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Help Me Find a Finder Eyepiece

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#1 Ty Williams

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Posted 10 January 2013 - 11:04 PM

Our first scope was a Meade 8" F/6 on an LXD75 mount. Once we got the GOTO working at all, the Series 4000 QX 26mm was a wide enough field to use as a finder eyepiece. Well, the LXD75 mount drove us nuts so we stopped using the telescope (and it seems we're not alone as I can't sell that mount for love nor money!).

We just got 10" f/4.9 dob. The 26mm QX is no longer working as well for me as I'd want. For one thing, the drop from f/6 to f/4.9 definitely didn't do it any favors. For another, when hunting like a noob, the TFOV isn't as wide as I'd like. Put those together and I'm in the market for a new finder eyepiece for this scope.

Given what I'm trying to achieve and what we can afford, I think the two real contenders are the Explore Scientific 68* 34mm and the 82* 30mm. Interestingly, those two eyepieces have darned near the same TFOV at just a skosh over 1.9*. The narrower 34mm has a magnification of 37x and the wider 30mm has a magnification of 42x. Given the $50 price difference between them and the ~10% change in magnification, is there any reason to prefer one over the other in my scope? Does one perform better in a slightly-speedy f/4.9 scope?

Thanks!

#2 beatlejuice

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Posted 11 January 2013 - 02:39 AM

How about this: The 30 gives you about 3.04 square degrees with an exit pupil of 6.1mm
The 34 gives you about 2.68 square degrees with an exit pupil of 6.9mm
The 30 therefore gives you an increased field size of about 13% at a slightly higher power and therefore slightly darker background.
The exit pupil of the 30mm is more accommodating to an average dark adapted pupil which generally decreases from 7mm as we age.
I have a 30 Meade UWA which is very similar to the ES30 and would not trade it for the ES34 + $50
Anyway, thats how I see it.
BTW you will do a lot more than finding with either of those eyepieces once you start looking through them.

Eric

#3 Scanning4Comets

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Posted 11 January 2013 - 05:59 AM

Ty,

I have tried Eric's eyepiece out in the field and it is indeed a nice eyepiece. The only thing to watch for with his eyepiece or the 30mm ES 82° would be the weight. I just picked up a 34mm ES 68° eyepiece and the weight isn't all that much really. For reference, the 34mm ES is 1.5 Lbs. I am still contemplating the 30mm ES 82° myself, even though I *DO* own the 34mm ES because of the points Eric made ~ Smaller exit pupil, darker background sky, a bit more edge correction, and a bit more mag.

See attachment for scale size in a 10" reflector. You'll also need something to bring the eyepiece out a bit more as there is a bit more "out focus" required with the 34mm ES 68. in my pic attached, you can see a black extension tube added in between the eyepiece and focuser, which did bring it into focus. However, I just ordered a 28mm Hyperion fine tuning ring which I will add to the 34mm ES and then add a rubber parfocal ring.

Pick your poison!

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#4 Jon Isaacs

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Posted 11 January 2013 - 08:46 AM

Given the $50 price difference between them and the ~10% change in magnification, is there any reason to prefer one over the other in my scope? Does one perform better in a slightly-speedy f/4.9 scope?



I can't really offer any direct experience with these two eyepieces. What I can offer is this:

The 30mm ES is similar to the 31mm Nagler in design, it's a Negative-Positive eyepiece, that is a Smyth, Barlow-like front section with a magnifying section behind that. The 34mm ES is similar in design to the 35mm Panoptic, both eyepieces can be traced back to the original TeleVue 32mm Widefield.

In general, the Nagler 82 degree style eyepieces are better corrected off-axis in a fast telescope than the Panoptic 68 degree designs, it's inherent in the use of the Smyth lens which effectively slows down the telescope for the rear elements.

Since your scope is F/5, the 6mm exit pupil of the 30mm is probably more reasonable than the 6.8mm exit pupil of the 34mm and the increased magnification and slightly wider field of view will allow you to see smaller, fainter objects. I have both the 31mm Nagler and the 35mm Panoptic and most of my scopes are around F/5 or faster. Between the two, the 31mm Nagler gets 95% of the eyepiece time.

Jon

#5 JayinUT

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Posted 12 January 2013 - 11:21 AM

I have the 30mm 82 degree ES in my 14 inch F4.6 scope. First, it weighs a lot in the focuser. I always make sure after putting it in that I secured it well. I don't need that thing falling. Guess that's just me using a strut scope with or without a shroud on it. Anyway, I usually have to put a 2lb counterweight on when I put that in.

Now to the good. There is a slight coma in the EP from my Zambuto mirror but if I find that disturbing the Type I Paracorr kills that coma on the edge off. Second, stars are sharps across the field of view. I have to say that some of my best views of large objects like the Veil, the Double Cluster, M31 have been just fantastic. Now, I don't use it as a finder eyepiece. I use either the 24mm ES 82 degree, the 27mm Panoptic, or often the 20mm ES 68 degree or the 20mm Pentax XW. Yes, I have duplicates but for a reason. Anyway, IF I had to pick a finder eyepiece I would use either the 20mm ES 68, the 20mm Pentax XW (both with Paracorr Type I) or the 27mm Panoptic. The 30mm ES 82 is a speciality eyepiece for me, for viewing large WOW objects or if I want a wider field of an object or if there are multiple objects (looking forward to playing with it in Virgo this spring if the clouds and snow ever end here in northern Utah). Could it be a finder? Sure. I just don't need it to be a finder as I am still toying with my collection at and over 20mm. Another reason I don't use it as a finder is that the weight means adding counter weight and then if I drop down to my Pentax XW collection for 14mm and under, I have to readjust the counterweight again. By that time I don't want to mess around with counterweights as I want to observe, record my observation and get into my sketching of the object. Thus the 30mm usually goes in and stays for a while and I observe the objects I want to see through that eyepiece before I adjust down again. Don't take me wrong, the 30mm ES will stay in my eyepiece collections, but the weight for me, makes it a speciality eyepiece. Yep, I'm lazy, the easier it is for me in the dark, observing the better off I am. Thus why I still am playing around with my collection of EP's for 20mm and over. I just picked up a 24mm 82 ES but haven't been able to test it yet. It weighs less than the 30mm 82 ES so it may also work. Not sure if that helps.

#6 jrbarnett

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Posted 12 January 2013 - 07:17 PM

I'd go with the 28mm ES 68 or the 24mm ES 82. Both are smaller and lighter and much less likely to generate balance problems with the scope, and each produces an exit pupil that should be fully usable by any eye even with a fair amount of light pollution. 1.5 degrees of TFOV is *plenty* and the contrast with the slightly smaller exit pupil should be better.

Regards,

Jim

#7 Jon Isaacs

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Posted 12 January 2013 - 11:43 PM

There is a slight coma in the EP from my Zambuto mirror but if I find that disturbing the Type I Paracorr kills that coma on the edge off.



Zambuto mirrors are very nice but coma is not a function of mirror quality, its a function of focal ratio, an average mirror and a perfect mirror have essentially the same amount of coma.

For a finder eyepiece, I would go with the ES-30, similar to the 31mm Nagler, nearly the widest possible TFoV while maintaining a reasonable exit pupil. If Balance is a problem, it can be addressed with some simple weights and I think it's worth it.

Jon

#8 Sarkikos

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Posted 13 January 2013 - 01:54 AM

My finder eyepiece is on the end of my 15x70 finder scope. My low-power wide-field eyepieces are used for a better view of the big stuff, but not to find anything.

Mike

#9 Starman81

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Posted 13 January 2013 - 02:20 AM

I'd go with the 28mm ES 68 or the 24mm ES 82. Both are smaller and lighter and much less likely to generate balance problems with the scope, and each produces an exit pupil that should be fully usable by any eye even with a fair amount of light pollution. 1.5 degrees of TFOV is *plenty* and the contrast with the slightly smaller exit pupil should be better.

Regards,

Jim


I agree. The ES68 28mm is a quality, relatively light-weight finder EP with good eye relief and it is lighter on the wallet than most of the other options mentioned.

#10 cjc

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Posted 13 January 2013 - 02:46 AM

If weight is an issue then the Baader Hyperion Aspheric 31mm or 36mm may be worth considering.

#11 SeattleScott

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Posted 14 January 2013 - 12:22 AM

I have the ES 24mm 82* with my 10" F4.8 and it does a great job. Don't really want to go heavier, both for balance an ergonomics. I would be scared of dropping the 30mm 82* eyepiece if I didn't handle it with two hands. A lot of people prefer a 5mm exit pupil for scanning anyway.

That being said, last year I picked up an affordable 38mm superwide. I got it largely with my F9 refractor in mind, and it rocks in that scope. But I also find I like the wider field in the reflector too, and the optical distortion isn't too bad from a dark site. I do tend to prefer the 24mm as my finder when in the city though. The oversized exit pupil produced by the 38mm makes the background sky rather bright in the city, and the optical distortions seem more noticeable than they do at a dark site. Not for everyone, and I am still in my thirties (pupil hasn't shrunk much yet), but might be a consideration. Especially if you have another higher F ratio scope to take advantage of it.

#12 Scanning4Comets

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Posted 14 January 2013 - 08:57 AM

Now that I have read about balance problems with the 30mm 82 ES, I'm sticking with my 34mm ES 68! If there is one thing I cannot stand, it would be messing with weights when changing eyepieces.

I have no balance problems when switching between any of my eyepieces when going back and forth from them and the 34mm ES 68. :cool:

Cheers,

#13 Sarkikos

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Posted 14 January 2013 - 09:15 AM

One way to solve balance problems in a Dob is to attach a counterweight toward the bottom end underneath the OTA (longitudinal balance) and another smaller counterweight toward the sky end opposite the focuser/finder/Telrad complex (lateral balance). Set up the weights to balance for the heaviest eyepiece you will use. Then if you put a much lighter eyepiece in the focuser, you can compensate for the loss of weight by attaching a magnetic weight or two on the OTA near the focuser. IMO & IME, this makes very good sense because you are putting weight back where you've taken it, not somewhere else on the scope.

This will work even if your Dob mount - like mine - does not have detention on the altitude bearings. And IME this method is more convenient, more stable and makes more sense mechanically than moving a weight up and down the back of the OTA.

Using this method, I can easily balance for my ES 82 30mm or my lightest ortho. It works just as well in my 5" Dob as in my 10".

Mike

#14 csrlice12

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Posted 14 January 2013 - 09:41 AM

I've had NO weight problems with ANY eyepiece in my 10XTi. This includes the old style ES 82 30mm (3.08lb) PLUS a paracorr. The XTi has teflon bearings instead of springs. So far, no problems. My favorite eyepiece with the 10XTI is the ES 82* 24mm. It is a little heaview then most (2.2lb), but the views are fantastic. Yes, too heavy for a "finder" in a lighter scope. I'd go for the ES68* 24mm (if it ever shows up). My ES68* 20mm works fine too....

But for a cheap economical finder---Generic 32mm plossel, hands down. Widest FOV in a 1.25" eyepiece on your scope.

#15 Scanning4Comets

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Posted 14 January 2013 - 03:22 PM

One way to solve balance problems in a Dob is to attach a counterweight toward the bottom end underneath the OTA (longitudinal balance) and another smaller counterweight toward the sky end opposite the focuser/finder/Telrad complex (lateral balance). Set up the weights to balance for the heaviest eyepiece you will use. Then if you put a much lighter eyepiece in the focuser, you can compensate for the loss of weight by attaching a magnetic weight or two on the OTA near the focuser. IMO & IME, this makes very good sense because you are putting weight back where you've taken, not somewhere else on the scope.

This will work even if your Dob mount - like mine - does not have detention on the altitude bearings. And IME this method is more convenient, more stable and makes more sense mechanically than moving a weight up and down the back of the OTA.

Using this method, I can easily balance for my ES 82 30mm or my lightest ortho. It works just as well in my 5" Dob as in my 10".

Mike


Why anybody would want to fuss with something else while putting in / pulling out eyepieces is beyond me. No thanks.

#16 csrlice12

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Posted 14 January 2013 - 04:34 PM

It's all six of one/half dozen of the other. The bother is more up front in that, once the eypeiece is changed, we're back to viewing without "nudging". That being said, I have no problems with "nudging". While I love my refractor and EQ mount, I'd just hate to think of putting a 10" on an EQ mount---what a monster....talk about a balancing act.....

#17 Sarkikos

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Posted 14 January 2013 - 08:32 PM

Mark,

Why anybody would want to fuss with something else while putting in / pulling out eyepieces is beyond me. No thanks.


Hmmm.... let's see... :thinking: Ah! So they can use heavy eyepieces such as the ES 82 30! Yes, that must be it.

The ES 82 30 is my favorite low-power wide-field eyepiece in both the 10" and 5" Dobs. Put that eyepiece in a Paracorr and you have rich field heaven. I would sell both my 100 degree eyepieces before I would give this one up.

:grin:
Mike

#18 Sarkikos

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Posted 14 January 2013 - 08:38 PM

Randy,

It's all six of one/half dozen of the other. The bother is more up front in that, once the eypeiece is changed, we're back to viewing without "nudging". That being said, I have no problems with "nudging". While I love my refractor and EQ mount, I'd just hate to think of putting a 10" on an EQ mount---what a monster....talk about a balancing act.....


Are you talking about a 10" Newt on a GEM? That is the worst of all possible worlds. Tried it once but never again. That setup never left the house.

My 10" is a solid tube on a Dob mount. But the Dob mount does not have any kind of detention for the altitude bearings. The movement is very smooth, but I pay for that by having to be inventive with balancing. That's OK. It is a very fine scope for planet/lunar and deep sky.

Mike

#19 Jon Isaacs

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Posted 14 January 2013 - 09:28 PM

Are you talking about a 10" Newt on a GEM? That is the worst of all possible worlds. Tried it once but never agai


There are advantages to Newtonians on GEMs that go beyond the ability to track. But most GEMs are not designed with Newtonians in mind, short piers are better than a tripod for a Newtonian, proper rotating rings are a must for a larger scope and a ladder may be required.

An Equatorially mounted Newtonian does keep the mirror end further from the ground and make excellent planetary telescopes.

Jon

#20 Sarkikos

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Posted 14 January 2013 - 10:07 PM

IME, there are a number of problems involved with mounting Newts on GEMs: an 8" or larger Newt on a GEM can be a bear to mount and handle (6" or smaller are OK); the focuser gets itself in precarious positions (rotating rings fix the problem, but are a bother); the focuser is often too high unless the observer stands; the extra weight and cumbersomeness of a GEM makes the scope more of a chore to move and setup; the OTA can hit the legs when pointed toward zenith. A better solution to heat rising from the ground is to only set up on grass and/or put a carpet under the scope.

In general, I prefer a Dob to a three-legged Newt.

:grin:
Mike

#21 Jon Isaacs

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Posted 15 January 2013 - 06:46 AM

IME, there are a number of problems involved with mounting Newts on GEMs: an 8" or larger Newt on a GEM can be a bear to mount and handle (6" or smaller are OK); the focuser gets itself in precarious positions (rotating rings fix the problem, but are a bother); the focuser is often too high unless the observer stands; the extra weight and cumbersomeness of a GEM makes the scope more of a chore to move and setup; the OTA can hit the legs when pointed toward zenith. A better solution to heat rising from the ground is to only set up on grass and/or put a carpet under the scope.

In general, I prefer a Dob to a three-legged Newt.

:grin:
Mike


Mike:

There are problems with any scope. And to be sure, large, equatorially mounted Newtonians have more than their fair share, any time someone is considering GEM mounted Newtonian, I strongly encourage them to try observing with one first.

But design is a question of addressing the various issues... Three legged solutions are a problem, Newtonians belong on piers. Historically large Newtonians were all on piers. Rotating rings, they are a necessity but they are available...

I have both GEM mounted Newtonians and Dobsonians. Most of the time I observe with a Dobsonian but if I want the best possible planetary views, I will roll out my 12.5 inch F/6 Equatorial. It's more effort, but it's on casters, it takes about 2 minutes to roll it out and a few more to connect the power, get the fans running and do the collimation. It has rotating rings. It sits on a pier. Of course it's on a driven mount. And it requires a ladder for most objects...

It's old, from a time before Dobsonians, they did everything right so the pay off is at the eyepiece... it's the closest thing to a 12.5 inch apochromat I have ever looked through..

Jon

#22 Sarkikos

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Posted 15 January 2013 - 07:07 AM

I mounted my first two telescopes on an Edmund pedestal GEM. They were a 4.25" f/10 and a 6" f/8. No tripod legs on the mount, so the long OTA's were unencumbered when pointing to zenith. I sold the mount back in the early '80's.

Mike

#23 Scanning4Comets

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Posted 15 January 2013 - 07:17 AM

I agree about GEM's putting the scope in all kinds of weird positions. This is where the fork mounted CAT comes into play with good positions to the telescope for every kind of orientation in the sky.

I think the fork mounted CAT is the way to go of you want tracking. If I were to get another scope with tracking, I'd buy an 11" CAT. My observing friend ,(JunoMike), has an 11" CAT and I have looked through it. Galaxies are a lot brighter than when viewing in my 10" scope, so the secondary obstruction seems to have no impact on brightness of dim objects. Bottom line is that a fork mount is better than a GEM IMO.

BTW, Nice scope JunoMike! :bow:

Now, back to the regular OP of "Help Me Find a Finder Eyepiece".

Cheers,

#24 Jon Isaacs

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Posted 15 January 2013 - 07:30 AM

I agree about GEM's putting the scope in all kinds of weird positions. This is where the fork mounted CAT comes into play with good positions to the telescope for every kind of orientation in the sky.

I think the fork mounted CAT is the way to go of you want tracking.



CATs certainly are handy but I believe a Newtonian with top notch optics is capable of providing better views. This is the eyepiece forum so it is probably best that it not drift too much more off topic. I will just say this:

Done right, a big Newtonian on a GEM is difficult to match when it comes to the quality of the view.

Jon

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#25 MRNUTTY

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Posted 15 January 2013 - 08:01 AM

Beautiful scopes Jon.






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