Visually Best 2" Diagonal

I want to buy the best 2" diagonal based on what the human eye is actually able to perceive using my SCT. I have scoured these forums reading posts until my eyes crossed, and these are the few points I believe I have discerned.

1) Anything above (smaller) than a 1/8 PV wave front error is not detectable by eye.
2) The telescope itself can/will add to the total wave front error of the view.
3) The manufacturers wave front error claims are ambiguous or at best provide
incomplete information to compare brands.

If I am wrong in any of the above statement's someone correct me please.

These are the major players in diagonals as I see things.

2" VERNONscope Quartz, Silver Coating 1/20th wave (or better) $445.00
2" Astro-Physics MaxBright Diagonal (PMDMAX) Dielectric Coatings $290.00
2" Televue Everbrite Star Diagonal 1/10th [TE-DPC-2002] $275.00
2" W.O. Dielectric Star Diagonal [WO-DIG2DI] 1/10th wave $139.00
2" Baader Maxbright 2" Diagonal 1/10th wave, Baader Maxbright coatings $399.00
2" Lumicon LumiBrite Diagonal 1/10th wave. $239.95

All are listed as 99% or better reflectivity.
Based on the above criteria this would eliminate the Vernonscope diagonal due to 1/20th wave.
Only the Baader diagonal states their 1/10th wave is actually a P-V measurement across the entire surface.
Only AP does not make any wave front error claims (but I know their reputation). They also are the only manufacturer to give you the actual dimensions for clearance of the mirror.

Based on all this "research" I think it comes down to either the Baader or the AP. I am leaning towards the AP because of price. I'm hoping that people more knowledgeable or that at least have a better understanding of all this will offer their opinions. I am in no way attempting to disparage any of the other brands. These are just the conclusions I have come to.

Any help would be appreciated.

Fred Dase

Astro-Tech also has a 2” Astro-Tech first-surface mirror star diagonal has state-of-the-art 46-layer dielectric mirror coatings for a full 99% reflectivity.

It uses brass compression rings. The mirror housing is precision-machined from solid aluminum and a rigid U-shaped die-cast metal backplate with stainless steel hardware holds the mirror in optical alignment in the machined body.

The interior of the body is lined with light absorbing materials, in addition to being anodized an antireflective matte black. The 2” focuser-side barrel is also anodized antireflective matte black, and is internally antireflection threaded for even higher contrast. The barrel is threaded to accept standard 2” filters.

Fit and finish is great. It weights 17 oz and costs about $120.

...looks like the WO diagonal...probably same OEM.

Fred,

You should be aware that your SCT is probably worse than 1/3 wave overall, so you can go with the cheapest diagonal. Having said that, a good AP or Baader diagonal has never hurt anyone.

Dmitri

Fred,
I sent you a Private Message.
Regards,
Paul

Hi Fred, I moved up from the 1.25" Meade diagonal that came with mine to the W.O. Dielectric 2" diagonal.
I actually can't see how you could get any better views than this with the human eye. It is the difference between daylight and the dark in the comparison of these two diagonals.
I have no desire to ever change, The W.O. is as good as I think I could use. Clear views are clear views, great contrast, 100% satisfied.

These eyes of mine would'nt know if I paid $500.00 or $139.00. Maybe if I was about 20 years old I could maybe see a difference, but I could see a big difference when I got rid of the Meade diagonal. The wave front on it had to be terrible but I did'nt know it until I changed it.

Maybe the other ones would be different but I'll just stand by my W.O. I'm not trying to get you to change your decision but to tell my own experience with the William Optics Dielectric star diagonal. Clear Skies, Darrell

Hello:
You can probably relax your 1/8th wave optical quality criterion. If your SCT is f/10, and the mirror is 2"-3" from the focal plane, then the beam size on the diagonal mirror is 0.2" to 0.3". If a 2" diagonal mirror has a smooth 1 wave error in its figure, then over a 0.2" patch this would be 1/10th wave! Errors in optics this close to the focus of a slow telescope mostly results in a slight amount of distortion and field curvature. For a SCT diagonal, a smooth polish, good reflectivity, and a true 90 degree angle are more important than 1/10th wave mirror figure.

Cheers
Mike Connelley

You left out Astro. Tech. 2" Quartz, OPT 2" Quartz, and Stellarvue.