New eye piece for impending new scope

[CedricTheBrave]

9 hours ago, Barry-W-Fenner said:

Morning Cedric,

Which FL Morpheus eye pieces did you purchase in the end?

Baz

the 9mm and the 17.5mm

 

[Barry-W-Fenner]

54 minutes ago, CedricTheBrave said:

the 9mm and the 17.5mm

 

Excellent choice. The 9 is my personal favourite, it gives some stunning mid power views I've only just acquired the 17.5 myself and am still waiting to get a good opportunity to try it out. I have read great things about it!

[CedricTheBrave]

25 minutes ago, Barry-W-Fenner said:

Excellent choice. The 9 is my personal favourite, it gives some stunning mid power views I've only just acquired the 17.5 myself and am still waiting to get a good opportunity to try it out. I have read great things about it!

going to give them a go on the 200pds as soon as i get some clear sky

[Louis D]

3 hours ago, Barry-W-Fenner said:

Excellent choice. The 9 is my personal favourite, it gives some stunning mid power views I've only just acquired the 17.5 myself and am still waiting to get a good opportunity to try it out. I have read great things about it!

Let us know if the 17.5mm is actually a 74 degree field instead of 76 degrees as I have heard from at least one report.  I measured my 9mm and 14mm Morpheus(es) to have 78 and 77 degree fields, respectively, so I know there is some variability.  This is way less variance than the variability in the Starguider/Paradigm and HD-60 lines (57 to 65 degrees instead of 60 degrees):

Edited December 8, 2020 by Louis D

[Don Pensack]

Ernest in Russia has measured the apparent fields of some of the Morpheus eyepieces:

4.5mm--78°

6.5mm--79°

9mm--78°

12.5mm--78°

14mm--78°

Alas, no 17.5mm measurement.

[F15Rules]

On 07/12/2020 at 12:48, CedricTheBrave said:

thanks everyone for the input

I have decided to go for a couple of the Morpheus ones to start and see how I get on with them

 

Great choice!!👍

Dave

[John]

27 minutes ago, Don Pensack said:

Ernest in Russia has measured the apparent fields of some of the Morpheus eyepieces:

4.5mm--78°

6.5mm--79°

9mm--78°

12.5mm--78°

14mm--78°

Alas, no 17.5mm measurement.

Makes a nice change to get a little more than the spec says

[CedricTheBrave]

how do you measure that?

[John]

57 minutes ago, CedricTheBrave said:

how do you measure that?

Drift timing is probably the most accurate method:

http://www.mikehotka.com/Measuring_field-of-view.htm

 

[Louis D]

1 hour ago, John said:

Drift timing is probably the most accurate method:

http://www.mikehotka.com/Measuring_field-of-view.htm

 

It's not accurate for measuring apparent field of view.  It doesn't take into account magnification distortion across the field which can vary widely.  The 26mm Meade MWA is an extreme example of this.  This method only gives you the true field of view which can be converted into the effective field stop size once the true focal length is known (probably from exit pupil diameter).

There are several methods to determine the apparent field of view based on projecting light through the eyepiece and measuring the projected circle or cone of light coming out of the eye lens.  The more accurate method is to split the exiting light cone across a sheet of paper and measure the angle with a protractor after tracing the edges onto the paper.  I use the more involved method that requires measuring the eye relief distance from the top of the eyepiece, the distance from the top of the eyepiece to the wall, and the diameter of the projected circle.  Then there's a trigonometric calculation.  I've found it a bit less accurate because it can be difficult to determine the exact eye relief distance and the diameter of the projected circle for certain eyepiece designs.  The formula is AFOV=2*arctan([circle_diameter/2]/[wall_distance-eye_relief_distance]) if you want to go this route.

The best method to project a circle is to put the eyepiece in a telescope and project light into the front of the scope.  Barring that, project light directly into the field end of the eyepiece after blocking it in a miter box to keep it from moving and to keep everything aligned.  Make sure to back the light away from the eyepiece until you get a sharp edged circle projection.  At first, I had the light too close and was getting fuzzy edged image circles as a result.

The exit pupil is where the cone of light exiting the eyepiece is at its narrowest.  Move a card back and forth until the projected circle is minimized and measure that distance to the eyepiece.  This can be difficult for some eyepieces that have a poorly defined exit pupil due to aberrations.

[John]

8 hours ago, Louis D said:

It's not accurate for measuring apparent field of view.  It doesn't take into account magnification distortion across the field which can vary widely.  The 26mm Meade MWA is an extreme example of this.  This method only gives you the true field of view which can be converted into the effective field stop size once the true focal length is known (probably from exit pupil diameter).

There are several methods to determine the apparent field of view based on projecting light through the eyepiece and measuring the projected circle or cone of light coming out of the eye lens.  The more accurate method is to split the exiting light cone across a sheet of paper and measure the angle with a protractor after tracing the edges onto the paper.  I use the more involved method that requires measuring the eye relief distance from the top of the eyepiece, the distance from the top of the eyepiece to the wall, and the diameter of the projected circle.  Then there's a trigonometric calculation.  I've found it a bit less accurate because it can be difficult to determine the exact eye relief distance and the diameter of the projected circle for certain eyepiece designs.  The formula is AFOV=2*arctan([circle_diameter/2]/[wall_distance-eye_relief_distance]) if you want to go this route.

The best method to project a circle is to put the eyepiece in a telescope and project light into the front of the scope.  Barring that, project light directly into the field end of the eyepiece after blocking it in a miter box to keep it from moving and to keep everything aligned.  Make sure to back the light away from the eyepiece until you get a sharp edged circle projection.  At first, I had the light too close and was getting fuzzy edged image circles as a result.

The exit pupil is where the cone of light exiting the eyepiece is at its narrowest.  Move a card back and forth until the projected circle is minimized and measure that distance to the eyepiece.  This can be difficult for some eyepieces that have a poorly defined exit pupil due to aberrations.

I stand corrected with regard to determining AfoV

What method does Earnest in Russia use ?

His data and opinion seems to be held in high regard by many

 

Edited December 11, 2020 by John

[Louis D]

4 hours ago, John said:

What method does Earnest in Russia use ?

I was wondering that myself.  I can't recall ever reading it anywhere.  His numbers do match up pretty closely with mine on eyepieces we've tested in common.

Here's Jon Isaacs's method, which I've duplicated myself.  It is slightly more accurate than sending the light unfocused through the eyepiece.

The relative photographic method combined with the above technique allowed me to calculate the numbers below by counting pixels and extrapolating the tangential relationships from known good values:

Given magnification distortion in the camera lens, it's probably wise to only apply this technique within a fairly narrow range of apparent fields of view and then cross correlate them with the projection measurements as a double-check on their accuracy.  It's also obvious from the image that it's difficult to determine where the edge of field lies when it gets fuzzy due to a lack of a distinct field stop or has chromatic smearing.

[CedricTheBrave]

My collection s growing!!