Zoom Converters (ISCO and others)?

[Ryan Gallagher]

These seem fairly rare, but I've been tempted by a couple used units... to have in a personal kit.

What are the pros/cons? I assume less light because of more optical elements, and perhaps some sharpness loss compared to the prime by itself?

From photos ISCO at least seemed to make a couple variants...

I've seen two variations from ISCO: the "Ultra-Star HD Zoom Converter Lens 0.65 x S" and another as "Ultra-Star HD Zoom Converter 0.65 x L" with a slightly different design.

Is one for "short" lenses and the other for "long" lenses? What would be the compatibility range on primes? What is the zoom range gain with one of these? Does adding one primarily give you range in the smaller or larger direction?

Were they strictly compatible with primes from the same lens series (Ultra-Star HD?)

At my current venue we could utilize one to perhaps push our 90mm Ultra-Star HD primes used for 1.85 to 100-105mm for our 1.66 solution? But which model?

Were there "better" zoom lenses than the ISCO Ultra-Star HD offerings?

Ultra-Star HD "S" model:
Zoom S.png

Ultra-Star HD "L" Model:
Zoom L.png

Advice appreciated before I pull any triggers on personal stuff.

[Ryan Gallagher]

I just checked my lens inventory sheet, unfortunately once again our two projectors have "personalities" in this department. Our 90mm lenses currently are a mixed pair of Ultra MC and Ultra-Star HD, one each. lol

So if they only work on HD primes, assuming they'd do the job at all, we'd have to replace our MC prime with an HD one too? And at least from a venue perspective it would probably make more sense just to buy the pair of 1.66 format primes that we lack.

But still curious about zooms from a personal kit perspective.

[Sean McKinnon]

Like you said one is better for shorter throws the other can be installed in either direction either a .65 or 6.5 (I think that’s how the math works lol) one caveat is they can introduce some pincushion distortion which may be helpful for curved screens but with anything more glass less light potentially less sharpness. But they are good to get out of vignetting or odd sizes etc…

[Ryan Gallagher]

Like you said one is better for shorter throws the other can be installed in either direction either a .65 or 6.5 (I think that’s how the math works lol) one caveat is they can introduce some pincushion distortion which may be helpful for curved screens but with anything more glass less light potentially less sharpness. But they are good to get out of vignetting or odd sizes etc…

Thanks Sean. Would my assumption be correct that if our venue's "flat" lens is 90mm and scope is 150mm already.... that the "L" (long) model is probably the more appropriate of the two?

If I wanted to use them at work anyway.

[Alan Lyman]

We are using the S-model in Imperial,with good result. A benefit is,we can match the screen with the sofar different 70mm formats.

alan

[Ryan Gallagher]

We are using the S-model in Imperial,with good result. A benefit is,we can match the screen with the sofar different 70mm formats.

alan

Nice use case. I was about suggest they might be handy for that reason in this contemporary era with labs doing weird things with under sizing modern prints. Especially useful if you don't have a full set of masking that can compensate.

I haven't considered it here b/c we have masking, and filing new plates for our keystone has always been a higher priority ticket item when we get a format we haven't seen or an oddball sizing on the print.

Also our 70mm format lensing is out in the 190mm territory... and ISCO ultra star HD doesn't really cover out there... though never tried an L model zoom on their longest lenses available.

[Ryan Gallagher]

Separately, I've also seen these "Schneider-Kreuznach 35mm VP Cinelux" zoom series lenses. They have a telephoto adjustment screw and lock on the front of the lens. But from what I have seen the intent was not to create a large zoom range, but rather a narrow zoom feature on otherwise prime lenses, permitting a bit of coverage to get sizing from "good" to "exact". All the ones I've seen listed are no more than 3mm in zoom range. So unlikely to let you double up on formats. But... perhaps useful for lab undersizing?

I've also not seen any over say 70mm at all (perhaps ultra rare?)... so maybe predominantly a short lens series, because the shorter you go the bigger an impact those jumps between primes has? Perhaps this approach permitted the series to have a lower number of primes in manufacturing?

But pretty cool feature. Never used one though. Reputationally unknown to me.

Schneider-K Zoom_adjust.pngSchneider-K Zoom_body.png

[Ryan Gallagher]

Schneider did also have an equivalent (or predecessor?) to the ISCO "L" model it seems called the "Min/Mag Focal Length Modifer".

Are these, as 65mm lenses, compatible with the ISCO HD and MC line too?

Schneider-Min-Mag.png

[Tj Hopland]

The S has a 1990's look to it and I don't recall running into those so I'm guessing what ever sort of throw issues they were designed to solve were not all that common or maybe clashed with popular models of projectors and or they were very expensive so owners didn't usually want to spend the extra money to really dial it in if they could just get close for less.


The L's have been around at least since the 1970's. I'm assuming perhaps later model gold vs black had improved coatings so maybe a little more light efficient and sharper? The black ones were known as Magnacom. That long of a run I would think would make them easier and less expensive to find so maybe you can find one of the older ones cheap as a proof of concept?

They were not usually used as a zoom, more to make a extreme for the time either long or short throw work with the usual at the time range of lenses. When you got long or short if they were even available you were introducing other issues so the issues you introduced with the L lens may have been the lesser of the evils. On the short throw side of things many of the projectors just were not designed for that so even if the lens existed there was almost no chance of the beam getting out of the front of the projector. I want to say down to 55mm you were usually pretty safe with most machines or like with a Super Simplex could take the front clamp off and get by but if you were talking like a 45 that could be a no go with some models or require a modified bushing.

They were also used at least in the USA with the earliest usually automated lens changers. Your prime lens in the projector was sized for your scope and didn't move. There was a sliding mechanism that held the anamorphic and then one of these. The L lens would blow the scope sized lens back up to the proper height to give you the a common height picture which was the more common design at the time which was the 1970's.

[Tj Hopland]

Are these, as 65mm lenses, compatible with the ISCO HD and MC line too

I think in your case of long to extremely long throws you should be fine. The compatibility comes in with the short throws where you quickly run into issues with the beam spreading too quickly and not having enough lens area to catch/pass it. Only solution to that is to make the sections (regular lens and this modifier) fit as close as possible and to make the elements of the modifier bigger. So that's where the notes about compatibility likely come in. That S lens is fairly large and short so I think that illustrates the theory nicely. Same issues happened with scope lenses on the shorter throws so that's where the integrated lenses came from, they were just trying to get things closer.

They are likely talking about basically the mechanical adapters and thread sizes needing to be compatible to get that close coupling. Once you are away from the 'big' barrel and threads which could have been SAE or metric or at least a different pitch if you are looking at older American stuff there are no real standards. If you take a less than 50 year old lens apart you will find that at some point you will have a fairly small self contained section that has the actual lens elements in it. That then threads into one or possibly several adapters to get the desired barrel size or possibly attaches to an anamorphic or what ever the final assembly is. Its this sort of raw basic lens section that doesn't likely have a common standard outside the brand or series within the brand.

I think in the later years when sub 50mm throws were getting common Schnider typically just had the 'raw' lens with no converter but Isco typically had a converter built in so to speak. Both I think offered both at least in some series and sizes but typically that was the split. The what I'm calling 'raw' lens had the possible issues with many projectors with the beam spreading too fast and hitting things like the lens barrel or the frame of the machine or another lens if it was a turret. The converter gained you a few inches of space in the projector before it started spreading and that was usually enough to work.

Later years they both had a mini zoom sort of thing that looked like a short integrated anamorphic. It would give you maybe 3-5mm worth of zoom. Where I saw these used were applications like say THX where someone was at least in theory checking how much picture cropping you had.

It was pretty rare for you to be able to find a perfect combo of flat and scope lenses with the available in 5mm or later in the short ones 2.5mm steps. if you didn't have 3 or 4 way masking many people just got close and called it good. Say the you got a 55mm scope and set your masking height for that. Calc says something like 36.3 is what you need for a full flat picture. Back when all this was still in production you could get a 35 which would be a little too tall or a 37.5 which would be too short.

At these short throws we are not talking about fuzz like you would be with a 75mm scope lens, its several inches or even feet. If it was late enough and they existed and you wanted to spend the money you could buy one of these short zoom deals which would be like a 35.6 to 38.5 sort of thing in this case and dial it right in. Super cool tech but it came fairly late in the game and wasn't cheap and we all know how many owners both large and small were when it came to spending money.

[Ryan Gallagher]

I think it was mentioned in a different thread about the older sliders run in front of a prime, one for scope attachment, and the other to make the same prime work on flat via a zoom adapter.

One such configuration is on eBay and now that I know what I’m looking at recognized that exact setup (minus the prime).

IMG_7139.jpg

[Tj Hopland]

Yep that looks like one of em. I'm not sure what brand that one was but it kinda looks like the top bar isn't threaded so that horizontal hole below the rod was maybe threaded so there was then a motor that spun a screw to do the shift. There were manual ones too but I think most people were not going to spend the extra money, if you were going to have someone go to the booth to pull a lever it wasn't that much harder to just change a conventional lens. I think I remember the manual ones still used a normal single plate which was a cost savings. Making the dual plate required modes to the trap of the projector so another additional cost to the whole process.

[Jim Cassedy]

Ryan- I've used a couple of those zoom converters as pictured in your original post in a couple
of "balcony auditoriums" at an old movie palace that had split the original balcony into two
seperate theaters. The throw wasn't particularly long, and the screens weren't huge, in fact
I always thought they could have put in bigger screens than they had. But, that being said, it
was an 'odd throw' and I guess they went with those lenses because there was no regular
lens with a focal length close to what they needed, so they went with the zooms. I don't recall
them being either good, or bad. I think it helped that the zooms were set to about their mid-range,
which probably minimized any image distortion that might have happened if zoomed either all the
way in, or all the way out. They just seemed to work well at that location. They were attached to
some mid-1960's Century 35mm projectors, with LP Associates Xenon lamphouses that somebody
had modified with larger blowers so that they could use a larger bulb than the lamphouse was
designed for. (Hey- - it wasn't my idea)

[Ryan Gallagher]

Yep that looks like one of em. I'm not sure what brand that one was but it kinda looks like the top bar isn't threaded so that horizontal hole below the rod was maybe threaded so there was then a motor that spun a screw to do the shift. There were manual ones too but I think most people were not going to spend the extra money, if you were going to have someone go to the booth to pull a lever it wasn't that much harder to just change a conventional lens. I think I remember the manual ones still used a normal single plate which was a cost savings. Making the dual plate required modes to the trap of the projector so another additional cost to the whole process.

Here is the link to more photos of that unit TJ:
https://ebay.us/m/oJi8J5

[Mark Gulbrandsen]

The problem with all Magna-Comms is one way you get Barrel Distortion, and the other way you get Pincushion Distortion. I worked for one chain a long time ago that insisted on using them with the Kelmar lens slider. Not the greatest thing in my book...