Bolex Lens Conversion to Elmo GP Deluxe!

[Shane C. Collins]

I just saw one listed for sale today -- from Australia. If it wasn't twist-to-focus I may have been interested.

What confuses me is that a 1.3 prime can be just as bright as a 1.1 zoom. I know what Lipton wrote about "potential", but I don't care about "potential", I care about execution up to that potential.

Anyway, like most things, the only way to know for sure is to try something. So I believe you when you say they are about the same brightness.

The 1.3 prime has less glass compared to a zoom. This translates to less light refraction, and more light is transferred onto the screen. The more glass elements within a given lens will cause this issue. A better quality 1.0 zoom, and you won't notice this as much. The one thing I've always noticed about the Bolex 1.3 primes, is their ability to hide imperfections from the film itself. A 1.3 lens will do this more than say a 1.0 or 1.1, etc. The Suprovar 1.0 zoom I use on the 709 does a pretty good job, and is extremely sharp. However, any time a film imperfection runs pass the gate I can usually notice it for a split second or so. Not something that would normally bother me, but it's there. I noticed last night, while using the 1.3 prime, the film I was using normally has a split second clinch or imperfections. I did not notice them this time around.

[Brian Harrington]

I guess I really don't understand those f-stop #s since I thought the higher the #, the less light is let through. If more glass in a zoom lets less light through you would think that the f-stop # would be higher then. I thought, incorrectly I guess, that the f-stop # was a measure of the amount of light allowed to pass through the lens.

I have noticed that my Elmo 1.1 shows lines on the screen very well, whereas a lesser 1.3 hides them a bit -- the price you pay for a better lens is you see more imperfections! I hear that from audiophiles all the time when talking about recordings. They claim to hear things that I can't hear on my modest equipment. And what they hear is not always good!

[Brian Fretwell]

The f-stop rating is a mechanical ratio of the focal length to the physical aperture of th elens. You need the professional T-stop rating (which is never shown, except for camera lenses on 16 and 35mm pro gear) to show the light transmission.

[Brian Harrington]

Figures -- why give customers the spec that really matters? Thanks for that -- I had always assumed comparing f-stop #s was apples to apples. I guess not.

[Shane C. Collins]

Figures -- why give customers the spec that really matters? Thanks for that -- I had always assumed comparing f-stop #s was apples to apples. I guess not.

The other factor to consider with brightness is the wattage of the bulb, and how well the projector transmits this light onto the screen. The Eumig Mark S 709 with the 100 watt FCR halogen (without reflector built into the bulb), seems just as bright as the Elmo GP Deluxe with a 150 watt halogen. The 709 uses a condenser lens system that positions the beam, from the halogen bulb, directly into the aperture, and then onto the screen. This system is quite accurate and well constructed. The Eumig Mark S 810D I once owned never seemed as bright. It also used a 100 watt halogen bulb with the regular reflector.

The Elmo GP Deluxe's 150 watt bulb is bright, and very comparable to the Eumig 709. The Bolex 'hifi" 1.3 prime is bright, as mentioned in an earlier post, but I'll have to see how it compares to the Eumig 1.0 Suprovar zoom. Obviously the 1.0 should be brighter with a side by side comparison.