Louis D

In addtion to what @NGC 1502 said above:

Truss tube primary mirrors can also cool more quickly because there's no large column of warm air above them as in a solid tube.

Truss tubes are more prone to stray light intrusion and "tube" currents induced by body heat unless a shroud is used.

10 inches (250mm) is about the break-even point between the two designs.

Well, the 17.5mm Morpheus eyepiece weighs 14 ounces while the AF70 is 17 ounces, so that might be an option if the Dioptrx will cam onto the 43mm threads, which is the same as the Morpheus's top threads.  I've actually successfully threaded the AF70 eye cup onto the 14mm Morpheus.  The 22mm AF70 (and its brand equivalents) is at least as well corrected as the 31mm Hyperion Aspheric, so that shouldn't be an issue for the OP.

That Skywatcher mirror might not have the best figure.  Having looked through 12" to 18" Dobs with Pegasus, Nova, Royce, Raycraft, Swayze, and Zambuto mirrors, I know that the planetary views can be spectacularly good at 200x to 300x with steady seeing, which Australia, like Texas, is more than capable of providing.  You might want to seek out a local astronomy club to see if one of its members could double check your scope for you.

The 22mm Nagler T4 is pretty good and Dioptrx compatible.  It's probably the best of the NT4s.  I don't have the 22mm Vixen LVW to compare it to.  The 22mm AT AF70 (same as Omegon Redline SW and TS-Optics Expanse) is nearly as good for a fraction of the price and 12 degrees less field.  If you screw off the eye cup, there's a 43mm thread that a Dioptrix might be able to attach to.  It has plenty of eye relief for eyeglass wearers with the eye cup removed.

Here's some images of and through my 18 to 22mm and 23mm to 28mm eyepieces for reference.

Too bad your scope didn't come with a removable section ahead of the focuser for binoviewer usage.  Some of the newer Chinese ED scopes are coming equipped with them.

8 hours ago, Buster said:

Hi, I am looking to buy my husband a telescope but he has a bad back so it has to be lightweight also he is a beginner and obviously we don't want to spend a huge amount. Can anyone advise on a telescope. I believe Celestrons are a good make. Thank you in advance.

How much weight can he lift if it is hugged close to his body?  My back isn't the best, so about 40 pounds is my max.  That's why I can't use my 15" Dob much any more because the mirror box weighs 65 pounds.  I figure I'll use it more when I get a vacation/retirement home in the New Mexico mountains where I can leave it setup and wheel it out of the garage or shed for observing.

The nm value is the passband width.  The narrower the better because more non-emission light is rejected increasing contrast.

58 minutes ago, sshenke said:

Thank you both. there are no water bodies nearby and i can't think of any local factors that might impact on dew formation.

Are you in a local low spot?  I've noticed on my drive in to work that ground fog and frost form much more commonly in a low spot along a small creek, even when it is dry.

I'm so glad my Dob has a Sonotube tube after following this thread.  It also never gets cold to the touch in the depths of winter, either.  It's just heavier than thin walled metal tubes.

4 hours ago, sshenke said:

i understand what you are saying. i wondered about that too, as i cannot see what's going on with the secondary mirror. however, it is absolutely clear that the main mirror dews up within a maximum of 1 to 2 hours. I have been using a fan with heating option to blow air from behind the main mirror, not directly down the tube from the front end

Don't be so harsh on yourself.  That's actually pretty nicely done job of wrapping the tube.  Too bad it didn't mitigate the dewing.  You must live in a very damp region.  Do you often get morning fog?

Do you get any dewing on the guide scope's objective lens?

11mm is one of the rare focal lengths I own no fixed focal length eyepieces in and don't feel like I'm missing anything.  It's just too close to 10mm and 12mm to matter in anything but a really long focal length scope.  The 11mm Nagler T1 was also discontinued fairly early in the T1 life cycle (during the smoothie phase) and became quite the expensive collectible as a result.

I used the Thousand Oaks Silver-Black eclipse glasses for the 2017 solar eclipse, and everyone agreed the image was much sharper than the view through typical Mylar eclipse glasses.  I've been using Baader solar film for almost 20 years on telescopes, and it is definitely better than the view through a 90s era glass solar filter I once owned.  However, I'll probably try the newer TO material for new home-made solar filters to see if it is any better.  Has anyone in the UK tried it out?

1 hour ago, sshenke said:

Carole, this is really puzzling for me, i have draped the sw 130 pds in exercise mat when i took it out on Monday evening. i will post the picture later, might be hilarious. Temp on Monday evening was 1 to 2 degrees at 8 pm. mirror dewed up promptly within 1 hour. never got to see a single image of interest. Can I ask, if the sw 130 pds you used, worked well in winter too?

Sorry to hear this.  Dewing is caused by the objective radiating energy to the clear sky and dropping in temperature below the local dewpoint.  I think your only option left is to apply dew heaters directly to the back and/or edge of the mirror.  A refractor is probably going to dew up just as quickly under these same conditions since the difference in thermal mass of the glass between a refractor objective and a mirror is going to be minor.  A dew heater is definitely in your future.

Yes, the 11mm NT6 and 12mm NT4 were both recently dropped, though I'm not sure in what order.  The 2.5mm NT6 was also dropped a while back along with the 20mm and 26mm NT5s.  The 2-4mm Nagler zoom was also discontinued in the not so distant past.  Any others dropped in the last 5 years or so that I left out?

3 hours ago, John said:

It's probably fairer to compare my Delos 17.3 to the ES 92 17mm rather than the Ethos 21 as the F/L difference will impact the views so it's not quite a level playing field.

I compared my 17mm and 12mm ES-92s accidentally to my 14mm Morpheus when I just working upward in power one night.  I was shocked to find myself thinking the Morpheus felt like looking through a porthole compared to the two ES-92s.  I went back and forth, and sure enough, just going from 92 degrees to 76 degrees was enough to induce the same feeling I get going from the 76 degree Morpheus to 60 degree Meade HD-60s and Paradigms/Starguiders.  16 degrees is 16 degrees even when its 92 to 76 rather than 76 to 60.  Come to think of it, going from 60 degree eyepieces such as the HD-60s down 16 degrees to 44 degree eyepieces such as my Celestron Regal zoom at 24mm is also claustrophobia inducing as well.  Yet, going from 92 degrees to 44 degrees (less than half as wide) just seems so entirely different that I don't get that same constrictive feeling.  Sort of like going from a car to a bicycle.  Two entirely different experiences that are not really directly comparable.  Going from the ES-92 to the Morpheus is more like going from a high performance sports car to an above average performance sedan.  Both are good performers, but after driving the high performance vehicle, the above average vehicle feels decidedly lacking in comparison.  If I had never driven the sports car, that performance sedan would have seemed terrific based on my own limited experiences.

4 hours ago, Deisler said:

I spent 30 mins or so, trying to find Andromeda galaxy - to my disappointment I did not manage to see it. But I did see a faint 'galaxy' near there - I suspect it was M110 but it could be M32 I am not so sure.

You more than likely found M31's core.  As can be seen below, if you can see M32 and/or M110, you can see M31 as much brighter and bigger than either in the same field of view.  From my own observing from my light polluted backyard, all I can see is the core of M31 (the pure white part below) and the cores of M32 and M110 as slightly larger than stellar light patches.  If you don't know what to look for and where to look for them, M32 and M110 can be easily overlooked in light polluted skies at lower powers.  Try increasing the power on that faint galaxy you found to see if you can resolve its companions as non-stellar.

According to Ricoh, Pentax's parent company:

So, it's 10g heavier and 10mm taller.

And here's a Ricoh/Pentax corporate group shot:

Here's a group shot of my 3.5mm Pentax XW with the 5.2mm Pentax XL which is about the same height as the 5mm Pentax XW.

On 16/11/2019 at 02:10, Deisler said:

I felt very uncomfortable as my left eye was left with a bright white spot even 30 mins after I came back in.

The most comfortable views of the full moon are with binoviewers because both eyes see the same brightness.  The discomfort you're feeling isn't because the moon is bright, it's actually as dark as asphalt at noon.  However, one eye sees noon-lit asphalt and the other eye sees blackness.  Your brain goes into overdrive trying to combine these two vastly different views and leads to all sorts of weird artifacts.  With two eyes, I can see details quite clearly across the face of the moon that elude me entirely with one eye no matter what sort of filtering I try.

For cheap, you can get a "moon" filter that has about a 13% transmittance to cut down on the brightness imbalance for starters.  If that's not enough, stack a second one for 2% transmittance.  Or, you could get a variable polarizer filter or both and combine them to really knock down the transmittance.  Check ebay for the cheapest prices on basic filters like these.

Just spitballing ideas here, you could also try wrapping the tube with ribbon heaters used to keep pipes from freezing underneath the foam mat insulation.  That should warm things enough to prevent dewing without causing tube currents.

4 hours ago, Deisler said:

Bought it. Thanks!

Now will order my BST EPs (5mm and 15mm) from FLO and they should make me happy for a while.

Be sure to let us know your thoughts on your purchases.  Every equipment report helps fine tune everyone's understanding of the pros and cons of each item.

How about a photo of your assembled setup?  If it's an AZ mount, can you mount the scope reversed and use in on the other side of the azimuth axis?  That would put the finder scope on top.  I had to do that with my DSV-1 mount and 127mm Mak.  It means using the scope on the "left" instead of "right" side of the mount.  I did have to loosen the handle mount and rotate it 180 degrees to avoid it being on the front side of the mount.

16 hours ago, Deisler said:

Cheers both @John @Louis D

 I am leaning towards Aero 2'' than Baader Aspheric 2''. 

I assume 30mm is better than 35 or 40mm, as 30mm is near the 'upper limit'?

I'm not really sure what you mean by upper limit in this context.  The 30mm Aero ED is a 2" eyepiece and has about a 35.5mm field stop, so it is 10.5mm smaller than the 2" maximum field stop of 46mm as found in the 40mm Aero ED (which is no longer in production and sold out worldwide).  The 35mm Aero ED has a 44.5mm field stop, so it is much closer to the upper limit for 2" eyepieces.  If you meant upper limit for exit pupil, that would be 7mm*6=42mm for most dark adapted observers, so no issues with even a 40mm eyepiece.

The 30mm is slightly better corrected than the 35mm, but it is narrower in field of view at 68 degrees versus 73 degrees for the 35mm.  If you were to compare well corrected true fields of view, the 35mm would probably slightly win out, just showing it at a slightly lower power.  I don't think you can wrong with either one as long as you concentrate on the central view and allow the edges to remain in your peripheral vision.

12 minutes ago, Deisler said:

@Louis D @John

Hi I wonder if you have used Baader Hyperion Aspheric 2'' 31mm? Seen people recommended it as wide field low-power EP a lot.

More specifically, how is it compared to Aero 2'' 30mm or even APM UFF 30mm? 

Cheers

Here's a comparison between the 30mm/35mm Aero EDs and the 31mm/36mm Hyperions.

2 minutes ago, vlaiv said:

In any case - I think that we can use your comparison as a good indicator of edge performance of eyepieces - all issues discussed above will probably have rather small impact at these magnifications.

I wouldn't have spent days captured and compositing images if I thought it wasn't representative of the reality I was seeing with my own eyes.  Until the advent of the most recent generations of phone cameras, I had neither the field width nor resolution nor edge correction to do this well.  I'll bet the latest generation of phone cameras are even better than what I was using.

2 minutes ago, vlaiv said:

That is not going to help much - it's a 12mm eyepiece - means that field stop is about 17.1mm - that is only about 8.6mm from axis - about a third of a distance from field center compared to edge of 46mm field. Even if you introduce large distance error for flattener - that part of the field will not be significantly distorted.

So this aberration doesn't scale linearly with magnification like coma in a Newtonian?

4 minutes ago, vlaiv said:

Not sure why would it be so?

If you place camera lens at exit pupil - all light from EP will certainly hit camera lens without any issues.

Try it yourself.  I keep an old Olympus C4000 with adapter tube that couples nicely with my 22mm AT AF70 for digiscoping.  No camera lens for my Canon DSLRs will couple with any of my eyepieces (except maybe the ES-92s with their 43mm eye lenses and the two Meade 40mm eyepieces).  Part of the problem might also be that the entrance pupils for most DSLR lenses are buried deep within the lens, so you can never get it to correspond to the exit pupil of most eyepieces to capture all the rays because the eyepiece would have to be inside the camera lens.  Perhaps those with 30mm+ eye relief might work.  I'm speaking from real world experience, not theory.  I would have loved to have used my high resolution DSLRs for this experiment, but it just isn't possible for 90%+ of eyepieces.