6mm UWA EP - good or bad?

[dreamliner]

Hey Guys!

I have just recently ordered this eyepiece from Astroshop.eu: Skywatcher Ultra Wide Angle eyepiece 6mm 1,25"

But I am now hesitating whether this was a good choice. Has anyone had any experience with this EP? Is it any good for observing planets such as Mars and Saturn?

I currently just have the 2 standard 10mm and 25mm EP's which came with my 8" dob and am looking to expand my collection.

Thanks a lot for all the input.

John.

[haitch]

Not got this EP but looking at the description on your link it is a 66 degree field which I would term Super Wide Angle Rather than Ultra Wide as they call it.

You don't mention what scope you've got EDit: sorry should read properly. If it is F6 or above I would guess it'll be fine anyhow. Any faster and the cheaper wide angle EPs tend to show their colours. That said, being SWA rather than UWA really, it may not be too bad and how much edge of field distortion you can tolerate is a personal thing.

Remember... beauty is in the eye behind the EP holder.

[russ]

It's not a bad eyepiece at all. Certainly a step up from the 10mm that comes with the scope. Eyerelief is good and it has a nice widefield. It's quite sharp on-axis (centre of field) and has good light throughput. Myself and Rob were quite surprised how well it performed. For the planets it's not a match for an Ortho or very good plossl but it won't shame itself either.

For me it's a better buy than a cheap 6mm plossl (about the same price) which won't be any sharper but will be short on eyerelief. As Haitch said, eye relief, edge correction and field of view is all a personal thing.

Russ

[dreamliner]

Haitch:

I have a Sky-Watcher 8” dob with the standard EP’s that came with the package. I am sorry for all these noobish questions but could you explain to me why should it be F6 or above? And what do you mean by tolerating edge of field distortion? Do you mean that the distorted view on the edges will make me sick or eyes hurt?

Russ:

Can you please explain in 2 words why eyerelief is important? I have seen this term many times but must confess that I don’t quite understand what it stands for. So would it be a better choice to get a 6mm plossl instead? If so then why…ugh, I feel so dumb asking all these questions :S especially after I already ordering the EP we are discussing here.

I really appreciate all the help guys, thanks!

J.

[TheThing]

There is a bit of a misnomer about certain EPs only being good in fast scopes and you have to pay a fortune for EPs to use with them.

[arad85]

F ratio is the ratio of focal length to aperture. A fast scope (i.e. relatively short focal length to aperture) has a steeper light cone. Think of lines going from the edge of the tube end to the focal point - as the tube gets proportionally shorter to the aperture, the angle of the cone at the focal point gets bigger and bigger. This means that any lens has more work to do in bringing the light to focus at your eyes as it has to bend the light further. this is more complex optically, and generally costs more to do it. If the lens cannot bend the light well enough (and all lens designs are a compromise) then you end up with distortions which get worse the further from the central point you are. A fast 'scope is generally F/6 or less, slow scopes (which are way more tolerant of cheaper eyepieces) tend to start at around F/10. Everything else is a medium speed 'scope.

Eye relief is important as it is where you have to place your pupil surface relative to the surface of the top of the lens. For me, it gets uncomfortable (feel I want to squint/hold my eye further away from the lens) at about 10mm. Any less than this and because I can't get my eye close enough, I start getting a smaller and smaller field of view as the light just doesn't reach my eye.

Google (or wikipedia) "eye relief" and "field distortion in fast telescopes" for further info

[russ]

Don't change your order for a plossl, here's my reasons why:

It is beneficial to have a widefield eyepiece when observing with a dob, especially so at higher powers. It means you can make less nudges on the scope to keep the object in view. I have some Ortho eyepieces which are simply superb optically but i find them a pain to use with the dob. I over look them in favour of some widefield eyepieces.

The 6mm UWA works rather well in the f6 Skywatcher dob.....it's the same scope i have and it's the scope that Rob and I were using when we were quite impressed with that eyepiece.

I've had a chinese Meade 4000 6.4mm and the 6mm UWA was on a par for sharpness in the centre of the field.

A plossl of that size will have very tight (short) eye relief which means you will have to really press your eye into the eyepiece to see the whole field of view. The UWA is very comfortable by comparison, you can place your further back and still see the field of view. Some will say that eye relief isn't all that important but for others (me included) it is.

Russ

[kniclander]

FWIW I have an f8 and an f4.8 newt and a range of up to £60ish eyepieces. The regular plossls seem to perform simlarly in both scopes. the super wide angle e/ps (ie 80 deg), whilst ok in the f8 are really horrible in the f4.8 the wide angle e/ps (ie 60deg or so) seem to do ok in both.

just MHO.

HTH

TTFN

[arad85]

FWIW

...

MHO.

HTH

TTFN

LOL (sorry, private joke )

[russ]

LOL (sorry, private joke )

I get them all except TTFN......i've heard before but can't for the life of me think what it is. Funny thing is i keep thinking of something the kids watch....Cartoon Network probably.

[russ]

Got it........Winnie the Pooh. ta ta for now.....is that it?

[dreamliner]

Arad85:

Thanks for the detailed explanation; it’s much clearer for me now! I now know that I have a fast scope. I had one chance to look at the moon through the 10mm EP and I don’t know if I am imagining this but sort of felt uncomfortable and even felt dizzy. I don’t know what was the main cause, perhaps bad eye relief.

Russ:

OK, that makes sense! I will wait and see how the EP performs in real life I can imagine that pressing your eye tightly against the eyepiece is not very comfortable.

Kniclander:

FWIW – HTH – TTFN – these must be some very specific astronomy terms I can’t decode

[dreamliner]

"For what it's worth."

"Hope that helps."

"Ta Ta For Now"

[russ]

Yep stick with it. Although technically an F6 is fast, it's not until F5 that a reflector is truly considered fast. F6 is bordering 'medium'.

[haitch]

Haitch:

I have a Sky-Watcher 8” dob with the standard EP’s that came with the package. I am sorry for all these noobish questions but could you explain to me why should it be F6 or above? And what do you mean by tolerating edge of field distortion? Do you mean that the distorted view on the edges will make me sick or eyes hurt?

Sorry I am may have confused you by writing my response without properly reading your post (hence the edit). The f ratio of your scope is fixed by its focal length divided by by its aperture (i.e. if its focal length is 5 times its aperture its an f5. I hadn't spotted that yours is an 8" Dob which (I think is around f5?) and had given a response to try to suit all scopes. The rule of thumb is f6 and up scopes are less fussy about the EPs you use with them because the pointier and thinner shape of the light cone being focussed is easier to manage. As you start to get to lower numbers the cone of light is a fatter shape and harder to bring to perfect focus across the field.

I'm not talking about eye strain or sickness - just about how noticable you find imperfections in an eyepiece. I had a 30mm 2" 80 degree ultrawide that, whilst I could see plenty of coma around the outer part of the field of vision in my f4.5, for what I paid I found it quite acceptable. I lent it to someone at my astro club to try in their F10 (which it shouldn't be as bad in) and they reported they found it awfully distorted. I think he's spent several hundred pounds each on some Naglers. Personally I was glad to have a healthier bank balance at the time. Just perspective I guess.

Hope my ramblings make sense!

[dreamliner]

That sounds perfect for me

Without trying to go very off topic here, allow me to ask... Which EP's would you recommend an average backyard astronomer to have in his collection. I don't have any specific requests like "I only want to see planets and not galaxies" but just in general. I am interested in absolutely everything, nebulas, galaxies, star clusters, planets and of course our precious Moon! So considering a relatively tight budget, what kind of EP's would be an ideal selection.

Hope I didn't sound too vague and stupid there

J.

[dreamliner]

haitch: they make perfect sense to me! thanks again for the explanation. I just don't want to spend money on equipment I will not find useful, hence my questions in the forum. Unfortunately, I am not the richest guy on this planet so have to be real careful before investing money in my newly discovered hobby...but so far I find it very rewarding. Too bad my face keeps freezing off in the -25 temperatures though

[arad85]

Got it........Winnie the Pooh. ta ta for now.....is that it?

See.. that wasn't too difficult now was it.... You can always google it - the first result for TTFN is the Wiki page which says how it was absorbed into the English langauage.

[michael.h.f.wilkinson]

Regarding eye relief: for people with glasses, I find 15-16mm the minimum workable, any lower and my glasses keep nudging the scope.

Regarding the question good or bad: there are very few seriously bad pieces of kit out there (apart from some platsic Huygens wannabe EPs in some department-store scopes). There's good kit, very good kit, excellent kit, and outstanding kit. I started out with little 24.5 mm (0.96") diameter Plossls and (wannabe) orthos. I had a lot of fun with them, saw a lot, learned a lot. Then I saved for the C8 I still have. Even the standard 1.25" diameter EPs that came with it outclassed the old. Had a lot of fun with them, saw and learned a lot more. Then I got fed up with the short eye relief of the 10mm Plossl, so I got some Vixen LVs (which I still have). Much more comfortable views, really enjoyed them. Still kept the other Plossls (26 and 36 mm)

Some years back I replaced the back end of my telescope to a 2" type to fit the Vixen flip mirror. Consequently, I got a TMB Paragon 40mm super wide angle, and a Meade 14mm UWA. Even more to see and even more fun.

I have now (just yesterday) replaced the last of my Plossls, and will discard one of the LVs in favour of the new Radian. So yes, there are always better EPs to be had, but that does not mean the older designs are bad. I also think you appreciate the (sometimes subtle) differences between EPs better with more experience.

Do not change your order, it is bound to show you much, teach you much, and you will have fun with it.

Let us know your experiences wen it arrives

Cheers

Michael

[arad85]

That sounds perfect for me

Without trying to go very off topic here, allow me to ask... Which EP's would you recommend an average backyard astronomer to have in his collection. I don't have any specific requests like "I only want to see planets and not galaxies" but just in general. I am interested in absolutely everything, nebulas, galaxies, star clusters, planets and of course our precious Moon! So considering a relatively tight budget, what kind of EP's would be an ideal selection.

Hope I didn't sound too vague and stupid there

J.

Dictated by budget! Generally, people will have some smaller length planetary specific eyepieces, followed by a mix of medium/low mag ones. Personally, I've gone with widefield for my medium/low power. The advantage of wide angle over narrow angle is that you can get "closer" to a particular object whilst still seeing all of it. This helps as the higher the magnification, the darker the sky background is.

For background, you may like to read:

Tele Vue Optics Article Page

and

Tele Vue Optics Article Page

Whilst there articles are from Televue, they are pretty coherent and illustrate what benefits you get with wider field eyepieces.

HTH

[kniclander]

That sounds perfect for me

Without trying to go very off topic here, allow me to ask... Which EP's would you recommend an average backyard astronomer to have in his collection. I don't have any specific requests like "I only want to see planets and not galaxies" but just in general. I am interested in absolutely everything, nebulas, galaxies, star clusters, planets and of course our precious Moon! So considering a relatively tight budget, what kind of EP's would be an ideal selection.

Hope I didn't sound too vague and stupid there

J.

I find that i generally use 2 e/ps the most - a 32 mm for finding things and DSOs and a 9mm TMb planetary for close ups and planets. i would suggest thinking about a couple of decent e/ps rather than a "kit" with half a dozen cheap ones.

[haitch]

Once you have topped and tailed your set (30 to 32mm at the other end as suggested - go for a 2" wide angle if your focuser and funds allow) You may feel you have a gap to fill between the 10mm & 25mm or you could use a barlow to achieve other focal lengths and that'll probably start a whole new discussion.

[russ]

Without trying to go very off topic here, allow me to ask... Which EP's would you recommend an average backyard astronomer to have in his collection. I don't have any specific requests like "I only want to see planets and not galaxies" but just in general. I am interested in absolutely everything, nebulas, galaxies, star clusters, planets and of course our precious Moon! So considering a relatively tight budget, what kind of EP's would be an ideal selection.

In terms of what size eyepieces to have i like:

32mm 1.25" or 2" for finding/widefield

13mm-18mm for workhorse eyepiece

5mm-9mm for planetary/close up

All depends on the focal length of the telescope as to which size to choose. Your 6mm that you have already ordered is absolutely spot on for your telescope. It gives 200x and that's a good planetary magnification most nights of the year.

Something around 16mm-18mm mark is a good workhorse eyepiece that will frame most objects nicely but can also be barlowed too 8mm-9mm for those nights that need a little less magnification than the 6mm.

And a 2" 32mm eyepiece is awesome for finding targets and seeing a big expanse of sky.

Russ

[haitch]

Should also say 32mm is the limit for field of view in a 1.25" Plossl type EP. Any more and you are just making the same field of view look smaller through the eyepiece. If you want to fit more in then you need 2" EPs. 32mm is probably around the max for exit pupil size (I'm guessing I haven't calculated that - someone may enlighten further) which means that you won't get all the light into your eye and the shadow cast by the secondary may begin to become visible I believe.

[russ]

Exit pupil with the 32mm will be fine, works out at 5.5mm. Even older eyes should be okay.