Quote:
Originally Posted by AlexN
My 8" is steel tubed however I've found focus shift to be minimal. If you were to add the cost of robofocus to the scope that will automatically adjust for any temperature induced focus shift, you are still looking at around $2500 less than a triplet refractor that will still undergo focus shift due to temperature. Mirror based systems are cheaper and provide much more light per dollar than any apo
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Quote:
Originally Posted by AlexN
I'm using a 5" newt with robofocus at the moment and once it was trained for temp compensation I get ccdsoft to autofocus St the beginning of an imaging session then walk away. It does the rest on its own. For a cheap scope I have 5" of aperture, 0 colour fringing issues, 0 focus shifting between subs.. The downside is 5 to 10 mins of collimation prior to imaging.. Small price to pay.
Diffraction spokes become the only other thing people don't always like. I'm considering a curved spider for the scope to remove spikes. Then I have all the upsides of a top notch apo with none of the drawbacks and 1/7th of the cost.
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Cheers Alex :-)
I've actually found with all of the APOs that I've owned that I get no focus shift in my imaging runs, in fact I can even go back the next day and as long as I'm shooting with the same filter, I can often leave it as-is. I've been spoilt with 'fracs :-)
Interesting that you don't have much of an issue with focus shift on a steel tube newt!
I think I'm pretty well sold on the TS ONTC 8" at the moment so I may pull the pin soon... sooner rather than later actually, since the wife was surprisingly agreeable... makes me suspicious!