Don Pensack

I asked Al Nagler once about field stop position, and he opined that placing the field stop at infinity focus was not usually preferred by observers because when they examined an object for details, most people found a closer in focus preferable.

So the optimum placement of the field stop would be a little closer focus than infinity.

The Delite eyepieces have a user-adjustable field stop, and TeleVue gave me a list of the placements of the field stops in the eyepieces after the controversy over field stop placements in their first production of 18.2, 11, and 7mm.

TeleVue corrected it on all the eyepieces, but I noticed I did not have a problem with where they were in the first place.

I "corrected" the field stops to the location TV recommended and found that they were fine there, too, pointing out that my eyes, even at nearly 70, still have some accommodation left.

Along the way, however, I discovered there is a fairly wide range of field stop position that works fine, so if a field stop is really badly out of focus for an observer with good vision, it might be very far from its optimum position.

If, on the other hand, the observer is a nearsighted person and viewing without glasses, expecting the field stop to be in focus might be expecting a bit too much.

Also available under these labels (needn't go to China to get one):

Oooh......quite a trip down memory lane.  I remember huge bell-bottom pants, with the belt about 3" or more below your waist.  And "Earth" shoes.

LOL.

1 minute ago, Singlin said:

Which eyepieces did you get for your astigmatism Don?

I tried a scattershot approach to see which ones I liked enough to keep.

So far, and all seem to work fine with glasses, 

30mm APM UFF Like this eyepiece--can't say enough nice things about it.

22mm TeleVue Nagler Type 4--I previously owned one from 1998 to 2010, and it's as good as I remember.

17.5mm Baader Morpheus--now, how is such a cheap eyepiece this good?  It is fantastic.

14mm Baader Morpheus--some people report field curvature but in my f/5.75 (effective FL 1826mm) coma-corrected/field flattened dob, I just don't see it.  It is a duplicate performance of the 17.5mm, but with a couple mm less eye relief.

12.5mm APM Hi-FW 84°--this is a strange eyepiece, and I sent it off to a friend to try.  It works fine with glasses and is sharp enough, but......maybe it's the angular magnification distortion that bothers me, just like the Docter/Noblex.

11mm TeleVue Apollo--this one is amazing--too bad there won't be more focal lengths.

Magnifications yielded are:  61x, 83x, 104x, 130x, 146x, 166x, way too close together. I probably only need 3 of the 6, but which 3?  I'll figure it out.  In the meantime, I'm having fun comparing.

10mm down, I can get by without glasses.

One think I learned right away is that if you use eyepieces with large eye lenses (long eye relief, ultrawide fields), your glasses' rims will be in the field of view.  I ended up buying a pair of glasses with enormous lenses (1980's style) to use at the scope (and no, I won't post a picture--how in the world did any self-respecting person ever wear these in public where they could be seen?) to put the rims outside the field of view.

7 hours ago, RickEm said:

The 13mm Ethos was my first one.  I liked it enough to later purchase the 21, 8, 6, 4.7 and 3.7.  I still have all of them.

You're missing the 10mm and 17mm.  The 10mm edges the 13mm in contrast, and the 17mm edges the 21mm in correction.

If I had a set of just 3, it would be the 17>>10>>6 troika.

If I added a 4th, it would be the 3.7mm

I had all eight for years, but recently astigmatism grew large enough to rule out the 13, 17, and 21mm in favor of longer eye relief eyepieces.

When I think about which one of those I miss most, it's the 17mm.

On 24/11/2020 at 14:41, Steely Stan said:

Filters - I know they are not eyepieces, but this seemed the closest category.

As I read more about optimising telescopes, I see suggestions that various filters might help with viewing planets or nebulae etc.  As a photographer of years and years I'm used to using them, especially when I used film (sniff, sniff, sob).  But I never fell for the ludicrous extremes of pricing, or at least never found the performance of boutique or so called "marque" filters worth the money, (well once....😬).

So, I'm perplexed to see its possible to spend twice the cost of a good eyepiece on a single filter.  I just ordered my first fixed focal eyepiece, a Baader 17mm Hyperian and I regard 95 sovs as fair (FLO), but I ain't spending that again on a filter, or perish the though £250-odd......am I?  

Do you?  

Is a £250 filter really 10 times better than a £25 one?

With my camera lenses I generally have a filter for each and leave them on, usually a rotating polariser on my DSLRs, as much for protection of the optics actually.  I'm not sure if that makes sense on eyepieces as I anticipate changing filters from time to time for different purposes, but I can imagine having more than one of each type.

If it were not for this ghastly virus I could join a local club and try a few out courtesy of the members but that's off the menu right now, on top of which 'er indoors is already referring to my spending reflex as the "Stargazers lunge"! 

You don't really need to spend a lot on filters, though you could.

1) Your "planet" filter should fit your high power eyepieces, likely to be 1.25".  The Baader Contrast Booster works great here.  Yes, there are others, but the CB is a sort of "Swiss Army Knife" of planetary filters and does everything well.

2) Your "Nebula" filter should fit your lowest power eyepiece, likely to be 2".  A good narrowband filter is the place to start and there are several good ones: Astronomik UHC visual, DGM NPB, Lumicon UHC Gen.3, TeleVue Bandmate II Nebustar.

These filters enhance contrast on emission nebulae like H-II gas clouds, supernova remnants, WR excitation nebulae, planetary nebulae, but do not help on dark nebulae or reflection nebulae.

Are there other filters a little more specific that can help on specific nebulae?  Yes.  Are they essential?  Depends on the size of your pocketbook, I guess.

For everything else, the best filter is gasoline (petrol)--you put it in your car and drive the scope to darker skies. 

2 minutes ago, vlaiv said:

Would that still hold at F/7 and could we possibly add another criteria - light weight - what would be options then?

Light weight implies fewer lenses and poorer correction, or smaller eyepieces with reduced field.

Some candidates for the latter would be the 30mm XW or the 30mm APM UFF or the 35mm Panoptic.

But if those are too heavy, then sticking to narrower fields is the best choice for good correction in the outer field at f/5.

At f/7, the criteria get a bit easier, but most of the inexpensive widefields are based on the Erfle design, which is not good below f/8 or so.

One advantage to the shorter GSO ED barlow is that it is available under at least 8 different labels.

Many companies import the GSO under private label.

2 hours ago, johnturley said:

I wasn't looking for an eyepiece with a smaller exit pupil, I already have a 24 mm Explore Scientific 82 degree eyepiece, just eyepieces around 50mm and 35mm to provide a wider field and/or less aberrations than my existing Meade 56mm Plossl and Baader 36 mm Aspheric.

I thought at first that the 50 mm StellaLyra Superview eyepiece with a stated APFOV of 60 degrees might provide an improvement over the 56 mm Meade, and although the level of aberrations appeared acceptable, it turned out that the actual APFOV was only around 48 degrees or less, giving a resultant actual field of view that was significantly smaller than both the Meade 56mm Plossl and Baader 36 mm Aspheric. There does not appear to be much available around 50 mm that might be better than the Meade, the Masuyama 50 mm might be slightly better, but at £499 it is a high price to pay for something that at best would only be marginally better.

At around 35 mm, there are more options, the Masuyama 32 mm looks good on paper, but it appears that the 85 degree APFOV from a 5 element design will result in a lot of aberrations towards the edge of the field, especially in a f5 instrument. The 35 mm Aero according to some reports might be an improvement over the 36 mm Baader, and at a relatively modest price of £105, or the 30 mm APM Ultra Flat, although the actual field of view of the latter will be significantly smaller than the 36 mm Baader.

John 

If you are looking for an inexpensive wide field eyepiece good at f/5, you will buy a lot of different eyepieces to discover that such an eyepiece doesn't exist.

Cheap---well corrected in the outer field---wide field.  Pick any two.

A couple candidates for you: TeleVue 41mm Panoptic, Pentax XW 40mm for maximum field with good correction.

21 hours ago, vlaiv said:

It is exit pupil - which is related to focal length and aperture.

With increased telescope focal length - magnification is increased and for the same aperture - brightness of background sky goes down, but if F/ratio is maintained, then larger aperture offsets effects of increased magnification and brightness remains the same.

Since all of these quantities are tied together in one way or another - we say that exit pupil is thing that governs background sky brightness but in reality it is aperture + focal length or magnification used.

You forgot to point out that increased focal length only leads to increased magnification and reduced sky brightness background if the eyepiece stays the same.

If you maintain the same magnification, the exit pupil and sky brightness remain the same at all f/ratios in the same aperture.

4 hours ago, Armand Popa said:

did anyone compare a Skywatcher planetary to a TS planetary?

Both of them are TMB designs, am I right?

I have a TMB planetary II, a 2.5mm chinese clone, but I am very pleased with it. It has good image and is is well corrected at the side of the field.

I want to buy a 3.2mm one but I am stuck at the differences between Skywatcher (5 elements) and TS (6 elements)

Thanks!

 

These eyepieces are all made by Barsta in China and the number of elements varies according to focal length.

Most re-sellers simply copy the specs from one focal length to another, hence, a claim of 5, or 6 elements.

Over the years, some people have taken them apart and found there are 4, 5, or 6 elements, varying according to focal length.

I don't remember, and didn't note, which focal length had which number.

On 16/11/2020 at 09:56, Johan03 said:

Appreciate your replys!
 

Actually, I just ordered the Pentax XW 5mm. I read some reviews that Pentax XW have a more neutral color tone than Televue. I think that is important when my main observing interest is in double and variable stars like ruby carbon stars.

Now I am searching for a eyepiece with a focal lenght that fit between 24mm Panoptic and 5mm XW. 

I will observe for some months before I decide if I need to buy another short focal length eyepiece, maybe a 3mm, for higher power.

I did not go for the Nagler zoom because I think the small AFOV may be a problem as I use a manual alt az mount. 

 

My daylight comparisons showed a bit more yellow in the field of the XWs than in the comparable TeleVue Delos.

I think both are indistinguishable at night, though, in regards to tint.

My comments about color tints in eyepieces can be found here:

https://www.cloudynights.com/topic/739868-best-eyepieces-diagonals-for-keeping-bright-whites-pure-white/?p=10658910

The point is, only believe about 10% of what you read about color tints in eyepieces.

Believe 0% of comments about tints if the reviewer's scope is a refractor.

And look at this to get an idea why the age of the reviewer counts too:

http://people.brandeis.edu/~sekuler/SensoryProcessesMaterial/eyesGetOld.html

The process of lens coloration in the eye is called brunification.  That "coffee color" is probably not in the eyepiece.

No one has defined a "neutral" tone in eyepieces.  Many observers identify it as a cooler tone, with less warmth to the image.  The truth is, that may be quite far from neutral.

The eyepiece may be filtering out the longer wavelengths.

Look t this test from several years back:

http://www.amateurastronomie.com/Astronomie/tips/tips3.htm

Notice how many of them peak at long wavelengths and yet most do not have reputations for being "warm" in tone.

My advice: get the eyepiece you want and can afford in the focal length you need and pay zero attention to comments about tint in the eyepiece.  You won't see it unless you start doing my daylight test to detect it.

If ES in Europe is out of the 17mm, ES in the US is not.

Because of the issues with Covid-19 and the effects on sales (4x last year's level) and production (interruptions have reduced output),

I now don't expect to see any more focal lengths in this series, especially any focal lengths longer than 17mm.

ES in the US is out of a lot of focal lengths of eyepieces, and it may take months just to fill up the pipeline with current product.

Anything new has been pushed back to "Indefinite".

One note about the VIP Barlow: it can be used in 1.25" or 2" focusers, but it only accepts 1.25" eyepieces.

Vixen alas, doesn't state the field stop diameters anywhere in their literature.  Because these are negative/positive designs, a measurement of the internal iris will not give you accurate, effective, field stop diameters.

What will is doing a star timing of a star on the celestial equator and backing into the field stop diameter with:

FS = (TF x TFL) / 57.296  Where TFL is telescope focal length, TF is true field in decimal degrees.

As for the accuracy of quoted apparent fields in eyepieces, NO COMPANY is accurate, even TeleVue (though they're close).

Look at the measured apparent fields of the eyepieces in Ernest's tests:

http://astro-talks.ru/forum/viewtopic.php?f=32&t=1483#p41976

I second Louis.

If you just use the defocused star test to see if astigmatism is visible in the defocused star image, you'll detect astigmatism down to about 1/2 the exit pupil in the TeleVue chart.

But if you evaluate astigmatism based on whether you see it in the focused star images, the TeleVue chart is very apropos.

My coma-corrected dob is f/5.75, and 11-12mm is almost exactly the point where I start noticing it in the in-focus star images.  I have 1.0 diopter of astigmatism in my observing eye,

and the chart suggests I should start seeing it at a 2mm exit pupil.  Bingo.

21 hours ago, Solar B said:

In response to the topic title I would say yes as you do get what you pay for 

But as ever they are subject (like any EP) to the laws of diminishing returns ...

My money would be on the Baader as you've got to go some to beat that , i normally 

use the Leica ASPH for everything now but would love to try the Pentax XL zoom  (not XF) 

Brian 

 

 

My advice: save your money.  The XL zoom is not very sharp, is very dark, and suffers from astigmatism in the outer 50% of the field.

The Baader Zoom is better in every way.

The 3-6mm TeleVue Nagler Zoom is NOT compatible with the DioptRx corrector.

Even if it were, it would reduce the eye relief to less than the depth of the pupil below the cornea of the eye.

The DioptRx sacrifices about 8mm of eye relief.  On an eyepiece with 10mm of eye relief, that's a No-Go.

46 minutes ago, scarp15 said:

I contacted by email most UK retailers Don and of those I contacted only the Widescreen Centre confirmed that they keep a stock of spare TeleVue caps. I do not think that any retailers even stock alternative replacement caps. These (alternatives) are available through Ebay UK vendors and I did place an order on some that seemed to match what I wanted, yet upon receiving, they were of a poor standard and to be honest I ended up returning them. Bolt cases are also not easily available in the UK either anymore, although again there used to be an ebay vendor that supplied a full range (when I got one for my 31T5). Sometimes the used market, I think astrobin have the odd one (boltcase) but again caps are of a lower quality. I got what I wanted from 'overseas' without problem, but to mention again; full credit to Widescreen Centre for stocking some surplus TeleVue caps, although I did not get as far as asking the cost.  

Try AgenaAstro.com in the US.  They ship to the UK and they carry a bigger selection of caps than anyone else I've seen.

1 hour ago, alan potts said:

I feel you may see a bigger difference when you use XW's in a faster scope. I had 8-5mm zoom with an 82 degree FOV, the name of which has completely gone from the dormant organ in my head. It was decent in the centre but at the edges the wheels feel off. Fully agree with the Nagler zoom. 

Alan

Speers-WALER

19 hours ago, scarp15 said:

A reference concerning TeleVue eyepiece caps, if you are looking for replacing a lost or damaged one. If you give them a call, the Widescreen Centre do stock them. Not listed on their website, need to ring or email. I had sourced some recently, not through the Widescreen Centre as they had responded to my email following arranging from elsewhere, would be best convenient for UK TV users. 

If you didn't care whether the cap had TeleVue stamped in it, isn't there a provider in the UK that sells a wide variety of eyepiece caps in different sizes?

The o-ring is there because, if I recall correctly, the same eyepiece was sold by several companies and the only difference was the outer barrel, which is just a sleeve threaded onto the upper section from the bottom.

The manufacturer just threaded different sleeves on the eyepieces to make different brands.

Zooms will be interesting to me when they go from 70° at the low power to 90° or so at the highest power.

The only one that even comes close is the Leica Aspherical Zoom 8.9mm-17.8mm which is 57°-78° (measured).

It is one of 4 expensive zooms, the others made by Nikon, Swarovski and Zeiss (which all need adapters to use in telescopes).

The Baader Mark IV 8-24mm is more of a mid-range zoom, while most of the others are of the inexpensive class.

All Zooms are fun to use, though, so even though I regard them as too much of an optical compromise, I still keep a Baader Zoom around for playing around.

It is a lot better eyepiece than the similarly-priced ones from other companies, especially from 12mm down to 8mm.

So far, though, the only one that has truly rivaled separate fixed power eyepieces is the Leica.

I wonder how many of these are the same zoom in a different housing:

TeleVue is switching over to a new single-sided cap that fits very well and stays on.  It's a running change, though.

The Apollo, Delites, and a few others now come with the new cap.

Baader, however, did it right--they provide eyelens caps for the eyecup in both up and down position, and two diameters of field lens caps for the Zoom (which can be used both ways).

I grant you that many brands come with poorly-fitting caps.

Bolt cases are not the answer, though.  In the field, they're just plain inconvenient.

Opening a case to pull out an eyepiece and pull off the caps is chore enough.  Having to open another case to get to the eyepiece is just heinous.

Eyepieces I've bought that came with a bolt case had their bolt cases stored in the boxes, somewhere in the closet where all the boxes are stored.

If you use an eyepiece case, they are "as useless as teats on a boar", as my Dad used to say.

On 08/11/2020 at 13:12, Dantooine said:

Ive just ordered 2 tv barrel extenders from widescreen centre and 2 parfocal rings from 365. I’m hoping to get my 6 & 8 ethos focal points near to my 13e. Have I done the right thing? Will it work?  Winding the focuser back and forth going to wear it out 😬

The 13E as a 2" focuses (with the shoulder of the 2" barrel as reference) 0.3" above the focal plane of the scope.

The 6mm and 8mm Ethos, used as 2", focus 0.7" above the focal plane.

Ergo, you will need parfocalizing rings installed so that the 6mm and 8mm are parfocal with the 13mm because they need to be an additional 0.4" farther out.

It can be done.  It also means all 3 would use the same setting in the Paracorr--setting H.

The parfocalizing rings will tighten down in the safety grooves on the 2" skirts, so you will need to use 3-screw parfocalizing rings to center the rings and keep them from moving.