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BrendanC

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Posts posted by BrendanC

  1. 23 minutes ago, tooth_dr said:

    Brendan do you mind explaining this?  My newt is pretty hard to collimate, and I used my phone in a holder like you have done.  However, it's only just possible to see the screen at a stretch, and working via TV would be ideal.  (I use AnyDesk, but perhaps the principle will be the same?

    Ah, sorry, missed that. 

    Yes, mine is hard to collimate too. In fact, I detest collimating it.

    So, to get your mobile device's screen onto your PC or laptop's screen, first install TeamViewer, both on your laptop/PC, and the equivalent app on your mobile device (just search in your device's app market, and you also might need to install a supplementary app for your specific device).

    Fire up TeamViewer on your PC, and set up your account.

    Fire it up on your mobile device, log in, and then you should see it appear as one of your devices on the PC/laptop.

    Then, when you've got the mobile in the bracket positioned over the collimation cap, and the image of the focuser tube and secondary mirror is viewable (using either your mobile camera's photo preview or video), go back to the PC/laptop, and click the mobile device to start controlling it. Your mobile device will ping and ask if you're sure you want the PC/laptop to take control, so you confirm that, and then your mobile device's screen should appear on your PC/laptop's screen.

    Now fire up Mire de Collimation on your PC/laptop, and place it over the mobile device's screen, being shown on your PC/laptop screen. So you now have Mire de Collimation superimposed over the TeamViewer app on your laptop, which is streaming the image from your camera, on your mobile device(!).

    Then, it's a case of pinching the mobile device screen to make it smaller or bigger, moving the Mire de Collimation app around, making it bigger/smaller, using more/fewer rings on it, until you have something that you can work with, to get the secondary mirror round, and centered in the focuser tube.

    This is all achievable without this complexity I know, but I think it's more accurate, and when you've got it up and running, it's far easier, especially with replacement collimation thumb screws (which I just mentioned in an addendum to that post detailing this technique).

    I hope this helps? Shout if not. I'd used TeamViewer a lot before, including to control my mobile device outdoors, so it was a fairly natural progression for me to then think about how it could help with this. Once you've got it working, it's fairly easy to get going with it again.

    • Like 1
  2. Thank you - another possibility struck off the list! Now it's down to tilt, collimation, and focus.

    I think the collimation was off. Looking back through old subs, I've always had a small amount of tilt, which hasn't caused these issues. And perhaps I just need to be more careful with my focus (I think I trust the APT Bahtinov tool a bit too much, maybe I should actually use my eyes more).

    I'm fairly confident the collimation is better now, so I just need a good night to see how things go. Fingers crossed. Everything crossed.

  3. Hi,

    I just used this technique again, and realised that @markse68 has a very valid point. Previously, I'd concentrated on getting the secondary perfectly round, as per the instructions on the classic Astrobaby guide.

    However, after some issues, I decided to take another look, and realised that the secondary wasn't aligned in relation to the focuser tube.

    Thing is, this technique helps with that too: if you pinch/zoom out from your mobile device, you can get both the secondary mirror and the dark edge of the focuser in the image. Then, you can use the Mire de Collimation app to get two circles, one mapping onto the focuser's edge, and one onto the secondary's edge. That way, you can make sure that a) the phone is properly flat against the collimation cap because the circle maps onto the focuser's edge, b) the secondary mirror is round, and c) the secondary mirror is centrally aligned in the focuser tube.

    And apart from anything, I still come back to the fact that this method is so much easier than peering into a collimation cap while fiddling with central screws and collimation screws. I would also very, very, very strongly recommend investing in some of these, which have also really helped with all this (I got mine from 365Astronomy but their page has gone - also unavailable at Amazon but at least you can see what I mean): Set of M4 Thumbscrews for Secondary Mirror Collimation https://www.amazon.co.uk/Set-Thumbscrews-Secondary-Mirror-Collimation/dp/B00UJUOXA4

  4. So, in case anyone benefits from this thread, latest is that I've re-collimated it. I think the secondary wasn't quite aligned up properly relative to the focuser tube (I used my patent-pending technique for this as outlined here). 

    Also, I'm kind of wondering whether my Bahtinov mask might be out. I have a feeling it's warped slightly, which could be damaging my focus. So, I might try and straighten that out or break the bank by buying another one.

    Saturday night is looking promising round my neck of the woods so fingers crossed things look a bit better then...

  5. So I've just been through old subs and looked at them through the marvellously useful ASTAP CCD inspector.

    Interestingly, they all show tilt to varying degrees. It seems I've always had a small amount of tilt. This is both looking at subs with my previous camera, and with my recent replacement when the old one died (both EOS1000Ds).

    However, even though they have tilt, they don't have the problems with the stars in the corners as per my latest subs, and the spikes are nice - sharp and even.

    So this seems to point to collimation and focus being the issue this time, I think? I hope...?

    It would also be handy to know whether a small drop of the camera could possibly increase the tilt - but as I say, it seems all my subs have a small amount.

  6. I just had a terrible thought,

    About a week ago, I accidentally dropped the camera - only a couple of feet, against a relatively soft vinyl floor, not concrete. I only just remembered.

    I've been checking previous subs from before that, and they're fine. 

    So, could I have misaligned the sensor?

    In which case, would the only really viable fix be to get a tilt corrector, something like this: https://www.firstlightoptics.com/adapters/astro-essentials-m48-t-tilt-adjuster.html

    The next question would then be, given that I have, what, about 5mm backfocus left, would this even work with my setup?

    I'm starting to get worried now...

  7. Hi all,

    I really, really hate collimating my 130PDS. I also don't like the way the focuser tube impinges on the image. And I'd rather not have to use a coma corrector. So, I'm just wondering, what would an equivalent refractor be? There is another thread similar to this on the forum but it sort of diverged from the original post.

    By similar, I mean a roughly similar field of view, for a roughly similar amount of money. I do understand that reflectors tend to be faster and have wider fields of view, but what could about £200-£300 buy me (ideally second-hand)?

    And to answer the age-old question about what I want to shoot: DSOs eg M42, Horsehead, globular clusters etc.

    Thanks, Brendan

  8. ... is a master taken from 25 flats in DSS, for which I used this: https://www.amazon.co.uk/dp/B07N128B74/ref=pe_3187911_185740111_TE_item

    Yep - cheap, probably not ideal, but I thought it was worth a go, just put it on the lowest setting, cover the scope, take the shots so the histogram is central (works out at around 1/80s on my DSLR).

    Out of curiosity, I loaded it into StarTools and stretched it. I've attached the result.

    If I zoom in, I can see lots of dots. Now, are those dots the individual LEDs from the panel, or the camera's matrix? Because if they're from the panel, I'm obviously going to have to think of a different approach, probably using paper or t-shirt to diffuse the light, or something completely different such as sky shots or laptop screen. If it's the camera's matrix then I guess that's ok. As is often the problem here, I'm doing this totally on my own with nothing to compare it with!

    master flat.tif

  9. Ha! I knew it. You know, I did the Pleiades too last night and got it hopelessly off with that as well. I have a nasty feeling I copied the RA from one and the Dec from the other and, well, very accurately pinpointed two completely irrelevant areas of sky. Oh well - another learning: double-check your plans!

    I also checked out Astrometry and Stellarium and that caused me lots of pondering and stroking of chin. Yeah... basically I got it wrong. Not the first time, won't be the last.

    Anyway, thanks for the replies, really appreciate the helpful suggestions. I've attached one sub, and the stacked FTS file from Deep Sky Stacker. I totally get that my subs are probably not of the best quality, but if you could take a look that would be fantastic.

    I don't think it's field rotation because going through the subs, apart from dithering, they're rock solid. I really hope it's not a bent spider. Would coma cause this at all, given it's at the very edge? It shouldn't because I have a coma corrector.

    Anyway, over to you! :)

    Autosave.fts L_9310_ISO800_60s__12C.CR2

  10. Hi all,

    Just processed this - it's supposed to be Mel 25, the Hyades cluster, although I think I probably either need to revisit my coordinates or put a mosaic together to get more of the cluster. I find it slightly underwhelming. I am underwhelmed. It underwhelmes me.

    Anyway, my concern is really regarding the big bright star top left. I don't understand why the diffraction spikes from my Skywatcher 130PDS are wider than they are tall? Is this something wrong with my optical train? Or is this ok? I don't actually see how it's possible unless something isn't right.

    1029101871_mel25hyades.thumb.jpg.f9ddaadf75e1020b5fcffc59308634e1.jpg

    Kit list is as per my signature.

    Thanks, Brendan

  11. All very interesting stuff! This is one of the reasons I'm doing what I'm doing: because it's helping me learn more about sunrise, set, moonrise, set, moon phase and so on. 

    It seems that, taking into account all the above variations, I have a choice: I can either copy/paste a set of phases (like I've done with moonrise and set after looking into how to calculate that), or use my calculation and accept that it's slightly out. I think I'll go for the former - only needs compiling once for the upcoming year and takes a few mins. I think it's worth it to get it right.

    Thanks again. I've learned something new - and I quite like that I noticed something odddddd, and the answer made so much sense. It's almost like rediscovering the basics of the solar system from the data!

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