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I am new to both the zwo EAF and narrowband filters. I have had clear skies for 5 nights under a full moon and I realize it is not great conditions in my Bortle 8 Portland Oregon area. However the focus of the EAF is terrible. I get a tiny curve and a red dot that says its focused but the results are not good. I could manually focus with a Bat mask and be spot on but its impractical with the Filter changes. Is it a bad EAF or is this common? I am imaging with an Askar 600mm f5.6, 2600mm camera and Zwo 2"filter wheel with Antila 4.5mm filters. |
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Hi, I have had good luck with the ZWO EAF. Assuming all of your set screws are tight and its not slipping, one thing with narrowband filters is that you have to increase the autofocus exposure time. With my slower PHQ, I have it set to 10+ seconds per exposure with narrowband filters. While it increases the autofocus time, it seems to work well. Having used both N.I.N.A and an ASI Air, the ASI Air is definitely more of an enigma. I have also had it "succeed" while not really being that well focused. Some of the same principals described in the N.I.N.A. manual are also applicable to the AA and maybe worth a look. Things like exposure time, step size and backlash. |
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| Hi Dan I am also in Portland. I travel to do all of my imaging. I would certainly try to image here in town with narrow band filters if I had more sky available in my yard. However for your situation I would try adding some time to the auto focus. Maybe you have a default of 2 sec? 4sec? You might try 10 sec? I had similar problem and lengthening the exposure time helped. |
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Thanks Aaron, I am experimenting as I type when changing filters tonight. I image mostly right in the middle of the city and if you look at my images, I am progressing. I go to Prineville when I can. |
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| For me the solution to exact same problem was to first measure the focuser backlash and then set up the measured value in autofocuser configuration. Did you do it? Its an important step. |
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Dan, I use the ZWO EAF with the WO81 and C9 and have no problems with either. If you are using ASIAIR you may need to increase the exposure time, also try decreasing or increasing the focus step. Aidas |
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There are a few things that can go wrong with autofocusing: 1) as others have said the exposure time for narrowband autofocusing needs to be quite long. 2) Finding a sensible step value is essential. Too small and you don't properly sample the curve so the fitting results are nonsensical. Too big and you run the risk of going so far off focus that the fitting points don't lie on the expected curve. I've found that no matter what metric is used (FWHM, HFD, inv-power etc) if you move too far from focus the curve stops being hyperbolic (or whatever ideal shape it should be) and the fit result will be poor. 3) Make sure the stepper has enough range either side of focus to properly sample the curve. I think you can set the '0' point arbitrarily on the ZWO EAF and it should probably correspond to when your focuser is fully racked in. This is a problem with some camera lenses with an infinity stop - but it shouldn't affect your setup. Probably the best way is just to dedicate half an hour at the beginning of a session to get all the offsets and stepper sizes sorted out. Manually focus with a bat mask and then play with the stepper values until the EAF can consisently land you on focus, then you should be all good to go. For a first attempt I'd do this with luminance so you can use short exposures. Once you've got it working with L, then you can up the exposure time and see if it is also consistent with the NB filters. Once you have everything correctly calibrated you shouldn't need to touch the values again. |
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I use the EAF with my f/5.8 refractor and use 1s for my UV/IR filter and 3s for my IDAS NBZ - given that your filters are narrower, you may need to bump up even further. The focusing software does not do well in low contrast situations (as you'd expect), so if the full moon is close by, it's going to struggle...but that's not where I'm pointing my camera anyway. At least in NINA, you can see the images it's trying to use for focus so if you can't see many stars, bump the exposure time and try again. The other thing I do is have the mount point straight up to the zenith at the start of the session for focusing. It's usually quite starry there and from my location, the moon is always far away. When it re-focuses mid-session, it just stays on the object I'm shooting and does its thing. I hope you can get it sorted because the EAF is an awesome upgrade! |
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| Yeah, I completely agree. EAF is great. I already own two of them. Let us know when you sort it out. I would be interested to know what caused the problem. |
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| When you have a good focus with your filter write down the EAF focus number. The next time you use the same filter in the same setup move the focus to that number before you start auto focus, this should help you get a faster and better average focus. |
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As others mentioned, you probably need to do the initial calibration if you haven't already. Here's a video from Cuiv, The Lazy Geek (great channel) about how to do it in NINA. https://youtu.be/-sHzbz3OcSo?si=XL0Y9nZayRHO08Mc If you're using ASIAir the same principles apply, you just need to find the right settings in that software |
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If you are using NINA you can use filter offsets. There is a plug in that will run through AF with all of your filters and establish what the difference is from filter to filter. Once done, all your AF are done with your luminance filter and the offset is then applied for your chosen filter. To get a good AF your step size should be such that your first point produces an HFR about 3x the size of what it is when you are in focus. So, if you are using 4 steps and a step size of 40 the focuser will move 160 steps of the EFW and measure HFR. If that point is less than 3x the starting HFR, then increase your step size. As mentioned above, it is also important to put in a backlash compensation. If you have uncompensated backlash, your AF curve will have a flat top because the EFW is moving but the focuser is not. |
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To add to what others have stated, see if your image capture software allows to increase the gain during focusing. I have four EAF's, and for narrowband I use 5 to 10 seconds of exposure, at a higher gain than during regular capture. But make sure the software switches the gain back. And to repeat: Correct starting point, correct step size between attempts (approximately 2X to 3X FWHM or HFD for entire range of focus attempts), and whatever backlash corrections are available (I use an "inward move" of around 200 steps in APT. NINA has an equivalent called "backlash compensation overshoot" under option>equipment>focuser>advanced settings" I'm not sure about ASIair) Good luck! Steve |
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| Posting your log file here will shed some more light on this issue. |
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Hi Dan, I had also Problems with the EAF, please try in N.I.N.A to chang: at first the the Autofocus step size (is it to big or to small then it didn't work). Autofocus step size 50-100. Next try Backlash start with 40/40 make a test. I use a 8"Newton exposure time = 5 - 6 sec. ist ok. Then Autofocus initial offset steps = 4 Take care: If you start the autofocus prozess -> the scope has to be nearly in focus! good luck, br and cs Hampo |
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Thanks for all the great replies! I will do all the steps recommended next time I set up. This site is a real resource for its members! |
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| Maybe I'll disappoint you, but the best focus is without batan mask and without autofocus. I know these two methods are the easiest, but they can never give you the perfect focus that you can get manually by trusting your eyes. When you approach the stars with 66% magnification in Sharpcap and slowly rotate the focus back and forth, then you have a chance to achieve perfect focus with a little patience. Personally, I'm tired of wasting hours of footage and finding out in the morning that the autofocus didn't make the stars perfect. This is why so many astro pictures on the internet are slightly blurry and unclear. If you want to make your life easier in this hobby use Duo Narrowband filters so you will only focus once or twice a night. Good Luck! |
