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I am looking to expand my travel rig and add this lens for a wider field of capture. In particular I would pair it with my QHY 268MC, C-sized camera. I have noticed a couple of mounting setups, each of which include mounts and connections that pair with the EAF focuser. Not sure if I favor the belt drive, vs. gear drive, but that is not the issue I have at this time. My first question is, how much value is autofocus for this setup? Reason I ask is that I have been using my WO z61, 360mm f.l. with my very much undersampling ZWO 071MC pro and have never had to refocus during any full night session. In fact, I have traveled with it and sometimes it has not needed refocus after setting up from scratch and that means removing the camera, adaptors and filter slider! It will be a little better match with the QHY 286 (ZWO 2600 for most of you), but still undersampled. I can't imagine that there are any larger sensor dedicated astro cameras that are not undersampling from a 360 mm f.l. telescope, let alone a 135. Should I save the money? Second question is, practically how well can autofocus work in such an undersampled situation? Yes, with my WO z61, I can get round stars (for the small stars), but only if I dither and drizzle. Otherwise, my stars are blocky and just a couple pixels in extent. Dither and drizzle cannot be part of autofocus, so just how does autofocus work and is it better than using a Bhatinov mask on a brighter star? I am happy to entertain both theoretical and practical answers. But the practical answers for those with experience is probably what I am needing in my purchasing decisions. Thanks, Alan |
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I use the astrodymium mount remotely. I prefer the belt drive system because I feel like it is less finicky than gears. I use my system with a 6200mc and the lens set to f/2.8. The focus system functions quite well. I find that refocusing is required for my system, and also I find eyeballing it with this lens to be pretty inconsistent. You could use a bahtinov mask as well, but I'd prefer to just go to sleep and let the motor do the job. Even if I wasn't remote, I would probably still use the AF just so I could sleep and not worry about focus |
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Thanks Bray! With your experience using that same sampling, etc. Do you set autofocus to reset on a regular basis (which I tend to do with my larger f.l. setups), or after a broadening of the hfr, etc? And if the latter, do you find the autofocus triggers often during the night and also, does it find a focal point (i.e. focus motor step) that is significantly different than the original set point? Sorry for the barrage of questions! |
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| I found that the focus stays put at my sampling of ~ 6"/px for the best part of an hour and needn't any change once dialled in the next night, so I assume it's pretty consistent and stable. Shooting at f/2 does yield a fwhm at 2/2.5 px in the central portion of the image with an APS-C sized sensor. Because the system (at f/2) is very senstive to even small amout of tilt the "best" focus is always a compromise between centre sharpness and edge correction unless you have the means to adjust it to a very high precision which @ f/2 isn't for the faint of heart. |
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Like Bray, I use the Astrodymium Ring system with my Samyang 135 and pair it with a ZWO 2600MC Pro and 533MC Pro, its been a solid performer for me and the addition of an EAF on this rig, while not essential, is really handy to have.  Prior to this I was manually focussing and although my copy of the lens held focus pretty well, I found the EAF a real time saver and liked that I could just leave my rig to get on with the image taking...I also like the compactness of the Astrodymium set-up, on a Losmandy plate. Good luck and its a fantastic lens and gets a good (and well founded) reputation...hope that helps! Best wishes from Scotland! |
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Alan, never mind. |
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Alan Brunelle: I just let it refocus every 45min! |
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andrea tasselli: Thanks Andrea! Useful info and the word of warning has not escaped me. I'm guessing I will need some time to dial things in. |
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Bray Falls:Alan Brunelle: I hear you! Never a bad approach! |
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Like Bray, I use the Astrodymium Ring system with my Samyang 135 and pair it with a ZWO 2600MC Pro and 533MC Pro, its been a solid performer for me and the addition of an EAF on this rig, while not essential, is really handy to have. Thanks! I do understand the convenience. And as I have taken to do most of my tweaking during setup while I am in my office, rather than at the scope this would be an advantage. However, as a travel rig, I think I will mostly be right along side the rig. I'm not just ready to pull the trigger on this just yet. And from what I am hearing, I am dissappointed that the Astrodymium Ring system is not available at this time. Illness has put the maker out of business for the time being. Wishing him the best... Thanks again! Alan |
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Alan Brunelle: Just to add to my discussion regarding the second question. No one who replied so far as to how autofocus works under such situations of undersampling. But since the replies seemed to not address this, I am guessing that autofocussing works just fine. I'll assume that means just as will with a fine Bhatinov mask. |
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I recently added auto focus to my Rokinon 135mm f/2. I had to work in Nina a bit to dial in AF to be reliable and ideal, which is no different than installing AF for any rig. It is very worth the effort, I no longer worry about focus, which when previously using a mirrorless camera and bahtinov mask was a bit of a struggle to get right. I never felt fully confident in my focus at f/2. My setup uses 3D printed parts and off the shelf components. Edit: I did not design this, the link above is to my "make" which also links to the designer and their work The only tricky part is rotation for framing, which requires taking it apart prior to a new session if changes are needed. |
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I also use the Astrodymium with my Rokinon 135 mm. Autofocus is a tremendous convenience and more precise than my ability to focus the lens. Also far more repeatable. Focusing every hour or 2 seems prudent and then you don't have to worry about it. Also, temperature is not the only thing that can shift focus. A meridian flip changes the forces on the the lens, there are a lot of elements that have the potential to slip from a flip. I have no empirical data this causes a problem, but have convinced myself it is one more thing to worry about. If you want to try my system, let me know. It will only take a few minutes to get it all set up for you. - Tom C |
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Tom Carrico: Thanks Tom! I may well take you up on that. With your comments on slippage, etc. and with @Joey Conenna 's similar comments, I would lean towards AF. And, I am having a challenge now focusing my 61 mm telescope. Unfortunately, the Astrodymium rings set is completely sold out, and his web site says his work is suspended because of illness. So I may look more closely at other similar solutions. There is one other 3D printed solution that uses an EAF geared to the lens. But I expect that the belt is a better, more forgiving solution. I could probably get that adapted using the rings that use the gear, just drop the sprocket and get the belt adaptors. I also like @Joey Conenna 's solution and may look into that. My concern with the rings, is they seem to support the lens just fine. And I would not hesitate to use that with my ASI071, which is a fairly small, light camera. My preferred camera would be my QHY 268, and that one is a beast as far as length and also weight. But it would be trivial to add some support under the camera along with the lens support rings. It would be nice to see your setup and take notes. CS, Alan |
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Alan, We can do a zoom or you can drop by for a hands on look at my setup. - Tom |
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Tom, Thanks for the offer! If you don't mind, I would opt for the hands-on. I think I will learn a lot more and probably it will raise more relevant questions. Let me know a good day and time. I can be pretty flexible. Alan |
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Looking for some tips on trouble shooting the Astrodymium belt EAF system. I've tried this on both my Askar 200 mm and my Rokinon 135 mm and in neither case can I get the system to autofocus. I can use the electronic focuser to iterate to focus 'manually' with a bahtinov mask so the electronic focuser is moving the lens focus tube but every autofocus run I've tried fails. I start with the lens at or near focus (using the bahtinov) and then run autofocus. What I've noticed is that if after the failed focus run I return the focuser to the original position the lens is way out of focus usually by several 100 steps. This has me thinking something is slipping but I have to say the belts are about as tight as I can imagine! Anyway hoping someone has trouble shot this before. Thanks in advance for any help. John |
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Hi I have the Astrodymium belt EAF system and I ended removing the belt and focuser motor since It never worked well for me. So I just installed a 3D printed manual focus system that adapts very well to the Astrodynium rings and upper finder bracket. However, from my experience, it was not worth to use an EAF motor for that systems since the focus never really changed even with significant drop in temperature. I think, one of the reasons is the lens does not have too much metal so there is less contraction and expansion as the temperature changes . Of course if you are adding a filter wheel then it may be worth to have that so you can automate your system. So I have this focusing mask that works very well https://www.amazon.com/Astromania-Bahtinov-Mask-Focusing-Telescopes/dp/B01MEGIA85/ref=asc_df_B01MEGIA85/?tag=hyprod-20&linkCode=df0&hvadid=652406890446&hvpos=&hvnetw=g&hvrand=17972959671414508270&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019123&hvtargid=pla-2257400825992&mcid=4861a1634c1534b28f1dd7487b4af784&th=1 |
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John, I can't speak to your experience with the Askar, but I just went through the learning process, setting up my Rokinon 135. For that lens, I am still working out the backfocus and tilt, but my autofocus is working. First, you give very little detail as to your autofocus routine. It might be best to work out the issue using information with just one optic. So I will make some assumptions to kick start. With your 135, I need to ask, when focused manually with your Bhatinov, how much further movement outside of focus do you have remaining? 135s are well known to have their focus stop very close to ideal infinity focus. If yours is that way and the autofocus tried to move the number of steps outside of focus you set (information you left out of your question, How many steps, and how many motor ticks per each step.) then the autofocus routine may have crashed the focus motor against the stop position. I noticed that when this happened to me (not during an AF run, but early on in setting the limits on my motor) the motor actually was strong enough to have the belt jump the cogs, and/or also cause the Astrodymium motor mount to flex to the extent that it could have broken the motor off the mount rings. I can also imagine that internal damage to the motor might occur. Unless you failed to tighten the grub screw on the motor shaft to cog, I can not imagine that the shaft could spin inside the cog. Something else would break. But if you did not tighten the grub screw into the flat part of the shaft and did so on the curved part of the shaft, these two could easily have spun and lost your position registration. Something to look for. When I set up my motor, and I have done it now several times since I have returned my 135 lense for a newer one (poor performance on the first one), I mount everything properly prior to slipping the belt onto the motor. That is the lens in their rings. The cog onto the lense focus ring. The motor and motor mount. Yes you can put the belt on to check the belt tension. But remove the belt after that leaving everything else intact. You do not need to have the belt as tight as you suggest you are doing. That may actually cause problems. Then manually rotate the lense focus to the infinity stop. Then I actually rotate the lense focus just a tad off of the stop. After this slide the belt on carefully, ensuring that you do not move the lense focus ring back into the infinity stop position. Turn on and go to your ZWO focus motor controller. Set this position as zero. That way no matter what tries to crash the motor back into the infinity stop, the motor will stop at zero and prevent the crash. You won't be able to crash it even with the manual motor control. Confirm that you have not accidentally pushed the motor to the back stop by using the manual controller or with your software. You need to also know which direction the motor rotates when pushing each button. If needed, you can check or uncheck the reverse mode, depending on your preference or AF requirements. Next, if your 135 lens (As it came delivered to you from the manufacturer) has no extra focuser play beyond true infinity. Or at least not enough to accomodate the AF travel necessary to go the number of steps you set past infinity, you will need to mod the lense to allow that. There is a Nebula Photos Youtube video describing the modification. There are also other sources of this information. Other things to concern yourself about AF issues with the 135. For example, my 135 with the mod seems to find focus at a bit over 600 motor ticks. That is 600 ticks from the 0 (the max out focus plus that tiny extra rotation I added) that I set. My routine includes an overshoot to compensate for motor backlash. Never set the overshoot outside of focus, because if may well send your motor to crash. I set my overshoot for at least several hundred motor ticks inside of focus and then the AF routine works from inside to outside of focus, never having to deal with backlash again during the routine. I use 4 intitial focuser steps (from the starting point, which is typically the last good focus point determined). I think my steps are 40 motor steps. So the initial offset in my routine is 160 motor ticks inside of focus. For some reason NINA still seems to always end up being 5 focuser steps outside of the target, but... So I plan on it going at least 200 ticks outside of focus at least, and depending on how the numbers work out, the routine might add additional points to try to get the numbers for a determination. Again having a too tight belt might also be your problem. In fact Astrodymium has a recommended method to manually focus your lense without unscrewing anything on the mount. And that is to slide the belt off! It would be a real struggle to do if the belt was so tight. |
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Alan, Thank you so much for the detailed reply - plenty to work on there. Ironically this is my second lens from Samyang as well the first was a complete lemon this one is near perfect! I know on the Askar it isn't the lens stop but I will check that on the Samyang now. The other thing is my experience is neither of these lenses need refocusing during the night or even night to night at times! So it's become more of an academic exercise at this stage, that said I'm still keen to figure it out. Thanks again John |
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John Noble: Not needing to refocus is something that I have experience with my 61mm refractor. I do not even have a motor on that one, nor do I intend to add one. But the expectation is that I would always be close by enough to make adjustments if needed during the night. The trick I am learning with my Rokinon is just getting focus in the first place. For that one, I do not have a Bahtinov mask to help and find that it is nearly impossible to make the fine adjustments to get to the best focal point. Yes the focus ring is firm to turn, which some seem to liken to quality, but I find it hard to know when the ring turns the fraction of a mm to achieve best focus. I am learning, as you, in my quest to get the best back focus, that literally 0.1mm spacer rings make a large difference in the focus position (the motor position). And that 0.1mm is making or breaking the position for best back focus as well! Just got success on that part last night! Now to deal with an ever so slight issue with tilt with my camera, which unfortunately uses a dovetail for attachment. Given the large effects on focus that just 0.1mm makes, I now understand why I struggled so much when trying to use hfr to focus. Additionally, I learned that stars in the center of the field defocus much less dramatically and much more symetrical than those in the corners. As one might expect in any optic. So what might be an acceptable very slight broadening of a nice round psf in the center becomes a deformed arc or coma in the corners. I too had asked local Rokinon users whether they really even needed the motor, and they all said yes. I did not understand why at the time, but I do now. However, I do believe that if I used one of those precise fine Bahtinov masks, I would be able to do a good job. I recall reading somewhere, not sure if on this thread, that the Rokinon 135 is of plastic construction and therefore should not be that sensitive to temperature-related defocusing effects. While the lens certainly has some plastic parts in the focus ring assembly, I believe the bulk of the lens structure is in fact metal. Best of luck and happy that you got a keeper with the Samyang! Alan |
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| Certified mad man shooting at F/2 with this lens here. Like others in the thread I use the belt drive for an EAF. However, I find the autofocus fails to consistently find a focus point that produces quality stars across the entire field. Again, I am at F/2 so there is not a lot of room for error. Thus, I manually focus using the EAF and usually babysit the rig throughout the night. I don't use a bahtinov mask because I look at the HFR values myself and judge them as I go. |
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Certified mad man shooting at F/2 with this lens here. Like others in the thread I use the belt drive for an EAF. However, I find the autofocus fails to consistently find a focus point that produces quality stars across the entire field. Again, I am at F/2 so there is not a lot of room for error. Thus, I manually focus using the EAF and usually babysit the rig throughout the night. I don't use a bahtinov mask because I look at the HFR values myself and judge them as I go. I hear you! For me, this is all at F2 and a c-sensor. I really do not want to have to stop down if possible. At least in the setup phase. I have heard that some take the bulk of their subs at F2 (or close), but are forced to stop down to get decent stars. I hope to do better than that with a less-than-full-sized sensor. Last night, working on getting backfocus optimized, I hit a sweet spot with my fine rings and wow, my stars hrf (NINA) hit an all time low. And the stars were tight (if not fully round) from corner to corner. Then, under the hope of doing some late night imaging, I did a rotation to set my camera up for a target and redid the focus and lost a few 1/10ths of sharpness. Still, good for me so far with this setup, but the corners on one side got less tight. So now it is an excersize in tilt adjustment. But for me the autofocus has been bang on, yielding a very good curve with very tight error bars on the individual points. I do 2 takes at each position and set up 4 position setup on each side of the target focus using 40 motor ticks for each position. Takes my hfr from around or just below 5 down to under 3, but close to 2 on that really good test. I do like being with the scope when possible. It is so wet here where I live. Cold and wet. I like dry at night. With your motor/manual focus, you can have the best of both worlds! From looking at many well done 135 images, I have to say that for some of the best, that corner stars may well be sharp, but they are rarely round. So I think the lens can do well. But expecting perfect psf at the corners may be expecting too much. At over 5.74" per pixel, it is hard to resolve even fine aberrations! |
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Alan I ran through all the checks etc and loosened the belt. Everything works. More importantly you were right when it hits the hard stop the motor is powerful to make the belt skip. The challenge is the hard stop is about 1500 steps from the focal point. What I’m struggling with is what’s the Autofocus doing moving that far from the start point. What I’ve read says the initial move is 150 steps then it comes back in 30 step increments then the fine focus goes out 45 steps and and comes in in 15 step increments. Perhaps that’s old data? Anyway I’ll need a clear night to solve it but I’m hoping the zero point trick will work! Semipro Just out of interest what kind of HFR do you get? Using the Bahtinov to focus moving the ring with the EAF mine settled at 1.8 pixels at f2.8 on the 2600 I think that’s about 10” - just curious if the HFR could yield even tighter focus! Thanks John |
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Hi John, I think it is a good thing that the hard stop position is 1500 motor steps from the focal point. That allows you a lot of plenty of room outside of focus for AF to work the routine. When I first set up mine, I was at about 1000 steps from focus to the hard stop. That has changed as I zero in on optimal backfocus position of my camera. With the light pollution/UV/IR cut that has moved my camera out a bit and now I am down to an optimal focus position in the range of 300 from the dead stop of 0. And that is with my stop moved to allow extra rotation outside of focus. But I know that I am close. Only a little tilt to resolve, if I choose to deal with it. Yes the motor is powerful. I saw mine actually flex the plastic mount to the Astrodymium mount rings, almost appearing to flex enough to break the motor mount, but with the angle generated, the belt just slipped the cogs. And this was when I was using the manual motor control. So stupid on my part. Had this not occurred, I am sure something would have broken, possibly the motor! It is odd that you had the missregistration at the end of your AF routine. At 1500 ticks from focus point to camera focus stop, there should be no way you ever impacted the camera stop. I am not sure what you mean by: John Noble: And you do not say what software you use to do AF. I assume that you are reading the log. The first part makes sense, of what you say about moving 150 steps, then comes back in 30 steps, if you set your focus increments at 30 steps and that you have AF taking 5 focus steps to do one side of the graph (for example 5 steps to draw the graph for the inside of focus point). The second part seems like you have your AF set up wrong. Once the AF goes to a position inside of focus and if you have your AF and motor set up correctly, you should have it overshoot to eliminate backlash (have you done this?). [Setting up this overshoot backlash correction should/can only be done in one direction. Never set backlash compensation both in and out. One or the other! For your Samyang, which has a hard focus stop, you really need to set this backlash step to the inside focus direction.] So lets say for your setup you have your rig at 1500 (which is close to ideal focus point) + 150, so the start position will be 1650 (inside of focus). 1650 will be the position where AF will take its first data point. When it first moves the motor to 1650, if you set the backlash compensation correctly, you will see the motor overshoot 1650 by several hundred (a number you choose) and then move back to 1650. From then on, it will only move in one direction during the whole AF routine (Unless the routine decides that it has to then move back to a higher position to complete a decent curve). Getting back to the beginning of the AF routine, then the motor will move downward in 30 tick increments, taking an image and hfr at each step. It will take 5 readings to get to 1500, plotting each point. It will then continue moving (going outside of focus) until it reaches 5 positions (150) outside of focus, or 1500-150 = 1350, plotting results each time. You should never have the AF routine do one part of the routine moving in one direction, then finish the other part in the other direction. All these motors have backlash and you will never get a good or consistent focal point. Because of this, your statement that "then the fine focus goes out 45 steps and comes in in 15 step increments." makes no sense to me and suggests you have it set up wrong. Also, you do not need to do a "fine" focus, or corellary to that statement, a "rough' focus, then a "fine" focus. If you know what the focal point is, then all AF actions should be fine focusing. You start the AF routine knowing that you are close to actual focus. If it is not the last focus point you used during your last session, then you can manually get into the ball park prior to doing the AF. That you check during session set up. I would suggest that you go to Patriot Astro Youtube: Setup NINA Auto-Focus Quickly and Correctly. It is specific for NINA but has some good general points. With my 135, I use 40 tick steps. That takes my AF routine from hfr of ~5 down to below 2. If you think that smaller steps will yield "finer" results, that is likely wrong. Seeing, and other issues may make the sampling at smaller increments may just make it more difficult for the routine to get a smooth curve. I use 2 second exposures. The routine does not need to see every star and at f2 you will not be short enough stars for focussing purposes. I also only do 4 increments. Somehow NINA alway finds a way to insert more, so I don't give it any reason to spend extra wasted time. However, I also do two exposure at each test point. This comes from my other rigs that are wind sensitive, so I needed that to get better error bars for each point. But still the goal is to get proper focus without consuming a large amount of time. And about accuracy, AF algorithms will use mathmatical interpolation to find the focus from the graphical data. You do not need to choose points close together to have one of the points "hit" the exact focus point. Oh, and I set my AF routine to only sample the inner 80% of the frame so that it does not have to deal with the the typically defective outer stars. John Noble: I know that this was directed at SemiPro, but for my setup, this number is really not comparable between our setups, even though I am using the same lens and camera pixel pitch. Reason being is that hfr readings are sensitive to the camera gain/offset/debayer/exposure time and even the stretch used in the imaging pane of the software. However the best I got when I had it nailed the other night was 2.17. Then I rotated the camera and it went up to 2.6. I have been doing all this work at f2. If I cannot get this to work well at f2 when using my c-sized sensor, I can be sure that I will have no hope of moving to a full-frame camera. Currently I have hope! In any case, if you can get good hfr readings manually, it seems perfectly reasonable to do the focus manually. With my old cold hands, I spend way too much time fiddling with all that and never get it to be consistent. And with AF, I can do it from within my office at home! I used to like being outside with my equipment, but doing astroimaging outside no way compares to doing visual astronomy outside. For all this stuff, you still have to be looking at the damn computer screen and that blows your night vision. I can't even see the stars hardly under such circumstances so being outside is only nice when it is actually nice out! Honestly, when I spend my time outdoors during an imaging session, the best part is when the imaging session is set up, I can turn off the damn computer, and sit in my recliner with my binoculars, or just naked eye the sky. Motors, computers, rotators, etc. have long lost their luster to me for entertainment purposes. |
