Eyepiece advice for a C925 Celestron.

[The_bluester]

Firstly, my scope is not an Edge HD, just a run of the mill 925.

Over the few years I have had my scope I have managed to collect a bit of a ragtag assortment of eyepieces (Mostly from Ice Trade!) some 2" Celestrons E-Lux, a nice widefield Meade (68 degree 34mm (edited to fix the typo! it is not a 43mm) the original 40mm Celestron E-Lux 1.25" that came with the scope, a couple of TV Plossls and an 11mm Nagler.

I am starting to think about consolidating my EP family a bit. I have found myself gravitating towards wider views lately and the Celestron seems to spend the most time in the scope.

The basic question, has anyone had an experience good or bad with the ES 82 degree line, specifically in a C925? And has anyone used them with a focal reducer? I would love a couple of long FL Naglers but the budget just does not stretch to it. I am considering moving anything up to ALL my existing family and starting again (I might hang on to a couple of the shorter FL 1.25" jobs for planetary views) At the extreme end I would like to eeke out the greatest useable true field that my scope can provide. I could probably afford to snag myself a secondhand dob off the trader section, but I am not sure that the marriage would stand explaining why I need another scope!

Any suggestions or experiences with the ES line? I do like the combination of wide AFOV and wide TFOV.

[Strawb]

Hi,
I find the LVW range just perfect for me - check them out

[The_bluester]

I was hoping to get to the recent ASV star party at Heathcote and see if I could try a few other folks EPs but life got in the way as it does.

at 65 degrees the LVW are on the low end of the apparent field I am looking for, but certainly a step up from the Plossl types that make up my main group of EP's Even the 2" E-Lux are 56 degrees so a little wider than the Plossls but not by much.

[casstony]

The ES eyepieces are generally very good performers and I've used quite a few of the 82 and 68 degree models. I'd avoid the focal reducer and just buy the appropriate focal lengths for your needs.

[The_bluester]

The reason I was looking at the reducer is that with the long FL of the 925, anything not worth a fortune is still relatively limited in TFOV. All things being equal, a reducer would stretch the capabilities of the scope a bit further.

Buying a second scope would not be too popular at home :-b though it may nearly be feasible if I can snag a good secondhand dob cheaper than I can set myself up to get a comparable TFOV.

[Merlin66]

You'll find the reducer is for imaging rather than visual....
As said, get the focal length eyepiece to suit your needs...
(I find the 32mm TV the most used on the C9.25 and the C11. I have the 40mm but.....)

[Amaranthus]

The f/6.3 reducer is also great for visual -- at least it is on my C8 (not Edge). I basically use it all the time for DSO observing due to the wider FOV and better edge correction, and only take it out when I'm doing planetary imaging. I get well over a degree of field with my 24 Panoptic that way.

[Merlin66]

Barry,
That's interesting to hear...I never did have the same level of success with the Celestron/ Meade original x0.63 reducer...
The NextGen x0.5 came close.....
(Note the latest Meade x0.63 reducer has a MUCH shorter focal length and hence a MUCH reduced spacing requirement....)

[The_bluester]

Interesting to see differences of opinion on the reducer, but then a secondhand 40mm 68 degree EP is not a huge difference in mag to a 30mm with reducer, even if the loss of apparent field might be missed.

I do wonder how low I can go before I might start seeing the shadow of the secondary?

[Amaranthus]

The new reducer for the C8 has 105mm (nominal) backfocus, but it can vary from 55 through to over 200 mm - the distance affects the magnitude of the FR.

[rrussell1962]

Hi Paul, Apologies if I missed something regarding your mount on the thread, but if you are thinking of a focal reducer it may be worth checking that you have enough clearance on the mount for the telescope to reach vertical with a focal reducer - particularly if you are using a 2 inch diagonal. I have a the Celestron focal reducer on my Nexstar 8SE and the diagonal hits the mount at about 80 degrees, not really an issue for me, I just set slew limits and wait a couple of hours for objects to swing into view. But I did have one of those "oh nuts" moments when I realised there was an issue.

[Merlin66]

Barry,
The new MEADE (not Celestron) x0.63 reducer has a focal length of 110mm and a "design" - for optimum performance - back focus of 45mm.
This really makes it's use for DSLR's very marginal....
http://www.iceinspace.com.au/forum/showthread.php?t=88098

[The_bluester]

I will have to recheck that. How deep is the reducer you use? I have a fair amount of clearance as things stand (I do have a 2" diagonal) so I would be surprised if a reducer would run me out of space.

The CPC925 has tall enough fork arms that even with the alt axis running through the rear cell the OTA can be parked facing directly down at the azimuth pivot point.

[Tony_]

Hello Paul,

I use an ES 18mm 82d with my c9.25".
Previously I used a WO 25mm 72d - the coma was fairly bad on this one so I got the ES.

I like the ES - there is still some coma in the outer 20% or so from centre - but overall the performance is very good. It gives good resolution of GCs and nebulae are quite good. I don't do a lot of visual observations - mostly imaging. I get used to the outer coma, mainly because it is so much better than the WO which I was also getting used to. If you aren't looking for round pin point stars to the edge then it is quite good.

There is a ES18mm for sale in the forums now - it is worth buying; even if you don't like it you can always sell it again. I think it is a good eyepiece for the price.

Regards,
Tony.

[The_bluester]

Just had a look, with the OT pointed at the zenith I have around 100mm clearance behind the diagonal, so a reducer should not give me a problem.

Tony, thanks for the feedback and the pointer to the for sale section. I will have to have a look, the budget is pretty stretched this year though after we were bushfire impacted and a couple of other things and is only just starting to recover! This is more for planning for medium future. I will have to see how I go.

I should put the 2" E-Lux that I have in FS. They just do not get used enough to justify keeping them.

[rrussell1962]

Hi Paul, with 100mm clearance you should be fine with the reducer. Just got in from work but I will measure the reducer thickness tomorrow and post just to be on the safe side. I will measure with the 1.25 visual back and also the 2 inch diagonal which attaches straight onto the reducer (or rear cell).

[byronpaul]

Hi Paul,

I regularly used a Meade 0.63 focal reducer on the CGEM1100 with great results.

Admittedly it was an EQ mount so I had no clearance issues to be worried about, and I had zero problems achieving focus.

I also ran an SCT micro focuser in the image train and a 2" diagonal. My go-to eyepiece at the time was a 24mm Panoptic, but I also regularly used Type VI Naglers, Baader Hyperions, an ES 14mm 82deg, as well as 26mm & 32mm GSO Wide Views ..... all successfully through the focal reducer.

With this configuration I can recall some spectacular views of Eta Carina that have been engrained in my memory forever :eyepop:

Paul

[The_bluester]

A question for people who might be more in the know.

When comparing eyepieces of the same focal length and field stop diameter (Meaning same TFOV) will an EP with a larger AFOV give a darker sky background due to spreading the same incoming light over a larger "area" or does it not work like that?

[rrussell1962]

Hi Paul, the Celestron reducer adds around 26mm to the distance from the rear cell to the back of the diagonal. My 2 inch diagonal plus reducer measures 124mm from the rear cell to the back of the diagonal.

[Amaranthus]

The scenario you suggest is not possible: AFOV(deg) = FSD/(Telescope)FL*57.3

[The_bluester]

Actually I think we are at cross purposes here somewhat (Also you have the terms wrong way around there, that is the TFOV formula not AFOV)

what I am is if you have the same mag (EP FL) and equivalent field stops, do different AFOV designs produce a difference in apparent contrast/sky darkness.

Looking a little deeper I think some marketing approximations might be leading to my question anyway. Compare a Nagler 31 and a 30mm ES 82 degree EP. Both supposed to be 82 degree apparent fields. Generally it is accepted that higher mag will result in smaller TFOV.

The ES 30mm has a larger field stop than the Nagler 31mm and thus both greater mag and greater TFOV in the same scope. I reckon either the Televue has a slightly smaller AFOV than stated or the ES has slightly larger.

I think my question has probably grown out of comparing things which don't really compare.

[Amaranthus]

Yes, you are right, I mis-typed AFOV instead of TFOV.

But my point still holds. (As far as I'm aware) It is not possible to have two different eyepieces with identical FSD but different TFOV. This is because TFOV is determined solely by the FSD (for a given telescope).

If you can point me to such a comparison, I'll withdraw in shame ;) But as I understand eyepiece design, what you suggest is impossible. Maybe the confusion here is 'equivalent' vs 'identical'.

[The_bluester]

I think I have miss explained what I was asking. I am after the other way around though I am not sure even that applies as FSD seems to grow with AFOV too.

What I mean is, if you had the same TFOV between two eyepieces (So same field stop) but different apparent fields (Say an 82 degree EP compared to a 68) do you get a darker background?

I suspect that it is probably a moot point as deeper digging seems to indicate that the smaller AFOV eyepieces have correspondingly smaller field stops and thus TFOV than equivalent FL wide AFOV ones.

The ones I am comparing directly don't quite make sense to me. The ES 30mm 82 degree has a larger field stop than the Nagler 31 and so should have a larger TFOV. How can you take a large TFOV and spread it over the same apparent field while having slightly higher mag? The field stop is directly measurable and hard to fake so I suspect that the AFOV of one or both is not actually 82 degrees, one is larger or one is smaller or both.

[Camelopardalis]

You can have two eyepieces that will show more or less the same field of view, but one with a larger AFOV will be shorter focal length and smaller corresponding exit pupil, and magnification. This would result in a darker background.

But you'd be better choosing the exit pupil depending and what and where you observe from. I find that anything much more than about 2mm just sucks in the City sky glow and spoils the view, not so at a dark site :D

Regarding the ES30/Nagler 31...the field stop isn't necessarily the same as the exposed glass at the bottom of the barrel...

[The_bluester]

I was taking the stop dimensions for both of those from the respective websites, but again, who knows if they are a truly equivalent measurement.

Regards exit pupil and LP, I live in a relatively dark area, not truly dark sky but hugely better than suburban Melbourne. I live about 6km out of Kilmore, so about 40 away from the urban fringe. I still miss the childhood skies though, we used to live about halfway be tween Echuca and Rochester in country Victoria. Black, black skies and just a hint of a light cone from the towns.

[casstony]

Seems like you're getting unnecessarily confused by technical aspects of eyepieces Paul. A 34mm ES 68 degree with a narrow band filter would be good with your scope accompanied by one or two 82 degree shorter focal length ES's.
I tried the 6.3 reducers a few times and thought the contrast suffered in comparison to using a longer focal length eyepiece alone.

The 31 nagler and ES30 performance is very similar in the scopes I've used them in.

[The_bluester]

Probably, but I am an ex tech and a nerd at heart so if something does not quite sound right to me that I have been told I tend to chase that rabbit hole to the bottom until I understand or debunk.

[brian nordstrom]

:) My Celestron Axiom LX 31mm is as good as a friends 31mm Telemangler in my C9.25 ,an awsome eyepiece at nearly 1kg a Monster 82* eyepiece .
I know these are not made any more but they pop up on CN;s from time to time at good prices , I don't need a TV 31mm Nagler , ;) ., but I find my 19, 22 24 and 27mm Panoptics get the most use in my C9.25 , great views that allow the Cat to shine .

Brian

[Camelopardalis]

Agreed Brian, the Axiom LX eyepieces, at least in the longer focal lengths, are a great match for an SCT :thumbsup:

I think the take home for the OP is that either of these three is going to knock the ball out of the park in the scope, arguably the Nagler is better...it must be, it's more expensive ;) :lol: I use the ES 30 in my scope and it's a great eyepiece.

[The_bluester]

Ah well, starting with the 18mm ES to get a taste of how their 82 deg works in my 925 at a relatively low cost.

Hopefully the 2" E-Lux set I have in the trader section sell in reasonable time. Once they go I can consider selling the 68 degree Meade I have as well and look at the ES30 to replace it if I like what I see in the 18mm.

I am keen to consolidate the EP line, I can not justify having hundreds of dollars sitting in the EP case if they don't get put in the diagonal at least on the majority of nights. TFOV has become an issue as my scope often ends up used as an advanced spotter so to speak when a friend comes out for an AP session, we often use mine visually to compare star fields an check he has his pointing right in a test sub. Nothing I have comes all that close to his FOV on the chip.

[Camelopardalis]

Don't pre-judge the 30 based on the 18mm. I've heard that the 18mm has short eye relief. The 30 is a very comfortable EP to use.

[The_bluester]

They list 13mm which should be fine for me, About the same as my existing Nagler 11mm which I don't have any problems with, I don't wear glasses but an observing mate does and he still gets good views out of it.

[The_bluester]

Well, a rough and ready first light (For me) with the ES18 and I am pretty happy so far. I pulled the scope out and briefly set up in the shadow of the garage to keep the moonlight off me and had a quick look though it.

There is some slight false colour on bright stars in about the last 10% of the FOV (If that, maybe less) but it seems to have the best match for the field curvature of my SCT of any EP I own. Stars are noticeably sharper in the outer portion of the FOV than in my 68 degree Meade EP.

Pretty happy so far, now to save up for it's bigger brother.

[Tony_]

G'day Paul,

I'm glad you like the ES 18mm - it's by far the main eyepiece I currently use. I would like to get the 30mm one day too.
The outer 10% doesn't matter much - when you are looking at the main central part the outer edge sort of just blends in. The ES eyepieces seem to get mostly good reviews and are reasonably priced.

Regards,
Tony.

[The_bluester]

I would note that I did not notice th false colour when I swung around and had a quick look at the moon, which pretty much filled the FOV, the moon was under a quarter but you could see the unlit portion by the scattered light easily.

[The_bluester]

OK, moving on, some eyepieces sold and now I am looking into the ES30. Has any one had recent experience buying from VTI or ExtraVision?

VTI seem to have the 30 as unavailable and have done for months. Do they only order them in on receipt of an order?

Either way, it is one case where if an Australian supplier is smooth to deal with, I would have trouble getting one in from overseas any cheaper.

[Andy01]

Pardon hacking your thread mate, but I had a good look at M42, Tarantula and 47 Tuc through a 13mm Ethos on a 12" dob at VicSouth on Sat night - OMG!!!!!
It was 3.00am - seeing was great and I have to say it was gobsmakking - even after looking earlier in the evening through 25" and 18" Obsessions.
Vote 1 for Ethos :)

Andy

[The_bluester]

Lol, not going to that level of pain (And I could never hide a lump of glass that big from the wife!)

I have had a look though an Ethos (Sitting in a PST of all things) and it was very nice!

At a guess, the 30mm ES in my F10 will probably give a similar TFOV as a 13mm in an average 12" dob, but it will certainly miss the AFOV of the Ethos. But is it a lot of $$$$ for an extra 12 degrees!

[Camelopardalis]

About 20% wider than the 13E in a 12" f/5...the ES30 is a hard to beat for price and performance in your scope ;)

[The_bluester]

The things which happen on forums.

I sold some Celestron EPs to another IISer as I ended up using them rarely. That thread (Or maybe this one) prompted another member to message me to see if I was interested in selling my 11mm Nagler, which I agonized about for a while as I really liked it, but I decided it did not get enough use to keep so we agreed a price and it is in a box as we speak (if you are reading this Rod I am just waiting on a tracking number from my wife, will message it to you soon)

And then another IISer offered me an ES30, which I have just bought and am keenly awaiting a tryout of.

I should sell my Meade 68 degree as the ES is likely to completely replace it as the goto EP.

Time to get new pick and pluck foam for my EP case, nothing fits any more!

[Gem]

Everyone has a different opinion - which is great.

As a C9.25 owner, I use the reducer and usually a TV 24mm Pano as my standard EP (for medium-low viewing). I personally don't feel the need for a higher FOV with a tracked scope like your C9.25. A non-tracked dob is a different matter. In general terms, the more elements an EP has (which most of the 82 degree plus EPs do), the less contrast an EP usually has.
I have a series of plossls covering a range of EP FLs.

[David Niven]

I like the ES eyepiece, the 82D and the 68D but stay away from the 100D.
The extra fov is not worth the prices they command.
Having said that, their prices are going up.
Agena Astro are selling the 68D at $195 AUD nowaday.http://www.ebay.com.au/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC 0.H0.Xexplore+scientific+eyepiece&_nkw=explore+scientific+eyepiece&_sacat=0

[The_bluester]

I finally had a decent chance to try out the new pair of EP's recently (An ES 81 and 30mm 82 degree pair to recap this thread)

Per my first thoughts, it has resulted in the 68 degree Meade being sold, a full night of observing and I was never even tempted to reach for it. The main EP of choice is the ES30mm which works nicely in the scope, no more field curvature than the Meade showed, perhaps a tiny bit of coma towards the edge of the field but very nice and easy to use.

[Camelopardalis]

Congrats Paul :thumbsup:

I use mine with my Edge HD and it's pretty darn good, and it has some tougher competition :D The C9.25 has slightly slower mirrors than the other SCT models for a slightly flatter field and a little less coma than the C8/11. Any coma is coming from the scope though. I think you'll be in the sweet spot for the scope...I've tried my Ethos in a C9.25 and the field was a little mushy around the edges, but with an 82 it was nice and "right" :)

[The_bluester]

I have just ordered a Celestron focal reducer to go with the wider field EP. They reckon they are a reducer/flattener and for visual as well as photographic use so we will see.

Looking at the Televue EP calculator and basing it off the Nagler 31 (Very similar obviously) it takes me to about 48x mag, 1.6 degrees TFOV and just under 5mm exit pupil versus 75X, 1 degree TFOV and 3.1mm exit pupil without the reducer.

At approx $140 landed at my door from the states versus around $400 plus post for Australian supply I figure I can make the experiment without too much remorse if it seems like a silly idea later. Getting substantially more of extended objects in the FOV would be very nice and if I play with AP a little more later on it would be easier at F6.3 than F10.

Still tossing up on buying a wedge versus making my own versus remounting it completely when it comes to that. A bought or built wedge makes more use of stuff I already own.

[Camelopardalis]

Reports I've read claim that the R/F takes the edge of the sharpness, so it'll be interesting to hear how you get on.

You may see some substantial vignetting out towards the edges, but again it'll be interesting to hear how it works for you. IMO edges are for framing, and if they're a bit darker than the centre it's no big whoop.

[Tony_]

Paul,

I have been using the Celestron reducer with my 18mm ES. Great combination - reduces the coma to just a bit near the edges. It also reduces contrast but is good for large open clusters and nebulae.

Regards,
Tony.

[The_bluester]

Tony, that is pretty much what I am looking for, more expansive views of nebulae is the biggest one. It will be interesting to see how I go vignetting wise with the 30mm.

Once I get it I will have a good compare with and without and post up my thoughts. Odds are it will be the next new moon, not this one coming, I can not see it arriving in time.

[Tony_]

Mine took less than a week from U.S. - I was surprised. It cost me $170 delivered. They are so much cheaper now - only $105 delivered. The price in Australia is ridiculous.
I don't do much visual observation - mainly just imaging. It is good for imaging - flattens the field nicely.
I doubt whether vignetting will be much of a problem visually - depends how fussy you are. If it is there you will probably get used to it.

Regards,
Tony.

[The_bluester]

Well, it is in transit in the states to the Aut Post depot, so I won't have it for this new moon. All good, the sky is not going anywhere.

[The_bluester]

Well, transit across the states was pretty slow this time (I did select the free shipping option) and Aus Post Shopmate is not exactly cheap for postage, but it should be on it's way here now from the states. Lets see how long this leg of the trip takes.

The postage is a relative thing, though I will beasure and weigh it when it arrives to make sure they did not rip me. They supposedly calculate on cubic weight, perhaps it is in a stupidly big box.

[Greenswale]

I have been watching this discussion with some interest, having just purchased a Celestron Evolution 9.25. I have fitted a focal reducer, and use Pentax XW 20mm, 10mm and 5mm. The Celestron 40mm doesn't appeal because of the limited fov.

The discussion has sot of centred on 30mm eyepieces without mentioning that all have a 2" barrel.

The question: Is there a quality low power 1.25" eyepiece that will provide a reasonable fov, or do I need to go to a 2" visual back?

[Merlin66]

Wren,
I use a 1.25" TV 32mm Plossl......

[Greenswale]

Thought about that Ken, but fov will be about the same as the 20mm XW.

Could be the only way out is to go for the 2" visual back and restrict altitude movement to give clearance to the mount. Decisions, decisions.

[Camelopardalis]

With a 2" diagonal attached the balance point is altered, so you just need to move the scope upwards through the clamp a bit further. The side-effect of this is that you will get more swing room for the diagonal. There are also shorter physical (and therefore focal length) solutions from Baader and Televue. Also more generic SCT diagonals can be found that attach directly to the rear thread also, so they don't have to be all that longer.

IMO the 2" diagonals are worth it, if you are interested in the widest FOV from your scope. Whether it's worth the investment, given that you have the reducer already...it's hard to say, and in an ideal world we'd like to do a back to back comparison :D

FWIW, I'd remove the reducer when increasing the magnification, for example when viewing planets, as the Pentax eyepieces are really quite sharp...

[The_bluester]

BTW, nothing to report yet, at last count my reducer was in Sydney. Hopefully next new moon is clear so I can give it a decent first light.

[The_bluester]

Well, Australia Post strikes again. As of now I have been waiting a week for parts sent from Melbourne (I live an hour form the CBD) and my reducer has apparently been sitting in Chullora NSW for a week, It has now taken longer to get to me from Sydney than it did to cross most of the US, and in the US I selected the slowest freight option as it was free.

Top work as usual

[The_bluester]

Well, the reducer finally arrived today so next new moon will be first light.