Step Size Terminology

This has always kinda bugged me, although it is not important functionally. I wanted to be sure I was clear (and maybe help anyone who is reading this to be clear).

SGP, refers to “step size” in the autofocus setup. To me, and most imagers I know, a “step” has always been one focuser tic. That probably came from “stepper motor” that some focusers use.

OTOH, unless I am mistaken, “step size” in SGP means the number of focuser tics (what I always called “steps”) between autofocus measurement exposures on the V-curve. Correct me if this is wrong but I think it is right.

For example, with my FSQ:

Physical step size is 1.2 microns (HSM motor), on the motor. The SGP “step size” 52. That means the focuser is moving about 62.4 microns between steps (samples) and over the 11 “step/sample” v-curve is moving about 686 microns.

I might suggest a different term be used to avoid confusion, especially for new users. I would suggest “focuser steps between samples” or something to that effect.

I, too, like precision in most things, particularly the software I use. In this case, ‘step size’ has always seemed pretty explanatory to me. The suggested new term is 4 words instead of 2, more complicated, and simplicity is a virtue. I could certainly go with something like ‘step count’, also 2 words.

Well, maybe I am just old school where step size always meant a physical measurement on the focuser. That is a long established, historically based, astronomical imaging meaning so it is not amenable to change. That leaves us with the SGP usage to change so maybe we could come up with some new, but fairly short and descriptive term.


“Sample Spacing”
“Measurement Spacing”

Slightly longer:

Steps/HFD Measurement
Steps/HFD Sample
Steps between Measurements
Steps between Samples

I like the last one best as it is the most descriptive, albeit a bit longer

How about just “focus steps” or “focuser steps”?


Well, sort of - but I was trying to find something that would not only not be confused with physical step size but also be a bit explanatory as to what it’s function in SGP is.

Not to deter feedback, but this is not likely to change. It has been this way for years and makes sense to most users.

It am sure it makes sense to current users since they have already figured it out but to users coming from other SW it is easy to confuse with the standard usage. It was confusing for me and for the two guys I know that have come from other SW (MaxIm and FocusMax).

What an SGP step really is is number of steps per “step”. I cannot see but how that is going to be confusing to a new user. In fact, even the hover info uses “step” in two different ways. I just think it makes sense to use a word in only one way or it invites confusion.

Recognize this is not for me or for other current users. It will have no effect on me if it stays the same or if it is changed so in that sense I do not really care if anything changes. Current users mostly understand it just fine, but I know at least many new users have been/are going to be confused.

Will come from the other side here, never seen this a problem and made perfect sense though I had not previously used other software with AF. I also watched the video from Jared on profile setup (could do with an update that) and read the documentation which makes it pretty clear what is being asked for. The same terminology is also used for fine and coarse focus values, all that said using ‘Auto Focus steps:’ may have been a better initial choice.

OK, I understand that no one wants to change the wording but I do still stand by the sentiment that technical words should never be used to mean two different things in the same endeavor or software. That is what is being done which is why I suggested the change but will defer to the authors if they feel no change is warranted.

I agree with you CCD man. I am brand new to SGP and found the term “step size” confusing. My Optec TSF “step size” is 2.2 microns. It just is.

I had to look up that emoticon. :smiley:

I guess I don’t spend enough times on forums - wait, is that a bad thing?