Specific Eyepiece Question

[Hayduke27]

Hi everyone,

I just bought my first telescope, a Celestron NexStar C8, and have been having a wonderful time learning to use it.  I bought it used, and it came with enough accessories to get me going.  However, I have recently been searching for nebula filters, and have learned a lot about both filters and eyepieces from reading through the forums.  My question is this:

My scope came with a set of eyepieces (the Celestron eyepiece case, 1.5") and a couple others that are 1.5" as well.  As I began researching eyepieces, I see that it is common to have 2" sizes as well.  Would my scope accommodate a 2" eyepiece?  If so, are there any benefits to me using a larger eyepiece?  The 1.5" filters and eyepieces are a little less pricey, but if I can increase my scope's performance through using 2" eyepieces I will strongly consider doing so.  Thanks for any and all info!

[John]

Your scope will accomodate 2" eyepieces but you will need to replace the 1.25" diagonal with a 2" one to use them. The benefit of 2" eyepieces is that they can show a wider field of view than a 1.25" of the same focal length but optical quality is not better with the 2" format.

 

[cloudsweeper]

As John says, the 2" diagonal is the way forward!  And as focal length reduces, you can slip an adaptor in, or fit twist-lock adaptors to some eyepieces for convenience.

Doug.

[Luna-tic]

To expand a little on the above, you'll need either a 2" visual back to use the 2" diagonal, or you can get a 2" diagonal that fits directly to the rear cell. Those still allow you to vary the angle of the diagonal. Most, if not all 2"  diagonals will come with a 1.25" adapter to allow use of your 1.25 EP's. This is the route I've taken for my Edge 8". I bought the 2" Baader Clicklock back, a 2" diagonal, and 2" Barlow. All but one of my EP's are 1.25" except for my Ultima Duo 13mm, which fits either 1.25" or 2" diagonals. I'll probably go with 1.25 filters when possible.

[Hayduke27]

27 minutes ago, Luna-tic said:

To expand a little on the above, you'll need either a 2" visual back to use the 2" diagonal, or you can get a 2" diagonal that fits directly to the rear cell. Those still allow you to vary the angle of the diagonal. Most, if not all 2"  diagonals will come with a 1.25" adapter to allow use of your 1.25 EP's. This is the route I've taken for my Edge 8". I bought the 2" Baader Clicklock back, a 2" diagonal, and 2" Barlow. All but one of my EP's are 1.25" except for my Ultima Duo 13mm, which fits either 1.25" or 2" diagonals. I'll probably go with 1.25 filters when possible.

You addressed exactly what came to mind next.  The wider field of view does interest me, and I would not mind moving in that direction so far as buying a nice diagonal and a new lens or two for starters.  I don't want to just give up on all of my 1.25" equipment, as I just got it all and would prefer to get some use out of it.  Having said all of this, I have been back and forth on whether or not to just get a 1.25" filter or two since I already have the remainder of the compatible equipment.  Thoughts?  In the long run, specifically for nebula viewing, does anybody have a strong preference either way, 1.25" or 2"?

[Luna-tic]

I should say, my main reasons for going 2" on the VB, diagonal and Barlow is for photographic reasons, they seem to be able to handle the weight of a camera better. The Clicklock visual back is outstanding, instead of thumb screws, it has a twist ring, and you could probably pull the rear cell off before being able to pull a diagonal out of it when it's cinched down. Very secure.

I'm going with 1.25 filters mainly for cost containment, but if there were an advantage for 2" in certain cases (yet to be determined), I'd buy one.

[Ricochet]

5 hours ago, Hayduke27 said:

You addressed exactly what came to mind next.  The wider field of view does interest me, and I would not mind moving in that direction so far as buying a nice diagonal and a new lens or two for starters.  I don't want to just give up on all of my 1.25" equipment, as I just got it all and would prefer to get some use out of it.  Having said all of this, I have been back and forth on whether or not to just get a 1.25" filter or two since I already have the remainder of the compatible equipment.  Thoughts?  In the long run, specifically for nebula viewing, does anybody have a strong preference either way, 1.25" or 2"?

2". If you get a 1.25-2" adaptor or 2" diagonal that is threaded for filters you can use the filter with both 1.25" and 2" eyepieces. For nebulae you want larger exit pupils that for wide fields of view will necessitate the use of 2" eyepieces in your telescope.

[Hayduke27]

Okay, so I have gone ahead and gotten myself an Orion 2" diagonal, and have been sifting through the mountain of options that is eyepieces.  I see that, as with all optics, there are tons of choices that vary greatly in quality and specifications.  For an 8" SCT like mine, I know a lot of people use plossel EPs.  I was just reading an article by a guy who highly recommended using Konig EPs for a SCT, as he said you have a higher FOV and they just let more light through.  Does anybody have any insight so far as this is concerned?  Thanks again!

[cloudsweeper]

@Hayduke27 - the SCT has a large focal length, which results in higher mags and lower true fields of vision.  This is why a 2 inch diagonal and EPs are favoured - to squeeze a bit more field out of the setup.

Most of the EPs I use with my 8SE are 82 degree Explore Scientifics, with 2 inch barrels for the longer focal lengths.

Doug.

[Hayduke27]

@cloudsweeper- Just this morning I have been looking at some Explore Scientific eyepieces.  I was really giving a hard look at a ES 2" 18-82.  A lot of people love theses eyepieces and it seems like the wider FOV would be pretty nice.  I then read some things that sort of made it sound like these EP's might be overkill for a SCT.  It would take me a touch longer to save up and make a collection, but if these EP's are the way to go, I'll take the plunge.  However, if there were other EPs that had equal performance through my scope that might save me some money, it would obviously be worth considering. Any thoughts?

[Ben the Ignorant]

The König is only a four-element (astro lingo for 4 lenses) eyepiece, and it's outdated. I don't know any current seller who stocks König eyepieces, because much better optics are available now. A wide-angle eyepiece needs at least six lenses in order to provide sharp view across a 60° field. Some designs stretch the requirements with 5 lenses for as much as 70° but the outer region of the image is soft.

These and their clones are very good:

https://www.firstlightoptics.com/bst-starguider-eyepieces.html

But to avoid underusing your scope on the deep sky you should always get the widest possible eyepiece, 68°, 82°, 100°, whatever you can afford, and your scope can balance. Your 2" diagonal allows all the light your scope provides to get through, put a translucent sheet of paper where the eyepiece should be, aim at a landscape, you'll see the whole field your scope produces. It's about 43mm-44mm in diameter.

Now look at the entry lens in your eyepieces, the diameter varies from that 43mm to a few millimeters. Say a 20mm/50° has a 15mm diameter entry lens, a 20mm/100° will have a 30mm entry lens; both will magnify the same but the 100° eyepiece will display an image twice as broad, twice as high, thus four times larger in viewing area. Doesn't matter much for planets in motorized instruments because they occupy a minuscule share of the field, but the deep sky has extended targets that will be amputated at certain magnifications if the eyepiece is narrow.

I just tested a Sky-Watcher Myriad 5mm/110° on my 5 scopes and the club's Meade 8" SCT, it was superb will all of them, stupefying across-the-field sharpness; even when a double star is against the field stop, the split remains the same. But they cost and weigh quite a bit.  These are the stargazer's compromises.

[cloudsweeper]

47 minutes ago, Hayduke27 said:

@cloudsweeper- Just this morning I have been looking at some Explore Scientific eyepieces.  I was really giving a hard look at a ES 2" 18-82.  A lot of people love theses eyepieces and it seems like the wider FOV would be pretty nice.  I then read some things that sort of made it sound like these EP's might be overkill for a SCT.  It would take me a touch longer to save up and make a collection, but if these EP's are the way to go, I'll take the plunge.  However, if there were other EPs that had equal performance through my scope that might save me some money, it would obviously be worth considering. Any thoughts?

The slow SCT would allow for lower cost EPs, but good ones should serve well and be useful in other, faster 'scopes.

Another suggestion to get started - Revelation Astro Superview 2 inch EPs - inexpensive, and perfectly serviceable.  I use the 42/65 and 30/68 in my SCT, as well as the dearer EPs.  And the Revs have the advantage of being quite light, whereas the ES 30/82 weighs in at a hefty 992g.

Doug.

[Hayduke27]

Allow me to sum up my thoughts and once again pick your brains for slightly more info.  From what I have learned since starting this thread, a 2" diagonal is going to be better not just because 2" eyepieces are wider and can allow a larger FOV, but it will allow the 1.25" EPs to receive the maximum amount of light intake, which leads to slightly better viewing. Also, I am learning that the different EPs have very different benefits based on the scope you are using, and there are many factors involved with this.

 

I currently have a pretty large set of Celestron EPs that I have been using to orient myself with the night sky and finding deep sky objects.  So far, I have plenty to keep me entertained other than the lack of a decent nebula filter, which should provide better views of a lot of DSOs.  Also, from what I have read getting the 2" dielectric diagonal should improve viewing through my current Eps simply because my current diagonal is a bit of a cheapy.  I also ended up buying a DGM Optics 2" Nebula Filter based on good reviews, but have no EP for it as of yet.

 

Having said all of this, I was wondering if it might be in my best interest, being a newbie and all, if I were to invest a higher amount in a one really nice eyepiece for viewing DSOs with my filter, and just stick with the other EPs I already have for continuing to explore the sky until I am a bit more experienced.  Along these lines, I might consider getting a ES 2" 18-82 or a Sky-Watcher MYRIAD 20mm 100° Eyepiece to use with my new filter, and just use the other EP's I have for star and planet gazing.  Even though the price point is much higher, I think maybe my current needs would be met regarding a good way to view nebulas if I got one nice 2" lens, plus the new diagonal would allow for improved viewing of planets and stars through my current 1.25" Celestron EPs.  Am I talking crazy, or does this plan make any sense?  Thanks to everyone who has taken the time to read and reply to all of this.

[John]

The 2" format eyepieces do not offer higher quality views or more light intake. What you get is a wider view than the 1.25" format can provide when the focal length of the eyepiece is about 16mm or longer.

If you have invested in a 2" DGM NBP filter (which is excellent) you have "forced your hand" to at least invest in a 2" diagonal so that you can use it. If you go further to a good 2" eyepiece then the 20mm Myriad eyepiece will provide very good views - here is my report on that range:

 

Remember that the filter will only enhance the views of nebulae, not galaxies or clusters.

Have fun

[Hayduke27]

@John- I am following what you say, and I guess that is what I was getting at.  It seems that not only the upgrade to the 2" diagonal but also just an upgrade in the quality of the diagonal will improve the viewing through all of my EPs.  I understand that the quality won't necessarily vary because certain EPs are only 1.25", but I will get a wider FOV with 2" EPs (or also improved FOVs with the 1.25" EPs).

 

I am going to read the article you provided and strongly consider your advice.   So far, when it comes to planet viewing and star clusters I have been very happy with my viewing.  I would love to be able to see Nebula a bit better, as even though my viewing site is a dark site, I have had trouble seeing some of the dimmer nebulas.

[John]

Just to be clear, the 2" diagonal will not improve the views with 1.25" eyepieces unless you have a poor 1.25" diagonal now. The width of the views that eyepieces deliver are constrained by the field stops fitted within the barrels of the eyepieces so the diagonal does not change this.

SCT's are good scopes but they are not wide field scopes even with 2" eyepieces in them.

 

 

[Hayduke27]

32 minutes ago, John said:

Just to be clear, the 2" diagonal will not improve the views with 1.25" eyepieces unless you have a poor 1.25" diagonal now. The width of the views that eyepieces deliver are constrained by the field stops fitted within the barrels of the eyepieces so the diagonal does not change this.

SCT's are good scopes but they are not wide field scopes even with 2" eyepieces in them.

 

 

Thanks for the clarification @John.  That's pretty much what I understood.  The diagonal I have now is the stock Celestron diagonal.  What I ordered is an Orion Dielectric 2" that seems to be a higher quality, so I suspect it will improve my viewing with my current EPs.  

 

As a side question, my SCT is my first scope, and I am happy with the performance of most of my equipment at current time, but what scopes make the best wide field scopes?  So far all of the DSOs (and all other objects for that matter) I have been viewing do not come anywhere near filling my FOV.  As a beginner, I've been focusing on viewing things with less magnification and just trying to get a nice clear picture of the basics.  It's hard to imagine needing a significantly wider field of view, but I know I am very new at this and the time will come...

[cloudsweeper]

@Hayduke27 - your SCT will give decent views of most objects except large nebulae and clusters, but that still means a huge amount of objects.  A low focal length frac (refractor) will however give much wider views (at lower mags).  For example, my 8SE gives at best about 1.34 deg of true field, whereas my ST120 frac gives about 4.55 deg.  Other factors also come into play here, but basically the frac gives lovely wide views of large starfields, which makes "hopping" to targets a lot easier.  

As is often said, no one 'scope can do it all!

Doug.

[Peter Drew]

I've have a C8 that I use when in Tenerife, I miss it so much that I've just bought another to use in the UK. There are really only a handful of DSO's that don't fit in the field, a large proportion of the rest need 8" aperture to see well. A short focus refractor will give you a wider field but are you going to get an 8"!.

Further ahead, to greatly enhance lunar and planetary views, it's worth considering a binoviewer.    

[Louis D]

11 hours ago, John said:

Just to be clear, the 2" diagonal will not improve the views with 1.25" eyepieces unless you have a poor 1.25" diagonal now.

Even an upgraded 1.25" diagonal is a major improvement over a cheap 1.25" diagonal.  Because of the plastic body, I had all sorts of flexure using a binoviewer with heavy eyepieces in a cheap 1.25" diagonal.  A 1.25" WO dielectric diagonal completely solved the flexure issues.

[John]

1 hour ago, Louis D said:

Even an upgraded 1.25" diagonal is a major improvement over a cheap 1.25" diagonal.  Because of the plastic body, I had all sorts of flexure using a binoviewer with heavy eyepieces in a cheap 1.25" diagonal.  A 1.25" WO dielectric diagonal completely solved the flexure issues.

If the diagonal that the OP is currently using is low quality then I agree that replacing it wiith a better quality one, even if it is still a 1.25", would be worthwhile although my experience is that the mechanical security of a better quality diagonal is of more benefit than the optical performance improvements, which are there but not always that striking.

The WO 1.25" is well constructed but there is an annoyingly thick ring holding the eyepiece holder onto the body that vignettes 1.25" eyepieces that have wide field stops. The Tele Vue Everbright 1.25" was my favourite 1.25" diagonal. Single piece construction machined from a single block of alloy. No chance of anything unscrewing even with heavy weights at precarious angles. Expensive though

 

[Peter Drew]

I replaced the stock 1.25" diagonal on my C8 with a TV dielectric one. I also found that, although much better mechanically, the optical improvement was subtle. 

[Louis D]

2 hours ago, John said:

The WO 1.25" is well constructed but there is an annoyingly thick ring holding the eyepiece holder onto the body that vignettes 1.25" eyepieces that have wide field stops.

I've never noticed it.  I'll have to look for it sometime.  Once I do see, I can never unsee it, unfortunately.  It's like edge of field astigmatism and coma.  Once you've seen a clean field, you can't ignore the now obvious imperfections you didn't even notice before in your old setup.

I guess I'll have to dig out that cheap diagonal again.  I took it with me to Nebraska to view the eclipse through my old ST80 with a 32mm GSO Plossl and a Celestron Regal zoom and Baader film solar filter.  I'll try having a monovision shootout between my various diagonals, including the two image erecting ones (45 and 90 degrees) and the 2" GSO dielectric.  I don't have any super premium ones to throw in the mix.  All this will have to wait for Texas to dry out and cool off.

[Hayduke27]

So I am having technical difficulties with the new equipment, and I figured I'd seek advice here.  I bought a new diagonal that will accommodate 2" EPs.  I got a  2" Orion Dielectric Mirror Star Diagonal and it arrived yesterday.  I took my C8 out to try and put the new diagonal on, and I'm not seeing an obvious way to fit it.  I unscrewed the 1 1/4" visual back from the OTA, but the remaining threaded piece on the OTA does not fit into the diagonal.  The description for this diagonal says it should work with Cassegrain telescopes.  Do I need an adaptor?  Am I missing something?  Are these parts incompatible?  Thanks for all the help!

[John]

Did you get a 2" push fit diagonal, like the one pictured below ?. Or did you get the SCT fitting type (2nd photo) ?.

If you got the 1st one, you need SCT to 2" adapter to get it to fit the SCT rear port. If you got the 2nd one it should screw straight on to the rear port in place of the 1.14" visual back.

Push fit type:

SCT fit type: