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Equipment Discussions >> Refractors

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steve-in-kville
super member

Reged: 12/24/07

Loc: Pennsylvania, USA

Correct-image diagonals?
#5689288 - 02/19/13 05:05 PM

Not sure if this belongs here or in the EP forum, but here goes: I would like to use my scope as a spotting scope on occasion. Does anyone have any experience using a correct-image diagonal? Are there certain makes/models I should be looking at?

Thanks.

Post Extras:

Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

Re: Correct-image diagonals? new

[Re: steve-in-kville]
#5689625 - 02/19/13 08:06 PM

Quote:

Not sure if this belongs here or in the EP forum, but here goes: I would like to use my scope as a spotting scope on occasion. Does anyone have any experience using a correct-image diagonal? Are there certain makes/models I should be looking at?

Thanks.

There are, I have a couple but I use a star diagonal. Sharper image and the mind soon adjusts to the left-right reversal....

jon

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Mark9473
Postmaster

Reged: 07/21/05

Loc: 51°N 4°E

Re: Correct-image diagonals? new

[Re: Jon Isaacs]
#5690271 - 02/20/13 07:16 AM

The (only) one that's worthwhile to have, because it is good even if you use high magnifications, is the Baader T2 90° amici prism.

Post Extras:

Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

Re: Correct-image diagonals? new

[Re: Mark9473]
#5690296 - 02/20/13 07:40 AM

Quote:

The (only) one that's worthwhile to have, because it is good even if you use high magnifications, is the Baader T2 90° amici prism.

And it has a limited clear aperture...

Jon

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Darren Drake
Carpal Tunnel

Reged: 10/09/02

Loc: Chicagoland

Re: Correct-image diagonals? new

[Re: Jon Isaacs]
#5690367 - 02/20/13 08:35 AM

I use a 2 inch version on my ST120 to match the star maps and computer displays for finding some of the dimmer objects. Works nicely but when I want to use the scope for higher reso stuf I switch to a regular mirror diagonal.

Post Extras:

Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

Re: Correct-image diagonals? new

[Re: Darren Drake]
#5690580 - 02/20/13 10:29 AM

Quote:

I use a 2 inch version on my ST120 to match the star maps and computer displays for finding some of the dimmer objects. Works nicely but when I want to use the scope for higher reso stuf I switch to a regular mirror diagonal.

Darren:

Which RACI, which scope?

Jon

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Darren Drake
Carpal Tunnel

Reged: 10/09/02

Loc: Chicagoland

Re: Correct-image diagonals? new

[Re: Jon Isaacs]
#5690594 - 02/20/13 10:37 AM

I believe its a baader 2 inch version and I use it on an Orion ST120. Makes an awesome finder....

Post Extras:

Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

Re: Correct-image diagonals? new

[Re: Darren Drake]
#5690601 - 02/20/13 10:41 AM

Quote:

I believe its a baader 2 inch version and I use it on an Orion ST120. Makes an awesome finder....

I use a handheld device for my star charts and a star diagonal in a refractor.. If I want to match the starfield, I just reverse the chart left to right on the handheld.

Jon

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Darren Drake
Carpal Tunnel

Reged: 10/09/02

Loc: Chicagoland

Re: Correct-image diagonals? new

[Re: Jon Isaacs]
#5690699 - 02/20/13 11:43 AM

I used to use the Sky program from my pocket computer and it did not have a mirror reverse function which was a pain and the reason I had to seek out a correct image 2 inch digonal. Now I have skysafari pro which can do a mirror flip but I save time by never needing to go back and forth.

Post Extras:

core
scholastic sledgehammer

Reged: 02/23/08

Loc: Mostly in Norman, OK

Re: Correct-image diagonals? new

[Re: steve-in-kville]
#5690798 - 02/20/13 12:36 PM

Quote:

I would like to use my scope as a spotting scope on occasion. Does anyone have any experience using a correct-image diagonal?

Televue 1.25" 60° diagonal, dielectric mirror, so it's L-R reversed. Occasional use on either my AT66 or C90, and compared with a Televue 45° amici (which looks to be re-badged generic unit), there is some difference during daytime. Planetary/Lunar use, the 60° wins hands down.

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timwetherell
sage

Reged: 09/03/10

Loc: A Land Down Under

Re: Correct-image diagonals? new

[Re: steve-in-kville]
#5691702 - 02/20/13 08:27 PM

I have William Optics 1.25" and 2" erecting prisms. Both work superbly at low magnifications and both go a bit soft at very high magnifications compared to a mirror. The 2" one is a bit pointless really since the clear aperture is only about 35mm (which they do state in the specs)so it vignettes with pretty much any 2" EP. The 1.25" is a great product for converting a refractor into a terrestrial telescope though

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Tamiji Homma
Carpal Tunnel

Reged: 02/24/07

Loc: California, USA

Re: Correct-image diagonals? new

[Re: timwetherell]
#5691765 - 02/20/13 09:11 PM

Hi Tim,

I have this William Optics 2" Erecting Prism Diagonal.
http://www.williamoptics.com/diagonalPrism/erectPrism2in90deg_spec.php

The spec says clear aperture is 40mm. I haven't measured actual clear aperture myself but I remembered Nagler 31T5 wasn't vignetting that bad.

So it must be bigger than 35mm

Tammy

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TONGKW
scholastic sledgehammer

Reged: 01/16/07

Re: Correct-image diagonals? new

[Re: steve-in-kville]
#5691813 - 02/20/13 09:52 PM Attachment (39 downloads)

I have a few correct image diagonals for Lunar observations and bird watching as shown hereunder.
From left is a William Optics 90-degree 2” giving quite a good view, though falls a bit behind a mirror diagonal.
The second, third and the last one are 45-degree and good for bird watching at low power up to 100x.
The fourth is a Orion 1.25” for low power observations up to 100x.

K W TONG
C8+CG5 GT, TSA102+HEQ5 PRO, MK67+Voyager, NexStar 6SE, C5+Mizar K, WO ZS80FD+Kenko NES, Megrez 72FD+Kenko KDS, Mini Borg 50, PST

Edited by TONGKW (02/20/13 09:53 PM)

Post Extras:

timwetherell
sage

Reged: 09/03/10

Loc: A Land Down Under

Re: Correct-image diagonals? new

[Re: Tamiji Homma]
#5692248 - 02/21/13 06:45 AM

yeah you may be right Tammy, I'm guessing 35mm from memory - may indeed be 40

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Lane
Post Laureate

Reged: 11/19/07

Loc: Frisco, Texas

Re: Correct-image diagonals? new

[Re: steve-in-kville]
#5693407 - 02/21/13 07:42 PM

Quote:

Not sure if this belongs here or in the EP forum, but here goes: I would like to use my scope as a spotting scope on occasion. Does anyone have any experience using a correct-image diagonal? Are there certain makes/models I should be looking at?

Thanks.

Ok for daytime use, but I would not use one at night. I have one of the better 2" ones made but it was discontinued. Comparing it to a regular diagonal at night it is easy to see that it does not measure up.

Update - I was wrong, only the Orion rebranded version was dropped the Williams Optics version is still around.

Edited by Lane (02/21/13 07:45 PM)

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JerryOrr
member

Reged: 03/08/13

Loc: Oracle, Arizona

Re: Correct-image diagonals? new

[Re: steve-in-kville]
#5723066 - 03/09/13 10:06 PM

I have one from Orion. I use it mostly for Lunar and planetary observing, when the seeing is not at its best. I simply prefer the correct-image for aesthetic reasons. But when the seeing is excellent, and there is a good chance to see some fine detail, I switch to the standard reverse-image diagonal. Remember, everytime the light is reflected off a mirror, there is a loss of light and resolution.

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Jim Romanski
Carpal Tunnel

Reged: 01/02/05

Loc: Guilford, Connecticut

Re: Correct-image diagonals? new

[Re: Jon Isaacs]
#5725964 - 03/11/13 02:20 PM

Jon no matter how you adapt your finder charts/program to the equipment there's nothing like a fully corrected view. When you move the scope it moves the way you expect it to. When you look up from the eyepiece everything in the real sky is oriented the way you expect it. Very important for finders and great if you can have it in the main scope as well.

My Father-In-Law who was my astronomy mentor was a big believer in corrected views. He built a correct view low power setup for his C8 using one of those old surplus tank sight telescopes. They have massive prisms and large erfle eyepieces. He built a setup to attach to the C8 and used it all the time. It was so nice doing a Messier Marathon with his scope and this setup.

Sure there are ways around it but I for one would welcome and pay good money for a quality amici prism that was large enough to use on my scopes that use a diagonal. I think lots of people would if they had the opportunity.

Post Extras:

Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

Re: Correct-image diagonals? new

[Re: Jim Romanski]
#5726691 - 03/11/13 07:42 PM

Quote:

Jon no matter how you adapt your finder charts/program to the equipment there's nothing like a fully corrected view. When you move the scope it moves the way you expect it to. When you look up from the eyepiece everything in the real sky is oriented the way you expect it. Very important for finders and great if you can have it in the main scope as well.

Jim:

I find it somewhat disconcerting when someone seems to be telling me how I experience the world. The fact is that I have no difficulties with properly moving a refractor with a left-right reversed image or a Newtonian with a straight through finder and totally reversed images both in the scope and in the finder.

But put a correct image diagonal on the refractor or a RACI finder on a Newtonian and my instincts are just wrong and its confusing. The human mind is a power processor and quickly adapts. Here's a for bit for you...

The image from a Newtonian it correctly oriented at the retina. It appears reversed because you eye lens inverts the image. Normally an image is upside down and backwards but your brain knows this and so automatically reinverts it...

Jon

Post Extras:

Jim Romanski
Carpal Tunnel

Reged: 01/02/05

Loc: Guilford, Connecticut

Re: Correct-image diagonals? new

[Re: Jon Isaacs]
#5727082 - 03/11/13 11:04 PM

Sorry Jon. I didn't mean to imply that there's anything wrong with the way you look at the world through a telescope or otherwise.

My point is that when I show a newbie or someone that doesn't observe much the view through a corrected diagonal vs. an inverted image they prefer the corrected one. And it's much easier to show them how to navigate the sky as well. I use Newtonians and refractors both straight through and left/right reversed. I've become used to the image and can correct in my head. But I still find it much simpler to use a corrected image in both finder and scope.

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Ziggy943
Post Laureate

Reged: 08/11/06

Loc: Utah

Re: Correct-image diagonals? new

[Re: Jim Romanski]
#5727274 - 03/12/13 12:58 AM

I also prefer a corrected image on the finder as well as the main scope. I have always used an amici prism on every refractor I have and have had. For me visualizing the actual mechanics of Jupiter and it's moons are much easier to see when the view matches reality. I have used other finders but find them not as intuitive as corrected vision. Jon's MMV

A corrected view in the main scope is more important to me than in the finder.

Edited by Ziggy943 (03/12/13 01:01 AM)

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