Louis D

55 minutes ago, Don Pensack said:

TeleVue's eyepieces and adapters were made to work with each other.

Too bad they weren't made to work with focusers and adapters in general.  I could see this attitude working if they were a huge telescope marketer with eyepieces as a side business, but the opposite is true.

On 08/05/2023 at 12:13, globular said:

On my XW16.5 it's recessed 4.5mm at the edge.  The top lens is concave on this EP, and it's 7mm recessed at the centre.

If we assume that it's 20mm design ER from the center, and we machine off the top of the barrel to be flush with the eye lens's edge (ignoring for now that it will fall out if tipped too far), that saves 4.5mm of usable ER at most.  So 20 - 4.5 = 15.5mm maximum usable eye relief for eyeglass wearers if the eye lens could somehow be flush mounted to the very top of the barrel.  That's quite tight for most eyeglass wearers with deep set eyes like Don and me.  Subtract a mm or so to secure the eye lens, and now you've got 14.5mm of usable eye relief.  Perhaps a monocle is in order for these eyepieces even if redesigned? 😄

4 hours ago, johnturley said:

Ed said that he liked eyepieces with a dual 2in/1.25in barrel which used to be quite common.

Personally I disliked them as it made the eyepieces more bulky and heavier than they otherwise needed to be, and I was always dropping the removable screw and then having to search for it in the dark.

I like my Redline (AT AF70, etc.) eyepieces' take on 2"/1.25" barrels.  For the 17mm on down (in terms of focal length), they have a screw-on/off 2" skirt that is parfocal with the 1.25" barrel.  You can leave it on all the time (as I do) or off all the time (for 1.25"-only scopes), or swap it in and out if that's your thing.  I'd like to see more eyepiece adopt this very useful feature.

I haven't found any particular advantage to the Tele Vue style non-removeable skirt on my 12mm Nagler T4 or 14mm Meade 4000 UWA smoothie.  There's generally not enough 1.25" barrel sticking out to safely lock it into a 1.25" focuser, not to mention it vastly increases the in-focus requirement in this mode.  Also, you can't use 2" filters with the skirt unless you screw on a 20mm 2" extension first.  It seems like a solution in search of a problem.

1 hour ago, Carbon Brush said:

Which is just as well as in most of the world fuel and oil are sold by the litre!

I thought it was sold in bbl or barrels on the open market.

10 hours ago, globular said:

How much wiggle room do you have when using the XW40 @Louis D?

I can't quite remember if I need to be resting my glasses on the eye guard or hovering just above it.  I'll have to check sometime.  On my 40mm Lacerta ED, I know have to have my glass resting on the retracted eye cup to see the entire view.  I might even need to push in a bit.  The 35mm Aero ED requires me to mash my glasses into the eye cup to see the entire field.  At the other extreme, my decloaked 40mm Meade 5000 SWA allows me to hover well above the eyepiece in relaxed comfort with 24mm of usable eye relief.  It also has better edge to edge correction and field flatness as compared to the Pentax XW-R 40mm, but it is more massive.

You could do like me and start playing with them indoors taking pictures of standardized targets through them. 😁

Thanks so much.  Yes, I was measuring at the edge.  That might explain the 20mm/12mm eye relief difference for the XW-85s if the 20mm refers to the design eye relief which will be ~8mm more than the usable eye relief (12mm).

6 minutes ago, saac said:

The intention is that the smart grid will be able to facilitate differential pricing which in turn would make VAT on electric charging possible.  But the smart grid is somewhere off in the distant future so I think you are right and we will gradually move toward road charging. 

Jim 

I have no idea how that would work with folks who charge at home using solar panel generated electricity.  The chargers themselves would have to have internet connectivity to report home charging for purposes of taxation.  This then has the issue of folks living off-grid who don't have internet connectivity.

On 26/03/2023 at 10:09, Don Pensack said:

Forget the Pentax 23mm, Louis.  It has only 12mm of eye relief from the eyecup up.

You MIGHT be able to use that, but I had to press my glasses into my eye socket until my eyelashes brushed the glasses in order to see the field edge.

That was not comfortable.

Has anyone posted a 3/4 image of the top of the 23mm Pentax XW to any thread anywhere?  I can't find one.  I'm just curious how much the eye lens is recessed from the top of the metal barrel.

I've measured my 40mm Pentax XW-R to have at least 7mm of eye lens recession from the lip of the exposed metal barrel once the eye cup is screwed off.  Have you measured the eye lens recession with the toothpick method on the 23mm XW?  It would be a shame if Pentax did the same with it and wasted 7mm of usable eye relief for no particular reason.

6 hours ago, Stephenstargazer said:

True, but well off topic! They can levy VAT at charging stations but not at home. We are likely to move to road charging instead (electronic tolls).

Agreed.  Down here in Texas, they're trying to vastly increase yearly electric vehicle registration fees to cover some of the lost fuel tax revenue as a stop-gap measure.

As far as the original topic, that 1/4"-20 UNC tripod thread is likely to live on for a very long time due to the sheer number of cameras, tripod heads, and other accessories that use it.  It has the inertia of heavily loaded freight train behind it.  The changeover from steam to diesel-electric locomotives went quicker than getting rid of this tripod thread for its SI equivalent, whatever it may be.

On 06/05/2023 at 14:20, bosun21 said:

Be great placed on the underside of your dobsonian for moving it around the sky. Depends how heavy they are.

Edit:- just read the listing and that’s what they are for. Lol.

Unless your Dob tube is a Sonotube or aluminum, then not that useful unless you put a curved steel plate on the inside of the tube.

7 hours ago, Stephenstargazer said:

Back to the rant........petrol is priced per litre in Europe because the cost per gallon is astronomical 😀

Just think how high your electrical costs will be when they apply road use taxes to it when EVs become dominant.

On 05/05/2023 at 17:21, Gibbous Mars said:

Thanks both for the friendly advice and quick responses too! 

While I love the idea of the 200DPS setup, I don't think I can currently justify the cost of a HEQ5 or EQ6. I think the 150 f5 on an EQ5 with motor drives is probably the best of both worlds to get going for both visual observing and first steps into photography.

As a quick aside, is there such a thing as a decent all-rounder camera suitable for general astrophotography and also 'regular'/daytime outdoors photography? Ideally something I can share the use of with my better half and justify the expense of a buying a quality camera in due course? 

My colleague at work rapidly switched from imaging with a ~5" Newtonian and DSLR to imaging with a ~80mm ED refractor and dedicated astro camera and filter wheel.  The difference in quality of results is like night and day, with the refractor winning big time.  I'm not saying to go the same route.  I'm just providing a recent anecdote of someone starting out in astrophotography like yourself.

On 05/05/2023 at 05:03, Mr Spock said:

It's 2023 - using disparate and archaic threads on equipment is ridiculous when the world standard is metric. Time for manufacturers to emerge from the dark ages I think 

Just to keep derailing this thread, do Brits go around discussing engine power in kW instead of horsepower?  If they do, they kudos for being consistent in using SI units.

Here's a great photo from a CN post showing the difference a UV/IR filter can made for DSO imaging:

And here is another image showing how Mars can benefit from an IR-pass filter:

No one really knows for sure if these are or are not blems that didn't pass the ES/Bresser quality control check.  I've read of people being satisfied with these rebrands, and of others having issues with theirs.

7 hours ago, Don Pensack said:

But APM is unlikely to pay Mark Ackerman to design a 35mm when the 30mm is already quite good.

No, I wouldn't either.  But someone in China paid an optical designer somewhere to interpolate/extrapolate Thomas M. Back's 30mm and 40mm Paragon designs to add a 35mm design.  It would not be absurd to think they'd do it again with the 30mm UFF design to adapt/scale it up or down.

7 hours ago, Ratlet said:

Do you guys have any suggestions for good reading materials on telescope optics?  This is all fascinating.

I often refer back to my copy of Telescope Optics: Evaluation and Design by Harrie G. J. Rutten and Martin A. M. van Venrooij.  Sky & Telescope took over Wilmann-Bell's catalog, so it might show up again in a new printing.  It mostly covers telescope optics and spends only a single chapter on eyepiece optics.  Still, it's an educational read that is less dense than telescope-optics.net.  It's still dense, but not overwhelmingly so.

I do have to wonder what makes refractors so much heavier than their Newtonian size equivalents.  Are two or three hunks of 5" or 6" diameter refractor glass that much heavier than one hunk of 5" or 6" mirror glass?  Is it that the refractor lens cell is much heavier than a Newtonian mirror cell?

5 hours ago, Mike Q said:

The one place you dont see it much... Road signs.  Its been years since i have seen a roadsign that says how many km to wherever you are going 

Don't drive much in Canada, do you?  It always freaked me out driving from Michigan to New York by way of Ontario to see all road signage in km instead of miles.  Now, you need a passport to drive through Canada, so I just take the slightly longer way through Ohio (your stomping grounds) and Pennsylvania.  That, and the border security lines became unbearable over the last 40 years.

2 hours ago, Mandy D said:

Yes, I recall this! Personally, I think we should move over to base 8 (octal). It would make life so much easier, all numbers would convert properly and easily to binary. I used to enter octal code into a Honeywell 516 mainframe at college and it was so easy to check against the binary. It would also make the 8 times table, which is the most complained about one, much simpler!

Warning! Esoteric computer hardware discussion ahead:

The problem with octal versus hexadecimal is that you need only 3 bits to represent octal digits versus 4 bits for hexadecimal digits (hexits).  This leads to a problem when storing values in memory locations that tend to be in multiples of 8 bits (1 byte) in modern machines (they were multiples of 6 bits in older machines, so octal worked).  Hexadecimal packs nicely with 2 hexits per byte and no waste.  Octal packs as 2 octal digits per byte with 2 bits wasted.  Thus, the shift about 40 or 50 years ago from octal to hexadecimal digits along with the shift from memory words in multiples of 6 bit to multiples of 8 bits.  If the octal digits are allowed to spill across bytes for packing efficiency, it becomes difficult to read memory dumps aligned on byte boundaries.

Are all the tripod fittings 100% metal with no plastic parts?

1 hour ago, Don Pensack said:

It's too bad the shorter focal lengths of UFF don't have the same internal prescription.  That would have been an impressive 70° line, albeit more expensive than they are.

I'm sure it would have been overkill and expensive as you say to go with 9 elements and an exotic telecompressor design when a more traditional Smyth group negative/positive design would suffice.  I'm sure it would have created a niche following, though.

I would like to see the 30mm design pushed until the telecompressor field lens fills the 2" barrel.  It's only a bit over 40mm wide in the 30mm UFF.  I looks like it could be pushed to having a 46mm clear aperture.  The upper barrel elements might have to grow wider as well if the design is simply scaled.  The internal field stop would grow to 35mm from 30.4mm.  If all remains linear, the effective field stop would grow from 36.4mm to 41.9mm, or roughly the same as the 31mm NT5.  The focal length would probably grow from 30.3mm to 34.8mm, or roughly the same as the 35mm Panoptic.  It would have a 3mm larger field stop diameter than the Pan and probably be somewhat lighter and slimmer.  Is KUO listening?

I'll have to look for EOFB sometime in it.  I once noticed my 12mm NT4 had brightening all the way to the center.  Only a small point appeared to be relatively dark in the center.  I swapped it with my 12mm ES-92, and the brightening went away.  Swapped them again, and the brightening was back.  I'm not sure what was going on that night, but it was highly disappointing to see in a TV product.  I even checked for fogging, but there was none.  I'll have to do a test sometime with those two plus the 13mm Redline, 12.5mm APM Hi-FW, and 14mm Morpheus.  It might even be scope specific.  I can't remember which scope I saw the EOFB in the NT4, but it was probably my Dob.

Having grown up in the 70s/80s in the US, we were constantly told to be ready for the inevitable switch to the metric (SI more properly?) system.  It never happened.  The US kind of stalled out part way there.  Engineering uses SI units for the most part.  Day to day living uses customary units.  I've got to admit, talking about how tall someone is in feet and inches seems much more intuitive than in meters, decimeters, and/or centimeters.  Pounds/kilograms, inches/centimeters, miles/kilometers are each close enough by themselves that I could make the switch eventually.  The mix of units for everyday nuts and bolts is a bit of a pain.  Of course, wire and nails have their own systems of units that are neither customary nor SI.

I'm still waiting for the SI version of time keeping with 10 hours per day, 10 decihours per hour, 100 centihours per hour, etc.  I'd love to see how they shoehorn 100 or 1000 days per year against the solar calendar.

Why was 10 chosen as the base?  Base 12 makes a lot more sense.  It's divisible by 1,2,3,4,6, and 12.  10 is only divisible by 1, 2, 5, and 10.  Being a computer engineer, I've grown quite adept at base 16 or hexadecimal arithmetic, so it should be doable to work in base 12.

I do often prefer the use of customary units' fractions to decimals for day to day functions as opposed to engineering usage for taking a swag at a measurement.