What was the largest telescope ever fitted with an eyepiece

Question

Serious modern telescopes use CCDs to capture the results. This makes it convenient to process or display the results halfway around the world. However, there is something visceral about looking through an eyepiece and seeing the results live.

My telescopic experience has been with smaller (<=8") devices in not-great-seeing conditions, and I've generally found the results dim and fuzzy. I've imagined what it would be like to look through an eyepiece on a serious telescope, showing a nebula bright and clear. Imagine stereo eyepieces on the Large Binocular Telescope!

Hence my question: what is the largest aperture telescope that was ever fitted with an eyepiece so that someone could look through it in real-time? This should include situations where a normally-digital telescope was temporarily fitted with an eyepiece.

Answer 1

A recent Twitter thread included a post by someone who had looked through an eyepiece on the 8.2 meter Melipal ("UT3") telescope of the ESO VLT.

Here's the original post:

Astro friends: anyone know the largest telescope in the world which has [can have] a real mountable eyepiece through which you can look? Palomar 200-inch is the biggest I know. Others? I know Subaru can project images to a screen, but I mean real look-through-it eyepiece.

... and here's the reply:

In 2003, I had the privilege to see Mars through an eyepiece installed on UT3, almost at its opposition (25" apparent size), with a 0.5" seeing. It was marvelous!

(Another reply cited a blog post about an eyepiece on a 6.5 meter telescope.)

And, a picture of someone looking through one of the 6.5-meter Magellan Telescopes. Which leads me to wonder; it must have been incredibly impressive, but I wonder how much of that giant mirror's light can actually get routed through a teeny eyepiece? The focal plane is clearly much larger than a human pupil, otherwise it wouldn't be able to use those enormous collections of CCDs...

Answer 2

From this answer, it seems that the Harlan J Smith telescope located at the McDonald Observatory, in Texas, with a 107-inch (2.7 m) aperture is the largest aperture telescope that was ever fitted with an eyepiece.

Some independent evidence is there to indicate that this indeed had an eyepiece.

Answer 3

Realize that a large telescope would have a large prime-focus image, that would in turn necessitate a very extraordinary eyepiece to fully utilize.

This said, if you look at this image from the 200 inch Palomar telescope (apparently published in Life magazine):

You see an astronomer inserting a plate in the camera at the 200 inch prime focus. Close to his right thumb you see a vertical tube. This is an eyepiece that is used to examine a star at the edge of the prime focus image outside of the plate dimensions. The astronomer will watch this star through the eyepiece and manually adjust the tracking of the telescope to keep the star stationary. For hours. In the dark. With no source of heat. And no plumbing.

So we have an eyepiece being used in parallel with a photographic plate. It may be a stretch, but...