24 replies to this topic

[T1R2]

If anyone was wanting one now is your chance, it looks like the Agnicy Outdoor Store on Aliexpress has all FL available, I was a little surprised to see them back

 

https://www.aliexpre...ler|query_from:

[CHASLX200]

I had one once and was not thrilled with it.

Edited by CHASLX200, 15 February 2025 - 10:38 AM.

[SeattleScott]

Ernest tested and found a newer, cheaper one was not as good as the original. 

 

These aren't especially cheap. Are they made like the originals, or the newer ones?

[25585]

I only have 25mm HD-60s, they are fine.

[T1R2]

I had one once and was not thrilled with it.

Right, some FL's are better than others. 

[TayM57]

Longer FLs = higher mags. Do keep that in mind.

[T1R2]

Ernest tested and found a newer, cheaper one was not as good as the original. 

 

These aren't especially cheap. Are they made like the originals, or the newer ones?

I read that also a while back, however I did buy the full set in 2023 and they were the real deal, with the 4.5mm, 6.5mm and 9mm being perfect edge to edge, while the 12mm, 18mm and 25mm were a little less so, about 40% less aberrations as a plossl which is what is advertised.  

[T1R2]

Longer FLs = higher mags. Do keep that in mind.

You mean shorter

[TayM57]

You mean shorter

No. I should of clarified I meant longer focal length scopes by FL.

 

For a given EP, it will yield a higher magnification the longer you go in focal length. For example, lets take the Apollo 11 eyepiece.

 

In a scope of 1200m, the A11 yields 109x.

 

In a scope of 700m, the A11 yields 63x.

 

 

So, yes, longer FL = higher mags for a given EP.

Edited by TayM57, 15 February 2025 - 04:47 PM.

[T1R2]

No. I should of clarified I meant longer focal length scopes by FL.

 

For a given EP, it will yield a higher magnification the longer you go in focal length. For example, lets take the Apollo 11 eyepiece.

 

In a scope of 1200m, the A11 yields 109x.

 

In a scope of 700m, the A11 yields 63x.

 

 

So, yes, longer FL = higher mags for a given EP.

Ok, I thought you were talking about the EP,  I already know that , but thanks for your comment.

[CHASLX200]

Field edge was soft in mine.

[T1R2]

Field edge was soft in mine.

Which one was it? 

[CHASLX200]

Which one was it? 

Been so long ago i don't know. 14mm?  It was in a faster scope.

[T1R2]

Been so long ago i don't know. 14mm?  It was in a faster scope.

Ah, the 12mm, yes that is not the best one, I don't like it either, but the others I do like, I thought it was the worst one out of the longer FL's in my AR127, and its the FL I use the most for M42, but I may switch it out for the 12mm AT Paradigm. However it is nice in my F13.3 60mm.  

[Starman1]

Longer FLs = higher mags. Do keep that in mind.

You might want to edit this, Tay. Got it reversed.

[TayM57]

You might want to edit this, Tay. Got it reversed.

I clarified what I meant in post #9. I simply mis-read other's posts of FL as the focal length of a scope, instead of an EP. I'm used to thinking of scopes in focal lengths, and I just defaulted to that mode of interpretation when I saw someone type FL.

 

But indeed, the longer the focal length in a scope is, the higher the magnification would be for eyepiece x. The shorter the focal length of a scope, eyepiece x goes down in mag.

[TayM57]

I no longer have the ability to edit post #6 for clarification, which is why I followed up in #9.

[vrodriguez2324]

With respect to telescopes, at least the ones that I have (doublet refractor and Newtonian reflector) Focal length is intuiative and I understand it.

 

Focal length with respect to eyepieces is a bit harder for me to wrap my head around. The distance between lenses? Which ones? Some of my eyepieces have 5, 6, 7, maybe 8 pieces of glass. Is it the distance from where I hold my eye to one of the inside lenses? Is it some type of virtual focal length? 

 

Victor

Edited by vrodriguez2324, 17 February 2025 - 08:44 PM.

[PKDfan]

With respect to telescopes, at least the ones that I have (doublet refractor and Newtonian reflector) Focal length is intuiative and I understand it.

Focal length with respect to eyepieces is a bit harder for me to wrap my head around. The distance between lenses? Which ones? Some of my eyepieces have 5, 6, 7, maybe 8 pieces of glass. Is it the distance from where I hold my eye to one of the inside lenses?

Victor

Hi Victor !

Eyepiece design is carefully balancing and minimizing aberrations and so AFOV size and eye relief distance is integral to designing an ocular.

Eg. Plössl design is two cemented doublets usually about 50degree AFOV and eyerelief is scaled to the focal length usually about .75times the focal length.

While Morpheus with eye glass friendly relief and about 80degree AFOV requires extra glass to fulfill that design goal.

And your scopes focal ratio is fairly critical to achieving a sharp view with a blazing fast F/3 or F/4 steep light cone demanding utmost care in fully correcting edge fidelity which usually means more glass elements.

The 30UFF is a good example of this as to get its superb edges it took 9pieces of glass and every piece of extra glass loses a slight bit of contrast.

Now if ypu've got a big optic that collects alot of light that might not mean ANYTHING while a small scope owner might see a detectable loss of contrast.

Use of an eyepiece with say 5 elements, a classic Erfle style with too fast a scope and too wide an AFOV means that edge performance gets progresively worse. Yet put that very same eyepiece in a slow Maksutov or Cassegrain and it'll finally show off its contrast 5 glass advantage.


Not so simple to intuitively understand eyepieces.

What works for others might not be so appropriate for you.



Hope that helps a bit !!


CSS
Lance

[vrodriguez2324]

Hi, Lance

 

I have a rudimentary understanding of eyepiece design insofar as needing more elements to achieve a wider afov, to correct for aberrations, bigger eyelenses to provide for longer eye relief, etc.

 

What about a simple design like the symmetrical? Is the focal length the measured distance between the two pairs of cemented doublets? 

 

 

Hi Victor !

Eyepiece design is carefully balancing and minimizing aberrations and so AFOV size and eye relief distance is integral to designing an ocular.

Eg. Plössl design is two cemented doublets usually about 50degree AFOV and eyerelief is scaled to the focal length usually about .75times the focal length.

While Morpheus with eye glass friendly relief and about 80degree AFOV requires extra glass to fulfill that design goal.

And your scopes focal ratio is fairly critical to achieving a sharp view with a blazing fast F/3 or F/4 steep light cone demanding utmost care in fully correcting edge fidelity which usually means more glass elements.

The 30UFF is a good example of this as to get its superb edges it took 9pieces of glass and every piece of extra glass loses a slight bit of contrast.

Now if ypu've got a big optic that collects alot of light that might not mean ANYTHING while a small scope owner might see a detectable loss of contrast.

Use of an eyepiece with say 5 elements, a classic Erfle style with too fast a scope and too wide an AFOV means that edge performance gets progresively worse. Yet put that very same eyepiece in a slow Maksutov or Cassegrain and it'll finally show off its contrast 5 glass advantage.


Not so simple to intuitively understand eyepieces.

What works for others might not be so appropriate for you.



Hope that helps a bit !!


CSS
Lance

 

Edited by vrodriguez2324, 17 February 2025 - 09:59 PM.

[PKDfan]

Hi again Victor !


I'm not an eyepiece designer just a buyer of them, usually the most expensive !


No its not the distance between the two doublets that would be design integral. Its more the size of the Field Stop maybe in combination with the size of the AFOV.

A 50 degree Plössl of 10mm will have approximately the same FS size as focal length while a 100° 10mm will be about twice as large.

Look at the new T7s the 5.5mm is extremely long and remarkably has about the same length as using a telecentric like 5X PM and placing a Plössl or similiar in it so a certain optical distance is needed to form the raypath correctly.

If you look at the new 16.5XW it has an extremely complex prefocal design with just 2 simple lenses and what looks like a cemented doublet after that.

Similiar to a telecentric and using an R.K.E. or Brandon or symmetrical in it. I imagine it optical scheme is quite simple with a complex Smyth component.

Don is the much better person to ask quite honestly.

I think i'm generally right but see above. Lol


CSS
Lance
Edit grammar

Edited by PKDfan, 17 February 2025 - 11:05 PM.

[vrodriguez2324]

In doing some quick research I don't think there is a simple answer to what I thought was a simple question . The material seems to be beyond my understanding attention span at the moment . Thank you for your insight Lance. 

Edited by vrodriguez2324, 17 February 2025 - 11:32 PM.

[PKDfan]

In doing some quick research I don't think there is a simple answer to what I thought was a simple question . The material seems to be beyond my understanding attention span at the moment . Thank you for your insight Lance.

Sometimes past my own comprehension too Victor.


Its a black(out) art !!


Most important to know is contrast is generally better with less elements so if Plössls view rocks your socks off, as i'm discovering, then your golden and saving a lot of cash in the process.

I want to try a ball eyepiece.

Just one piece of eyeball hugging glass excellence or so i hear !


Cheers !



CSS

[Starman1]

Hi, Lance

 

I have a rudimentary understanding of eyepiece design insofar as needing more elements to achieve a wider afov, to correct for aberrations, bigger eyelenses to provide for longer eye relief, etc.

 

What about a simple design like the symmetrical? Is the focal length the measured distance between the two pairs of cemented doublets? 

No, usually it's usually 1/2 the focal length of each doublet separately.

[Starman1]

Hi again Victor !


I'm not an eyepiece designer just a buyer of them, usually the most expensive !


No its not the distance between the two doublets that would be design integral. Its more the size of the Field Stop maybe in combination with the size of the AFOV.

A 50 degree Plössl of 10mm will have approximately the same FS size as focal length while a 100° 10mm will be about twice as large.

Look at the new T7s the 5.5mm is extremely long and remarkably has about the same length as using a telecentric like 5X PM and placing a Plössl or similiar in it so a certain optical distance is needed to form the raypath correctly.

If you look at the new 16.5XW it has an extremely complex prefocal design with just 2 simple lenses and what looks like a cemented doublet after that.

Similiar to a telecentric and using an R.K.E. or Brandon or symmetrical in it. I imagine it optical scheme is quite simple with a complex Smyth component.

Don is the much better person to ask quite honestly.

I think i'm generally right but see above. Lol


CSS
Lance
Edit grammar

Typical ultrawide eyepieces these days have a negative field lens and a positive upper assembly.

This has the advantages of letting the upper see a longer focal ratio light cone, reducing aberrations, while keeping the longer eye relief of a much longer focal length upper section.

 

Though not the exact equivalent (negative/positive designs are a little more complicated), think of a 14mm eyepiece being a 28mm eyepiece with a 2X Barlow built in.

It would be a 14mm eyepiece with the eye relief of a 28mm; actually, a little more eye relief than that.