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First question really is do I go for 1.25" or 2", ive had a look and it looks like the 2" are a lot more expensive, but are they better on certain scopes or particular objects ?

I understand some EP's wont be suitable for my scope (F5) but how do I know what is, and what isnt suitable ?

Ive received some advice in an earlier thread on some possible choices of EP's, such as BST Starguider/Explorer range, if you can stretch to £100ish then the Explore Scientific 68°/82° ranges or Vixen SLVs. How would I choose between 68°/82°, is that a personal choice or would one be better than the other on my scope.

I currently just have the supplied EP's, im not looking to buy the very cheapest budget EP's, my dad is a photographer by trade for over 30 years so I understand the value of good gear, but also you usually get diminishing returns, where the very best are better, but not *that* much better that the prices can sometimes be. Also as this is all new to me I do want to limit expenditure to an extent, so no more than £100, probably more around the £50-70 range really. Im open to suggestions on the best way to go about things, im sure you have all bought various things, and if you had the time again would have made different choices.

Thanks

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There's no fast rules for this one, EP selection is not easy, due to the vast amount of EP's out there, and although you have an f/5 scope, its not essential to buy the most exotic eyepiece to get the job done!

Any one of the eyepieces in my collection would probably work well on your scope, and only by having an eyepiece in the scope will you know if its right for you.

 

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Most modern eyepieces, starting with Plossls at about 20-25 pounds, will give you acceptably sharp views in the centre area of your field of view. The two variables are what happens at the edge of your field of view, and how large you want the field of view to be. If you really want a near perfect view across a wide fov in a fast telescope (I think yours is f4.7), expect to pay money! 250 pounds for Pentax, more for many of the Televues.

At the other end of the spectrum, the supplied eyepieces that came with your telescope will be the very cheapest that the manufacturers think they can get away with! Plossls if you're lucky, or maybe Kellners. They are probably sourcing these in bulk at well under 10 pounds each. Most eyepieces will be an improvement on these :icon_biggrin:.

Which eyepieces work best for you is a very personal choice. The Explorers, ESs and Vixens are all excellent EPs - each with their dedicated followings. If you can attend a viewing session of a local astronomical club, you will have an opportunity to look through different eyepieces belonging to members. Two well established clubs in your area are the Liverpool and Manchester Astronomical Societies: http://www.manastro.org/  and http://liverpoolas.org/

 

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2" barrels are used on wider field, lower power eyepieces to show more sky than can fit in a 1.25" barrel.  As a photographer's progeny, I'm sure you understand the concept of image circle and how it varies from compact camera lenses through 35mm, medium format, and large format lenses.  It's the same here with eyepieces.  The larger the field lens on the backside of an eyepiece, the larger the chunk of the image plane in the focuser it can show.  It doesn't stop at 2", either.  Some large refractors come with 2.5", 3", 4", and even 5" focusers for larger format photography or for using wider field, lower power eyepieces.

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If I could only buy one eyepiece for your scope with 100 pound budget then I would buy the 8.8mm ES 82 degree eyepiece

https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-82-degree-series-eyepieces.html

With a focal length of 1200mm, this gives a magnification of x136.

136 is great mid-range magnification perfect for galaxies. The 82degree FOV will mean less nudging of the scope.

if you later decide to sell it, you can get two thirds back selling second hand. So it's a 35 pound gamble!

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Am I right in thinking that you would need to go down on the EP size to get the same view on the 82's over the 68's ?

What I mean is, say you have both EP's at 16mm, would the 68 have more magnification than the 82, or doesnt it work like that ?

Im not really sure how they work, but looking it seems most EP's are about 50, does the 68 or 82 mean they 'fish eye' the image or anything like that ?

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26 minutes ago, BRUN said:

Am I right in thinking that you would need to go down on the EP size to get the same view on the 82's over the 68's ?

What I mean is, say you have both EP's at 16mm, would the 68 have more magnification than the 82, or doesnt it work like that ?

Im not really sure how they work, but looking it seems most EP's are about 50, does the 68 or 82 mean they 'fish eye' the image or anything like that ?

No it doesn't work like that.

16 is 16 is 16.

82 degree will show a widescreen view, whereas 68 will be less wider view with fewer objects seen.

the wider view covers more sky that's all. Magnification identical.

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You'll get the same magnification from any 16mm eyepiece, regardless of whether it has a 50, 68 or 82° field of view. All fov means is that you'll see more of the surrounding sky. Imagine that looking through an eyepiece is like looking down a tube, all the field of view does is widen the diameter of that tube. So I've got a 32mm plossl with a 50° field of view, and I can just about get the Pleiades to appear within that. If I had a 32mm eyepiece with a 70° field of view, the Pleiades would still appear the same size, but more of the surrounding sky would be apparent and it would easily fit in the view.

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You'll get the same magnification from any 16mm eyepiece, regardless of whether it has a 50, 68 or 82° field of view. All fov means is that you'll see more of the surrounding sky. Imagine that looking through an eyepiece is like looking down a tube, all the field of view does is widen the diameter of that tube. So I've got a 32mm plossl with a 50° field of view, and I can just about get the Pleiades to appear within that. If I had a 32mm eyepiece with a 70° field of view, the Pleiades would still appear the same size, but more of the surrounding sky would be apparent and it would easily fit in the view.

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Sounds like sorcery lol, but also ideal, god knows how they do that but if the image appears the same size, but you can see more around it for the same size eyepiece that sounds really good to me, id imagine it helps to keep things in view too esp on a dobsonian

In simple terms, is it a bit like viewing on a 2" EP but in 1.25" ?

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Wide angle eyepieces do enable you to keep something in your field of view for longer. I've always used 50° EPs, it's never been an issue for me as anything I want to look at is in the middle anyway so I've never been bothered much about the surrounding sky, and I don't mind having to nudge the scope a little more often. It would certainly help with high-power viewing though - at 200x I need to nudge the scope a bit every 30 seconds, a wider field will give you more respite.

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Hi Brun, it often the price that makes the difference, personally I went for the 82's, as I went for the best I could afford, you should do the same.  On your 'fisheye' question earlier, no, it doesn't work like that, the views are completely flat in a good quality eyepiece, the ES are fine examples of the very best available.  At the end of the day the choice between 68's and 82's is purely personal and one of cost. 

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Once you get beyond a certain apparent field of view (~40°?) it becomes impossible to design an eyepiece that has no abberations, it becomes a case of the designer choosing the abberation(s) that are least problematic. In the case of the ES 68/82 ranges it is generally accepted that they are roughly copies of the Televue Nagler and Panoptic ranges and so I assume that the general optical trends are similar and that what (I think!) I've read about those also applies to the ES equivalents (I haven't tested this myself, hopefully there is someone with both ranges that can confirm it).

For this there are two abberations that we have to know about. The first is field curvature. If you imagine that you could view the image plane side on then in a perfect world this would be completely flat. However, in the real world this isn't always the case and there can be a bit of a curve to this plane. The effect this has when you look through the eyepiece is that when the centre of the image is perfectly in focus the edge might be slightly out of focus. Stars that appear as perfect points of light in the centre will start to defocus into circles as they move to the edge of the field. 

The second abberation is called pincushioning. This is when things that are straight lines in real life look curved at the edge of the field when viewed through the eyepiece. It is easier to understand visually: 

13.PNG

If you are viewing terrestrial objects then pincushioning is bad and can be quite disconcerting/sickening while panning but for astronomical observations we are generally looking at a particular spot and so there is only ever a small drift speed to deal with which is no problem at all. 

The Panoptics (68s) by design have some (a very small amount of) field curvature and some pincushioning. Apparent fields of view of about 70° are reported by many people as the optimum size to be able to comfortably concentrate on everything in front of you.

The Naglers (82s) are designed to be even flatter than the Panoptics but at the expense of showing more pincushioning. This makes them unsuitable for a terrestrial scope but fine in an astronomical one. They also have a wider field of view which makes it harder to notice the field stop and you may feel that they give a more imersive experience. Many people love the "spacewalk" effect given by ultra wide apparent fields of view.

If only I could find the article I got the differences from... 

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What sizes to go for depends on what you intend to observe. As you can see from the EPs in my signature, I basically added a 6mm as a high power planetary eyepiece, and a 15mm for medium-sized DSOs. Of these EPs though, leaving aside the 32mm which I always use as a finder, my 10mm is easily the most used as it's excellent for just about anything other than large DSOs, and is very good for planetary observation on the numerous occasions when conditions aren't good enough for my 6mm.

I think the best advice is not to buy anything just yet, as there are a baffling array of choices and it may be very difficult for you to decide what you really want. I'd recommend spending a couple of months with just your 10 and 25mm. Observe a few planets and different sized DSOs if that's your thing, and constantly ask yourself questions about whether you are satisfied with the 50° field of view which these eyepieces give you, and whether you feel the need for a little more or a little less magnification. This way you'll start to understand what apertures and fields of view are right for you, and will be able to make a choice which you won't regret. It'll also buy you time to research the different eyepiece ranges.

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What sizes to go for depends on what you intend to observe. As you can see from the EPs in my signature, I basically added a 6mm as a high power planetary eyepiece, and a 15mm for medium-sized DSOs. Of these EPs though, leaving aside the 32mm which I always use as a finder, my 10mm is easily the most used as it's excellent for just about anything other than large DSOs, and is very good for planetary observation on the numerous occasions when conditions aren't good enough for my 6mm.

I think the best advice is not to buy anything just yet, as there are a baffling array of choices and it may be very difficult for you to decide what you really want. I'd recommend spending a couple of months with just your 10 and 25mm. Observe a few planets and different sized DSOs if that's your thing, and constantly ask yourself questions about whether you are satisfied with the 50° field of view which these eyepieces give you, and whether you feel the need for a little more or a little less magnification. This way you'll start to understand what apertures and fields of view are right for you, and will be able to make a choice which you won't regret. It'll also buy you time to research the different eyepiece ranges.

EDIT: Apologies about the double posts, not sure why the forum's doing that, I'm only clicking once...

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For planetary I generally say to get something in the 150-200x range. You'll find that in the UK the atmosphere (including the bit inside the tube, don't forget to let the scope cool properly) dictates what is best on any given night (or hour/miute/second). My 8" dob has the same focal length and I usually end up using a 7mm. Sometimes I can go shorter, sometimes longer is needed but if you only have one short focal length then that is a pretty good bet. The other option would be a good quality zoom (i.e. The Baader click stop and barlow) that can cover the range and then you can dial in the ideal magnification at any given time. 

For DSOs then you're probably better off thinking in terms of exit pupil. A 2mm exit pupil is good for globular clusters and small galaxies. Exit pupil x telescope focal ratio = eyepiece focal length so for 2mm exit pupil you'll want a 10mm ep. I've read that 2.4mm is actually the ideal exit pupil to minimise spherical aberrations from your eyeball so maybe a 12mm would be slightly better, or if you're going with those ES82s split the difference and go with the 11mm.

If you're observing from a truly dark site then your eyeball can probably dilate to about 7mm but this decreases as you get older and from a light polluted site you will probably want to stick to exit pupils of 5mm or smaller. Fill in the gap between 2mm and your maximum exit pupil with a couple of other options but you probably want to keep at least a 25x magnification jump between the steps so that you can appreciate the difference between any two eyepieces. Our senses respond to exponential changes rather than linear so maybe you want to do something clever like double the area of the exit pupil between steps which would give you exit pupils of 2mm/2.8mm/4mm/5.6mm which would correspond to eyepiece focal lengths of 10mm/14mm/20mm/28mm.

And now I've just realised that using a 2.4mm exit pupil as my base point and halving/doubling exit pupil size either side produces a set of focal lengths almost exactly matching the Pentax xw range for my f6 scope. I should have left it at 2mm which matched the eyepieces I've already got. :happy7:

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........three double entries so far? I  hope this  text stays single!

Magnification is determined from dividing the telescopes focal length by the eyepiece focal length.
I have several 6mm eyepieces at present, and no matter which one I insert into the focuser, I`m still going to see the target at 200x power. 
What should  be different is the field of view between each eyepiece,  due to the nature of their design and specification, and possibly the contrast between the eyepieces will differ dependent on the quality of any coatings  applied to the optics!

The price difference between the  various eyepieces may say something about  their optical quality and brand,  but when put to the eyes,  if like me, its possible the  optical differences  may not be apparent straight away, except for  the  field of view.
Don't be fooled by price alone, buying expensive could  be a  costly mistake ?  Your own eyes will decide what looks and feels right, regardless of whats printed on the body of the eyepiece. 

Its typically raining again tonight, I have the scope ready to travel afar, dark site,  well about 45 mins drive, to continue  further testing  my 6mm eyepieces. I  just want to satisfy my needs for a comfortable eyepiece, and depending on the various targets, how narrow or wide the field of  view I  actually need, and why?  Maybe I need them all, I wont know until I test them!

 

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Hi Brun, the first upgrade I ever bought was the SW PanaView 32mm, a great widefield ep at 70°, this ep transformed my viewing habits and was an eyeopener to the vast sky above - the other thing was, still at only £71 it represents the greatest value for money for any eyepiece I have ever known, the on-axis view is pin-sharp and second to none.  There is a little distrortion in the outer 10% in fast scopes of f/5 or below, but the benefits far outweigh this slight compromise. 

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