schneider componon s 50/2.8

[whojammyflip]

Hi, I've had a componon s cleaned up. Trouble is that its a lot faster than my other lenses, as in almost 2 stops faster, which means at f16 its really f8. I've sent it back to the guy who fixed it, and he says he cannot see how to adjust the blades, and that there is likely no way to adjust them. I can understand a lens being out by a bit, but almost two stops seems ridiculous. I've measured this using a EM10 and three other lenses for benchmarks. Anyone taken one of these apart? Can anyone advise as to whether I am having my chain yanked, or whether its really true. I am wondering whether he replaced the blades last time with blades from a different lens. I am a bit gutted about this, as the lens cost 30 quid and having it cleaned cost 30 quid....

 

[Rick A]

How did you verify the blade settings and compare them to other lenses? F numbers are a product of dividing the objective lens diameter by the actual diameter of the aperture setting. You really cannot compare one lens against another and declare it off. Two different make lenses will have diferent lens diameters and hence different amounts of light passage. True, the componon may act as if it's two stops faster than a comparable lens, but it may have a much larger front lens and allow more light through naturally.

 

[pstake]

I don't know a whole lot. Rick is sure to know more than me. But I believe the Schneider coatings also are designed to maximize the efficiency of light transmission. If the Componon was recently cleaned and the other two (benchmark lenses) were not, the superior coating and clean glass might account for more light transmission ... maybe?

 

[Rick A]

You make a good point.

 

[octofish]

hold on this is freaking me out...

If f stops mean different things in terms of brightness on different lenses, what's the baseline that light meters are referring to? how is it possible to ever get a proper exposure?

Can you count on nothing in this world any more? Oh the humanity!

 

[Gerald C Koch]

The Schneider Componon lenses are designed so that the iris is not fully open even when the lens is at its widest f-stop. Even when your lens is opened to f2.8 it should look as if it is stopped down a stop or so. Perhaps your lens was incorrectly re-assembled after cleaning. If it was incorrectly adjusted to be fully open at f2.8 then this would explain the greater speed.

 

[MattKing]

hold on this is freaking me out...

If f stops mean different things in terms of brightness on different lenses, what's the baseline that light meters are referring to? how is it possible to ever get a proper exposure?

Can you count on nothing in this world any more? Oh the humanity!

That is why cinematographers use T-stops.

Light transmission will definitely vary with condition.

That is one of the reasons why particularly careful photographers will use different EIs with different camera lenses.

But 2 stops seems a lot - I would suspect a problem with re-assembly.

The aperture scale may have been aligned incorrectly.

 

[whojammyflip]

A lens f stop refers to the ratio of the diamter/length ratio. Therefore (less transmission losses which in MC primes is about 1%) same focal length lenses with same f stops transmit the same amount of light. Otherwise ISO settings on cameras would need adjusting for every lens.

All the lenses were mounted to the enlarger with the same light setting, at f8 and an EM10 lightmeter was placed on the baseboard to verify matching intensity. A Nikon 50/2.8N, Vivitar VHE 50/2.8 and Minolta CE 50/2.8 all agreed with each other.

The Schneider didn't. It required f11+1/2 stop to hit the equivalent to the f8 on the EM10. I am pretty annoyed about this, as it means I cannot use f11 or f16 for accurate timing of test strips etc. I guess in the end, I can just send it to another shop and get my money back from the first guy if he has damaged it.

 

[ic-racer]

It required f11+1/2 stop to hit the equivalent to the f8 on the EM10.

And before you sent it to be cleaned it measured the same as the others?