Louis D

I would add "at a given aperture under good seeing conditions". For example, years ago at a star party, on the same night that Jupiter looked featureless at 200x in 4" APOs and 8" SCTs, it looked rich in details in a 15" custom Dob at over 300x. That convinced me to buy a used 15" Tectron Dob. It did not disappoint. 300x felt like 100x in a small scope. Of course, I had very steady skies to observe from here in Texas.

For low power star hopping, I would stick to the lowest cost option available. The Baader would probably shine at high powers, but who star hops at high powers? Remember, though, the clear aperture on these lower cost Amici prisms is somewhat less than 27mm, so you will probably see vignetting with widest true field 1.25" eyepieces. Also, they're plastic bodied, so I wouldn't put a heavy, expensive 1.25" eyepiece in them.

The WSP location in the Florida Keys is at about 24.6° N, 81.3° W. It is more or less in the The Straits of Florida between mainland Florida, USA, and the island of Cuba. Its seeing is influenced by the Florida Current that eventually merges with the Atlantic Current to form the Gulf Stream. The Florida Keys are generally well south of the jet stream.

In a good way or bad way? The Winter Star Party in the Florida Keys is known for very steady seeing conditions.

My thoughts exactly. I went from an 8" tube Dob to a 15" truss Dob and found the improvement massive on DSOs and planetary detail (remember, steady Texas skies here). Of course, after a massive auto accident 23 years ago that ripped up my back, I have barely been able to lift the 15" out of the back of the hall closet because the mirror box weighs 60+ pounds. I figure I'll move it to a dark sky vacation/retirement home at some point and place it on a roll-out platform with jacks to keep it steady.

I was surprised by how claustrophobic the 14mm Morpheus felt when swapping it in between the 17mm ES-92 and 12mm ES-92. I wouldn't have ever thought a 76 degree AFOV would feel that way until I did the swap. However, if you never swap in a wider eyepiece, you'll never feel that way using a Morpheus.

I generally think in terms of percentage jump. Going from a 60mm to a 72mm is a 20% increase in aperture. Going from a 72mm to a 100mm is a whopping 39% increase in aperture. However, going from 100mm to 120mm is only a 20% increase once again. Going from 120mm to 150mm is 25% increase, so slightly larger, but not massively so. Certainly not enough in my mind to justify the cost, weight, and difficulty of mounting a 6" refractor (APO or not) over a 6" fast-ish Newtonian. A 150mm APO refractor is going to run you about 20x or more the price of an f/5 Newtonian which is APO by definition. By contrast, going from a 200mm reflector to a 240mm reflector would be a 20% increase. However, the increase in number of observable objects is not nearly as much as the jump from 60mm to 72mm. Increases in aperture are thus much more noticeable at the lower end in my experience than at the higher end. For instance, going up in 25% increments starting at 50mm rapidly opens up the number of objects the human eye can detect or resolve. However, once you get up around 10 to 12 inches, the jumps need to be larger in my experience to open up a significant number of new objects. Thus, I see mostly 16 inch and under Dobs at star parties because of this. You also need really dark skies to justify using 18 inch to 36 inch Dobs.

Good point. 👍 Mathematically, it should have about 5mm more eye relief (16mm vs 11mm) at 45° rather than 60° due to its 13mm eye lens diameter and 60° AFOV. Of course, I measured closer to 8mm usable eye relief or slightly less at the short end of the zoom range, so figure on 11mm to 13mm of usable eye relief at a 45° AFOV. Most folks find 12mm usable eye relief without eyeglasses to work well for them, so this makes it a comfortable replacement for short focal length Plossls and Orthos for non-eyeglass wearers willing to live with a 40° to 45° AFOV, which is reasonable for most high power observing situations. Even folks like me with strong astigmatism can often get good enough results at tiny exit pupils without eyeglasses.

It really depends on how much tension you have set in the altitude axis. I'm pretty sure that mount has adjustable tension. If you crank it up, you may be able to avoid any balance issues. The bigger problem you're going to run into if you run with light tension for a smoother altitude motion is the tendency for the tube to swing upward when you remove the eyepiece for an eyepiece change no matter how well balanced your tube is. There are no clutches on Dob mounts to lock it during eyepiece changes. You'll need to become adept at keeping the scope from swinging upward during eyepiece changes if you aren't keeping a high level of tension in that axis.

Why not just buy an Astronomik OWB Type 3 Clip-Filter EOS APS-C? It seems like the most reasonable solution for you. Here's the tech info:

@HollyHound Do you observe with eyeglasses at those focal lengths? I have such strong astigmatism in my eyes that I need a minimum of 17mm of usable eye relief to comfortably see the entire field of view of an eyepiece. My 12mm and 17mm ES-92s exactly tick that box, so I have no incentive to get the 16.5mm XW. My XL, XW, Hi-FW, Delos, and Morpheus eyepieces all provide at least 18mm of usable eye relief, so are also quite comfortable to observe with. I've held off purchasing the 23mm XW to replace my 22mm NT4 because I've read that the eye relief is marginal for eyeglass wearers.

I use a GSO 6" f/5 on a DSV-2B alt-az mount without any major issues. However, anything bigger, and I would prefer a Dob mount. One issue I have with my alt-az mount is that if I move my rig to a different spot in the yard to dodge sky obstructions, any bit of being out of perfectly level and the azimuth axis swings around to the low side. This pretty much does not happen with Dobsonian mounts unless you've got a really heavy load in the focuser. Having to relevel a mount in the dark is a pain, so there's a win for the Dob.

In head to head comparisons with the 30mm APM UFF, 27mm Panoptic, and 35mm Baader Scopos Extreme at f/6 and faster, I found the ES-82 30mm to have slightly bloated stars across the entire field of view at best focus. Enough so that I found it annoying. If the bloat were confined to the field outside the TFOV of these other eyepieces, I'd be totally good with that, but it's there even in the central region. I suppose if I had no frame of reference from never having tried those other eyepieces, I might not have ever noticed the central bloat. I was in this situation for years before getting a coma corrector. Once I knew what the field could look like with a CC, I could never go back to not having a CC in my Newts. Why pay big bucks for an APO to have pinpoint stars only for those same stars to be bloated by your eyepiece? That's why I have other eyepieces in this range, because no one eyepiece does it all (ultrawide field and pinpoint stars center to edge) in my experience at f/6 and faster. Due to its prohibitive price, I haven't yet tried a Nagler T5 31mm to see if it manages to have pinpoint stars center to edge like the UFF, Panoptic, and BSE.

Are these OO Newts intended for imaging? Otherwise, why suffer the consequences of a large enough secondary to illuminate a focus point well outside the tube?

Your best budget bet for visual is a GSO coma corrector that is sold under numerous brands around the world. I have two, each with a 25mm spacer ring added between the optical section and the eyepiece holder for best correction with my eyepieces that focus near their shoulders. They're really good except at high powers when the spherical aberration they introduce degrades the view. I remove it at high powers as a result. I've found they require 11mm of additional in-focus as I have them configured.

I have the original ES-82 30mm decloaked, and the APM UFF 30mm is sharper across the field, especially toward the edges. The ES-82 splits red from blue, giving two images of planets in the last 15% as they drift across the field of view. Point is, give the APM UFF 30mm a try if you were looking to improve the image quality over the Axiom 31mm at the expense of a bit of field of view. It's much lighter and more compact as well.

Or at least be pronounceable.

I haven't tried it for astrophotography, but I have one that I used for years for stage photography under available light. Stopped down to f/2 to f/2.2, it is sharp edge to edge with little to no light falloff with a crop sensor EOS DSLR. Autofocus is also quiet, fast, and instantly manual overridable. Not that any of that matters for astrophotography. However, it could do double duty for school stage performances by your kids. I probably shot over 125,000 exposures with it over a decade of dance studio performances by my daughter and the rest of the dancers, so it's also quite durable.

If you're referring to item at the lower right, give it a few years/decades to take on that vintage brass patina, then we'll see if it resembles a plumbing fitting. 😏 Right now, it's too shiny to be mistaken for plumbing parts.

I had to go back to my Svbony zoom write up to remind me of what I saw in the 3.5mm Pentax XW versus the Svbony zoom at 3mm: So, I'd recommend looking for color fringing on bright stars as you move them center to edge. The XW shows none anywhere while the Svbony zoom shows increasing amounts toward the edge.

From your Stellarview filter review: I employed a special approach and sent this curve to Vic Can you post what that curve was that you suggested? I'm wondering how similar it looks to the Baader Semi APO curve in dark blue below: I have that one, and it does a good job of avoiding adding a yellow cast to the image. However, it doesn't suppress all the unfocused violet and none of the unfocused red. I've found a Hirsch #12A Light Yellow and a Hirsch #82B Light Blue (Cyan) combine for a yellow-green view that suppresses pretty much all of the unfocused violet and red and really sharpens up planetary views without darkening the image too much like a #11 Green or especially a #56 Green does. I recently picked up an X0 Yellow-Green filter, and it looks promising as well.

Given all the tarnished brass, I'd first have guessed it was some sort of old plumbing fitting were it not for the optics. 😁

Do the same test holding one up to each eye, but with zoom and the SLV. It could be that if you are concentrating on the central region against a dark sky, you aren't noticing the wider FOV. It could also be the tighter eye relief coming into play. You really need to mash your eye into the zoom's eye cup to take in the entire FOV, especially from 3mm to 6mm.

You need not have bothered with the in between setting. I measured the 3mm setting to actually be 3.5mm in the central region. It grows to 2.5mm at the edges due to distortion. And I also noticed considerable softening at the "3mm" setting. I consider it a bonus focal length to be used when you don't have anything better.