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Bargain widefield EP performance in a flatfield scope?

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20 replies to this topic

#1 gezak22

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Posted 02 January 2017 - 02:55 PM

Hey all,

 

I've been selling off my hard-to-use eyepieces (orthos) to build a more comfortable line-up that will see more use. I am considering a 100 degree eyepiece in the 6 mm range, and the 6mm Ethos and 5.5mm ES are on the short list (as are the 5mm XW and the 6mm Delos). But let's focus on the widefields for now.

 

Can I expect pinpoint stars out to the edge in the TV101+6mm Ethos combo? What about the 5.5mm ES? I am asking because I was expecting pinpoint stars to the edge in the 9mm 100 degree Lunt/APM, but that is not the case. It's not a big deal given the price. Also, the outer edge where the stars are distorted is only used for peripheral vision, so perfect performance is not a requirement.

 

What kind of edge performance can I expect from an Ethos and ES?

 

Thanks.



#2 tony_spina

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Posted 02 January 2017 - 04:00 PM

TV NP 101 with the Ethos 6mm will give you stars sharp to the edge. I don't have the ES 5.5mm so I can't provide you an answer.

 

I can tell you that the ES 82 degree line is a little soft at the last 10-15% of the edge


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#3 gezak22

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Posted 02 January 2017 - 05:22 PM

TV NP 101 with the Ethos 6mm will give you stars sharp to the edge. I don't have the ES 5.5mm so I can't provide you an answer.

 

I can tell you that the ES 82 degree line is a little soft at the last 10-15% of the edge

I have noticed that as well. I had an ES82 6.7mm, and while it was great for the money, it was definitely soft in the edges.

 

It's good to hear that the Ethos is sharp to the edges, and it is pretty much what I expected from a TV eyepiece given that fast flatfield refractors are their thing.



#4 junomike

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Posted 02 January 2017 - 06:05 PM

I have tried all these (but not in the shorter F/L's).

IME the ES 100 and Lunt/APM were a little soft on the edges.  The Delos seemed much better controlled.

None are bad IMO and finances usually dictate the end result.

 

Mike



#5 areyoukiddingme

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Posted 02 January 2017 - 07:48 PM

I have a TV 101, and the 5XW and 6 Ethos. Both are sharp to the edge in the Televue.

 

I have not used the 5.5 ES or the 6 Delos. My guess is that the ES will be like the others in the series that I tried (9, 14, 120)--namely, a little bit of astigmatism or possibly field curvature at the very edge.



#6 gezak22

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Posted 02 January 2017 - 10:48 PM

I have a TV 101, and the 5XW and 6 Ethos. Both are sharp to the edge in the Televue.

 

I have not used the 5.5 ES or the 6 Delos. My guess is that the ES will be like the others in the series that I tried (9, 14, 120)--namely, a little bit of astigmatism or possibly field curvature at the very edge.

Thanks. I'm comfortable extrapolating the performance of the 9mm to the 5.5mm, I'll aim for an Ethos or XW.



#7 Tank

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Posted 02 January 2017 - 11:29 PM

If money is not a major factor stick to

Ethos, Delos or XW



#8 gezak22

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Posted 02 January 2017 - 11:36 PM

If money is not a major factor stick to

Ethos, Delos or XW

This is what I intend to do. I just wanted to have a sanity check by more knowledgeable observers.



#9 Ernest_SPB

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Posted 03 January 2017 - 01:27 AM

> I've been selling off my hard-to-use eyepieces (orthos) to build a more comfortable line-up that will see more use. I am considering a 100 degree eyepiece...

 

Hm... I would not consider 100 degree eyepiece as comfortable especially in comparison to ortho. Eye relief is quite short (11-13 mm), AFOV is extra large. So you can not see stars at edge by direct vision without cut off more then 50% FOV. Observing in even short focal Ortho looks for me more comfortable.

 

You need 100 degree EP if you need extra wide field of view, not if you look for convenience. 

 

Looking for convent short focal EP consider Delos, XW, Delite or at least Radian.

 

> Can I expect pinpoint stars out to the edge in the TV101+6mm Ethos combo? What about the 5.5mm ES?

 

Ethos is excellent and you will get your pinpoints... ES a bit more softer in outer area of FOV. 


Edited by Ernest_SPB, 03 January 2017 - 01:31 AM.


#10 Jon Isaacs

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Posted 03 January 2017 - 02:10 AM

Hm... I would not consider 100 degree eyepiece as comfortable especially in comparison to ortho. Eye relief is quite short (11-13 mm), AFOV is extra large. So you can not see stars at edge by direct vision without cut off more then 50% FOV. Observing in even short focal Ortho looks for me more comfortable.

 

I think this is a personal preference.  An ortho has a 40 degree AFoV and in the focal lengths we are discussing, the eye relief will be approximately 4mm.  

 

With a 100 degree eyepiece, one will have to be quite close to the eyepiece to see the entire field of view but it will not be as close as the Ortho.  More importantly, one does not need to see the entire field of view, seeing "only" 80 degrees will be quite comfortable and still provide twice the field of view of the Ortho... 

 

Jon



#11 Jon Isaacs

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Posted 03 January 2017 - 02:12 AM

As far as eyepieces to consider, I have the 3.5mm, 5mm, 7mm and 9mm type 6 Naglers, they are excellent performers in my NP-101 and qualify as sharp to the edge.  

 

Jon



#12 Ernest_SPB

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Posted 03 January 2017 - 02:21 AM

 

Hm... I would not consider 100 degree eyepiece as comfortable especially in comparison to ortho. Eye relief is quite short (11-13 mm), AFOV is extra large. So you can not see stars at edge by direct vision without cut off more then 50% FOV. Observing in even short focal Ortho looks for me more comfortable.

 

I think this is a personal preference.  An ortho has a 40 degree AFoV and in the focal lengths we are discussing, the eye relief will be approximately 4mm...

limited AFOV of ortho lets observer to place his pupil more distant from EP than exact eye relief without any loss in FOV

eye_relief.PNG

 

So for adapted (fully open) pupil real eye relief of Ortho can be extended +10 mm (depends from level of adaptation to darkness) becoming comparable to ER of Ethos and 100ES


Edited by Ernest_SPB, 03 January 2017 - 02:32 AM.

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#13 gezak22

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Posted 03 January 2017 - 03:30 PM

 

 

Hm... I would not consider 100 degree eyepiece as comfortable especially in comparison to ortho. Eye relief is quite short (11-13 mm), AFOV is extra large. So you can not see stars at edge by direct vision without cut off more then 50% FOV. Observing in even short focal Ortho looks for me more comfortable.

 

I think this is a personal preference.  An ortho has a 40 degree AFoV and in the focal lengths we are discussing, the eye relief will be approximately 4mm...

limited AFOV of ortho lets observer to place his pupil more distant from EP than exact eye relief without any loss in FOV

attachicon.gifeye_relief.PNG

 

So for adapted (fully open) pupil real eye relief of Ortho can be extended +10 mm (depends from level of adaptation to darkness) becoming comparable to ER of Ethos and 100ES

 

 

 

Fair points, but comfort is more than just ER. Eye placement (centering) is more cumbersome with orthos, especially when I add 10mm of eye relief. Now add manual tracking of a target (because orthos aren't so good in the edges) and the orthos are at a disadvantage.

 

I find 10mm eye relief plenty IF the stars are sharp to the edge. But if they aren't sharp to the edge then I would much rather have a little more ER and a narrower FOV.

 

But we can close the topic. A used 5mm XW popped up for an excellent price and I managed to jump on it.


Edited by gezak22, 03 January 2017 - 03:31 PM.

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#14 Procyon

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Posted 03 January 2017 - 04:28 PM

That's a great buy, congrats. That was the first eyepiece I ever bought to use in my first scope, an XT10. Great eyepiece, great glass, great sharpness and nice fov. Just remember it's the size of 5 orthos.


Edited by Procyon, 03 January 2017 - 04:30 PM.


#15 YKSE

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Posted 03 January 2017 - 09:48 PM

 

 

Hm... I would not consider 100 degree eyepiece as comfortable especially in comparison to ortho. Eye relief is quite short (11-13 mm), AFOV is extra large. So you can not see stars at edge by direct vision without cut off more then 50% FOV. Observing in even short focal Ortho looks for me more comfortable.

 

I think this is a personal preference.  An ortho has a 40 degree AFoV and in the focal lengths we are discussing, the eye relief will be approximately 4mm...

limited AFOV of ortho lets observer to place his pupil more distant from EP than exact eye relief without any loss in FOV

attachicon.gifeye_relief.PNG

 

So for adapted (fully open) pupil real eye relief of Ortho can be extended +10 mm (depends from level of adaptation to darkness) becoming comparable to ER of Ethos and 100ES

 

Thanks for the explanations. :waytogo:

My experience seems to agree with you too.

10mm BCO has less ER than 16mm Maxvision (8mm vs 12mm), with my glasses on, I could see about 2/3 of field stop with BCO, while only about 1/3 of field stop in Maxvision. The volcano top of BCO increases a couple of mm useful ER, but your sketch shows another more mms.

Also,14mm Nikon compare to 12.5mm Docter, both has 18mm ER, 72° vs 84°, about the same physical build when eyecup is down on Docter, easily seen field stop in Nikon without glass on eyecup, while I really need to push my glass on Docter to see the whole field stop.



#16 Jon Isaacs

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Posted 03 January 2017 - 09:59 PM

 

 

Hm... I would not consider 100 degree eyepiece as comfortable especially in comparison to ortho. Eye relief is quite short (11-13 mm), AFOV is extra large. So you can not see stars at edge by direct vision without cut off more then 50% FOV. Observing in even short focal Ortho looks for me more comfortable.

 

I think this is a personal preference.  An ortho has a 40 degree AFoV and in the focal lengths we are discussing, the eye relief will be approximately 4mm...

limited AFOV of ortho lets observer to place his pupil more distant from EP than exact eye relief without any loss in FOV

attachicon.gifeye_relief.PNG

 

So for adapted (fully open) pupil real eye relief of Ortho can be extended +10 mm (depends from level of adaptation to darkness) becoming comparable to ER of Ethos and 100ES

 

My point is this:

 

The eye lens of the 20mm ES 100 degree is 30mm in diameter. This implies the eye relief is about 12.5mm.  But if I am OK with only viewing an 80 degree AFoV, double that of the ortho, I can be back about 18mm.. 

 

Jon



#17 Sard

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Posted 04 January 2017 - 01:51 AM

But if you are only going to view 80 degrees, why get the 100 degree eye piece? 80 degrees and 12.5mm of eye relief can be had for less money.

Edited by Sard, 04 January 2017 - 01:53 AM.


#18 csrlice12

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Posted 04 January 2017 - 03:13 PM

Just me, I like the 100s because (for the most part) the field stop gets out of the way, giving a more "natural" view.  And a 4.7 Ethos, a 10" dob, and M13 were made for each other.



#19 peter k

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Posted 05 January 2017 - 02:37 PM

 

 

 

Hm... I would not consider 100 degree eyepiece as comfortable especially in comparison to ortho. Eye relief is quite short (11-13 mm), AFOV is extra large. So you can not see stars at edge by direct vision without cut off more then 50% FOV. Observing in even short focal Ortho looks for me more comfortable.

 

I think this is a personal preference.  An ortho has a 40 degree AFoV and in the focal lengths we are discussing, the eye relief will be approximately 4mm...

limited AFOV of ortho lets observer to place his pupil more distant from EP than exact eye relief without any loss in FOV

attachicon.gifeye_relief.PNG

 

So for adapted (fully open) pupil real eye relief of Ortho can be extended +10 mm (depends from level of adaptation to darkness) becoming comparable to ER of Ethos and 100ES

 

My point is this:

 

The eye lens of the 20mm ES 100 degree is 30mm in diameter. This implies the eye relief is about 12.5mm.  But if I am OK with only viewing an 80 degree AFoV, double that of the ortho, I can be back about 18mm.. 

 

Jon

 

Good point, Jon.  I  never thought of it that way.  By extension, the short ER Naglers and ES 82s can be used as long ER 68s if you can give up seeing the field stop.


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#20 peter k

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Posted 05 January 2017 - 02:39 PM

But if you are only going to view 80 degrees, why get the 100 degree eye piece? 80 degrees and 12.5mm of eye relief can be had for less money.

I think you're missing Jon's point.  Back away from the short ER 100 and you have a long ER 80.


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#21 Jon Isaacs

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Posted 07 January 2017 - 07:33 AM

But if you are only going to view 80 degrees, why get the 100 degree eye piece? 80 degrees and 12.5mm of eye relief can be had for less money.

 

The 20mm ES-100 provides about 18mm of eye relief at 80 degrees AFoV, I am not sure where I could buy such an eyepiece, particularly one that offered a 100 degree AFoV if I moved forward a bit...

 

Jon




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