Mirror erecting Diagonals

[PatrickO]

Is there such a thing as a MIRROR erecting diagonal or is it only prism?
Thanks 

[Bivanus]

Hello, I think this article covers the whole shebang quite nicelly

Zenith mirrors and erecting optics (astroshop.eu)

Edited March 22 by Bivanus

[PatrickO]

Thanks for that. TBH I don't think it answered my question.

Edited March 22 by PatrickO

[mikeDnight]

A mirror diagonal will give an erect image but it will be E/W reversed. As far as I'm aware, only the Amici prism gives what I think you're looking for. A good Amici prism will deliver outstanding performance, but you may still see the spike on bright objects. 

Edited March 22 by mikeDnight

[Bivanus]

Yup, right there in the article:

Refractor with 45° Amici prism: Image is upright and right-sided

Refractor with 90° zenith mirror: Image is upright BUT laterally reversed

EDIT: At night I tend to use the mirror diagonal because is a dielectric 1/12 lambda 99% reflectivity , however , my not so glamourous plastic-fantastic Amici goes places far away from home-base and also gets used for day vision so each has it's perks.

Edited March 22 by Bivanus

[plyscope]

The Matsumoto system uses two mirrors to give an erect image. These can be used in binocular pairs.

http://ems-bino.com/ems-product-line-english/

[Louis D]

For straight through correct image viewing, there used to be erecting porro prism units sold by Celestron in particular.  Technically, you could substitute high reflectivity mirrors for each prism reflecting surface.

IIRC, if you have enough back focus, you can use two right angle mirror diagonals in sequence and then view looking in from the side of the scope.  Perhaps if you adjust the angles as with the Matsumoto unit, you could view from behind the scope.

I haven't played with this concept in years, so my memory might be a bit faulty.  About 25 years ago, I was trying to make a correct image, compact viewfinder scope using 2" clear aperture, surplus right angle prisms bonded at right angles to each other.  It worked rather well, but it was insanely heavy due to all the glass.

[Captain Scarlet]

I have two 90-degree 1.25” diagonals, and I did just that a year or so ago out of curiosity when my SV140 arrived. It worked very well, but as @Louis D says, to get the image upright you have to view it from the side. Attached a picture of it when _not_ viewing from the side, where the image would have been 90 degrees rotated IIRC.

Magnus

 

[Don Pensack]

I do a fair amount of terrestrial observing with my 4" using a conventional 90° diagonal.

The image is upright, but reversed left to right.

Birds, trees, buildings, etc.  are still birds, trees, and buildings.

I really don't see what the big deal is.  I just remember to push the scope so the objective moves in the direction I want it to go.

It really doesn't take any brain power.

At night, it doesn't hurt in identifying craters on the Moon, or looking at celestial objects.

But the Amici prisms require too much in-focus, cost a lot, weigh more, and transmit less, with poorer image quality.

I really don't see the point unless it's in a finder scope attached to the main.

 

[Highburymark]

1 hour ago, Don Pensack said:

I do a fair amount of terrestrial observing with my 4" using a conventional 90° diagonal.

The image is upright, but reversed left to right.

Birds, trees, buildings, etc.  are still birds, trees, and buildings.

I really don't see what the big deal is.  I just remember to push the scope so the objective moves in the direction I want it to go.

It really doesn't take any brain power.

At night, it doesn't hurt in identifying craters on the Moon, or looking at celestial objects.

But the Amici prisms require too much in-focus, cost a lot, weigh more, and transmit less, with poorer image quality.

I really don't see the point unless it's in a finder scope attached to the main.

 

I agree that most aren’t suitable for astronomy, but the Baader/Zeiss amici prism really is as good as the horizontally reversed diagonals - just a very faint spike on the brightest stars.