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andrea tasselli: Hello Andrea, I used a program called Bahtnov mask “something” (cant remember the full name) and did what your explaining. When I checked it I was surprised that the readings were as consistent as they were. I did this a while ago so I don’t remember all the numbers but from what I remember I didn’t think they were off enough to be concerned about but I’ll keep that process in mind moving forward if I need to go back to that. I’ve never used APT but heard about it. I’ll look into it more, thanks! BTW I looked at that tilt adapter you gave me the link for and it looks like its a really nice unit but I don’t think I’d have enough room in my imaging train to use it. I wish my tilt adapter was larger in diameter so that I could adjust the screws without taking anything off the imaging train! Dale |
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Matthew Proulx: Hello Matthew, You bring up very good points here, both of which I have done my best to address. Your correct about the laser moving around a bit from the center spot on the primary. There was actually several things that I did which I posted pix above in my 1st couple of postings about the OTA configuration. 1st I put in 2 7x8 reinforcement plates at the focuser, 1 outside and one inside. In this pix you can see the outside reinforcement plate that I made and attached to the OTA. 2nd, In reference to the mirror shifting in the cell it used to move a little but it was mainly because of the 2 piece mirror cell which I disassembled and rebuilt the collimation screws to larger but finer threaded bolts along with heavy duty compression springs that I used to use in my DBA Certified line of scopes. 3rd to help with the “slop” of the mirror cell to the mirror itself, I used shims between them to help eliminate as much slop as possible without causing pinching or anything on the primary mirror itself. As for the “slop” between the draw tube of the focuser and the coma corrector, your correct about the screws! My Moonlite only has 1 screw. I’d prefer it to have 3 120º apart from each other but unfortunately the design prevents me from even modifying the draw tube. What I have done here is use a special type of tape that is used in refractors where they use it to hold the lens’s in place. Can’t remember the name of the tape but its sold in different thickness and I’m using .002” think pieces around the Coma Corrector’s diameter to snug things up. In all honesty I’ve tryed it with and without the tape and I really don’t see any difference, but prefer the snugger fit so I used the tape. The tolerance used in Moonlite focusers and the diameter of the Quattro CC is very little but it is there and I’ve attempted to address that as well. HERE IS A BETTER PIX I FOUND OF THE MOUNTING PLATE DURING THE REBUILD.  |
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| I am retired from Steward Observatory Mirror Lab where I was a Staff Tech in the Large Optics Polishing Lab. Only say this to indicate that I have some dangerous knowledge about telescopes; mirrors in particular. I am currently building a 10" f/4 astrograph so I understand fully the design and mechanical aspects of your scope. I constantly remind myself of the old "Oliver overbuild" principle. I happen to suffer from that principle. Sometimes, in an effort to make things better I inject problems by overbuilding. An earlier post referred to this regarding your primary cell springs. All of the mechanics of the tube are intended for only one thing, placing and keeping the primary and secondary where they belong. Using too much "support" hardware can actually increase problems. Only use the hardware necessary to accomplish your mission and avoid "overbuidling". The other thing that has been observed is that the "star" problem is uniform across the image. This suggests that whatever is wrong affects the optical train uniformly and consistently. The only thing I can think of that I am applying to my own scope is the use of a fan to aid the primary in meeting and staying at ambient temp. If you use a fan it should never be "hard" mounted to the tube or cell. The best of fans still generate micro-vibration just from the friction of the blade moving through the air. If you use a fan, suspend it behind the primary using something elastic that will absorb these vibrations. You can test it by turning off the fan during imaging. The other thing I can think of is air turbulence in the tube. A suspended fan would help. Make sure the inside of the tube is either flocked or painted with a high texture black paint. The distance between your spider and the tube end should be no less than the diameter of the primary (12 inches). Your tube sounds short since my 10" is 48" long. You can use a dew shield to extend the tube length. In any case, it sounds like a design problem since it is so uniform. Just some thoughts based on my research in building my own astrograph. |
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Hi Dale, I had a possibly similar problem with both my big Newts - elliptical stars even in 1s subs (so nothing to do with guiding) similar across all the frame and - this was the clue - always nearly orientated with the long axis near the RA direction. I investigated further and found that I did in fact see round stars when I took the frame length down to 100 ms - but not at exposures > 600ms. I then looked at videos of 100ms frames using high gain and used M3 as a relatively bright detailed object as subject The video revealed high frequency oscillation of the mount more or less aligned with RA - in other words the RA movement was not smooth on the subsecond scale. PHD2 won't reveal this problem because by sampling at only 2s or so intervals it acts as a low pass filter. May not be relevant to your case but I posted the story in more complete detail on the Sharpcap Gallery forum https://forums.sharpcap.co.uk/viewtopic.php?f=16&t=5467&p=29932&sid=0890ff74946a021c69dcc408e34df227#p29932 Tim PS I note that Nikko made the same point above |
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Patrick Stevenson: Hello Patrick, Thank you for your response! I'm also glad to hear your similar to me in that we both have experience with optics, me thru DBA Astronomy Products back in the day. Like you I do tend to "overbuild" anything I make (Retired Tool and Die Maker) however I'm not to sure that the springs are over kill. That said I do have a 2nd set of springs to help take up any (sag if you will) between the collimation screws and locking screws (which I do not use). If I decide to pull the mirror cell assembly I'll definatly remove the 2nd set of springs. As for the cooling fan, I only use it when I'm not imaging to only keep things fairly close to ambiant temp before an imaging session. I've done tests in the past with and without the fan and you are correct that it does introduce vibrations to your image thus the reason for not using the fan during the imaging sessions. I've attached an image of the back of the mirror cell with the fan which is bolted directly to the back of the cell. This come from the factory years ago and as I said I never use it during an imaging session so I never pulled it off and use what I'd preferably use Velcro. There was another mention of the cooling fan in the ZWO camera that I use that does hold some weight that I'm going to give a try shutting it off during a testing image run and see if that makes any difference. I've not heard of the ZWO cooling fans going bad or causeing issues but I'll definatly look into this thats for sure! The length of my OTA is 55" and I do use a light shroud on the front for stopping stray light especially when the moon is out! That adds about another 10-12" of length to the front of the OTA. Inside of OTA is flocked down on the primary end about 18" as well. Dale  |
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Tim Hawkes: Thanks for your response Tim, I'll look into this more. Not to familiar with doing this video stuff other than moon and solar imaging. Dale |
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HI Dale, Just out of curiosity; how is the primary cell attached to the tube? I have a double spider but I can see only one in your case. As for telescopes my maxim is: what isn't there can't go wrong. IOW, make it as simple as you can but not any simpler. |
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andrea tasselli: Hello Andrea, The cell is attached with 6-8 screws around the circumference of the OTA. Yes I just have 1 spider that holds my secondary mirror. I agree, don’t complicate things more than what they are. I’ve always tried to make things solid and as easy as possible. I’ve installed this Megaguide and got things up and running with the help of @Robert Shepherd in the hopes you and he are right that its just a collimation issue. I’ve never really had collimation issues before, but maybe this instrument working with this fl things need to be a notch or two better then I’ve worked with in the past. My plan if that doesn’t work then will be pulling the mirror cell out and removing the second set of springs to eliminate stress/pressure there (as @Patrick Stevenson eluded to) and I’ll also pull the fan off the cell frame and use a suspended method to see if its this “air” layer over the primary some are talking about, so I do have a few things to do before I decide what’s next. I think at that point it’s what you had suggested, break the imaging train down and start with whats necessary and then add in the next piece trying to eliminate one thing at a time. Dale |
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Dale Penkala: So, to collimate the primary how does it work if the cell is attached to the tube? Somehow I feel like I'm missing something here. This said, I feel the 6 screws equispaced arrangement is a poor performer (I have the same on the 6") as they tend to undo the collimation over time with temperatures going up and down between day and night. I sure need to get my acts together and start collimate with the sensor in place. On other news I stripped down my 10" to single components and found out that the secondary was waaaay off. How that happened I don't know but it did. So here the lesson is to expect the unexpected... |
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andrea tasselli:Dale Penkala: Hello Andrea, Ok so its a 2 piece mirror cell/tube ring. This is one of the reasons that I’ve use 2 sets of springs to add stability to the whole assembly as well as more control of the collimation bolts. @Patrick Stevenson did bring up a good point about “over building” of things that can cause issues down the line so thats why I think if the collimation adjustments don’t work I’ll go ahead and remove them and also the cooling fan seeing as though I’ll have to remove the mirror in order to do this. I took a couple pix of a spare mirror cell for you that will help you understand how the assembly is attached to OTA. Dale   |
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| I see John Hayes has chimed in with some suggestions and he mentioned amongst other things the coma corrector. The machining of these optical tubes is all done on a cnc lathe but is done from either direction and gripped in machined soft jaws, so its quite possible that the threads and seating faces for the optics could be slightly out of alignment and concentricity from one side to the other. Never trust any machined surfaces unless you know for sure, especially when you're chasing needles in the haystack. We have Newtonians ranging from 10" to 30" and have had done all sorts of trouble shooting over the years (as well as managing an aerospace machine shop for 25yrs) so can sympathise with your frustrations. At least the CC is easy to check by taking it out of the system and looking to see if the stars in the centre of field are round. If they are then you've found the problem and if not at least you have eliminated that option. Good luck Dale. |
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Stargazers SA - Andrew: Hello Andrew, As a 30+ year tool and die maker myself I understand about the machining aspect of it. Your correct that its easy to check and I will definitely check that part out by doing exactly what you said when I disassemble the imaging train like what @andrea tasselli had mentioned and then gradually add in the items I’m using. The thing is I’ve never had issues with this CC with any of my other newts, now that doesn’t mean there wasn’t issues but I certainly see them now. Maybe because I’m working with a 1500mm verse 1200mm fl. I don’t know all I know is using the same setup with this scope something is different. BTW I had this issue before adding the OAG so I think I can rule that piece out. That was added because a friend of mine said that he’d bet that was the culprit. I think in the end it isn’t but, now that I have it integrated into my imaging train I’ll stay with just to help rule out differential flexure. Thank you so much for your input! It is noted and will be checked! Dale |
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Hello all, I had the chance to go out last night for about 3hrs and I did some testing based on many of the things that were posted here on this thread. 1st, If I didn't thank everyone for their input, I want to do that! All the responses make a person go back and look at everything to make sure that you didn't miss something or in some cases just flat out overlook a standard "check items" So the 1st thing I did was check out if the cooling fan on the primary mirror to see if it had anything to do with my "eggs for stars" issue. I'm pleased to say that when I checked this, I didn't see any different in the star shapes. What I saw was more "bloated" like stars when the fan was running, same shape but the size I saw just got slightly bigger and kinda soft/fuzzy looking. The obvious thing here was leave the cooling fan off and image without the cooling fan on the primary mirror running. 2nd, I checked the same situation in regard to the camera's cooling fan. I'm glad that I did this because a friend of mine has an OSC QHY camera (don't know what model it was) that had this exact same issue. He said it was pretty bad and in the end, he replaced the fan in the camera and that fixed his problem. In my case I could not tell the difference with or without the fan running, and btw this was also with the primary fan NOT running! 3rd, I did what @andrea tasselli had suggested, and that was point the scope at the NCP and take a few different exposure lengths from 5-10 seconds long. They should be round if everything is correct. Well unfortunately everything I shot from 5-10 seconds were still egg shaped, so you can imagine, ok now what's next? 4th, Ok, so I have been PM @Robert Shepherd about this MetaGuide program for collimating the scope better. Before I go here, I want to tell you I'm picky here and when I zoom in to look at a diffraction pattern I'm at least 100% and if the seeing allows it, more! I center things to the best I can visually on the 40" monitor in the observatory. I will admit I was very skeptical about it being my collimation, but as I posted in the very beginning, I swallowed my pride and asked ALL of you for suggestions/help to get my issue figured out. After communicating back and forth with Robert, and getting the correct drivers for my camera to work with the program, I finally got things going, and I'm really glad I did. Now I checked the collimation prior to using this program, and I'll just say it was extremely close the way I normally check it, and under normal circumstances, I'd probably have left it alone because it was just flat out that close! It took me about 45 mins to get things figured out (using gamma, exposure time and gain) how to actually get what I'm supposed to have to look at & for but when I started to make the adjustments I could see what was described, and I continued to do the best I could to get this dang RED DOT to the center of the dot that represented the "star" or I'd call it more like the airy disk. This red dot bounces around quite a bit because of seeing, but I got it, so it was on the star but would bounce off in different directions but when it was consistently in the center or close to center of the star I called it good and gave it a VERY SKEPTICAL test. Well, I went back to the Iris Nebula and did a 120x sub to see if I got any improvement. Well ok, stars seem round I zoomed in 100% and HOLY _ _ _ _ I have round stars. UMM, Ok, let's try 180s subs, Freaking round stars! So alright, let's really test it 300s subs. I've attached a soft stretched (nothing else was done) sub for you ALL to look at. I think I still have a very slight something on in the lower left part of the sub but if you look at what I had to what I have now, this is a significant improvement, at least to me, it is! 5th, ok to verify this actually did work, I went back to the NCP and did what @andrea tasselli suggested and bingo round stars, so this definitely made a difference! I do plan to go back and tweak collimation again because I know seeing was not great last night, although I did have FWHM numbers that ranged from 2.3 - 2.8. That's good for me here in my location, btw I'm not sure if I want to tweak my sensor tilt anymore. I don't want to kick a sleeping don! Time will tell, but collimation I'll definitely continue to work on. Again, I want to thank everyone for chiming in here! Even if you felt it was trivial or not, it wasn't! It's always good that even the obvious things get reiterated, just so you don't forget about these things! Dale  |
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| Congrats Dale. The image is too small on my screen to judge the fine points there but it seems you nailed it. As some suspected, it was collimation. |
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andrea tasselli: Thank you, Andrea! |
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Good stuff...glad to hear that you figured it out! John |
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John Hayes: Thanks John! Dale |
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Hey Dale, Good to hear you're making progress. As I said, metaguide can take a bit to get used to. In order to not being chasing that red square around, you could try increasing integration time. If I recall correctly, I use exposures around 3 ms (yes, milliseconds), stacking time 4 sec. This should leave you with a bright star which is not overexposed and at the same time the square will not chase the seeing that much. If it still is jumpy, further increase the integration time. It is also important not to overexpose...the red square will otherwise seem to be stuck in one side of the false colour view of the star. Did you btw find a good guide for collimation with metaguide online? It would be good to know if there is one out there to point to. As I mentioned, I am a great fan of collimation with metaguide and would always recommend it as the number one methode for fine-tuning collimation. Robert |
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| What isn't quite clear is how you can see the Airy disk when your image scale is more than 2 times the Airy disk angular diameter. |
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Dale Penkala: MOLY ? Congratulations but reading such threads just make me even more afraid of Newtonians. Is it just the size and focal ratio or are all Newts such a hassle? Clear skies Wolfgang |
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Robert Shepherd: Hello Robert, Yes I’m glad I made some progress with this issue! Its been a long time coming! I’m still surprised that as close as I had my collimation just this little bit made that much difference, but then again I’m at a quite long fl I guess. Yup in the end Robert thats what I did with the settings and it did help, but it still jumped around (not as much) and it was never stationary. So like I had mentioned either the seeing was causing this erratic movement or maybe I still didn’t have things set just right for my setup. But I was able to get that dot to end up in the middle of the pattern that represented the star and it would only jump off it a couple times in say a 5-7 second period. Funny you should mention that Robert, I looked online for a tutorial and couldn’t find anything either. Based on this experience I wish there was some kind of guide to have helped me get things figured out. Plus if there was another process for the extra fine tuning with an in focus star. In my case I wasn’t able to use the star in focus. Dale |
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andrea tasselli: Hello Andrea, I’m just calling it the airy disk for lack of a better word to use. When you get the settings finally tweaked in there is a bright spot that appears and represents “something” which I can only assume the airy disk. It may not be but that bright “dot/spot” is what you use to make this red dot that floats around to become centered on that pattern. Maybe I should use pattern instead of airy disk. At any rate that airy disk/pattern is what is used to make the red dot centered to it. Dale |
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Dale Penkala: Hello Wolfgang, LOL I’ll let you fill in the blanks,  I’ve had many newts over the years and in the case with my 8” & 10” I never had this kind of trouble with getting round stars. I can only assume the fl & ratio of this instrument must have something to do with it, however I’m surprised with my 12” being an f5. F4’s I’ve heard are difficult to work with but many get them tweaked in and do phenomenal work with them. I guess in the end once you get them tweaked you have one heck of an instrument to gather photons. In my case here this is one of my DBA Certified Newts that has a lot of sentimental value from the late Steve Swayze, but thats another story. I can’t wait to see what I can do with this instrument once I get everything tweaked and some clear skies to work with it! Its been horrible here in Michigan for clear skies! Dale |
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Dale Penkala: It can get much worse than that, rest assured. |
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Dale Penkala: Hi Dale, Got it. If I may ask, was all this collimation procedure performed with the full kit in place, CC, off-axis guider and so on? |
