Explore Scientific 20mm 100 degree eyepiece any good?

[nitram100]

Hey guys, 

I have a 14mm 82 degree eyepiece from Explore Scientific and it works really well in my below telescope. 

I am thinking about purchasing the 20mm 100 degree, I was wondering would the increase in degrees from 82 to 100 increase the risk of showing really bad coma? I don't seem to notice any on the 14. 

Thanks

[emadmoussa]

Didn't you email me?

OK, different point of view...

http://hyperionzoomlover.blogspot.co.uk/2011/09/johns-100-explore-scientific-20mm.html

[John]

I've owned the ES 20mm / 100 and I now have a 21mm Tele Vue Ethos. Very little difference in performance that I can see in all honesty. There will be some coma in an F/4.8 newt (it's a feature of all newts) and I saw just a touch right out by the field stop with my 12" F/5.3 but nothing intrusive at all. Great eyepiece and very immersive, especially with the rubber eye cup rolled down

[nitram100]

Didn't you email me?

OK, different point of view...

http://hyperionzoomlover.blogspot.co.uk/2011/09/johns-100-explore-scientific-20mm.html

Oh yeh lol I emailed you on ABS. Thanks for the link mate, will give it a good read! Thanks John as well for your input mate. 

Martin

[Mark in Macc]

Very good eyepiece indeed. Very immersive experience, huge fov.

[Bart]

My favourite EP in my16" LB. Lovely eyepiece.

Barry

[MoosBros]

I opted for the ES 18mm 82* instead of the ES 20mm 100*....now I regret that choice, not that the 18 isn't good, but I settled when I shoulda listened to that little voice in my head saying it would the right way to go........the ES 9mm 100* is my most used EP........the Televue Delos series would be a good choice too, especially below 9mm or 10mm....smaller fov, but more contrast and brightness that even the Ethos...for distant dim fuzzies, just what the Dr ordered...

[wolfpaw]

A well-corrected, 100 degree eyepiece at anything over 20mm in an f/4.8 telescope is going to show a hell of a lot of coma.

[emadmoussa]

A well-corrected, 100 degree eyepiece at anything over 20mm in an f/4.8 telescope is going to show a hell of a lot of coma.

That's just an assumption. in my f/4.9 the 20mm showed very minimal coma. On the other hand, some eyepieces showed a horrendous amount of trailing and astigmatism.

[wolfpaw]

That's just an assumption. in my f/4.9 the 20mm showed very minimal coma. On the other hand, some eyepieces showed a horrendous amount of trailing and astigmatism.

It's not an assumption, emad. It's a scientific fact. Wide angled eyepieces of more that around 20mm will show more of the telescope's inherent coma. The greater the angle the more of the coma that will be seen. Astigmatism is another issue limited primarily to the quality of the eyepiece. Explore Scientific eps should be nicely corrected and, at 100 degrees, will reveal sizeable amounts of coma. It's entirely normal and to be expected.

[John]

That's just an assumption. in my f/4.9 the 20mm showed very minimal coma. On the other hand, some eyepieces showed a horrendous amount of trailing and astigmatism.

Coma exists in fast newtonians and the faster they get, the more coma is present. It's inescapable I'm afraid in the same way that chromatic aberration is present in achromat refractors.

Both can be controlled by optical means (in the case of coma) or filtration / optical correction in the case of CA. 

What I would say, judging from the posts I read on here and personal experience is that some folks are less bothered by it than others and the subject being viewed and the magnification used can affect how much it is noticed. 

Designs such as the maksutov-newtonian and schmidy-newtonian show much less coma - around 30% as much as a conventional newtonian.

[spaceboy]

I have the ES 14 82° & 20 100° in a 250PX f/4.8 and they are both superb eyepieces for the money but your always going to have something or other going on in the outer edges of a fast Newtonian. Better and often more expensive EP's seem to clean up this distraction a little more so than cheaper EP's but coma will remain until a corrector of one type or other is used. 

As for your question I would say the views of an 82° and 100° will show the same ratio of coma. What I mean is that the later 40% will often show one aberration or other depending on the quality of the EP and  F ratio of the scope.

While I do really like the views through my 20mm 100° and shortly after purchased the 14mm 100° to replace the 14mm 82° the eyepieces themselves are heavy and large and there is always the worry that gravity may one day win the battle.

[wolfpaw]

I have the ES 14 82° & 20 100° in a 250PX f/4.8 and they are both superb eyepieces for the money but your always going to have something or other going on in the outer edges of a fast Newtonian. Better and often more expensive EP's seem to clean up this distraction a little more so than cheaper EP's but coma will remain until a corrector of one type or other is used. 

As for your question I would say the views of an 82° and 100° will show the same ratio of coma. What I mean is that the later 40% will often show one aberration or other depending on the quality of the EP and  F ratio of the scope.

While I do really like the views through my 20mm 100° and shortly after purchased the 14mm 100° to replace the 14mm 82° the eyepieces themselves are heavy and large and there is always the worry that gravity may one day win the battle.

Do you mean that 40% of the field of view is affected by aberration?

[emadmoussa]

I wasn't disagreeing, but like mentioned above people differ as far as their fixation on coma is concerned.

Yes, there's coma in the 20mm and 14mm 100-deg EPs, but I found it fairly negligible and never really bothered me. Anyhoo, if I start getting fussy I'll get a coma corrector

One thing though, even if there's, say, 10% of the filed of view you still get a large FOV that is perfectly fine. It's a 100-deg after all...

[wolfpaw]

I wasn't disagreeing, but like mentioned above people differ as far as their fixation on coma is concerned.

Yes, there's coma in the 20mm and 14mm 100-deg EPs, but I found it fairly negligible and never really bothered me. Anyhoo, if I start getting fussy I'll get a coma corrector

One thing though, even if there's, say, 10% of the filed of view you still get a large FOV that is perfectly fine. It's a 100-deg after all...

Perhaps, but then I don't really see the point in having 90% of the field of view filled with coma either. It seems to make low-power, wide-angle eyepieces rather redundant.

[crashtestdummy]

My favourite EP in my16" LB. Lovely eyepiece.

Barry

Ditto,was about the only eyepiece I used for 95% of my viewing with my old 16" LB and I'm sure it will be just as good in the 22"

[crashtestdummy]

I have use the 20mm 100° in an f4.5 and there nothing like the coma you describe plus isn't coma from the optics rather than the eyepieces?I could live with some coma in the es 20mm compared to the 21mm ethos as it's half the price.I used mine with and without a paracorr and the difference isn't massive anyway

[John]

I have use the 20mm 100° in an f4.5 and there nothing like the coma you describe plus isn't coma from the optics rather than the eyepieces?I could live with some coma in the es 20mm compared to the 21mm ethos as it's half the price.I used mine with and without a paracorr and the difference isn't massive anyway

Coma is generated by the newtonian optics and the faster the scope, the more coma is present. In my 12" F/5.3 the ES20 / 100 showed just little coma (not astigmatism) right at the edge of the FoV as does the Ethos 21 that has replaced it. In my F/4.8 10" there was more coma as you would expect. If I'd stayed with that scope and wanted to use the lower power 100 degree eyepieces I'd have invested in a coma corrector I think.

As I said in another thread, coma is a fact of optical design. Some folks notice it more than others though, I reckon. Personally I find coma less annoying than astigmatism but my ideal is pinpoint stars right across the FoV if possible which influenced me to grab the 12" F/5.3 when it came up for sale. It's also why I like the views through refractors.

[jetstream]

Perhaps, but then I don't really see the point in having 90% of the field of view filled with coma either. It seems to make low-power, wide-angle eyepieces rather redundant.

I own an f4.8 dob NONE of my eyepieces have coma in 90% of the FOV,including my worst the 23mm Luminos(which is great on nebula BTW).The view with my 17mm Ethos 100 deg,10mm Ethos 100 deg is superb,with coma just showing in the 17mm.My 21mm Ethos offers great views but with more coma-however it is not 90%,40% thats for sure-maybe 15% depending on the viewing angle.

Good quality widefield eyepieces are not redunant, as the view they offer in a well collimated Newt is something to behold.Carolines Rose was spectacular in my Ethos from dark skies the other night.Everybody should have a look through one

ps I understand the 20mm ES 100 provides same view as the Ethos

[wolfpaw]

I own an f4.8 dob NONE of my eyepieces have coma in 90% of the FOV,including my worst the 23mm Luminos(which is great on nebula BTW).The view with my 17mm Ethos 100 deg,10mm Ethos 100 deg is superb,with coma just showing in the 17mm.My 21mm Ethos offers great views but with more coma-however it is not 90%,40% thats for sure-maybe 15% depending on the viewing angle.

Good quality widefield eyepieces are not redunant, as the view they offer in a well collimated Newt is something to behold.Carolines Rose was spectacular in my Ethos from dark skies the other night.Everybody should have a look through one

ps I understand the 20mm ES 100 provides same view as the Ethos

So only 60% of the field of view is coma-free. Again, I don't see the point in wide-angled eps if 40% is unviewable because of the coma. Why spend £££s on, for example, a 100 degree eyepiece if you only only see 60 degrees without the coma. Just my personal opinion.

[emadmoussa]

So only 60% of the field of view is coma-free. Again, I don't see the point in wide-angled eps if 40% is unviewable because of the coma. Why spend £££s on, for example, a 100 degree eyepiece if you only only see 60 degrees without the coma. Just my personal opinion.

have you ever tried a 100 deg eyepiece?

[jetstream]

So only 60% of the field of view is coma-free. Again, I don't see the point in wide-angled eps if 40% is unviewable because of the coma. Why spend £££s on, for example, a 100 degree eyepiece if you only only see 60 degrees without the coma. Just my personal opinion.

LOL!!Forgot the comma in regards to the coma...!   Maybe we can insert "or" in there not 90% or 40%.Maybe we should also underline the 15% that is the coma seen to me too.I'm glad I'm picky on collimation,not grammar Have you tried any Televue,ES 100 deg EP's?

[wolfpaw]

have you ever tried a 100 deg eyepiece?

Nope, but if coma shows across 50% of the field of view in my 68 degree Maxvisions then I doubt 100 degree ES eps will be an improvement. And I've been told to avoid low power, wide angled eyepieces in an f/4.7 telescope because of the coma they create. It seems that only high power, wide angle eyepieces work well in a fast Newtonian. As I said, forking out for 100 degree wide angle eyepieces when potentially half the view is marred by aberration seems self-defeating. Anyway, I've said my bit about it. If people get on with them then that's fine. I just wanted to put an opposing opinion.

[crashtestdummy]

Did anyone say that 40% was unviewable?just because coma is present doesn't mean it's a bad view.you will ALWAYS get some coma in wide angle eyepieces,nothing other than a coma corrector will stop that.

[Damo636]

Nope, but if coma shows across 50% of the field of view in my 68 degree Maxvisions then I doubt 100 degree ES eps will be an improvement. And I've been told to avoid low power, wide angled eyepieces in an f/4.7 telescope because of the coma they create. It seems that only high power, wide angle eyepieces work well in a fast Newtonian. As I said, forking out for 100 degree wide angle eyepieces when potentially half the view is marred by aberration seems self-defeating. Anyway, I've said my bit about it. If people get on with them then that's fine. I just wanted to put an opposing opinion.

No harm at all in an opposing opinion, each to their own and all that! I get the feeling however that you find coma particularly bothersome, even with your 68° eyepieces. Some are more bothered by it than others, and once noticed, (an f4.7 scope will generate a fair bit!) it's hard to ignore. If you are detecting it as far in as 50% from the field edge with your Maxvisions, I would highly recommend a coma corrector of some sort to clean the view up? Just my 2 cents!