Louis D

1 minute ago, Raph-in-the-sky said:

It might sound like a stupid question but I ve got to ask at one point or anouther... What do you call the shoulder exactly? 🙂 

It's where the insertion barrel (1.25" or 2") meets the wider part of the eyepiece that stops further insertion into the focuser.  In TeleVue's eyepiece specifications page, the following diagram shows this clearly as where the white part meets the black part.  Dimension F is the focus position in their table.  Positive means below (the little x in the diagram) and negative means above the shoulder.  Often, the focus position does not correspond to the physical field stop if there is a Smyth lens in the insertion barrel, so I think their diagram should have labelled F as focus position rather than field stop (perhaps effective field stop would also be acceptable), because that is what it indicates in my experience with their eyepieces.

1 hour ago, Jiggy 67 said:

You need to go shopping more often 😀😀

I was raised as a thrifty Scotsman (descendant) by parents who grew up during the privations of the Depression and WWII.  My parents patched my jeans for school until the new school year started when I would get new ones simply because I had outgrown the old ones, so I became accustomed to getting every last bit of mileage out of each bit of clothing.  The fact that today's generation wear pre-distressed jeans with holes in them from the factory is mind-boggling to me.  I was never happier than when I got stiff, dark blue jeans once per year.

Ideally, put a piece of vellum/tracing paper/thin copier paper across the focuser opening and focus on the moon.  This can be difficult if the magnification is low due to a short focal length.  Note the focuser tube position.  Next, insert each eyepiece and refocus to see if they require in-focus or out-focus relative to the native focus position that you just determined.  Note the direction and how much.

Alternatively, start with your 11mm Nagler T6 and focus on anything.  All of the T6s focus 1/4" (~6mm) below the shoulder.  Note where each eyepiece focuses relative to the T6 and add or subtract the 6mm offset appropriately to determine each offset from their own shoulder.  If one focuses 10mm further in, that would be 4mm above the shoulder (10-6=4), for instance.  On the other hand, the 12mm NT4 would be 19mm-6mm=13mm further out (what you would measure), thus 13+6=19mm below the shoulder.

And after the Meade bankruptcy fallout, Bresser appears to be JOC/Explore Scientific associated (owned?) while Celestron is owned by Synta and Meade is owned by Ningbo Sunny.  Thus, this 14 year old discussion might not mean much in today's marketplace.

Regardless, I think this thread would best be put back to rest:

I was skeptical at first, but the general consensus in that thread seems to be that they are actually pretty good for the money.  Is that the impression you got as well?

I use retired 100% cotton T-shirts or the upper part of retired, near 100% cotton crew socks for lens cleaning.  Cotton is less likely to scratch than any wipe made from wood pulp, and cotton is absorbent enough to easily hold the cleaning fluid to prevent it from wicking under retaining rings at the edge.  Having been washed literally hundreds of times before I retire them (did I mention they develop some holes by that point?), the are basically lint free.  I would make sure the last few washes are done with allergen free detergent to avoid leaving any residue in the fibers.  I've been cleaning camera, telescope, and eyepiece lenses for years in this manner with nary a scratch or streak left on any of them.

Yep, pretty much correct.  This all assumes that your eyepieces focus close to their shoulders (+-5mm is fine).  A counter example for me would be my 12mm Nagler T4 which focuses 19mm below its shoulder, so I added five 4mm thick 50mm ID O-rings and a 20mm 2" extension to the bottom of the eyepiece to make it closer to parfocal and still be able to be securely held in the focuser.  The difference in coma correction is noticeable.

For 1.25" eyepieces, just put an adapter in the CC and you're pretty much good to go.  Many 1.25" TeleVue eyepieces focus about 6mm below their shoulder, so the adapter would probably put the focal plane at just about the right distance.  The GSO CC is designed to have good correction from 70mm to 80mm of separation.  I don't notice much difference up to about +-10mm.  That 12mm Nagler is really the only eyepiece I have that really needs to be parfocalized.  Check your eyepieces to see how far they focus from their shoulder to get some idea about your own need for parfocalization.

This image I found online of a Heritage 130 secondary holder seems to show the same nut on bolt assembly to tighten it to the upper tube assembly.  Perhaps yours is missing and you just need to pick one up from the local hardware store?  Perhaps your secondary holder shaft is screwed all the way in and needs backed out a bit to better center it above the primary and to allow the tightening nut to be added?

I don't know if the Heritage 130's focuser and strut assembly is stout enough to resist the long moment arm of a Powermate and zoom eyepiece hanging off of it.  I'd start with an 8-24mm Vixen LV zoom clone as from Meade, Celestron, Skywatcher, Seben, etc.  See how you like it before getting the much more expensive Baader Hyperion Zoom (BHZ) which is still pretty cheap compared to the Leica, Zeiss, and Swarovski spotting scope zooms.

If you opt for a high end zoom such as a Leica or Zeiss, you might be on to something.  You'd still need a low power, wide field eyepiece because zooms aren't all that wide at the low end.

3 hours ago, John said:

I'll have to check this lateral colour issue with the XW 7mm tonight. I can't say that I have noticed it up to now despite owning the eyepiece for a couple of years

What would be a good test target Louis ?

 

 

As I recall, on bright stars, the 7mm XW would develop color smearing as the stars got to the last 15% of the field.  If I turned my head and eye just right to align everything perfectly, I could minimize it.  I'll have to get it out again and look for it to characterize what I saw in the past better.

The eyepiece was frustrating enough after having owned the 14mm and 5.2mm XLs for years, which did not exhibit such color issues, that I seriously considered returning it.  I've slowly warmed to it as long as I keep objects centered and not use the outer regions of the field.

I think I'm seeing something similar to what this CN reviewer saw in his 2004 comparison of the 10mm XW to the 10.5mm XL.  He consistently noted color issues farther in from the edge and of greater magnitude in the XW than in the XL.  Apparently, compromises were made to extend the field 5 degrees.

2 hours ago, tingting44 said:

Thanks Louis, nice one

 

Edit, thats the same price?

Click through to the checkout page.  There's a $5 discount applied there thanks to the discount code "CLOUDYNIGHTS".

3 hours ago, tingting44 said:

Just see this! Anyone here tried this? Seems perfect

 

https://nyxtech.us/

And if you use this link, you'll get $5 off via Cloudy Nights where the owner posts development updates.

7 hours ago, Adam Barnsley said:

Hello again, I have another dilemma. Delos6mm appeared on the Market at a good price. Initially, I had to buy a Pentax XW 7mm , what is the difference between the two?

I have a 7mm Pentax XW, and it has significant lateral color as you near the edge for such a premium eyepiece.  I've also experienced some difficulty holding the exit pupil compared the older 5.2mm XL which has a rock stable exit pupil and lacks any lateral color at all.  I also have the 10mm Delos, and despite reports from others to the contrary, I have had zero issues holding the exit pupil.  It is also quite sharp and color free to the edge.  I'd probably get the 6mm Delos without hesitation in your situation.  The 3.5mm XW by comparison has no exit pupil issues and no lateral color, so it would be a toss-up between it and the 3.5mm Delos.

The knob is probably a safety stop to keep the OTA from sliding all the way through the dovetail clamp were it to loosen.  If they're on both ends and you can't tip your dovetail into your clamp, you'll have to remove one temporarily to slide the dovetail into your clamp and then put it back in place when clamped securely.

On 18/01/2020 at 02:57, Geoff Lister said:

I managed to get a set of small Allen keys for a quid at my local "Pound Shop".

Geoff

Off topic, but I put it here because I had to think for an extra second what a quid and a pound shop were.

I literally couldn't find a single online translator that could handle this UK to US conversion.  My best would be:

I managed to get a set of small hex keys for a buck at my local dollar store.

OR

I managed to get a set of small Allen wrenches for a buck at my local dollar store.

At first, I was like, why is he using squid for money and second, why did he go to an animal rescue to find hardware?

Two countries separated by a common language.

Point them to this thread.  They might not be aware this is being played out in a public forum where other potential customers might be reading about your customer service experience.

I'd stick with the Celestron/Meade 8-24mm zoom and their generic equivalents.  They are a known good quantity very similar to the Vixen LV zoom from which they were cloned.

The 7.2mm to 21.5mm zooms are of good quality optically, but they have very limited eye relief and are very stiff to zoom in my experience with them.  They also have narrow apparent fields of view.

Watch out for the cheapest zooms.  They're a mix of glass and plastic lenses.

The reason the two rings are separate is to allow for camera angle adjustment.  It was more important with T2 camera lenses back in the day.  Now, you just loosen the focuser tube lock screw(s) and rotate the 1.25" or 2" adapter and tighten it back up.

54 minutes ago, rwilkey said:

Hi Simon, the Baader Hyperions will work well in your f/10 but not in the Newtonian f/3.5, as John refers above.  Have you considered the BST StarGuiders which work well in most scopes, they also have 16mm eye relief which should be good with spectacles, found here: https://www.firstlightoptics.com/bst-starguider-eyepieces.html

Unfortunately, due to the design of the eye cup, they only have 12mm of usable eye relief in reality, except for the 25mm which is usable with eyeglasses at 18mm of ER.  I compared the AT Paradigm (BST SG equivalents) to the Meade 5000 HD-60 line in this thread.  I'll repeat my table of eye relief values here.  The HD-60s are much easier to use with eyeglasses.

6 hours ago, Barry-W-Fenner said:

The slightest pressure on the focus tube and it lowers, Very frustrating. I dont do imaging so would only use it for visual.

1 hour ago, banjaxed said:

There is a locking screw on the under side of the focuser, I discovered this when I accidentally tightened it, mistaking it for the eyepiece retaining screw. Took me a while to figure out why the focuser wasn’t working  🙄

Also, in the center position of the R&P cover plate, there appears to be a hole adjacent to the locking thumb screw pointed out by @banjaxed.  This hole most likely has a grub/set screw that adjusts the focuser tension.  Once you find the right hex key, you can loosen and tighten it to your particular preference and save using the locking screw for its intended purpose to lock down the focuser completely.  To be honest, though, I set the tension on my focusers kind of at a middling setting and then slightly tighten the locking screw if I put a really heavy eyepiece in the focuser that exceeds the tension I set.

3 hours ago, Barry-W-Fenner said:

I have tightened it back up and was trying to align with my laser but the beam is bouncing around in the tube all over the place!

First, crank the focuser all the way down when using the laser to avoid focuser tube wobble.  If the focuser tube is wobbling all over the place as it likely is with these cheap focusers, the laser spot is meaningless.

Second, adjust the secondary so the laser spot hits the center of the primary.  Even if it's not center spotted, you should be able to guesstimate the center pretty well.

Third, adjust the primary so the laser spot returns to the secondary's center.

With your tube so far out of alignment, sweep your hand across the open end of the tube before looking down it to avoid being blinded by the laser.  You need know where the spot is before looking down the tube.  If it isn't hitting your hand, it's either hitting the secondary (good!) or the tube wall (bad!).  If it's the latter, you'll be able to see it obviously hitting the wall.  Carefully move the primary to bring it back on center to hit the secondary while avoiding blinding yourself in the process.

Fourth, continue with fine primary adjustments to bring the laser spot back to the laser output port.  If it's at least returning back up the focuser tube, you're really close.

You'll still need a sight tube to verify the secondary is centered under the focuser tube, although there may be very little you can do to adjust that.

4 hours ago, SimM said:

If the field stops are less than 1 1/4" (28mm is 28.5mm) is there any value gained by switching to a 2" diagonal for the same lens (probably not) and only a benefit for longer/ultra wide eyepieces?

It's mostly a benefit for really heavy eyepieces like the 12mm ES-92.  It's field lens could probably fit within a 1.25" barrel, but hanging over 2 pounds of eyepiece on that small barrel and small diagonal  would seem iffy.

4 hours ago, SimM said:

Is vignetting in an eyepiece likely with any of these with a 1 1'4" diagonal?

No, though there is the possibility of vignetting with a 2" diagonal and a widest field eyepieces like the 41mm Panoptic because the rear baffle is likely around 38mm in diameter if it is similar to older Celestron 8" SCT designs.

4 hours ago, SimM said:

A 2" diagonal is a lot bigger and the light path is longer, but for the OTA and an eyepiece, the focal length is somehow increased for reasons I don't understand.

An SCT focuses by moving the primary mirror forward and back.  To throw the focal plane back far enough to clear the optical path length of a 2" diagonal, the primary mirror must be moved forward a much smaller amount thanks to the magnification factor of the secondary.  This then causes the overall focal length of the telescope to grow.  It also induces some spherical aberration because the scope is designed with a 1.25" diagonal's path length in mind, so now the scope's working focal length is slightly off-spec.  Thus, for best planetary performance, swap out the 2" diagonal for a 1.25" diagonal.

4 hours ago, SimM said:

The complete range is 5/8/10/13/17/21/24mm, so approximately 400x, 250x, 200x, 150x, 120x, 100x and 85x magnification.

I'd recommend a 35mm Aero ED SWA for widest field viewing.  They work pretty well even at f/6, let alone f/10, and have just enough eye relief to work with eyeglasses if you push in a bit.  This would give you 57x.

I wouldn't go much above 200x in an 8" with such a large obstruction.  You're down to a 1mm exit pupil at that power.  I find I can't go much below 0.7mm with any sort of comfort due to floaters in my eye.  Technically, that would be 285x with a 7mm eyepiece, but seeing most nights probably won't support that much magnification.

3 hours ago, SimM said:

There is also the Aspherics as well

A wee bit overpriced for the amount of astigmatism and chromatic aberration they show in the outer field.  At 30mm, I'd get the APM UFF instead and the 35mm Aero ED instead of the 36mm.  With an SCT, you could also get the 56mm Meade Plossl to open up your exit pupil to 5.6mm for viewing nebula with a nebula filter.

Rigel Aline for a quick primary collimation check each night and as a focuser plug with ventilation hole during storage.

5 hours ago, Sweep said:

Are there any recommended dso’s targets at 21 x  that experienced observers view quite regularly?

Perhaps the North American nebula?  You'd need it to be large, otherwise it will be hard to pick out details at such a low magnification.

I just remembered the Veil Nebula for another possible target at low power.  As a whole, it is quite large in angular diameter at about 3 degrees.