #4 · Techart PRO FAQ


artur5 wrote:
Like Jim said, with disregard to lens focal length or design, if you move the focus ring of the lens from infinity to, let's say 1.5 mtr., the Techart will provide usable AF range from 1.5mt. downwards, never above.
As a general rule for optics with regular focusing (i.e. non internal ) an adapter with helicoid provides normal focus range for lenses with a focal =10x the helicoid extension. In the Techart case, if I'm not mistaken, this is 4mm. So. any lens up to10x4 = 40mm. or below will get AF range from infinity to the usual MFD of
...Show more

Except that I did a brick wall test using the TAP + Tele-Tessar 85/4 ZM + A7R II on a tripod. With the lens focused at 1.5 meters, I moved the camera gradually towards the wall until AF failed, then very slightly back until the AF found focus. Next I moved the camera away from the wall until AF failed, then slightly forward until the AF found focus. With the focus ring set to 1.5 meters, the focus range extended from 1.05m (3.44ft) to 1.75m (5.74ft). Perhaps my methodology was faulty but I can't see how.



Nov 18, 2016 at 09:42 AM
Slalom
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p.11 #5 · p.11 #5 · Techart PRO FAQ


I agree with Artur5 and Genji yes you seem to have nailed the real world Variance on theory, what aperture were you using as the Range would be smaller wide open and greater stopped down.


Nov 18, 2016 at 12:59 PM
genji
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p.11 #6 · p.11 #6 · Techart PRO FAQ


Slalom wrote:
I agree with Artur5 and Genji yes you seem to have nailed the real world Variance on theory, what aperture were you using as the Range would be smaller wide open and greater stopped down.


Actually, we're manipulating the relationship between the focusing distance and autofocus range, not the depth of field (although that will be impacted as the distance between camera and subject changes). The results I got could be influenced by the aperture because the TAP's AF accuracy changes as less light reaches the sensor. The lens was wide open when I ran my test. I'd have to do more testing to see the effect of changing the aperture.



Nov 18, 2016 at 06:19 PM
artur5
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p.11 #7 · p.11 #7 · Techart PRO FAQ


It's possible also that the Techart, in retracted position, focuses slightly past infinity, although it seems unlikely that it would allow you to reach 1,75mt. According to a simple optic calculation, to change the focus of a 85mm. lens from 1.5mt to 1.75mt you'd have to retreat 0.87mm. the helicoid extension.
Anyway, if you're able to do it, either the camera, the adapter, the lens, or all of them, must be faulty !



Nov 18, 2016 at 08:59 PM
genji
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p.11 #8 · p.11 #8 · Techart PRO FAQ


artur5 wrote:
It's possible also that the Techart, in retracted position, focuses slightly past infinity, although it seems unlikely that it would allow you to reach 1,75mt. According to a simple optic calculation, to change the focus of a 85mm. lens from 1.5mt to 1.75mt you'd have to retreat 0.87mm. the helicoid extension.
Anyway, if you're able to do it, either the camera, the adapter, the lens, or all of them, must be faulty !


In your list of what could possibly be faulty, you forgot to mention the operator!



Nov 18, 2016 at 11:25 PM
genji
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p.11 #9 · p.11 #9 · Techart PRO FAQ


artur5 wrote:
It's possible also that the Techart, in retracted position, focuses slightly past infinity, although it seems unlikely that it would allow you to reach 1,75mt. According to a simple optic calculation, to change the focus of a 85mm. lens from 1.5mt to 1.75mt you'd have to retreat 0.87mm. the helicoid extension.
Anyway, if you're able to do it, either the camera, the adapter, the lens, or all of them, must be faulty !


Bingo! The densely populated area in which I live lacks open space and, consequently, very distant subjects. So today I went elsewhere, taking with me the A7R II, Sonnar C/Y 85/2.8, TAP, and a Novoflex C/Y->E adapter. I found that when I focused on a distant construction crane using the Novoflex adapter, a sign on the crane snapped into focus exactly when the focusing ring hit the infinity mark. But when I switched to the TAP, fully retracted and in MF mode, the same sign snapped into focus at the 15m/50ft mark, confirming Artur's suggestion that the TAP when retracted focuses past infinity.

I'm not sure what relevance this has for landscape photography but I also wonder what advantage the TAP -- or autofocus for that matter -- offers to landscape photographers. I would have thought the most efficient way to attain accurate focus and to optimise depth of field in landscape photography is to use MF and something like either OptimumCS-Pro or TrueDoF-Pro or both. But what would I know? My favourite landscape photographer is William Eggleston.



Nov 19, 2016 at 07:29 AM
navmannz
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p.11 #10 · p.11 #10 · Techart PRO FAQ


genji wrote:
Bingo! The densely populated area in which I live lacks open space and, consequently, very distant subjects. So today I went elsewhere, taking with me the A7R II, Sonnar C/Y 85/2.8, TAP, and a Novoflex C/Y->E adapter. I found that when I focused on a distant construction crane using the Novoflex adapter, a sign on the crane snapped into focus exactly when the focusing ring hit the infinity mark. But when I switched to the TAP, fully retracted and in MF mode, the same sign snapped into focus at the 15m/50ft mark, confirming Artur's suggestion that the TAP when retracted
...Show more

That's exactly my experience, too, and with both the adapters I've had. That raises two issues for me - first, because of this, its not possible to use predetermined hyperfocal settings based on the focus scale, and second there is a risk that you might incur some reduction in image quality when using an internal focusing lens, because you have to put the lens focusing setup into a mode designed for intermediate distances, while the TAP is focusing it at infinity. I haven't tested rigorously the second of these, but suspect that its probably so minor it would be hard to detect. But the first is significant enough for me that I prefer to use my metabones manual adapter when doing landscapes.

BTW, I've discussed this in a blog post in which I've reviewed the TAP from an end-user perspective, referencing this thread as the most comprehensive technical reference source for use of the TAP. It can be found here.



Nov 19, 2016 at 08:13 AM
 

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genji
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p.11 #11 · p.11 #11 · Techart PRO FAQ


navmannz wrote:
That's exactly my experience, too, and with both the adapters I've had. That raises two issues for me - first, because of this, its not possible to use predetermined hyperfocal settings based on the focus scale, and second there is a risk that you might incur some reduction in image quality when using an internal focusing lens, because you have to put the lens focusing setup into a mode designed for intermediate distances, while the TAP is focusing it at infinity. I haven't tested rigorously the second of these, but suspect that its probably so minor it would be hard
...Show more

John, I've added a link near the beginning of the FAQ to your elegant and comprehensive review, describing it as "in essence a concisely written distillation of the most important information in this FAQ".



Nov 19, 2016 at 09:32 AM
Fred Miranda
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p.11 #12 · p.11 #12 · Techart PRO FAQ


I've noticed that with slower lenses like the ZM 85/4 in low light, it's essential to keep focus on the center of the frame. It works surprisingly well as long as it stays there.
Fred



Nov 24, 2016 at 04:59 PM
genji
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p.11 #13 · p.11 #13 · Techart PRO FAQ


Fred Miranda wrote:
I've noticed that with slower lenses like the ZM 85/4 in low light, it's essential to keep focus on the center of the frame. It works surprisingly well as long as it stays there.
Fred


Thanks, Fred. I've added your tip to the "Why is my Techart PRO having difficulty finding focus?" section of the FAQ.



Nov 24, 2016 at 11:00 PM
rji2goleez
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p.11 #14 · p.11 #14 · Techart PRO FAQ


genji wrote:
Thanks, Fred. I've added your tip to the "Why is my Techart PRO having difficulty finding focus?" section of the FAQ.


I have found this to be the case with many lenses and not necessarily slow lenses. The further to the edges of the frame the focus point is moved, the slower or more difficult it is to get AF confirmation.



Nov 25, 2016 at 12:33 AM
DavidBM
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p.11 #15 · p.11 #15 · Techart PRO FAQ


Fred Miranda wrote:
I've noticed that with slower lenses like the ZM 85/4 in low light, it's essential to keep focus on the center of the frame. It works surprisingly well as long as it stays there.
Fred


Yes; this is an annoying feature. It's rare that in a portrait the central position is the right one, and focus and recompose is unlikely to get it just right (and isn't really possible on a tripod with the remote ap). And for landscape stuff, and other uses where the central point is fine, manual is also fine. (one exception: using TAP to focus the APO Lanthar 180 at infinity is great because the helicoid in the lens has so little throw near infinity getting it spot on is very, very hard and is I suspect what has lead to it's slight rep for being less good at infinity)



Nov 25, 2016 at 12:43 AM
genji
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p.11 #16 · p.11 #16 · Techart PRO FAQ


rji2goleez wrote:
I have found this to be the case with many lenses and not necessarily slow lenses. The further to the edges of the frame the focus point is moved, the slower or more difficult it is to get AF confirmation.


Thank you, FAQ modified accordingly.



Nov 25, 2016 at 01:01 AM
DavidBM
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p.11 #17 · p.11 #17 · Techart PRO FAQ


genji wrote:
Thank you, FAQ modified accordingly.


Yes: sometimes very fast ones! I've noticed that the Zuiko 50mm f1.2 is more than usually sensitive to off centre focus point placement, even wide open. I'm guessing it's because the contrast drops off and aberrations increase off axis in a way that fools the focusing. Or even that the angle of incidence of the rays at very fast apertures confuses the PDAF.



Nov 25, 2016 at 02:21 AM
genji
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p.11 #18 · p.11 #18 · Techart PRO FAQ


DavidBM wrote:
Yes: sometimes very fast ones! I've noticed that the Zuiko 50mm f1.2 is more than usually sensitive to off centre focus point placement, even wide open. I'm guessing it's because the contrast drops off and aberrations increase off axis in a way that fools the focusing. Or even that the angle of incidence of the rays at very fast apertures confuses the PDAF.


Thanks, added to the FAQ. It's worth keeping in mind that the TAP can struggle to acquire focus with both fast and slow lenses, the only solution being to keep the focus point close to the centre of the frame and recompose if necessary. But then Leica and Contax RF users have been focusing and recomposing since 1932.



Nov 25, 2016 at 03:06 AM
DavidBM
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p.11 #19 · p.11 #19 · Techart PRO FAQ


genji wrote:
Thanks, added to the FAQ. It's worth keeping in mind that the TAP can struggle to acquire focus with both fast and slow lenses, the only solution being to keep the focus point close to the centre of the frame and recompose if necessary. But then Leica and Contax RF users have been focusing and recomposing since 1932.


True; and sometimes it's fine to do that (and with many lenses fairly off centre points work well).
But generally in situations where I'm happy to focus-and-recompose I'd rather manual focus with the magnification box off centre.



Nov 25, 2016 at 05:00 AM
Fred Miranda
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p.11 #20 · p.11 #20 · Techart PRO FAQ


The link to this FAQ is now part of TechArt Pro Main page.



Dec 02, 2016 at 09:12 PM
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