Louis D

3 hours ago, bomberbaz said:

my brother in law refers to his other half as the entertainments manager when I ask if they are coming out

When asked if I'm free on a certain day or evening, I always say I first need to check with my social events coordinator.  I just go where and when I'm told to go. 😊

Only the two negative/positive design versions suffer from kidney beaning.  Those would be the 6mm and 9mm versions.  The 15mm and 20mm versions are straight positive designs like a Konig variant, so they don't have that issue.  Kidney beaning tends to happen mostly in negative/positive designs or when pairing a positive only eyepiece with some Barlows in my experience.  Of course, without the negative section, they don't perform so well in faster systems.  Even with the Barlow element on the BV, I didn't notice any kidney beaning with the 20mm Svbonys.  Since I was able to pick up the pair for under $50, I was willing to roll the dice with them.

I'm glad the Morpheus pair worked fine for you.  The added weight and lever arm can be an issue as you say.

Around here in Texas, we're usually well south of the jet stream, so our skies are often very stable (it also leads to prolonged droughts).  If you have the aperture, 100x to 200x is cruising and 350x to 400x is quite usable.  It's part of the reason big Dobs are popular in these parts because aperture is really what limits resolution, not the atmosphere.  Of course, these same dead calm conditions are perfect for mosquitoes for a few weeks during our long summers after the infrequent rainstorms (I was batting them away last night despite our last rain being 2+ weeks ago).  200 miles west of here, and they are no longer much of an issue because of how arid it gets that direction (away from the Gulf).

Having lived in New York state for 6 years near NYC, I totally sympathize with your weather predicament.  I couldn't realistically take up astronomy there at all because of it.  I simply looked at lunar eclipses and planetary conjunctions with binoculars while living there.  My hat's off to anyone in the UK trying to stargaze.

3 hours ago, bosun21 said:

Thanks Louis, it’s actually the 16mm Nirvanas that I was looking at. Either that or I could buy one more Morpheus to make a bino pair.

  ATB  

    Ian 

Watch out for the space left between them for your nose.  I tried it with two Astro-Tech AF70 17mm eyepieces, but my large nose prevented me from comfortably using them.  I would have had to approach them with chin tucked downward and looking through the very top of my eyeglasses to use them.  I experimented by pairing my 17mm with my 13mm in my BV, pulling the shorter one outward in its holder to mimic having a a pair of 17mm eyepieces.  If their tops had been sufficiently tapered, it might have worked.

Ultimately, I went with narrower, simpler 65-68 degree designs that perform well once Barlowed by 3x to reach focus.  Last night, I used a pair of 20mm Svbony UWA 68 degree eyepieces to view Jupiter for 1.5 hours.  They were comfortable, sharp, contrasty, and displayed no ghosting even with super bright Jupiter.  The long eye relief even allowed me to hold filters between my eyeglasses and the eyepiece (one side only seemed to work best).

What focal length?  It's dependent on the field stop of the eyepiece, not the AFOV.  Pretty much any eyepiece with a FS of about 26mm or less would not vignette since that is BM2's clear aperture.  That covers all but a few widest TFOV eyepieces like a 32mm Plossl and 24mm Panoptic/ES-68/APM UFF which have ~27mm field stops.

The widest 82 degree Nirvana in a 1.25" barrel is the 16mm which has a 21mm to 22mm diameter field stop, so it shouldn't vignette.  However, since it is a negative/positive design, we also need to look at the field lens diameter which is 25mm because we don't want to block the edges of it.  Again, it is less than the BM2's clear aperture of ~26mm.

2 hours ago, billhinge said:

I must admit I love the crawler back from Saturn V days - cool video!

Reminds me of putting a car in a garage.  I'm picturing someone on the crawler with the VAB remote control to open the doors.

46 minutes ago, billhinge said:

Shows how far advanced our Brit design is compared to NASA  😜

Your mission control must be contained in a totally mod, mid-century mansion as in the video as well. 😉

On 26/09/2022 at 11:11, DaveL59 said:

Unlikely to see this launch till November now

Hurricane Ian forces Nasa to shelter Artemis Moon rocket - BBC News

Rolling back to the shed because of extreme weather.

Artemis 1 is pretty nimble after all. 😉

On 27/09/2022 at 06:57, DaveS said:

Or a dormant volcano 🌋. With a retractable roof.

I'm picturing SpaceX moving from Boca Chica to a volcano and Elon Musk getting a high backed chair and cat:

6 minutes ago, DaveS said:

Video blocked in the UK

I swapped it for an unenhanced, shorter clip.  I have no way to know if it's blocked over there as well.

On 26/09/2022 at 15:38, billhinge said:

They need something like the Thunderbird 1 launcher

On 26/09/2022 at 15:48, Mr Spock said:

It would be great to see it launch from under a retractable pool 

Alright, as a Yank, I had to look up these references since even us oldies are only vaguely aware of the Thunderbirds shows.  I found the below clip to clarify your references:

If y'all do launch for the moon or Mars someday, we'll hold you to launching from beneath a retractable pool. 😁

40 minutes ago, Piero said:

Here is my current large set: XWA in, delos out.   Will sell the delos when I have some spare time.

If you already swapped a Delos for an XWA, why haven't you swapped the 22mm NT4 for a 20mm XWA?  You'd have some extra cash in your pocket as well.

For more on my Jupiter observing tonight, check my post below:

I was out tonight between 1am and 2:30am with my 90mm f/6.6 TS-Optics Photoline FPL-53 Triplet APO.  Jupiter was nearly 60 degrees above the horizon for me, and the atmosphere was super calm and clear thanks to a front that moved through Texas Monday morning.  I used my Arcturus binoviewer with Meade 140 2x Barlow element to reach focus and boost magnification by about 3x.  I used a pair of Svbony 20mm UWAs (68 degrees) all night for about 90x.  The image seemed plenty big and bright, and contrast was right at the acceptable limit, so I didn't increase magnification.

The Ganymede transit shadow was very clear, although I couldn't make out the moon against the face of Jupiter.  It was super neat watching the moon emerge like a pimple off of Jupiter's limb.  I thought I was seeing things until I realized what was happening.  Being just past opposition, Ganymede and its shadow weren't separated by very much.  I then watched it completely separate from Jupiter.  Next, I watched its shadow slide off the edge of Jupiter.  All the while, I had a nice view of the GRS.  Toward the end, the NEB had a noticeable darkening toward its center.

I tried a multitude of filters to see if any improved the view.  The best was a generic green filter over my dominant eye held above the eyepiece.  It really helped bring out the GRS and NEB shading.  Orange was the second best followed by magenta.  Those helped with contrast in their own ways without overly darkening things.  Blue was too dark, red obliterated all detail, and both light yellow and dark yellow (an actual #12 from OPT) were too subtle.  A moon & skyglow filter did almost nothing for me.

Here's the 6 piece set from China via ebay I was using most of the time.  Its green filter was more useful than my green Meade interference filter tonight.  It wasn't as saturated or dark as the Meade.  I don't know if it's actually a #56 or not, but I suspect it's lighter.  I highly recommend this ebay set, especially for the price.  Where else are you going to find a reasonably priced magenta filter?

A binoviewer helps immensely as well.  I had much better views when both eyes saw the same brightness tonight.

A light green filter like a #56 was helpful when used over my dominant eye to increase the contrast of the GRS and NEB.  It also cut down on the dazzling brightness even with two eyes.  I think it also sharpened the view by cutting out the slightly unfocused red and blue ends of the spectrum due to atmospheric dispersion.

I use a 1990s AstroSystems dual 1.25"/2" laser collimator.  The new one is 2"-only, but it does come with the Barlow attachment that mine did not.  I only use mine in 2" mode due to 2"-1.25" adapter uncertainty.

I mostly use it for secondary mirror alignment to the center of the primary.  I use a sight tube to center the secondary under the focuser and a Rigel Aline to do final alignment of the primary.  On my truss Dob, I do use the laser to align the return beam with the outgoing beam on the face of the secondary while crouching at the rear of the scope since I don't have 6' long arms to adjust the primary from the focuser.  I figure all the optical axes should then be aligned well enough at that point.  I do peep through the Aline as a double-check, though.

I just realized I do have a use for so many eyepieces.  It allows me to directly compare eyepieces without having to rely on memory (which is getting pretty iffy as I age).  That, and I can do direct tests on similar eyepieces so others can get an idea of where a particular eyepiece slots in with respect to known eyepieces.

23 minutes ago, F15Rules said:

I make that about 39 eps, Chris..so you're njust over halfway to Louis' total...👍😋

Dave

It's not a race.

BTW, I'm a rank amateur compared to Tamiji Homma over on CN.

2 hours ago, IB20 said:

Ha, love this. Nothing wrong with collecting eyepieces, quite enjoying comparing them myself in different conditions/targets etc.

And different telescopes. 👍

72 unique eyepieces.  Several are duplicated for binoviewing.  I also have dedicated microscope eyepieces for my microscopes, but I only use one pair of them for astronomy, so not counting the rest.  I have a TMB Planetary II 2.5mm incoming, so 73 then.

A couple of newer ones didn't make it into that the group photo like the 20mm Meade 5000 UWA and 40mm Lacerta ED.

5 hours ago, vlaiv said:

I haven't had luck with electronic lenses in that regard. On all mine - focusing ring is actually just electronic control/sensor for focusing motor. No power - no focusing. For that reason I just look at fully manual lens to use with astronomy cameras.

I just checked my Sigma 50mm I mentioned above, and I was right.  The manual focus ring moves the internal focusing group back and forth even when not attached to a camera.  When it reaches either end of travel, the ring just slips.  When focusing on a camera body, the focusing group moves and the ring stays stationary, so the slip is completely normal.  It's kind of a neat manual/electronic hybrid design.

5 hours ago, vlaiv said:

F/ratio = aperture / focal length

The front element is nearly the entire 77mm filter thread opening, so does 77/50=1.54 indicate mild vignetting wide open on a full frame 35mm sensor?

1 hour ago, vlaiv said:

Say we have 56mm lens and we want to use it at F/2.4 (we concluded that F/2.4 gives us good sharpness for our sensor). We then make cardboard piece with hole in the center that is 56/2.4 = 23.3333mm in diameter. We glue or otherwise secure cardboard in that filter ring so we can screw on our fixed circular iris whenever we want to shoot at F/2.4

Is 56mm the clear aperture of the objective lens?  My 50mm Sigma lens has a 77mm filter thread, and the front lens is a bit smaller.  I don't have it handy to measure it exactly, so let's presume for these discussions it is 77mm.

Wouldn't the calculation involve a ratio between the wide open f-ratio and the desired f-ratio?  For my lens, being f/1.4, wouldn't you want the reduction to be 1.4/2.4=0.58 or 77*0.58 = 44.9mm opening?  Just dividing 77mm by 2.4 yields 20.8mm which seems way off.

As a check, f/2.8 would correspond to half the diameter (1/4th the light gathering), so I'd want a 77*0.5 = 38.5mm opening.  Does 1.4/2.8 equal 0.5?  Yes it does.

To get to 38.5mm, I could use a series of step-down rings until I got to a ~37mm opening since 37mm is a pretty common filter size.  For f/2.4, I could look for step rings ending up at 45mm.  They're not quite as common, but still available.

I hadn't thought of using step-down rings for this purpose before.  Thanks for the idea!

Using this method, you could use the lens with any camera since you don't need an electronic connection to control the actual lens iris anymore, and it defaults to wide open.  The focus ring is still manually coupled as I recall.

13 hours ago, Mr Spock said:

Finally a couple of test images. Apologies for the quality, my iPhone XR doesn't really do this very well and I'm not very good at positioning or holding it steady.  It does give some indication of the field curvature though. However, in context, the distortion on view isn't really any worse than other eyepiece designs.

I think it was this group of sentences that might make it sound like field curvature is being described as distortion.  In my experience, it is nearly impossible to photograph field curvature with a cell phone camera due to the wide angle lens having enormous amounts of depth of field, bringing everything into focus at once.  In your images, I'm not seeing any defocus due to field curvature at the edges.  In fact, focus sharpness looks pretty good to the edge.  Perhaps if you posted a full resolution edge crop showing the defocus, it would be clearer.  You were clearly were using the term field curvature correctly and without confusion elsewhere as you replied.

Here's my classic example of field curvature being tamed by a wide angle camera phone.  Notice how good the 30mm Agena UWA looks to the edge.  As seen by my fixed focus eyes, it was a blurry mess out there in the last 30% without refocusing.  I verified how good this eyepiece could be by overcorrecting the scope's field flattening by extending the separation between the TSFLAT2 and the eyepiece.  The 30mm Agena UWA looked pretty darned good with very low amounts of edge astigmatism.

I haven't tried it for astrophotography, but I used the heck out my Sigma 50mm f/1.4 EX DG HSM for indoor dance performance photography for years.  Autofocus was always fast and on target despite hundreds of thousands of exposures, and it was very sharp to the edge stopped down to f/2.4 or f/2.8 on an APS sensor Canon DSLR.  It was a tiny bit soft at the edges below that, but nowhere near as bad as the Canon 50mm f/1.8 offering.  It can be picked up used for quite a reasonable price.

My old Olympus Zuiko 50mm f/1.8 and f/1.4 were terrible in comparison, and they were manual focus only.  I don't know if there are some better manual focus contenders out there for cheap.

8 hours ago, great_bear said:

I know - it isn’t wasted light - that’s the myth (albeit a common one). 
 

It’s not “wasted” any more than the sunlight on the ground when you go out for a walk during the day. 

I've heard it more as "wasted" aperture.  In that, your entrance pupil is cutting of some of the exit pupil from the telescope system, so the latter is operating at a smaller aperture and higher f-ratio.  The argument goes, at that particular exit pupil, why not just haul out a smaller telescope.

Other than the night sky background tends to get a bit washed out in suburban skies at large exit pupils with refractors, I don't really care about the slight loss of aperture because it allows me to view a wider true field of view without having to swap telescopes.  In obstructed systems, the CO can sometimes start to become quite intrusive, especially on bright objects as with solar and lunar observing when your eye's iris contracts to the projected size of the CO.