Most of the time when I start threads like this, it's out of pure curiosity. But occasionally I do follow through.
A few days ago, I took the plunge on the 18mm Baader Classic Orthoscopic eyepiece, in part, to pair it with my Questar. Here are the critical specs per Agena's product page:
- Magnifications with 3.5-inch Questar (1300mm focal length):
- Without Barlow lens engaged: 72x. This sits decently between the 24mm Brandon's 54x and the 16mm's 81x.
- With 1.7x internal Barlow lens: 123x.
- Eye relief: 14.7mm.
- Field stop diameter: 16.8mm.
- Apparent field of view: 52 degrees.
- True field of view in the Questar: 0.74 degrees (i.e., 16.8 / 1300 x 57.3 = 0.74). This sits roughly halfway between the TFV of the 24mm Brandon (1.06 degrees) and the 16mm Brandon (0.53 degrees).
And some photos that compare the 18mm Baader ortho with the 16 and 24mm Questar Brandons:
Note the similar color of the coatings:
My impressions after spending an evening with this new eyepiece while observing a nearly full moon in the eyepiece under skies with hazy high-level cloud cover that cleared quite significantly as the evening went on.
No barrel undercuts -- yay! The barrel slides into the eyepiece holder nice and smoothly, and the nylon set screws on my Questar diopter eyepiece adapter seat nice and squarely against the barrel.
In finder mode, the eyepiece almost comes to focus for my unaided eye. With my glasses on (I am mildly nearsighted), focus improves somewhat but is still not quite tack sharp. At bottom, it's just fine for finder mode.
The moon was actually quite pleasing to observe in the 18mm Brandon Classic Ortho. There was enough space around the moon’s disk to frame the moon well while still providing a good amount of magnification, which enabled me to see lunar features in good detail.
Since my phone camera cut off part of the field of view when I pointed it into the 18mm Baader ortho, I made a rough simulation of what I saw using the clone stamp tool to make a complete circle:
The eyepiece gave me an all-around pleasing view.
The coatings and arrangement of lens elements appear to be doing a decent job with controlling glare and reflections. I saw a slight reflection of the moon off my eye when I moved the moon off to the side of the FOV, which showed more dark space around the lunar disk. Those reflections weren't bad, though.
I saw a breakdown in sharpness maybe a quarter of the way from the field stop to the middle of the FOV. Not bad given that Baader widened the field stop diameter beyond what one normally sees with orthoscopics in order to widen the apparent field of view to 52 degrees. I understand that orthos normally have something like a 40- or 45-degree AFOV.
Yellow fringing was quite pronounced when I positioned the moon's limb so that it was nearly touching the field of view edge:
With moon centered in FOV, though, the disk was reasonably sharp at the limb with only a subtle amount of yellow fringing visible at the limb.
With internal Barlow engaged, I saw no change in where I needed to position my eye, though blackouts did increase mildly -- not a lot, just mildly. There was a slight reduction of the FOV similar to what happens when the Barlow is engaged with 24mm Brandon except I have to pull my eye back a bit further with the Brandon than what I have to do with the 18mm Baader ortho. Ghost reflections were really well controlled in the 18mm Baader ortho with Barlow engaged.
For comparison, I popped in the 16mm Brandon, and in most respects it was very much superior to the 18mm Baader ortho especially concerning edge sharpness and false color. In the 16mm Brandon, there was none of that yellow fringing I saw in the 18mm Baader ortho even when the moon’s limb was nearly touching the FOV edge of the 16mm Brandon. The only downside was that the moon overwhelmed the field of view of the 16mm Brandon, filling it nearly end to end.
The 24mm Brandon was more pleasing still. Offering a more appropriate magnification for a full moon, the 24mm Brandon also showed better contrast. The difference was obvious. Still, the 18mm Baader ortho offered really decent contrast. It just was not as good as what the 24mm Brandon offered.
Bottom line: based on my initial impressions of this eyepiece, I'd say that, if one were on a budget and were looking for the one perfect modern eyepiece to use with a Questar, I’d say at this early point that one could do a lot worse than the 18mm Baader Classic Ortho. I’m looking forward to more meaningful testing especially when Jupiter and Saturn reappear at a convenient hour.
Edited by Gregory Gross, 15 May 2022 - 07:52 PM.