Why are eyepieces getting larger and larger ?

[skysurfer]

It strikes me that modern eyepieces are getting larger, bulkier and heavier with a few exceptions.

Currently there are 120º FOV eyepieces available from Explore Scientific which weigh 1.3kg and require extra counterweights or other balancing devices on smaller and medium sized telescopes. Ethoses are not lightweright as well even the shorter FL ones, weight and size are at least like (filled) 500ml beer bottles/cans or (filled) jam jars.

No I don't want to go back to the crappy 24.5mm barrel Huygens or orthoscopic tunnel vision eyepieces, but currently some eyepiece sizes are outrageous. Myself I have relatively small eyepiecelets with the Panoptic 24mm as the largest (250g) and no 2" eyepieces at all.

Can the manufacturers not 'downscale' the large and long FL eyepieces like the Ethos 21 'downscale' (resizing all elements) retaining its design ?
E.g. make a '1:2 'scale model' of a 21mm Ethos which means a 10mm 'mini Ethos' with 100º FOV and fits well in a 1.25" (32mm) barrel (and even in an old 24.5mm) and weighs only 1/(2^3)*900 = 110-120 grams ?

Presumably I think too simply.

[brian nordstrom (As avatar)]

I think the TV Delos range is what you are looking for ?
These look very nice and not to big or heavy .
Brian.

[Profiler (Profiler)]

Hi Brian

I had a play with quite a few TV EPs including the Delos the other week when I visted Bintel and unfortunately I wouldn't classify either of the current 2 Delos Fls as small or even modest in size. They are roughly the size of the bigger Pans or a smallish ethos. The T6 Naglers strike me as intricate little marvels crammed solid full of metal and glass with the aim of being small but giving a big FOV. Curiously, the 2" Pan's did impress/surprise me as despite their size I found them to be relatively light in weight. The 35mm was particularly light despite its coke can dimensions. IMHO the best kept secret in terms of size v performance in the Televue range which I nick-name 'mighty-mouse' are the Nagler-zooms. You can only really begin to appreciate these marvels once you have played with one in a good quality refractor (however brace yourself for $400+ for an EP smaller than a 20mm plossl).

The one general trend I can perceive in the TV EP range is that biggish/bulky EPs are from ROC Taiwan whereas all the small ones and their barlows seem to all come from Japan.

The Terminagler might be an exception to this pattern though as I didn't look at that particular EP

[skysurfer]

Originally Posted by Profiler

The 35mm was particularly light despite its coke can dimensions.

You call 725g light ??

http://www.bintel.com.au/Eyepieces-a...oductview.aspx click on 'Specs'.

[OICURMT]

Originally Posted by skysurfer

Can the manufacturers not 'downscale' the large and long FL eyepieces like the Ethos 21 'downscale' (resizing all elements) retaining its design ?

Presumably I think too simply.

I noticed no one actually answered your question... so I shall try, using my *very* limited knowledge in eyepiece design (i.e. none, but I'm an engineer, so I B.S. very well ... and love BS'ing... )

<Potentially USELESS Information>

Consider the FOV claimed by the manufacturer. If one considers the overall design from a "reverse engineering" point of view, then the only way to get that type of apparent FOV is to have a medium that allows an exit large enough to encompass it (i.e. the last ocular must be the size of the pupil, diverged away at the distance of the eye relief such that the angle of the FOV equals the diameter of the last lens, holy smoke did that make sense???)

So, this defines the minimum diameter...

From there, we back calculate all of the elements to the point where we get to the entry point for a 1-1/4" or 2" eyepiece barrel and presto!, we have the overall design...

figure in the weight of glass, steel/aluminum/carbon fibre/any material required to hold the elements together and you get the eyepiece... who's weight is the summ of its parts.

</Potentially USELESS Information>

OIC!

[Max Vondel (Peter)]

I think that size is related to the EP designs

From a cynical point of view..the bigger and heavier they are...the more they can charge......so a case of economics and design......

Still the Nagler 31mm is a wonderful EP!

[Profiler (Profiler)]

The 35mm was particularly light despite its coke can dimensions.
You call 725g light ??

When you physically look at one in front of you it is a big EP but when you actually pick it up - it is surprisingly light for something that size. To put it in perspective for you without physically having them in front of you the 17T4 (IMHO a great EP) is the same weight (i.e. 725g) but only a bit over half the size of the 35 Pan.

[erick (Eric)]

Here you go!

http://www.cloudynights.com/ubbthrea...l/fpart/1/vc/1

[Gurutronic (Ernie)]

The 16mm ES 68 is pretty small compared to others in the ES range, but it sure does provide nice views! So I guess manufacturers are able to perform a little shrinkey-dink magic now and then.

[erick (Eric)]

I figured it out as I carried my eyepiece case tonight - exercise and muscle development! Saves all that time pumping iron in the gym!

[GrahamL]

I've had a 13 ethos for a while now and whenever I pick it up think they must of left something out of it as its so light for the size 520 g

While that weight isn't insignificant it "feels"
very light compared to anything above say 600 g , my 22 nagler at 680 g feels like a lead weight , above that they are all made from depleted uranium imo

maybe the really simple answer is they are bulky and heavier in the wider FOV and longer FL 's because they need to be.

The explores are a good example , you can scratch out a better price point in the 100 fov , but you get 2 full beer cans instead of one

[Wavytone]

There are several reasons.

The first problem concerns the design of the lower-power 2" eyepieces - a focal length > 20mm and a wide apparent field of view means some pretty big thick lenses are needed to bend the light to produce such an extreme angular field of view.

Closely related is the large clear aperture needed for the eye lens of the eyepiece, if it is to (a) provide decent eye relief and (b) a wide field. Simple geometry will tell you the eye lens MUST be big.

My Vixen LV 50mm is an extreme example of the above - the eyelens is wider than many finderscopes, and the eyepiece feels like half a housebrick (and almost as big).

Hence all the low power eyepieces from ES, the Naglers, Pentax and even my Vixen ones are B-I-G and heavy.

The smaller sized eyepieces can be smaller sure, for example the TV Naglers.

But - here come the second issue - rebalancing your 'scope if you change eyepieces, and also having to swap between 1.25" and 2" (hence adapter rings). I have tried using eyepiece sets that have widely different weights and on a refractor or Newtonian it can be quite annoying. Hence one of the things I like about my Vixen LVW set - Vixen made the LVW range all weigh about the same, and all except the largest ones have dual 1.25/2" barrels, so the need to use adapters and rebalance the scope is eliminated.

Saving weight on eyepieces isn't a priority. Convenience is.

[Varangian (John)]

The problem with loading up on big 2" eyepieces, barlows etc. is that there is a far greater tendency to lose collimation due to the extra weight on the focuser (most focusers have a bit of give in them).
I find the laser collimator hits a completely different spot on the primary and on the bulls eye of the laser collimator when I have 1.25" eyepieces in and 2" eyepieces in.
When I'm using 2" eyepieces I have to 'offset' the mirrors very slightly to allow for the extra weight of 2" eyepieces and 2" barlows.

[alanwilko (Alan)]

bigger is better ---! nothing ever changes

[clive milne]

Originally Posted by skysurfer

Can the manufacturers not 'downscale' the large and long FL eyepieces like the Ethos 21 'downscale' (resizing all elements) retaining its design ?
E.g. make a '1:2 'scale model' of a 21mm Ethos which means a 10mm 'mini Ethos' with 100º FOV and fits well in a 1.25" (32mm) barrel (and even in an old 24.5mm) and weighs only 1/(2^3)*900 = 110-120 grams ?

.

No, it would not be practicable to simply scale a 21mm ethos down to 10mm because you would end up with 7mm of eye relief.

The 15mm of eye relief on the 21mm is stretching the friendship as it is.

[Don Pensack]

Well, how much field of view do you want, and how well-corrected do you want it to be?
Want a widefield with superb edge correction? Then more elements will be added to correct residual aberrations. Want even MORE field (like 100 degrees, 110 degrees, or 120 degrees)? Then, add even more lenses.
Want usable eye relief? Likely means the eyepiece will have a negative lens ensemble at the bottom and larger lenses up on top (because most eyepieces today resemble long focal length designs with negative lens ensembles added). 100 degrees? Maybe 9 elements. 120 degrees? 12 elements.
What makes that possible is incredibly expensive and elaborate coatings on the lenses. Otherwise, that many elements would be too dark.
So, make the lenses bigger, add more of them, scale the barrels up to hold those lenses, and what do you have? Heavy eyepieces.
I saw a 6" diameter eyepiece used in the 200" Hale telescope for testing. It was 18 lbs!
Sort of makes all our little 2 lb eyepieces seem light, eh?