Guest zidder Posted February 5, 2015 Share Posted February 5, 2015 Given the scope I have is there any way, other than just looking, of working out if the optics are in good condition I.e. not deformed, coating not damaged ? Link to comment Share on other sites More sharing options...
Brantuk Posted February 5, 2015 Share Posted February 5, 2015 If you've had it from new in the past year or two it will be fine - unless it's suffered extreme abuse. Mirrors rarely need cleaning unless they get very dusty - but it has to be very heavy to affect the views. You can check the optics and collimation with a star test. Imperfections in the coatings can reveal themselves in blobs/marks, discolouring, or peeling, which become obvious when you look down the tube with a flashlight - usually prompting removal of the mirror for a closer inspection. To ensure the primary isn't deformed you'd have to take it out and ensure the mirror clips aren't too tight. This is usually evident when it's impossible to collimate and stars appear spiked or deformed. But if you can collimate easily and you get nice round, concentric, airy disks in a star test then it's a good sign the optics are fine. Orion 1 Link to comment Share on other sites More sharing options...
Guest Tweedledum Posted February 5, 2015 Share Posted February 5, 2015 Good advice above. Follow these steps if you think the mirror needs cleaning 1. Think about cleaning mirror. 2. Make cup of tea. 3. If thirsty goto step 2. Link to comment Share on other sites More sharing options...
Doc Posted February 5, 2015 Share Posted February 5, 2015 If it's like this one then clean it. https://www.eastmidlandsstargazers.org.uk/gallery/image/92-100-7193/ catman161 1 Link to comment Share on other sites More sharing options...
Guest Tweedledum Posted February 5, 2015 Share Posted February 5, 2015 Yup , but that ain't a think about, that's a straight disaster Link to comment Share on other sites More sharing options...
Daz Type-R Posted February 5, 2015 Share Posted February 5, 2015 It looked OK when I saw it, granted we did not do a star test due to the high wind and cloud but it was collimated to within an inch of its life, so unless you have dropped it since we popped round, next time it is clear, focus on a bright star, then slowly de-focus either way, if you get nice, circular concentric rings like what Kim describes above, your sorted. Like I say, when I saw your mirror, it was in top condition other than a few marks round the clips where the previous owner has cleaned the mirror without taking it out of the cell, I think your scope and mirrors are fine. Link to comment Share on other sites More sharing options...
Orion Posted February 6, 2015 Share Posted February 6, 2015 If you ever removed the mirror for cleaning, at that stage, you could get an interferogram done on it. I don't know how it's done, but it involves shining light, sodium lamp is sometimes used, and looking at the interferance fringe pattern. The separation of the fringes can be used to calculate the surface accuracy of the mirror. A good mirror surface would have an accuracy of at least 1/8th to 1/10th wave accuracy. Link to comment Share on other sites More sharing options...
Orion Posted February 6, 2015 Share Posted February 6, 2015 If it's like this one then clean it. But I definitely wouldn't use sand paper Link to comment Share on other sites More sharing options...
Guest Tweedledum Posted February 6, 2015 Share Posted February 6, 2015 Wire brush & dettol??? Link to comment Share on other sites More sharing options...
BAZ Posted February 8, 2015 Share Posted February 8, 2015 Unless you can plant stuff on it, then don't worry about it. It's surprising how much can be on the mirror and still remain totally functional. The real problem for mirrors is when they are put away without being dried off, so don't be tempted to stick it in a warm environment such as the conservatory, and store it upright. This lets any condensation pool on the mirror, and if you are really unlucky, small insects drown in this and stick to the mirror. I know you put yours away so that it remains at ambient temp, but put it horizontally, so any water can drip off. Here's what mine looked like before and after a clean. Again, don't do this unless you are utterly confident in what you are doing, there are some good guides online. Before. After. Link to comment Share on other sites More sharing options...
Guest zidder Posted February 8, 2015 Share Posted February 8, 2015 Just done a star test, this is what it looked like. Link to comment Share on other sites More sharing options...
Doc Posted February 8, 2015 Share Posted February 8, 2015 What you seem to be showing here is collimation Gary which if the donut is dead centre then your collimation is good. When you did the star test did you see concentric or non concentric rings when you defocused the star, depending on how the airy disk looked then you can adjust your collimation to get exact focus, Link to comment Share on other sites More sharing options...
Guest zidder Posted February 8, 2015 Share Posted February 8, 2015 What you seem to be showing here is collimation Gary which if the donut is dead centre then your collimation is good. When you did the star test did you see concentric or non concentric rings when you defocused the star, depending on how the airy disk looked then you can adjust your collimation to get exact focus, No Mick no concentric circles at all, as I took it out of focus I got the obvious blurring then it went into this patten Link to comment Share on other sites More sharing options...
Brantuk Posted February 9, 2015 Share Posted February 9, 2015 The concentric circles appear very close to perfect focus so if you wind the focuser dead slow as you approach focus you should see several faint concentric circles. Once it's focused then keep going the other side of focus - again dead slow - and the same pattern of circles will appear the other side of focus. The circles either side of focus should appear very "airy" - sort of faint and grainy - and should all be concentric and exactly the same either side of focus. The picture above is wound out (or in) quite a way from the focus point - but it's a good start position to work from. Link to comment Share on other sites More sharing options...
Orion Posted February 9, 2015 Share Posted February 9, 2015 Adding to what Martyn says, imagine dirt the size of your thumb area blocking part of the mirror. If you put your hand over part of the scope entry at the top, thus blocking some light, you can still see a decent enough image. That shows if the reflective area of the mirror was reduced, it only becomes significant when sufficient area is blocked (or covered with dirt). It may affect subtle detail in planets but if the views still look good, then probably not worth cleaning. If you reduce the aperture of the mirror by half with cardboard, that's effectively equivalent to adding dirt to reduce the reflective surface by half - yet you still see an image. Just thought this rough analogy might put things in context. Link to comment Share on other sites More sharing options...
Guest zidder Posted February 9, 2015 Share Posted February 9, 2015 I have just done another star test using capella, had 2x barlow with 15mm eyepiece, def. no concentric circles even just off focus, just goes fuzzy. Link to comment Share on other sites More sharing options...
Daz Type-R Posted February 9, 2015 Share Posted February 9, 2015 Have a look at Jupiter, can you make out the 2 bands, next, try looking at the Ofion nebula (M42) how many stars can you make out in the trapezium? Link to comment Share on other sites More sharing options...
philjay Posted February 9, 2015 Share Posted February 9, 2015 Is it like this? https://www.flickr.com/photos/14172600@N03/4214881996/ This does show concentric circles of the airy its just that they are not striking, they are there however. Cos if you had a refractor, youd see them no probs and there wouldn't be a big blob in the middle Link to comment Share on other sites More sharing options...
Guest zidder Posted February 9, 2015 Share Posted February 9, 2015 Is it like this? https://www.flickr.com/photos/14172600@N03/4214881996/ This does show concentric circles of the airy its just that they are not striking, they are there however. Cos if you had a refractor, youd see them no probs and there wouldn't be a big blob in the middle Sort of but a lot fuzzier Link to comment Share on other sites More sharing options...
Guest zidder Posted February 9, 2015 Share Posted February 9, 2015 Have a look at Jupiter, can you make out the 2 bands, next, try looking at the Ofion nebula (M42) how many stars can you make out in the trapezium? got Jupiter can just see two bands, Orion 4 stars Link to comment Share on other sites More sharing options...
Daz Type-R Posted February 9, 2015 Share Posted February 9, 2015 Then without seeing it I would say its fine. It looked in great condition when I came round, you can tell by the marks on the mirror that the previous owner has not had it out of the mirror cell, so he would not have tightened it too much to cause the mirror to get pinched. Link to comment Share on other sites More sharing options...
Guest zidder Posted February 9, 2015 Share Posted February 9, 2015 (edited) This is my secondary mirror, is it in need of clean and if so is lens cleaner OK to use ? Sorry to be a nancy but I am always wary when I buy second hand stuff Edited February 9, 2015 by zidder Link to comment Share on other sites More sharing options...
Brantuk Posted February 9, 2015 Share Posted February 9, 2015 (edited) Don't use Baader wonder fluid - and I dare say dont use lens cleaner on mirrors. The standard is luke warm water with a spot of pure soap (eg fairy liquid) then wipe with surgical coton wool after a good soaking. Then rinse off with distilled water followed by isopropyl alcohol. Same for primary mirrors. Edited February 9, 2015 by Brantuk Orion 1 Link to comment Share on other sites More sharing options...
catman161 Posted February 9, 2015 Share Posted February 9, 2015 Have a look at Dion's video if you're desperate to clean your mirror. I followed it to the ether when I had my 200P and it went very well. Here's the link: http://youtu.be/0tRHYSzaRLk Link to comment Share on other sites More sharing options...
Guest Tweedledum Posted February 9, 2015 Share Posted February 9, 2015 err Kim, would not use isopropyl alcohol, propan 1-Ol is the main buffered constituent of Baader wonder fluid (35%), which is an isomer of iso propyl alcohol (propan 2Ol). Which is not recommended for mirror coatings. Link to comment Share on other sites More sharing options...
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