Quote:
Originally Posted by Bendy
I presume that this is due to poor seeing conditions as in each case I was unable to conduct a star test (the airy disc was jagged and in constant motion),
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Bendy,
You answered your question yourself!
That the image was jagged and in constant motion means seeing conditions were poor!
Expanding on what Raymo wrote: It does not matter your scope. It does not matter about collimation. When the image is jagged and moving, it means that there is a lot of thermal disturbance in the atmosphere. If the atmosphere is stable, then you can ramp up magnification. When really stable, you can take things to the maximum your scope's aperture will allow. And you've just hit the jackpot!
Collimation (if your scope is a reflector of any type), if not as good as it can be, will show a different set of aberrations.
'Seeing' refers to thermal stability. Typical 'seeing' will only allow upto 150X magnification before the image degrades with a constantly moving mage. Good seeing and you can take things to 250X. Excellent seeing and 400X is possible, and even more, if your scope's aperture is large enough. And it does not matter the size of aperture - seeing affects all scopes the same way as magnification is the same in all instruments.
The rule of thumb for max. magnification is 50X per inch of aperture. So a 4" scope will allow for upto 200X before the image begins to degrade. You can increase the magnification more, but the image quality just degrades. Take, say, my 17.5" dob. I 'should' be able to punch that puppy to 875X. The most I've taken her is 400X, and only a handful of times over 6 years. The 50X rule of thumb is a conservative figure. The better the optics the higher this can be taken. And elevation above sea level also plays a part in this.
Then there is 'transparency'. This means how clear the atmosphere is. Easiest way to think about it is a bushfire. If there is no fire, no smoke, then you can see the horizon clearly. If there is a fire, and there is smoke, how clearly you see the horizon is determined by the density of smoke.
Seeing and transparency are easy to confuse.
Mental.