C8 eyepiece recommendations

[Chris]

Hi, I'm getting back on track with kit in my little obsy and I've recently managed to get some half decent aperture back, this time in the form of C8 Edge HD.

Can I ask for some help with deciding which widefield eyepiece to buy in order to get the best out of it on dso's? I have a 2 inch diagonal and visual back available.

Ideas for any reasonable budget, I know f10 isn't very demanding but I would be willing to pay more if the viewing experience justified the cost.

Any idea's or input appreciated:-)

Chris

[Dave In Vermont]

Two very good EP's fit the bill - and won't break the bank. One are the 68-degree ES series. At about $139/ea, this are very nice indeed:

http://explorescientificusa.com/collections/eyepiece

The other brand I suggest you look at are the Baader Hyperion EP's, which are also 68-degree FOV and also go for about $139:

http://www.baader-planetarium.com/pdf/hyperion_brief_description_e.pdf

The Baader EP's can be used in a 1.25" focuser and, by unscrewing the bottom set of lenses, be used in 2" focusers. The pdf. will explain this to you.

I hope this helps.

Clear & Dark Skies,

Dave

[Mark in Macc]

I have the ES 82 deg 30mm and it is excellent. I believe that 365 Astro are now stocking them at a very good price.

[YKSE]

I see that you have a 28mm MV in your sig, therefore I'd like to think something around 40mm would be a good addtition,  to get maximum FOV for the scope and nice spread of exit pupil.

Pan 41 will be the best you can get, the downside is the cost and weight. A budget but still reasonably good choice (my choice) is Skywatcher Aero 40mm. Edge correction is not as good as Pan, but clearly better than budget Erfle eyepieces. It weighs a little less than your 28mm MV, should work quite well in your 80mm too as low power and finder EP (5.6 degrees FOV if I'm not misstaken).

[Ruud]

How big is the diameter of the baffle of the 8" Edge HD? You might get vignetting if the field stop of the eyepiece is wider than the baffle of the telescope.

[Dave In Vermont]

I have a F10 SCT 12" scope. I am going to be experimenting with several focal-reducer combinations/spacing, etc. Hopefully I will find the "Goldilocks" combination that will turn my F10 into an F4-ish with a wider FOV without need to get more EP's - and no problems with vignetting. I will post my findings. 

Clear & Dark Skies,

Dave

[YKSE]

How big is the diameter of the baffle of the 8" Edge HD? You might get vignetting if the field stop of the eyepiece is wider than the baffle of the telescope.

I think the vignetting is so little that it's not  perceivable to our eyes.

My standard C8 has 38mm baffle diameter, I bought the 31mm Baader Ashpheric with 38mm Filed Stop because of that, then 40mm Aero because I wanted widest possible FOV and more exit pupil, it turned out to show no vignetting to my eye, as confirmed by many others.

The reason is that the baffle is not right at the field stop, the light fall-off at the edge is not much more than usual fall-off in reflectors/catadioptrics.

[Chris]

How big is the diameter of the baffle of the 8" Edge HD? You might get vignetting if the field stop of the eyepiece is wider than the baffle of the telescope.

Hi Ruud, good question, I read somewhere that it has a fully illuminated image circle of 42mm. I'm not that clued up on such things but I'm guessing the inside of a 2 inch barrel would be larger than this, maybe more like 52mm? Therefore I'm guessing there will be some vignetting with say a 40mm eyepiece. I'm just wondering how bad??

I notice that celestron stop there luminos range at 31mm 82 degrees, is this to prevent vignetting with there sct range I wonder?

[Chris]

I have a F10 SCT 12" scope. I am going to be experimenting with several focal-reducer combinations/spacing, etc. Hopefully I will find the "Goldilocks" combination that will turn my F10 into an F4-ish with a wider FOV without need to get more EP's - and no problems with vignetting. I will post my findings. 

Clear & Dark Skies,

Dave

Yes please do post your findings :-), a very worth while experiment! I wish you luck:-)

[Chris]

I think the vignetting is so little that it's not  perceivable to our eyes.

My standard C8 has 38mm baffle diameter, I bought the 31mm Baader Ashpheric with 38mm Filed Stop because of that, then 40mm Aero because I wanted widest possible FOV and more exit pupil, it turned out to show no vignetting to my eye, as confirmed by many others.

The reason is that the baffle is not right at the field stop, the light fall-off at the edge is not much more than usual fall-off in reflectors/catadioptrics.

Thanks YKSE, that's very reassuring:-) ok 40mm or thereabouts it is!

[Chris]

Thanks guys some great suggestions:-) as you can imagine I had a few candidates in mind but wanted to see what th general consensus would be with the C8:-)

I was thinking of adding the MV40mm to my collection but was worried about the sheer physical size and weight of the thing, 1250g!!. I still might go for it?

The SW Areo is one I hadn't even considered, it's certainly lighter and might be a good compromise in terms of quality so I'm going to give that one some thought.

Also didn't think about the ES82 30mm, might give better contrast with the higher mag and compensate with the wider fov.in which case maybe I should consider celestrons own luminos 31mm 82 degrees:-?

I also see that FLO have the Swan 40mm on sale for just 69 pounds! Not as good quality as the ES or TV Pan obviously, but it's light and maybe at f10 with edge optics it would work well ?

Any thoughts on above guys?

Many thanks for all the great responses:-)

[Grotemobile]

http://www.firstlightoptics.com/pentax/PentaxXF85.html

I have a CPC 800 Edge.This is the 

one I bought for it.Gives a mag of

235.I have a  ES 82 deg11mm as well.

Prefer this .

Steve

[coulthamst]

I am happy with my 38mm 70 degree SWA - sold as Agena, Skarp, and other brands - in my C8. No vignetting that I have noticed, good viewing, and easonable price for what you get.

[YKSE]

I also see that FLO have the Swan 40mm on sale for just 69 pounds! Not as good quality as the ES or TV Pan obviously, but it's light and maybe at f10 with edge optics it would work well ?

Any thoughts on above guys?

If you're using this eyepiece only in C8, my guess is that it should work quite well.

Possible issue might be when you use it in you f6 tripplet. I tried a TS 38mm 70 deg (same FLs and specifications as SW Panaview, same Erfle design as Swan) in  my f7.5 80ED, Vega was so distorted in the edge that it was really distracting, I replaced it with 31mm aspheric directly and I consider myself as not very fussy about edge performance since I always observe on axis.

[Chris]

If you're using this eyepiece only in C8, my guess is that it should work quite well.

Possible issue might be when you use it in you f6 tripplet. I tried a TS 38mm 70 deg (same FLs and specifications as SW Panaview, same Erfle design as Swan) in  my f7.5 80ED, Vega was so distorted in the edge that it was really distracting, I replaced it with 31mm aspheric directly and I consider myself as not very fussy about edge performance since I always observe on axis.

I was initially looking for an ep purely for the C8 but good point!

I thought the exit pupil might be on the large side to use a 40mm ep with my 80mm f6 apo, but I think it works out to be around 6.8mm which might just be doable for 38 year old eyes :-D

Maybe I should invest in better glass and go for the 34 or 40mm ES maxvision, 31mm 82 degree Luminos, or ES82 30mm. I guess it's not worth buying a cheaper EP if can only use it in very slow scope!

[Ruud]

Hi Chris,

in your APO you don't have to worry about the exit pupil getting too big. I used to use a 55mm 50° as a 9x finder on my 500mm f/5 refractor. The exit pupil was 11mm big and the TFOV was 6°. Terrestrial views showed parallax when I moved my head a bit and my pupil picked up different parts of the exit pupil. Everything was extremely bright and 3D.

in a refractor, the image becomes wider and brighter as the exit pupil increases. Beyond where the exit pupil matches the observer's pupil, the image stops getting brighter, but it won't become any dimmer, and the TFOV still grows. A maximally bright view, by the way, will show you your light pollution more clearly than ever. This is why I parted from my TV 55mm Plossl and got a dedicated finder instead.

Too large an exit pupil for an obstructed telescope is a bad idea because there is the shadow of the secondary mirror that sits in the middle of the exit pupil. This shadow gets bigger as the exit pupil increases and the image will begin to dim when the exit pupil diameter exceeds that of your own pupil. And as this happens the shadow of the secondary begins to fill up your pupil.

The 40mm Maxvision, by the way, is HUGE! If you get it we shall really want to see a picture of it on your 80mm.  And if you have light pollution, a 30+ mm focal length 82° eyepiece would be a better choice.

When two eyepiece have the same size field stop, they will have the same true field of view in the sky. In a 2" barrel, the maximum field stop will be around 48mm in diameter, the filter size for 2" eyepieces. The field stop needs to be bigger when the focal length of the eyepiece increases, and also for bigger afovs. 

[Chris]

Hi Ruud, thanks for the explanation, i knew a bit of that like a large exit pupil with central obstruction not being a great idea with the inverse vignetting it causes. I always thought that the downside of an oversized exit pupil even with a clear aperture was that it wastes light thus effectively stopping down the aperture, I.e your iris becomes the aperture mask. Sounds like it has some interesting effects though moving your eye around in an oversized light cone:-)

I also think you make a good point about low mag and light pollution, I think this is partly why the 13mm Ethos works so well at showing amazing contrast, not that I've had the pleasure of looking through one yet:-D

Slightly shorter focal length and bigger fov might be a good idea for getting as much contrast as possible with my town skies, I am in the red on the map! Still I've occasionally seen hints of the milky way from my garden after midnight when they turn a lot of the street lights off, so it's not as bad as it sounds:-)

[Chris]

Oh yeah, as for the Maxvision 40mm, yes I think it's massive, my 28mm is big, I think the 40 weighs about twice as much! 1250g!

I've got quite a small head so I might have to buy it just for comedic value:-)

[Chris]

I just done a Google image search to try and find an image of a MV40 on a scope or next to a bean can but no luck :’-(

[Chris]

Ok I've taken the plunge and ordered the monster maxvision 40mm! I just love ExSc stuff so much I couldn't resist in the end:-)

Due to the lack of online pics of this monster eyepiece next to anything suitable for scale I'll be taking lots of pics, next to a bean can and on my scopes etc. Hopefully this will help others who are thinking about buying it but also can't comprehend the size, which I still can't? :-D

I'm also giving some serious thought to selling my ES82 8.8mm plus my 9mm BGO in order to purchase the 9mm 100 degree eyepiece? Hmm? Need to read more reviews firstly though.