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jif001

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About jif001

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    Warrington, England
  1. Yes that’s it - your starting point needs to be correct if your end point is to be correct. the red cross won’t move when you rotate RA, but if it’s in the wrong position to start with then it will always be in the wrong position. in the example the dodgy reticle red cross is aligned to a position to the left of the pole, not the right - have another look Think of the reticle as a wheel you can roll along the ground. In the first image the 6 is in contact with the ground. If I roll the wheel to the left so that the Polaris yellow cross is in contact with the ground and the broken line is vertical - i.e. it’s moved to the position in the second image - then the central red cross will have moved to the left.
  2. See if this helps ... Here I have two reticle screen shots. One has zero exactly at the top, which is what I want, and the other has an error whereby zero is not exactly at the top, and I’ve grossly exaggerated this error to illustrate the point I’m about to make (I’m not good at judging when it’s exactly vertical but I’m better than this!). Ignore the blue lines for a minute Remember, what we want to achieve is polar alignment, which means the red cross in the reticle needs to coincide with something we cannot see - the celestial pole. Luckily there’s a nearby star that we can see, Polaris, and we use it as a guide. By getting Polaris in the right position in the reticle, at the correct angle, we know that the red cross hairs are aligned with the celestial pole. An app or other means will tell us the angle we need. Look at the broken line joining the position of Polaris (yellow cross) to the central red cross in each case. In the second image my exaggeration of the tilt has made this line deliberately vertical so it’s easier to illustrate the error it creates. The true position of the celestial pole is where the red cross is in the first image, but you can see that the rotation of the reticle in the second image has moved the red cross to the left of where it should be - imagine superimposing the second image on top of the first so that the two yellow crosses exactly coincide. What you would see is the red cross of the superimposed second image approximately where my blue lines cross each other in the first image. What this shows is that if my reticle is tilted when I polar align then my scope is NOT aligned with the pole. If I used the tilted reticle below to polar align then I would be aligning with the blue cross in the first image. The real error you might get by having your reticle not exactly vertical is much smaller than this, because it won’t be this far out, but it’s an error nevertheless and will affect your tracking. Remember also that you need to establish the correct (vertical) reticle position (as in the first image) once only, and then mark your mount so you don’t have to do it again - just align the marks on the mount and you know you have the equivalent of image 1 and no tilt as in Image 2.
  3. I can’t comment on the ‘bubble’ reticle with any authority because I have the clock-type (as above) but I’m sure the principles are the same ... if you look at the reticle screen shot above you’ll see a yellow cross. That’s where I need to put Polaris in my polar scope reticle in order to polar align. Get it there and I’m done. However, for my polar alignment to be accurate I need to know that when I do this the reticle zero marker is at the top - i.e. exactly at the top, dead centre, with the line between it and 6 exactly vertical and the line between 3 and 9 exactly horizontal. That’s something I cannot achieve by eye because my eye is simply not accurate enough. I may get zero to look like it’s at the top, but is it exactly at the top, I mean, EXACTLY? So I used the method I described - get Polaris (actually any star will do for this bit but Polaris is best placed) dead centre in the cross and then using ONLY the vertical adjustment of the mount move the star up to the circle. Having done that I know EXACTLY where the zero should be and I adjust the RA axis so that the zero in the reticle exactly coincides with the star position, then I lock it and mark the mount so that I can find this position again without using the polarscope. I can then be confident that my reticle is in the precise rotational position for aligning with Polaris when I need to polar align. All of this is aimed at finding the correct reticle position only. It’s a one-off procedure and the marks on the mount are now my reference points for getting the reticle in the correct position prior to polar alignment. The video you’ve seen elsewhere using the bubble reticle is just applying this principle - getting the reticle in a known rotational position so that polar aligning can be done accurately. You can polar align without doing this, but it won’t be as accurate. That doesn’t matter for observing where a bit of drift won’t spoil it, but if you are imaging then any drift at all is to be avoided. Let me know if it’s still not clear - I’m happy to try and explain it again if necessary because I would have been glad of some guidance like this myself and I get why it might be difficult to grasp! I’ve already suffered your frustration!
  4. Thanks for the response. There’s more to this than I thought. Having been enlightened by it I googled ‘chip size vs filter size’ and it led me right back here to this useful thread:
  5. Had a good old rummage around but haven’t found an answer to this so here goes... 40 years after life got in the way of astronomy, and after 35 years of employment, I’m now in the happy position of being able return to a great hobby and to kit myself out with proper stuff, my aim being ultimately mono imaging with filters. I have a scope (Altair Astro StarwaveAscent 102ED) and Mount (EQ5 Pro GOTO) and currently use it with a Nikon D7200. The next step is a mono camera and filters, but which filters to buy? This isn’t a question about Ha, Hb, Oiii, Sii, but about the merits of 1.25” vs 2” It seem logical that the larger aperture of a 2” filter would be better, but is that the case? Would an all-2” setup be significantly better than an all 1.25” setup? Does it warrant the extra cost?
  6. 1) yes you can if you unlock then clutches, as stated. ‘Alignment’ can mean two things - polar alignment and GOTO alignment. The clutches don’t affect polar alignment so you will not lose polar alignment unless you also move or otherwise adjust the mount. However you will lose GOTO alignment. Your GOTO relies upon starting from a known position called ‘home’. In this position it knows where the scope is pointing at the start. If you then unlock the clutches and move the scope the GOTO doesn’t know anything about it. see my comment near the bottom of this thread regarding home position and how the GOTO works:
  7. Sticking my neck out a bit here... This is aimed at SmokeyJoe and Anthony1979 with whom I share a frustration at having an angled reticle and difficulty getting to grips with the machinations of polar alignment. Many kind folk here and elsewhere have tried to explain these things but I have yet to see an explanation that a newbie like me would fully understand without raising new questions about why it’s like that. Understanding the ‘why’ is at least as important as knowing the ‘what’. Anyway, I believe I have had a Eureka! moment and the penny has finally dropped inside my capacious but seemingly vacant cranium, hence my post...and I’d be grateful if those more experienced than I could (constructively) put me right if I’ve got any of this wrong. Please don’t say ‘you don’t need to do that!’ unless it is absolutely unnecessary for imaging, for that is my ultimate aim - this post is not about visual observing. I also go a bit beyond the original question because these are the issues I needed to get to grips with, and did the hard way. It may help the aforementioned folk too. Polarscope Reticle Orientation Firstly, there is a difference between ‘polarscope reticle orientation’ and ‘polarscope RA alignment’ and this isn’t the only thread in which the topic has unhelpfully drifted from a question about the former into an answer about the latter. Polarscope RA alignment is about ensuring that the axis of the polarscope is aligned with the mount RA axis, and has been explained well enough here. But that wasn’t the question, which was about polarscope reticle orientation - i.e. which way up it is. My advice is that you should not dismantle the polarscope to reorientate the reticle. You may end up ruining it. There’s an easier, quicker and safer way to solve your reticle orientation problem. Read on... Solving the reticle orientation issue (clock-type reticle) 1) Firstly, level the mount and set it up pointing north as if making it ready for polar alignment. Try to be quick with steps 2 to 4 because Polaris is on the move (slowly though, so no need to panic). 2) Next use the Alt and Az bolts to centre Polaris in the reticle - i.e. put Polaris right in the centre of the cross-hairs, not on any circle. Be as accurate as you can. 3) Now using ONLY the Alt bolts, move Polaris vertically upward in the reticle from its central position until it reaches any of the circles. 4) Because you started with Polaris dead centre and moved it only vertically, Polaris is now exactly in the zero (12 o’clock) position on the circle. Now rotate the RA axis to put the reticle zero* mark in exactly the same position as Polaris. Again, be as accurate as you can. 5) Lock the RA axis in this position and using a marker pen put alignment marks on the mount housing so that you can find this position again without the need to use the polarscope. That’s it - now you know accurately where zero (12 o’clock) is and the marks on the mount allow you to find it instantly. * if you can‘t get zero in this position use any number you like - it doesn’t matter as long as you treat this number as if it is zero. Polar alignment Oh how I wish someone had expressed it in these terms instead of me having to work it out for myself ... it definitely isn’t obvious to the uninitiated when small but vital details are omitted (as they often are - remember, it’s not enough to know what to do, it’s important to know WHY). 1) Firstly, level the mount and set it up ready for polar alignment 2) Rotate the RA axis to the zero position you established above and lock it there (use the marks you made on the mount) 3) Determine the hour angle of Polaris using the handset (if you have one) or other method such as the Polar Align app. 4) Using the Alt and Az bolts adjust the mount until Polaris is in the required position on the reticle circle, regardless of what number you have in the 12 o’clock position. If the app says Polaris needs to be a third of the way around from the 12 o’clock position then put it a third of the way around from whatever number you have in the 12 o’clock position. 5) You are now polar-aligned. That’s the ‘what’. Here’s the ‘why’... What you have just physically done is align your reticle with Polaris, but that isn’t your true aim. What you have also achieved using this method is alignment of the central cross-hairs with the celestial pole using Polaris as a guide. The cross-hairs mark the central axis of your polarscope, which is in turn aligned with the RA axis of your mount, and so what you have actually achieved is alignment of your RA axis with the earth’s axis. Polaris is not exactly at the pole, but it’s near to it and the method above is merely a means of finding the celestial pole. The clue is in the name: ‘polar alignment’, it is not ‘Polaris alignment’ even though the latter is what you do in order to achieve the former. Having achieved alignment with the pole you no longer need to care about Polaris and where it sits on the circle (as long as it remains somewhere on the circle). Your RA axis is aligned with the earth’s axis, and that’s what you want. Home Position: Not part of the original question but hey ho... If you have a Goto mount your next task is to set the RA and Dec axes in the ‘home’ position - weight bar down and north, dec axis up and pointing at the pole. The home position is important as the Goto system needs to know where it is starting from in order to know where it’s going. Think of a pirate’s treasure map: ‘take ten steps forward and three steps right, and there be treasure!’. Well that’s great, but where do I start from? Is it the corner of my living room? How about the top deck of the bus? The instructions are useless without a datum - a starting point. That’s the home position on your mount. The controller determines its position by assuming a default start position and then counting pulses sent to each motor. That way it can drive the mount to any object you choose. Think of those pulses as steps forward / back / left / right on the way to the treasure (the object you want to view). They are only meaningful if the whole process starts from a known position. The one- two- and three-star alignment procedures are then used for fine-tuning the Goto. Home position has no use if you don’t have a Goto system because you need to find the celestial object yourself, and you don’t do it by counting drive pulses.
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