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Delite - new Televue 62 deg 7mm, 11mm, 18.2mm


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Alan,

I'm not sure that a f4 scope is in everyone's most wanted list. Besides, even your 18" is slower than f5 with paracorr.

On the other hand, I do see transmission and on-axis sharpness difference in my f10 C8, which is why my BSTs found new home.

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Yong,

It was without Paracorr where as the Panoptic didn't look at all bad, just slight coma at the edges but 85% was superb, that could not be said for the Meade. With the PC in place it was better as the coma had gone but by then the TV was sharp across the whole FOV. I can see differences between eyepieces at F10 but don't forget I am really looking for them, if I were not they are very good eyepieces at this speed. In most of the work I have done, which runs into hundreds of scope hours, the differences are always small but for me it is worth the extra outlay to have that clean view, the sole reason I bought a Paracorr.

Alan.

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Alan,

Astigmatism grows proportional to the inverse of focal ratio, while coma grows proportional to the SQUARE of inverse of focal ratio, comparing a f5 scope to a f4.5 scope, f4.5 scope should show 11% more astigmatism, 23% more coma, of the same eyepiece. Your eye seem to acommadate coma better than astigmatism, good for you. :smiley:

As to transmission and on-axis sharpness, I have looked for details in galaxies and nebulae, which needs some hours to do too, using difference focal length eyepiece to bracket an eyepiece is an easy tell to find out transmission difference e.g.

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Yong,

A little off subject but I find BGO orthos really are hard to beat for pure transmission as well as scatter, Delos seem very good too though I am not a big galaxy fan but have been looking a bit more of late with the larger scope, the trouble with this scope and the afore mentioned eyepieces is having to nudge every few seconds. The real reason I made the comment about the new TV De-lite, I am sure if it ticks all the right boxes for ortho type planetary qualities the sales will take off from the Dob Mob alone. Lets face it we are not far from wide field orthos with short Pentax XW's and Delos so I really hope these makes further inroads.

alan

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Hi Alan,

Reference to the BST's somewhat tounge in cheek, but why produce an ep with a 62deg fov????

Damian,

I think to really answer that question we really need to see what they bring to the table. If though it is ortho equalling performance at a 62 dergee FOV then they will fly off the shelf.

The only other thing I can think of is the Radian had a 60 degree FOV and they were sort of forced to stop making them due to glass shortage, so they could be an even better replacement, in short we have to wait any see because outside of the TV factory in the words of SPM "we simply don't know", I'm going to have to buy one now.

Alan

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Alan,

I totally understand your point about nudging a big dob :smiley: . Therefore a tracking platform is of great help in my mind.

More glasses in eyepieces doesn't necessary mean worse transmission, there're many more other factors.  Ethos, Delos, Naglers, etc, with many glasses have all proven to be excellent faint fussy hunters.

As I have OCD about eyepiece weight and size, Delite is surely a welcome development from Televue.

PS. I dont quite see explanation for Radian, sure they use Lanthanum, but Vixen LVWs use it too, and it has never been a problem for Vixen's production.

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Alan,

Astigmatism grows proportional to the inverse of focal ratio, while coma grows proportional to the SQUARE of inverse of focal ratio, comparing a f5 scope to a f4.5 scope, f4.5 scope should show 11% more astigmatism, 23% more coma, of the same eyepiece. Your eye seem to acommadate coma better than astigmatism, good for you. :smiley:

As to transmission and on-axis sharpness, I have looked for details in galaxies and nebulae, which needs some hours to do too, using difference focal length eyepiece to bracket an eyepiece is an easy tell to find out transmission difference e.g.

Astigmatism also grows with the square of the FOV angle, so is much harder to control. We are also talking about two different issues: coma from the objective (mainly, there may be some astigmatism too, but the angles are too small to show it) and astigmatism (mainly, there is bound to be some coma too) in the EP.

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Michael,

you're right about astigmatism grows square of the FOV angle, because it grows linearly off axis. Since coma grows linearly off axis too, it grows cubic of the FOV angle consequently. That's what I've understand about astigmatism and coma, if I've not missread it.

Yes, they are from different sources, but for an observer behind an eyepiece, they are aberrations nonetheless. Since we all have different preferences (minimum astigmatism, long eye relief, wide FOV, transmission, etc) and prerequisites (can or want to spend money), we make different choices (long focal scope to get minimum aberrations, paracorr to correct coma, accept aberration to some degree etc), to overcome the issues, which is great as we have quite good range of stuffs to choose from, the most important thing is to enjoy the beauty of night sky. :smiley:

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For planetary work, which I assume is the main purpose of this eyepiece, a bit of distortion doesn't matter. As long as it's sharp and contrasty ;)

Once we get some good reviews I'm going to be looking hard at that 11mm.

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I wonder if trying to judge the quality of an eyepiece using an image of a dollar bill viewed through it, taken with a camera of unknown type, streamed on the web, viewed via Youtube, from footage taken at a daytime equipment show is really going to tell us much ? :smiley:

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For planetary work, which I assume is the main purpose of this eyepiece, a bit of distortion doesn't matter. As long as it's sharp and contrasty ;)

Once we get some good reviews I'm going to be looking hard at that 11mm.

True, but orthoscopics get their name from lack of distortion and they are very sharp. It's just that their eye relief doesn't suit me

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I wonder if trying to judge the quality of an eyepiece using an image of a dollar bill viewed through it, taken with a camera of unknown type, streamed on the web, viewed via Youtube, from footage taken at a daytime equipment show is really going to tell us much ? :smiley:

Absolutely. The camera itself may be introducing the pincushion distortion

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To my eyes, that's just the correct pincushion in Televue eyepiece.

Any eyepiece with FOV wider than Abbe ortho's 42-44 degrees will have either Angular Magnification distortion(AMD) or Rectilear Distortion(RD, i.e. barrel distortion or pincushion distortion), because AMD and RD can't be corrected at the same time with wider FOV.  if you decrease AMD, RD will increase, and vise versa. The wider FOV of an eyepiece, the more distortion will be present.

 An eyepiece with AMD will show straight lines in edge, but with small distances between the lines near edge than on axis, sort of looking at telephone posts. Televue's view is that RD is better for astronimical eyepieces because it keeps the star distances the same in the edge(with distorted orientation of course), therefore their eyepieces have zero AMD, consequenly more RD.

Aslo Televue eyepieces have goal to minimize astigmatism, with only spherical lens, the possible trade off  are: having field curvature, increased spherical exit pupil aberration or increased RD. Since TV would like to keep  flat field, hence having field curvature in eyepieces are out of question for them, and increasing spherical exit pupil aberration has to be restrained not to cause kidney bean effect, there's only increased RD to minimize astigmatism, a logical trade off.

As a side note, Meade SWA (Maxvision 68 degree eyepieces) are said not having as much pincushion as Panoptic despide of very similar design, the result is slightly more astigmatism and field curvature than Panoptics.

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I told you that they would not measure up for you Russell :smiley:

No John - You incorrectly surmised what might measure up for me.

I've long since learned to take anything anybody "tells" me with a pinch of salt. I've often found other's opinions to be based on their expectations, rather than mine, so I'm happy to spend my money and make up my own mind.

On that basis, I restate: TV Delos and Plossls have quite a lot of AMD, as abbreviated by Yong above. There is no harm in this being stated and it does not affect my expectations. It does mean that Dob users who like a planet to drift across the field of view will notice that it changes shape as it approaches the field stop, but on the flip side, your oblate planet will remain very sharp. It's up to others to choose if that balance matches up to their expectations.

I expect the Delites will perform better than Delos, because they lopped off 10deg AFOV. This is not unexpected, because when Baader did the reverse increased the AFOV of their famously orthoscopic Orthos, it simply revealed all the stuff that Orthos hide behind the field stop to remain, err? Orhtoscopic.

As it stands, for their/my purposes, the TV Plossls are doing very nicely because I 'expected' to want them to preform on axis.

Russell

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Russell,

Throwing out new abbreviations as I did, risks always mxed-up because unclear explanation. Here's another try:

1. Angular Magnification Distortion(AMD): the straight lines near edges are still straight, i.e. lines in the utmost left and right edges look like  |  |

2. Rectilinear Distortion(RD): there're two types of RDs, pincushion distortion and barrel distortion.

   2.1 pincushion distortion: the straight lines close to edges will be curved inwards, i.e. lines in the outer left and right edges look like  )  (

   2.2 barrel distortion:  the straight lines close to edges will be curved outwards, i.e. lines in the outer left and right edges look like  (  )

As said before, all wide angle eyeepice will have some kind of mixture of AMD and RD, simply because these two distortions cannot be corrected at the same time, and the total amount of distortion is growing with wider FOV,

Another side note: our eyes have minor amount of barrel distortion, so a wide field eyepieces showing straight lines in the edge actually have minor amount of pincuhion distortion, and eyepiece showing pincushion actually have more than seen in out eyes. Holger Melitz' test worth a read in my opnion.

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