Ethos + power mate?

[John]

23 minutes ago, Dantooine said:

Don,

thank you for the information. So what you are saying is to get a true 1.6x from the barlow, the ethos would need to be used with the 1.25” Part of the dual barrel and that by using the 2” part I was actually getting a much lower magnification than I thought I was getting?

would this also explain a minimal noticeable change in eye relief On the 6 & 8E?

If this is the case I will need to spend an evening trying them in 1.25” mode. 
 

Forgive my ignorance on this as I never thought I would use a barlow and it’s the first time I’ve used one. 
Dale. 

That's not the way that I used the 1.6x Barlow when I was comparing it with other 5mm eyepieces as the photo I posted earlier in this thread shows

I think I would have noticed if the Ethos 8 plus 1.6x barlow combo was delivering more (or less) than a virtual 5mm eyepiece as I compared the views with true 5mm eyepieces.

By all means try it though - nothing to loose !

 

 

[John]

I've been reminding myself of stuff relating to barlowing / Powermating Ethos. Makes my brain ache !!!:

https://www.cloudynights.com/topic/132768-ethos-mag-factor-with-tv-barlows-powermates/

[Rob_UK_SE]

1 hour ago, John said:

I've been reminding myself of stuff relating to barlowing / Powermating Ethos. Makes my brain ache !!!:

https://www.cloudynights.com/topic/132768-ethos-mag-factor-with-tv-barlows-powermates/

I quite agree, John (having just attempted to read through those pages with varying degrees of success this end). I didn’t realise that using an Ethos 13/10/8/6 with the 2” barrel -into a barlow- would impact on the barlow’s ability to achieve 1.6x. I don’t like securing the 13/8/6 Ethos using the 1.25” barrel and have been considering purchasing the Antares 1.6 since hearing about Dale’s successes with this combination.

It would be interesting to hear, Dale, how your 8E+ barlow compares to your 4.7E in terms of magnification. Does it feel similar, in a non-scientific way? I am wondering just how much the magnification is affected by using the 8E in ‘2” mode’?

Stardaze, I’m sure that you will be delighted with the 5mm XW. I had been planning on ordering it due to the clearance sale, but you beat me to it 😀. I have recently purchased the 30mm, 10mm and 3.5mm XW to complement my Ethos set and have been very impressed with them, thus far. I have heard nothing but good things about the 5mm so I can’t imagine that it will disappoint. Hope that you get some clear skies to test it out.

Edited September 7, 2020 by Rob_UK_SE

[Dantooine]

30 minutes ago, Rob_UK_SE said:

It would be interesting to hear, Dale, how your 8E+ barlow compares to your 4.7E in terms of magnification? Does it feel similar, in a non-scientific way? I am wondering just how much the magnification is affected by using the 8E in ‘2” mode’?

Well I had a quick look at the barlow figures but to be honest without the maths degree it’s not what I come on here for. 
 

next time out I will try the 8E+ barlow against the 4.7E on its own. This way I will get a non scientific idea of any difference in size at what I’m looking at. This is after all my main aim, observing. 
 

All I know is I got to focus, it was nice to use and gave me good views.

I have put 6 & 8 into a 1.25” click lock and it did make me nervous to the point of getting a 2” baader diagonal. I definitely would be unhappy about the 13E clinging on in this way so I’m with you on that. 
 

this looks safer

Edited September 7, 2020 by Dantooine
1.2” to 1.25”

[Stardaze]

3 hours ago, Rob_UK_SE said:

I quite agree, John (having just attempted to read through those pages with varying degrees of success this end). I didn’t realise that using an Ethos 13/10/8/6 with the 2” barrel -into a barlow- would impact on the barlow’s ability to achieve 1.6x. I don’t like securing the 13/8/6 Ethos using the 1.25” barrel and have been considering purchasing the Antares 1.6 since hearing about Dale’s successes with this combination.

It would be interesting to hear, Dale, how your 8E+ barlow compares to your 4.7E in terms of magnification. Does it feel similar, in a non-scientific way? I am wondering just how much the magnification is affected by using the 8E in ‘2” mode’?

Stardaze, I’m sure that you will be delighted with the 5mm XW. I had been planning on ordering it due to the clearance sale, but you beat me to it 😀. I have recently purchased the 30mm, 10mm and 3.5mm XW to complement my Ethos set and have been very impressed with them, thus far. I have heard nothing but good things about the 5mm so I can’t imagine that it will disappoint. Hope that you get some clear skies to test it out.

Eventually I’ll add the Ethos 6 and XW 3.5, which should complete my little set and complement each other. No need for a Barlow at that point either. I’m quite happy now,  having plugged the gaps and still have an ES 6.7 for the moment in between the 8 and 5. I have been intrigued with the XW’s and the 5 was always going to be where I fancied dabbling. Seem to have gone a little crazy this last month so looking forward to getting to use them now.

[Stardaze]

3 hours ago, Dantooine said:

Well I had a quick look at the barlow figures but to be honest without the maths degree it’s not what I come on here for. 
 

next time out I will try the 8E+ barlow against the 4.7E on its own. This way I will get a non scientific idea of any difference in size at what I’m looking at. This is after all my main aim, observing. 
 

All I know is I got to focus, it was nice to use and gave me good views.

I have put 6 & 8 into a 1.25” click lock and it did make me nervous to the point of getting a 2” baader diagonal. I definitely would be unhappy about the 13E clinging on in this way so I’m with you on that. 
 

this looks safer

Mine didn’t seem too bad in the 1.25” click lock, but the 2” would certainly feel bomb-proof. Still waiting on the barrel and rings from FLO but I suspect another item that I ordered is holding it back for a few days.

[omo]

If i am understanding this correctly, with the Antares having a T2 fitting it would be quite easy to add a T2 spacer to extend its length and get nearer the full magnification  with the Ethos in 2 inch mode

[John]

Just now, omo said:

If i am understanding this correctly, with the Antares having a T2 fitting it would be quite easy to add a T2 spacer to extend its length and get nearer the full magnification  with the Ethos in 2 inch mode

I think it works at 1.6x in 2 inch mode anyway. The one that I used to have did.

 

[omo]

4 minutes ago, John said:

I think it works at 1.6x in 2 inch mode anyway. The one that I used to have did.

 

I was thinking about what @Don Pensack was saying about the 8mm Ethos putting the focal plane much closer to the barlow glass so lengthen the barlow to get nearer to the 1.6x. The connection between the nosepiece and twistlock is T2

[John]

12 minutes ago, omo said:

I was thinking about what @Don Pensack was saying about the 8mm Ethos putting the focal plane much closer to the barlow glass so lengthen the barlow to get nearer to the 1.6x. The connection between the nosepiece and twistlock is T2

Well, I used it with the 8mm Ethos in 2 inch mode and it provided the same image scale as the 5mm eyepieces that I was comparing it with at the time.

 

[Dantooine]

8 hours ago, John said:

Well, I used it with the 8mm Ethos in 2 inch mode and it provided the same image scale as the 5mm eyepieces that I was comparing it with at the time.

 

Then it opens the can of worms.. Morpheus? How about all the difference in barrel lengths in same set eyepieces?

My opinion, make your own mind up if the views are pleasing or not. 

You could spend a lifetime looking at theory’s and mathematical figures rather than just looking through the telescope. 

[Don Pensack]

On 07/09/2020 at 07:44, Dantooine said:

Don,

thank you for the information. So what you are saying is to get a true 1.6x from the barlow, the ethos would need to be used with the 1.25” Part of the dual barrel and that by using the 2” part I was actually getting a much lower magnification than I thought I was getting?

would this also explain a minimal noticeable change in eye relief On the 6 & 8E?

If this is the case I will need to spend an evening trying them in 1.25” mode. 
 

Forgive my ignorance on this as I never thought I would use a barlow and it’s the first time I’ve used one. 
Dale. 

The lower the power of the Barlow, the less it affects the eye relief of the eyepiece.  So a 1.6X barlow is going to have a minimal effect anyway, in that regard, and if the magnification factor is lowered even more, by placing the eyepiece's focal plane closer to the lens, then a change to the eye relief might not even be measurable.

Most barlows yield their rated powers when the focal planes of the eyepiece are level with the opening of the barlow.  If the focal plane of the eyepiece is lower (closer to the lens), the magnification is less, and if the focal plane of the eyepiece is higher (farther from the lens), the magnification is more.  

The 8mm and 6mm Ethos have their focal planes low in the barrels, so using them as 2" will not yield the rated magnifications with barlows.  Their focal planes will be closer to, but possibly above, the opening of the barlow if used as 1.25" eyepieces, but judging from where the focal planes in those eyepieces are, you'll be a lot closer to the rated power of the barlow if they are used as 1.25" eyepieces.

[Don Pensack]

12 hours ago, Dantooine said:

Then it opens the can of worms.. Morpheus? How about all the difference in barrel lengths in same set eyepieces?

My opinion, make your own mind up if the views are pleasing or not. 

You could spend a lifetime looking at theory’s and mathematical figures rather than just looking through the telescope. 

The Morpheus eyepieces from 14mm down have their focal planes at the shoulder of the 1.25" barrel.  Hence, used as 1.25" eyepieces, the magnification factor of the barlow will be fairly close to the manufacturer's claim

(assuming the barlow is properly rated, and not all are).  If used as 2" eyepieces, the focal planes will be lowered toward the barlow lens, and the magnification factor will be lower.

[John]

I understand the point that you are making Don and the optical principles that underlie it but I'm rather baffled all the same.

I've read many reports of the Antares 1.6x barlow being used with the Ethos in 2 inch mode on the CN forum (Lawrence Sayre was a great exponent of this approach, among others) and yet I have not read that these combinations result in more than very small variations, if any, from the 1.6x amplification. My own experience of using the barlow with the 8mm and 6mm Ethos, in 2 inch mode, and comparing the resulting combination with eyepieces with a native focal length of 5mm and 3.7mm is that there was no noticeable difference in the image scale that was achieved.

Maybe I've missed something though, either from my own experience or the reports from others

I guess it's fairly academic now because I don't use this barlow or any others with my principle eyepiece sets but I'm puzzled all the same !

 

 

[globular]

As we all know (from the link John supplied earlier in this thread) the formula for magnification for a common barlow design is
M = 1 - X / Fl
where M = magnification, X = distance of focal plane to barlow lens group, Fl = focal length of barlow lens group.

Now I don't know what either X or Fl are for the Antares 1.6x, but because it claims 1.6x magnification this gives (by rearranging the formula) that X = -0.6 * Fl 
(Let's check that by plugging it back into the formula;  M = 1 - -0.6*Fl / Fl = 1 - -0.6 = 1 + 0.6 = 1.6).

If we make up that Fl = -100mm as a guess (the Big Barlow is apparently -90.8mm so it's probably somewhere around there) then we get X = 60mm.

The Ethos 8mm focal plane is not at the shoulder so we need to adjust X and plug the new value into the formula to get the revised magnification.

As we can see from this table, when used as a 1.25" eyepiece the shoulder of the Ethos will sit C (plus any adaptor height) above the top of the Antares and the field stop is F below the Ethos shoulder.  Lets pretend we have a zero light path adaptor so we need to add C and subtract F (both converted to mm from inches) from X to give our new X' = 60 + (0.94-0.7)*25.4 = 66.1
And the 1.25" mode magnification M' = 1 - X'/Fl = 1 - 66.1 / -100 = 1.66x

Now, when using it as 2" the Ethos shoulder sits on the top of the Antares and the field stop is F below.  So X'' = 60 - 0.7*25.4 = 42.2
And the 2" mode magnification M'' = 1 - X''/Fl = 1 - 42.2 / -100 = 1.42x

If we alter Fl (we just guessed it's value after all) then the results naturally change.  At Fl=-50 M'=1.72 and M''=1.24 and at Fl=-150 M'=1.64 and M''=1.48. 

Maybe this means the Antares has a large focal length so that John's observation might be consistent with the science? 
Or maybe the design of the Antares means this simple formula does not apply?  
Or maybe the claimed 1.6x is a little out - it will likely be a rounded figure from the actual. If it's really a 1.69x (and the marketing guys rounded down the most they could reasonably get away with) then the 2" M'' recalculates at about 1.51x (at Fl=-100).
I suspect it's a little bit of all three.

I pretty sure, John, that your observations will have been be about right - but I think it's also likely that if you repeated them in 1.25" mode then slightly more magnification would have been apparent. 

But what's 0.1x or 0.2x higher magnification between friends?  Surely the view in the eyepiece is more important than the numbers on a piece of paper?

[Dantooine]

I’m really like my 2 inch Antares 1.51x  👍

 

[Dantooine]

7 hours ago, globular said:

As we all know (from the link John supplied earlier in this thread) the formula for magnification for a common barlow design is
M = 1 - X / Fl
where M = magnification, X = distance of focal plane to barlow lens group, Fl = focal length of barlow lens group.

Now I don't know what either X or Fl are for the Antares 1.6x, but because it claims 1.6x magnification this gives (by rearranging the formula) that X = -0.6 * Fl 
(Let's check that by plugging it back into the formula;  M = 1 - -0.6*Fl / Fl = 1 - -0.6 = 1 + 0.6 = 1.6).

If we make up that Fl = -100mm as a guess (the Big Barlow is apparently -90.8mm so it's probably somewhere around there) then we get X = 60mm.

The Ethos 8mm focal plane is not at the shoulder so we need to adjust X and plug the new value into the formula to get the revised magnification.

As we can see from this table, when used as a 1.25" eyepiece the shoulder of the Ethos will sit C (plus any adaptor height) above the top of the Antares and the field stop is F below the Ethos shoulder.  Lets pretend we have a zero light path adaptor so we need to add C and subtract F (both converted to mm from inches) from X to give our new X' = 60 + (0.94-0.7)*25.4 = 66.1
And the 1.25" mode magnification M' = 1 - X'/Fl = 1 - 66.1 / -100 = 1.66x

Now, when using it as 2" the Ethos shoulder sits on the top of the Antares and the field stop is F below.  So X'' = 60 - 0.7*25.4 = 42.2
And the 2" mode magnification M'' = 1 - X''/Fl = 1 - 42.2 / -100 = 1.42x

If we alter Fl (we just guessed it's value after all) then the results naturally change.  At Fl=-50 M'=1.72 and M''=1.24 and at Fl=-150 M'=1.64 and M''=1.48. 

Maybe this means the Antares has a large focal length so that John's observation might be consistent with the science? 
Or maybe the design of the Antares means this simple formula does not apply?  
Or maybe the claimed 1.6x is a little out - it will likely be a rounded figure from the actual. If it's really a 1.69x (and the marketing guys rounded down the most they could reasonably get away with) then the 2" M'' recalculates at about 1.51x (at Fl=-100).
I suspect it's a little bit of all three.

I pretty sure, John, that your observations will have been be about right - but I think it's also likely that if you repeated them in 1.25" mode then slightly more magnification would have been apparent. 

But what's 0.1x or 0.2x higher magnification between friends?  Surely the view in the eyepiece is more important than the numbers on a piece of paper?

Thank you for spending the time and putting this in a way that’s easier for my tired brain to understand. Much appreciated and yes the views are more important. 

[Dantooine]

1 hour ago, Dantooine said:

Thank you for spending the time and putting this in a way that’s easier for my tired brain to understand. Much appreciated and yes the views are more important. 

John, from those simple calculations it should be easy to work out the in travel for ethos in the Antares 🤔

[John]

8 hours ago, Dantooine said:

John, from those simple calculations it should be easy to work out the in travel for ethos in the Antares 🤔

Piece of cake

[globular]

26 minutes ago, John said:

Piece of cake

Thanks John - nice moist carrot cake please 😇

[Stardaze]

Used the XW last night for the first time and really found the eye placement very strange. I do love the 8mm Ethos though, very different moving from that to the XW 5. I'll get used to it, I'm sure. Got an early glimpse of Mars which is encouraging for the month ahead.

[Dantooine]

56 minutes ago, Stardaze said:

Used the XW last night for the first time and really found the eye placement very strange. I do love the 8mm Ethos though, very different moving from that to the XW 5. I'll get used to it, I'm sure. Got an early glimpse of Mars which is encouraging for the month ahead.

Trouble is you were expecting a 5mm ethos. It’s an adjustment to get used to. I’m sure it will come.
 

I expect you noticed things moving a bit quicker with the difference in FOV. It probably frames mars nicer though. 
 

I think I’ve got to spoilt with the 100 degrees and it sounds like you have too. My manual setup makes me prefer a “sitting target”. 
 

how do you feel it performed optically?

[John]

1 hour ago, Stardaze said:

Used the XW last night for the first time and really found the eye placement very strange. I do love the 8mm Ethos though, very different moving from that to the XW 5. I'll get used to it, I'm sure. Got an early glimpse of Mars which is encouraging for the month ahead.

They are very different eyepieces I agree. Do you have the eye cup in the "up" position ?

If you wear glasses when observing though, the eye cup should be twisted down.

 

 

[Stardaze]

15 minutes ago, Dantooine said:

Trouble is you were expecting a 5mm ethos. It’s an adjustment to get used to. I’m sure it will come.
 

I expect you noticed things moving a bit quicker with the difference in FOV. It probably frames mars nicer though. 
 

I think I’ve got to spoilt with the 100 degrees and it sounds like you have too. My manual setup makes me prefer a “sitting target”. 
 

how do you feel it performed optically?

 

12 minutes ago, John said:

They are very different eyepieces I agree. Do you have the eye cup in the "up" position ?

If you wear glasses when observing though, the eye cup should be twisted down.

 

 

I've definitely been spoilt with 100 degree vistas. I felt from 200x and greater, that that wouldn't be such an issue for planetary and doubles, it's just going to take some time to get used to. It was nice and sharp, the colour seemed crisp too so no qualms there. M13 looked pretty spectacular, but the 8mm Ethos is the sweet spot for me still with that target. 

I'm not a glasses wearer John, but it felt better twisted almost fully up, but even then I kept just 'blobbing' the front element. Best position seemed to be hovering well above the rubber, however high that was. Getting in close just seemed to black out, odd. Maybe I am used to just getting in close to take in the 100 degree views?

Edited September 10, 2020 by Stardaze

[Dantooine]

27 minutes ago, Stardaze said:

 

I've definitely been spoilt with 100 degree vistas. I felt from 200x and greater, that that wouldn't be such an issue for planetary and doubles, it's just going to take some time to get used to. It was nice and sharp, the colour seemed crisp too so no qualms there. M13 looked pretty spectacular, but the 8mm Ethos is the sweet spot for me still with that target. 

I'm not a glasses wearer John, but it felt better twisted almost fully up, but even then I kept just 'blobbing' the front element. Best position seemed to be hovering well above the rubber, however high that was. Getting in close just seemed to black out, odd. Maybe I am used to just getting in close to take in the 100 degree views?

What does your 8E give you, around 150x? You have other ethos?