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APM 10 MM Ultra Flat

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#76 Starman1

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Posted 08 September 2021 - 11:08 PM

Very interesting report and comparisons.

It’s abundantly evident: the designer who created the original UFF eyepiece designs for APM is quite talented.

Mark Ackermann
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#77 Thomas_M44

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Posted 08 September 2021 - 11:37 PM

Mark Ackermann

That’s the guy!

 

Couldn’t pull the name from memory.

 

Thanks Don


Edited by Thomas_M44, 08 September 2021 - 11:38 PM.


#78 Ohmless

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Posted 14 September 2021 - 09:55 PM

I took out the 10mm UFF tonight in my f/5.5 coma corrected 150mm Newtonian scope.  There was an hour of observable skies right after sunset.  This was the first time using my coma corrector so my progress with a report was slowed.  It wouldn't have given much detail as seeing and transparency were poor anyways.  Beggars can't be choosers.  I played with the distance between the coma corrector and the eyepiece some while observing Jovian satellites.  The coma appeared well corrected with the eyepiece out about 3/16" from the top of the GSO coma corrector.  I didn't see any problems in that regard.  I did find the last 90+% of the field had some effect where the moons would become doughnuts(they we able to be refocused).  This was reproducible multiple times so I don't think the seeing was the culprit.  The targets crossing the FOV appeared to have a uniform speed(unlike the 12mm Dual ED) and the view was pleasant when there were breaks in the atmospheric turbulence.

 

There should be better opportunities in the near future for better observing circumstances with this eyepiece according to Astrospheric.  Sorry, the jury is still out on this, but my preliminary opinion is that this is a lot of value for the outlay.  I am leaning toward not using my 12mm dual ED anymore due to the more uniform speed of the targets and the lessened field curvature with this 10mm.

 

The 10mm UFF produced 82.5x magnification, 0.7 degrees TFOV, and an exit pupil of 1.8mm. and the 12mm Dual ED produced 68.8x, 0.9 degrees TFOV, and an exit pupil of 2.2mm.


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#79 Voyager 3

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Posted 15 September 2021 - 03:40 AM

What do you mean by crossing with a uniform speed ? If you keep an object in the field of an eyepiece , it will always cross the other side at a uniform speed .

The only way to change the transit speed is to observe something that is different in declination , but it's an effect of the curvature of the earth and the rotation and it has nothing to do with eyepiece or any component in the optical chain for that matter .
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#80 Bkoh

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Posted 15 September 2021 - 05:41 AM

What do you mean by crossing with a uniform speed ? If you keep an object in the field of an eyepiece , it will always cross the other side at a uniform speed .

The only way to change the transit speed is to observe something that is different in declination , but it's an effect of the curvature of the earth and the rotation and it has nothing to do with eyepiece or any component in the optical chain for that matter .

Eyepieces often have some distortion. If there is AMD, the object changes in size as it crosses the field. If there is RD, the object will appear to change speed as it crosses the field. From what has been written, it appears that the 10mm UFF has less RD than the 12mm Dual ED.

Edited by Bkoh, 15 September 2021 - 05:42 AM.

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#81 SeattleScott

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Posted 15 September 2021 - 09:42 AM

It was recently mentioned that the 10mm appeared slightly brighter than a 9mm Meade. This is to be expected as lower magnification produces brighter views.

Scott
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#82 Starman1

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Posted 15 September 2021 - 10:18 AM

Yes, an object crosses the field at different speeds depending on the distortion in the eyepiece.

Angular magnification distortion (AMD), if present, usually compresses the field at the edge, so an object slows down as it nears the edge because the scale is smaller

and it has to travel a larger distance in arc-seconds to travel the final couple millimeters of field.

Think of being in space and watching the Earth--a city appears on the edge and takes a long time to move laterally because it is farther away (smaller),

then speeds up as it crosses directly under you, then slows down as it nears the other limb.

 

This is why timing the passage of a star across the field can derive an accurate true field for the eyepiece--any distortion will be accommodated for in the timing.

 

AMD usually means magnification at the edge is lower, like AAAAA

The effect is that of looking at a globe, or rolling ball as the field is panned.  

If of the opposite sign, the magnification at the edge is higher, but I haven't seen this in a telescope eyepiece.

 

Rectilinear distortion (RD) is a linear, radial, distortion that either stretches or compresses a radial line as it nears the edge of the field.

When present, it is usually positive, in the form of pincushion distortion, so the edge is stretched out, radially.  

Barrel distortion, the opposite sign, compresses the edge and appears like AMD with the edge compressed.  Straight lines curve with pincushion as they approach the edge, like ) | (.  And Barrel is the opposite  ( | ).

https://www.learning...lens-distortion

 

 

The thing is, distortion is distortion, and its presence in eyepieces grows larger the wider the apparent field.  An orthoscopic eyepiece (meaning, without distortion) must, of necessity, be a narrow eyepiece.

The consensus opinion is that AMD is the more noticeable form of distortion in astronomy, so typical astronomy eyepieces reduce that to a minimum while allowing the predominant distortion to be RD.

For Daytime use, keeping straight lines straight is important, so RD is reduced to a minimum, allowing AMD to predominate.  There have been several eyepieces designed for daytime use adopted to astronomy, and there have usually been comments on the distortion type in those.  If the scope tracks, and the night sky field in the eyepiece doesn't move, it would be hard to tell any distortion was present, for the most part.

And if the scope does not track and the field moves in the eyepiece, AMD would typically be the most noticeable form of distortion.


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#83 Starman1

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Posted 15 September 2021 - 10:20 AM

It was recently mentioned that the 10mm appeared slightly brighter than a 9mm Meade. This is to be expected as lower magnification produces brighter views.

Scott

There is a bit of evidence to suggest the eyepiece is actually closer to 10.5mm than it is 10mm,  That would make the difference even more apparent.


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#84 Voyager 3

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Posted 15 September 2021 - 10:54 AM

Thanks Don and Bkoh , educational .


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