Meade MWA 10 mm

[EMS]

Hi out there, i have just recieved my new 10 mm 100˚ meade eyepice,

i have see on other forums some talk about the size of the field , with a drift time through the field 

is twice the time as a 10 mm pl 50˚  i think 100 degree is close,  pinpoint to the edge in a f/ 8  but is not a beginner item 

if yuo ask me  ( kidney been)  it takes a exactly eye position, i learn it with a little  exercise.

[Ben the Ignorant]

Hi. I have three Myriad 100°/110° eyepieces so I know how you feel about the mega field. Don't worry about claims of less 100° in those Meade eyepieces, some reviewers are just not competent. I bought a Celestron NexYZ smartphone adapter which has friction adjustment screws on all three axis, yet several reviewers complain there is no way to adjust friction.

The screws are easily visible and described in the paper and online instructions but some folks are so quick to blame and so lazy they didn't bother to look. Countless newbies buy stuff and rant that it doesn't work well or lack features, they often return the things. If they are lucky they eventually find out they were wrong when they ask in a forum. If not, they lose opportunities for ever. I never believed the nonsense about those Meade eyepieces not possessing the 100° they need to have eventhough I didn't try one.

I trust opticians know what they design and what they build. And no one in a serious corporation would market something grossly lacking a measurable feature when anybody can expose it. The "barely 80°" claim was just an opinion, the guy never measured the field; that's what makes a review suspicous, vague claims and no experimenting. You did the measurement and found twice 50°, which is no surprise at all.

Meade and other businesses are careful to not look mean so they won't call bad reviewers incompetent or dishonest but private individuals in forums are free to do that, fortunately. For a long period (maybe it's not over in certain minds) stupid claims were made that large Teleskop Service apos are falsely advertized as containing FPL-53 glass when they really have the cheaper and less efficient FPL-51 glass.

All that because they were not "expensive enough", as if there was no trend to make better and cheaper things in the last two centuries of industry!

[Louis D]

The true field of view (TFOV) could very well translate to that of a 100 degree eyepiece of the Ethos type at that focal length, but with less pincushion distortion yielding a smaller than 100 degree apparent true field of view (AFOV).  The best way to measure AFOV is the flashlight (torch) projection method.

I'll give an example of this situation.  I have a 35mm Baader Scopos Extreme.  It claims a 70 degree field of view.  I measured 59 degrees by projection.  A German reviewer here measured 60 degrees, so we're consistent.  It looked bigger than that to my eye, so I photographed the image circle and did some math to arrive at 66 degrees AFOV by that method, which seemed more correct since it appeared nearly identical to a Pentax XL which are spot-on 65 degrees each.  I still can't reconcile the difference between the two methods for this eyepiece.  It matches for other eyepieces quite closely.

I then measured the TFOV via a yardstick/telescope combination and again applied some more math to arrive at a field stop diameter of 39mm which is pretty close to the German reviewer's 41mm value.  Guess what?  That puts it slightly ahead of the 35mm Panoptic's 38.7mm field stop despite the Panoptic's larger AFOV of 68 degrees.

The Panoptic has so much pincushion distortion that it stretches the outer edges of the field from 2 degrees to possibly 9 degrees more AFOV.  Thus, I hypothesize the marketing wonks said, "Hey, this shows more TFOV than the 35mm Panoptic which is accepted to have a 68 degree AFOV, so it must have a slightly bigger AFOV as well.  Let's label it as 70 degrees."  The only problem is that it displays much lower distortion levels than the Panoptic and thus has a much smaller AFOV.

Even the Scopos's effective AFOV (eAFOV) is only 64 degrees.  Compare that to the Panoptic's 63 degree eAFOV.  My definition of eAFOV is what AFOV when divided by the power yielded by the eyepiece/scope combo yields the observed TFOV (which is determined by the field stop independently of distortion).  The Panoptic adds 5 degrees of AFOV distortion compared to only 2 degrees for the Scopos.

In summary, TFOV tells you nothing about the AFOV.  The AFOV must be measured by projection or photography of the actual image circle.  It is heartening that @EMS has determined it to have twice the TFOV of a 50 degree eyepiece.  Thus, it actually shows four times the area on the sky as a 50 degree eyepiece.  The only question remains, how is that view presented to the eye?  Is it 100 degrees AFOV, 95 degrees AFOV, or some other value?  It would appear to have an eAFOV of 100 degrees for certain, assuming that 50 degree reference eyepiece has an eAFOV of 50 degrees (zero distortion).