Doug S replied to the topic 'Question about focuser module' in the forum. yesterday

The learning curve is part of the fun... It will be over quite soon enough. If confused, just ask (lots of folks are willing to provide help when you need it).

About backlash, simply put, this is just some mechanical slop in the gear mesh of your focuser motor. It's normal. The effect of backlash is that when your focus motor reverses direction, some amount of steps are required before that slop is taken up and the motor actually causes shaft motion. You can eyeball this by carefully watching your coupler's set screw or anything else (as close to the motor shaft as possible) that moves as you push focus-in or focus-out controls.

The test is pretty simple. To set up for the test, move one direction with a reasonably small jog until you know you're causing motion in that direction. Once you know you have motion in that direction, you're ready to begin the test. Using something like 20 steps (progressively refining as you start to learn what the real value is), jog focus in the REVERSE direction. Keep jogging IN THAT DIRECTION, noting total steps as you go. When you first detect motion, the total number of counts it took is your backlash value. Repeat the same test now in reverse again (the other way). Do those tests repeatedly (both directions) until you convince yourself you have the smallest number of steps required to cause focuser motor shaft motion in either direction. That's the number you want to set in the Ekos/Indi backlash value. FWIW, my EAF motor has 95 steps of backlash. An educated guess might be that you're looking for something on the order of 25 < backlash < 100? Hope this helps. Good luck...

Read More...

Doug S replied to the topic 'Question about focuser module' in the forum. 2 days ago

I think you've got it. Nice looking focuser BTW. About having gone through the learning curve to knowing your CFZ size, it's going to help you down the road.

FWIW, I highly recommend you begin logging your autofocus results (you'll need to turn on verbose focus logging for that). This will begin to create a record of temperature versus focus position (plus some altitude residual information) for your gear. You only have 50 steps in good seeing to stay in the CFZ. Getting a feel for where you normally reach focus and how much it changes (in steps) is a good step towards knowing how often you need to autofocus. Autofocus has some definite quirks, and these are being at least partially addressed by Adaptive Focus Control (temperature and altitude focus compensation). That feature when released will automatically analyze your historical data and add some sophistication and efficiency to focus management. Wasting open-shutter time on AF runs isn't where most of us want to be spending time. ;-)

Read More...

Doug S replied to the topic 'Question about focuser module' in the forum. 2 days ago

These aren't dumb questions at all. Most people are confused the first time they do this. I mentioned reading those instructions carefully because many focusers are slightly different in how they mount. I don't have your focuser. What I see from the picture is that there's a brass colored knob (likely the fine focus), and a black knob (likely the coarse / slow) focus. In my case, my motor vendor had me remove both knobs and attach the motor coupler to the slow focus knob. If you connect to the fine focus, it will take 10x the number of counts to move a revolution. I'm sure that once you git fiddling with it, you'll get it figured out pretty quick.

On the CFZ, note that the "new" way of calculating this is somewhat important. The reference is a good read for why. You don't want to get complacent and assume your CFZ is actually 2x as big as it really is....that leads to wasted exposures.....

Read More...

Doug S replied to the topic 'Question about focuser module' in the forum. 2 days ago

I think from reading your telescope specs, and using 2 arcsecs seeing and 7% focus tolerance, you actually have 62.4um CFZ size (full width). Now, using your 1600 motor steps/rev divided by 2000 um/rev focuser travel, you have 0.8 steps/um or 1.25 um per step. So, you have 50 steps through your CFZ (+/- 25). This is fine. Read those mount instructions carefully. I suspect you'll be using the slow knob, not the 1/10 fine focus. You're sampled sufficiently. You will enjoy the motorized autofocus that Ekos provides. If you have access to a temperature sensor, you may even benefit down the road from automatic focus adjustments between exposures via AFC, but that's a topic addressed by a different thread. ;-) Good luck, Cheers, Doug

Read More...

Doug S replied to the topic 'Question about focuser module' in the forum. 3 days ago

From the specs you posted, you've got it right.....16K steps/revolution. Nice motor resolution! Ok, now you want to measure your telescope focuser drawtube motion (unless you already know it). If you don't know this, just rack the focuser some measurable distance while paying attention to the number of revolutions. Divide the travel distance by the number of revolutions, and convert to microns. Finally 16K cnts/rev divided by N microns/rev focus travel = Y motor cnts per micron travel. Now compare to your CFZ size, and you'll know how well your motorized focuser will sample your CFZ. I suspect you're going to have plenty (maybe too many) counts through your CFZ. Being oversampled isn't really a problem other than it works the motor a bit more. Better oversampled than undersampled!

Read More...

Doug S replied to the topic 'Question about focuser module' in the forum. 3 days ago

A couple of thoughts here. First, can you post your electronic focuser model? 16K steps/revolution is quite a bit! Could this be a typo? Second, it's been my experience that motor vendors typically recommend *not* using the fine focus shaft for attaching the motor. In your case, with 16K counts/rev, you may find this will be problematic (overkill on resolution). What you REALLY want is to match your motor counts per revolution and distance of focuser drawtube motion (commonly referred to as thread pitch) such that the number of motor counts per micron (motor + focuser) is well matched to your telescope's Critical Focus Zone (which is a function of your telescope's aperture and f-ratio).

You've got motor counts per revolution (but it should be verified). Your next unknown to resolve should be to know how far (microns) your telescope's focuser drawtube moves per knob revolution. Once you know this, you can detemine motor counts/micron. That's an important number because you can then evaluate it against your telescope's CFZ . You want enough "resolution" to have at least several counts through the CFZ. Too many is overkill, and too few will have you jumping over the CFZ.

If you're confused about CFZ size and you haven't already looked at this page, it should help:
www.goldastro.com/goldfocus/ncfz.php
Don't let the equation scare you.... If you use seeing of ~2 arcsecs, and a focus tolerance of say 7%, you can calculate a good value for CFZ. Finding your focuser drawtube distance per knob revolution will finally get to your counts/micron. Good luck...
Cheers, Doug

Read More...

FYI, automation of coefficient calcs has been added. No more need for spreadsheets. To achieve this, an AFC analyzer function needed to change how autofocus<date>.txt files are created/stored. It also needed to change the CSV file format to include a filter offset. This implies that old autofocus<date>.txt files, while still very valuable, need to be pre-processed before AFC can analyze them. Old files will need to be concatenated into a single file with filter offset values added. If anyone out there is good with awk/sed scripts (and might be willing to help write a simple concat/conversion script), let me know. It probably took me longer to type this than a good script developer would take to write a script to convert the old files! FWIW, AFC could just start over collecting data for analysis, but it would be a shame to ignore anyone's precious historical data. The old & new autofocus CSV file formats are below:

Old format (one file per date; "autofocus<date>.txt"):
date, time, position, temperature, filter, HFR, altitude
2021-02-19, 7:24:37, 54295, 15.1, Luminance, 1.382, 52.0
2021-02-19, 8:32:02, 53949, 14.4, Red, 1.791, 74.2
etc., etc., ....

New format (all dates in one "autofocus.txt" file, plus added filter offset for each row):
date, time, position, temperature, filter, offset, HFR, altitude
2021-02-19, 7:24:37, 54295, 15.1, Luminance, 0, 1.382, 52.0
2021-02-19, 8:32:02, 53949, 14.4, Red, 100, 1.791, 74.2
etc., etc., ....

Be aware that unless a script/tool is provided to convert old files, if you want to analyze your historical data, you'll have to convert these (or just let AFC start over collecting data to be analyzed for coefficients calculation).

Also FYI: A modification to the focus GUI (new tab) is in the works. It replaces the "gen-1" AFC configuration file. Consistent with the config file, separate controls for enabling/disabling autofocus start position ( the AF "seed"), updating focus between Light frames, <optional> altitude residuals compensation, and performing historical analysis (calculating coefficients) are anticipated. A focuser move control will suppress sending move commands until a threshold value is crossed. Finally, a couple of buttons will allow updating analysis (coefficients update) and saving settings.

Finally, a git branch was created for the first code revision (updated last night for the latest kstars/ekos release). While usable now by those with development environments (via config file control), this branch hopefully will be updated with a GUI in the coming days/weeks. A hearty thanks to the volunteer alpha testers who provided early support as AFC progressed! Hopefully in the near future, all who have reasonably stable motorized focusers and an ambient temperature sensor will enjoy more sophisticated focus control(s). I hope to have good weather for several nights remote testing on-sky this coming week and will report findings afterward. Until then, Cheers, Doug

Read More...

Doug S replied to the topic 'Two camera of teh same manufacturer' in the forum. 1 week ago

A datapoint on the other side. I have ASI imaging cam and also ASI guide cam running on Pi4 through powered USB hub using the standard INDI asi driver(s). I've never experienced any issues like those described. Not sure what to attribute this to, but I guess I'll thanks some lucky stars. Could it be that using a powered USB hub and reducing Pi's USB to just the hub data cable might help to eliminate these types of issues? It's something to think about.

Read More...

FYI, I released AFC code today to a few "alpha" testers with their own development environments. There's still some room for additional people who might be willing to receive and check out this code. If you're interested in temperature and altitude focus compensation (autofocus start position seeds and/or "between exposures" focus adjustments), please send me a PM and I'll get you the code and bring you up to speed on how to build/run it.

For everyone else who might be interested in using this feature in the future, this is a second heads-up that you should enable verbose focus logging now to start storing successful autofocus summary (CSV) data needed to create a model for AFC. The needed data currently is logged to a file in CSV format here:
~.local/share/kstars/focuslogs/autofocus<date>.txt.

You don't need to save kstars/ekos logs if you don't want them for other purposes, but save those autofocus<date>.txt files! A good set of autofocus logs containing a spread of temperatures and (optionally) target altitudes will make for progressively better models. Getting a leg up on collected data before it's needed is a word to the wise. Cheers, Doug

Read More...

Hi Ken, FYI, I sent you a PM (in case you haven't noticed it). Please take a look and reply via the PM reply interface. Cheers, Doug

Read More...

I can't say whether the Optec's probe will work or not (I suspect it will, but the only way to know for sure is to turn on the focus verbose logging and look at the result as given in the OP). You'll need that information as it's the basis for AFC. I'd be very interested in having an f/5.5 test point! Please send me a PM and I'll bring you up to speed on what's required. First....the focus log to be sure your focus probe is being recognized.... Cheers, Doug

Read More...