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APS-C lens on SL factor question


rafael_macia

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everything in the above 2 posts makes sense; but,

again my situation was this;

 

The short clip I noticed exposure drift (darkening of the overall image), was exposed at f11.

Zooming from 21mm to about 30mm with the Vario Elmar 3.5-4  R lens darkened the picture.

Exposure drift.

That happened because the 21-35 Vario Elmar 3.5-4 is a variable aperture lens.

A fixed aperture lens would not have darkened.

i.e.. the 35-70 or 80-200 (both f4 fixed aperture) Vario Elmars would Not have darkened.

My need is to have a wide fixed aperture zoom. I don't think Leica makes one.

That's all I am saying.....

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everything in the above 2 posts makes sense; but,

again my situation was this;

 

The short clip I noticed exposure drift (darkening of the overall image), was exposed at f11.

Zooming from 21mm to about 30mm with the Vario Elmar 3.5-4  R lens darkened the picture.

Exposure drift.

That happened because the 21-35 Vario Elmar 3.5-4 is a variable aperture lens.

A fixed aperture lens would not have darkened.

i.e.. the 35-70 or 80-200 (both f4 fixed aperture) Vario Elmars would Not have darkened.

My need is to have a wide fixed aperture zoom. I don't think Leica makes one.

That's all I am saying.....

(Bolder) This is not a valid conclusion and cannot be generalized. It so happened that that lens behaved this way. There's no way to conclude from this observation that all variable aperture lenses behave that way, or that even other examples of the same lens do. In fact, we can prove that not all variable aperture zooms behave this way by testing two other variable aperture zooms—I performed that test with both the SL24-90 and SL90-280 lenses this morning. Neither of them exhibit this behavior.

 

You should be very careful about generalizing your experiences with one lens as being applicable to the use of all lenses based on a single point of observation. There are many possible causes for the behavior... one case does not prove anything.

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(Bolder) This is not a valid conclusion and cannot be generalized. It so happened that that lens behaved this way. There's no way to conclude from this observation that all variable aperture lenses behave that way, or that even other examples of the same lens do. In fact, we can prove that not all variable aperture zooms behave this way by testing two other variable aperture zooms—I performed that test with both the SL24-90 and SL90-280 lenses this morning. Neither of them exhibit this behavior.

 

You should be very careful about generalizing your experiences with one lens as being applicable to the use of all lenses based on a single point of observation. There are many possible causes for the behavior... one case does not prove anything.

 

I was only speaking of my particular lens behaving as I described. My experience has only with that lens. I doubt other 21-35 Varios would behave differently. Why don't you give Duclos, the Los Angeles company who specializes in modifying still lenses for cine use, a call? Ask them if a variable aperture lens is a good idea for video. I guarantee they will tell you use a fixed aperture lens.

Thanks for your help in any event.

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I was only speaking of my particular lens behaving as I described. My experience has only with that lens. I doubt other 21-35 Varios would behave differently. Why don't you give Duclos, the Los Angeles company who specializes in modifying still lenses for cine use, a call? Ask them if a variable aperture lens is a good idea for video. I guarantee they will tell you use a fixed aperture lens.

Thanks for your help in any event.

I don't have to, thank you. I'm sure they're not familiar with the Leica SL and its special feature for use with the f/2.8-f/4 zoom lenses anyway. I doubt they'd ever modify one of the Leica L/SL mount lenses for cine use since these lenses are designed to be driven by the SL and T cameras with all their implied electronic control capabilities and camera-to-lens protocols; they cannot operate in any sensible way adapted to a camera that doesn't know how to control them appropriately.

 

If that's true of all 21-35 Varios, I'd call that a deficient lens design. f/11 should always be f/11, regardless of zoom setting. It is with every zoom lens I've owned. Otherwise, what's the point of using a standardized light transmission notation on the lens to set the lens opening?

 

I don't know any true cine lenses that aren't 100% manually controllable. Invariant maximum aperture was a fundamental part of cine zoom lens design from the beginning, as was parfocal design. It was only in the late 1960s that the cine zoom lens started to be applied to still camera photography, and it took essentially thirty years for it to achieve the kind of image quality that still camera users really expected out of a top notch lens, and most of those lenses have a variable maximum aperture and are not 100% parfocal either. These qualities are not very important for still photography, although they're important for cine work.

 

Leica, of course, offers a full lineup of excellent cine lenses and an adapter for the SL. If I were doing motion work professionally, I'd look into which of that range would be suitable for my uses.

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In only a couple of words:

I mentioned Duclos because I thought It would help you understand why variable aperture lenses are not suited for video.

The Vario Elmar f4 R lenses (35-70/80-200) are probably the most popular lenses for conversion.

We are in agreement that the SL and T lenses would not make sense to convert.

No ill will intended.

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In only a couple of words:

I mentioned Duclos because I thought It would help you understand why variable aperture lenses are not suited for video.

The Vario Elmar f4 R lenses (35-70/80-200) are probably the most popular lenses for conversion.

We are in agreement that the SL and T lenses would not make sense to convert.

No ill will intended.

Thank you for your good intention, Rafael, but I honestly don't need to be educated. I was doing cine work with zoom lenses as long as fifty years ago and studied the technology and practices in my class work from my first years in college...

 

No one choosing a specific zoom lens for cine work would normally choose a variable aperture, likely non-parfocal lens. I mentioned the SL's floating ISO capability simply because this is something new that I have not seen any other manufacturer offer, and it's obvious from your subsequent responses that you were unfamiliar with it. It makes the lack of constant maximum aperture with T/SL lenses used on the SL irrelevant in the case of motion capture.

 

The T system lenses would be one good choice for motion capture on the SL. There are certainly others, but I have to say that I have very little faith in the adaptation of Sigma or Canon still camera lenses for this purpose, on this camera, in anything but a fully manually operated working mode.

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everything in the above 2 posts makes sense; but,

again my situation was this;

 

The short clip I noticed exposure drift (darkening of the overall image), was exposed at f11.

Zooming from 21mm to about 30mm with the Vario Elmar 3.5-4  R lens darkened the picture.

Exposure drift.

That happened because the 21-35 Vario Elmar 3.5-4 is a variable aperture lens.

A fixed aperture lens would not have darkened.

i.e.. the 35-70 or 80-200 (both f4 fixed aperture) Vario Elmars would Not have darkened.

My need is to have a wide fixed aperture zoom. I don't think Leica makes one.

That's all I am saying.....

Maybe this explains the effect.

https://petapixel.com/2016/12/30/f-stops-vs-t-stops-difference-explained-plain-english/

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That is quite true, but it will not explain the effect on a Vario lens, as the difference between  a T-stop and an aperture value is caused by the transmission loss in the optical elements of the lens, and those will remain unaltered despite the focal length changing.

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That is quite true, but it will not explain the effect on a Vario lens, as the difference between  a T-stop and an aperture value is caused by the transmission loss in the optical elements of the lens, and those will remain unaltered despite the focal length changing.

 

I'm not an expert in opticts but maybe the transition loss varierd a little bit because the distance of the lens groups changes. But this could also be nonsense. :)

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Only nitpick with that page is this expression:

... The F-Stop is a theoretical value, while the T-Stop is an actual tested value. ...

 

The word "theoretical" isn't quite correct. They mean "calculated." There is a difference between something which is theoretical and something which is calculated. :D

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Only nitpick with that page is this expression:

 

The word "theoretical" isn't quite correct. They mean "calculated." There is a difference between something which is theoretical and something which is calculated. :D

Let's discuss this with a linguist ;)

 

 

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Ok then;

The major contributors to this thread seem to agree that there is no significant difference between a fixed aperture zoom lens and a variable aperture zoom lens.

or, in other words....

it's a non issue.

zooming does not change the exposure (exposure drift).

yes no ??

The real life situation is  ........shooting in manual exposure mode, Leica SL, manual focus.

Not shooting wide open.

 

in short again

I believe a variable aperture zoom lens in use will produce exposure drift.

Edited by rafael_macia
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Ok then;

The major contributors to this thread seem to agree that there is no significant difference between a fixed aperture zoom lens and a variable aperture zoom lens.

or, in other words....

it's a non issue.

zooming does not change the exposure (exposure drift).

yes no ??

The real life situation is  ........shooting in manual exposure mode, Leica SL, manual focus.

Not shooting wide open.

 

in short again

I believe a variable aperture zoom lens in use will produce exposure drift.

 

 

In my experience, it doesn't with any of the zooms I've owned or own. None of my Olympus, Nikon, Canon, Panasonic, or Leica SL zooms have ever shown any exposure variation as long as I wasn't using wide-open aperture. Zooming from max to min (or the reverse) focal length has never changed the exposure I set at any aperture other than settings for a larger aperture than were supported by a specific focal length. 

 

I think we've beat this horse to death now.  :lol:

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Ok then;

The major contributors to this thread seem to agree that there is no significant difference between a fixed aperture zoom lens and a variable aperture zoom lens.

or, in other words....

it's a non issue.

zooming does not change the exposure (exposure drift).

yes no ??

The real life situation is  ........shooting in manual exposure mode, Leica SL, manual focus.

Not shooting wide open.

 

in short again

I believe a variable aperture zoom lens in use will produce exposure drift.

 

One more time... Just so this horse never comes back to life....

1.YES, variable maximum aperture lenses can produce the exposure drift, as the amount of light reaching the sensor indeed changes with the focal length change. This effect is the most pronounced wide open and diminishes when stopping down.

2. YES, the variable maximum aperture lenses DO produce the exposure drift, provided they are not native SL or TL lenses.

3. The reason why the exposure stays constant with native SL and TL lenses despite their variable maximum aperture is that  SL is capable of recognizing the change and offsetting it by adjusting ISO.

 

If this summary is not clear enough, I do not know what is :D

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One more time... Just so this horse never comes back to life....

1.YES, variable maximum aperture lenses can produce the exposure drift, as the amount of light reaching the sensor indeed changes with the focal length change. This effect is the most pronounced wide open and diminishes when stopping down.

2. YES, the variable maximum aperture lenses DO produce the exposure drift, provided they are not native SL or TL lenses.

3. The reason why the exposure stays constant with native SL and TL lenses despite their variable maximum aperture is that  SL is capable of recognizing the change and offsetting it by adjusting ISO.

 

If this summary is not clear enough, I do not know what is :D

 

 

#3:  ... Not if you have floating ISO turned off. That is the configuration I used when doing my tests. 

 

I repeat: I've never seen exposure drift with any of my variable aperture zoom lenses. Never, not once in 50 years, with multiple different systems' lenses.

 

You're essentially saying the diametrical opposite of what I'm saying. I've proven to myself by testing that the zoom lenses I have now (Leica SL24-90, SL90-280, Olympus ZD 11-22, 50-200) exhibit no drift whatever. I could post the results but if there's no difference between the cases, they're not going to prove anything if you don't take my word in the first place. If you have a test clip that exhibits an exposure drift with the Leica SL lenses, with the floating ISO feature turned off, please show it. 

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One more time... Just so this horse never comes back to life....

1.YES, variable maximum aperture lenses can produce the exposure drift, as the amount of light reaching the sensor indeed changes with the focal length change. This effect is the most pronounced wide open and diminishes when stopping down.

2. YES, the variable maximum aperture lenses DO produce the exposure drift, provided they are not native SL or TL lenses.

3. The reason why the exposure stays constant with native SL and TL lenses despite their variable maximum aperture is that  SL is capable of recognizing the change and offsetting it by adjusting ISO.

 

If this summary is not clear enough, I do not know what is :D

Ok then ...... just what I was saying .... thanks!

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I'm not an expert in opticts but maybe the transition loss varierd a little bit because the distance of the lens groups changes. But this could also be nonsense. :)

iIn theory there might be a minimal change but you would never notice.
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https://vimeo.com/222892750

zooming in

https://vimeo.com/222891351

zooming out

 

the drift is best seen in the floor tiles.

 

the 21-35 is blister sharp, I put this up via Vimeo not at maximum res.

 

I notice the change, but the next person might not. I understand that.

Often with Leica lenses subtle items are not acceptable to me, but absolutely fine to the next person.

These clips show the subtle exposure drift.

Edited by rafael_macia
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