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Planetary Eyepieces


bosun21
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1 hour ago, Piero said:

....Regarding the 10mm BCO, my copy bought new was functional but nothing special. Possibly, its low cost is due to poor QA?

I have seen evidence of QA errors in a new Baader Genuine Ortho that was sent to me for testing. The issue there I think was that the lens groups were touching in the centre due, I suppose, to an incorrect spacer or similar. It took me quite a while to work out why the view was sharp everywhere in the FoV apart from a small area right in the centre of the field where it went decidedly mushy as a target passed through it.

So it does happen.

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39 minutes ago, John said:

I have seen evidence of QA errors in a new Baader Genuine Ortho that was sent to me for testing. The issue there I think was that the lens groups were touching in the centre due, I suppose, to an incorrect spacer or similar. It took me quite a while to work out why the view was sharp everywhere in the FoV apart from a small area right in the centre of the field where it went decidedly mushy as a target passed through it.

So it does happen.

That's interesting, John.

My copy was fine on-axis and showed a bit of chromatic aberration near the edge. The eyepiece was completely functional to my eye. Having said this, the delivered view was okay / good, but not something that I would have called "impressive". In other words, it was not an eyepiece I would have kept.. and in fact, I let it go! 🙄

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26 minutes ago, Piero said:

That's interesting, John.

My copy was fine on-axis and showed a bit of chromatic aberration near the edge. The eyepiece was completely functional to my eye. Having said this, the delivered view was okay / good, but not something that I would have called "impressive". In other words, it was not an eyepiece I would have kept.. and in fact, I let it go! 🙄

I think it was the folks in the USA using their very large scopes under dark skies that found the Baader Classic 10mm such a good performer on small DSO's. They placed theirs somewhere between the Zeiss ZAO 10mm and the Delos 10mm in terms of ability at that task.

I guess some quality variability in complex products is inevitable even with the best brands.

Academic really - it looks like the OP has gone for another option and I hope that works out well  :smiley:

 

 

Edited by John
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8 minutes ago, John said:

I think it was the folks in the USA using their very large scopes under dark skies that found the Baader Classic 10mm such a good performer on small DSO's. They placed theirs somewhere between the Zeiss ZAO 10mm and the Delos 10mm in terms of ability at that task.

I guess some quality variability in complex products is inevitable even with the best brands.

Academic really - it looks like the OP has gone for another option and I hope that works out well  :smiley:

 

I am aware of that plot in Alvin Huey's website. It's here: https://www.faintfuzzies.com/AboutUs2.html . I do have some doubts about the validity of it though. In fact, 1) there is no information about the data (and how these were collected!), 2) what is the Y axis ?. As it is that plot seems artificial, if not even speculative. Even after by-passing the row data issue, I am not convinced that differences between eyepieces are "magnified" with aperture as the plot suggests. According to that idea, I should not have noticed any difference between eyepieces with my TV-60, whereas I should start noticing them with my 16". Instead, I saw plenty of eyepiece differences with my TV-60, and the way I can explain this, is because these differences are between 30-150x, far below an average seeing. Therefore, as the telescope was easily operating at its limit, any difference was due to the eyepiece.

In contrast, with fast telescopes of 22" or 30" apertures, a 6mm eyepiece is not even close to the theoretical telescope resolution (~1mm exit pupil), but the delivered magnification is high enough to require almost superb seeing conditions, something which is only rarely met.

Also, those folks observe with ~f4 telescopes without coma corrector. I tried to observe with my 16" f4 without coma corrector for curiosity and the views were degraded nearly on-axis. Now, I don't want to comment on whether a PC2 is required or not in a fast dobson, but my doubts remain: how can one spot substantial differences between eyepieces and spot extremely faint targets in the presence of severe coma like that when details tend to be washed out? And from a theoretical perspective, let's consider the term called `coma free region` which identifies the region where the introduced coma is smaller than the Airy disc. This region is tiny at f4 (e.g. 0.022mm x f/ratio^3 ) and is generally defined on the Rayleigh criterion. If one is assessing top quality eyepieces on threshold targets, it means that s/he is judging way above a Strehl of 0.8. Taken this in consideration, the `coma free region` (which is actually just a dot really..) is even smaller.. So.. to me there is something which does not work quite right there.. 

 

Regarding transmission with modern eyepieces, the only eyepiece which I repeatedly thought it had more transmission than the others is the Vixen HR. Having compared the 2.4mm against a Vixen SLV 5mm with my TV-60, it was quite obvious to see that the image in the HR was almost as bright as the image in the SVL despite half focal length of the former eyepiece. This was also quite striking considering the short exit pupil of the 2.4mm ep using a 60mm refractor (150x). Apart from that standalone case, the other eyepieces I compared showed a noticeable difference in contrast, not transmission to my eye (for instance, both the Docter and the Zeiss zoom show more contrast than the Vixen SLV, Delos, Naglers, Morpheus I've tried).

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32 minutes ago, Piero said:

 

I am aware of that plot in Alvin Huey's website. It's here: https://www.fainthttps://www.backyardastro.org/topic/692-gso-stellalyra-superview/fuzzies.com/AboutUs2.html . I do have some doubts about the validity of it though. In fact, 1) there is no information about the data (and how these were collected!), 2) what is the Y axis ?. As it is that plot seems artificial, if not even speculative. Even after by-passing the row data issue, I am not convinced that differences between eyepieces are "magnified" with aperture as the plot suggests. According to that idea, I should not have noticed any difference between eyepieces with my TV-60, whereas I should start noticing them with my 16". Instead, I saw plenty of eyepiece differences with my TV-60, and the way I can explain this, is because these differences are between 30-150x, far below an average seeing. Therefore, as the telescope was easily operating at its limit, any difference was due to the eyepiece.

In contrast, with fast telescopes of 22" or 30" apertures, a 6mm eyepiece is not even close to the theoretical telescope resolution (~1mm exit pupil), but the delivered magnification is high enough to require almost superb seeing conditions, something which is only rarely met.

Also, those folks observe with ~f4 telescopes without coma corrector. I tried to observe with my 16" f4 without coma corrector for curiosity and the views were degraded nearly on-axis. Now, I don't want to comment on whether a PC2 is required or not in a fast dobson, but my doubts remain: how can one spot substantial differences between eyepieces and spot extremely faint targets in the presence of severe coma like that when details tend to be washed out? And from a theoretical perspective, let's consider the term called `coma free region` which identifies the region where the introduced coma is smaller than the Airy disc. This region is tiny at f4 (e.g. 0.022mm x f/ratio^3 ) and is generally defined on the Rayleigh criterion. If one is assessing top quality eyepieces on threshold targets, it means that s/he is judging way above a Strehl of 0.8. Taken this in consideration, the `coma free region` (which is actually just a dot really..) is even smaller.. So.. to me there is something which does not work quite right there.. 

 

Regarding transmission with modern eyepieces, the only eyepiece which I repeatedly thought it had more transmission than the others is the Vixen HR. Having compared the 2.4mm against a Vixen SLV 5mm with my TV-60, it was quite obvious to see that the image in the HR was almost as bright as the image in the SVL despite half focal length of the former eyepiece. This was also quite striking considering the short exit pupil of the 2.4mm ep using a 60mm refractor (150x). Apart from that standalone case, the other eyepieces I compared showed a noticeable difference in contrast, not transmission to my eye (for instance, both the Docter and the Zeiss zoom show more contrast than the Vixen SLV, Delos, Naglers, Morpheus I've tried).

I didn't take much notice of the plot to be honest. I read their comments in their blogs and thought them positive about the 10mm BCO plus I enjoyed using the eyepiece myself when I've had one.

We each have to find what suits us best though. I don't tend to analyse much - if I like the views consistently and on a range of targets through a few different scopes, I'm happy with the eyepiece :smiley:

Too easily satisfied I guess :rolleyes2:

It sounds like you are a much more critical observer than I am :icon_salut:

 

 

Edited by John
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1 hour ago, Piero said:

spot extremely faint targets in the presence of severe coma like that when details tend to be washed out?

Hi Piero, does f4 level coma make threshold objects invisible outside the coma free area? Will it render detail in small PN invisible in large fast dobs?

1 hour ago, Piero said:

Regarding transmission with modern eyepieces

The Nagler zoom 3-6mm is a "low" transmission eyepiece ie lower than the Delos, orthos etc. My 10mm BCO delivers more transmission than my 10mm Delos with and without a coma corrector.

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2 hours ago, jetstream said:

Hi Piero, does f4 level coma make threshold objects invisible outside the coma free area? Will it render detail in small PN invisible in large fast dobs?

The Nagler zoom 3-6mm is a "low" transmission eyepiece ie lower than the Delos, orthos etc. My 10mm BCO delivers more transmission than my 10mm Delos with and without a coma corrector.

Hi Gerry, coma spreads the light over a much larger surface, and this depends on the focal ratio. A threshold target can simply be invisible due to coma. This is valid unless you call that target "threshold" as observed without a coma corrector, which means that the same target is quite well visible if a coma corrector is added. In an F4, coma is so severe that dim stars can be washed just about half the field of a 70 Deg eyepiece. Stars are point sources, therefore much easier than dim low contrast galaxies.

 

Saying that a Nagler zoom set at 6mm has less transmission than a Delos 6mm means that the image in the former is somehow dimmer than the image in the latter. Given that the design of the former is much simpler, I doubt that. I haven't observed through a Nagler zoom, but I can accept the possibility that it shows less contrast than the Delos 6mm. This would mean that certain faint features can be detectable in the delos, but simply washed out in the zoom. I saw that with a Nagler T6 3.5mm vs Delos 8+PM2.5x: nearly identical image brightness, substantial difference in terms of features when observing details on Jupiter.

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  • 2 weeks later...
On 30/11/2021 at 01:05, jetstream said:

Hi Piero, does f4 level coma make threshold objects invisible outside the coma free area? Will it render detail in small PN invisible in large fast dobs?

The Nagler zoom 3-6mm is a "low" transmission eyepiece ie lower than the Delos, orthos etc. My 10mm BCO delivers more transmission than my 10mm Delos with and without a coma corrector.

Jerry

Can you explain more on the transmission part please ? What does "low" transmission mean ? Does that mean , low contrast features are more easily seen in one than the other?

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12 minutes ago, Voyager 3 said:

Jerry

Can you explain more on the transmission part please ? What does "low" transmission mean ? Does that mean , low contrast features are more easily seen in one than the other?

It does not affect planetary or lunar to my eyes, the NZ 3-6 is a great eyepiece. On faint PN etc I use Delos or orthos which are better for me. Some eyepieces like the 10 BCO, Delos , Docter etc offer both high transmission and great planetary detail.

I like to "cherry pick" eyepieces that offer it all, eventhough the NZ 3-6 is vg in its role , same goes for my Zeiss zoom, razor sharp, high lunar/planetary contrast but lower transmission than the ones mentioned above.

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There have been tests of eyepiece transmission from time to time in the past.

This is rather out of date now but covers a few types:

Eyepiece(1).doc

As Gerry / jetstream says though, this is less critical for planetary / lunar observing.

 

Edited by John
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46 minutes ago, John said:

There have been tests of eyepiece transmission from time to time in the past.

This is rather out of date now but covers a few types:

Eyepiece(1).doc 99.5 kB · 1 download

As Gerry / jetstream says though, this is less critical for planetary / lunar observing.

 

That's an interesting table, John - more variation than I would have expected.

I'd be interested to know how the ES ranges compare. I have an 82° 6.7mm, and while it often exceeds my other EPs for sharpness, contrast and scatter, I do find (or perhaps imagine) that the image is slightly dimmer.  

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6 minutes ago, Zermelo said:

That's an interesting table, John - more variation than I would have expected.

I'd be interested to know how the ES ranges compare. I have an 82° 6.7mm, and while it often exceeds my other EPs for sharpness, contrast and scatter, I do find (or perhaps imagine) that the image is slightly dimmer.  

The french magazine "Ciel et Espace" used to do really detailed and rigorous comparative tests of eyepieces which included an array of optical tests, light throughput tests, spot testing etc, etc. They stopped those some time back unfortunately - perhaps some of the "runners up" brands decided not to play ball any more !

 

 

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1 hour ago, John said:

There have been tests of eyepiece transmission from time to time in the past.

This is rather out of date now but covers a few types:

Eyepiece(1).doc 99.5 kB · 5 downloads

As Gerry / jetstream says though, this is less critical for planetary / lunar observing.

 

It is interesting to note that the so called top tier planetary eyepieces all have better transmissions in the yellow-red region compared to the wide fields . A good exception is the radian , which some swear by for lunar/planetary so nothing to he surprised at . 

This maybe the reason why observers feel that Jupiter/Saturn has better structures with all those orangish-creamy bands, swirls,barges stand out better in the ZAO , Pentax orthos et all .

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26 minutes ago, Voyager 3 said:

It is interesting to note that the so called top tier planetary eyepieces all have better transmissions in the yellow-red region compared to the wide fields . A good exception is the radian , which some swear by for lunar/planetary so nothing to he surprised at . 

This maybe the reason why observers feel that Jupiter/Saturn has better structures with all those orangish-creamy bands, swirls,barges stand out better in the ZAO , Pentax orthos et all .

One thing that I've noticed is that the characteristics of one eyepiece might make it a champion on, say, Jupiter while another is a little better suited to, say, Mars. Of course this could just be an excuse to own a wide range of eyepiece designs at short focal lengths.

Any excuse will do ! :evil: 

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  • 1 month later...

I use my 8 to 24 variable and a Barlow to do planetary imaging.  Even though my scope will go to 500x the skies here limit me to about 300x.  I usually find a sweat spot between a Barlowed 6 to 10.

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