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Posts posted by AlentejoSkies

  1. Always interested, but I bought my first scope at the age of 43, for my 4 year old daughter. It's a 76mm f/4, good for looking at the moon. She loved putting stickers on it, and I found out that it was much more difficult than I expected to find anything of interest just by looking.

    A year and a half later, thanks in no small part to this forum, and also to a lot of looking up as well as reading, I'm the local astronomer.  That's a great position to have, because all the interesting questions come my way, and by the time I have researched good answers I know a lot more than I would have ever expected.

    • Like 2

  2. So many great suggestions - which from my side will have to wait a couple of weeks until I get back from the summer holidays...

    Two weeks without any optics... has its advantages and disadvantages.

    And then I will go for the grease redistribution idea first and put the result here for posterity.  Any modifications will be only once I have a feel for the instrument as it is. It is still such an unknown to me compared to my other equipment. It's so new I am still getting to grips with collimation.

    I'd better stop now, I'm starting to miss it...

    Thanks for all the answers and support.


    • Like 1

  3. Sounds like there is a fair variation between instruments in any case. I haven't got a feel for this one yet but I guess that will come with practice. This was the first time I had it out on my own.

    From now on, I will be finishing with a CCW focus adjustment. Thanks for the tip.

  4. Actually it was a great night. Once I stopped messing around with the telescope and started looking at the moon.

    Trying a new addition to the stable - a C8 with carbon tube, on long-term loan. I really want to get to like this instrument, but it's a steep learning curve from my dob.

    Anyway, it works great with my WO binoviewers, having such long focus range, so I could use the supplied 20mm eyepieces and no barlow last night, giving a view which seems to be a hot air balloon ride over the surface of the moon. Stunning! 3D. I'm again amazed at what goes on in the brain when two eyes are involved. Like I had never seen the moon before. I spent the evening there, switched off the motor drive and let the moon drift through the field, again and again. It's a natural landscape, nature not as we know it, but also similar. Savannah-like. Unforgettable.

    I could have got the same effect more easily with the little dob and barlowed the binoviewer, but that's not the point... last night was great just as it was.

    • Like 6

  5. So just as I thought I had the basics sorted out after over a year with two dobs a couple of times a week...

    I have a C8 on loan from a friend, and I am back to the beginning with some basic questions:

    Image shift - how much is 'normal' ? I estimated last night that the image shifts a few percent of the field when I change focus direction. Is that just the way it is when you move the primary to focus and I need to get used to it? It's a bit disconcerting but more of a distraction than a real problem.

    Field curvature - I'm only going to use this instrument for visual, but even so, center to edge sharpness needs what seems to me like a lot of refocus. Would the f/6.3 reducer/flattener be a good item to put on my wish-list?

    Vibration sensitivity - there is a certain springiness in the OTA/dovetail itself. Guess that is not going to change. It's just that I never even had the issue before.

    By the time I had carried the mount, field tripod, power supply and OTA around, let the whole thing cool for an hour, I was missing my 6 inch 'grab and go' dob...

    I do have to say though, it was also a great night once I started looking at the moon rather than the telescope...

  6. I'm also around 18-month vintage. Loved your post and fully stand behind what you say.

    One thing I would add is that having had Sky Safari 4 on my phone for a while and then upgrading to Sky Safari 4 Plus for a few quid has meant that I can always check what will be visible tonight, or in a few days etc. and read a bit about the history, mythology and observing hints for pretty much anything I will be able to see. That little app has made a big difference to my astro-life.

  7. Regarding the acid in silicone - I would not put it in a sealed box to cure, for sure. But I think the acetic acid is gone after a few days. It would be in direct contact with the back surface of the secondary, and the plastic of the secondary holder.

    (I did once leave an open tube of silicone in a sealed tool box for a year, made a real mess... everything heavily corroded and smelling of fish & chips.)

  8. Hi,

    Gradually putting my Darkstar back together after a bit of maintenance...

    The secondary was originally held in place with epoxy around its edge, still strong after all these years. Had to take it off though to recoat, and now I wondered about using silicone to give a bit more flexibility, but with such a small contact area I am worried it could come loose with catastrophic results. So actually I guess it will be epoxy again and I have answered my own question. Unless anyone with experience tells me otherwise?


    secondary holder.jpg

  9. Thank you for your comments.

    As far as leaving well-enough alone, the Darkstar did need some attention coming into my hands after a good few years unused: missing focuser, damaged spider, corroded collimation screws, coating damage to secondary... so it is anyway a project - and with it in pieces anyway the temptation to tinker is just too high... and then I would like to add a fan, for which the exisiting cell is not ideal...

    Actually I just enjoy it. And now reading Suiter's inspirational book I'm in the mood to play around a bit. But slowly, slowly.

    Looks like there is already a range of opinions on this one. Good, I can enjoy the planning!


  10. So I have a David Hinds mirror set, the generous gift of a certain Tom Yates (he's a jolly good fellow!)

    It's present home is a darkstar telescope that is not really doing justice to such fine optics. As time and budget allows, it's going to become my favourite instrument...

    For now, secondary is going in the post to Orion Optics for a recoat, and the primary - coating still fine - is getting a new cell.

    First discovery is that the 8 inch primary is actually 223mm diameter. That's nine inches. Great! (Is that normal?)

    Second is that it's quite thin. 25mm.

    And now the question: Is my planned mounting method of three blobs of silicone at around 2/3 of the diameter a good idea, or do I need to go into this a bit more deeply? It looks like there's a whole world of mirror cell optimisation out there. Do I need to open that chapter?

    Thanks for any  advice,



  11. I'd also add that it's good to use what you have - almost whatever you have - for a while and develop a sensitivity to what you want to do next (although it's for sure also good to ask advice so that even if you take the next step quite quickly it will be a good one...)

    • Like 1
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