I've been musing about getting a 'quality' apochromatic refractor for imaging on a 'solid' mount with a 'good' CCD and 'sufficient' autoguider, etc. You can see a lot of adjectives I've put in quotes here - these things are relative, not absolute. This has led me to think about the general issue of 'sweet spots' in telescope purchases (for both visual , imaging, as well as mounts, CCDs etc).
There is a general rule that applies in a remarkable number of situations, the Pareto principle (
http://en.wikipedia.org/wiki/Pareto_principle). Basically, you get 80% of your 'value' from 20% of your 'investment' (to generalise). It is strongly related to the law of diminishing returns (
http://en.wikipedia.org/wiki/Diminishing_returns).
For just one example, let's say you buy an apo OTA for $8000. Will this yield an image that 4 times better than an apo that cost $2000, all else being equal (mount, imager, person, etc.). No, it may be twice as good, or 50% better or whatever - the exact value is always 'it depends' and to the degree that quality of images can't be quantified, it is a personal choice.
But to generalise this, given the wealth of experience here, I wondered if people had formed opinions on the 'sweet spots' for astro equipment? It could be for an imaging apo, or a visual Dob, or a grab-n-go (and could expand to eyepieces, imagers, mounts etc. - the list is almost endless).
The key to addressing this question is to consider the trade-off/incremental gains relationship between quality gains and $$ spend. Indeed, in theory, if you could plot quality per $ spent, in most cases the function would be non-linear and typically have a peak value (or range) that could be optimised. Although it is difficult to precisely quantify 'quality'...
So going back to my original example, say I was looking for a 'quality' apochromatic refractor for imaging on a 'solid' mount with a 'good' CCD and 'sufficient' autoguider.
In one case I might spend what I thought was a sweet spot:
$3500 on the OTA, $2000 on the mount, $1000 on the CCD and $500 on the autoguider = $7000
Or I could be on a budget and spend: $1000, $1500, $600 and $400 = $3500
Or I could say quality is paramount and money is no object, and spend: $8000, $10000, $5000, $2000 = $25,000.
The 3rd example will yield the best image and the 2nd the worst, but at what point does a normal guy on a normal income stop along the quality vs $ curve? This is my overarching point -- treat the above as just an illustration.
Thoughts?