Which 14mm??

[emadmoussa]

I've been always a proud owner of the SW Panorama 15mm up until I started using it with my 10" Dob. The f/5 scope simply exposed it's ugly face...on both my fracs it works wonderfully, but in the Dob I'm sorry to say it's a complete pain. You basically lose 1/3 of the field of view. It gets a bit blurry around the edge and astigmatism takes over 20-30% of the FOV.

So yes...I am considering the Explore Scientific 14mm 100-deg as a replacement. However a bit worried that 100-degree FOV is more than the human eye can naturally handle.

I looked around and saw that the Televue 14mm Delos is also a good candidate.

I'll probably grab myself a new toy this week, so what do you guys reckon??

Thanks!q

[Daniel-K]

Mmmm id go for the delos no wait the ES ahh just get both and send one back lol

[michael.h.f.wilkinson]

Just to confuse matters, I would consider the 14mm 82 deg ES. I gather it is every bit as good as the 14mm Meade Series 5000 UWA I used to have (may even share the same optical design). My only problem was that its eye relief was a touch tight, but otherwise it performed well, even in an F/4.2 Newtonian. It compared nicely with the 17T4 I still have. If you don't need glasses, the eye relief is fine, so in that case I can whole-heartedly recommend it. If eye relief is an issue, I would go for the Delos, as the eye relief of the ES 14mm 100 deg is no more generous than for the 82 deg. The 82 deg saves you a lot of money!

[emadmoussa]

Humm...the ES 14mm 82-deg seems tempting as well...

[Dude_with_the_tube]

i dont have the 14mm ES 100 deg version but its brother from another mother:TV Ethos 13mm as at the time i was looking for 14mm ES there where none on s/h market but i got offered Ethos for same price as ES so i grabbed that. As for differences between 82 deg and 100 deg:

1.price:you pay more for 100

2.FOV: much much bigger then 82 and i mean MUCH bigger.Dont worry about that tho as you can perfectly handle the FOV.A small learning curve will be required,but it is a WOW for sure.

3.Eye relief:not a big difference as 14mm/100 deg ES will have 14mm and 82 deg 15mm.

4.weight.:100 deg will be heavier as 82deg version so your scope balance will be crucial.

5.Coma. with my 10" f4.7 i didnt need any coma corrector on 82 deg and i am sure i could walk away without needing any on my new 14" who is F4.64,however,as 100 deg FOV is so much wider,coma became properly visible in new scope and i had no other choice as to get one as i couldnt even use 20mm ES due to coma.

however,with only 3 100 deg EP you can cover whole range of 82 deg (8 EP).

tuff call on this one and you will have to make your mind up yourself

good luck with whatever you go for.

[emadmoussa]

I know- the 100-deg 14mm is my first choice. But like you say...probably a bit of getting used to is required - which is doable I guess.

How large does it feel on a 10" Dob?

[Dude_with_the_tube]

took me not too long to get used to hyperwide fields  and i love them now.

weight wise :82 deg will be 259grms where 100 deg 14mm will be 833grms so 3 times heavier. in comparison the 30mm es 82 deg is 1kg so i reckon the 14mm 100 deg is the same weight as 24mm ES in 82 deg. i hope you have one of these in the house to check how the balance works on your scope.

Where difference in FOV between 82 and 100 will be like this:

[emadmoussa]

Well, I'm not worried much about the balance as I already use big eyepieces such as the Hyperion Scopos 35mm which is 1.2Kg. Plus I can always I adjust axis on the dob. As for the fracs, that's not a problem...all use 2" heavy duty diagonals.

[michael.h.f.wilkinson]

Measured on my screen that looks like a comparison between 100° and 50°. The 100° one should be about 20% larger in diameter, giving roughly 40% more sky.

[Dude_with_the_tube]

blehh,wrong image.its comparison of 100 degs vs 50deg plossl.

my apologies.

[michael.h.f.wilkinson]

blehh,wrong image.its comparison of 100 degs vs 50deg plossl.

my apologies.

Thought as much. I gather the difference would be similar to the difference between 68 and 82 mm EPs (sizeable step).

[Dude_with_the_tube]

Thought as much. I gather the difference would be similar to the difference between 68 and 82 mm EPs (sizeable step).

absolutely correct.

[John]

My human eye finds a 100 degree field of view very acceptable 

The ES 100's are really good eyepieces. 

[AlexB67]

Emad, would it be worth trying one before buying if you intend to use it without a CC. Whether you can get on with the 100 degrees is one thing.  I find in terms of coma 68 degrees is acceptable in my f4.7 with my MV as it appears to me astigmatism is very well behaved in that eyepiece ( to my relatively neophyte eyes in this field I should add), but I don't think I'd want to go much wider without coma correction  (personally). Anyway, that is just my feeling, just to throw it into the pot. In the end of the day I have never used anything bigger than 68 degrees in my Dob and find it a luxury already  I appreciate it will very much depend on personal pref.

If I did my quick calculation right, your f/5 should perhaps behave similarly in terms of coma with a 82 degrees as a 68 degrees would in my f4.7, roughly based on coma free field, fratio cubed, (f4.7/f5)^3 ~ 0.83.   68/82 ~ .83 is also roughly the proportion in field gained, crude back of the envelope thinking I hasten to add. Shocking how quickly these things grow going from f5 down to f4.7    Now a 100 degrees would be an different animal though. I suppose if you go for 100 degrees you want it to be usable. 

No doubt many different opinions will come in here. :0)

[Andy_E]

I find coma not to be TOO much of a problem with the 14mm ES82 (@f4.7)... it's there but I have to look for it. Can't comment how this is going to look on the 100deg mind.  As Alex states though this is all down to personal taste, the coma corrector is now permanently attached to the 24mm!

[emadmoussa]

I've got an ES 24mm 82-deg and it doesn't have any astigmatism. While like I said above...the more expensive 15mm Panorama is not fun to use with an f/5 Dob. So based on that I'm assuming if the same level of corrected optics is applied to the 100-degree version then it should be fine. I stand corrected though.

And yeah, will be great if I could have a test first...

[emadmoussa]

I find coma not to be TOO much of a problem with the 14mm ES82 (@f4.7)... it's there but I have to look for it. Can't comment how this is going to look on the 100deg mind.  As Alex states though this is all down to personal taste, the coma corrector is now permanently attached to the 24mm!

I'm just thinking a coma corrector - most likely won't need - with the 100-degree attached to it will look like a baby telescope sticking out of the dob or growing out of the frac diagonal..

[John]

I've got an ES 24mm 82-deg and it doesn't have any astigmatism. While like I said above...the more expensive 15mm Panorama is not fun to use with an f/5 Dob. So based on that I'm assuming if the same level of corrected optics is applied to the 100-degree version then it should be fine. I stand corrected though.

And yeah, will be great if I could have a test first...

The 100 degree ES eyepieces are very well corrected for astigmatism. The extra field of view does tend to show more coma though, which is a scope generated aberration. As you move away from the optical axis of the scope, the coma increases so when you use a hyper-wide eyepiece, which shows more off axis field, you see more coma.

[Andy_E]

I'm just thinking a coma corrector - most likely won't need - with the 100-degree attached to it will look like a baby telescope sticking out of the dob or growing out of the frac diagonal..

Ha ha, it's true they do add a substantial amount of extra bulk. My thoughts are that it probably wont be a problem, you can always add one in to the mix later if it starts to bug you.

[emadmoussa]

The 100 degree ES eyepieces are very well corrected for astigmatism. The extra field of view does tend to show more coma though, which is a scope generated aberration. As you move away from the optical axis of the scope, the coma increases so when you use a hyper-wide eyepiece, which shows more off axis field, you see more coma.

Totally.

[YKSE]

The 100 degree ES eyepieces are very well corrected for astigmatism. The extra field of view does tend to show more coma though, which is a scope generated aberration. As you move away from the optical axis of the scope, the coma increases so when you use a hyper-wide eyepiece, which shows more off axis field, you see more coma.

Out of curiosity, will a Coma Corrector like ParaCorr has any other effects besides correcting Coma? does it affect the balancing? AFOV? etc..

[John]

Out of curiosity, will a Coma Corrector like ParaCorr has any other effects besides correcting Coma? does it affect the balancing? AFOV? etc..

I understand that CC's do have other implications as you indicate but I don't know the details as I've avoided needing one by going for a slower scope (F/5.3). 

This thread in the scopes discussion section includes some feedback from CC users which is interesting:

http://stargazerslounge.com/topic/200961-does-bigger-aperture-mean-more-magnification/page-6#entry2128907

[YKSE]

Does it mean that by paying extra for wider FOV (getting 100 deg EP instead of 82 Deg), you'll get worse edge performance because of increased coma, then you need to pay extra to get a Paracorr to reduce coma, by reducing the FOV at the same time? For fast scopes i.e.

[John]

Does it mean that by paying extra for wider FOV (getting 100 deg EP instead of 82 Deg), you'll get worse edge performance because of increased coma, then you need to pay extra to get a Paracorr to reduce coma, by reducing the FOV at the same time? For fast scopes i.e.

As I've said in that other thread, it's about about compromises and which you are prepared to make. I don't think you loose very much in the way of FoV through the use of a coma corrector though.

In my F/5.3 dob, my 82 degree 31mm Nagler is sharp more or less right across the FoV wheras the ES 20mm 100 degree eyepiece just starts to show the coma being produced by the scope right out by the edge of the field stop. Not enough to mess the view up in my opinion. 

[AlexB67]

As I've said in that other thread, it's about about compromises and which you are prepared to make. I don't think you loose very much in the way of FoV through the use of a coma corrector though.

In my F/5.3 dob, my 82 degree 31mm Nagler is sharp more or less right across the FoV wheras the ES 20mm 100 degree eyepiece just starts to show the coma being produced by the scope right out by the edge of the field stop. Not enough to mess the view up in my opinion. 

Interesting observation John. This tallies  if I were to extrapolate my experience with a 68 degrees. Perhaps there is some value in the back of envelope method I used earlier. Comparing your scope with mine (f4.7/f5.3)^3  ~ 0.69, Now FOV 68/100 = 0.68.  Don't we love simple sums if they can tell us something useful.