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NGC 1502

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NGC 1502 last won the day on October 25 2013

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About NGC 1502

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    Essex U.K.
  1. Hi John from another Essex member. You have some good advice already given. I’d like to add that before drilling holes it’s best if the optical parts are removed. If you’d rather not do that then you could work with the tube at a downward slope so that any debris doesn’t fall onto the primary. The secondary could be very carefully covered with something soft, and fitted so that the the optical surface is not in contact with the covering. The holes will leave a burr on the inner side, removable with a hand held larger drill or a countersink bit. Make sure any remaining debris is removed. You’ll be absolutely fine if you work carefully Ed.
  2. Enjoying following this, your planning and persistence is great. I’m often fixing up all sorts of things, don’t like today’s chuck it and buy a new one mentality. Learn’t this off my old dad because back then a lack of money meant he had no choice but to fix it. Dad used a garage in the next road to keep his old banger an early 50s Anglia. One time he removed the engine, wheelbarrowed it home and spent the winter renovating it in the spare room. Fortunately the spare room was downstairs, saved him the problem of humping the engine up the stairs at the other end of the car he fitted a new crown wheel and pinion in the back axle........ Keep up the good work Ed.
  3. Hi Garry, welcome to SGL Good advice above. I’d like to add - some instructions for setting up an equatorial mount are for imaging purposes, you need precise set up for that. If you just want to observe then quite literally near enough is good enough - I. Find and set the altitude adjustment. It’s usually just above the top of the tripod with a scale that goes from zero to 90 degrees. Set your latitude as best you can. I’m in Essex so thats about 51 degrees. You only have to do that once, unless you take your scope significantly further north or south. 2. Identify the polar axis and point it north, turn the whole mount for that. 3. Balance the optical tube by shifting it within the tube rings. 4. Adjust the counterweight for balance. 5. Align the finder. You’re pretty much sorted Ed.
  4. John, sincere apologies if my comment caused any offence, absolutely none intended, just clarification. Ed.
  5. I misunderstood the original post. If the image above shows the correct scope, it has 3 colliimation and 3 lock screws. ( a 6 or 9 point mirror cell is not relevant here, that refers to how many points the primary mirror sits on in the cell, not how many adjustment and lock screws there are ). If collimation is frequently lost, there’s several possible reasons. Not enough tension on 1 or more collimation springs, loose primary cell to tube bolts, loose mirror to cell clips ( mirrors must NOT be clamped, but if you take that too far then the mirror can flop around), something loose at the other end - check spider etc for loose bolts, no tension on spider vanes etc. Ed.
  6. Some primary mirror collimation screws also have lock screws, easy to tell, if there’s 3 pairs of screws 3 will be for adjustment 3 will be for locking. Some cells just have 3 spring loaded adjustment screws, the adjustments being held by spring tension, from what you’ve said sounds like yours. As long as there’s adequate tension on each of the 3 screws then you could raise or lower the primary a bit. Usually if the collimation screws are tightened this will draw the mirror further from the secondary. Suggestion - tighten all 3 fully (without over-tightening) you’ll reach a point when no more tightening is possible. Then collimate by releasing tension as necessary. That way all 3 springs will be under some tension. If 1 or more springs have little or no tension then collimation is easier to lose, especially if the whole scope is shifted around or transported. Ed.
  7. That’s an excellent example of a properly ventilated cell. It’s very different from older OO UK cells that were poorly ventilated, a solid closed back with just one central 10mm hole. Ed.
  8. Well of course the Tak Mewlon is a premium instrument and well designed........but when I read the Kreige & Berry book on making Dobs I think I recall the upper tube assembly opening always being larger than the primary. I’m certainly no optical expert but possibly as the 2 types of scope are very different alters the necessary design of the upper tube opening ? I’d be interested if anyone has views on this
  9. Indeed, that’s one of several things I don’t like about OO UK Newtonians, the tube diameter is not much more than the primary diameter, and the upper tube trim has an opening virtually the same diameter as the primary. Having said that, my OO UK 10” Dob is a great scope that I enjoy using, but would be better without those issues. I lessened those problems by increasing the primary cell ventilation (earlier OO mirror cells had a solid back with just a single 10mm diameter hole) and removing the lip from the upper tube trim. Ed.
  10. Indeed, my Takumar 35mm f2 lens from the early 1970s is supposed to be very mildly radioactive. But it’s too big to swallow so not a problem....
  11. I’m thinking that this applies to very large mirrors that can take hours to cool, and if the ambient temperature keeps on dropping struggles to get there. I used to have a rear mounted fan on my 10” Dob, I fitted that more to prevent the primary dewing up, I had that happen twice at my local club’s dark site. However to my horror on another occasion I turned the fan on when it got very damp and dewey - result was almost instant dewing of primary
  12. I’ve not seen that type of curved deflector before to direct air towards the mirror surface. On the other hand someone has to be first and maybe that’s you The usual way to cool the mirror surface is a fan(s) in the side of the tube blowing across the optical surface, in conjunction with a rear fan. Some favour fans that blow, others that draw air away from the mirror. You’ve not mentioned the size of the mirror. The larger the mirror the more that active cooling is a good idea. Other good factors are a mirror cell that’s not sealed but with plenty of ways for air to freely circulate. There’s lots of online telescope making advice, just do a search. Stellafane is a US based source that has loads of ideas. HTH Ed.
  13. Great report your enthusiasm is nice to read. I’m a double star fan. The whole sky is stuffed with them, they are fascinating in their variety, doubles, triples, quads....well seen even with a light polluted sky or when the moon is up. Also in Lyra is - the double-doubles double, easily resolved at low power and well worth checking out Ed.
  14. Whatever piece of kit we own - if we like it that’s all that really matters...... There’s always the danger of reading online reviews and comparisons and wondering if we’ve done the right thing - been there done that - so do you like them ? Great Ed.
  15. Hi Jim, you have some good advice above. I’d like to add that I once owned a 33mm Swan and with my Dobs it was only sharp in the centre of field of view and deteriorated rapidly towards the edges. Probably much better in something like an f10 SCT but that’s not what you have...... Ed.
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