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laser_jock99

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Posts posted by laser_jock99


  1. 10 hours ago, alacant said:

    The only alternative I can find which may work out of the box is the priced-like-a-small-refractor cr ontc.

    Please note that i am not an expert on this stuff and must credit @laser_jock99, our resident Newtonian modification expert, for the influence on the above.

    Cheers and HTH but do tell us what you decide to do.

     

    I wouldn't go as far as 'expert'!

    I have certainly fettled these things to try and get the best performance.

    There is a bit of fun/sense of acheivement to be had from modding scopes - but there is also a slight chance the main mirror is a complete lemon and you won't get anywhere with it.

    At the end of the day though these are 'budget' scopes and I would set my expectations accordingly.


  2. On 03/06/2020 at 02:35, Adam J said:

    The issue I always have with these is that you dont need to level a pier top to polar align and so you introduce a vibration source in making the leveling device using threaded rods.

    Quite right. I'd avoid the 'leveling bolts' approach. So many times we see good solid piers sunk into x tonnes of concrete- only to have the entire scope balanced on some M12 studding!!!!!

    Another issue to be aware of with wider brake discs is the possibilty of the scope clashing with mount. This could become apparent when pointing the scope close to vertical.

    A better solution is to get a local machine shop to make a custom, drop in puck for your steel tube.

    42309883994_75f9212fe4_b.jpg

    A drawing I made for the puck.

    33573877258_8d3bff7825_o.jpg


  3. Here's a picture of my 6" F4 scope on the outside pier. The 80mm refractor is the guide scope (or an alternative imager). Note though how I use a top & bottom dovetail bar for extra stability. You will also notice they are 2x longer than supplied dovetail bars- this is important to reduce tube flexure in the Newt's steel tube. If you can get Lossmandy type long dovetail bars- use those. Much stiffer than Skywatcher type.

    38659143754_5e062cfe3d_o.jpg

    The 6" F4 optical tube assembly is quite cheap- but I found it requires a bit more investment to get the best out of it.

    • Like 2

  4. Working at F4 isn't too trying- F2.9 is a different ball game. Only go down that avenue if you like being told 'it can't be done'!

    I have bunch of F4 Newtonians and use the 0.73x Coma Corrector on all of them at times. So the 12" F2.9 scope is interesting.....M51 in just 140 seconds.

    11755944213_1b6074ded3_o.jpg

    • Like 4

  5. These fast Newts are 'interesting' scopes and capable of good results but probably not 'out of the box'. Be prepared to modify & fettle the scope to get the best results.

    A good laser collimator is a must and these are not cheap. A good coma corrector is also required for best results.

    Think about the following mods- stronger primary collimation springs, longer top & bottom dovetail bars.

    Be prepared to re-check the focus and collimation of the scope as it cools during a session- at F4 small changes in teperature can have big effects in the focus position with metal tube Newts.

    Now- if you're a complete nutter add one of these 0.73x coma corrector reducers to your scope to make it F2.9!

    NGC7000 in 159 seconds with a 6" F2.9 Newtonian

    38094447296_106483f063_o.jpg

    • Like 1

  6. On 09/03/2020 at 11:38, sploo said:

    Thanks. I'd be happy just to get a 1 minute exposure! Because I currently only have DSLR camera gear I understand that long exposures aren't a good idea.

    With the off-axis adaptor, doesn't the prism/mirror intrude into the image being captured? I guess not, but it seems odd that it doesn't.

    I only use DSLR's at the moment. With a DSLR you have a rectangular imaging area superimposed over an imaging circle. The trick is to get the pick off prism in the area of the long side of the DSL image rectangle so it doesn't intrude into the imaging area.

    • Thanks 1
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