Don Pensack

Flocking will make a huge difference:

https://www.cloudynights.com/topic/523747-deadening-a-6-f5-newtonian/?p=6993629

Having bought glasses from 3 on-line merchants, I recommend GlassesUSA.com as their lenses seem to be better and more uniform in optical quality, even single vision.

4 hours ago, Louis D said:

If the quartz is laid down via vapor deposition on a substrate like a coating, it can be flat to the atomic level because it is crystalline, but I doubt that's how it would have been manufactured.  I think it just means it's pure silica amorphous glass.

Yeah, what we call "quartz" is really "fused silica".

Even then, it can be polished smoother than glass:

example:  

Fused silica is harder than almost any other substrate material. Typically, it will polish 2 to 4 times smoother than Pyrex glass. The atomic force microscope (AFM), with its sub-angstrom resolution capability, reveals the difference. These AFM scans were produced for Protostar by Charles Evans & Associates (Sunnyvale, California), and are of actual Protostar production samples.

On 25/04/2022 at 13:49, Louis D said:

Since the Tele Vue Nagler T6 series is $14 cheaper in the US than the Vixen SSW series, and does not suffer from SAEP, I would have just bought the TV NT6 series to start with.  I don't understand why the SSW costs more than the NT6.

Moot point, since Vixen discontinued the SSW eyepieces a couple years ago.  Any SSWs still left are from before then.

I'd avoid them because of the SAEP,  but they might be able to be obtained for less now if you bargain.

On 25/04/2022 at 11:44, Louis D said:

This depends heavily on what distance your eyes are fixed focus at.  In my case, my eyes focus somewhere around 8 to 12 inches without correction; thus, I just look under my distance-only eyeglasses to read things while at the scope.  My eyes have yet to change from highly myopic to somewhat more farsighted as I age.  The lower part of my bifocals has almost zero distance power, just astigmatism correction.

Surprisingly, my 2.0 diopters of astigmatism don't bother me much at all when reading for short periods of time.  I actually have my optometrist prescribe the reading part of my bifocals for focus at 18 to 24 inches so I can read things laying on a table without having to lift it.  That also makes them handy for reading things on shelves in stores without having to get so close.  However, I despise the near/far line intruding into my field of view with wide field eyepieces; so I have the distance-only pair for astro.

Yeah, I'm not nearsighted, just presbyopic with astigmatism.  My vision "froze" at about the 20' distance, so I need correction near and far and every other distance except 20'.

So I am stuck with bifocals at the scope.

I tried large lenses (50mm round) with only 8mm of bifocal section at the bottom, and that worked, but I eventually went to single vision glasses for infinity and another pair of glasses at the table where I record notes and look at charts.

The distance glasses hang around my neck during the table visits.

Presbyopia is a pain, because my prescription is different at 6", 12", 18", 2' 6', 12', 20' etc.

Were it not for progressives, I'd have 10 different pairs of glasses.

I believe Markus had the factory, United Optics, make the top compatible with a DioptRx, which means the eyepiece under the eyecup has to be in the 41.-43.9mm range, not 37mm.

On 09/04/2022 at 14:17, Louis D said:

About $14 at today's pricing here in the States (see added links above).  Less facetiously, I quote from the quartz diagonal's description linked above:

High quality diagonal mirrors are usually made of BK7 glass. Quartz glass goes a notch higher - it offers greater thermal stability, resulting in minimal thermal expansion and contraction as compared to other glass types. The result is a minimal, if any, shift in focus due to temperature changes over long observation sessions, making this quartz diagonal ideal for photographic and imaging applications.

I can't say that I've ever noticed the difference.  I just picked up the used quartz version because it was being offered for the same price as the used regular glass version.  I wouldn't have picked it up otherwise.

Who would image through a diagonal?  Who observes long enough at one focus setting to notice thermal shift?  If the difference is only $14 at the retailer, it's probably much less at the manufacturer and could become the standard if used in all diagonals which would further drive down the price differential through economies of scale.  However, it's a case that no one would ever notice the difference; so why drive up the price, even slightly, for every diagonal just to have quartz in it?  It's just a marketing ploy in my opinion.

In theory, though it might vary according to who makes it, quartz can be made smoother than glass because it spalls a smaller chip when it is polished.

In practice, I doubt there is a visible difference unless it is a LOT more expensive.

In a normal prism, the light path length is equal to A because the light only travels inside a path equal to A from outside to outside.

Due to refraction, it is typically shorter than if the prism was replaced by a mirror.  The light path is therefore A - a certain %.

In a reflector diagonal, the light path is A. [or the prism is A and the mirror is A+ some %--same result, different point of view].

In the Amici, the light path inside is longer because of 2 internal reflections.  It is what Edmund says because the prism is longer from outside to outside and also because of the internal second reflection.

1.707 seems about right.

Now, the light path through a prism is not the light path distance through the diagonal prism.

That is measured from the front looking face of the diagonal body that bumps up against the focuser to the opening where the eyepiece inserts.

And that can be reduced with clever machining and a shorter eyepiece tube.

In a 2" mirror diagonal, that is from 100 to 115mm on average, and about the same for a prism.

A standard 90° prism will focus  bit farther out from a mirror diagonal, however, due to the refraction of the prism.

Prisms can sometimes be used to solve a problem of not having enough in travel to achieve focus.

Plus, it's cheaper than the Orion, Meade, Celestron, et.al.

At least it is in the US, so I imagine it might be there as well.

I don't know how it compares to the Altair Astro version for UK customers.

My observing glasses:

https://www.glassesusa.com/gold-medium/ray-ban-6392-ja-jo/44-000164.html

The frame is outside visibility no matter how large the eyelens is.  They work on Morpheus, Delos, ES 92, etc and no frame is visible in the FOV.

I corrected for infinity vision.  I have another pair for reading at my charts and for writing notes when I move to my table to do so.

My vision is good enough to read the DSC at night, even if it is not sharply in focus.

I went for lenses to reduce CA and the best anti-reflection coatings.

I only use them observing.  I call them my "John Lennon" glasses.

See: https://www.onthisday.com/people/john-lennon

Louis' comment about coatings peeling away after years made me laugh.  I have my eyes checked yearly, and my prescription has only been the same two years in a row once since age 40.

I usually get 3-5 new pairs of glasses a year (computer, driving, daily life, transitions, astronomy).  I can afford it, plus I notice the difference at the telescope.

On 24/04/2022 at 07:07, Froglord said:

I'm new to astronomy - just bought a Skymax 127 and I only have the included Super MA eyepieces (25mm and 10mm) which I'm looking to upgrade.

So far, I have been observing without my (varifocal) glasses because it seemed more natural. Then I remembered I have astigmatism in both eyes, so perhaps I should be putting on the specs after all! (I might try a slightly older, non-varifocal pair).

I think I wear my glasses slightly further away than many people do (comfort, eyelash issues), so what sort of eye relief will I need? 20mm? Even more? I was looking at the much-recommended BST Starguiders (I'm not looking to pay Tele Vue money) but will I find the 16mm eye relief too tight?

Also, will I really get the benefit if I splash out on a wide-field 68 degree eyepiece, or will my glasses restrict my FOV?

Any moderately-priced eyepiece recommendations gratefully received ...

Owned the same scope for several years.  Per the S&T review, and my own measurements, this is actually a 121mm scope.

With a 90° mirror 1.25" diagonal, the focal length is 1540mm (f/12.7).

A 1.25" prism can reduce that to 1518mm.

The Visual back has a thread on the outside that can be cut off/removed and doing so reduces the focal length to 1510mm with a 1.25" mirror diagonal and 1488mm (f/12.3) with a 1.25" prism diagonal (assuming BK-4).

The claimed 1500mm focal length is only approximate and only applies to a 1.25" diagonal.

If your telescope came with the 2" mirror diagonal, this increases the focal length to about 1615mm (about f/13.3)

As for astigmatism, the f/ratio of this scope is so long it will take a 25mm eyepiece to yield close to a 2mm exit pupil, the cutoff point for 1 diopter of astigmatism.

So, for the most part, except, perhaps, for a 32mm Plössl (the lowest power I recommend), you won't need glasses.

A typical run of eyepieces for the scope will run from 32mm to 10mm.  It will be a rare circumstance when the atmosphere, cooling of the scope, and dimness of image in the eyepiece will allow for more than that, so I wouldn't plan on it, except for, perhaps, close double stars.

A 32mm Plössl or 24mm 68° eyepiece will yield about a 1° field with the scope, which is wide enough for all but the very largest objects.  Yes, it's a narrow field of view telescope, but it is also quite good optically and very compact.

Progressive glasses will only allow a small strip of the field to be in focus at one time.  If you can afford to do so, get a pair of reading glasses, let them hang around your neck and use them for charts and notes,

and simply observe without glasses.  Your astigmatism will only affect the lowest power.  If you need glasses to see the sky sharply as well as read, a pair of bifocals will work as long as you have the lab make the bifocal section at the bottom as small as possible.

That will help keep the reader section out of the field of view.  If you do use glasses at the eyepiece, look for 20mm of eye relief unless you wear the lenses very close to the eye.

5 hours ago, Steve said:

^ Thank-you 🙂

At SGL a retailers opinion, any retailer, is not considered inherently more worthy than a members opinion. 

And that is just as it should be. 

I, for instance, do not post here as a retailer, but only as an amateur astronomer who's been doing this for nearly 60 years.

Like others, I only speak from my experience, and others speak from theirs.  That is how forums should work.

10 hours ago, Mr Spock said:

As a practical astronomer with 40 years experience those in between magnifications are little used. x143 would be useful on globulars, x179 on planets. The lower magnifications for wide field and deep sky. This is a 102mm after all.

I use a 102mm f/7 apo refractor a lot.

How many magnifications you need is a lot dependent on the objects you view.

On the Moon, I usually start around 102x and use 143/179/and 238x a fair amount.  Low powers?  Why?

But, on deep sky objects, my preferred magnifications range all over the place.

For large star clusters, the 30x-65x gets used a lot.

For globular clusters, 79x-102x get used a lot.

For galaxies, anything in between 65x-119x.

I probably have too many eyepieces, but having magnifications available in smaller jumps enables me to frame each object well and find the right magnification.

I suppose a good Zoom eyepiece with a Barlow could accomplish the same with less eyepiece switching, but I find the fields too narrow for my taste.

It depends a lot on whether or not you take a minimalist approach to eyepieces (I obviously don't).

If you did, one eyepiece in the 5-10x/inch range, one eyepiece in the 10-20x/inch range, and one eyepiece in the 20-30x/inch range would probably be enough as long as planets

weren't the primary focus.  Then you could merely add a 2X Barlow and you're set.  In a 4", that's 20-40x, 40-80x, 80-120x, and a Barlow.

Now, if planets ARE a primary focus, I think putting the high power eyepieces closer together might be wise because you will bump into seeing limits a lot.

I know a number of planetary people who actually have high power eyepieces 0.5mm apart to "inch up" on the seeing limit.

There is no right or wrong answer for eyepiece selection.  Whatever works for you is perfect.

One other thing to consider is that:

--binoviewers with glass path corrector lenses typically generate high powers, so no low-power wide field views.

--binoviewers are often found on refractors because refractors are small scopes and users tend to concentrate on Moon, planets, double stars.

--binovewers lose a lot of light in the path (inches of glass, less than perfect coatings, and dividing the image) so are best on Moon, planets, double stars.

Now, a bino-scope is a different animal:

--low powers with wide fields are possible

--they work fine on faint deep-sky objects

--the light isn't divided between the eyes--each eye sees the full brightness.

Personally, rather than binoviewers in the scope, I'd look for a pair of binoculars with 80mm (or larger) lenses where they can accept 1.25" eyepieces.

But, if the whole point of binoviewers for you is Moon/planets/double stars, then they work great.  In most applications, they need a magnifying glass path corrector/OCA,SCT and MCT scopes being the exceptions.

Louis pretty much summed it up.

At f/5, no coma corrector, narrower apparent fields mean less coma visible.

That leans toward a 68-70° eyepiece over anything wider.

Add a coma corrector, and the wider apparent fields will yield larger true fields at each power.

That leans toward an 82-100° eyepiece.

The Pleiades are a huge cluster of stars.  The best view is through telescopes that can yield a 3° field or more.

That is a wider true field than you will find in an 8-12" dob.

If you, for example, picked and eyepiece of 30mm/82° in a scope of 1200mm focal length, the field would be 43/1200 x 57.3 = 2.05°.

That's wide enough to capture the main 12-16 stars, but not all the stragglers.

Compare this image:

https://www.space.com/pleiades.html

with this image, to see what I mean:

https://en.wikipedia.org/wiki/Pleiades#/media/File:Pleiades_large.jpg

The Pleiades is truly a fantastic object for the 80mm refractor at 20x, but not great in a dob at low power.

However, that being said, if you're looking for the nebulosity around the stars, an 8-12" dob at around 100x, though it won't see the entire cluster in one field,

will show a lot of nebula and even details within the nebulosity.

Different horse for different courses, as the saying goes.

11 hours ago, Mr Spock said:

I own a 102mm f7 Starfield Fpl-53. I already have many eyepieces so don't need to make a choice. If I were starting from scratch on a budget of around £400, here's how I'd go. It's not as simple as £100 per eyepiece though. Money needs spending where it counts most. This is of course my personal choice, and others' may have equally valid choices.

Barlow: it may seem controversial to some, but I would skip a x2 and go for a x3. Why? With a x2 you often end up with duplicated magnifications. With a x3 you can space things out more.

Here's an example I did in excel along with the eyepieces I'd use. I'd stick to 1.25" eyepieces for now; for ease of use and cost, as going 2" is expensive.
 

Aperture	F/L
102mm	714
fl	x	x3		Barlow - Teleview x3 £123
24	30	89		Explore Scientific 24mm 68° £174
15	48	143		BST Starguider 15mm £49
12	60	179		BST Starguider 12mm £49
				Total cost £395

That sort of works.  But the 48 to 60x jump is very small and not a really noticeable increase in magnification, whereas the 89 to 143 jump is quite large and the user might find a need for something in between.

Jumps are: 18x/12x/29x/54x/36x

On 13/04/2022 at 08:24, Bluemoonman said:

At 63 I decided to buy myself my first scope to use at home and to take away on trips.Got this, Altair Astro Starwave 102ED-R FPL53 Refractor Telescope which seems ideal for home and travel.So a complete newbie.

As I won’t be getting a mount and tripod until the summer it won’t get used yet but I do have some cash for bits and pieces.

My question is for advice on eyepieces.I wear reading glasses and my long sight isn’t too hot either(love getting old).I think it’s probably better to start with maybe just 3 or 4 including a Barlow but having researched different makes am as confused as when I started.

Any recommendations would be appreciated from others who have the same problem.

Budget between £120-140 per lens as I don’t want to spend a fortune then find out I don’t enjoy it.

Many thanks

 

With a 102mm, jumps of 30x between eyepieces works fairly well, and I don't think you need more than 180x on the top, so 30/60/90/120/150/and 180x would be a complete set.

That could also be accomplished with a 2x Barlow and the 30x-60x-90x eyepieces, missing only 150x (probably not used that much anyway).

Divide your scope's focal length by the magnifications to find the focal length of eyepieces at each power.

714mm/30 = 24mm, for example, so a 24mm, 12mm, and 8mm with a 2X Barlow would work well.

It's also possible to go up and down in focal length to match a favorite model or brand.

Look for eye relief of at least 18mm for glasses.

Here is a list of what is available:

https://www.cloudynights.com/topic/813708-2022-eyepiece-buyers-guide/

Sort any way you want to and I would suggest not going narrower than a 60° field nor wider than 82° until you've had more experience.

There are a lot of options in your price range.

12 minutes ago, kev100 said:

Interesting ... This is what I've read ...

https://stargazerslounge.com/topic/183154-explore-scientifc-82-degree-eyepiece-range-first-light-report/#comment-1900802

I've used the eyepiece in an f/5 dob with coma correction, and I can see astigmatism in the outer roughly 10° of field.

Your scope is f/5 I believe, so you'd see the astigmatism added to coma if you're not using a coma corrector.

Coma is more visible the wider the apparent field, so an 82° replacement for your 16x68 (the best in that series, though a small eye relief, as you mention) would show more coma.

Center sharpness and contrast is good in the 14x82, but your 16mm is sharper farther out in its field than the 14x82.

If you truly want sharpness to the edge and contrast equivalent to your 16mm, the Morpheus and APM I mentioned above would work.

As would the APM XWA 13mm, or the StellaLyra 14mm 80° (good buy!), or TeleVue Nagler 13mm T6, just to name a few.

8 hours ago, kev100 said:

Hiya,

I’ve posted before on this issue. The 16mm MV is probably my most used ep - the mag is good, it’s a reasonably flat view, but I find the 68 deg field of view and the eye relief a bit tight. Ideally, I’d be looking for a 16mm 82 degree ep, suitable for an f4.7 scope (funds prevent TVs and the like, such as the 16mm Nagler). I was looking at the 14mm Explore Scientific 82 deg, but I feel that the increased mag offsets the wider fov. The only advantages that I see are increased eye relief and a smaller exit pupil, so better contrast. Just wondered if anyone has any thoughts?

Cheers,

Kev

 

 

The magnification half way between a 20mm and a 8.8mm is a 12.2mm eyepiece.

The 12.5mm Morpheus is very close (it measures at 78°)

And the APM Hi-FW 12.5mm is 84°, another possibility.

Now, if you want 2 eyepieces, equally-spaced, in between the 20mm and 8.8mm, they should be 14mm and 10.2mm to keep magnification gaps equal.

7 hours ago, kev100 said:

I had considered the 16mm nirvana, but the reviews I've seen weren't great with faster scopes ...

Neither is the 14mm Explore Scientific.

You need a case like this one:

https://www.cloudynights.com/topic/462248-good-eyepiece-case/?p=6014464

3 hours ago, chrispj said:

Adding to this, this morning I tried an old TeleVue 2.5x Barlow I just picked up,  without the 2x Barlow that came with the binoviewer.  This freed up around 2cm of in focus, but appears to magnify to perhaps 4x given approx only half the FOV I could see with the 2x Barlow was visible. Intriguing,  I might try a similar long 2x Barlow and see what result that gives (I presume somewhere between the 2) since its easier to swap out the Barlow than 2 eyepieces...

 

A Barlow's magnification increases with distance from the eyepiece, so all 2x Barlows will yield high powers that far from the eyepieces.

To move the focal plane back and keep magnification lower, try a telecentric Barlow like the TeleVue PowerMates or Explore Scientific Focal Extenders or Harry Siebert Optics telecentric Barlows.

4 hours ago, badhex said:

Yes agreed Peter, the fit is what you are buying and most manufacturers don't make claims to the clear aperture, excepting maybe a handful. 

I guess though there's also perhaps an unspoken expectation that the aperture you are getting is not unnecessarily and significantly stopped down.

Obviously we know that a cat or a newt loses some aperture due to central obstructions, but unless they are designed badly that loss of aperture is unavoidable. On the other hand the EP barrel stop lip inside the SW diagonals really only needs to be at most a couple of mm to be functional and minimise aperture loss instead of a pretty significant 5mm meaning 10mm total aperture loss. Although it's not as bad, the inner threaded sleeve on the telescope side also seems completely perplexing - what is it even there for?

Once I started to think about the whole thing it just seems pretty unnecessary to have these 'features'. 

Obviously these are just my musings and I don't have the technical and manufacturing knowledge or rationale behind the decisions, and maybe they are all for very good reasons!

2" O.D. is 50.8mm.  A 48mm filter thread reduces wall thickness to 1.4mm.

That could be enough (marginal) to support a 2.5 lb eyepiece plus a 1.1 lb Barlow, but not if the insertion tube of the diagonal has an undercut say, 0.5mm, deep, reducing wall thickness to 0.9mm.

So the interior step up to a 47mm I.D. adds the depth of the undercut back to the wall thickness.

The thickness of the ring/stop for the eyepiece likewise would seem to be adequate if equal to eyepiece barrel thickness, even with a beveled lip at the bottom of the eyepiece.

So any justification for a smaller opening than 48mm is a bit hard to swallow.  Of course that assumes the external threads that attach the piece have at least the same thickness as the wall of the eyepiece tube itself, and on some diagonals,

that thread is the 2" SCT thread, which means, without a safe wall thickness the wall will be less than 1.4mm with a 48mm I.D.  For safety, increasing thickness at the threads and reducing I.D. slightly is prudent.

The older Lumicons got around this by making body and inserted tube in one piece with a through aperture of 48mm and having the eyepiece tube have an outward facing flange on its bottom end that was bolted to the top of the diagonal body.

Originally, this was 50.8mm clear aperture all the way to the mirror, but in later years they added a ring stop (don't know the I.D.).  The Lumicon also had just about the shortest light path through a 2" diagonal I've seen, though the eyepiece tube

was shorter than some 2" barrels.

In today's 3-piece diagonal construction (not counting mirror), I.D. has to be a tad smaller to account for larger heavier eyepieces without breaking a tube off the body of the diagonal and to account for those accursed undercut grooves.

10 hours ago, Mr Spock said:

As you can see from the image, there are no restrictions inside the tube. It is as the size stated 👍

The inside of the housing needs to have the same blackening the insides of the barrels do.

That is really reflective.

Largest 2" eyepiece field stop 46.5mm

TeleVue 2" diagonals--47mm on the scope side, 45.5mm eyepiece barrel stop on the eyepiece side.