Don Pensack

10 hours ago, Martyn A E said:

Being relatively new to the hobby I've found most UK suppliers have little or no stock of many of their advertised eye pieces such as Televue, Baader, Explore scientific etc.,

Is this normal at this time of year or as a result of the Pandemic?

It seems very difficult even to get information of when they'll receive new stock.

the factories making the raw materials have had staff shortages and increases in labor costs.

the factories that gather the raw materials and make the products have had staff shortages and increases in labor costs.

the shipping companies--overland, sea, and overland again have all had staff shortages and increases in labor costs.

the distributors who import have paid higher costs and received reduced shipment sizes.

The freight delivery companies have had staff shortages and increases in labor costs.

The retailers have paid more (a LOT more in the US due to very high tariffs paid by the importers) and had staff shortages and increases in labor costs.

ALL of this is due to the Pandemic except the politically-motivated tariffs in the US.

People are staying home and are not eating in restaurants, or traveling places or driving as much.

For the first time in a generation, Americans saved more last year as a % of income.  It had steadily gone down.

That extra cash created demand 300-400% higher than it was 2 years ago.

Had that happened without a pandemic, it would have created shortages.

But add the supply chain problems due to Covid, and the shortages became even worse.

My Orion H-ß filter was a surprise--a 12nm bandwidth and a 94+% transmission.

It was a pain to thread in, and I had a couple others with even narrower bandwidths, so the Orion went.

But, given it is typically at a lower price than other high-end H-ß filters, it is certainly a good option.

It might be useful to know that the actual focal length is around 10.5mm, in case that matters to anyone.

On 16/01/2022 at 02:22, Saganite said:

Hi Dave,

 

My Fullerscopes catalogue from 1975 or 1976, has one.

 

I had one of those zooms around 1970-1974 (can't remember exactly when) and used it in a Unitron 4" f/15 refractor with wooden tripod, hex eyepiece turret, and weight-driven clock drive.

I think mine was from Edmund Scientific, but my memory is foggy.

By the way, the "Erfle" eyepiece in the picture is not an Erfle design.

It's described as a "Wide Angle" here:

http://www.quadibloc.com/science/opt04.htm

No other design comes close, so who designed it is unknown.

I owned one of those, too, but it wasn't all that sharp and had very short eye relief.

Sorry, I can't resist.

This is a LongPerm:

https://www.hadviser.com/perm-hair/24/

and this is a Long Perng:

https://www.longperng.com.tw/goods.php?act=view&no=98

Thanks for the chuckle.😁

On 13/01/2022 at 09:52, stevo58 said:

Is the Octoplus a Long Perng? I know the others they sell are the same old same old, but I thought the Octoplus was their own design. I may have fallen for marketing hype, though. 

The focus mechanism says Long Perng, but it could be their own design.

The VIP Barlow is long out of production, but if you can find one, it is one of the best Barlows ever made.  Beautiful polish.

But, like all negative-only (telenegative) Barlows, it will add to the eye relief of the eyepiece.

If not adding eye relief to the eyepiece is important, then you should be looking at telecentric Barlows like the TeleVue PowerMate or Explore Scientific Focal Extender.

4 hours ago, cajen2 said:

Well, I've finally decided. I really wanted the Morpheus 4.5mm, but none of my trusted sites had any in stock. In fact, one of them contacted the suppliers and was told that Baader are now quoting June for the next supply!😥

So I've pulled the trigger on a Pentax 5mm from Flo (now at the normal price, of course!). I'm very happy with my 14mm, so can't go wrong. I just wish the FOV was slightly wider....

You could add the 4.7mm APM XWA (they call it 5mm).  It's a different enough experience from the Pentax that they might have different uses.  But 110° is plenty wide if wider is what you want.

And less costly than the TeleVue Nagler T6 in 5mm.  With such a small exit pupil, you probably won't need glasses, so extra long eye relief isn't critical.

2 hours ago, stevo58 said:

You could try this one:

 

https://en.lacerta-optics.com/index.php?menuliste=Non-optical accessories

It’s been used on SkyWatcher, though not a FlexTube:

 

https://www.cloudynights.com/topic/737238-lacerta-508n-octoplus-2-focuser-for-skywatcher-telescopes/

I was planning on buying one myself, but they were out of stock, and a Moonlight became available. I’m not certain I made the right decision. 
 

Strven

Bearing-wise, the Moonlite is a step up from the Long Perng (Lacerta), but Moonlite no longer makes visual-only focusers--they're all motorized now.

There are very few high-end visual focusers left in production.  There is the Starlight Instruments Feather Touch (with long back orders) and little else.

JMI is out of production, Moonlite is gone as a visual-only focuser, Baader SteelTrack is another Chinese focuser.

GSO and Long Perng seem to be cornering the market.

Which is OK, I guess, as some of their focusers are quite nice.

1 hour ago, Highburymark said:

In search of a slightly more flamboyant tailor.

Whoa!  Was it one of the prototypes of the new barrel design?

If that is the 20mm, replace the bottom cap with a hard plastic cap--the rubber caps get pressed in to contact the bottom lens and leave a smear there.

On 04/06/2018 at 14:33, John said:

I did compare the Myriads with Ethos and Pentax XW equivalents (I didn't have the 3.7 or 4.7 Ethos SX at that time). Maybe not detailed enough but the best that I could manage . I did try the WO XWA 9mm but though it to be identical to the Myriad 9mm. The question is, are the Myriads related to the APM/Lunt HDC XWA's in any way ?

Anyway here is my little piece on the Myriads:

 

These 100° eyepieces are made by United Optics and are or have been sold under the names

APM

Antares

Tecnosky

Telescope Service

William Optics

Stellarvue

Skywatcher

Lunt

Astrotech

Sky Rover

Think of them as all the same man wearing different suits.

One thing to know is that the difference between an inexpensive eyepiece and an expensive eyepiece, on axis, doesn't amount to much.

Any difference there will be related to seeing more than the eyepiece.

But that does not mean there are no differences.

You should review this, because it will give you a lot of things to look at to compare eyepieces.

https://www.cloudynights.com/topic/795988-how-to-evaluate-or-compare-eyepieces/?p=11463451

One simple rule is this:

Well corrected to the edge of the field in short f/ratio scopes......Wide to ultrawide field.....Inexpensive:  Pick any two.

On 07/01/2022 at 08:40, vlaiv said:

I don't think they quite are.

Imagine following scenario, you have two eyepieces.

You look thru one eyepiece with your left eye and thru other eyepiece with your right eye and let your brain try to merge image.

Image consists out of full moon in the center of the field and surrounding sky up to field stop (sky is bright enough against field stop so that you can easily distinguish it in each eye).

If focal lengths are the same - then moon will overlap perfectly from both eyes - there will be no double image of it.

If AFOV is the same - then field stops will align perfectly - there will be no double image.

You can have the same moon image and different surrounding sky images and you can have different moon sizes for same sky/field stop image. There are third and fourth cases - when both are the same and both are different.

This shows that AFOV and magnification are not effectively the same thing.

(you don't need the moon to compare AFOVs of two different eyepieces - you just need blank well lit wall - hold two eyepieces - each against one eye and let brain try to merge the image - if you have trouble and can't align field stops - that means AFOVs are different - and in fact, you can judge which one is larger by favoring each eye in turn).

This is the reason I asked in the first place about percent of distortion. Televue has same formulae about relationship of AFOV, field stop and focal length on one of their pages:

https://www.televue.com/engine/TV3b_page.asp?id=113

Now, as you mentioned:

If that eyepiece has zero AMD, then we need to use

and if we use that formula on 24mm FL and 27mm field stop we get:

beta = 27 / 24 = 1.125 radians = 64.46°

But if we do something else - and assume that AFOV is indeed ~68° then we can do following:

68° = 27 / actual_fl => actual_fl = 27mm / 68° = ~22.75

So maybe Panoptic 24mm is actually 22.75mm FL eyepiece.

Or maybe there is some middle ground and FL is something like 23.4mm and AFOV is from there 66° and for marketing purposes it is declared as 24mm 68° to be in line with rest of Panoptic EPs.

In the end - maybe field stop is not precisely 27mm but a bit more?

 

I agree,  perhaps the focal length is not exactly 24mm, or the field stop is not exactly 27mm, or the apparent field is not 68°.

However, those calculations seem to be assuming orthoscopy, and distortion can alter the figures.

I just measured a new one, and the field stop is 27.15mm +/-0.02mm

1 hour ago, Louis D said:

As far as I'm concerned, they're the same thing.  If you increase image scale to stretch the image over a larger area, then you must have locally decreased the eyepiece focal length.  Vice versa, if you decrease image scale to squeeze more image into the same or a smaller area, then you must have locally increased the eyepiece focal length.  Is there another explanation as to how image scale can be changed in the apparent field of view without changing the local magnification power of the eyepiece across the field of view?

Yes.  Magnification can stay the same and the object be distorted in shape.  

Take the example of a double star, which, with AMD, changes its apparent separation as the star nears the edge of the field.

With RD, it does not, though the position angle may change.

6 hours ago, vlaiv said:

How can we be sure that all additional AFOV is due to distortion and not perhaps change in focal length?

Normally, I would ask the same question.

But TeleVue's stated design philosophy is to reduce angular magnification distortion to as close to zero as possible, leaving RD wherever it falls.

So in this particular case, the extra field is due to pincushion distortion, not a change in focal length/magnification.

10 hours ago, rwilkey said:

Hi Steve, have you considered Lumicon at all, I don't know the techy details but find my 2" version perfectly adequate.

Lumicon no longer makes an H-ß filter.

TeleVue or Astronomik, if available, are your best choice.  Just remember, this will be a low power filter.  If your focuser uses a 2" eyepiece,  don't buy a 1.25" filter.

You will be using this below 10x/inch of aperture, and 2" filters fit the bottoms of many 1.25" adapters so are usable on 1.25" eyepieces.

You could just buy direct from APM......

Have you tried overhauling or adjusting the stock focuser?  The 2" and 1.25" adapters are not the ideal way to do it, but almost any replacement focuser will be a low profile focuser,

which will require a fairly thick stand-off block adapter between the tube and focuser.  You used to be able to get these from Moonlite in the US, but I'm uncertain if that is still true.

Plus, Moonlite no longer sells visual-use focusers.

Perhaps Starlight Instruments (long lead time)?

Maybe Baader makes such blocks for its SteelTrack focusers.  They don't advertise them, however, so such a tall block with specific mounting holes might be a custom piece from a local machine shop.

You see, other focusers don't use the dual adapters setup, so the tops of any other focuser would automatically be a lot lower than your current focuser with one of the 2 adapters.

It's a good reason to see about adjusting your current focuser to be smoother and more accurate in its movement.

On 05/01/2022 at 08:28, vlaiv said:

You mention percent of distortion. Can you elaborate a bit on that? I'm not quite familiar of what that could mean.

I understand two edge cases - AMD and rectilinear. Those two can easily be explained with a bit of geometry.

Zero rectilinear is first image - each angle is mapped to its "projection" on field stop. Same angles near the center are smaller on focal plane than angles near the edge (see segments on straight line in first image).

Second image is zero AMD. Each angle is mapped onto equal part on focal plane and focal plane is actually made up of joined segments along the arc (drawn in the image). This keeps all angles the same (zero angular magnification) - but bends straight lines.

When you say 10% distortion that gives 41.6° while max that I can imagine is case of zero AMD - and it is ~39.25° - what the mapping looks like in that case?

Positive rectilinear distortion stretched the field radially.  It allows a certain field stop to hold a larger apparent field than its size indicates.

As an example, the TeleVue 24mm Panoptic has a 27mm field stop and a 68° apparent field.

With zero RD, the apparent field would be 58.7°  With a 15.8% distortion, the field becomes 68°.  Observers have noted for years that the design has a lot of RD and many observers remark that it is quite noticeable.

In contrast, take the 24mm APM Ultra Flat field, which has a 27.3mm field stop (from timing) and a 63° apparent field (from the flashlight test).

The zero RD figure for that focal length and field stop would be 59.3°.  A 6.3% radial distortion gets to the 63° measured.  

Both eyepieces have pincushion distortion, but at very different levels.

Tests of visibility for distortion in a moving field shows that roughly a 7% RD is seen by the eye as distortionless in a moving field, which is why many reviewers of the 24mm APM point to seeing almost no distortion.

Alas, the eyepiece is not completely without lateral astigmatism.

With zero RD, any widefield eyepiece will have significant AMD, and this leads to "globe" or "rolling ball" distortion when panning a field.

In practice, in the hundreds of pairs of binoculars I've looked through, no designer opts for zero RD (straight lines always seem to curve very slightly near the edge), but RD is minimized while AMD is usually the predominant issue.

18 hours ago, vlaiv said:

What sort of distortion?

They are both distortions of some sort. You can't map sphere onto flat plane without some type of distortion.

AMD vs Rectilinear distortion.

Two edge cases are:

y = f * tan(angle)

and

y = f * angle

where y is distance from center of the field to field stop and f is focal length of EP. If we take 27.4mm, half of that is 13.7 so we have:

13.7/40 = tan(angle) => angle = ~18.9 or AFOV = 37.8° for zero rectilinear distortion

13.7/40 = angle = ~19.6238 or AFOV of ~39.25° for zero AMD

 

 

You're right.  I was referring to rectilinear distortion.  I should have specified.  I edited.

8 hours ago, Joacim said:

Thanks, some good alternatives to think about. I read about the Omegon Redline yesterday and it seems to be a gem. 

Omegon Redline = Astromania SWA 70 = Astrotech AF70 = Celestron Ultima LX = Arcturus Ebony = Olivon 70 = Skywatcher SWA = Telescope Service Expanse.  Some would be used, others new.  Shop for price.

However, the focal lengths all have different internal designs.

32mm--an average Erfle--best at f/8 or longer

22mm--very very good for a cheap price--a real bargain

17mm--the same as the 22mm, with just a *trace* of edge of field brightening.

13mm--Horrible.  The worst edge of field brightening I've ever seen in an eyepiece, with 50% of the outer field looking like you're looking through a nebula.

8mm, 5mm, 3.5mm.  Just average.  Baader Hyperions are better.  For f/6 and longer, they're OK.

On 04/01/2022 at 05:38, Louis D said:

I suppose it's entirely possible for a 40mm 1.25" eyepiece to have a 52° apparent field of view (AFOV) if it has enough edge distortion to stretch the outer regions far enough to fill the extra 8°.  After all, the 25mm ES-100 and 26mm (really 25mm) Meade MWA have roughly the same true field of view (TFOV), but the ES shows it in a ~100° AFOV while the Meade shows it in a ~82° AFOV.  That's a massive difference in edge distortion for the same TFOV.

However, I don't think the 40mm Meade Plossl in question has that amount of edge distortion.

The maximum without rectilinear distortion is 37.8° with a 27.4mm field stop.

4% distortion yields 39.3°

6% distortion yields 40.0° (the average 40mm Plössl)

10% distortion (very large for this type of eyepiece) yields 41.6°.

You can see how unlikely even 43° is.

22 hours ago, Splodger said:

Interesting. I had a hunt around and found that about half of the sites selling, or were selling as they are all sold out, the eyepiece have it at 52° and the other half, including meade.com, at 44°. Perhaps I bought it a telescope.com https://tinyurl.com/meade-40mm who are marketing it at 52°. Anyway Ive been bamboozled one way or another.

If they quote 52°, it is because they merely copied the information from a shorter focal length.  The maximums are 43° on a 40mm, 49.5° on a 32mm, so if you see figures quoted that are larger, they are advertising figures, not actual.

I believe the instrument comes with a 1.25" star diagonal and visual back, but has a standard SCT thread which will accept a 2" visual back and 2" star diagonal.

I don't think the scope comes with those, however.  They would have to be added.

On 31/12/2021 at 08:08, JeremyS said:

Excellent advice thanks Don.

One further question. Given its greater cleansing potential, and the inclusion of things like ammonia, is there any chance it will degrade rubber eyepiece parts like eye guards on even eyepiece carapaces such as on the Pentax range? And related to that, it is possible that it extracts chemicals like plasticisers from the rubber and deposits them on the glass? Probably worrying unnecessarily, but do you avoid contact with rubber.

I see you can get ROR in dropper or spray bottles. What do you recommend?

To clean the eye lens well on nearly any eyepiece, removal of the eyecup is desirable.  However, ROR is very gentle and will not damage rubber or plastics, or your skin if you get a drop on it.

I recommend the drip bottle.  The spray wastes a lot of fluid and you cannot spray it directly on the lens anyway.