On Tue, Jul 6, 2021 at 11:16 AM, Brian Valente wrote:

please do NOT use lithium grease.?

we use arctic lube here at the shop, and many others use superlube

I use SuperLube on my GM811G.? What are the specific issues with lithium grease?? Just want to know.? Thx
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Jim W
Phoenix, AZ. USA

Losmandy GM811G, NINA 1.11, ASI2600MC Pro, Sky-Watcher Scopes

开云体育

I recently switched from super lube to moly based CRC brake and caliper lube.? The moly based stuff, to my senses, handles higher friction loads considerably better.? I am using custom spring loaded worms that have constant pressure, and no back-off bolt like the OEM SLW has.? Due to the constant pressure of the spring, I felt the super lube wasnt robust enough to stay in place over time.?

However with a stock 2-piece worm block and static mesh, super lube is cheap, readily available, and has been proven to work well across many many mounts.? I'd also suggest steering clear of lithium grease.

Good luck,
-Tony

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I have just finished taking out the backlash from my 1992 steel wormed CG11.? I had the gearbox off and the Oldham connector.? During this process I removed a small amount of lube from the bearings (reduced to thick guck) and from the steel worm gear.? Now it is all back together I see that the worms and gears assemblies? look a bit under lubricated.? I do not wish to dismantle the whole thing and clean off the old worm grease.? I would rather add a small amount of lube to what's already there.? Questions, what?

I quite like white lithium grease but am reluctant to mix it with what has already been doing a fine job since 1992.

What product do I use on the worms please.

Thanks.
Pete

Yup, that's basically it. A few bigger popular galaxies here & there but mostly the bigger nebulae for now
Thanks for your help Edward !

I would not worry about the under-sampling per se.? At that image scale, you are probably going to target larger emission nebula. If you have enough subs, you can drizzle x2 or x3 and certainly improve the star shapes but unlikely to see much difference unless you are cropping the image down to a central target.


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Edward

So after bashing my head a few times on the bahtinov mask I finally remembered it was a Carey mask and not a bahtinov after all !

Downside is that NINA can’t analyze that for me. Upside is I feel less insane.?

I know my eyes are no computer but as far as I can see this is focus. Admittedly it’s on Vega and ideally some kind of smaller art would be ideal but unless someone sees something off I’m going to call this good

Thanks, I will post up a stretched version - the stars visually look good to me, so maybe I should just stop obsessing ?

Regarding the undersampling - I guess the only solution there is a smaller sensor or a longer FL scope (or a reducer) or maybe applying drizzle to the stack ?

I've been doing "CFA drizzle" to reduce the blur of the debayer process, but keeping scale=1 and not blowing up the image. Maybe it would be something to play with

Due to the image under-sampling, I am not sure the star sizes are really 6-7 arcsec.? I was hard pressed to find stars more than 2 pixels across in the image. Perhaps it would help to stretch the image to see what the star shapes look like.?

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Edward

Thanks Edward. Yeah 3.5 pixels I believe is what NINA reports, that translates into 6-7 arc seconds (2.18 as/px scale)
Many people report getting 2-3 arc/sec which seems not achievable to me

That link is actually a 10 minute sub from my target. I dont think NINA saves the images it takes for AF (at least not that I know of)

This is a Nikon D5300 for the imaging camera

Without the duo-band filter, I can get into the high 2 "pixel" scale but it was still 5+ arc seconds which just seems huge - many people report tossing *any* sub over 4" for instance ... very odd

My skies are not great (Bortle 6 but also feel very "milky" for want of a better word

Nick,? Thanks for posting some curves.? You might temporarily bump up number of points it computes on either side of the minimum (keeping the AF step size the same) to make sure the curves continue to go up on each side.

Putting aside the actual absolute HFR values for a moment (which could be many things related to sampling, exposure etc), as well as the slight lumpiness and asymmetry (which is likely the ZWO mechanic), note that the curve looks well enough sampled that you are not likely to be jumping over a central position which has substantially better focus. Eyeballing the curve, your best achieved HFR appears to be about 3.5 (in what ever units of measure are being used here).? If that is the same HFR measure you are getting on the final AF test exposure NINA returns, you are probably at your best focuser position.?

The test image you said is 10 min exposure.? I assume you meant the 10 sec you are using for AF?? Anyway, this looks pretty under-sampled and no real evidence of star bloat.? I think you are done playing with AF at this point :-)


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Edward

Nick,

A couple of things come to mind if you are not getting HFR low enough:

-Double check your sampling. If you are far less than one this could cause bloating. If you have a mono cam try binning 2X2 or 3X3 and see if the HFR changes.

-Try an object or area where no large stars are present. A bright star can alter the average HFR for the whole image and affect your V-curve.??

-With the ZWO EAF (what you have?) I have never found auto-focus to work that well (in SGPro) and the V-curves are pretty bumpy. My MoonLite CHL produces very symmetrical curves all the time. With the ZWO I usually just try to move in and out with the position controls and check the HFR number after each click and check where the lowest HFR is.

All the best,

John?

This is a link also to a 10 min test sub (NEF format) - no processing done on it

Good point. I have a couple of "normal" looking ones and the first one thats a bit odd - I think because I had changed the exposure time to 4 seconds which is not enough

HFR of my subis is around 3.2-3.6 pixels at a scale of 2.2

You might also post a picture of the AF curve you are getting.?

Definitely do your experiment with Bahtinov mask and have NINA measure all of the image HFR values.?
Goal here is to see whether there is a limit to what focus you can get or whether NINA is going back to a poor focal position due to backlash.

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Edward

OK so I measured 1000 steps = ~4mm (no calipers but I have a set on order since I need them only)

= 4/1000 mm per step = 4um/step

My scope is an AT60ED so f/6 = 6 x 6 x 2.2 = 79.2um

Width of zone = 79.2/4 = 19.8 steps

So my step size starting point should be 19.8 * 1.5 = 30, so I am not far off at 25

Thanks again! I am going to run a few tests if the weather holds tonight.

I fail to believe 6a/sec is the best I can do here

Thank you Edward, this is amazing info! Yes, the ZWO has some backlash and I am hoping the NINA "Overshoot" method will minimize this

I am going to do the calculations you present above and see what I come up with, this is super interesting and helpful !

Recommending settings as absolute numbers is meaningless. I still suggest you start by?computing:

(1) how many microns your focuser moves per stepper motor step. You can command the focuser to move a large number of steps and measure this physically how far the focal plane moves. Alternatively, knowing the gear ratios and stepper motor specs you can compute this from first principles. For my scope, it is about 3.98 um/step

(2) the width of your critical focus zone in microns. The formula is f * f * 2.2.? ?So, for my f/7 scope, this is 7.0 * 7.0 * 2.2 = 108 um. The faster the scope, the smaller the window.

(3) width of the CFZ in steps by taking the ratio of the above. For my scope, it is? 108 um / 3.98 um/step = 27.1 steps.

Two observations from this:?

First, the focuser system? has at least 10 or so motor steps in the CFZ so the AF system is not "under-sampled".

Second, a good starting point for the NINA AF step size is 1.5x this value. For my system, that is about 40 motor steps. This ensures that NINA will not jump completely over the CFZ yet not waste time "over-sampling" the parabolic portion.?I then choose an initial move of 5 AF steps.? Unlikely you have to change this if you get the AF step size right. This heuristic will get you out on the "arms" of the hyperbola.

Once you have this, you have to deal with focuser backlash. It is my understanding that ZWO AF can have substantial backlash. In Cuiv's video, he found something like 100 or 150 steps of backlash. On my DIY focuser, I have 8 steps of backlash which is less then halve the CFZ. You may need to enable and tune some form of backlash compensation. Conflicting recommendations out there about whether to measure the backlash physically (motion of draw tube) or optically (changes to HFR). The new NINA mode for overshoot-based compensation looks very promising .... I don't use either because I programmed backlash compensation in the focuser controller itself, not in NINA, and do not have much backlash to start with.

Finally, I have had good success with the nominal choice of Trend and Hyperbola, but that is my system. The choices are all work-arounds when your focuser measurements do not trace out a decent hyperbola, either due to mechanical issues like backlash or due to lousy seeing.?

The rest of the settings look fine. Don't bother with enabling more exposures per AF step. I found a good presentation on why this is not as effective as sampling the curve in more places.



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Edward

I am using 1.10 HF3 - I have had enough to worry about so far without being on nightlies :)
I also use overshoot with 300 as the backlash, which seems to work - I dont get flat curves, just ... not low enough in the middle