Louis D

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.

It's not a race. BTW, I'm a rank amateur compared to Tamiji Homma over on CN.

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.

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. 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?

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.

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.

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.

Here's one last check for eye astigmatism. Rotate your head around the optical axis of the eyepiece as you view through it to see if the star spikes rotate with the rotation of your head. If so, it's your eye causing it. My employer's insurance covers one free eye exam and one free pair of eyeglasses every year, so I've been very diligent about keeping my prescription up to date. It's also good to go to check for glaucoma, cataracts, retinal tears, etc.

No, astigmatism makes point sources spiky. Extended objects will appear blurry due to all the point source spikes overlapping, but point sources like stars will be starbursts. Astigmatism focuses light into lines. The human eye can have multiple axes of astigmatism of varying strengths. Eyeglasses attempt to correct the most egregious offender, so there's always some remaining uncorrected astigmatism unless you get LASIK which corrects all defects at once. Have you had an eye exam in the last year? If so, check your CYL or cylinder correction number on your prescription. If it's above 0.5, you'll probably see spiky stars at large exit pupils as with this 40mm eyepiece. Also, don't expect the outer field to be in focus at the same time as the center of field unless you're using a visual field flattener with that scope. Short focal length refractors have strong field curvature.

Were you wearing eyeglasses? It sounds like you might have astigmatism in your eye if you weren't. How did the view compare to other ~40mm eyepieces you own? That's the exact scope I did my testing in, and stars looked sharp out to about 75% from the center to the edge.

If cost and weight is no object (and if Don is still making them), the Clement focuser would probably work for you with the appropriate adapter. It's natively a 3" focuser.

I've got a 2.5mm Planetary TMB II Eyepiece on order from China via ebay. For $35+tax I thought it would be worth a try. Once I get it, I'll compare it to my 3.5mm Pentax XW and my 5.2mm Pentax XL Barlowed. It might end up being a project eyepiece where I have to blacken or flock the interior to control stray light if the optics pan out. If the optics are bad, I'll do an exposé on it here on SGL and write it off as a learning experience. If I like it, I might get the 4mm version as well.

I have the Astro-Tech 72ED (original version), and it easily comes to focus with 2" accessories. However, the focuser slips under heavy 2" loads, so I wouldn't recommend it. If you're going to use heavy 2" diagonals and eyepieces near zenith, makes sure to look for an R&P focuser to help control slip. As @Ricochet says above, it takes a long dovetail bar to reach balance. It just barely works with a 6" and is better with an 8". However, the focuser knobs then need to be at an angle to avoid hitting the bar. I doubt the 45 degree Amici prism would cause backfocus issues with most eyepieces with the Sky-Watcher version. They don't require all that much more infocus relative to 90 degree mirror diagonals.

There's nothing stopping you from putting both the EQ platform and Dob on a cart together. To make the stack more compact, the Dob's original ground board can be replaced by the EQ platform's upper board. You just have to transfer or replicate the sliding materials from the ground board to the EQ's top board. Depending on the design, you may need to use tie-downs of some sort to lock the upper and lower platform boards together during transport so the upper board doesn't slide or slip off the lower board.

My attic here in Texas regularly hits over 130° F in the summer. In my experience, certain thermoplastics shrink (like those clear, custom fitting display packages) and some glue types dry out and crumble (like hardback book bindings) up there. My A/C-Furnace electronics seem unfazed, though. However, they were designed for those conditions. Foam, rubber parts, and urethane finishes seem unfazed as well. As long as it's a dry heat (the usual case here), I haven't noticed any other problems with things stored up there. It's well ventilated, so there's no mustiness.

That's a DSC kit which is intended to help locate objects. You still have to push the Dob about to find the object and to continue tracking it once found. Maybe you were thinking of a GOTO kit?

@WJC Is that true regardless of where the magnification originates? If a BV is used with the same eyepieces in a 400mm versus a 2000mm telescope, will collimation error be 5 times more obvious in the 2000mm telescope?

Wow, the top of the BHZ is totally different from the Celestron Regal 8-24mm zoom: There's nothing flimsy about its eyecup once it's screwed on. It has an inner plastic track that the outer ring twists up and down on. I'm surprised Baader chose such a flimsy eyecup attachment method. I've read that the Leica ASPH also has an easily broken eyecup.

The problem for me with this particular zoom is that at high powers on manually tracked alt-az mounts, wide fields of view become much more useful for extended dwell time to examine your object between nudges and settling times.

I'll probably stick with my Speers-Waler 5-8mm in that range despite it being wildly non-parfocal throughout its range. That is, unless this zoom is inexpensive. If it comes it at $200 to $350, I'll have little to no incentive to buy it.

I have one of these I stash in the back of the van when moving boxes: 165 lbs. Capacity Aluminium Folding Dolly Push Hand Truck in Black It might work well for you as an alternative.

Probably due to spherical aberration. I remove it for planetary observations as well.