Don Pensack

3 hours ago, SuburbanMak said:

Thank you for replying, really interesting.  As it stands I've been quite happy with the Baader's performance in the mid range (I'd say 18mm down to 10mm is its sweet-spot) so wasn't really thinking of doubling up in that range. Are are you saying you'd rather barlow a 13mm to get to a higher mag than buy a dedicated short focal length?  

Also would really value your opinion on an upgrade for that max field 24mm 68 degree - the one that keeps coming up is the Televue 24mm Panoptic. 

There are alternatives in that size (like the APM/Altair Ultra Flat Field 24mm), but if you don't wear glasses, it's the 24mm Panoptic.

I used one in the same scope for several years and it is a great combination.  A 32mm Plössl will give the same true field at a lower power with a larger exit pupil and brighter image, which could be important for use of nebula filters.

On 13/04/2021 at 02:05, IB20 said:

I’m thinking of getting the 17.5mm Morpheus for my 8” dob. Does anyone have any experience with this eyepiece in similar equipment?  What’s the contrast like, as the 25mm BST which it would compete against seems to present fairly bright background skies. Does anyone know how the Morpheus range barlow, particularly the 17.5mm?

👍

Any 17.5mm, from any manufacturer, will have a darker background than any 25mm, simply because of the magnification (i.e. smaller exit pupil).

All the Morpheus line will barlow well. (use a 1.25", not 2", Barlow).

The Morpheus line performs well at f/4, so f/6 is a cinch.

Bear in mind that though the eye relief on the line is fairly constant, the eye relief does decrease with focal length.  I view the 4.5mm and 6.5mm as "marginal" for glasses (some won't find them compatible, some will),

though the longer focal lengths are fine.

Those viewing without glasses will find all focal lengths fine.

Even then, the issue with the 14mm seems to be scope-specific.

In my 12.5" dob with Paracorr II, (1826mm effective focal length) the 14mm seems to only deteriorate right at the field stop.

And who looks at anything right at the field stop?

18 hours ago, Ags said:

I had a chance to try out the turret tonight. It was a short session between clouds taking in a few doubles.

1. I must remember to turn the turret clockwise - turn it the other way and my cheap diagonal starts to disassemble!

2. Eyepieces on turrets fog. Make sure the turret is twisted as far away from the face as possible. 

3. I really like not changing eyepieces!

If you use eyepieces in a turret, but do not observe in a dry desert environment, it is customary to keep the eyepieces not in use capped to prevent fogging.

It's even easier if all the eyepieces use the same caps--then you can simply move one cap each time you change eyepieces.

Search for "90° correct image star diagonal".  I found about 50 different ones easily.

Many of them on Amazon and eBay, too.

All have small clear apertures, alas.

17 hours ago, Alien 13 said:

 

I do agree that a dirty lens pen does not good but its the same with a microfiber cloth, the trouble with fluids is that they don't "magic" the grime away but dissolve it only so spread it everywhere when the solvent evaporates, this requires 10 mins of vigorous rubbing with a cloth to get rid of. The lens pen is a single swipe.

Need to buy a decent lens pen though, not one of the e-bay cheapies.

Alan

Alan

When a fluid is used to clean an eyepiece, you don't let it dry on the surface of the lens--you mop the lens surface while it is still wet, picking up the suspended or emulsified debris.

Done that way, no additional rubbing is necessary.  The world's best lens pen is only clean on its first use and since it is not used with a fluid, merely scoots the grit around.

Perhaps this video will show what I mean:

https://www.youtube.com/watch?v=kz2O1ly2W3k

9 hours ago, Tyke 123 said:

Lens pen by a country mile.

If anybody is daft enough not to prep a lens before using a lenspen OR cloth then more fool them!

Blower-cleaning fluid-lenspen.

Then lenspen is superb at getting shut of the film that cloths sometimes cannot remove.

Sorry, I strongly disagree:

Lens pens:

--are only clean on the first use (maybe).  After that they are merely smearing around whatever it picked up on the first use.

--are used dry. NOTHING should be used dry on a lens because grit will be dragged around on the dry surface, scratching the lens permanently.

--have a brush on one end that merely smears oils around.

So, in lieu of a lens pen, what can you use?

1) a wet Q-tip to mop up the dirt and oils by suspending the débris in fluid.

2) a wet alcohol pad to do the same

You can use Kleenex AFTER the eyepiece lens has been mopped.  Kleenex, however, leaves a bit of dust on the lens that requires being blown off.

Which brings to mind that you need some form of device to blow dust and particles off the lens, like:

--rubber squeeze bulb with a directed nozzle

--electric blower (no heat) with a directed nozzle

What should not be used is canned air because these have a tendency to blow liquid on the glass.  Not to mention the temperature of the gas can cause thermal shock to 

the lens because it often comes out at a very cold temperature.

What does TeleVue recommend for cleaning their eyepieces?

https://www.televue....page.asp?id=103

Also sold under the labels:

Orion Edge On Planetary

Altair Lightwave LER

Omegon LE Planetary.

All the same eyepieces made by Long Perng in Taiwan.

I see it as a shoulder of Orion.  His arm is a series of stars curving upward:

http://www.seasky.org/constellations/constellation-orion.html

And it's either bettle-jooz (bettle rhymes with kettle) or baytle-jooz in English.

I have no idea where beetle-juice came from.

On 02/04/2021 at 14:10, Louis D said:

I think pressure washing might get the job done as well:

 

That was very satisfying.  Hard to explain why.  I watched the whole thing.  

Probably not applicable to eyepieces or telescopes, but my patio does need cleaning...........

Some severe problems with lens pens:

1. the brush just smears eyelash oils around, making the problem worse.
2. the brush and rubber ends are only clean once.  After that, they smear around whatever is imbedded in them.  If that is dust, you can scratch the lens.
3. Many lens pens have a black powder in the rubber end, which is supposed to burnish the lens.  That is an unmitigated disaster on a lens surface.

Every eyepiece I've inspected with a loupe after someone has used a lens pen has a series of micro scratches on the lens.

The key here is to never touch a dry anything to a dry lens unless the lens is perfectly clean already.

Conclusion: don't use a lens pen.  Ever.  They should be banned.

Instead, us a blower to blow off dust, and a wet Q-Tip to wipe the lens, and always use a cleaning fluid of some sort.  Only after all the debris on the lens has been cleaned off

should any dry cloth or Q-Tip touch the lens.

3 hours ago, bingevader said:

And then I forgot to ask!

Don, do you notice any deleterious effects of any of the ingredients on the lens coatings?

I use BWF too btw, sparingly.

I've cleaned some eyepieces at least a hundred times, and they look brand new (in the case of a couple, cleaner than new).

3 hours ago, bingevader said:

You need a good make-up remover, Don, not a lens cleaner!

LOL.

I once worked in a store that sold binoculars in large numbers.  We had many many pairs on display for people to try out.

Every few days, we had to clean the goo off the eyepieces of the binoculars.  One particularly dirty set had what looked like black crayon streaks across the lenses.

Isopropyl alcohol simply wasn't strong enough.  ROR took it right off on the first pass.

I also used to use a Nikon Lens Cleaning fluid, and it was pretty good, too.

I also learned that the cheapest binoculars' anti-reflection lens coatings was simply a dye applied to the lenses, as the Q-Tips came off the lenses tinted blue and the "anti-reflection" coatings simply wiped off with the fluid.

We are talking binoculars that sold for less than £20, though.

23 hours ago, neil phillips said:

Alcohol is fine, as in undiluted ?

Not heard of ROR cleaner

 

http://www.ror.net

Alcohol is fine, but it isn't as good a solvent for some organic debris as something else.

I prefer a commercial cleaning fluid called ROR.

Its ingredients include alcohol, ammonia, soap, salt, and distilled water.  It's used in the phot industry to clean lenses before they are assembled into camera lenses.

It's the best cleaner I've found for removal of eyelash oil, mascara, and other similar crud.

Not surprising, since ROR stand for residual oil remover.

As to how faint we can see visually, the eye can see some prodigiously faint stuff if you are fully dark adapted and observing in dark skies.

Several posters on cludynights.com have done experiments to see how deep one can go, and it seems to hover around magnitude 28 per square arc second.

At that point, the brightness of the field stop begins to match that of the field.

Which explains why so many visual observers see IFN that takes extremely long exposures to catch in an image.

Pannekoek visually drew a sketch of M31 that went out to 5° in length, yet I have seen exactly 1 image that showed the galaxy that large.

Me Bartels regularly sketches IFN around many famous objects that he sees visually in his 25" f/2.6 scope.

And I can tell you that, visually, if the sky is sufficiently dark, a good nebula filter will reveal nebulosity from one side of the Veil Nebula to the other, something I've never seen in a photograph.

And M16 and M17 are merely bright points on the same nebula--something you can see visually yet is shown only in 1 in a 1000 images of either nebula.

In skies of magnitude 22 per square arc second,  seeing out to magnitude 25 isn't easy, but it's also not that hard. 

The sizes of galaxies are typically gauged on the mag.25 isophote, and I'd say that's not far off the visual size.

The key is simply to have dark skies, say mag. 21.5 or darker.  

On 25/03/2021 at 03:58, bendiddley said:

So I have read somewhere that a larger exit pupil and getting the 'right amount' of magnification from an eyepiece can maximise light transmission of nebular filters. Is this the case? Also some people have said that 40mm gets that 'sweet spot'. Anyone found this?

Take the f/ratio of your scope and multiply by 2.5.  That will be the highest power, shortest focal length, eyepiece to use with nebula filters in your scope.

Multiply the f/ratio by 7.  That will be the lowest power, longest focal length, eyepiece to use with nebula filters.

On an f/5 scope, for example, that would be eyepieces from 35mm down to 12.5mm.

Generally, the lower power end of that range will be better than the upper end of that range, simply because that will yield a brighter image (albeit smaller).

Why such low powers?

Nebula filters work by dimming the background sky about 2.5 to 3 magnitudes while only dimming the nebula 0.05-0.1 magnitude.

As you raise the power, the background in the eyepiece gets dimmer anyway.  By the time the background is already quite dark, the efficacy of dimming the background further is significantly reduced.

Then the 0.05-0.1 magnitude dimming of the nebula starts becoming more important.

So above a certain point, the nebula filter just isn't helpful any more, and that occurs around a 2.5mm exit pupil (about 10x/inch of aperture).

One thing to note about silver--it's response rolls off below 500nm, and transmission is poor at 400nm.

Aluminum doesn't roll off significantly in the 400-500nm range.

The way to bring silver up to the aluminum level at the 400-500nm range is with special UV-enhancing coatings added.

It think it possible those are applied in some cases, but you would want to find out if they are.

Dielectric coatings can be optimized for any wavelength bandwidth and reflective angle desired, but might require custom coatings if going deep into the infrared is desired.

https://www.photonics.com/Articles/Mirrors_Coating_Choice_Makes_a_Difference/a25501

For pure infrared use, gold is great--high reflectivity and it doesn't corrode at all.  Not good for all visual, though perhaps OK for planets?

https://www.cloudynights.com/topic/346824-gold-diagonal-better-contrast-on-planets/

Someone out there offers a gold-coated star diagonal--Vernonscope?

Gold is soft, though, and should be overcoated for protection from scratches, just like silver and aluminum.

On 20/03/2021 at 10:52, Deadlake said:

If you are using the flattener on a fast scope F6 will there still be an advantage of using a mirror diagonal over a prism at all? I ask this as BBHS mirror diagonals are hard to come by at present. I want the stars at the edge to be sharp.

I don't think the type of diagonal relates to whether or not field curvature is present or visible.

But the prismatic smear that occurs with prisms gradually gets worse below f/8.  I wouldn't use a prism diagonal at f/6.

Baader BBHS mirror diagonals are not the only good star diagonals out there, by the way.

17 hours ago, Louis D said:

Which lens in the diagram was flipped?  It looks like only the negative lens in the lower barrel could be flipped and still get the whole thing to screw together.

In the 13mm, they had flipped the mushroom-shaped lens right where the lower barrel joins the upper barrel.

In the 10mm, they had flipped the lowest main lens so the flat surface was up instead of down.

Both were returns from customers complaining of distortion and aberrations.

One other thing that occurs to me is that I have run into a couple KUO eyepieces that were misassembled.

Once assembled correctly, they worked fine.

I just last night tried the 18mm APM UFF in my 102mm f/7 triplet refractor (no field flattener) and noticed no abnormal field curvature

and the moon images were good across the field.

That scope is short enough that I think I would have seen any extensive field curvature in the eyepiece if it was there.

One 13mm XWA had incredible distortion at the edge of the field and the field looked like a deep bowl.

I was going to return the eyepiece, but took it apart and discovered one element had been installed upside down.

I corrected it, and the eyepiece worked great, with just the typical edge distortion common to 100° eyepieces.

The same thing happened on a 10mm UFF several months later.

So I wonder if the eyepiece is misassembled.  The 18mm I checked out was very nice and had a quite flat field presentation.

You can find the assembly orientations for each lens right here:

https://www.landseaskyco.com/altair-ultraflat-24mm-65-eyepiece-stainless-steel.html

9 hours ago, Deadlake said:

How do you determine the curvature of a scope?

Edit:

I’ll get number crunching

https://www.telescope-optics.net/curvature.htm#For_a_doublet

Telescope in question would be a 130mm/F6.

The field flattener reduces the focus length, presume you need a flattener that can screw directly to a prism with a short light path?

 

Geometry.

The curvature of the field is indirectly related to the focal length of the scope, and can be calculated at different distance from the center axis.

The difficulty with refractors is the Radius Of Curvature, ROC, is about 1/3 of the focal length, whereas with a newtonian, the ROC is equal to the focal length.

That means field curvature issues are more present in refractors, and definitely explains the use of field flatteners for imaging, and even for visual use if the refractor is short.

That applies to doublet lenses.  Quite often, in some triplet designs, some field flattening is part of the formula, so you cannot necessarily assume a triplet will have the same FC as a doublet of the same focal length.

Some 4-lens refractors start with a long focal length objective, then add a focal reducer/field flattener later in the optical path to produce a flat field short focal length refractor.  That's a superb idea.

But, if the refractor is not inherently flat, adding a field flattener is a good thing to do for imaging.  Surprisingly few visual observers use field flatteners, but they work well, and allow the use

 of a lot more different eyepieces without seeing a lot of field curvature.

Field flatteners have a "working distance", so it's important to try to get the distance from the FF to the eyepiece focal plane at least approximately right.  To that end, it is useful to know the light path length through the diagonal

and where the focal plane is in the eyepiece.

The radius of curvature in your refractor is about 270mm.  That means a flat field eyepiece will show you field curvature.

| + ( = (

It's only if the curves match that you get a flat field:

( + ( = |

So, just about any flat field eyepiece will show you curvature.

If the scope had a longer radius of curvature, this wouldn't be an issue.

Or, if your scope had a flat field.

Telescope Service sells a field flattener that would work in your scope.  This might allow you to use most eyepieces successfully in that scope.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10307_TS-Optics-REFRAKTOR-1-0x-Flattener-Bildfeldkorrektor---2--Anschluss.html

Otherwise, you'll have to confine yourself to eyepieces that have field curvature that matches (an expensive, trial and error proposition), or very narrow fields of view (narrow field stops).

Th ability to handle field curvature with accommodation in the eye diminishes as you age, too, so a correction to the scope seems the best option.

Flatten the scope's focal plane and just about every eyepiece will improve.

Isn't it ironic that binoviewers have gotten popular while smooth barreled eyepieces have all but disappeared.

Vixen has one model with a smooth barrel.

APM has 1 model with smooth barrels.

Baader has 2 models with (relatively) smooth barrels.

Explore Scientific has none.

TeleVue has none.

Pentax has none.

Stellarvue has none.

Maybe some Siebert or Russell eyepieces have smooth barrels.

It's "slim pickings" out there.

Those holes are for a lockring spanner to unscrew.

You need a tool like this one:

https://www.amazon.com/Neewer-Professional-pointed-Spanner-Repairing/dp/B00J5F6O92/ref=asc_df_B00J5F6O92/?tag=hyprod-20&linkCode=df0&hvadid=312021382923&hvpos=&hvnetw=g&hvrand=2188723598470281462&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9061089&hvtargid=pla-304889665671&psc=1&tag=&ref=&adgrpid=60647562605&hvpone=&hvptwo=&hvadid=312021382923&hvpos=&hvnetw=g&hvrand=2188723598470281462&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9061089&hvtargid=pla-304889665671

https://www.cloudynights.com/gallery/image/107350-20200612-125114/

https://www.cloudynights.com/gallery/image/107349-20200615-154956/

https://www.cloudynights.com/gallery/image/107348-20201020-140843/

https://www.cloudynights.com/topic/645478-baader-hyperion-zoom-repair-disassembly/