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184mm F/.9 Industrial CRT Lens by Lenzar Optics
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Craig Gerard



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PostPosted: Sun Apr 03, 2011 11:15 pm    Post subject: 184mm F/.9 Industrial CRT Lens by Lenzar Optics Reply with quote

184mm F/.9 Industrial Lens by Lenzar Optics.

Does anyone know anything about or had any experience with this industrial 'CRT' lense?

Quote:
This lens was made for taking 1:1 photos of a faint traces on CRT screens.

Whatever that means?











The last thing I need is more glass; but interesting oddities keep popping up Rolling Eyes They are selling for $30.00


Craig
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ChrisLilley



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PostPosted: Mon Apr 04, 2011 5:14 am    Post subject: Re: 184mm F/.9 Industrial CRT Lens by Lenzar Optics Reply with quote

Craig Gerard wrote:

Does anyone know anything about or had any experience with this industrial 'CRT' lense?

Quote:
This lens was made for taking 1:1 photos of a faint traces on CRT screens.

Whatever that means?


Exactly what it says. The results of some measurement are displayed on an oscilloscope and the waveform or whatever is captured by this lens.

One interesting item (besides the magnification=1, focal length and aperture) I notice it says λ = P-11. λ is wavelength, and a handy table of standard phosphor types says that P11 is a blue phosphor with a dominant wavelength of 460 nm.

Since the lens is intended to be used with a monochromatic subject, it might well show significant lateral CA or other aberrations when used with a full colour subject.
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ChrisR
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PostPosted: Mon Apr 04, 2011 5:23 am    Post subject: Reply with quote

The Nikkor CRT lens has a curved field to suit the oscilloscopes of the day apparently, though all the scopes I used were flat ( after the Cossor 1035 which was born a long time ago! ). I have a JML 55 1.2 CRT lens which also has the curved field. Perhaps the one you've found uses smaller apertures to cover the curve.

I can see the need for a wide aperture, because traces could have been feint, but nothing very remarkable in terms of resolution, because the displays weren't super-fine by any means.
1:1 would suit 5x4" film. So, no merits as a tube lens, probably!
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Lou Jost



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PostPosted: Fri May 25, 2018 7:50 pm    Post subject: Reply with quote

I just bought one of these. Very cheap. I will pick it up next month. Chris, you argued that a CRT lens doesn't need high resolution, but I am not so sure. The Nikon CRT lens has a resolution much higher than most consumer lenses. I am always an optimist about these things....especially when they are not expensive. This looks to me like a cross between a CRT-Nikkor and a Repro-Nikkor, and may be better than either one (it is faster and longer). Will report when I have it.

Craig, if you are still around, what has been your experience with this lens? (I should have asked before buying...)
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harisA



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PostPosted: Sat May 26, 2018 2:43 am    Post subject: Reply with quote

Is this having a front element with diameter of 184/0.9 =204mm?
If this is the case the lens must be really massive however this not evident from the pics here.
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Lou Jost



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PostPosted: Sat May 26, 2018 7:26 am    Post subject: Reply with quote

That relationship is not the precise definition of f-number. This lens is analogous to, and has the same proportions as, the Repro-Nikkor 85mm f/1.0.
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rjlittlefield
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PostPosted: Sat May 26, 2018 9:20 am    Post subject: Reply with quote

harisA wrote:
Is this having a front element with diameter of 184/0.9 =204mm?

Lou Jost wrote:
That relationship is not the precise definition of f-number. This lens is analogous to, and has the same proportions as, the Repro-Nikkor 85mm f/1.0.

I have never held either of these lenses in my hands. However, to clarify what I think is going on...

The effective f-number of a lens is well defined by the angle of the cone of light that it delivers to the sensor.

When a lens can be used at infinity focus, then the nominal f-number is also well defined -- it is just equal to the effective f-number at infinity focus. That number will be equal to the focal length divided by the entrance pupil diameter, which is certainly no bigger than the front element diameter and is often smaller.

However, when a lens cannot be used at infinity focus, then the nominal f-number is not so well defined and the entrance pupil may be larger than the front lens element. (In some cases it can be much larger, for example with telecentric lenses where the entrance pupil diameter is theoretically infinite!)

In this case one approach is to measure the effective F-number when the lens is used as designed, then specify a nominal F-number by inverting a classic formula like
F_effective = F_nominal * (magnification+1) , so that
F_nominal = F_effective / (magnification+1) .

I expect that is what's being done here. That is, in use, I expect the lens is delivering effective f/1.8 at 1:1, leading to a calculated value of f/0.9 for nominal f-number.

A good model may be to think of this lens as two f/1.8 lenses placed close together, with their "infinity" sides facing each other.

Perhaps Lou can tell for sure when he gets the lens in hand.

--Rik
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Lou Jost



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PostPosted: Sat May 26, 2018 9:37 am    Post subject: Reply with quote

Thanks for that clarification Rik. I'll check that out when I get it in my sweaty palms. I also have the Repro-Nikkor f/1.0 waiting for me there, a lens I have been after for years. Finally found one at a reasonable price from what seems like a trustworthy source. I think these should both be useful as relay lenses for some of my optics, as well as being interesting fast optics themselves.
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ChrisR
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PostPosted: Sat May 26, 2018 5:04 pm    Post subject: Reply with quote

Lou Jost wrote:
Chris, you argued that a CRT lens doesn't need high resolution, but I am not so sure. The Nikon CRT lens has a resolution much higher than most consumer lenses. I am always an optimist about these things....especially when they are not expensive. This looks to me like a cross between a CRT-Nikkor and a Repro-Nikkor, and may be better than either one (it is faster and longer). Will report when I have it.


I never saw a scope from "back then" which provided anything I could call fine detail - HP, Tek, Gould etc. Maybe there were special instruments.
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Lou Jost



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PostPosted: Sat May 26, 2018 5:41 pm    Post subject: Reply with quote

My recollection of scope traces is the same as yours. But these lenses were not for consumer scopes, they were apparently used to image atom bomb testing instruments, and it may be that extreme precision was important to some aspect of that. If we goofed up in the lab, the worse that would happen would be a blown capacitor or transformer. May need to be more careful when playing with atom bombs.
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ChrisR
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PostPosted: Sat May 26, 2018 8:07 pm    Post subject: Reply with quote

You need more detail if you're blowing thing up big?

Hmm, I suspect there's an unknown unknown.
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Lou Jost



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PostPosted: Sat May 26, 2018 8:27 pm    Post subject: Reply with quote

Yes, building an atom bomb probably needs more precision than building a ham radio....
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ChrisR
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PostPosted: Sun May 27, 2018 2:02 am    Post subject: Reply with quote

But an oscilloscope wasn't the way to get precise readings, and the width of the trace wouldn't need many cycles per mm to resolve it. A normal 50mm or 55mm macro (eg Micro Nikkor) would have been more than adequate - apart from being a smaller aperture, as above,

"Military" does get silly. I had a spell peering at specimens to check heat treatment of steel tubing, for a navy requirement. The manganese content was out of spec!!!

Shock Horror. The fate of the nation could depend on it?

I checked the application. It was dockside railings.
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Lou Jost



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PostPosted: Sun May 27, 2018 4:51 am    Post subject: Reply with quote

The Nikon 55mm CRT lens had a resolution of 250 lpmm which is very high indeed. I'm rooting for the military-industrial complex this time around....
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RobertOToole



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PostPosted: Wed May 30, 2018 8:16 pm    Post subject: Reply with quote

Lou Jost wrote:
Yes, building an atom bomb probably needs more precision than building a ham radio....


Hi Lou,

Glad you picked up one of these up, be sure to tell us what you find ok?

I would be careful about using certain terms nowadays Lou. I don't want to have to bail you out of the fed pen.

Robert
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