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Televue 32mm Plossl - Dissapointed


Alan White

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On 06/07/2020 at 14:11, jetstream said:

Does this design show its a pair of symmetric doublets?

Yes it does Gerry, if you check the labelling then the radii, thickness and the other specs of each pair appear the same.

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On 06/07/2020 at 22:35, Highburymark said:

For ha solar, they are unquestionably the finest plossl. Substantially brighter and more detailed than Synta/GSO Plossls. Very similar views to Fujiyama orthos (on solar), but again I marginally prefer TV Plossls. I’ve never actually used any of my TV Plossls for normal night viewing

That’s good to know Mark. I currently use Celestron Omni Plossls in my PST mod, but if moving back to TV Plossls would help them I would certainly do that at some point.

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5 hours ago, Stu said:

That’s good to know Mark. I currently use Celestron Omni Plossls in my PST mod, but if moving back to TV Plossls would help them I would certainly do that at some point.

The Celestron Omnis are terrific Stu. I keep a 32mm as a finder eyepiece when travelling - and great value - think it was £32 a couple of years ago. Just a step below the TVs in transmission and sharpness. Can you use your 25mm Zeiss microscope orthos with the PST mod? 
 

Interesting discussion elsewhere in this thread about what constitutes a plossl and what doesn’t. From the images posted earlier, is it right to conclude that the true plossl design is asymmetric, and the TV patent symmetric? 

 

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1 hour ago, Highburymark said:

Interesting discussion elsewhere in this thread about what constitutes a plossl and what doesn’t. From the images posted earlier, is it right to conclude that the true plossl design is asymmetric, and the TV patent symmetric? 

More or less, the original Plossl design was asymmetric while the current usage has mostly come to refer to symmetric designs.  I saw mostly because there are the 5 element "super" Plossls out there that are even more remotely related to the original Plossl design.  Meade marketed a line of 60 degree, 5 (and in one case, 6) element Plossls (their 5000 series) a few years back just to muddy the Plossl waters even further.

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1 hour ago, Highburymark said:

Can you use your 25mm Zeiss microscope orthos with the PST mod? 

On a good day I may be able to but I normally find that the 32mm are the max magnification because I use a barlow to reach focus with my binoviewers. I also have a pair of 40mm which I use when the seeing won’t co-operate.

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There is info out there to help with picking which distortion and how much of it you can live with. I dislike a lot of pincushion distortion for some viewing and this may explain my choices. I tend to shy away from pincushion for all except widefield nebula viewing.

http://www.holgermerlitz.de/globe/test_distortion.html

http://www.holgermerlitz.de/globe/distortion.html

                                           ^^

"This indicates that the amount of distortion generated by the human vision might differ from individual to individual. "

An example:

helmholtz_bs.gif

eye_k05.gif

Edited by jetstream
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On 07/07/2020 at 18:53, jetstream said:

The Docter shows less distortion than some of my Abbe orthos....and much less than most TV's- at least to my eyes and the TV's I've tried. It might be my eyes and the type of distortion.

You are only referring to rectilinear distortion (e.g. pincushion), which the Docter has almost none of.

On the other hand, it has a LOT of angular magnification distortion.

If you looked at a billboard letter and moved it from the center of the field to the edge, it would not bend, but it would shrink substantially.

That is not the distortion you are looking at and it is hard to see in a star field.  But you would see it easily while panning across the Moon.

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9 hours ago, jetstream said:

There is info out there to help with picking which distortion and how much of it you can live with. I dislike a lot of pincushion distortion for some viewing and this may explain my choices. I tend to shy away from pincushion for all except widefield nebula viewing.

http://www.holgermerlitz.de/globe/test_distortion.html

http://www.holgermerlitz.de/globe/distortion.html

                                           ^^

"This indicates that the amount of distortion generated by the human vision might differ from individual to individual. "

An example:

helmholtz_bs.gif

eye_k05.gif

And it is just that globe distortion (AMD) the Docter eyepiece has in abundance.  Between that and the pincushion form of rectilinear distortion, I'll take RD any day.

That article explains distortion very well, by the way.

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6 hours ago, Don Pensack said:

You are only referring to rectilinear distortion (e.g. pincushion), which the Docter has almost none of.

On the other hand, it has a LOT of angular magnification distortion.

What Holger seems to indicate in his research is that distortion IS viewer dependent eventhough the distortion in the optic is obviously a "fixed" amount for each eyepiece design.

I personally see less distortion in the Docter (in the form of barrel distortion)- than in eyepieces with an abundance of pincushion ie Ethos. Yes I can see 2 close stars get a bit closer near the edge of the Docter but I like this much better than having the moon "egg out" in my Ethos at the edge. I see no "rolling ball" or golbe effect in the Docter.

The Docter is an extremely "sharp" eyepiece, with high transmission (to my eyes).

Question: did APM clone the Docter 12.5mm UWA somewhat with their 12.5mm 84 deg?

https://www.apm-telescopes.de/en/eyepieces/more-74-ultra-wide-angle/apm-lunt-eyepieces/apm-high-eyerelief-flat-wide-84-degree-12.5-mm-eyepiece.html

APM-Hi-FW125_totale.jpg

 

"31 - Design based on the published configuration for APM "Ultraflat" 84° eyepiece (originally 12.5mm f.l.) with no other data. It also turned out to be a viable configuration, with a very good correction over the entire, flat field, and long eye relief"

                                                                   

Edited by jetstream
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"28 - Fukumoto 100° eyepiece (the 1st of 5 examples in the patent application) is a basis of the Nikon NAV-HW ultrawide (7/10 arrangement). There is obvious similarity in the general configuration with the Ethos, but it is also a design with its own characteristics, such as more complex Smyth lens, and near non-existent spherical aberration of exit pupil.
29, 30 - Another Fukumoto-Nikon design from the same time frame is 82° AFOV design with a very complex Smyth lens and relatively simple positive counterpart. Five of the six examples in the patent application do not feature the front two singlets; most have similar edge performance as the one shown here, but somewhat more astigmatism in the inner field. Reduction in the overall size is very obvious. Subsequent 2015 Fukumoto-Nikon patent expands the field of this eyepiece type to 100°. Patented version shown (the preferred one, out of five) shows very good correction up to 45°, or so, and the astigmatism flare up toward field edge doesn't show on the astigmatism graph in the patent application. Since a small change in one of the radii (R8, box to the right) nearly brings it to where it should be, there is probably a typo in the patent prescription.

31 - Design based on the published configuration for APM "Ultraflat" 84° eyepiece (originally 12.5mm f.l.) with no other data. It also turned out to be a viable configuration, with a very good correction over the entire, flat field, and long eye relief."

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1 hour ago, jetstream said:

Yes I can see 2 close stars get a bit closer near the edge of the Docter but I like this much better than having the moon "egg out" in my Ethos at the edge.

Doesn't the moon get tangentially flattened in the Docter at the edge (like it's squished up against the field stop)?  I see that in the Meade MWA 26mm.  Both forms of distortion are unfortunate but unavoidable in UWAs.  Perhaps the "egg" distortion is worse on the moon aesthetically.

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1 hour ago, Louis D said:

Doesn't the moon get tangentially flattened in the Docter at the edge (like it's squished up against the field stop)?  I see that in the Meade MWA 26mm.  Both forms of distortion are unfortunate but unavoidable in UWAs.  Perhaps the "egg" distortion is worse on the moon aesthetically.

Personally I find the Docs AMD minor but again maybe its the interaction of the eyepieces design AMD and my eye/brain. No I don't see the moon getting "squashed" lol!

Years ago I tested every eyepiece I own for distortion- wrote it all down, comparisons etc, it was enlightening but I threw the list out and now just enjoy my shortlisted eyepieces.

BTW, there is more pincushion in many EPs than there is AMD in the Doc- to my eyes. Interestingly enough there are a few sets of eyes that report the same.

Edited by jetstream
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2 hours ago, jetstream said:

What Holger seems to indicate in his research is that distortion IS viewer dependent even though the distortion in the optic is obviously a "fixed" amount for each eyepiece design.

I personally see less distortion in the Docter (in the form of barrel distortion)- than in eyepieces with an abundance of pincushion ie Ethos. Yes I can see 2 close stars get a bit closer near the edge of the Docter but I like this much better than having the moon "egg out" in my Ethos at the edge. I see no "rolling ball" or globe effect in the Docter.

The Docter is an extremely "sharp" eyepiece, with high transmission (to my eyes).

Question: did APM clone the Docter 12.5mm UWA somewhat with their 12.5mm 84 deg?

https://www.apm-telescopes.de/en/eyepieces/more-74-ultra-wide-angle/apm-lunt-eyepieces/apm-high-eyerelief-flat-wide-84-degree-12.5-mm-eyepiece.html

APM-Hi-FW125_totale.jpg

 

"31 - Design based on the published configuration for APM "Ultraflat" 84° eyepiece (originally 12.5mm f.l.) with no other data. It also turned out to be a viable configuration, with a very good correction over the entire, flat field, and long eye relief"

                                                                   

With different number of lenses, different field stop diameters, different eye relief, different eyepiece diameters, different eye and field lens diameters, and different % of geometric field distortion, I would say no, the APM is not a clone of the Docter/Noblex.  Just similar in that it is an ultrawide with long eye relief.

As for visibility of the angular magnification distortion, it depends on whether the scope tracks and how wide the true field is in the scope.  I found the Docter intolerable in my dob, but it worked fine in a tracking SCT.

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14 minutes ago, Don Pensack said:

With different number of lenses, different field stop diameters, different eye relief, different eyepiece diameters, different eye and field lens diameters, and different % of geometric field distortion, I would say no, the APM is not a clone of the Docter/Noblex.  Just similar in that it is an ultrawide with long eye relief.

As for visibility of the angular magnification distortion, it depends on whether the scope tracks and how wide the true field is in the scope.  I found the Docter intolerable in my dob, but it worked fine in a tracking SCT.

Hi Don, I've often wondered about the APM vs the Docter. Have you done an on axis comparison between the TV plossl, Delos and the APM? Would be interested to hear how the APM stacks up against these.

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4 minutes ago, markse68 said:

Were does one find a Highly-Orthoscopic eyepiece (number 9)- is it just theoretical or were (are) they made by anyone?

Out of production now but Takahashi used to do a 2.8mm and 4mm Hi-Or which might be that design ?:

ヤフオク! - 高橋製作所 タカハシ Hi-Or 4mm TAKAHASHI

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18 minutes ago, John said:

Out of production now but Takahashi used to do a 2.8mm and 4mm Hi-Or which might be that design ?:

ヤフオク! - 高橋製作所 タカハシ Hi-Or 4mm TAKAHASHI

Just found this that says the Tak Hi-Ortho was a high eyepoint ortho acheived by basically barlowing a longer fl ortho so not the H-ortho referred to in Gerry's diagram I think John

https://www.cloudynights.com/articles/cat/user-reviews/eyepieces/eyepieces-3mm-13mm/takahashi-28mm-hi-ortho-r329

Edited by markse68
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6 hours ago, Littleguy80 said:

Hi Don, I've often wondered about the APM vs the Docter. Have you done an on axis comparison between the TV plossl, Delos and the APM? Would be interested to hear how the APM stacks up against these.

Axial sharpness varies on paper, but not actually that much in the field.

When the seeing is really superb, ALL eyepieces do well on axis.  When the seeing is bad, all eyepieces do poorly.

The eyepiece differences on axis are the residual 0.01% after seeing conditions are concerned.

I found the APM excellent on axis and for nearly the entire field in a coma-corrected f/5 12.5" dob.

Since I used it with glasses, my complaint wasn't the eyepiece, but the fact the frame of my glasses was visible in my peripheral vision inside the field of view.  Think about it--do you have to lift your eye 42° to see over the frame of your glasses?

For me, maybe 30°, which is why I don't notice the frames of my glasses with a 62° eyepiece.  The 11mm Apollo had a sharper outer field but the difference was slight.

My next outing, I'm going to specifically look for the edge of field brightening some have reported.  I didn't see it the last time I was in the field, but I was doing an evaluation of several other eyepieces, so this one didn't spend that long in the focuser.  I haven't owned or used a Plössl since the early '90s.  My last long experience with the Delos was when they came out (not sure the year), and they struck me as being long eye relief, slightly narrower field, Ethos.  I wasn't wearing glasses for eyepieces back then.  Even today, I don't really need glasses at all below 12mm.  

Whether glasses are needed for the best images has an easy test: defocus the star on one side of focus and do the same on the other.  Do you see any ovality to the ON-AXIS star image?  They you could benefit from glasses.

I can see very slight astigmatism that way down to a 4.7mm eyepiece, but the stars are sharp enough in focus at 11-12mm.  And when I wear glasses?  Stars are completely round out of focus in both directions all the way up to a 30mm focal length.

The absence of astigmatism is a marvelous thing--if the apparent field is not larger than your glasses.  My next observing pair need to be those over-sized '80s glasses that hit my cheek on the bottom and extend well above the eyebrow on the other. 😀

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15 hours ago, Don Pensack said:

When the seeing is really superb, ALL eyepieces do well on axis.  When the seeing is bad, all eyepieces do poorly.

It is my experience that excellent seeing shows up the differences in eyepieces more than anything else. It is under these conditions that I rate my eyepieces and there are differences in on axis sharpness between some of the "top" contenders.

Obviously vg optics are needed for a discriminating test and ones that are in good collimation. After noticing differences in the 15" dob, I checked all again in the TSA120 which is as close to a perfect optic I'll ever own and the differences remain.

Is it possible that those who don't see the differences don;t have the eyes to see them?

Don, do you see differences in sharpness between the Nagler 3-6 zoom vs the Vixen 3.4mm HR?

Edited by jetstream
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Yes, I see the difference.  But it's more of a contrast difference than a sharpness difference.  Star images on axis in both are the Airy disc with a single diffraction ring.

But I don't use eyepieces that narrow.  The narrowest I go is the 62° of the Delites.  And the 3mm Delite is super sharp--it's my go-to moon eyepiece in the 4" apo.

But back to the 2 eyepieces you mention: the difference in sharpness on axis between the two is less than the seeing fluctuations of the atmosphere from minute to minute.

It's not like one is going to prevent you from seeing something the other one sees.  The difference is not profound.  And the Zoom can handle variations in seeing easily without changing eyepieces.

In the 12.5", my high power planetary (and planetaries) eyepiece is the 3.7mm Ethos SX.  It's a non-tracking scope and I appreciate the longer drift time between nudges.

It takes exceptional seeing to be sharp at 500x, but I've seen it often enough to know the eyepiece is excellent, revealing details on Uranus and Neptune.

 

Edited by Don Pensack
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