Recently Browsing 0 members
No registered users viewing this page.
How does the Baader Aspheric 36mm match up against the Baader Eudiascopic 35mm?
Unable to find a twin for the latter, I have begun to ponder pairs. Baader have suggested the 36 is recommended modern replacement for the 35, especially with its switchable stem for either 1.25 or 2 inches.
Has anyone had experience with both models?
Televue state that the Ethos21 has 15mm of eye relief and 100 degree actual field of view in their published specification.
Has anyone actually MEASURED the eye relief and can confirm that this is indeed what it has?
Can anyone confirm that the Ethos21 actually does show 100 degrees FOV or is it actually less?
Thanks in advance,
Eye relief (ER) is a recurrent topic here, not least by glass-wearers, many eyepieces do provide nominal ER, assuming the numbers are correct (not always the case), there're still other factors affecting the actual available ERs, such as recessed or concave eyelens etc, since ER is defined from eyelens center to eye ploint.
There's an interesting aspect brought up in the other site, which might affecting the ER positively
Here's the illustration picture:
The point is: when observer's eye pupil is larger than the exit pupil produced, he can actual move his eye further away from exit pupil position and still see the whole FOV.
I've made a couple of graphs to see its effect, the first one assuming dark-adapted eye pupil of 5mm, and eyepieces have 3mm recessed eyelens,
It shows that an ortho (42° AFOV) with 4mm nominal ER (red line) behaves like having 10mm ER, despite 3mm recessed eyelens, that's about the same ER with a plossl (52°AFOV) of 6mm nominal ER, in another words, 5mm ortho is about as comfortable as an 8mm plossl.
Second graph is with not well-dark-adapted eye, i.e. 3mm eye pupil, everthing else the same,
The same ortho has only 7.5mm available ER now, compare to 10mm when pupil was wider,and the plossl drops to 8mm.
Whats' your experience?
By Ben the Ignorant
Why crave for long eye relief, and then restrict it with a raised eyecup? Why conceive wide fields optics only to make them narrow with same raised eyecup? My Myriads and Nirvana/TS/William clones have a rotating eyecup that resists turning firmly, they never spin unless I want them to. The Meade/Maxvision 18mm/82° and 34mm/68°, on the other hand, possess a rubber eyecup that also serves as a grippy external frame. These oversize grips offered so much leverage to the turning mechanism, they triggered it often with no will on my part.
Almost each time I handled them, the integral cup spun, reducing the eye relief and field, plus it made me doubt if I had fully seated and locked them in the diagonal. The 34mm was the worst offender, its mechanism had almost no resistance at all. That was very annoying, when you observe you want quietness, your gear shouldn't be doing irritating things of its own.
Having had enough of that, I lifted the rubber with a handy little tool I always carry in my back pocket: the Dunlop Ultex guitar pick. Ultex is plastic, but it's the glassiest pick material, dump it on something hard and its sounds almost like glass foil or stone foil, if such a thing was possible (Dunlop's more rubbery Tortex was great but it's outdated, just compare). Still Ultex is flexible, a mandatory quality of guitar and bass picks. And it won't scratch anodized aluminum.
A 1mm thick pick did the job after a 0.73mm colleague broke; not tough enough. 0.60mm's give out the most harmonics but they were too thin at first sight for this. I don't play 1mm's anymore, they mute too much harmonics, however this one got a nice alternate occupation.
Experience from many other little jobs similar to this one made me keep the broken pick when most folks would dump it right away. Never trash something until the work is over. This piece of scrap plastic proved the ideal tool, with the right curvature and bite, to remove the crystalline superglue that remained on the metal cylinder.
The mechanism is simply a stud that moves inside a curved slot. I wiped the now-useless grease, and filled the slot with a short piece of electric wire to block the stud. Sorry for the blurry shot.
No need to glue the wire, the tight-fitting rubber housing keeps it in place. I did put three drops of glue to attach the rubber to the inside metal housing. I kept the caps on, but I should have taped them to better protect the lenses against tools and glue, big sin here! I didn't use superglue, I'll wait and see if that all-purpose Pattex sticks hard enough to both metal and rubber. If it doesn't, superglue it will be. The "tire" fits the "wheel" tight enough that even no glue could do temporarily.
Did the same with the 34mm:
Interesting how the crown's edge has some green anodizing that was destined to match the green deco of the eyepiece, had it been sold under the Meade brand. It was impossible to lift that massive rubber housing with a pick, I had to do it with a screwdriver, but it inevitably scratched the black barrel, which I patched up with a black marker. These are the black smears under the wire.
There is some risk in opening a high-grade eyepiece, so don't try before you have praticed on cheap or damaged ones. It also voids the warranty, be careful. Waterproof eyepieces are obviously a no-no for that mod! Assuming one could unscrew the sealed parts, humid air would enter through the thinnest opening, and ruin the anti-fogging protection.
I hope this is interesting even if you don't get to use the tip. I didn't know what I would find in there, nor did I know how I would fix the sloppy eyecup. Simply opening a bits drawer made me notice that piece of wire, bulb switched on inside my head. I had considered drilling the frame to insert a locking screw but what an awful lot more work and risk it would be!
Somehow it escaped my mind that I also own a 24/82 Meade/Maxvision ocular that has a turning integral rubber frame and eyecup, but much firmer fortunately; I might do the same mod for it or not. And a 7mm Panorama, if a preliminary, partial takedown shows it can be done safely. I'll keep you posted.