Telescopic image addition

Has anyone ever attempted to bring the images from two separate objectives
to the same focus? Basically, the opposite of what a binoviewer does
(i.e. send a single objective's image to two separate focal planes).

Such a setup would actually allow increasing the brightness of extended
objects. The details strike me as problematic, however.

Obviously parallax would restrict how close the target can be, but I'm not
sure by how much.

I expect some kind of tilted off-axis reflection will end up being
necessary, making distortion an issue as well (unless the primary and
secondary/tertiary/etc. can be figured oddly to compensate).

If it's doable at all, it may also be possible to make a small
two-dimensional array of objectives, all sharing the same ultimate focal
plane.

Any info on previous attempts, or reasons why it won't work?


--
- Mike

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Mike Ruskai wrote:
Has anyone ever attempted to bring the images from two separate objectives
to the same focus? Basically, the opposite of what a binoviewer does
(i.e. send a single objective's image to two separate focal planes).

Such a setup would actually allow increasing the brightness of extended
objects. The details strike me as problematic, however.

Obviously parallax would restrict how close the target can be, but I'm not
sure by how much.

I expect some kind of tilted off-axis reflection will end up being
necessary, making distortion an issue as well (unless the primary and
secondary/tertiary/etc. can be figured oddly to compensate).

If it's doable at all, it may also be possible to make a small
two-dimensional array of objectives, all sharing the same ultimate focal
plane.

Any info on previous attempts, or reasons why it won't work?



On a large scale, the original version of the MMT in Arizona did
this. It had a very limited field of view in common focus, because
the beams from the six optical systems arrived from different
directions after coming through a beam combiner. To get around
this problem, the individual optical systems need to be more
complicated, the equivalent of off-axis systems, so that the
common focal plane is the same for all of them. On the other
hand, if you're only interested in planets or double stars, maybe
that small field would be OK...

Bill Keel

Mike Ruskai wrote:
Has anyone ever attempted to bring the images from two separate objectives
to the same focus? Basically, the opposite of what a binoviewer does
(i.e. send a single objective's image to two separate focal planes).

Such a setup would actually allow increasing the brightness of extended
objects. The details strike me as problematic, however.

Obviously parallax would restrict how close the target can be, but I'm not
sure by how much.

I expect some kind of tilted off-axis reflection will end up being
necessary, making distortion an issue as well (unless the primary and
secondary/tertiary/etc. can be figured oddly to compensate).

If it's doable at all, it may also be possible to make a small
two-dimensional array of objectives, all sharing the same ultimate focal
plane.

Any info on previous attempts, or reasons why it won't work?



On a large scale, the original version of the MMT in Arizona did
this. It had a very limited field of view in common focus, because
the beams from the six optical systems arrived from different
directions after coming through a beam combiner. To get around
this problem, the individual optical systems need to be more
complicated, the equivalent of off-axis systems, so that the
common focal plane is the same for all of them. On the other
hand, if you're only interested in planets or double stars, maybe
that small field would be OK...

Bill Keel

Other that the logistics that you mentioned I would guess that it is doable,
but it doesn't sound too practical.

I would think that alignment issues would be the biggest reoccurring
problem, as well as cost.

Interesting question though!

Francis Marion

Other that the logistics that you mentioned I would guess that it is doable,
but it doesn't sound too practical.

I would think that alignment issues would be the biggest reoccurring
problem, as well as cost.

Interesting question though!

Francis Marion

You have to be very careful, as the light cones approach close alignment, all the photons between the two views become coherently aligned. This is like a million weak lasers and it's brightness dependant, so for example you could burn the pattern of bright mountain tips of the lunar terminator permanently into your retina or glasses. (My eyeglasses have crater Copernicus permanently etched from using 2 Celestron 14 ' SCTs in this fashion.) Make sure you wear welders glasses as you try this.

You have to be very careful, as the light cones approach close alignment, all the photons between the two views become coherently aligned. This is like a million weak lasers and it's brightness dependant, so for example you could burn the pattern of bright mountain tips of the lunar terminator permanently into your retina or glasses. (My eyeglasses have crater Copernicus permanently etched from using 2 Celestron 14 ' SCTs in this fashion.) Make sure you wear welders glasses as you try this.

On Fri, 09 Apr 2004 11:03:57 GMT, "Mike Ruskai"
wrote:

Has anyone ever attempted to bring the images from two separate objectives
to the same focus? Basically, the opposite of what a binoviewer does
(i.e. send a single objective's image to two separate focal planes).

There was a time when I wasted a fair amount of time working (on
paper) on such a beast. I was after the ultimate comet seeker and
realized that if I could superimpose the light paths from four
six-inch objectives it would be possible to achieve a 2+ degree true
field of view at 30x with the light grasp of a single twelve-inch
objective while maintaining an optimal 5mm exit pupil.

I was never certain I would be able to get it to work; but I
eventually became convinced that even if I could, the added optical
components -- something along the lines of rather large beam-splitter
(in reverse) prisms -- would involve too much glass, too much expense,
and quite likely too much light loss and/or contrast loss to remain
practical.

Nonetheless, it is a rather fascinating concept . . .

Sketcher
To sketch is to see.

On Fri, 09 Apr 2004 11:03:57 GMT, "Mike Ruskai"
wrote:

Has anyone ever attempted to bring the images from two separate objectives
to the same focus? Basically, the opposite of what a binoviewer does
(i.e. send a single objective's image to two separate focal planes).

There was a time when I wasted a fair amount of time working (on
paper) on such a beast. I was after the ultimate comet seeker and
realized that if I could superimpose the light paths from four
six-inch objectives it would be possible to achieve a 2+ degree true
field of view at 30x with the light grasp of a single twelve-inch
objective while maintaining an optimal 5mm exit pupil.

I was never certain I would be able to get it to work; but I
eventually became convinced that even if I could, the added optical
components -- something along the lines of rather large beam-splitter
(in reverse) prisms -- would involve too much glass, too much expense,
and quite likely too much light loss and/or contrast loss to remain
practical.

Nonetheless, it is a rather fascinating concept . . .

Sketcher
To sketch is to see.