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600mm nikon lens vs Refractor

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27 replies to this topic

#26 NuclearRoy

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Posted 17 February 2020 - 12:01 PM

Point at a bright star and slap the Bahtinov mask on.

Set APT to short exposure, max gain, 1:1 (sometimes even add the magnifier if the nearest bright star isn't all that bright) and very gently manually focus the lens.

When it looks good, I take a longer sub so I can really see the diffraction spikes well and verify they are centered.

REMOVE BAHTINOV MASK :)

Then back to the target and resume the imaging plan.

Takes less than 5 minutes. (I also plate solve/sync/goto/platesolve/display in Stellarium again when I get back to the target so that is part of the 5 minutes.The CEM 60 is rarely very far off, but I'm OCD.)

 

APT has an autofocus routine (obviously worthless for Nikon glass) but I haven't been able to get it to work better then the Bahtinov yet on my Edge 8.

I am just setting up an AT115EDT (added the Pegasus FocusCube over the weekend) so maybe that will work better with APT??



#27 Carl N

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Posted 17 February 2020 - 12:53 PM

IMHO, if are satisfied by your stars' shapes, there is very little to be gained and a lot to be lost.
Take also note that, especially if use a large sensor, refractors could struggle to provide good shaped stars across all the frame


That's true, but also true for a large camera lens.

#28 Carl N

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Posted 17 February 2020 - 12:55 PM

Several advantages come to mind:

  • Cheaper
  • Typically, fewer optical elements
  • Typically, fewer optical aberrations
  • Focusing is achieved while optical elements remain fixed
  • Designed to focus at infinity
  • Can easily be used for visual
  • Many robust and rigid mounting options available that allow for critical payload balancing
I think it would really be nice to see some raw images from such a lens to see how well it does. I have a similar experiment planned, I am just struggling with a secure way to hang my camera lens on my telescope mount.

Umm, It ain't cheaper to buy a refractor than use a lens he already owns.
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