well…except that speedometers do lie. It is known!
It is illegal in a Germany to sell a car with a speedo that reads higher than the car is going. So they reduce the speed displayed by a lot. About 4mph at 60.
So VW just extended that philosophy to their emissions readings?
I’m pretty sure what they did was illegal.
Could you let me know what question you’re wondering about? There’s a lot in this thread and I’m not sure I follow what you’re asking.
Also: if you have questions, Problems & Support are the best (and only) place to be sure they’re addressed - Beyond the Manual is the only section of the forum that staff do not read regularly (including me), and I never check my tags.
The question is “why does GF claim to have a 0.5” focal range when the lens only moves 0.4"?
The problem was reported to support: 0.5" focus range not achievable and they claimed black was white.
The machine isn’t physically capable of focusing at 0.5" and it doesn’t position the lens any differently for settings between 0.4" and 0.5". So for 0.5" materials it must be 0.1" out of focus.
Well, the general gist is about the focus range capability.
It is advertised as having a focal range of 0.5". However, through examination and experimentation, it seems to be significantly less.
The first limitation appears to be physical. Measuring the difference between the physical travel extremes results in roughly 0.470". It seems the head assembly has physical limitations preventing a full travel distance of .500" (and certainly much more room would be needed to overcome tolerance build ups if an accurate calibration is desired).
The second limitation appears to be in software. The number of steps sent in the file to the unit for the focus stepper never exceed 30. When the focus point is ~0.000, the number of steps is 0. At 0.500", it is 30. The stepper motor, combined with the gearing, is capable of advancing the lens in 0.0139" increments. This means the lens never moves more than 0.417".
Furthermore, the number of steps is proportional to the expected focus, until it reaches just under 0.400", then it slopes drastically. This is illustrated here:
(Image courtesy @palmercr)
The question: Is the stated claim of a focal range of 0.5" accurate when the device appears to only be capable of a range of 0.417".
Where are the units on your axes man! And what’s with the 8 zeros after the decimal point on what should just be integers?!
Whoa, whoa! Please note the image credit.
(He sent it as part of an informal chat between us, so pretty wasn’t as important as functional.)
I cleaned it up a bit:
Regarding the second half of your question, we don’t guarantee any particular range of motion, and in fact there’s some variation on maximum physical travel from head to head. We mistakenly put a specific range of motion on the website before, then realized the error and corrected it.
Regarding the first half, the focal point of a lens is infinitesimally small; any optical system “in focus” will necessarily have some distance between the focal point and the surface. I don’t know of any universal quantitative definition of “in focus” across all optical systems; it typically means “close enough to the focal point that the desired goal can be achieved” - for example, an in-focus picture is one where bluriness isn’t noticeable, or is below a certain wavelength, or grain size, or somesuch.
Interlude: just checked Wikipedia to make sure I wasn’t too far off base. It says:
An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. The border between these is sometimes defined using a circle of confusion criterion.
It seems to agree that the definition is subjective, although it doesn’t propose a functional test.
In any case, the Glowforge lens can move sufficiently to place that focal point close enough to the surface of material to cut (up to 0.25") or engrave (up to 0.5"). Since it can focus sufficiently to accomplish its goal - yes.
For those curious about history, we first designed it so it can engrave 0.5" materials; then later, wrote the website copy as best we could to convey that, as well as address questions like “well, can I engrave over the full 2” height of a 2" tall object?". As always, our goal is to try and convey the best information possible to the largest number of people, and we may occasionally fall short. We did initially (with range of motion) but I think the current language is accurate and leads people to the correct conclusion.
I think this was a practical question about what you can do with your Glowforge, which I’m happy to do my best to answer. In the unlikely event that folks want to use this as an opportunity to debate the definition of technical terms, I will respectfully allow them to do so without interrupting.
Thank you for the response, @dan. That’s an answer I can live with.
In this forum?
First up I think we ought to define “term” and “definition”…
Before we go defining things, shouldn’t we define what “define” means?
What does “mean” mean?
I think it’s like an average or something.
So 0.1" out of focus has no effect then? I don’t understand how that can be the case when support are constantly telling people PG has to be absolutely flat to cut properly with PG settings.
As Scott said that was just part of a discussion and was built from incorrect data. This is what the motor actually does.
It does nothing at all between 0.4" and 0.5", so it has a range of 0.4" where it can focus.
For engraving it’s generally fine to be a bit off. It’s cutting where you run into trouble. And they don’t officially support cutting anything over 1/4” thick.
They might not sell any PG more than 1/4" but they advertise “maximum Cut & Engrave height: 0.5″ (13mm)”
Maximum material depth: 18" (455 mm) for Basic; unlimited for Pro Maximum material width: 20″ (515 mm) Cutting area: 11.5″ (290 mm) deep and 20″ (515 mm) wide Maximum material height: 2″ (50mm) Maximum material height with tray: 0.5″ (13mm) Maximum Cut & Engrave height: 0.5″ (13mm)
Completely Internal — Lens moves internally up and down inside the head to focus on materials up to 0.5” (13mm) thick Exquisitely precise — laser height measurement can measure the surface of the material to within 0.004 inches (0.1mm) Multipass — Focus can be shifted between engrave passes, allowing detailed depth engraves. Focus Override — the laser can be defocused to experiment with a range of techniques that require less intense heat
The camera does not move enough to focus on 0.5" material, it will focus 0.1" below the surface. And the fact it can measure height with an accuracy of 0.1mm is irrelevant when the focus moves in steps of 0.7mm .
I think a big concern has always been about having perfect focus for cutting. There has always been much todo about the material being absolutely flat.
However, the focal points the machine is capable of are limited to: 0.000, 0.028, 0.056, 0.083, 0.111, 0.139, 0.167, 0.195, 0.222, 0.250, 0.278, 0.306, 0.334, 0.361, 0.389, 0.417.
So, with only 10 focal points over the 1/4" cutting range, you can be as much as 0.014" out of focus. Per Dan’s response, this is within spec for the machine. It appears that focus may not be as super critical a factor as we thought.
I’m one of the first people that found the slightest bit of warp (0.01") could have a profound effect on ability to cut through. I tried to explain at the time that it wasn’t that a cut needed to be within 0.01" but that an additional error of 0.01" over what was used for the automatic settings could cause a problem. For example if the company assumed a range of 0.014" in focus accuracy for their settings to work, then adding another 0.01" to that could be a problem.