Drbobcameraguy Loc: Eaton Ohio

I have reinken focal pro. I use it to decide if my lenses need calibration and a lot of other information about the lens. It's worth the money if you ask me. I will state I'm a Pixel peeper. I had an issue with my 300mm f2.8. It was back focusing what at 2.8 appears to be a bunch. I sent it back to be recaled but didn't send my camera. When I got it back I recaled it with reinken. It works great now. Spend the 100 bucks and get the results you are wanting

SuperflyTNT Loc: Manassas VA

This is quite different than making an in camera adjustment to fine tune the lens. The Tamron Tap-in takes several adjustments at different focal lengths and different focusing distances and creates a curve based on those numbers that is applied in the lens rather than the camera. I know with the 18-400 it took 18 entries, 3 distances at 6 different focal lengths.

BartHx

Since you asked your question for a physics answer, here is a physics answer:
A point source object seen at infinite distance is at infinity when two rays of light from that object arrive at a lens parallel to each other. A lens focusing those rays when set at infinity is then able to focus those rays as a single point at its focal plane. The problem is that if you are able to define such a distance you could then also define a distance one millimeter farther away and your original definition would no longer apply. Since that distance cannot be achieved, we need to settle for a more practical definition. If we construct a device that emits two point sources with parallel beams (at best a very close approximation since black holes demonstrate that light is effected by a gravitational field) the lens is focused at infinity when it focuses those two beams as a single point at its focal plane. In yet more practical terms, a lens is focused at infinity when a point source at a great distance (potentially different for each different lens) is focused as a circle of confusion at the focal plane such that the circle of confusion produced remains within an acceptably small size when viewed under normal viewing conditions.

Drbobcameraguy Loc: Eaton Ohio

That's what is great about the tap-in console. It helps solve the zoom issue. That's also why a program like reinken focal can help immensely. I have a Sigma contemporary 160-600. I gave it to my wife. When I did I had to recalibrate it to her camera. Unfortunately my 300-800mm f5.6 cannot be calibrated at several focal lengths. Fortunately I use it a 800mm the most.

imagemeister Loc: mid east Florida

I know it is different - but, for ME irrelevant .....
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SuperflyTNT Loc: Manassas VA

As was your comment in relation to this post.

imagemeister Loc: mid east Florida

One of my points is, to at first, before doing multiple points of distance and focal lengths, and worrying about infinity - focal at one distance and focal length you are most interested in as a test to see if the lens' sharpness satisfies you - if not return it ! Personally, I think it folly to expect near perfection focus at multiple distances and focal lengths of these large f6.3 zooms and the jumping thru complicated hoops to try to make it so ! Indeed, most applications of these large zooms is at or very near the maximum extension and, in the case of most birds, a distance of 30-60 feet. F6.3 is capable of covering up most wide ranging errors. If this was an f4 lens, I might agree with complicated jumping thru hoops.
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walkurie Loc: East Stroudsburg, PA

I just received my 150-600 G2 and 70-200 G2 back from Tamron after calibration with my D500. So far so good. I'm impressed. Here is a description of the orocess from Tamron.
Thank you for contacting Tamron. I’m sorry that you’re having trouble with the calibration and the tap in console. It sounds like we may need to calibrate your lens and camera directly here. Would you mind sending the equipment in for us to pair the two together? We use your camera as a common denominator to see where we have to push/pull the values within the lens at each focal length and distance. We essentially rewrite the software in the lens so in the future, if you ever had to use the tap in, you could add or subtract to it.

 

JimH123 Loc: Morgan Hill, CA

Let me add to this discussion that there is really only one "infinity" with a lens. And it doesn't matter what focal length you desire to set a zoom to. And it is easy enough to see this infinity point. Using live view, manually focus on a star and do your best to achieve a best focus. Once you are at your best focus, look around that star and notice dimmer stars start to come into view. When a star is at infinity focus, all the light from that star is concentrated on a single point (within the restraints of the IQ of the lens of course). If you move the tiniest bit beyond infinity or short of infinity, a star gets fatter and the light intensity drops fast. The best point is infinity.

Now back to those formulae. There are compromises that we find acceptable meaning that at a normal viewing distance, we aren't going to notice that we aren't in perfect focus. Of course, at what point this is can be debatable since we are not all in agreement with how much we are willing to compromise.

Now back to your formula: 600 mm x 200 = 120000 = 393.68'

Now I'm not entirely sure if they mean by this that if you are at real infinity, that it will still look reasonably sharp at 393.68'. Or if they intend for you to focus on something 393.68' away, and that infinity would look reasonably in focus. Doesn't matter, the fact is that it is depending upon our inability to tell the difference with normal viewing (i.e. NOT pixel peeping!)

Now I don't pay much attention to the distance markings on any of my lenses. I could paint over them and it wouldn't affect my use of the lens. Those numbers are crude and just approximations. If you study those markings, you will find that as you approach infinity that the marks become closer together. And at infinity, the difference between 393.68' and the real infinity would actually be a very, very tiny amount of turning.

Next, depending upon the type of camera being used, the need to calibrate the lens either is important (DSLR) or doesn't even exist (Mirrorless). On a DSLR, the light is reflected to a separate sensor for focusing when the mirror is down. When the mirror goes up, it depends upon having the same distance to the image sensor. The micro focusing adjustment is how this is adjusted. And it is possible that a perfect adjustment at one FL will not be so accurate at some other FL on a Zoom lens.

A mirrorless camera has no such need since the focus happens on the image sensor and nothing changes while shooting.

I do have the Tamron 150-600mm lens you were talking about, except mine is the G1, original model. I bought it when I had the Sony A99 and I did have to do a MFA. Now I have a Sony A6600 (1.5x crop factor) and a Sony A7iii (full frame). Since the lens has an internal focus motor, I do not need to use the Sony adapter that has the SLT mirror (LA_EA4) which means that no MFA is needed and instead use another Sony adapter (LA_EA3 or more recently the LA_EA5) that does not have the SLT mirror.

Now for an example. First image is the original shot taken at 600mm using the Sony A7iii at f6.3. I don't know exactly how far away the plane was except that it is small within the image.

Second image, I cropped it a lot and resized it 6x with Gigapixel AI. We can use this as a sort of pixel peeping to show that the image is plenty sharp. No need ever to do a MFA.

Note: The number on the plane can be googled and I see this is a Cessna Skyhawk.

Original

(Download)

Cropped and resized 6x with Gigapixel AI

(Download)

nervous2 Loc: Provo, Utah

I'd be tempted to use the moon--or a distant mountain. But then, I'm no expert.

WDCash Loc: Milford, Delaware, USA

I saw a video of a fellow talking about something like this. Couldn't remember its name. Thanks

BebuLamar

Infinity is infinity and there is no subject you can aim at that is at infinity. However if you ask how far is close enough to infinity then it depends on the focal length of the lens, the longer the focal length of the lens you would need to use a subject further away.

imagemeister Loc: mid east Florida

Since I am not shooting anything at infinity ( with a 150-600mm - with a 20 or 24mm for astro yes ) I am NOT worried about it !
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