Best eyepieces for new Celestron 9.25" SCT

[Commanderfish]

Hi everyone,

I'd love your advice on what eyepieces will be most useful for observing on my new scope.  It's a C9.25" SCT XLT on an advanced VX mount.  Focal Length is 2350mm F10.

Max magnification for planetary and lunar observing:

Going by the rules of 30 times mag per inch in reasonable seeing, this gives a max magnification of x277

Going by the rule of 50 times per inch in perfect (fictional) seeing, this gives a max magnification of x463.

So why do Celestron quote a maximum useful magnification of x555?  Is there something about SCTs that affects this calculation, or is it just hopeless marketing drivel?

Lowest magnification for DSOs - I'm a bit worried that my highest focal length eyepiece is too high magnification and too small an FOV for DSOs.  Here's what I have (not including freebie Skywatcher 25mm and 10mm modified achromats).  All are 1.25" except the Moonfish:

30mm Moonfish 2" 80 degree yielding x78 mag and 1 degree TFOV

24mm ES Maxvision 68 degree yielding x98 mag and 0.7 degree TFOV

14mm Meade Series 5000 60 degree yielding x168 mag and 0.36 degree TFOV

9mm Meade Series 5000 60 degree yielding x261 mag and 0.23 degree TFOV

6mm TMB Planetary II 58 degree yielding x392 and 0.15 degree TFOV

In my 120mm Evostar F8.3 Frac, all give good views and comfortable eye releif (for me), though the 9mm Series 5000 5 element "plossl" is a little on the low side.  The TMB Planetary II gives a ghost image on Jupiter if not looking down the eyepiece jsut right, but is fantastic for lunar observation.

Advice on what is going to work best in terms of focal length and FOV for planetary, lunar and DSOs appreciated!  Budget:  Hmm let's say £30-50 per eyepiece, maybe £70 if I'm only buying one.  Happy to buy second hand of course.

Does the VX mount keep tracking the selected target or will the target float across the view gradually like on an unpowered mount?  This will affect the FOV I need, I think.

Thanks all

Fish

[michael.h.f.wilkinson]

In the SCT these EPs will work well. The 6mm won't see much use, except under very good conditions. Replacing the 9mm "Plossl" with something with more eye relif might be the way to go. My old GP mount tracks like a soldier, I would not expect the VX to be worse, if the scope is properly polar aligned and balanced, so large FOV is a bonus rather than requirement. I would consider getting second-hand Vixen (N)LVs or even SLVs. Very good on planets and loads of eye relief. The Pentax XF 8.5 mm is amazing, but probably a bit beyond your price range. The Celestron X-Cel-LX line has a good rep. You could look for one of those to replace the 9mm. I personally would replace just one EP at a time, starting with the one that annoys most, and keeping everything that works well.

[russ.will]

The good news is that in a F10 scope, you can get away with a lot of EPs that an F5 Newtonian would tear apart, especially at the edges. I'd also stick to narrower AFOV EPs in the 50-70 degree range at this price, because they'll simply be sharper EPs overall. Ultra-wide field is nice, but it costs to do it well.

At that focal length (my SCT is a tad shorter) I'd stick to 10-12mm as a minimum, which is already 200-235x and therefore borderline useful on nights of unstable viewing and there are plenty of those.

The next sensible magnification to partner that with, would be 14-16mm, which will give you a workhorse EP in the 150-170x range. This EP will probably spend more time in the scope than any other. It will give clear stable views on pretty much any night and anything from Bodes Nebula, Globs, Planets and the Moon's surface will look great in it.

Next up would be something 20-24mm giving 95-120x for much the same reason as above, but giving an alternative framing for slightly more extended objects.

Finally, something in the 32-40mm range as a finder, come as wide as you can get, EP in the 65-75x range.

So, your list looks pretty good, but the 6mm will be largely useless. If you must buy something in that range, make it a good Barlow, because that will work with all of the EPs.

Also, at this stage, I'd stick with 24mm SWA and down, because longer FL EPs in the 1.25" size are like looking down a straw, so restricted is the apparent field of view. If you can make the jump to a 2" visual back and a 2" diagonal, then Erfles like the Skywatcher Panaviews are pretty much made for scopes like SCTs and the 38mm will be bang on the money at 65x, 70deg AFOV, sub 4mm exit pupil.

I couldn't argue with the 24mm Maxvision which is in a class of one for an EP combining sharpness and correction in fast scopes with that sort of price. Only wearers of specs might find something to complain about.

For the rest, Meade HD-60, Celestron X-Cel LX & BST Starguiders are all a very similar experience and capability. All can be had for peanuts second hand.

Russell

[Northern Soul man]

Hi Ya Fish - I think the set you already have are going to work well, at F10, on axis whilst tracking, your only going to basically use the centre of the EP, my scope works at F10 and I find a 12mm EP probably about my most used EP when it comes to planetary (Jupiter right now) - at this magnification things look very nice and probably what I can get away with regarding the seeing and the Atmosphere on most of the nights I'm out under the stars - some nights I try a 10mm, but find this a little too much, here things get very "mushy" - its not the eyes or the scope - its just down to the quality of the seeing.

The 925 is a really nice scope that will excel on the Moon and Planets - make the most of Jupiter now - your mount will track very well - I think its the next step up from my CG5 GT mount, when using this mount, I make sure its level using the little bubble level on the mount,  I just align Polaris roughly in the centre of the "hole" where the polar Scope should fit ( never got around to getting one, and a little awkward - your nearly lying on the floor at this point!!) do a 2 star auto align and add a couple of calibration stars - don't even bother with the All Star Polar Align - at this point its accurate enough and it'll happily track Jupiter all night bang in the Centre FOV.

Paul.

[michael.h.f.wilkinson]

I tend to use my XW10 most on planets (203x) and XW7 when seeing is good (290x) in my C8. With a bigger scope, 10mm might be stretching it on many nights, sso 11 or 12mm might indeed be useful

[Mark in Macc]

Binoviewers are highly recommended for this set up. Well worth the extra outlay.

[damnut]

Hi Commanderfish,

I had a 10" Lx200 sct. The 30mm moonfish rarely left the diagonal! All said above really, just don't over mag things. Thats a great setup you have there and you could consolidate your selection a wee bit in the lower focal length range..But you have another scope to consider and you can never have enough ep's I am told.  .

There is a great guide to eps on SGL by the Warthog and on Swindon astro site by R.Wilkey :-- http://www.swindonstargazers.com/beginners/eyepieces.htm

[nightfisher]

Here is a good one to add to the collection, the Revelation 2" 42mm ep, a bargain for slow scope users at about £40

[Commanderfish]

Hi guys,

Thanks for your very helpful responses. I invested in a 2" Baader back adapter and will be using the 2" diagonal from my frac, so the Moonfish will get a lot of use. Isn't it wierd that my 350 quid SW Evostar frac and eq3-2 came with a 2" diagonal whilst my 1500 quid SCT comes with a cheapie 1.25" diagonal? Celestron obviously spent the extra money on copious packaging!

I'm glad you think most of my EPs will be useful, I only got my first scope a month ago and have managed to collect these EPs after a lot of research.

Yes the Revelation 42mm does sound like a good cheap investment!

For an 11mm, what do people think of the Explore Scientific 11mm 82 degree? Seems to get great reviews.

[Commanderfish]

Hmm, just thinking, my 30mm 2" 80 degree moonfish gives x78 mag and 1.01 degrees TFOV; the Revelation 42mm would give x58 and 1.16 degree TFOV. Is that a significant difference? The Revelation is dirt cheap...

[Northern Soul man]

Hi Ya Commander - nice 1, with the SCT your never going to get a very large field of view, and at F10 - I think most EP's will be good on axis with very little and I mean very little difference to a high end EP - Planetary wise - being on axis and having tracking,  really you only need to get stuff in the centre and then let the scope track - its a bit of an "ideal" night for me when Jupiter is placed so well and the atmosphere is playing ball - I can just sit there for a few hours and watch the detail just move on round.

I think that the accessories with the majority of new scopes has a lot to be desired - its always been like this - the scope is just the start of the "money pit" - glad I'm just visual and not have to worry about all the extras needed for imaging - that's an even deeper pit!!!

The 925 is a very nice scope - I've never owned one, I went from an 8"SCT to the 11" - so sort of missed the 925, but I must say that I've been observing for many years, the last 8 or so with the humble SCT - I find it to be a very nice instrument on the Planets, some say that you "loose" a lot with such a large central obstruction - and the contrast is not so good - but have found this about as far from the truth as it can get!! - just the last couple of years with Jupiter's Oppositions been so favourable, the detail, colour and overall contrast, I have found that it really couldn't be any better for me, I've never owned a Frac - probably because of the light pollution I suffer with, the larger aperture Fracs are a bit of a pain to mount properly - never even had a look through one either - so really, I probably don't know what I'm missing, but I bet on the best nights that 925 will take some beatin!!!

Paul.

[Commanderfish]

Thanks Paul, I'm really looking forward to using it - arrived yesterday!  We had a nice afternoon today so the SCT is all set up in the garden - but as soon as the kids were in bed and the sun ahd gone done, the cloud cover has gone solid!  It's supposed to be intermittent cloud tonight so I'll have dinner and see if I can get out there.

[YKSE]

Hmm, just thinking, my 30mm 2" 80 degree moonfish gives x78 mag and 1.01 degrees TFOV; the Revelation 42mm would give x58 and 1.16 degree TFOV. Is that a significant difference? The Revelation is dirt cheap...

If you're only looking at star fields or open clusters, the 30mm with its TFOV is mostly better than the 42mm because of darker sky background. But with faint extend DSO, such as Monkey head nebula (NGC 2174) in Orion, the bigger exit pupil of 42mm will show you clearly more detail than the 30mm, even though both eyepieces frame the nebula very well.

[Mr Spock]

I also have a TMB 6mm with my C9.25 - I use that for double stars at which it excels. For planets, it's a too much power on all but the rarest nights. I had one night of viewing the moon in perfect seeing with the TMB 6mm and it's not something I'll forget.

For planets I mostly use a 10mm Vixen NLV. I find x235 gives the perfect balance between image size, detail, contrast and not overdoing it in moderate seeing. Your 9mm will be fine on most nights.

The 14mm you have is a bit no mans land for a C9.25 - a 12mm would be more useful allowing x196 for planetary viewing in average seeing.

So, if it was me, I'd lose the 14 and the 30, then get a decent 12 and 40 (as wide as you can afford). The rest will be fine, though you should use the MA's as paperweights

[Commanderfish]

Thanks YKSE and Mr Spock, very useful info. I should probably pick up a revelation 42mm. I might go for an 11mm ES 80 degree if I don't find a 12mm NLV first.

[russ.will]

The ES82 11mm is a very, very nice EP. That and the 8.8mm (okay, the 30mm too, but not relevant here) were my favourites of the range.

If you're going to be critical, the ES82s are slightly warm on colour rendition, but that's also a criticism leveled at the nominally slightly superior Naglers. Perhaps the ES82 are a copy that is too faithful? No matter, in an F10 scope, the Nagler advantage (generally stated to be at F5 or below) will be irrelevant and the ES are a lot cheaper. Only eye relief could be a sticking point and if you don't wear glasses to observe, the ES have more than enough.

Russell

[Commanderfish]

Yep no glasses here. I like the eye relief on the 14mm Meade s5000 but it doesn't get used much on my 120mm F8.3 frac as it gives a slightly random x111. If it's not much use on the c925 either, I'm tempted to sell it.

The eye relief is ok but slightly low on the 9mm Meade s5000 too so I could sell that.

Maybe I should spring for second hand ES80 11mm AND 8.8mm. That would also help keep my scope balanced as all but my TMB would weigh about the same.

[Owmuchonomy]

Mr Spock makes a great point above with which I totally agree. I have had my 9.25 SCT since 2007 and my overriding experience is that there is a 'no mans land' with this scope for good reasons. I have several eyepieces and several scopes. Only 2 eyepieces ever see use in the SCT. The first is my Baader 8mm which with fine tuning rings gives you 3 different focal lengths. Actually I would probably recommend the 10 mm. This EP gave me the most stunning views of Mars I have ever witnessed visually, but you need good seeing hence I would recommend the 10mm and the FTRs. You can also attach your DSLR directly to it (see my Flickr page). The second EP that sees a lot of use is my Celestron Omni 40mm. This is a stunning EP in this scope, with great eye relief and clear views edge to edge and I use it inmy 12" Dob at f/5 where it is good enough. For the money it's got to be the bargain of the century.

I find no advantage with 2" over 1.25" in this scope, other scopes yes, but not this one.

Enjoy your scope, mine gets less use than the others but I wouldn't trade it.

[Commanderfish]

Well then I think the question is, which gives the better views (10/11mm range)? The Baader Hyperion or the Explore Scientific 82 degree?  

The Baader will work out cheaper if I buy the FTR rings, as that would give me 8.4mm and 10mm.  However the ES has a wider FOV and I've read it's a more modern design - don't know if it makes a difference in what you see though.

Am I right in thinking that although the Baader will fit in a 2", the field stop is the same as the 1.25"?

Cheers

Fish

[Northern Soul man]

Hi Ya Fish - yeah the Baaders are essentially 1.25 EP's with only the larger Aspheric's being a true 2 " EP - the shorter focal length Baaders have a "negative" field lens on the very bottom of the EP - so really you can't do without this lens, you can screw a 2" skirt on the bottom, but the lens still has to stay in place - they work well at F10 - I've got most of the set (except the 3mm) - but I've been using the Baader Zooms more lately in the Binoviewer on Jupiter - they work really well with the WO Binoviewer I have.

Just a point the Eye relief is very nice in the Baaders, I think the ES are a little tighter on Eye Relief - I wear glasses, but not at the scope and find the Eye relief very comfortable at F10 - but I've not used the ES's but reviews say much tighter Eye Relief, but much better edge correction in faster (F5 ish) scopes - my scopes are F10 and F11 - so they are fine.

Paul.

[Commanderfish]

Thanks Paul, very helpful.  I did some googling and the 10mm Baader seems to have a 20mm eye relief whilst the 8.8mm and 11mm ES 82s have 15.6mm eye relief:  http://www.explorescientific.com/eyepieces/82_degree_series.html

15.6mm seems fine to me (my 9mm plossl most be around 7mm) , maybe the short eye relief is on the shorter focal length ES82s, or maybe on another ES model?

Cheers

Fish

[Northern Soul man]

Nice 1  - I think the Eye Relief really depends on if you have to wear YOUR  (not yours but a more general for everyone else) glasses at  EP - there are a tremendous amount of different prescriptions, also the actual layout of the EP - is the eye lens recessed into the body someway - this will all add or subtract how close we can get our eyes - its only until you can actually get the EP and have a practice with it, do we know its a keeper or not - I think I read somewhere that for good ER, it has to be more towards the 20mm rather than nearer the 15mm.

As said, I'm ok with my left eye, I have a little Astigmatism in the right eye, but the left is my mono choice - so I can take my glasses off whilst observing, but i do have a look through the right eye time after time - I can focus ok this way, but much prefer my left - even to a certain extent it needs a certain amount of practice with new EP's to get the placement just right.

Have a look at the ES threads, some observers can get away with the ER and others say its real tight - so I think it actually depends on the individual, the thickness of the lens in the glasses, the amount of "recess" the eye lens is down inside the barrel - but I think i prefer the longer ER even though I don't wear my glasses at the EP - I just work out which part of my nose has to be pressed against the barrel - I just much prefer the Binoviewers on long Planetary sessions and I can just take up the difference with the diopter - but not sure how long this will last!!

[Commanderfish]

Hmm,I'm actually thinking about the Baader mkiii zoom. The 8-12mm range will be useful, the higher FLs not so.

Expensive, but could be cheaper in the long run, and easier too.

Could sell my 9mm, 14mm and possibly the Maxvision 24mm roo. Any opinions?

[Commanderfish]

I'm thinking I could run the Baader Zoom, the Moonfish 30mm 2" and possibly a Revelation 2". All would be 2" and roughly the same weight. That means no messing with 1.25" adapters at the star diagonal and no rebalancing the scope. Also it will be easier to star align my VX goto system using the zoom.

Does anyone feel I would lose image quality using the Baader Zoom instead of a Baader Hyperion 10mm with FTRs?

[YKSE]

Your all 2" solution is a very neat and convient one

I've not used a 10mm hyperion, from the reviews I've read, you'd not lose perceivable image quality by using the zoom, or rather, it might be just the opposite, simply because that you can dial in just right magnification for every moment.

Having two zooms, I'm clearly bias in this question, because 60-80% time there is a zoom in the focuser.