13mm or 17mm Ethos for C9.25?

[AussieBurger]

Hi, long time reader, first time poster to the forum. Always an educational read and hoped I might get some help from yourselves on the below question!

Need some advise regarding best Ethos Eyepiece choice for a C9.25 (non Edge HD). As a bit of background, I have a Evolution 9.25, with a Denkmeier PowerSwitch Diagonal (S2 model) which allows for slide in barlow and focal reducer, and have 35mm extension tube giving options for 2x barlow, 1.5x barlow, normal, x.83 reduce and x.66 reduce for every eyepiece. Great bit of kit and cant imagine observing without it with my SCT. To get most out of it, looking to ratify my eyepiece collection and looking to get a premier eyepiece as the workhorse for observing (when not binoviewing).

Kind of narrowed it down to Ethos 13mm or 17mm (having looked through 100 degree ep it works for me), and leaning towards the 13mm. Reasoning is that currently the best experience I tend to have is with my 11mm ES82 (pin point sharp to edge of FOV), and nice level of mag particularly with the x.66 reduce in place (not bad without too). Just a happy place kind of combo, so keen to replicate in 100 degree if possible.

Also have a 30mm ES 82 (amazing eyepiece), but find a dont use / like the view of 2x or 1.5x barlow as much (15m / 20mm equivilent) as edge isnt quiet as nice in these modes (still pretty good though). Not sure if it is indicative of c9.25 with higher mm eyepieces, so considering investment needed for an ethos was keen for any feedback of anyone you has tried a C9.25 (or any Cx SCT) with either 13mm or 17mm Ethos, and how the edge of field held up with or without a Focal Reducer in either? Any help is greatly appreciated and thanks again!

[AG Hybrid]

Personally I would choose the 21 Ethos over either of those in your scope. It gives the ideal 2.1mm exit pupil. Which is pretty much the perfect exit pupil for hunting galaxies but also for general deep sky objects. ~2mm exit pupil is ideal due to its balance of surface brightness and contrast/darker sky background.

That being said. For the cost of 1 Ethos 21, consider the Explore Scientific 14mm and 20mm 100 degree eyepieces. At a gentle F10 they perform brilliantly. I've tested and Ethos 13 and ES14 in a C11 both Edge and non Edge and they are sensibly identical.

[brian nordstrom]

:) Welcome mate , I dont personally have Ethos's but I find my 17mm Nagler gets more air time in my C9.25 than my 13mm Nagler , easier to look thru and still a nice 137x with a big flat and sharp FOV , sweet combo .
Brian.

[AussieBurger]

Thanks guys for input, always great to hear from those that have tried different options. Agree the 17mm range is definitely better suited based on focal length of 9.25. Guess my thinking was that with x.66 reduce in place with a ethos 13mm or es14mm would give about same TFOV / mag and exit pupil as a 20mm would. Also with the powerswitch diagonal and factoring in 46mm baffle of 9.25, something in 13mm / 14mm range can allow for reduce without vignette, whereas a 20mm or 21mm would definitely vignette if x.66 reducer used so would be a barlow / normal only with that option. Guess without extension tube and at x.83 reduce, 20 or 21 would be fine though.

As for ES vs Ethos, you know what its like trawling through forums and you read one stating that edge correction better with ethos and it sticks in your head.. Love the ES 82's I have though. ES 30mm gives 1.05 deg and reading Uncle Rod's blog and his success with 13mm ethos and reducer was what was kinda leading me down this path of a lower mm option to compliment.

Tough choices, if anyone has tried an ethos 17mm in a c9.25, love to hear if edges held up as well as a 13mm would?!

[The_bluester]

I have an older C925 and nowadays the EP that sits in it the most is a 30mm ES 82 degree. It does Vignette if I put in the .63 reducer but not so much that it offends me. I have an 18mm 82 degree as well but use that far less often.

I used to have an 11mm Nagler and it was lovely but I found I was using it less and less and eventually sold it to an IIS member who wanted to match another he had for bino use. I was finding broad expanses more interesting to view than the high power views of small areas (Though it did tease out really nice details in M42)

For planetary use I head for the other end of the range and have 25 and 15mm TV Plossls and a X2 barlow.

[AussieBurger]

Thanks Paul, yes the ES 30mm spends most time in too I find. 11mm ES 82 a close second (use two in my bino's too and that is a very fine combo). Find that my TV 32mm plossl (be it standalone or with barlow) certainly brings out more detail than the ES 30mm, albeit at a much smaller AFOV of course. Reckon the ES30mm with a reducer gives almost 1.3 deg, and even with vignetting is a lot nicer than my GSO 42mm which is around 1.2 deg by looks. Having tried a 100 degree, love the lack of noticeable fieldstop, but it sure will cost some $ by looks!

Question though, do you find with you 9.25 that focusing is a little harder with the ES30mm to get in focus across the field? As in, to sharpen up the edge you got turn a good quarter turn which brings center out of focus a bit? Can normally find a good middle ground, or just move a bright object out of center a bit to give a good view, but just wondering if just me?

[The_bluester]

It is not just you, the 30mm does show a little field curvature in my C925 but I have never found it objectionable. Really only the Plossls show none discernible in my scope.

The 30mm is better with the reducer installed but the vignetting may be masking a little of it as well. I actually find that to feel a little like the larger AFOV, you still need to look around to take in the whole field and the vignetting softens the field stop.

[Camelopardalis]

+1 what Adrian said...

I'd go for the ES100 20mm and then get something nice and sharp for the higher magnification work...the 100 degree aFOV is superfluous for that.

I've used my 17mm Ethos in a C9.25 non-Edge...the combo isn't pin sharp right to the edge of field, but I don't recall anything to really spoil the party. IMO the 13/14 is a more useful magnification. For wide, you already have the 30mm.

[AussieBurger]

Thanks Adrian, good to know some first hand on ethos 17mm in a 9.25.

For ES 100, what's people's thoughts on better optically between 14mm or 20mm? Anyone tried the WO / Skywatcher 100 deg offerings?

Thanks again all!

[AussieBurger]

Hi Paul, just as an update and side note, found a great workaround to curvature in the 30mm ES. May sound funny but unscrewed the Barlow lens from GSO 2" 2x Barlow and inserted barrel component only between the eyepiece and the diagnonal (in my case just messing around as slide in Barlow / reducer effect is based on distance) but as a side affect when in straight through mode without either, and using this extension with the 30mm, it greatly improves the edge of field / removed any noticeable curvature in my 9.25! Lengthens focal length and does therefore decrease fov by about 5-10%, but to have better overall feel to it seems worth it. Anyway, random as it is hope it helps someone else.

Thanks

[AG Hybrid]

The imagery of that description seems almost alien. But, I think I understand what you did. As long as you like it.

[AussieBurger]

I know right! Basically just a 50mm extension tube between diagnonal and eyepiece. Sometimes fun to play with different equipment combos just for giggles but this one had a unexpected outcome. Barlow I can understand would improve edge by simply removing it from fov. But in this case no Barlow just the tube worked really well!

[Don Pensack]

The 17mm yields 138x and a nice 1.7mm exit pupil.
This would become your workhorse eyepiece and probably get more use in the scope than any other.
I also think the 17mm yields better contrast than the 13mm, but that is really subtle.
The 13mm (181x) would just be a bit too small a focal length for everyday use on tons of objects. Seeing would interfere more and the 1.3mm exit pupil is getting kind of small (i.e. dark).
I think you'll enjoy the 17 more, and when you need another, get the 10mm first. I find it identical in optical characteristics to the 17.