21mm Ethos decision

[Allan]

Hi guys. I've got a 31 Nagler which gives me 1.7 degrees FOV and 48x, and a 13 Ethos which gives me 0.9 degree FOV and 115x. I always saw a 21 Ethos in my collection, but now that I've got these I'm wondering how much use it will get in my 12" Dob.

Anyone out there with a similar setup or experience care to comment. Thanks for your help.

[Satchmo]

Hi Allan- You have ep's for a 6mm Pupil and a 2.6mm Pupil - you definitely need something around the 4mm pupil mark to fill the gap. 4mm is really optimal pupil for balance between rich field and contrasty sky background and enough magnification to suit many objects . The 21mm would fit in well but so would 22mm Type 4 with 82 degree apparent field for a lot less money. Don't be distracted by true field comparison too much - the exit pupil is a more important parameter to consider in having a balanced collection that will suit many types of objects .

[MattT]

Hi Allan,
Where do you do most of your observing? Dark site or a LP site? The exit pupils are where I would make my decision...hence my eyepiece choice in my signature. Smaller Exit Pupil for LP sites is better. What is the fl of your dob?
Have you used the TV eyepiece calculator?
Matt

[Allan]

I will admit I haven't really thought about the exit pupil. And I'm not sure what an optimum range of exit pupils would be in an eyepiece set. The 21 Ethos would give a pupil around 4mm.

The sky here in the south of Newcastle is fairly dark. The Milky Way looks brilliant later at night after everyone goes to bed!

[barx1963 (Malcolm)]

Allan
I used a 21mm Ethos on my 12" f5 for a short while and found it very pleasant and easy to use. Just be aware it is a heavy beast, I had to adjust my balancing weight even when switching from the 17mm Ethos.
Marks point about exit pupils is correct, and also his comment about the 22mm Nag is certainly valid, unfortunately I haven't used the 22 in my 12" so cannot give a practical view.
Having said that I have done a direct comparison between the 13mm T6 Nag and the 13mm Ethos and the Ethos won easily. The larger field was complemented by much sharper definition and better contrast.

Please note I am in no way an expert on optics, I only try stuff out and see if they appear better to me!

Malcolm

[dannat (Daniel)]

If it were me I'd rate the 31 terminagler for either the 22 nagler or 21 ethos, 6mm expup does nothing for me in a scope, even in binoculars I like nothing more than 4-5mm exit pupil

[Satchmo]

Originally Posted by Allan

I will admit I haven't really thought about the exit pupil. And I'm not sure what an optimum range of exit pupils would be in an eyepiece set. The 21 Ethos would give a pupil around 4mm.

The sky here in the south of Newcastle is fairly dark. The Milky Way looks brilliant later at night after everyone goes to bed!

If price is no object a really good range is 6,5,4,3,2,1,0.5

An adequate range is 6,4,2,1

And a if I had to lose one more eyepiece it would be a slightly different selection . 5, 3 ,1.

As you become experienced you find that a jump of 2mm is massive and there are some objects such as galaxies of a certain size or brightness that really require those 1mm increments to have the perfect balance of detail and surface brightness.

If I were allowed only one EP on a desert island it would be a 3mm pupil or thereabouts !

[Allan]

Love your work Mark.

I'm heading into Bintel tomorrow to make the most of the TeleVue sale. I will let you know what the family looks like after that.

Thanks everyone for your advice so far.

[GrahamL]

Good luck with your choice Alan
I had a 22 mm t4 for quite a while in my 12" and its a nice eyepiece

I found I tended to use my 13 ethos most of the time and eventually sold the 22, though if I had the cash and could carry the weight I could easily convince me to buy the 21.

one of them will call you today

[Allan]

A funny thing happened at Bintel today. I tried parting ways with a decent chunk of money, and they wouldn't take it. In their opinion the 31 Nagler and 21 Ethos were too much like similiar eyepieces, and they thought I would be much better off with the 17 Ethos.

With a TV Paracorr, the 21E will give 80x and 3.8 exit pupil. The 17E will give 101x and 3.0 exit pupil. What I already have in the 31N gives 55x and 5.5 pupil, and the 13E gives 132x and 2.3 pupil.

So in light of this I have to decide which of the 21E and 17E to get to fill the gap. It still looks to me that the 21E sits better in the middle, but I'm not sure now. Anyway, it was all too hard today, so I bought neither.

However I did pick up an 8 Delos, just in time for the rain headed this way tonight! If they are as good as everyone says, I will pick up 1 or 2 more at the shorter end which should then keep me out of trouble for a long time.

So for those of you fortunate to have experience with both the 21E and 17E, what do you think? Cheers

[Satchmo]

Originally Posted by Allan

A funny thing happened at Bintel today. I tried parting ways with a decent chunk of money, and they wouldn't take it. In their opinion the 31 Nagler and 21 Ethos were too much like similar eyepieces, and they thought I would be much better off with the 17 Ethos.

Not good to be in an environment when you don't feel comfortable to make the purchase you feel like, and then come home empty handed.

The 13 and 17 are much closer in purpose than the 31 and 21 mm- I would still go for a 21mm as a 4.2mm pupil sits in a very special place , particularly in a dark sky - you can always fill in the gap later !

[Camelopardalis (Dunk)]

If the 17 and 13 weren't so close together, I'd say go for the 17... It gives half the field area of the 31N and is the "ideal" companion to it

Have you thought about selling the 13 and getting the 10 instead?

[Max Vondel (Peter)]

Hi Allan

I use a 12" Dob
My usual sequence would be
31 Nagler, 22 Nagler, 13 Ethos, 8 Ethos

I think the 21 Ethos would be your best bet
the 17mm is too close to the 13mm
TV suggest a sequence of 8,13,21 or 6,10,17

But don't under rate Satchmo's suggestion of the 22 Nagler
I'm very happy with mine, but the 21 Ethos would be better

Happy shopping

[Allan]

Peter I agree with you. TeleVue do suggest 6, 8, 13, 21 as a logical sequence. After all the great advice that's what I have decided to stick with. But just the 13 and 21 in the Ethos. I've heard the eye relief gets tighter in the shorter focal lengths, which I don't think I will like.

Still haven't had the chance to use the Delos. First impressions are that it is a great looking eyepiece and the sliding eye cup design looks really good. If it is just as nice to use, I will grab some more shorter focal length ones while they are on sale. Fingers crossed for tonight.

[Shano592 (Shane)]

Hi Allan,

If you want to try a 21mm Ethos out, hopefully the skies will clear enough for a trip to the Pony Club at Mangrove Mountain this weekend.

It is definitely my EP of choice, for general viewing. And you are most welcome to give it some light through the dob.

Fingers crossed for a clear start.

[Allan]

Thanks for the offer Shane. Haven't been to the Pony Club yet but was keeping an eye out for it. What night is it planned? I can't make it Saturday but Friday is ok.

[Shano592 (Shane)]

Hi Allan,

I was actually thinking of Friday for myself. I am a keyholder, so access isn't a problem.

The weather is really the big issue right now. It is so fickle from one hour to the next.

I also need to fix the power cable for my Meade at some stage this week. Somehow, the centre pin in the cable broke away, and is still attached to the scope. Hopefully Jaycar have a replacement piece.

It will probably pay to keep an eye on the Pony Club in June thread, to see what is happening on the day.

[Don Pensack]

Originally Posted by Allan

Hi guys. I've got a 31 Nagler which gives me 1.7 degrees FOV and 48x, and a 13 Ethos which gives me 0.9 degree FOV and 115x. I always saw a 21 Ethos in my collection, but now that I've got these I'm wondering how much use it will get in my 12" Dob.

Anyone out there with a similar setup or experience care to comment. Thanks for your help.

I have a 12.5" and use a 31 Nagler and 21 Ethos.
(next step is a 13mm).
I have discovered some things over the time I've owned both:
--the field of view of the 31 is wider, but not by a huge amount.
--at 62, my dark adapted pupil seems to show more natural astigmatism with the exit pupil of the 31 than with the 21, so the 21 gives generally sharper images to my eye, from edge to edge.
--the 21 yields a darker sky background in the image (noticeably), so the contrast in star fields is greater in the 21, making a more pleasing image quality.
--though the 31 sees a greater extent of nebula than the 21, the detail in the nebula is superior in the 21. I've used both on the Veil, and the 21 yields superior detail and slightly fainter nebulosity than the 31 when both are used with the same filter.
--the 21 gives superior views of nearly everything except the largest clusters. These tend to loose their "clusterness" and look more like random field stars with the increase in magnification.

I find myself using the 21 a lot more than the 31. I haven't brought myself to sell the 31 yet, but I really doubt I'd miss it. Both the 31 and the 21 are parfocal and use the same Paracorr setting, so there is no disadvantage to owning both. It depends on your age and your eyes. If you're older than 60, the 21 would be a great choice as a low-power eyepiece.

As for the possibility of the 25mm Explore Scientific 100 degree, which is a lot less expensive than the 21 Ethos, the transmission seems lower, the correction less, and the eyepiece a little more difficult to use. It is obviously a lower-priced eyepiece than the 21 Ethos, but does fill a niche.

One point: the wider the apparent field, at every focal length, the more visible is coma. If you are not using your scope with a coma corrector (and it sounds like you are not), coma will become obtrusive in the outer field in a 100 degree eyepiece. If you plan to stick with no coma correction, from that standpoint a 22 Nagler would be a better choice for the "in between" eyepiece.

[Allan]

Hi Don

I always really enjoy reading your input both here and on cloudy nights. It's timely that you posted as I finally had the chance to buy the 21 Ethos yesterday. I picked up the last one from Bintel in Sydney.

I re-read the advice given here, and I had the chance to try the 17E and 21E last weekend, and the 21E did seem the more logical choice. I thought the 17E was slightly more comfortable to use, but it was too close to the 13E I already have. I notice a lot of people have both the 17E and 21E, but I'm not sure that I would use the 17E often enough, except for the fact that it felt like a really comfortable eyepiece.

So I spent a few hours with the 21E last night, and it is definitely the wow eyepiece in my line-up. All of Don's observations are vindicated by what I saw. While the 31N is a great eyepiece for max FOV, the 21E had the nice dark background and pinpoint stars which makes it the eyepiece of choice for cruising the Milky Way and more.

Thanks everyone for your input. If these things weren't so expensive we could just go out and buy them all and try them out. Unfortunately at close to $1000 a pop it doesn't work that way. Cheers

[SingleMalt]

Glad to hear the 21E is working out, I was hoping to get into Bintel this week to grab one myself and complete the 21-13-8 collection but unfortunately my schedule didn't allow. The only consolation was that the weather wouldn't have let me use it anyway!

I'd be keen to see your thoughts on the 21E vs the 31N after a few observing sessions, I agonised over that choice for a long time... But still could be swayed as I haven't had a chance to buy the Ethos yet!