Quote:
Originally Posted by tlgerdes
Hi Chris,
You can use just about any sort of optics for the guide scope, my first was a 70-300mm zoom camera lens. As long as the camera attached can achieve focus and you can mount it steadily on you scope.
Your camera though is probably more important, most guiding software will not talk to DSLRs. So you will probably want to look at potential guide cameras and see what software is supported by it.
One of the most popular is the QHY5/Orion SSAG (essentially the same beasts). Relatively cheap, reliable and supported by every man and his dog from a software perspective. It also has the benefit of inbuilt guide port, so it will talk straight to your CG5s guide port.
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Thanks for this, Trevor. So I'm assuming the longer the focal length of the guidescope, the better the guiding and subsequent correction - as it can correct smaller movements? Though there will obviously be a limit to how much a motor can be corrected. I will look at the QHY5 and Orion SSAG
Quote:
Originally Posted by Wavytone
Chris,
There is no such thing as 'semi APO'. Either a lens is an APO, or its not.
There are achromats - which bring 2 wavelengths to the same focus, or apochromats, which bring 3 wavelengths to the same focus. For some lenses designed for astronomy, one of the 3 wavelengths may outside the visible spectrum.
Until about 10 years ago, to make an APO meant either the lens had to be a triplet, or for a doublet, one element was fluorite - which is very fragile, easily damaged by moisture, as well as expensive.
In recent years the use of ED glass has allowed doublet designs to achieve apochromatism, and are frequently diffraction limited at f/7. ED doublets that are apochromatic are a huge improvement over achromatic doublets. However a well designed triplet or four-element lens should be even better especially when the size of the field f view and field curvature are taken not consideration.
The other issues to consider are
- whether the lens is truly diffraction-limited,
- the amount of'secondary spectrum' and
- lateral chromatic aberration off-axis,
- the amount of field-curvature present, and whether to use a field flattener to correct it.
With three of four elements a lens designer can do a great deal to control all these aberrations over a pretty decent field of view For example http://www.vixen.co.jp/en/index.html
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In larger apertures however, the best of all however are all-reflecting optics where all wavelengths are focused at exactly the same point from UV to infrared, or those with thin correctors such as the maksutov-newtonian or Riccardi-Honders. |
Thanks for clearing that up, Wavytone