BrendanC

Just thought I'd report back, after my second attempt at doing this seriously, that it worked! Followed Astro Baby's guide again - this time with a much clearer idea of what I was doing (yes, it really does help to leave these things a while) - and everything seemed to go ok. Then, as an afterthought, I decided just to chuck the laser in and see what I could see. Absolutely dead centre! Jubilations ensued. Just a tiny little tweak needed to the primary to get the laser dead centre in the collimator target, checked again, still dead centre in the primary. So it is possible. I think the difference was that I could just do it, in the right order, without tweaking this and changing that, puffing, panting, swearing (a lot), starting again, etc etc etc I'll be doing a star test tonight, as well as trying out APT's collimation tool.

I like that answer! So, it's as I first thought: it's not the size of the mirror, it's the parabolic effect of that mirror that is important. I think. This page is interesting - gives some of the maths behind resolving power and size: https://www.astronomynotes.com/telescop/s6.htm. Makes it very obvious that the amount of light is non-linearly related to the size of mirror, and how that relates to the distance of an object. Happy for this thread to stop now. Thanks for all the suggestions!

I'm not even contemplating upgrading! It genuinely is something I've recently been thinking about. I mean, obviously a larger mirror means more photons, like a bigger bucket. But going back to my original analogy, the moon in a small mirror will be the same size as the moon in a big mirror, but the big mirror would have more peripheral detail than the smaller mirror. So, more photons, yes, but not more photons of the moon. Just the same number of photons of the moon, plus the extra photons of the additional stuff the bigger mirror reflects. Also, I don't think I've been 'told' the answer! I'm quite surprised such a thread ensued. Aaaaanyway, it was just a thought. I'll go through the answers and see which one makes the most sense. I mean, I'm sure bigger mirrors are better, but I'm not absolutely certain it's as simple as 'because it collects more light'. Right, so, next question: how do we REALLY know the earth's not banana-shaped...?

Told you it wasn't that simple! Sorry, I seem to have created a bit of a kerfuffle. I'm sure the answer's simple. I just don't know what it is.

But it's not the same as a tea cup vs saucepan! That's the analogy I keep coming up against. Put them both out in the rain, they both fill up to the same point. The saucepan however will get more 'diameter' of rain, which equates to a greater field of vision - which is the same as saying the larger mirror would reflect a bigger patch of light. The patch is bigger, which is more light, but it's the same amount of light per square cm as a smaller mirror, right? I think the parabolic shape is key here. I'll follow that other link provided and get back to you when I have an answer! Sorry, it's just like those basic questions that you suddenly realise you don't know the answer to, and feel you should, like why did that apple fall downwards...

Hi all, So, having used my scope for nearly two years now, there's something I still don't 'get'. I have a Skywatcher 130PDS so it has a mirror of 130mm. Apparently, a 200PDS, with a bigger mirror, should be able to capture 'more light', so that I can make out dimmer objects and more detail. But how is this? Say I have a small hand mirror, and I look at a reflection of, say, the moon in it. Then I get a big wall mirror and do the same. The moon doesn't look any bigger in the big mirror! So does 'more light' really mean a bigger field of view? As in, you can see more of the sky around your object of interest? Or is this more to do with the mirror in the scope being parabolic, so that more light is focused into the eyepiece? Or a bit of both? Told you it was basic! Thanks, Brendan

Yep, it's probably made worse by the current conditions but I've been looking for a while longer than that! I thought there would be more, that's all, as people ascend the upgrade path. I'm just reluctant to get one new (there are places with them in stock), hence the second-hand stipulation. Btw, I'm not a prince really. I'm not very young either, and definitely not handsome.

Once upon a time there was a handsome young prince (ie me) who decided he must seek the fabled HEQ5 Pro Goto mount. It was a mythical creature of such beauty that songs were sung of it throughout the land. However, search high and low as he did, for many moons, he could not find one second-hand for a reasonable price. Not one single one. Not a sausage. Not on the realm of eBay, after searching (ok, one, but it came with a scope attached and went for more than he wanted to pay ie £500 because despite appearances he wasn't a very rich prince). Nor on the dark plains of Astro Buy and Sell. Nor could this earnest young(ish) man find one on the sunny uplands of the SGL forum. The prince was even more frustrated by videos such as this, in which someone else just seemed able to procure such mounts at will: https://www.youtube.com/watch?v=JRoFUj0cNt8 "What am I to do?" he cried. "For I have searched and searched, and spotted a herd of unicorns, several dragons and even a flying hogfish, yet I cannot find the fabled HEQ5 Pro mount."

Interesting. Thanks for this. I did experiment with the zoom and image preview settings. I also recently upgraded APT. I'll see how I get on next time. It's a puzzler! Thanks for the suggestion, really appreciate it.

Hi, I have a problem. Every time until tonight, I do this: centre the Liveview from my Canon EOS1000D in my software (Astrophotography Tool, APT), also centre the object in the zoom square in APT, then zoom in to 5x, then focus with my Bahtinov mask (usually aided by the APT Bahtinov tool). Works every time,. However, tonight, this happened: get star centred, zoom 5x in Liveview - and the star disappears! After much headscratching, I decided to use something a bit bigger that might give me a clue - the moon. Got it centred nicely in Liveview, zoomed 5x in APT - and it disappeared! Slewed around a bit, found it, got it centred in zoom, and zoomed back out to see what was going on. The moon was now to the left and up. So the problem is: centre in the Liveview without zoom, is quite radically different from centre with zoom. I've been through all the camera settings, all the software settings, and cannot figure out why this is happening. When I look at the zoomed Liveview, I can see that it almost looks like the zoomed view is portrait because there are black stripes either side of the image, whereas the Liveview without zoom is landscape. I want it to be landscape, which is why I've turned off auto rotate. Can anyone shed some light on this? I've reset the camera's settings, but now the clouds have rolled in and I don't have an opportunity to do more tests. But, if anyone can suggest anything between now and when the clouds roll out again, I'd appreciate it. It's really weird. I always thought zoom was a software zoom, but the same seems to happen in EOS Camera Movie Record, so I think it's something to do with the camera. Thanks.

I have been experimenting with an hour either way and it seems ok so far (for imaging). But that's with at least some astro darkness in between. I think I'm resigned to not being able to do anything from mid-May to mid-July.

But, also more difficult to access with an AZ mount!

I think this a great photo, beats the pants off mine. One way to preserve the cores of galaxies is to have the original photo - or something less stretched - on a layer below, and then use a mask to expose those cores. That way you get the less blown-out core in the middle from the less stretched version, together with the fully stretched edges. It's something you can readily do in Photoshop, not sure about the packages you're using.

That's a pain. I mean, we all like a good drool, but I also like to be out there! I'm at 51°N so I think I get a bit more time than you, but that's not for long. I think I'll spend the time doing more observing, getting to know the sky better. With an eyepiece in one hand and a nice cool beer in the other!

Nice one, thanks! I think I'm going to go for it.

I'm getting frustrated with capturing M101 the Pinwheel Galaxy. I got some subs a few weeks ago and want to get some more, but my lowly AZ mount isn't at all happy tracking it at the alt it reaches after astro twilight (around 22:30 where I am). So I'd like to start a bit earlier and get more subs, say, 21:30, while it's lower in the sky and my mount can handle it. Is this feasible? If I reduce the exposure time or dial down the ISO setting (I use a modded EOS1000D) would this counteract the fact that it's not quite fully dark? Or is it a total no-no? Also, I guess the wider question is around imaging generally during the summer months where, for a lot of us, there is no actual astro twilight at all. What's the way around this? Or do we just give up, twiddle our thumbs, or actually have to look through our eyepieces and - shlock horror - observe?

That's really good.

I thought long and hard about a mini PC. Problem is, I realised I would need some sort of input mechanism ie a keyboard. Then I realised it would be good to have some means of display, ie a screen. I could control it from my PC but then I thought: actually, what I need is a laptop! Image acquisition etc is not processor-intensive. You should be able to use a very low-spec laptop, save it all locally, but if you can get wifi or ethernet connectivity outside then invest in something like OneDrive so that it uploads at the same time. I keep my laptop outside, but in a box, running a powerline ethernet cable out to it, then I monitor inside from the PC or tablet using Chrome Remote Desktop, which is completely free and doesn't start dropping out which I've noticed the free TeamViewer starts doing after a while. I could probably get away without the powerline and just use wifi but if the connection ever breaks, I have to go out an re-establish it. It works very well - I can see OneDrive uploading on the laptop after each photo, and then a few seconds later it downloads locally to the PC.

Good grief! So, Cheshires, caps, lasers, concentres... and none of them agree with each other! It's a bit like UK politics, albeit before the upcoming Great Realignment. Thanks all though, lots of food for thought, and I've had an offer from a very kind person who lives not far from me to pop round with his scope and go through it all with me when all this nonsense has ended.

Thanks all - and yes, I do appreciate the eagerness to help me spend more money...! I'm going to stick with what I have for now. I actually cannot face collimating all over again so I'm going to see what sort of results I get tonight, maybe do a star test. If I have problems, I'm going to learn how to use the Cheshire properly and forget the laser. I've used the laser lots in the past but it was more out of curiosity than anything that I took a good hard look through the cap which I bought a while back, and the Cheshire was just thrown in when I got the 130PDS and frankly I didn't think more of it. Good to know what else I can spend my hard-earned on later though. I like the look of the Concentre, I 'understand' it which is half the battle for my tiny addled little brain. Post-edit having seen DaveL59's post - this is for imaging, but I'm just using a Skywatcher AZ Goto mount and EOS1000D camera so really, I'm not after any awards or anything. I've been satisfied with what I've done so far. I just felt deep down inside I should really address collimation at some point, and I'm rather wishing I hadn't now...!

Interesting stuff, thanks both. So, now that I've been recommended to buy two new pieces of kit for around the £70 mark each, should I: * Stick with the collimation cap/Cheshire (assuming I eventually understand what the target on the Cheshire is for) and ditch the laser? * Buy a Concentre to set up the secondary? * Buy a glatter so that I can use the laser as well as the Cheshire? Votes please.

Happy to ditch the laser, but what would account for them being out of agreement with each other? Also I just took another look at the Cheshire. So, the part that looks like a target on a laser, is actually really just another cross-hair to aid accuracy and also bounce some light into the Cheshire to help with this? Is that what it's for? I normally try and find this stuff out myself but there are no Cheshire guides on YouTube that I can find!

Thanks - I have come across the concept of caps and lasers not agreeing! There's actually an entire thread about it here (sorry, rival forum): http://www.astronomyforum.net/dobsonian-telescopes-forum/167415-laser-collimation-disagrees-collimation-cap-collimation-what-gives-3.html - but the guy does eventually get it to work. I was kind of hoping that would happen to me, but every time, starting from fresh, I get precisely the same result: seemingly perfectly aligned via the cap, then needs adjusting with the laser, look back into the cap and it's out in exactly the same way by the same amount. Lasers get a bad rap but I'm pretty sure mine is collimated, and absolutely tightly held in the eyepiece holder. But, perhaps you're right: maybe I should stick with the cap, forget the laser, and do a proper star test. One thing I still don't get however: whereas the collimator cap and end of the Cheshire perform the same task (to centre the eye), and the laser sends light through the optics which are bounced back into the target, I still don't quite understand how the target on the Cheshire works. I've tried shining a torch into the scope to see if anything appears on the Cheshire's target but nothing of any real note, also the other way ie down through the hole in the Cheshire's cap to see if anything appears. Nada. Any recommendations?

Hi all, I'm having collimation woes with a Skywatcher 130PDS. I've just spent most of the day having read every guide online, using a collimation cap, Cheshire and laser, and just cannot get the laser alignment to agree with the cap alignment. It's a common problem, but one I just cannot seem to fix. The laser's collimated, I've done everything by the book, several times, including Astro Baby's guide. I just cannot get them to agree. So, I'm going to pay someone else to do it instead. I don't care. So, does anyone know of anyone who can do this, in the Buckinghamshire area? Obviously if/when lockdown has ended. I've pinged my local scope dealer but they're not very responsive recently (probably very busy I'd imagine). Btw, I know you might have a helpful suggestion as to what could be going wrong, but honestly, I really have tried everything and basically I cannot do it, so recommendations for people who can do it would be more welcome...!

Ah, very interesting, thank you. I hadn't considered that. My drawtube does actually have a locking mechanism which I don't believe I've ever used, so that's definitely worth checking. Thanks!