Don Pensack

North America smoke map:

https://fire.airnow.gov/?lat=34.0778841&lng=-118.491626&zoom=10

TeleVue has a recommendation:

https://www.televue.com/engine/TV3b_page.asp?id=103

Way past time to clean the lens.

55 minutes ago, Giles_B said:

Thanks for these replies, and the tip on open star clusters - I'll try these next time I get some clear skies.

 

I don't think I explained myself well enough about magnification and switching to 2" eyepieces. I think I understand that 2" will offer low magnification and a wider field of view and perhaps better eye relief. I'm interested in the wider field of view of 2", but would also like to be able to use 2" eyepieces at high magnification (when viewing the moon and the planets). The most economic way of doing this could be by combining a 4x Barlow with a medium focal length eyepiece (20mm or less), but I'm concerned the weight may be prohibitive.

 

However, as moving to 2" would also in part be with upgrading to a larger scope in mind, I'm interested to hear that I'd be unable to visualise galaxies clearly without delving into astrophotography. Would this still be the case even if visualising through a high aperture like an f12? Sorry if this is a silly question, just wanting to make sure I get this right.

 

 

 

So add 1.25" to 2" adapters to 1.25" eyepieces to convert them to 2".  Because there is no reason for an eyepiece shorter than 14-17mm to be 2" when the field fits in a 1.25" barrel.

I like the convenience of 2" eyepieces too but do it by adding adapters to my eyepieces shorter than ~14mm.

I don't know where he got 14mm as the effective eye relief of the 22mm Nagler type 4.

I need at least 17.5mm of effective eye relief to see the field stop of an eyepiece with glasses on with that apparent field, and I have no problem whatsoever with that eyepiece with the eyecup in the down position and the eyeguard

in its maximum inward position.  My glasses touch the rubber, but they don't press hard against the rubber, and the edge of the field is easily seen in peripheral vision.  I'd put the effective eye relief at or about 17.5mm.

Ditto the 30mm APM UFF, which is even easier to use than the 22mm Nagler.  I barely have to touch lens to rubber to use that one.

My personal experiences with most of the eyepieces on that list differs by only about a mm from his figures, but a few are way off, differing by 4mm or more from his figure.

He has the 17mm Astrotech AF70 at 17mm, for instance.  On my sample, the rubber eyecup could not be flipped down, and when it was at its minimum height it put the effective eye relief around 10mm--it was completely unusable with glasses, and only the central 50-60% of the field was visible.

So how was the Effective eye relief figure derived?  Glasses use?  Or subtracting the depth from the top of the eyecup from the mfr's quoted eye relief figure?

One thing occurs to me: You may not need as much eye relief to see a narrower field of view.  A 10mm Design eye relief on a 16mm 82° eyepiece, for instance, was so tight that seeing the field stop was very difficult.

A 10mm Design eye relief on a 50° eyepiece, however, seemed comfortable and easy.  So perhaps glasses-friendly eye relief will vary according to the apparent field of the eyepiece.

If that is the case, then using ones glasses to gauge effective eye relief may not be an accurate way to measure the effective eye relief.  Alas, if that is the case, it also means that knowing both Design eye relief and Effective eye relief may

not tell you if the eyepiece is glasses-compatible.

In addition to what Louis has posted, it's important to understand 2 concepts:

Design eye relief, which is the distance of the exit pupil from the top center of the eye lens in the eyepiece, and

Effective eye relief, which is the distance from the top of the rubber eyecup (when folded down) to the exit pupil.

There can be (I've measured) as much as 15mm between these two figures.

In essence, one eyepiece could have 20mm of eye relief and be unusable with glasses, while another could have 18mm of eye relief and be very easily usable with glasses.

The factors that influence that are:

--the flatness or concavity of the eye lens in the eyepiece

--the amount of depth to the eye lens in the eyepiece into the body of the eyepiece

--the shape of the rubber eyecup and how high it rises above the eyepiece body.  One recent eyepiece with a 20mm eye relief has an 8mm tall solid rubber eyecup that can't be folded down, so makes the eyepiece unusable with glasses.  It's usable with glasses if the eyecup is removed, but

         then there is no protection for the glasses from the aluminum top of the eyepiece.

--your tolerance for how hard you are willing to press your glasses against the eyepiece.  I haven't found an eyepiece yet where my glasses don't at least touch the rubber, but some required a hard press that isn't comfortable after a while.

This is why I think about the only way to be sure the eyepiece is usable with glasses is to look for at least 18mm of eye relief, then read reviews of the eyepiece, then try it for yourself.  Otherwise, it will be difficult to know.

There is some math you can use to decide whether the manufacturer is lying about the design eye relief:

Apparent Field of View= 2*Tan^-1(eye lens radius/eye relief)

The eye relief in the formula assumes a flat eye lens, so if the center of the eye lens is 2mm concave, and the mfr claims a 20mm eye relief, then you would use 18mm in the formula.

One recent eyepiece claims a 20mm eye relief and the eye lens is ~2mm concave.  It has a 30mm eye lens and a claimed apparent field of 80°.

Plugging 18mm of eye relief into the formula gets an apparent field of 79.6°, close enough to 80° to say the mfr is telling the truth.

Alas, the eyepiece only has 10mm of effective eye relief, so isn't usable with glasses as is.

Had the manufacturer had a smaller eye lens, then you could know they were either lying about the apparent field or the eye relief, or both.

You could try a stronger solvent.

A step up from the normal lens cleaning fluids is pure acetone.  It's also safe for lenses, but don't let it drip inside as it could dissolve some of the paint on the edge of the lens.

The next step up from that is paint thinner, but if acetone doesn't touch it (use cotton Q-Tips), then your supposition that something got on the lens and harmed the coatings could be correct.

If it's organic, though, acetone will take it off completely.

Note for some viewers: some case foams outgas when a case is kept closed for a long period of time.  This stuff can coat the lenses in an eyepiece with hard-to-remove exudate.

So ALWAYS store the eyepieces in the case with caps tightly on.

In between those extremes would be the APM Ultra Flat Field 10mm 60° (also available from Altair Astro), a good step up from a Plössl.

And the Pentax XW 10mm at 70°, one of the best in that line.

For visual use, and to not make the image too dark and cut out too much of the nebula, an O-III filter that passes both the 500.7nm spectral line (strength of 75) and the 495.9 spectral line (strength of 25)

is desirable.  Since high contrast is desirable, which means narrow bandwidth, the 493.1nm O-III line (strength of <1) is always excluded.

So, what is the optimum O-III filter?

To catch both of the strong visual lines, yet still have a narrow bandwidth for better contrast:

about 11.5-13nm bandwidth, >90% transmission at both spectral lines (w/94%+ being even better), and close to zero out-of-bandwidth (OOB) transmission in the 400-700nm range.

O-III targets: planetary nebulae (e.g NGC7293, NGC246), supernova remnants [some, not all] (e.g. The Veil nebula), Wolf-Rayet excitation nebulae (e.g.NGC6888, NGC2359)

My personal TeleVue BandMate II O-III filter has a tested 12nm bandwidth (most current model since 2018), 99.2% transmission at the 495.9 line, and 98.2% at 500.7nm, with OOB <1% anywhere else.

My personal Lumicon O-III Gen.3 O-III filter (most current model since 2018) was tested to have an 11.5nm bandwidth with 95.1% at 495.9nm and 94.7% at 500.7nm, with OOB <1.6% anywhere else.

The two are virtually indistinguishable in the field on O-III targets.

Another O-III filter of note is the current version of the Astronomik O-III (they make the TeleVue filter).

With such narrow filters, it is best to use exit pupils of 2.5mm or larger at the scope, and preferably >3mm.

Some small and bright O-III targets can be seen better without a filter with exit pupils <1mm, however.

NOTE: large hydrogen/helium gas clouds are usually best if the H-ß line at 486.1nm is also passed by the filter.  This includes nebulae like M8, M20, M17, M16, M42/43.

If the filter also passes the H-ß spectral line, it is referred to as a "narrowband" filter, and these vary from 22-27nm bandwidth.

Some good examples: Astronomik UHC, DGM NPB, TeleVue BandMate II Nebustar, Lumicon UHC.

It is important to realize that many filters in the market today are much wider than the aforementioned bandwidths.  These cheaper (usually) filters do provide some contrast enhancement,

but are much less effective at making the nebulae stand out because of lower contrast.

That looks like a smudged fingerprint on the outside.

Did you try removing the lower lens and cleaning both sides?

5 hours ago, badhex said:

Thanks John, good to know. If I do go for the 4.5mm I'll be interested to see how the C5 performs with it. I suppose that there's a much better chance of a decent outcome with something like a Morpheus, although I am guessing I'll still need very good conditions. 

One major disadvantage to an eyepiece that yields an exit pupil of 0.5mm or smaller (0.45mm, in this case) is that the exit pupil is so small that not only is the image very dim, but floaters in the eye can intercept the light and cause those annoying aberrations.

You won't view the Moon at small exit pupils for long before the presence of dots, amoebas, bacilli, and arcs that fall in front of the craters become extremely annoying.

Keep the exit pupil larger and this is much less of an issue.  I such a case, a 6.5mm might be a lot more usable on Moon and planets than a 4.5mm.

What are you looking for?

1. more eye relief?  Given your choice of eyepieces, probably not this one.
2. a wider apparent field?  This is a good reason to upgrade.  You have a LOT of choices.
3. Sharper star images?  If you are talking about the center of the field, given your scopes, this may not be a reason to upgrade at all.  Possible, but not guaranteed.
4. Better contrast in the eyepiece?  Possible, but the dryness and transparency of the air matters more, given what you already own.
5. less chromatic aberration of star images in the outer field?  Again, possible, but not guaranteed.
6. a flatter field?  This might be accomplished, but if you see no curvature of field (edge and center focus at different points) in what you have, not a good reason to change.
7. a higher light transmission to see fainter stars and more details in other DSOs?  Today's eyepieces all transmit within a few %.  Sharp differences here are extremely unlikely.
8. less field distortion when panning?  Possible, but not guaranteed with other eyepieces.
9. less edge of field brightening?  Have you noticed any?  If not, be sure to read reviews before buying, or ask on the forum.
10. an easier-to-obtain-and-hold exit pupil?  Possible, but not guaranteed.
11. Better color fidelity?  Cooler in tone?  Warmer in tone?    Warmer tone helps on planets and Moon and seeing carbon stars, while a cooler tone may seem more natural.  Most discussions of this are "tempests in a teapot".
12. Less internal light scatter?  HIGH likelihood of improvement here.  But read the reviews.  Many higher end eyepieces yield a lot of internal light scatter.

So it helps to identify what you want to change before you upgrade.  The one place you are sure to see a major difference is if you go to eyepieces with a wider apparent field.

On 22/07/2021 at 18:10, Louis D said:

All I can do is comparative analysis on this, and both the 12mm and 17mm ES-92s require no refocusing center to edge in the same scopes, and at a wider AFOV.  Neither does the 9mm Morpheus require refocusing for best edge image.

And, neither does the 14mm Morpheus in my scope.  Or any of the Morpheus eyepieces, for that matter.  I have so little accommodation left, I'd see it if it was there.

So, my comment about it being scope-specific.

On 23/07/2021 at 01:54, Franklin said:

I had a Vixen Lanthanum 8-24 Zoom which I think is probably the same as the Stellalyra and it was brill. However, I did move on to the BHZ MkIV because of the wider AFOV.

The Vixen Lanthanum 8-24 zoom was made by a different company than the StellaLyra zoom, and in a different country.

On 23/07/2021 at 07:19, Ags said:

Had a brief session viewing the top ⅔ of the Moon (the remainder was below the garden wall) and was using the 4.9 mm for 80x magnification at f5.9. The view was nice and sharp (and comfortable), but the eyepiece does have a lot of lateral color.

With the Moon that low in the sky, I'm surprised you could differentiate chromatic aberration in the eyepiece from atmospheric refraction.

5 minutes ago, omo said:

Light weight, is a 7mm Delite too narrow?

The 7mm Delite is only 12g lighter and actually slightly larger in O.D.

When looking at them, though, they appear similar in size.

38 minutes ago, JeremyS said:

Today’s first world problem.....

I have been enjoying Saturn and Jupiter the last few nights using the Tak TSA 120, Tak 1.5  ED extender = 1350 mm FL.
I especially like the views with 7 mm eyepieces, x 190.
My 7 mm Or is probably best, but the FOV is a bit narrow when I am using an undriven mount. My Pentax KL 7 is also wonderful, wider field, but a bit bulky and heavy.
So I turn to my set of Naglers and immediately fall into the gap of there being no 7 mm in my collection. I like Naglers cos of the wide FOV and relatively light weight + small size (please: nobody mention the darned undercuts). My OCD has always been calling for the gap to be filled.
The obvious solution is to get a Nagler T6 7mm, so I have a wanted ad posted. 
But should I be considering the Morpheus 6.5? OK, it’s not 7 mm, but it is light and compact (I’ll forgive its safety smurfs). How closely parfocal is it with the Naglers?

The Morpheus is not even closely parfocal with the Nagler.  Well, it's about 1/4" apart (the Morpheus is more inward, the Nagler more outward), which is not a really long distance as eyepieces go.

My own eyepieces focus over a 3/4" range, which is fairly typical.

6 hours ago, Deadlake said:

I've seen the EP measurement's on CN, marketing over actual dimensions? 😀 

The ~3.5 mm XWA seems a specialist EP then, very happy with the XWA 5 mm. 

@Don Pensack The Ethos versus the APM 3.5 mm.  
   On CN some observers have complained that the lack  of baffling on the APM lets in too much stray light, is that the case with the Ethos as well? 

I've not used the 3.7mm on the Moon, which is where I'd expect to notice.

On Uranus, Neptune, small planetaries and close double stars, I've not noticed any notable level of light scatter.

I've only spent about an hour with the two APM short focal length 110° eyepieces, not long enough to have an opinion about light scatter.

John,

I think it is actually a 3.6mm.  At least that's what Stellarvue measured.

If it's 3.55mm, it would depend how you round off as to what you call it.

The APM XWA 100° "5mm" has been measured at 4.7mm, 4.77mm and 4.9mm by different testers.  It might be wise to call it 4.8mm +/- 0.1mm.

Just as apparent fields are rarely exactly as stated, so too focal lengths vary a bit, usually by only 0.1mm which makes little difference in the scope.

My scope has over a 1.8 meter focal length, and the difference between 4.7mm and 4.9mm is only a difference of 16x.  I doubt I could see that if I tried at that high a power.

I guess it depends on the focal length of your scope and the resultant magnification.

The eyepiece has to yield a usable magnification, and that depends a lot on your seeing conditions.

I use a 3.7mm Ethos eyepiece at 495x in my 12.5" quite often for small planetary nebulae or Neptune or Uranus,

but not for anything else.  I rarely go above 300-400x for Jupiter or Saturn.

4 hours ago, Louis D said:

At f/6, the 9mm Morpheus is all but indistinguishable from the 10mm Delos as far as aberrations.  The Delos is maybe a hair contrastier and more pinpoint, but it is ever so slight and might just be me wanting to justify the higher price.  The 14mm Morpheus has detectable field curvature and chromatic aberration at the edge at f/6 with my fixed focus eyes.  Younger eyes probably won't see it.  My 14mm Pentax XL has much more field curvature, but refocuses to pinpoint perfection at the edge, unlike the Morpheus which has a bit of residual astigmatism at the edge.  20+ years ago, my 14mm Pentax looked flat field to my accommodating eyes.  When it came time to choose one to keep in the A-team case, those extra 13 degrees (I've measured the Morpheus at 78 degrees AFOV vs 65 for the XL) of field more than make up for this slight issue.

Hmm.

My 12.5" is coma corrected, so operating at f/5.75 (1826mm FL), and the Paracorr is known to have a slight field-flattening characteristic.  I'm 70, and my eyes are pretty much fixed focus at this point, and I see no field curvature at all in the 14 Morpheus.

That could simply mean the FC matches my scope, but if you do the calculations, my scope's field is essentially flat over a field stop diameter of the size of the 14mm, which means the 14mm must be pretty flat itself.

You aren't, of course, the only one to see FC in the 14mm, so I presume a lot has to do with the scope the eyepiece is used in.  It may very well be, like the 14mm Pentax XW, that the scope has to have a very flat field to yield a flat field in the eyepiece in use.

As has been written by others:

| (eyepiece)+ | (scope)= | (field you see)

| + ) = )

) + | = )

) + ) = |

Version IV is available now.

On 06/07/2021 at 10:37, John said:

Thanks Don.

How can you tell which Gen Lumicon filter you own ?

Are there visual distinguishing marks for each generation ?

 

No.  You can't tell unless you bought it new.

The first Lumicon filters had no labels on the filter, had rounded edges on the filter housing, and came in small square transparent blue boxes.  Livermore, CA. 1979-2001  They sold the seconds as "standard" and the decent ones as "premium".

The 2nd generation came in the blue boxes, and a clear version of the same box with a snap-shut and a black bottom.  Simi Valley, CA.  Some were unlabeled, some were labeled, but all had a slightly knurled lip. 2001-2012 (there were more than one version in this time)

The 3rd generation came in the same clear/black boxes and looked the same but you could see the coatings didn't extend quite to the edge of the filter.  Knurled lip on the filter. 2012-2016 Simi Valley CA.  

The 4th generation, for a very brief period, were Chinese-made and came in squarish boxes.  Rancho Cordova, CA

The 5th generation (actually more than the 5th generation--maybe the 9th--but called "Generation 3") come in a translucent plastic box with rounded corners (Rancho Cordova, CA  2016-now for the UHC and 2018-now for the O-III)

In tests, the 2005-2012 filters had the narrowest bandwidths and the 2018+ filters have the highest transmissions.

The Livermore CA ones are all failing due to oxidation by now.  I haven't seen that same deterioration in the later ones.

The first 3 were all individually tested.  Later ones only have a batch sample tested.

The following filters perform almost identically in the scope:

Group 1

Astronomik UHC (post 2015)

TeleVue BandMate II Nebustar (2018+)

Lumicon UHC Gen.3. (2018+)

one that performs a little different, but which is also excellent: DGM NPB

Group 2

Astronomik O-III visual (2016+)

TeleVue BandMate II O-III (2018+)

Lumicon O-III Gen.3 (2018+)

If you have any of the ones in each group, you don't really need to switch.

18 hours ago, jetstream said:

This transmission stuff is something I don't understand...the difference in measured transmission doesn't always reflect what the eye notices IMHO. The optical experts say the levels of difference cant be noticed and yet I personally do see it.

The 10BCO is my king of "transmission" i.e. object detection. The Nagler 3-6 zoom is near the bottom of "transmission" to my eyes even though it is a great lunar/planetary eyepiece.

All I know is that the top DSO observers all use orthos at high mag for faint threshold objects. It is an absolute bonus that these orthos, Circle T included offer top tier views of the moon and planets.

I have a UO Tani 4mm ortho that is unbelievably good, so good that it takes the Vixen 3.5mm HR to knock it off the stump, and that is quite an accomplishment.

Our nighttime vision sensitivity peaks at about 500nm (dropping from a daytime peak at 550nm--this is known as the Purkinje Effect).  And peak sensitivity at night is about 450-550nm with the range from ~425 to 600nm.

Ergo, the spectrum of transmission makes a difference in the perceived brightness of the image.

If one eyepiece has a transmission of 99% at 750nm and the other a transmission of 89% at 750nm, that would be a profound difference in the lab, but pretty much invisible to the eye.

What is the transmission in the 450-550nm range?  That would be more telling because we could see it.

That is why we can see fainter blue-white stars than we can red stars, and the difference is large.

Eyepieces with types of glass that filter the violet-blue end of the spectrum will appear to be brighter on red giants, but have poorer transmission for the blue spiral arms of galaxies.

This is likely the case with lanthanum oxide glass, which tends to yellow the image.

Plus, focus of the star image plays a role.  Not all eyepieces have identical spot diagrams, i.e. focus the image to a point smaller than the Airy disc, leaving only scope size and seeing the determinant of the visibility of faint stars.

Lens polish enters into this, since a slight amount of light scatter may obscure the faintest stars.  It's the same with coatings.  If the coatings are poorly applied or not matched to the index of refraction of the glass, this can have

an effect on transmission and scatter.

And how the image in the eyepiece is modified by the steepness of the light cone from the scope can play a role in determining the sharpness of the image, and sharpness is also related to the ability to see faint details.

This is why excellent seeing seems to make small details in DSOs more visible.  Light transmission didn't change, but sharpness did.

And, there is the psychological effect of having a very dark field outside the field stop in a narrow field eyepiece that makes the object in the field appear brighter.  This doesn't work for all observers, but it does for some.

We equate the faintness of the image we see or can see as equating to transmission, but it isn't simply a matter of light transmission through the eyepiece.  The perceived brightness or dimness of a particular object in the eyepiece

is related to multiple factors.  Otherwise, you can't explain why a 4 element eyepiece with 2 groups (4 air-to-glass surfaces) is outperformed by a 5 element eyepiece with 3 groups (6 air-to-glass surfaces).

When we say "poor transmission" we are probably referring to multiple factors.

It's the same with contrast by the way.  Contrast has a definable lab measurement, but that is not how we use the term.  It, too, is related to a confluence of many factors.