Need advice on choosing eyepieces for 18" skywatcher

[raanany]

Hi guys

I need your advice. 

I'm new here. It's my first post and I'll be receiving my first scope in a few weeks. Kind of a lifelong dream for me. I'm 43 btw.

What I really wanted was an obsession 18"UC. I was even considering the 15" version but owing to freight and tax (I don't live in the U.S.) the total cost of even the 15" would have eaten my eyepiece budget. 

Instead I've ordered a skywatcher 18" 450p from a local dealer for $5K. I hope it works well, there aren't any user reviews that I could find. 

My question is actually about eyepieces. The optics on my scope have the same figures as the obsession 18” UC. It's a 458mm objective with 1900mm focal length. This means f/4.15. 

My dilated eye-pupil seems to be around 6.5mm

Questions:

For the low magnification end, which of these would you recommend best

Model   Fe    AFOV    TFOV      Dep     Mag    Price

Nagler  26    82      1.055     6.267   73     $615

ES      25    100     1.236     6.026   76     $800

Nagler  31    82      1.266     7.473   61     $650

Panop   41    68      1.387     9.883   46     $510

For the high magnification end, I was thinking about ont of these:

Model   Fe     AFOV   TFOV      Dep     Mag    Price

Ethos   4.7    110    0.270     1.133   404    $610

Ethos   6      100    0.314     1.446   317    $575

Do take into account that I might in the future get a coma correction lens (equivalent to 15% increase in objective focal length)

Thanks,

Raanan

[John]

Hi and welcome to the forum

I would put a coma corrector high up the priority list if you are going to get good value from those ultra-wide eyepieces.

With a focal ratio of F/4.15 maintaining an effective exit pupil at lower magnfications means the Ethos or ES 100 eyepieces really come into their own.

I'd be trying to go for the longer and medium focal length Ethos / ES 100's and perhaps 70 degree Delos eyepieces or ES 68's for the shorter focal lengths. Obviously the Tele Vue options are expensive but they are totally in their element in these large aperture / fast focal ratio instruments. The lower cost ES alternatives also do a good job though.

[raanany]

Thanks John.

Think I'd better move the post to the eyepiece discussion section.

[John]

I'll merge the two threads then.

[Dave Lloyd]

Welcome Raanan, that's a heck of a starter scope.

[Chris]

Welcome to SGL

Great advice from John.

I've had lots of scopes over the last 30 years, none above 8" net alone 18" !          

[niallk]

Hi - I've looked longingly at the SW 18" - Enjoy!!! I read some great reviews of this scope from some guys in France ...

Would be really interested in how you get on.

Best of luck,

-Niall

[swamp thing]

Hi

I've been using quite large scopes a while now and can say with absolute certainty. THE eyepiece you want is the 21mm Ethos. The combination of contrast, field of view and image scale make this the stand out eyepiece in large dobs. I have the 31mm nagler and have used the 26mm many times both are great eyepieces but the 21mm ethos kills them stone dead in big scopes.

For high power the 8mm Ethos provides unbelievably good views and I rate this as THE most immersive eyepiece I've ever used. I was standing next to my scope looking at M5 floating accross the eyepiece before I even got my eye up to the scope. It actually felt like one could reach out and pick the glob up out of the eyepiece. Stunning.

That's my pick.

[raanany]

Thanks guys.

Swamp thing - using the paracorr with the 21mm ethos will leave me with just 0.949 deg of TFOV. Is this what you're using as a wide view eyepiece? What's the focal length of your scope? I thought that the 31mm nagler would still be of value for the 1.1 deg TFOV and increased brightness.

Am I wrong about this?

As for the 8mm ethos, I'm wondering - what's the magnification you're getting with it?

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[Stu]

Raanany, sounds like a lovely scope you have coming, should be great.

Steve (swamp thing) knows his onions when it comes to large aperture scopes and eyepieces so his advice is worth listening to.

Having used both 21e and 31 nag in my 16" under reasonably dark skies I wouldn't say the 21 blows the 31 out of the water exactly, but under most circumstances it is the better choice.

I did find one target in particular (the Crescent nebula) which was definitely better in the 31.

I would say get the 21 and 8 for starters, but a 31 is a nice to have at a later date perhaps, depending on budget.

[estwing]

It's thee ep to have in an 18"+ plus scope everything swampthing says has to be underlined and it Does kill the 31nag I'm not kidding we had had great skies SWSP and on several targets there was no competition get a 21E a 8E and a x2 powermate and a coma corrector it's a big outlay at first but you will not need another ep for years and years

[alan potts]

Hi and welcome.

I have an 18 inch F4.3 and the one thing I would consider tops is a Paracorr if you are going to buy TeleVue eyepieces, I don't see the point in paying out on high quality that shows sharp to the edge if we then allow the mirror, no matter how good it may be, to then mess things up a bit.

Now as a Paracorr will change your focal length you may wish to reconsider eyepiece choice. On these scopes I put Ethos at the top but though I don't have one I would have thought 4.7mm was a little high, 6mm may be top end, I find 8mm is for me at the moment though i am sure my nudging skills with the scope will improve. As Steve say's the 21mm is not bad.

I find the 31mm Nagler is made for my scope and now would never sell it, unless Nagler 2 comes along. The 41mm Panoptic is also a very good finder and the lowest power you can get just about.

I think the reason that there are no reviews on this is because I really don't think they sell many, it's not really 10 a week prices, I am sure one or two will come to light in time, it looks nice though.

There is a review of my scope in Members Equipment and a first light report in Observation reports, it may help you a bit. I am also sorry my answers seem to be expensive ones. BTW next scope Hale Polama 200 inch?

Don't cut from your thoughts the Delos range for higer powers, say 10/12mm and 6/8mm.

Alan

[raanany]

Thanks Alan

I'm willing to pay for the right stuff. Been waiting so long for this.

Reading all this I'm closing in on the following list:

6 ethos when I'm at my nearby desert

10 ethos when I'm not...

21 ethos because it's a must

31 nagler for very big objects (I must see Andromeda)

Paracorr

Lawyer - if my wife opens the credit card bill before I get to destroy it

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[alan potts]

I think on reflection I must start using my 8mm and 21mm Ethos as I appear to be underworking them.

Personally being new to Dobs but not new to TeleVues I find the massive field of view on offer from Ethos helpful, I am still in the which way do I pull it or push it syndrome.

I feel 8mm would be great and I use this in my scope, though so far not the 6mm which I also have. I see the advice of 21mm and 8mm very strong and as Stu said the 31mm would be nice too, I don't really see a Powermate fills that gap though. I don't not use a Powermate, had one never really used it and sold it. I do however have a good few eyepieces.

I would fill the gap with something around 13mm. Oh look there is a 13mm Ethos. For me it would be top set 31,21,13 & 8mm.

Sorry but I do love spending others cash .

Alan

[estwing]

Get a nice finderscope that will stop you buying a 41 and a 31 ep.....21,8, powermate your done

[raanany]

I'm thinking of getting a nexus so wasn't planning on relying on a finder scope that much. Worth considering though. Thanks.

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[raanany]

Also, wouldn't a 10mm be better than 21+powermate?

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[alan potts]

I like Calvin's idea of buy a nice finderscope, I tried to do the same thing for the second time. I have the Baader Vario Finder which for the cost is poor at best so I tried the TS version as Sumerian deal with them and this is not much better. I find the 2 Skywatcher's 9x50mm I have are much better. Oh the one on the Meade scope is poor to. You can't say I don't try things out.

I too was going to get the push to option as well next thing on the list. I think next I may try Borg 50mm as finder see if they please me.

[RikM]

Don't bother with a nexus. To make the most of large aperture you want it DARK. Killing your night vision with a tablet is a no no. I don't use TeleVue myself but have looked through a fair few. The 21E, 8E +PM combo is world class and will cover almost everything you might want to look at.

I use mainly 20mm, 14mm and 7mm Pentax XW for deep sky observing that give similar levels of light throughput and contrast, with longer eyerelief and a smaller aFOV, which I prefer.

For Andromeda, get a smaller scope. A big Dob gives you image scale, they are not meant for viewing huge objects in one go.

[Stu]

Don't bother with a nexus. To make the most of large aperture you want it DARK. Killing your night vision with a tablet is a no no. I don't use TeleVue myself but have looked through a fair few. The 21E, 8E +PM combo is world class and will cover almost everything you might want to look at.

I use mainly 20mm, 14mm and 7mm Pentax XW for deep sky observing that give similar levels of light throughput and contrast, with longer eyerelief and a smaller aFOV, which I prefer.

For Andromeda, get a smaller scope. A big Dob gives you image scale, they are not meant for viewing huge objects in one go.

Rick, before SGLX I would totally have agreed with you, but have now completely changed my opinion.

Using it with the brightness turned down, in red light mode and decent rubylith covering the screen it did not affect my vision at all, certainly no more than a red light torch and maps.

Using the Nexus to find my way around the Virgo cluster was brilliant. It's so easy to keep track of what you are looking at and to find new targets.

I saw a mag 14.2 galaxy and could have gone deeper I think, that was while using the Nexus so I really do think they are fine.

Stu

[John]

Rick, before SGLX I would totally have agreed with you, but have now completely changed my opinion.

Using it with the brightness turned down, in red light mode and decent rubylith covering the screen it did not affect my vision at all, certainly no more than a red light torch and maps.

Using the Nexus to find my way around the Virgo cluster was brilliant. It's so easy to keep track of what you are looking at and to find new targets.

I saw a mag 14.2 galaxy and could have gone deeper I think, that was while using the Nexus so I really do think they are fine.

Stu

I found even my illuminated watch face slightly annoying when it's really dark. 

[RikM]

Rick, before SGLX I would totally have agreed with you, but have now completely changed my opinion.

Using it with the brightness turned down, in red light mode and decent rubylith covering the screen it did not affect my vision at all, certainly no more than a red light torch and maps.

Using the Nexus to find my way around the Virgo cluster was brilliant. It's so easy to keep track of what you are looking at and to find new targets.

I saw a mag 14.2 galaxy and could have gone deeper I think, that was while using the Nexus so I really do think they are fine.

Stu

Adding a sheet of rubylith as well as turning it down and setting it to red light might make all the difference Stu. I find them far too bright without it. Will have to give that a try.

[Stu]

Adding a sheet of rubylith as well as turning it down and setting it to red light might make all the difference Stu. I find them far too bright without it. Will have to give that a try.

Do give it a go. I used an iPhone rather than a tablet so less brightness still.

John, it's possible to turn them down so as to be pretty much invisible, so they are no brighter than using a red torch and maps.

Certainly some of the red head torches I see around are enough to burn your retina off!! [emoji6][emoji6][emoji12][emoji12]

[estwing]

Do give it a go. I used an iPhone rather than a tablet so less brightness still.

John, it's possible to turn them down so as to be pretty much invisible, so they are no brighter than using a red torch and maps.

Certainly some of the red head torches I see around are enough to burn your retina off!! [emoji6][emoji6][emoji12][emoji12]

...it was a new battery!!

[alan potts]

I use a laptop often with the screen brighness on minimum, I find it's where you position the things most important, don't think I would want it next to the eyepiece even if I could get it there.

alan