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Eyepiece FOV images for all my eyepieces


Louis D

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I decided to create eyepiece field of view (FOV) images for all of my eyepieces with my newer cell phone camera and an ultrawide angle camera on another junked cell phone camera for the ultrawides.  I'll post them here one group at a time to break them up into manageable sized posts.  The ultrawide angle camera images (labelled "full view" below) were up-sampled to match the center magnification of the regular camera images since distortion should be at a minimum there.  This allows for easier comparison.  However, the regular camera has higher resolution to start with and a much larger percentage of the field is being utilized, so the ultrawide angle images are rather low resolution and are presented mainly so the reader can more easily grasp the relative width of the ultrawides.  I also ran into severe spherical aberration of the exit pupil (SAEP) with several eyepieces, so you'll see varying levels of blackouts in some images.  The eyepiece exterior images are in the same order left to right as the FOV images from top to bottom.

Edited by Louis D
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Hi Louis,

that looks interesting, I've been interested in measuring the FOV of my eyepieces for a long time now, but never came around to do it. Can you elaborate how you mount eyepiece and smartphone? When calculating the FOV, which distance is relevant? Sensor to tape measure?  

 

Sven

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Louis, what an effort this must have been and what a great result you have here!

I have a question regarding kidney beaning.  Do you still have EXIF information for the images? It would allow calculating the entrance pupil (= camera lens effective aperture, "focal length / focal ratio used for the picture") for each photograph. Most of us use our astronomical eyepieces with observer pupils of around 5 mm or larger.

For an observer, a messy exit pupil causes kidney beaning mainly when the pupil of the observer is only slightly wider than the exit pupil of the eyepiece. Especially the Nagler T4 12 mm and the Meade 4K UWA 14mm both show severe kidney beaning in the second of the two images you post for each, which may have been caused by an entrance pupil that is only slightly wider than the exit pupils of the eyepieces. In that case, even the mildest SAEP would show as kidney beans. That being said, both of the first images for each of these eyepieces also show kidney beaning, though very much milder. I wonder how big the exit pupils of these eyepieces and the entrance pupils of the camera lens were for these four shots.

The Nagler T4 12mm and Meade 4K UWA 14mm may indeed have particularly messy exit pupils. I actually tried the NT4 12mm in a bright daylight test. From the dealer's shop it showed a strong tendency to kidney beaning so I decided against it. My pupil must have been pretty small at the time, but since it is also small when I observe the Moon I thought this eyepiece was not for me.

Thanks for the thread. I think it is epic and deserves to get pinned.

 

 

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5 hours ago, freiform said:

Hi Louis,

that looks interesting, I've been interested in measuring the FOV of my eyepieces for a long time now, but never came around to do it. Can you elaborate how you mount eyepiece and smartphone? When calculating the FOV, which distance is relevant? Sensor to tape measure?  

 

Sven

I keep the distance from the telescope to the ruler(s) constant across tests.  I also use the same camera for all tests (except where noted for ultrawides).  You have to move the camera up and down relative to the eyepiece until the field stop just pops into view.  This guarantees that the magnification is the same across eyepieces.  You also have to adjust for centering and tip to exactly center the image on the sensor.  I also take advantage of the wider field of view across the diagonal of the sensor for wide angle eyepieces.  I lock down my alt-az mount once I have the image where I want it.  I then hold my cell phone camera above the eyepiece using my index finger and thumb to brace between the two.  I then practice shallow, careful breathing to avoid inducing vibrations as I finalize the alignment and take a series of images by lightly tapping the screen each time I think I've got the best image possible.  I then select for the best image at the computer after downloading them.

SAEP becomes a problem because some eyepieces blackout horribly once the entire field of view is seen.  Today's cell phone cameras very closely mimic the reaction human eyes have to various eyepieces.  In particular, camera lenses with smaller maximum apertures (larger f-numbers) are more sensitive to SAEP, just like a human eye with a constricted iris as in daytime viewing.  The regular camera above is more immune to SAEP because it has a maximum aperture of f/1.7 while the ultrawide camera has a maximum aperture of f/2.4.

If you have to tip your head to the side to see the edge because the field stop is the end of the barrel (as is the case for the 29mm Rini MPL above), the camera will show a fuzzy edge before the true edge of field.  This is because it shows what can be seen from the center of the eye lens.  You can tip the camera to capture the edges as I did for the ultrawides above to show the true edge because the regular camera didn't have a wide enough field of view to capture it or because it is hidden from the center.

You can calculate the true FOV (TFOV) but not the apparent FOV (AFOV) with this technique (though someone might prove me wrong on that last point).  You can appreciate the relative differences in AFOV, but directly calculating it is not straight forward at all, so I'll leave the derivation to others.  TFOV and thus the effective field stop diameter can be easily calculated using similar triangles.  The distance shown on the ruler is directly related to the diameter of the field stop by this relationship.  The only trick is calibrating the scaling coefficient.  I did it by noting the relationship between my Televue eyepieces which have published effective field stop numbers and the distances I measured.  This measurement is immune to magnification distortion across the field of view.  If you don't have any Televue eyepieces for calibration, I'd start with a 1.25" 32mm Plossl which generally has a 27mm field stop diameter.  I could never work out what distances are relevant to use the similar triangles method directly, so I back into it using known good values as described.  Using this method, I'm generally within 0.1mm of the values measure by others using calipers on accessible field stops (those below the eyepiece's field lens).

To calculate AFOV, I use the flashlight (torch) projection method.  It is immune magnification distortion across the field of view.  First, use a miter (mitre) box to keep the eyepiece and flashlight aligned and stable.  Second, I mount the eyepiece in a 2" extension tube (with 1.25" adapter as needed) to back off the flashlight slightly and to contain stray light not entering the eyepiece.  I then move the flashlight forward and back until the projected image circle has as sharp a field stop image as possible.  Sometimes, you just can't get a sharp field stop image due to the design particulars of certain eyepieces.  This makes the measurement a bit "fuzzy" because you have to make a judgement call as to where the field actually ends.  I then measure the distance from the top of the eyepiece to the projection screen (a white box works well for this purpose).  Next, I measure the diameter of the projected image circle.  Lastly, I move the screen and eyepiece toward each other until the image circle reaches its smallest point.  I then measure the separation between the top of the eyepiece and the screen as this is the usable eye relief.  Again, this can be a fuzzy measurement when there are exit pupil aberrations causing the minimum point to cover a range of distances as is the case with SAEP and chromatic aberration of the exit pupil (CAEP).  I generally accept the center of these distances as the eye relief.  Finally, get out the scientific calculator and perform the following calculation: AFOV=2*arctan[((circle diameter)/2)/(screen distance - eye relief)].

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40 minutes ago, Ruud said:

Louis, what an effort this must have been and what a great result you have here!

I have a question regarding kidney beaning.  Do you still have EXIF information for the images? It would allow calculating the entrance pupil (= camera lens effective aperture, "focal length / focal ratio used for the picture") for each photograph. Most of us use our astronomical eyepieces with observer pupils of around 5 mm or larger.

For an observer, a messy exit pupil causes kidney beaning mainly when the pupil of the observer is only slightly wider than the exit pupil of the eyepiece. Especially the Nagler T4 12 mm and the Meade 4K UWA 14mm both show severe kidney beaning in the second of the two images you post for each, which may have been caused by an entrance pupil that is only slightly wider than the exit pupils of the eyepieces. In that case, even the mildest SAEP would show as kidney beans. That being said, both of the first images for each of these eyepieces also show kidney beaning, though very much milder. I wonder how big the exit pupils of these eyepieces and the entrance pupils of the camera lens were for these four shots.

The Nagler T4 12mm and Meade 4K UWA 14mm may indeed have particularly messy exit pupils. I actually tried the NT4 12mm in a bright daylight test. From the dealer's shop it showed a strong tendency to kidney beaning so I decided against it. My pupil must have been pretty small at the time, but since it is also small when I observe the Moon I thought this eyepiece was not for me.

Thanks for the thread. I think it is epic and deserves to get pinned.

 

 

I spent 3 or 4 days of solid work on this.  My back has been paying the price from hunching over all these eyepieces with a cellphone.  Editing at the computer sitting in a nice office chair was a delight by comparison. 😁

All of the "regular" camera images were taken at f/1.7 and 4mm focal length.  All of the "ultrawide" camera images were taken at f/2.4 and 2mm focal length.  It's pretty obvious that the latter camera is much more sensitive to SAEP than the former.

The weird part about using these eyepieces with SAEP is that I had never noticed it in the Speers-Waler because I can't get close enough in normally due to its somewhat short eye relief (despite Waler meaning Wide angle long eye relief).  The 12mm NT4 is much less bothersome to me than the 17mm NT4 despite them showing about equal amounts.  The 22mm NT4 shows the least by far of the three; and indeed, it is the easiest to use.  The 14mm Meade UWA also is not normally very bothersome.  Of the 5 with dramatic SAEP, I'd say the 17mm NT4 is my least favorite because even with a fully dilated pupil, it is still incredibly difficult to hold the exit pupil once the field stop comes into view.

Thanks for your appreciation of my efforts.  I just want to help others get a better idea of what the view looks like through various eyepieces if they don't have easy access to them at retail shops.

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I guess I forgot to mention the telescope and diagonal.  I was using my AstroTech 72ED with a 2" GSO dielectric diagonal with a TSFLAT2 field flattener attached to the front of the diagonal with 20mm of spacing between it and the diagonal.  The net result is very close to a perfectly flat field from edge to edge.

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Dear Louis,

thank you very much for the very detailed description! Your procedure sounds sounds relatively straightforward. Since it apparently is never going to stop raining here, I will give this a shot this weekend.

Thanks again

Sven

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How about some discussion of the results?

I'm surprised by just how good today's step-up 60 degree eyepieces are relative to premium eyepieces from 12mm on down.  The HD-60 and Paradigm eyepieces are very good across their fields.  I was a bit disappointed with the field curvature of the 12mm Pentax XF by comparison.  I'll have to see if it has superior polish under the stars allowing for better contrast and dimmer details to be picked out to atone for its edge issues.

I just can't get over how much SAEP some eyepieces have.  I always knew I had issues with some of them even with fully dilated pupils.  They're definitely easier to use under those conditions, but they're still fussy.

The AstroTech AF70 eyepieces are quite good for 70 degree eyepieces if you're on a budget and can pick them up used for a good price.

The older Konig and Erfle wide angles are very sharp in the center, but fall off rapidly toward the edges.  They really make you appreciate modern wide angle eyepieces.

Those generic Kellners, the RKE, Plossls, and the zooms are really pretty good, all things considered.  Even the $10 Aspheric is decent.  The same can't be said of the reversed Kellner.  Thus, there are some good budget choices out there if you know what to look for.

Televue eyepieces are sharp across the field if you can get past the SAEP of some of them.  Only the 22mm Nagler is in my A-Team case, though.  The rest have been ousted by newer, better designs.

ES-92 eyepieces are phenomenal eyepieces.  Given their size and price, they'd better be.  They ousted my 12mm and 17mm NT4s from my A-Team case.

The Speers-Waler zoom is very sharp across the field.  Again, if you can live with the SAEP (which I find mild in use).

The Morpheus eyepieces are very sharp across the field.  The 7mm Pentax XW is rather disappointing by comparison.  I may get the 6.5mm Morpheus the next time it goes on sale.

The Meade MA Astrometric is no replacement for the Celestron Ortho Astrometric.  The former is not sharp across the field.  What good is a wider field if it isn't sharp in a measurement eyepiece?

The 15mm and up HD-60s and Paradigms are definitely not the in premium eyepiece category, but by comparison to Konigs and Erfles, they're not all that bad.  Again, they're good budget buys, just not great budget buys like the 12mm and below versions.

The 24mm APM UFF is a bit of a disappointment given its size, price, and hype.  The 30mm APM UFF really does live up to the hype by comparison.  It ousted my venerable 27mm Panoptic from its spot in my A-Team case.

The 30mm Kasai Super Wide View, which was their $400+ copy of the 30mm Leitz Super Wide, is just awful by any measure.  It's not even as good or wide as the $50 Rini MPL.  The Agena UWA looks very usable by comparison.  Under the stars, I find the Agena UWA very sharp in the center 50% and very easy to hold the view with eyeglasses.  It just suffers from massive field curvature and some edge astigmatism.  The ES-82 is slightly less sharp in the center (compare the barcodes between the two).  Of course, it is very nearly sharp to the edge, just suffering from chromatism out there.

The Scopos is a real keeper.  It is very sharp in the center and holds most of that sharpness to the edge.  It is a huge and heavy eyepiece, so it had better do something well.  The Aero ED is a nice compromise on size and weight by comparison.  The military eyepiece show how far premium eyepieces have come over the last 50 years.

The Meade 5000 Plossl while sharp in the center is a bit of a disappointment further out.  The 5000 SWA is a keeper showing a nice sharp field nearly from edge to edge.

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  • 1 year later...

Reposting detailed description from another thread of how I captured these images so I can find it more easily in the future:

  1. I taped some rulers and yardsticks together on their back sides with packing tape and then wedged them under the edge of one of my kitchen cabinets, but hanging off to the side.  I always align the 17 inch yardstick mark with the edge of the door for consistency.  I turn on every light in the kitchen/dinette area and open all the blinds to maximize the available light.
  2. I put my AstroTech 72ED telescope on its leveled alt-az mount at the other end of our rather open plan house, about 35 feet away and close to level with the yardstick and close to perpendicular with it.
  3. I put a 2" GSO dielectric diagonal in the focuser with a TSFLAT2 field flattener spaced 15mm in front of the diagonal body on the scope side.  This pretty effectively flattens the otherwise severely curved focal plane of the scope.  Luckily, I don't need to add any extension tubes to reach focus, unlike when I try this with a 127mm Synta Mak.
  4. I put each eyepiece in the diagonal and focus the image with my eyeglasses on so the afocal image is focused close to infinity for the camera.  This allows the field stop to be at its sharpest if it was correctly positioned during assembly and allows the camera to focus at infinity.
  5. I then center the yardstick in the field of view and lock the altitude clutch.  Next, I nudge the mount left/right to put the edge of the ruler at the edge of the visible field stop, or at least the edge of the field for those without field stops.  This can be a judgement call for eyepieces that use the barrel for the field edge as the edge will fuzz out.  Also, you can move your eye off center and see more of the field with them by peeking "around the corner" of them, so to speak.  That's why some don't show the edge when the camera is centered.  I'll sometimes take an image with the camera way off to the edge looking at the other edge at an angle to get a clearer image of this effect, just like your eye would be doing in this situation.
  6. I use the high resolution, normal wide angle rear facing cell phone camera for most of my images.  In my case, a Galaxy S7.  I cup my thumb and forefinger around the top of the eyepiece to make a landing pad for the phone.  I start well away from the eyepiece and move the camera in toward the afocal image using the screen to guide my movements.  It's important to keep the camera level and centered.  That's where your thumb and forefinger come into play.  With practice, you can get it down to a fraction of a millimeter.  You can roll your fingers get fine height adjustment.  I've tried using adjustable height eye cups on eyepieces that have them to do this, but I couldn't get them to work very well.
  7. Now, you have to move the camera phone in and out until the edge of field or field stop just pops into view.  You're at the correct exit pupil distance for that camera at that point.  Any further out, and you miss some of the field.  Any closer, and you start to get blackouts.  If there is spherical aberration of the exit pupil (SAEP or kidney-beaning), you're going to be fighting a dark shadow all around the field.  If you are perfectly centered, you will get a dark circle with a bright center and a bright edge ring.  This cannot be helped as it a defect of the eyepiece and not the camera or scope.  In this situation, you may need to turn down exposure to -1.5 to -2 to avoid the autoexposure circuit trying to make the shadow 18% gray while blowing out the bright areas.
  8. Make sure to use the camera's diagonal to get the widest image possible for super wide angle and wider eyepieces.  You'll have to rotate the image in image processing software later.
  9. I then proceed to take a series of 3 to 5 images to later pick out the best of the bunch on a large computer screen.  I've found that it's impossible to critically judge these images on the phone's screen.
  10. I then take an angled image of the edge for super wide angle or wider eyepieces since the edge of field of even the best camera lenses is not as well corrected as the center.  It may also be cropped off for ultra wide field and wider eyepieces, so this is a necessity for them.
  11. If your phone has an ultra wide angle camera, use it to take all-at-once images of ultra wide field and wider eyepieces.  I bought a second hand LG G5 phone for $25 off ebay just for its ultra wide angle camera since my S7 doesn't have one.  That's what I use to take my "full view" images.  I scale them up to match the scale in the center 20% of the S7 images.  Differences in angular magnification across each camera's field of view accounts for the slight width difference in the final images when using the same eyepiece.  Unfortunately, the G5's a 5 megapixel camera compared to the 12 megapixel S7 camera.  When combined with the smaller image scale, these "full view" images are pretty low resolution by comparison.  I'd love to acquire a 24 megapixel or higher ultra wide camera for this purpose.  Anyone know of used ones that sell for cheap on ebay?
  12. In post-processing, I do not do any exposure adjustments or sharpening.  I just rotate and flip them to be more readable.  I also crop and composite them for comparison images.
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On 04/10/2019 at 06:16, Ruud said:

Louis, what an effort this must have been and what a great result you have here!

I have a question regarding kidney beaning.  Do you still have EXIF information for the images? It would allow calculating the entrance pupil (= camera lens effective aperture, "focal length / focal ratio used for the picture") for each photograph. Most of us use our astronomical eyepieces with observer pupils of around 5 mm or larger.

For an observer, a messy exit pupil causes kidney beaning mainly when the pupil of the observer is only slightly wider than the exit pupil of the eyepiece. Especially the Nagler T4 12 mm and the Meade 4K UWA 14mm both show severe kidney beaning in the second of the two images you post for each, which may have been caused by an entrance pupil that is only slightly wider than the exit pupils of the eyepieces. In that case, even the mildest SAEP would show as kidney beans. That being said, both of the first images for each of these eyepieces also show kidney beaning, though very much milder. I wonder how big the exit pupils of these eyepieces and the entrance pupils of the camera lens were for these four shots.

The Nagler T4 12mm and Meade 4K UWA 14mm may indeed have particularly messy exit pupils. I actually tried the NT4 12mm in a bright daylight test. From the dealer's shop it showed a strong tendency to kidney beaning so I decided against it. My pupil must have been pretty small at the time, but since it is also small when I observe the Moon I thought this eyepiece was not for me.

Thanks for the thread. I think it is epic and deserves to get pinned.

 

 

I've used nearly all of the eyepieces in question and found the same results at the telescope as his photos, i.e. SAEP in some of them, out of focus images at the edge of the field, astigmatism, etc.

Some of the eyepieces are so bad I wonder why they're being saved.

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On 04/10/2019 at 08:09, Louis D said:

How about some discussion of the results?

I'm surprised by just how good today's step-up 60 degree eyepieces are relative to premium eyepieces from 12mm on down.  The HD-60 and Paradigm eyepieces are very good across their fields.  I was a bit disappointed with the field curvature of the 12mm Pentax XF by comparison.  I'll have to see if it has superior polish under the stars allowing for better contrast and dimmer details to be picked out to atone for its edge issues.

THE XF HAS A LOT OF LIGHT SCATTER INTERNALLY AS WELL.

I just can't get over how much SAEP some eyepieces have.  I always knew I had issues with some of them even with fully dilated pupils.  They're definitely easier to use under those conditions, but they're still fussy.

The AstroTech AF70 eyepieces are quite good for 70 degree eyepieces if you're on a budget and can pick them up used for a good price.

ALSO AVAILABLE AS ASTROMANIA, OMEGON, OLIVON, ETC--SEVERAL LABELS STILL AROUND.

The older Konig and Erfle wide angles are very sharp in the center, but fall off rapidly toward the edges.  They really make you appreciate modern wide angle eyepieces.

FOR SURE--MANY HAVE SEVERE EDGE OF FIELD ASTIGMATISM, EVEN AT F/10.

Those generic Kellners, the RKE, Plossls, and the zooms are really pretty good, all things considered.  Even the $10 Aspheric is decent.  The same can't be said of the reversed Kellner.  Thus, there are some good budget choices out there if you know what to look for.

Televue eyepieces are sharp across the field if you can get past the SAEP of some of them.  Only the 22mm Nagler is in my A-Team case, though.  The rest have been ousted by newer, better designs.

IT HAS BE EVOLUTIONARY WITH TELEVUE: NEWER DESIGNS LIKE ETHOS AND DELITES ARE TRULY BETTER THAN SOME OF THE EARLIER EFFORTS.  I'M WITH YOU ON THE 22MM, THOUGH.

ES-92 eyepieces are phenomenal eyepieces.  Given their size and price, they'd better be.  They ousted my 12mm and 17mm NT4s from my A-Team case.

IF ONLY THEY WEREN'T SO PORKY.  BOTH EXCEED A KILOGRAM.

The Speers-Waler zoom is very sharp across the field.  Again, if you can live with the SAEP (which I find mild in use).

THERE IS A SPEERS-WALER SERIES 4.  THESE NEED TO BE TESTED BY SOMEONE........

The Morpheus eyepieces are very sharp across the field.  The 7mm Pentax XW is rather disappointing by comparison.  I may get the 6.5mm Morpheus the next time it goes on sale.

I'M WITH YOU ON THAT, THOUGH THE DECREASED EYE RELIEF OF THE 6.5MM AND 4.5MM MAKE THEM NOT GLASSES FRIENDLY.  WITH THE SMALL EXIT PUPILS LIKELY TO RESULT, THAT MIGHT ALLOW GLASSES TO BE REMOVED.

The Meade MA Astrometric is no replacement for the Celestron Ortho Astrometric.  The former is not sharp across the field.  What good is a wider field if it isn't sharp in a measurement eyepiece?

THAT WOULD BE MY COMMENT AS WELL.

The 15mm and up HD-60s and Paradigms are definitely not the in premium eyepiece category, but by comparison to Konigs and Erfles, they're not all that bad.  Again, they're good budget buys, just not great budget buys like the 12mm and below versions.

THAT WAS MY IMPRESSION AS WELL.

The 24mm APM UFF is a bit of a disappointment given its size, price, and hype.  The 30mm APM UFF really does live up to the hype by comparison.  It ousted my venerable 27mm Panoptic from its spot in my A-Team case.

THE 24MM IS A DIFFERENT DESIGN, AND FAIRLY GOOD IN A COMA-CORRECTED AND FIELD FLATTENED SCOPE.  IT ISN'T ON THE LEVEL OF A 24MM PANOPTIC, BUT IT IS GLASSES-FRIENDLY.

The 30mm Kasai Super Wide View, which was their $400+ copy of the 30mm Leitz Super Wide, is just awful by any measure.  It's not even as good or wide as the $50 Rini MPL.  The Agena UWA looks very usable by comparison.  Under the stars, I find the Agena UWA very sharp in the center 50% and very easy to hold the view with eyeglasses.  It just suffers from massive field curvature and some edge astigmatism.  The ES-82 is slightly less sharp in the center (compare the barcodes between the two).  Of course, it is very nearly sharp to the edge, just suffering from chromatism out there.

I ALSO NOTE A LOT OF EDGE OF FIELD ASTIGMATISM AND LIGHT SCATTER IN THE ES 30MM 82°--SOMETHING NOTED IN THE FIELD.

The Scopos is a real keeper.  It is very sharp in the center and holds most of that sharpness to the edge.  It is a huge and heavy eyepiece, so it had better do something well.  The Aero ED is a nice compromise on size and weight by comparison.  The military eyepiece show how far premium eyepieces have come over the last 50 years.

I THINK THE SCOPOS WAS DISCONTINUED BECAUSE OF WEIGHT AND PRICE, NOT BECAUSE OF THE IMAGE QUALITY.

The Meade 5000 Plossl while sharp in the center is a bit of a disappointment further out.  The 5000 SWA is a keeper showing a nice sharp field nearly from edge to edge.

YES, MEADE PUSHED THE FIELD TOO FAR.  THE S5000 PLOSSL WOULD HAVE BEEN A FINE 50° EYEPIECE.  THE S5000 SWA IS A CLOSE COPY OF A PANOPTIC, AND PERFORMS LIKE THE CURRENT ES 68°.

QUITE AN EFFORT.  WHEN THIS PANDEMIC THING IS IN THE PAST, IT WOULD BE GREAT TO EXTEND YOUR PIX TO A LOT OF NEWER EYEPIECES AS WELL.  PERHAPS WITH LOANERS FROM FRIENDS.

I FIND IT VALIDATING THE PICTURE RESULTS MATCH MY FIELD IMPRESSIONS.  THE CAMERA AND THE EYE MUST NOT BE TOO DIFFERENT IN THAT REGARD.

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3 hours ago, Don Pensack said:

Some of the eyepieces are so bad I wonder why they're being saved.

Because the return on trying to sell them is so much less than keeping them around for reference purposes.  The only exceptions I can think of right off hand are the 12mm/17mm Naglers and 27mm Panoptic.  Those are tying up over $700 of funds.  I'm thinking of donating them to my daughter someday if her interest in astronomy grows more.

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3 hours ago, Don Pensack said:

THERE IS A SPEERS-WALER SERIES 4.  THESE NEED TO BE TESTED BY SOMEONE........

Only if they had at least 18mm of usable eye relief.

I am toying with the idea of getting a 40mm Pentax XW for Christmas at the current sale price.  I'd mostly be comparing it to my decloaked 40mm Meade 5000 SWA.  What do you think, @Don Pensack, should I do it?  Worst case, I figure I can resell it for $500 or more in 5 to 10 years once they're discontinued and become sought after on the secondary market again. 😁  After all, I only paid $125 for my 40mm Meade SWA in 2012 or thereabouts and could probably get around $150 for it today.  With inflation, I'd at least be close to breaking even.

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4 hours ago, Don Pensack said:

I FIND IT VALIDATING THE PICTURE RESULTS MATCH MY FIELD IMPRESSIONS.  THE CAMERA AND THE EYE MUST NOT BE TOO DIFFERENT IN THAT REGARD.

Look at the size of the taking lens on most cell phone cameras.  They're very similar in size to the human eye and react very similarly to eyepiece exit pupils.  Once I realized this, I decided to embark on my AFOV imaging odyssey.

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