How fine should we be cutting it?

My friend Clay Cooper has some interesting experiences to report in a recent message:

I got a new 2" eyepiece this week - a GSO 30mm Super View ($58). Ordered it from Agena Astro on Monday morning and received it Wednesday. I spent at least an hour last night comparing the views thru it with my old $250 Televue 32mm Wide Field (heavy hand grenade), which I've had since the early 1980's at least. I could not distinguish much difference between their optical performance - it was very close IMO. Edge of field clarity on both was acceptable in my 6" f/5 Newt. This really makes you realize how lucky we are to live in an era when such inexpensive quality equipment is available for our use. I wish the GSO had a few more mm of eye relief, but it's a keeper anyways.

I bought a 32mm Plossl on AM a couple of weeks ago, and when I got it
I noticed that it is only MC instead of FMC. Would you expect to be able
to notice a difference between the two if someone gave you two identical
EPs, one with FMC and the other with MC? It puts out a quality image it
seems, but it just bugs me that it is not FMC (my fault for not asking the
guy that was selling it, but live and learn). Maybe I'm trying too hard to
find fault with it and am suspicious of its performance because of its MC
coatings. It has more comfortable eye relief than the new GSO mentioned
above.

I think you're on the right track in terms of believing your eyes rather than obsessing over the specifications.

First, I'm not sure if there are any legal definitions for these terms? Do you know? I mean, generally speaking "multicoated" - MC - is good. It's a step up from "fully-coated." Usually. But how many air-to-glass surfaces are involved and how many of these received the multicoating? I don't think the label really tells us. FMC - fully multicoated - does tell us all surfaces were involved. Doesn't tell us if the coatings were put on well - and as I understand it, there isn't even an industry standard to define this, so I'm not at all sure FMC means the same thing from one optical seller to another.

Finally, I just am not convinced that these coatings always make the significant difference we assume they make. Garrett Optical, on their Web site, says this about coatings on binoculars:

"Such binoculars are normally advertised as having “Coated Optics”, and are unacceptable for all but the least demanding uses. The simplest form of coating is a single thin layer of Magnesium Fluoride. This is a good coating, but Magnesium Fluoride coatings lose about 1.5% of light per surface. That may not sound like much, but keep in mind that most binoculars have 14 to 20 optical surfaces that the light must pass through before reaching your eye. That can translate to some serious light loss - in excess of 25% - for a magnesium fluoride-coated binocular."

Now I know eyepieces don't have as many elements as binoculars, but what gets me wondering here is the 25% loss idea. Let's say you lose 25 percent of the light striking your six inch mirror. Isn't that about a tenth of a magnitude? ( A full magnitude difference occurs when there's a 250 percent change - unless my math is totally cockeyed.)

So what's a tenth of a magnitude between friends? Can you detect a 10th of a magnitude difference between stars? The AAVSO assumes you can. Their observers report magnitudes in one-tenth magnitude increments. And when I've done variable star observing I feel I can estimate to one tenth of a magnitude, but I feel a bit dicey about the final step. My estimates become more like guestimates. So, when we look at a star field, or a DSO, and one eyepiece reveals stuff to 11.8 and the other to 11.9 can we really notice that difference?

And the real question is this - assuming we do notice that difference, does it really impact our viewing pleasure? Is our typical observing that critical - that precise - that we feel robbed when we don't get that last one tenth of a magnitude? Or is it simply that we don;t really know if we can see it or not, but we figure any little technical edge has to help?

If money were not an object, I would not hesitate to purchase the best optics around - because very little edge may help and why handicap yourself. But when money is an object - and it is with me - then I really think we tend to obsess far too much over high quality optics that yield gains that we can barely detect at prices increases that put huge dents in the bank account.

The cold truth about astronomy is we really receive very little visual information through our telescopes when looking at most objects. The key to our enjoyment doesn't. IMHO, lie in a tad more visual information. It lies in what's in our heads before, during, and after we observe. The paltry visual information we get is a stimulant that can release that sense of awe primarily because of all that we know about what we are seeing.