Anyone suspect the Voigtlander 35mm f1.4 MC might be slower than rated?

[ckuang]

Hey guys, recently I've been doing lots of exposure tests with the voigtlander 35mm F1.4 MC and was wondering if anyone felt that the speed of the lens rated at F2.0 and F1.4 might in actuality be half a stop slower with a true rating of around F1.8 and F2.4? At 2.8 and beyond the rating seems accurate.

While it doesn't make a considerable difference when shooting negative film, i'm finding that it makes quite a big difference when shooting on the M8/M9. Am I the only one finding this characteristic with the lens?

[ampguy]

One review of the lens estimates the speed of this lens is 1.5 or 1.6.

I've asked a few times if someone with the lens could tell me if the shutter speed on their AE doubled from f2 to 1.4 when metering an evenly lit subject like a wall or something. Never got an answer.

[maggieo]

Originally Posted by ampguy

One review of the lens estimates the speed of this lens is 1.5 or 1.6.

I've asked a few times if someone with the lens could tell me if the shutter speed on their AE doubled from f2 to 1.4 when metering an evenly lit subject like a wall or something. Never got an answer.

Just did that a few seconds ago and got this result from my M8:

f2 @ 1/1000 sec.

f1.4 @ 1/2000 sec.

[ampguy]

That clears that up, it appears to truly be a 1.4 lens.

Originally Posted by maggieo

Just did that a few seconds ago and got this result from my M8:

f2 @ 1/1000 sec.

f1.4 @ 1/2000 sec.

[maggieo]

Yep. Just tried it again and got the same results. It's a pretty great lens, IMO. As long as you don't get a lemon.

[ampguy]

Just have to sell some other stuff first. Oh, and hope for some luck ... to avoid a lemony one

Originally Posted by maggieo

Yep. Just tried it again and got the same results. It's a pretty great lens, IMO. As long as you don't get a lemon.

[ampguy]

But as long as the 1.4 setting is letting in approximately twice the light as f2, as seen by a Leica M8 or M6 meter, that's a step in the right direction.

Originally Posted by photomoof

The f-stop is a purely mathematical focal ratio, and is very likely correct.

However lenses exhibit variation in transmission, so all lenses also have a T-stop. Just how close the t-stop is the f-stop is a product of coatings, number of elements, air surfaces.

[ckuang]

Maggieo, yes, the shutter speed would be right if you're only measuring it relative to each other ie, if the lens is really a 1.8 vs a 2.4. to test it properly, you'll need to measure it versus a light meter, and also whether there is a full 2 stop difference between 1.4 and 2.8 and if that difference is also reflected in the histogram. Or maybe i just got a lemon of a lens.

[ckuang]

oh also forgot to elaborate, that for my lens, at 2.8 the lens measures up correctly at 2.8, however, at 2.0 and 1.4, it seems like the true speed of the lens is actually slower than the rated speed.

[ampguy]

Can you elaborate? Is it like 1/3rd stop slow?

Do you have any Leica, Canon, or Nikon 1.4 lenses to compare 1.4 and 2 with?

Thanks.

Originally Posted by ckuang

oh also forgot to elaborate, that for my lens, at 2.8 the lens measures up correctly at 2.8, however, at 2.0 and 1.4, it seems like the true speed of the lens is actually slower than the rated speed.

[maggieo]

Just FTR...

My first copy of the Nokton 35/1.4 was a lemon. See Sean Reid's test of the lens- mine one of the ones he tested. Stephen Gandy graciously exchanged my first copy for my current one, which has proved to be a gem.

[ckuang]

yeah it's official, F2.0 on my voigtlander is about half a stop under compared to my Leica 90mm AA. It's also half a stop under when measured against my light meter. I wonder what causes this?

[gliderbee]

Originally Posted by maggieo

Just did that a few seconds ago and got this result from my M8:

f2 @ 1/1000 sec.

f1.4 @ 1/2000 sec.

I'm not sure these data are valid: I think these are the shutter speeds indicated by the camera. You should take a picture and have a look in the EXIF for the real shutter speed used by the camera.

Stefan.

[ampguy]

The t-stop is the actual corrected transmission of light.

The f-stop is just a calculation of focal length div by entrance pupil.

I am not expecting any 1.4 lens to equal another in t-stop, at least measurable.

But I have been wondering how the relative CV 1/4's 1.4 f-stop is in relation to a) it's own settings at f2, 2.8, etc.

and b) other rf lenses.

It's possible they did not accurately measure the area of the aperture's 10 blades with corrections for an imperfect circle at all settings, or just rounded for convenience.

Originally Posted by ckuang

yeah it's official, F2.0 on my voigtlander is about half a stop under compared to my Leica 90mm AA. It's also half a stop under when measured against my light meter. I wonder what causes this?

[Sparrow]

Why is it Cosina attracts these “damn with faint praise” type threads? surely all lenses must be slower than the calculated speed

[Brian Sweeney]

Pop Photo used to give marked F-Stop, measured F-Stop, and Measured T-Stop for lenses. Some manufacturers were spot-on with marked and measured F-Stop, others were a bit looser. For example, the Nikon 55/1.2 was a measured F1.2 and a T-Stop of T1.25. Other manufacturers, Olympus, were closer to F1.3.

[hans voralberg]

If you find it a half stop slower pump up the ISO or shutter speed? What's the fuss?

[Turtle]

Originally Posted by hans voralberg

If you find it a half stop slower pump up the ISO or shutter speed? What's the fuss?

I suppose the fuss is that if you buy a CV f1.4 lens to conquer low light and find it gives the same shutter speed indication as another lens (say Leica) would at f1.8, then you are not getting all the light sucking ability of a true 1.4. Even if a lens halves the exposure between f2 and 1.4 does not mean it is actually letting in as much light at these marked f stops as another lens - just means the f stops are a stop apart.

This would mean that, if correct, a Leica at f1.4 would indicate a shutter speed 1/2 stop faster than the CV because more light would be hitting the sensor, allowing you to shoot in light a 1/2 stop dimmer before getting camera shake. Whether this is the real situation with this lens or not I have no idea, but I suspect this is the concern.

I would be gutted if I bought a 1.4 lens and found it was only admitting half a stop more light than my f2 lenses. Kinda defeats the object!

[LeicaFoReVer]

that is the price you pay. I bet leica glass has better transmissions compared to other brands...On the other hand who needs that sensitivity?

Someone can make a test to be more scientific. I bet the difference will be small.

[ampguy]

then why not just mark the lens as 35/1.7 (or whatever) so someone with a mixed bag of lenses can know where the 35/1.7 fits in with the other glass?

I'm wondering if the glass used varies so much, that sometimes with really clear glass, or the SC version, it transmits light with a t-stop of ~ 1.4, but with some of the more opaque samples of glass they get, or maybe the MC version, it's more of a t-stop of 1.7 or 1.8.

In any case, shouldn't the ring (it has detents, right) stop at relative stops to each other? It sounds like it doesn't??

Originally Posted by LeicaFoReVer

that is the price you pay. I bet leica glass has better transmissions compared to other brands...On the other hand who needs that sensitivity?

Someone can make a test to be more scientific. I bet the difference will be small.

[Sparrow]

Originally Posted by ampguy

then why not just mark the lens as 35/1.7 (or whatever) so someone with a mixed bag of lenses can know where the 35/1.7 fits in with the other glass?

I'm wondering if the glass used varies so much, that sometimes with really clear glass, or the SC version, it transmits light with a t-stop of ~ 1.4, but with some of the more opaque samples of glass they get, or maybe the MC version, it's more of a t-stop of 1.7 or 1.8.

In any case, shouldn't the ring (it has detents, right) stop at relative stops to each other? It sounds like it doesn't??

Do you think it could be that Cosina are simply following the precedent set by the European manufactures over the previous two centuries? It would seem a particularly stupid commercial strategy to not follow Leica's established practice don't you think?

P. S. clearly the MC version would transmit more light than the SC one anyway

[ckuang]

Interestingly in Steve Huff's review of the lens, he notes that it also tends to underexpose by a stop on the M9. I'm not sure if he means it literally underexposes or it underexposes relative to another lens of his which is rated at F1.4. Don't get me wrong the Voigtlander is a good lens. Unfortunately for me, on digital and chrome half is stop is a big deal, and given the number of images I need to shoot a week half a stop difference can make hours of difference in post production.

[Sparrow]

Originally Posted by ckuang

Interestingly in Steve Huff's review of the lens, he notes that it also tends to underexpose by a stop on the M9. I'm not sure if he means it literally underexposes or it underexposes relative to another lens of his which is rated at F1.4. Don't get me wrong the Voigtlander is a good lens. Unfortunately for me, on digital and chrome half is stop is a big deal, and given the number of images I need to shoot a week half a stop difference can make hours of difference in post production.

As I said, why is it Cosina attracts these “damn with faint praise” type threads?

[ampguy]

I'm not sure I follow, are you saying that other manufacturers are over-rating their f/t stops by 1/3 or 1/2 or more stops? Who? Are my Summiluxes really 1.8 or something?

What about when a lens is compared to another lens and at same f stop, has t stop 1/2 stop lower?

You're following the thread here, I presume??

Originally Posted by Sparrow

Do you think it could be that Cosina are simply following the precedent set by the European manufactures over the previous two centuries? It would seem a particularly stupid commercial strategy to not follow Leica's established practice don't you think?

P. S. clearly the MC version would transmit more light than the SC one anyway

[Sparrow]

Originally Posted by ampguy

I'm not sure I follow, are you saying that other manufacturers are over-rating their f/t stops by 1/3 or 1/2 or more stops? Who? Are my Summiluxes really 1.8 or something?

What about when a lens is compared to another lens and at same f stop, has t stop 1/2 stop lower?

You're following the thread here, I presume??

Well, let me explain more clearly, for hundreds of years the lens speed has been expressed as the ratio of focal-length divided by the diameter of entrance pupil, Zeiss, Leica and Voigtländer traditionally used that ratio to express lens speed.

Clearly that is not an expression of light transmission, if your lenses are physically f1:1.4 then they cannot be t1:1.4 as some light is, no must be, absorbed and some reflected by the glass and it's coatings. Are you understanding it so far?

My point is not that, but, why is Cosina being required to reach a standard higher than the traditional manufactures? and why do we get these threads which while purport to be one thing but are in fact simply inviting criticism of the only company who is providing us with entry level RF equipment?