asaint
Carpal Tunnel
Reged: 04/25/03
Posts: 2019
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William Optics 45-deg Erecting Prism
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timmbottoni
Pooh-Bah
Reged: 08/25/05
Posts: 1109
Loc: W Chicago suburbs, IL USA
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Thanks for this review. I was thinking about getting one of the these for daytime use in my Megrez II as I already have a WO 2" Dielectric for night time use.
This confirms what I was thinking - that this is a great high quality choice for daytime use. While I could continue to just use the 90 deg star diagonal I have, I see the value in having the 45 deg erect image for spotting scope use, as this would provide not only a correct image viewed left to right, but also a more comfortable viewing angle for use on my photo tripod. It would also allow the use of 2" eyepieces which might prove to be extremely valuable for spotting scope use.
Thanks,
Timm Bottoni
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WO Megrez 80FD, Celestron C8
WO SWAN 33mm, UWANs 4mm, 7mm, 16mm, WO SPLs 3mm, 6mm, 12.5mm, WO Zoom II 7.5-22.5
WO EZTouch & Celestron Nexstar GT modified mounts
SV F50B2 Finder in WO Quick Release 50mm bracket
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Phil Wheeler
Pooh-Bah
Reged: 12/31/05
Posts: 1192
Loc: Los Angeles Beach Area
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Quote:
This confirms what I was thinking - that this is a great high quality choice for daytime use. While I could continue to just use the 90 deg star diagonal I have, I see the value in having the 45 deg erect image for spotting scope use, as this would provide not only a correct image viewed left to right, but also a more comfortable viewing angle for use on my photo tripod. It would also allow the use of 2" eyepieces which might prove to be extremely valuable for spotting scope use.
I believe WO also sells an erect image 90 deg diagonal which one of their folks recommended to me over the 45 deg one reviewed. It is described here:
http://www.william-optics.com/wowebs/prod_diag/2in_90ep/features0.htm
A tad more expensive, but likely lacking the shortcomings noted in the review.
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Phil / W7OX
Nexstar8GPS XLT w/SkyAlign Upgrade
WO 10th Anniversary ZS-80FD APO, UA Microstar
Denk II Power x Switch, Vixen LV 8-24 Zooms, PST Corrector
Celestron C5+
Coronado P.S.T, Bogen 410 Geared Head,
Binos: Konica Minolta 7x35; Carton 7x50, Orion 9x63, Ob 15x70; Canon 12x36 IS II; Canon 10x42L IS
UA Unimount, SkyWindow
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Ben Cacace
member
Reged: 12/17/05
Posts: 21
Loc: NY, New York
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The review was great. Thanks for pointing out the limitations of night-sky observing with the W-O prism. I've used the prism for solar observing and found no problems viewing the Sun with a Baader filter. Glad to know that there is no need to pack the prism diagonal when observing the stars.
Turning a TV-76 into a true (albeit heavy) spotting scope is a treat. The views are stunning and the ability to turn the eyepiece to any direction while keeping the view upright is 'infinitely' better than using a diagonal where you need to view objects with the eyepiece upright at all times or else the wildlife appears to defy gravity.
Ben Cacace
Manhattan, NYC
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Ben Cacace
Manhattan, NYC
http://novahunter.blogspot.com
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ATY
sage
Reged: 01/01/05
Posts: 494
Loc: Castro Valley, CA
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I believe the glare you saw on either sides of a bright image at night was the spikes created by the roof edges of the erecting prisms. Even the more expensive Baader erecting prism has this same problem. As such erecting prisms are not recommended for high power astronomy use.
Alex
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After much buying and selling these remain:
TEC 140 F/7 APO #201 on EQ6 Skyscan
Bushnell Spacemaster 60mm on photo tripod
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denebman
member
Reged: 06/03/04
Posts: 27
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Very objective review. The spike is in fact a result of design.
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10" Zambuto (coming)
TAK Mewlon 210
TMB 115
Fujinon 10*50
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Kimmo Absetz
member
Reged: 10/12/05
Posts: 99
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I would like to make a few short comments upon your interesting and precise review of the W.O. 45 degree erecting prism.
I have no experience with that particular prism, but what I do have is a lot of experience with all the top-of-the-line birding scopes with built-in 45 deg. prism assemblies.
Based on star testing a large number of these, I would dare to guess that either your W.O. was a true lemon or they have chosen a very poor design for their prism. What you describe looks like a poor Amici prism, and the performance you got with it would not qualify for proper daytime use any better than for night views of the sky.
The Scmidt one-piece 45 degree prisms used by Swarovski and Zeiss have, in the better samples of the scopes, provided clean diffraction images with almost no flare and no astigmatism. Their manufacturing specifications for the prism is sufficiently high that the roof edge can be invisible in the image. Swarovski prisms seem to be a bit better, while many of the Zeiss prisms show the roof line in defocused diffraction patterns. Good samples of the Zeis are nearly flare-free in best focus, though. However, with birding scopes quality control standards are not as good as with better astro optics, and I have seen samples with very obvious prism-induced astigmatism and rather prominent spiking, although more commonly the problems that are found result from poor collimation. It is thus unfortunately possible to buy a 2000 dollar scope sample with very poor optics, as your experience with that one Swarovski shows.
The best 45 degree prism I have encountered is the modified Schmidt used in Nikon Fieldscopes. This design uses an oversized prism which offsets the outgoing light cone to the side of the incoming light cone, thus avoiding the roof edge completely. The quality of the scope themselves vary (like with all brands), but the best specimen have diffraction-limited performance and have no prism-induced aberrations I can detect even at 225x magnification.
Obviously I cannot know how well the Nikon prism would perform on a Tele-Vue since it is only available in-built into the scope (or a spare part if you claim you have broken yours, I would guess). However, it has shown me that it is possible to construct a 45-degree prism of a very high quality indeed.
Kimmo
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yagon
sage
Reged: 01/23/06
Posts: 204
Loc: Sydney, Australia
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Thanks for the great review.
I have alway swondered about using an erect image prism for astronomy because it should enable more intuitive nagivation of the skys, especially at low magnifications.
However, based on your feedback, it sounds like erect images are not possible for quality astronomical images.
Regardless, I'd like to ask the forum: does anyone use erect image prisms for astronomy? How much compromise is involved?
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Alessandro
member
Reged: 11/29/05
Posts: 90
Loc: Magenta, Milano, Italia
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I don't know if you made the wrong choice or not but...
I've got the Baader T2 90° Amici prism (32mm clear aperture ad more lightweight and compact).
I use it side by side my 2" W.O. mirror diagonal and I can't see any difference at high power.
Yes, the Baader Amici prism has the spike on very bright object but is clear and crisp as a good mirror.
I can easily split very close double stars and each star shows a perfect airy disk even at 300x or more.
It is especially useful to couple with a T2 binocular turret.
Try it...
Clear sky !
Alessandro
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14" f/4,5 Dobson made in Italy (Ariete)
C8 & Vixen 120NA / CG5-GT
C5 & C80ED / Vixen Portamount
Nagler zoom 3-6mm, 13mm T1 & T6, 7mm T1, Panoptic 24mm
Baader Maxbright binoviewer & 2 Antares 19mm/70°
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timmbottoni
Pooh-Bah
Reged: 08/25/05
Posts: 1109
Loc: W Chicago suburbs, IL USA
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Quote:
Quote:
This confirms what I was thinking - that this is a great high quality choice for daytime use. While I could continue to just use the 90 deg star diagonal I have, I see the value in having the 45 deg erect image for spotting scope use, as this would provide not only a correct image viewed left to right, but also a more comfortable viewing angle for use on my photo tripod. It would also allow the use of 2" eyepieces which might prove to be extremely valuable for spotting scope use.
I believe WO also sells an erect image 90 deg diagonal which one of their folks recommended to me over the 45 deg one reviewed. It is described here:
http://www.william-optics.com/wowebs/prod_diag/2in_90ep/features0.htm
A tad more expensive, but likely lacking the shortcomings noted in the review.
Hi,
Yes - I know but I was hoping for a 2" 45 deg one, since it would be more comfortable to use.
Timm
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WO Megrez 80FD, Celestron C8
WO SWAN 33mm, UWANs 4mm, 7mm, 16mm, WO SPLs 3mm, 6mm, 12.5mm, WO Zoom II 7.5-22.5
WO EZTouch & Celestron Nexstar GT modified mounts
SV F50B2 Finder in WO Quick Release 50mm bracket
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Mr. Bill
Carpal Tunnel
Reged: 02/09/05
Posts: 2748
Loc: Just passing through.....
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Thanks for the warning; I was considering one of these. I'll just stick with my AP diagonal and put up with the upright left to right reversed images in my refractors.
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10x50 Fujinon FMT-SX binos
15x70 AP binos + Paragon p-mount
Oberwerk 100BT 45 degree + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/6.5 Antares achromat
150mm f/8 homemade achromat....EE Barnard MW Sweeper
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery split tube
35mm Pan, 26mm Nagler, 17mm Nagler, 13mm Ethos, 8mm Ethos
Member IDA
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denebman
member
Reged: 06/03/04
Posts: 27
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Quote:
...
Based on star testing a large number of these, I would dare to guess that either your W.O. was a true lemon or they have chosen a very poor design for their prism. What you describe looks like a poor Amici prism, and the performance you got with it would not qualify for proper daytime use any better than for night views of the sky...
Kimmo
I used the same type and it exhibited the same problem. I think it is more likely a design issue no matter where you got it. After extensive testings and comparisons, now I only stick to 2" dielectric coated mirror or 1.25" prism diagonal.
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10" Zambuto (coming)
TAK Mewlon 210
TMB 115
Fujinon 10*50
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Steve Napier
Carpal Tunnel
Reged: 05/10/04
Posts: 1559
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Unfortunately I bought one of these a good few months ago and I can see a massive difference between the erceting prism and a TeleVue diagonal even at powers of 15x,Im VERY disappointed with mine.
I now use it as a paper weight.
It is beautifuly machined and finished but opticaly very poor.
I was using it on a TMB 80/480
Steve.
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rcg
Pooh-Bah
Reged: 04/27/05
Posts: 1409
Loc: Saint Charles, Missouri
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On the issues of spiking on the 2" prism, woudl the larger prism by contrast in the 1.25" WO erecting prism with the 2" insert barrel improve the images, I was wondering about getting an erecting prism for a small Mak?
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Bob G.
8" F/6 Achromat home assembled on home made AltAz w/Pearl Nighthawk finder; currently parting out since return shipping fees for bad APM 8" Achro lenses are killing me  who would have thought you wouldn't get reimbursed for return shipping for optical junk? Live and learn!
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rcg
Pooh-Bah
Reged: 04/27/05
Posts: 1409
Loc: Saint Charles, Missouri
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On the issues of spiking on the 2" prism, would the larger prism by contrast in the 1.25" WO erecting prism with the 2" insert barrel improve the images, I was wondering about getting an erecting prism for a small Mak?
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Bob G.
8" F/6 Achromat home assembled on home made AltAz w/Pearl Nighthawk finder; currently parting out since return shipping fees for bad APM 8" Achro lenses are killing me who would have thought you wouldn't get reimbursed for return shipping for optical junk? Live and learn!
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Mark9473
Carpal Tunnel
Reged: 07/21/05
Posts: 2664
Loc: 51°N 4°E
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Bob, I have the 1.25" WO erecting prism with the 2" barrel on the side of the scope. It gives fine images for terrestrial viewing at low power, say up to 40-50x or so, but if you want to look at Saturn at high magnification (from 100x onwards) you definitely want another diagonal.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63
WO Megrez II 80 FD + Baader 90° T2 Amici
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NoiseJammer
member
Reged: 09/16/07
Posts: 41
Loc: Toronto, ON
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I just bought one and - like Steve - am extremely disappointed.
The prism has a clear aperture of 27 mm which is right for a 1.25" eyepiece but wholly unsuited for a 2". In the extreme case of pluging in a 41 mm Panoptic, I obtained tunnel vision that limited the field to about 1/3 of the area.
IMO, there is no credible reason for advertising this as a 2" diagonal - people purchase 2" eyepieces because they want field of view. The diagonal is simply not capable of delivering it.
FWIW, when used with a 22 mm Panoptic I also noted a LOT of chromatic aberration which negates any benefit of using it in a premium refractor.
(I'm going to return mine to the shop as faulty. Yep... I should've checked here first...)
Clearest & darkest
Bruce D
FLT110 / LX200-12 / lots of other toys
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LX200/12 & Borg 60ED f/3.8
TOA-150F / Denk II on DM6
... and way, way too much light polution.
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Monroe
member
Reged: 11/10/06
Posts: 10
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I had purchased one of these (2 in model) for use in either of a SV80ED and Orion 100ED (SV with feathertouch 2.5 in focuser). Much to my dismay, of all my EP's, only a 40 mm Paragon and UO 18 mm ortho would come to focus in either scope. No focus in Hyperion 17 mm, 8 - 24 zoom, LVW 22 mm, couple UO orthos, couple Sirius Plossls. Puzzled, picked up their 1.25 in w/ 2 in barrel and all work well (save the Paragon with it's 2 in fit requirement). I suspect some issue of excessive light path within the 2 in prism (approached focus as tube was drawn in) but I'm really puzzled as to the breadth of EP's that would not come to focus. Moreso as WO had been surprised that this had been the case.
Read a separate 'for sale' posting that had suggested that this prism is ideal for SCT and not so for refractors? However, plenty of instances where this had been used in refractors (this thread, for instance).
Any and all appreciated as I'm still teaching myself fundamental optics. thanks
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rodb
member
Reged: 05/19/08
Posts: 66
Loc: MD, USA, Chevy Chase (just nor...
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Since it was mentioned earlier in this thread, I'd like to share my experience with the Swarovski 80mm HD spotting scope, with 45 degree erect view and zoom eyepiece from 20x-60x. The focus is on the body of the scope while the zoom action is at the EP end.
I was suprised to see the almost quarter moon quite sharp at 60x, as was Jupiter with its two bands clearly defined and moons point-like. I will say at the lowest power, Jupiter showed so much flare that the two bands were barely visible.
Stars are well shown w/o obvious errors. Albireo was split easily and showed good color contrast.
And, of course, daytime views of birds and everything else are sharp enough for my pleasure.
So, all in all, even considering the expense, I'm very pleased with the scope. I have it riding on a Swarovski-labeled but Bogen made carbon fiber tripod and head. Very light at around 9#s total: liftable with one hand.
Regards, Rod
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Canon 10x42 IS Binos
Zeiss 8x42 T* FL Binos
Aus Jena 10x50B Nobilem Binos
Swarovski 80mm HD (birding/nature scope)
WO 90 Megrez and 4 TV eps (waiting on delivery as of 8/25/08)
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