Rank Taylor Hobson Varotal ??
Henry Kolesnik
wonder if someone can shed some light on it. But first I apologize if I've
cross posrted to the improper groups.
On the front barrel the inscription reads: TV Lens Made in England by Rank
Taylor Hobson VAROTAL V 1.6 INCH ( 40 mm - 400mm) f/4 T 4.5.
On the rear it has VAROTAL IX 21 mm- 210mm (0.83 INCH - 8.3 INCH) f/2.
I was told it was from an old color TV camera and cost a small fortune.
I'm interested in making it into a telescope if I can find the right
eyepiece, preferably one to make an upright figure. Am I wasting my time?
If there's a more appropriate group for this question please let me know.
tnx
--
73
Hank WD5JFR
John Savard
wrote, in part:
>On the front barrel the inscription reads: TV Lens Made in England by Rank
>Taylor Hobson VAROTAL V 1.6 INCH ( 40 mm - 400mm) f/4 T 4.5.
It is, of course, a zoom lens.
Could you make it into a telescope?
Certainly; 400mm is a respectable focal length for a telescope, and the front
area of even a tiny vidicon tube is large enough to cover the active area of a 1
1/4" eyepiece.
But a zoom lens has *lots* of elements and internal refractions; thus, it is
hardly an optimal choice for a telescope objective. Still, one is putting the
lens to some good use.
From Google, I see that...
http://www.cookeoptics.com/cooke.nsf/history/1980
a 25 - 250mm lens of this general type was used to film the Superman movie. Such
lenses apparently go for $2,000 or thereabouts on eBay even today. But the ones
for TV use may be less valuable, possibly having a simpler design since their
required resolution is much lower.
John Savard
http://home.ecn.ab.ca/~jsavard/index.html
Isaac Wingfield
"Henry Kolesnik" <kole...@sbcglobal.net> wrote:
RTH made some of the earliest TV "zoom" lenses (the other big name was
"Zoomar" IIRC). As a variable focus lens, it has a lot of pieces of
glass in it, so I suspect it loses a lot of light, and scatters a bit,
too.
It might work well if you stuck a 35mm body behind it; I think the
imaging area on early camera tubes were similar in size.
Isaac
RolandRB
I know just a little bit about this so I am happy to be corrected. I
don't know of eyepieces that will put the image back upright. Hope you
can find one. But the trouble, I think, with what you are planning to
do is that you are using a very good lens that will give a sharp
picture and a flat field over quite a wide area and yet you will be
using an eyepiece that covers a tiny part of that imaging area. So you
will have a good but maybe bulky lens and you will only be able to use
about 2% of its capability. You will have a zoom telescope, which is
nice, but how will you adjust it while using it? It will be awkward to
twist the front of the telescope which you are looking through the
eyepiece. And you can change the magnification of a fixed lens
telescope, in any case, by having a set of eyepieces of different
focal length.
If I had such a lens I would be thinking of how to attach it to the
front of an SLR camera. Maybe a 35mm format M42 mount camera, if it
will cover that area. And then I would have to think whether the
aperture could be coupled with the camera shutter release.
Phil Wheeler
to achieve a zoom telescope is by using a zoom EP vs. a zoom objective.
Phil
Lassi Hippeläinen
<...>
> If I had such a lens I would be thinking of how to attach it to the
> front of an SLR camera. Maybe a 35mm format M42 mount camera, if it
> will cover that area.
I doubt that it would focus to infinity with an SLR. Probably its
registration distance is pretty short. A rangefinder would work, but how
can you focus and frame with it? So it seems that only a digicam with an
LCD is feasible.
That also means that image inverting prisms (like in binoculars) won't
work. A custom eyepiece with two lenses (one inverting, one viewing)
would be needed to make a terrestial telescope.
To get forward, it would be nice to know the registration distance and
the circle of sharpness.
-- Lassi
Paul Friday
Wingfield <i...@witzend.com> writes
>As a variable focus lens, it has a lot of pieces of
>glass in it, so I suspect it loses a lot of light, and scatters a bit,
>too.
But if it's an F4 lens with T4.5 stamped on it, it's losing less than a
third of a stop. Aren't T numbers actual transmission, rather than F
numbers which are calculated?
--
----------------------------
Paul Friday
Mark W. Lund, PhD
However, F numbers can tell you the exit cone size, with T numbers
you can only guess.
Best regards
mark
--
----------------------------------------------------------------------
Mark W. Lund, PhD ** Custom Battery Chargers
CEO ** Bulk Cells and Custom Battery Packs
PowerStream Technology ** Custom Power Supplies
140 S. Mountainway Drive ** DC/DC Converters
Orem Utah 84058 ** Custom UPS
http://www.PowerStream.com ** Custom power management electronics
Alternate e-mail address las...@netscape.net
RolandRB
Could you please put a ground glass screen behind your lens and focus
an image on it and tell us the diameter of the circle it covers
without edge falloff?
If we know that then we can give you better advice.
Henry Kolesnik
Thanks for the suggestion. I don't have a ground glass except in my Nikon
SLR and I'd like to know where I can find one so I can do the test. Any
tips appreciated.
--
73
Hank WD5JFR
"RolandRB" <rolan...@hotmail.com> wrote in message
news:52970945.04072...@posting.google.com...
k
> Roland
> Thanks for the suggestion. I don't have a ground glass except in my Nikon
> SLR and I'd like to know where I can find one so I can do the test. Any
> tips appreciated.
scratch up a CD cover with fine sandpaper and use that :-)
btw, I too have one of these lenses and found the image circle to be ample for
35mm and the registration distance is longer than found on any 35mm camera.
I spoke to a TV tech who actually worked on such a lens/TV camera many years
back and her words were that the tube was substantially bigger than the 35mm
format.
I also notice that there are thorium elements in this lens .. you have the
concave front element right?
karl
Henry Kolesnik
a tripod. I can rotatye the iris for the f stop but I'm not sure what the
zoom mechanism is.
--
73
Hank WD5JFR
<fela...@PING.com> wrote in message
news:410b7bea$0$16318$5a62...@per-qv1-newsreader-01.iinet.net.au...
Dan Fromm
Henry, its really hard to tell what you have from your description,
but you may well have a really fine zoom lens, one of a group of
lenses for which G. H. Cook, Taylor Hobson's chief designer, was
awarded a technical Oscar. THOSE Varotals have extraordinarily high
resolution, no chromatic aberration, and are distortion free. Not
only that, they cover at least 35 mm still.
Even so, I think you'd be best off selling it and getting a decent
telescope.
Cheers,
Dan
k
"Dan Fromm" <daniel...@att.com> wrote in message
news:d32d23bf.0407...@posting.google.com...
> > You are right the front element is concave.
yay! you have one impressive lump of glass there, thorium elements and all :-)
>>This unit is "hose clamped" to
> > a tripod. I can rotatye the iris for the f stop but I'm not sure what the
> > zoom mechanism is.
it's internal and connects through one of those lumps on the side of the lens -
both have holes in the back through which the focus and zoom controls are
connected. they are a pair of cables which terminated in rotating handles, I
haven't got a set either but with a bit of machining and fiddling alternative
methods can be set up.
> > > I also notice that there are thorium elements in this lens .. you have the
> > > concave front element right?
> Henry, its really hard to tell what you have from your description,
> but you may well have a really fine zoom lens, one of a group of
> lenses for which G. H. Cook, Taylor Hobson's chief designer, was
> awarded a technical Oscar. THOSE Varotals have extraordinarily high
> resolution, no chromatic aberration, and are distortion free. Not
> only that, they cover at least 35 mm still.
yup, it sounds very much like one of THOSE Varotals :-)
>
> Even so, I think you'd be best off selling it and getting a decent
> telescope.
I can't comment on it's appropriateness as a telescope so Dan's advice may be
the best, however if you've got the lens already and you're just wanting to
press it into service.. ?
k
Henry Kolesnik
with the paper flush against the rear of the lens. Later I used a piece of
opaque vinyl (Ziplok freezer bag) and it looks like the cirlce of focal is
flush with the rear element holder. The focused image is about 42mm in
diameter as best I can tell the image is the size of the rear element. It's
inverted.
--
73
Hank WD5JFR
"Lassi Hippeläinen" <lahi...@ieee.orgies.invalid> wrote in message
news:40FF896B...@ieee.orgies.invalid...
RolandRB
the image to the lens is going to be a major stumbling block.
"Henry Kolesnik" <kole...@sbcglobal.net> wrote in message news:<0pTPc.1899$xZ....@newssvr23.news.prodigy.com>...
Lassi Hippeläinen
>
> I just tried to focus it on a white piece of paper and it appears to focus
> with the paper flush against the rear of the lens. Later I used a piece of
> opaque vinyl (Ziplok freezer bag) and it looks like the cirlce of focal is
> flush with the rear element holder. The focused image is about 42mm in
> diameter as best I can tell the image is the size of the rear element. It's
> inverted.
To invert the image, your only choice is an extra inverting lens. The
ocular will be focused to the place where the image from the inverter
is. The inverter should have as short focal length as possible, because
the "eyepiece" will be one ocular + four inverter focal lengths long. I
don't know where to get an eyepiece like that off the shelf, but it is
buildable. Magnification will be the ratio of the focal lengths of the
zoom and the ocular.
You can still use it as an "astronomical" telescope (i.e. with inverted
image). Just focus your eye through the ocular to the rear surface of
the lens, where the image is formed.
-- Lassi
brian
> You have just enough to cover a 35mm format frame but the closeness of
> the image to the lens is going to be a major stumbling block.
>
>
Depending on the exit pupil location the OP might be able to cobble
together an excellent relay from a pair of face-coupled 35mm SLR
lenses. A single macro lens might also do the trick.
Henry Kolesnik
tnx
--
73
Hank WD5JFR
"brian" <brian...@aol.com> wrote in message
news:3c459ba.04080...@posting.google.com...
Louis Boyd
> What's an optical relay?
It's a set of lense which form a new image. The erector assembly in a
rifle scope is an example. Unfortuantely such a set of lenses which
will work on a fast camera lens would be as expensive and complex as the
lens itself, and more difficult to find surplus.
jjs
> What's an optical relay?
A relativistic Olympic event.
Dan Fromm
Um, Brian, the Vade Mecum, which has errors large and small, reports
seeing a Tayor Hobson brochure with a figure of a Varotal mounted on a
35 mm camera. No mention of which Varotal or camera, though.
I'm a little confused about the unit being described because it
doesn't quite conform to what I thought I knew about them. Should, I
think, be a prime lens with a zoom unit behind it, and the description
doesn't sound like that. Can you tell us more about Varotals, as
opposed to general principles?
Cheers,
Dan
brian
I think I didn't explain myself clearly enough. You can easily make a
very good high speed relay using inexpensive off-the-shelf 35mm SLR
optics. For example, put two 50mm f/1.8 lenses together with a macro
coupler and you've got a very fast high quality 1:1 relay. A macro
coupler is just a simple double-sided adapter ring that screws into
the filter threads of each lens. The lenses must be placed with their
front ends facing each other in order to achieve good results.
To vary the magnification of the relay you just use two lenses having
different focal lengths. You can pick up these lenses for a song on
EBAY, and they are readily available. For eyepiece use you won't even
need all of this speed. The biggest problem is not the optics but the
mechanical interfaces. Extension tubes, together with some clever
machining and perhaps a little duct tape can work wonders, however.
Although the resulting relay system has very good image quality there
may be some problems with vignetting if you plan to use eyepieces
covering a large image circle. A custom relay solution (which really
would be expensive) would incorporate a field lens to ensure proper
pupil matching to eliminate this vignetting, but the low-cost approach
I've outlined doesn't have this luxury.
brian
I don't really know much in particular about these Varotal lenses,
except what I've read in this thread. I did look up some of Gordon
Cook's old patents (e.g. 3,594,066), some of which show 10:1 f/4
designs which would cover 24x36mm format when scaled to 40:400mm.
Oddly enough, all of these designs show plenty of BFL, contrary to the
OP's observations. Granted, you can't always rely on patent data.
One thing I can say is that the lens is almost certainly a
conventional zoom type consisting of a zoom front end followed by a
prime rear group. The reverse configuration is very rare, although it
has recently taken on much more importance. Also, I would not expect
the quality of these lenses to be very good. 1960's TV quality maybe,
but certainly not up to today's 35mm still format standards.
Dan Fromm
> daniel...@att.com (Dan Fromm) wrote in message news:<d32d23bf.0408...@posting.google.com>...
> > brian...@aol.com (brian) wrote in message news:<3c459ba.04080...@posting.google.com>...
> > > rolan...@hotmail.com (RolandRB) wrote in message news:<52970945.04080...@posting.google.com>...
> > > > You have just enough to cover a 35mm format frame but the closeness of
>
> I don't really know much in particular about these Varotal lenses,
> except what I've read in this thread. I did look up some of Gordon
> Cook's old patents (e.g. 3,594,066), some of which show 10:1 f/4
> designs which would cover 24x36mm format when scaled to 40:400mm.
> Oddly enough, all of these designs show plenty of BFL, contrary to the
> OP's observations. Granted, you can't always rely on patent data.
>
> One thing I can say is that the lens is almost certainly a
> conventional zoom type consisting of a zoom front end followed by a
> prime rear group. The reverse configuration is very rare, although it
> has recently taken on much more importance. Also, I would not expect
> the quality of these lenses to be very good. 1960's TV quality maybe,
> but certainly not up to today's 35mm still format standards.
>
> Brian
> www.caldwellphotographic.com
Thanks for the reply, Brian.
I have a TTH lens patented by G. H. Cook whose back focus don't
conform well to the patent; it seems shorter than the patent claims.
Mine is a 12"/4 telephoto, US Pat 2,660,095, and I'm very happy with
it. You've made the point before that patent data can't always be
relied on; my lens agrees with you.
It seems that Varotals were much used in motion picture production in
the '80s and were well respected. As I said, in 1989 (might have got
the year wrong) G. H. Cook was given a technical Oscar for TTH Cooke
zoom lenses, not primes.
One of the troubling aspects of the lens being discussed here is that
it seems to have come from a TV camera, not where Varotals were
normally used. TTH's lines of zoom lenses for TV cameras seem to have
been engraved Monital or Ortal, and are supposed to have been no
sharper than needed, i.e., not fit for use on film.
I think this is another instance where questions about the lens in
question are best addressed to it.
Regards,
Dan
Bandicoot
news:10h2c5p...@news.supernews.com...
ROFL!
Peter
Winfried Buechsenschuetz
> What's an optical relay?
An optical relay is an optical assembly usually not changing the size
(or the magnification) of the image, i.e. not altering the optical
characteristics of the base system, but allowing access to the image
projected by the base system.
Winfried