Reflective lenses

[bob prohaska]

Given the proliferation of small drones for observation, has any
progress been made on reflective optics for cameras? Mirrors weigh
less than lenses, usually, and drone mounted cameras seem a very
attractive application for them. Reflecting optics work in the IR,
which would seem to be an added benefit for certain applications.

Thanks for reading, and any insights!

bob prohaska

[Incubus]

Nikon had some mirror lenses, most notably the 500mm f/8. The bokeh is
very ugly and the aperture isn't variable, which is why they don't get
used.

[nospam]

In article <slrntvesic....@localhost.localdomain>, Incubus

<u953...@gmail.com> wrote:

>
> Nikon had some mirror lenses, most notably the 500mm f/8. The bokeh is
> very ugly and the aperture isn't variable, which is why they don't get
> used.

the donut bokeh is not great, but some do have a variable aperture:
<http://mirrorlens.blogspot.com/2007/09/ohnar-300mm-f56-mirror.html>

[Alan Browne]

On 2023-02-22 21:44, bob prohaska wrote:
> Given the proliferation of small drones for observation, has any
> progress been made on reflective optics for cameras? Mirrors weigh
> less than lenses, usually, and drone mounted cameras seem a very
> attractive application for them. Reflecting optics work in the IR,
> which would seem to be an added benefit for certain applications.

Most drones are quite small and so are their cameras - to the point
where any "gain" in weight savings is too small v. the limitations that
a cat lens would bring.

One point of using drones is you can get much closer to what you're
observing, most often undetected, so the need for a longer lens is less.

It's germane to note that the dominant small drone maker is DJI, a
Chinese company. They purchased a majority stake in Hasselblad in large
part to get access to their sensor and lens design expertise. This has
not yielded a cat to date that I know of.

To date the trend on such drones has been ever smaller drones and
cameras (at least for the lower end of the market).

For larger (small) drones that carry larger cameras for professional
use, (film making, defense, security, inspection etc.), including IR
sensors, they tend to go with the optics systems provided by the camera
maker. I haven't seen a cat to date (not that I've been looking very
hard at such...)

--
“Donald Trump and his allies and supporters are a clear and present
danger to American democracy.”
- J Michael Luttig - 2022-06-16
- Former US appellate court judge (R) testifying to the January 6
committee

[Whisky-dave]

On Thursday, 23 February 2023 at 15:34:41 UTC, Alan Browne wrote:
> On 2023-02-22 21:44, bob prohaska wrote:
> > Given the proliferation of small drones for observation, has any
> > progress been made on reflective optics for cameras? Mirrors weigh
> > less than lenses, usually, and drone mounted cameras seem a very
> > attractive application for them. Reflecting optics work in the IR,
> > which would seem to be an added benefit for certain applications.
> Most drones are quite small and so are their cameras - to the point
> where any "gain" in weight savings is too small v. the limitations that
> a cat lens would bring.
>
> One point of using drones is you can get much closer to what you're
> observing, most often undetected, so the need for a longer lens is less.
>
> It's germane to note that the dominant small drone maker is DJI, a
> Chinese company. They purchased a majority stake in Hasselblad in large
> part to get access to their sensor and lens design expertise. This has
> not yielded a cat to date that I know of.
>
> To date the trend on such drones has been ever smaller drones and
> cameras (at least for the lower end of the market).
>
> For larger (small) drones that carry larger cameras for professional
> use, (film making, defense, security, inspection etc.), including IR
> sensors, they tend to go with the optics systems provided by the camera
> maker. I haven't seen a cat to date (not that I've been looking very
> hard at such...)

I'd say the biggest drone with a camera that uses mirrors is the James Webb telescope.
But maybe that is pushing the definition of what a drone and a cat lens is :-)

[Alan Browne]

;-)

[danny burstein]

In <2e5a1a7f-7008-43b7...@googlegroups.com> Whisky-dave <whisk...@gmail.com> writes:

[snip]

>> For larger (small) drones that carry larger cameras for professional
>> use, (film making, defense, security, inspection etc.), including IR
>> sensors, they tend to go with the optics systems provided by the camera
>> maker. I haven't seen a cat to date (not that I've been looking very
>> hard at such...)

>I'd say the biggest drone with a camera that uses mirrors is the James Webb telescope.
>But maybe that is pushing the definition of what a drone and a cat lens is :-)

<aol> Plus one

--
_____________________________________________________
Knowledge may be power, but communications is the key
dan...@panix.com
[to foil spammers, my address has been double rot-13 encoded]

[RichA]

Most of them are pure garbage, optically. Forget the donut caused by the central obstruction, the optics themselves are almost uniformly awful.
Excepts are Tamron 350mm f/5.6, Olympus 500mm f/8, Questar 700. But those lenses cost what good lenses do. I got a no-name mirror to play with at a recent camera show for $10 and I wouldn't wish
it on any camera, even if it only had one pixel.

[-hh]

It also did what drones do, which was to “zoom with your feet”, rather than a longer lens,
which in this case was to move just far enough away to get out of the atmosphere and
also into a slower moving orbit than what Hubble has.

-hh

[Alan Browne]

Webb is placed to avoid thermal radiation from the earth and moon. That
is the reason they placed it around L2. This has no "gain" in terms of
zoom compared to Hubble. Its orbit about the L2 is considerably large -
the main benefit being that it is never in the Moon's or Earth's shadow
(thermal stability (constant sun load on the shield)).

[bob prohaska]

[regarding reflective objectives for cameras]

>
> Most of them are pure garbage, optically. Forget the donut caused by the central obstruction, the optics themselves are almost uniformly awful.
> Excepts are Tamron 350mm f/5.6, Olympus 500mm f/8, Questar 700. But those lenses cost what good lenses do. I got a no-name mirror to play with at a recent camera show for $10 and I wouldn't wish
> it on any camera, even if it only had one pixel.

8-)

But, reflective optics in the form of a three mirror anastigmat appear
to offer the best of all worlds: no distortions and wide spectral limits.
In principle they can be lightweight as well, which really matters on a
drone. True, they don't zoom, but drones are free to move.

Admittedly the tooling costs for aspheric optics are high, but production
is cheap(ish) and the ability to image from near UV to IR limited only
by the detector and maybe diffraction would seem seem to offer vast
advantage, exemplified by seeking/tracking imagers for weapons.

Way back when, the only usable materials for refractive IR optics were
things like germanium, or binary compounds like zinc selenide, only a
few of which would even transmit shorter wavelengths. Has that limitation
been overcome?

Thanks for reading,

bob prohaska

[Alan Browne]

On 2023-02-26 19:14, bob prohaska wrote:
> [regarding reflective objectives for cameras]
>>
>> Most of them are pure garbage, optically. Forget the donut caused by the central obstruction, the optics themselves are almost uniformly awful.
>> Excepts are Tamron 350mm f/5.6, Olympus 500mm f/8, Questar 700. But those lenses cost what good lenses do. I got a no-name mirror to play with at a recent camera show for $10 and I wouldn't wish
>> it on any camera, even if it only had one pixel.
>
> 8-)
>
> But, reflective optics in the form of a three mirror anastigmat appear
> to offer the best of all worlds: no distortions and wide spectral limits.
> In principle they can be lightweight as well, which really matters on a
> drone. True, they don't zoom, but drones are free to move.

1) As I pointed out above, as sizes get smaller, then the gain by
"getting smaller" is .... wait for it: smaller.

2) As I also pointed out, since drones are free to move, you don't need
to have long FL.

So the advantages of a cat are not appealing enough for small drones.

> Admittedly the tooling costs for aspheric optics are high, but production
> is cheap(ish) and the ability to image from near UV to IR limited only
> by the detector and maybe diffraction would seem seem to offer vast
> advantage, exemplified by seeking/tracking imagers for weapons.

As I pointed out, the optics for specialized cameras, notably IR, are
provided by the sensor maker. And again, since the drone "zooms in" to
the target, having a longer FL is less important. Further, these camera
systems are one trick ponies - they work in their little chunk of the
spectrum and so they have the optics that suit them.

> Way back when, the only usable materials for refractive IR optics were
> things like germanium, or binary compounds like zinc selenide, only a
> few of which would even transmit shorter wavelengths. Has that limitation
> been overcome?

As I pointed out, (twice) the optics for IR are provided by the sensor
maker. They don't seem to be in a rush to adopt cats.

Of course, if you believe the technical and business case favours cats,
nobody is stopping you from taking your case to DJI and the other drone
makers, or the FLIRs of the world.