50mm APO-Summicron - reported aperture smaller than 50mm Summilux-ASPH?

[Chazphoto]

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Hi,

Quick check to see if anyone else has noticed that the 50mm APO reports an aperture that is smaller than the 50mm Lux ASPH, when they are both set to the same stop and photographed in the same light?  I can't be at all sure, since I was only testing lenses in a shop and this is far from a controlled experiment.  I know that the reported aperture is a guesstimate, but am curious if anyone else sees the approximation being wider with the 50mm Lux ASPH than with the 50mm APO.

Is there any chance that the amount of light admitted is actually less with the APO, for each aperture?  Would the vignetting account for that?

Just curious not complaining.

Thanks

 

Chazphoto

[frame-it]

55 minutes ago, Chazphoto said:

reports an aperture

what do you mean by "reports an aperture" ?

there is no electrical connection between the lens and camera.

[Chazphoto]

Sorry for the confusion.  I meant that the aperture shown in Capture 1 Pro, or in Lightroom.  The point being that photos taken at the same aperture according to the ring on the lenses are presented as being at a smaller aperture on the APO than on the Lux.  In neither case is the reported aperture "correct" (i.e. what was set on the lens) but it is the difference between the two lenses that surprised me.  

Like I say, there was nothing controlled about the photos I took; just from the same position of the same display case, in the same lighting.  I was actually trying to see what difference there would be in resolution or anything else between the two (and there is a clear difference outside the centre of the image, even with both lenses at f5.6).  I'm in the office and don't have the information with me about the differences in apparent aperture, but can provide more details tonight.  Was wondering if anyone else had noticed a consistent pattern and had then investigated more scientifically.  

Thanks

Chazphoto

 

[TomB_tx]

I wouldn't worry about the reported aperture; as you note it is an estimate only and can be affected by a lot of things. I'd check actual transmission more by metering the same scene with both lenses and seeing what f-stop/shutter speed is selected for both. For example in manual mode set the same shutter speed and then stop down until it shows correct exposure, then note the aperture. There can still be differences, as f-stop is a geometrical calculation, while T-stop is light transmissive measurement. On Leica lenses they should be close.

[IkarusJohn]

I ignore the f/stop recorded in the EXIF data for M images.  It’s relatively meaningless.

[RexGig0]

I will join the chorus, in saying that the reported aperture often differs from the actual aperture, when using M lenses and/or M cameras. M lenses have no electronic contacts. M cameras have no electronic contacts at the lens mount.

Here is a system for recording M lens aperture data:

 

[IkarusJohn]

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There is another point here - is there a difference between f/2 with the APO Summicron and the Summilux ASPH?

While there may be variability in some lenses (particularly older ones?), I doubt this is a real possibility.  If you take an incident light reading, or carefully spotmeter as part of zone system, then you do need some confidence that the ISO setting, aperture and shutter speed are accurate, within tolerances.  With slide film and digital, those tolerances are reasonably tight.

As the lens and body on the M cameras are uncoupled (save for focus), I would expect that both bodies and lenses are pretty accurate in this respect.  The real test would be to take a test image with each lens, at the same settings, then mark or record that a particular lens under or over exposes.  Then, you could repeat that test for every aperture for every lens, and then every ISO and shutter setting for your camera.

You might find variability.  Then again, you could invest that considerable time just taking photos.

[pedaes]

18 minutes ago, IkarusJohn said:

You might find variability.

With the price of the APO, and Summilux, I would be pretty pissed if the apertures were not accurate. At this scale of minushie I would think it more likely to find variance in shutter speeds.

 

 

[IkarusJohn]

17 minutes ago, pedaes said:

With the price of the APO, and Summilux, I would be pretty pissed if the apertures were not accurate. At this scale of minushie I would think it more likely to find variance in shutter speeds.

 

 

Yeah, you’d need a controlled tested to work out which was which.  I really doubt that there is any variance in aperture sizes - it would make accurate exposure a lottery.  One of the consequences of an interchangeable lens system, with no electronic contact between the camera and lens, means the lenses have to be optically and operationally perfect, unlike the SL system where software can be used.

Completely off topic, I recall reading an article about wildlife photography.  AF and automatic triggering was relatively new, and the photographers discovered that, while the Nikons (?) they were using were accurate at 1/8000, there was a significant lag in firing the shutter.  So, a bird or whatever would fly into the spot of focus, but would fly off before the shutter fired.  The camera maker was disinterested, so they found their own solution - as I recall, the camera maker wasn’t interested in that solution either.

A very specific case, I know.  For most photographers, you anticipate the action and any built in lag, so it probably isn’t an issue.

[farnz]

5 hours ago, IkarusJohn said:

With slide film and digital, those tolerances are reasonably tight.

With due respect, John, digital: yes; print film: yes; but slide film: no.

Having exclusively shot landscapes using medium format slide film for 15 years I can confirm that slide film is unforgiving, probably because there's no 'interneg' stage, ie you're shooting positives (transparencies) so getting the exposure right in camera is crucial because it can't be tweaked or fixed like (negative) print film can during developing and printing.

Pete.

[IkarusJohn]

37 minutes ago, farnz said:

With due respect, John, digital: yes; print film: yes; but slide film: no.

Having exclusively shot landscapes using medium format slide film for 15 years I can confirm that slide film is unforgiving, probably because there's no 'interneg' stage, ie you're shooting positives (transparencies) so getting the exposure right in camera is crucial because it can't be tweaked or fixed like (negative) print film can during developing and printing.

Pete.

That's what I meant, Pete.  The tolerances with slide film are tight - ie, unforgiving if you stray; I've found digital similar, so I tend to under-expose by 2/3.

I had the unfortunate experience of using Kodachrome 64 all the way through Asia (trekking in Nepal) in 1986.  All my carefully composed images of villages had the mountains blown out.  A hard lesson!  Perhaps you're right with digital, but recovering blown highlights is also impossible.

[Chazphoto]

Hi,

Having kicked this off, I thought I should record further observations.  In short, I think that the APO-Summicron 50mm requires half a stop more exposure at f2 than the 50mm Summilux ASPH, v1.  Here are my findings.

I popped into Leica Store Mayfair today with my M10-P and 50mm Summilux ASPH (BC version 1) and borrowed their 50mm APO-Summicron.  It has been an overcast, drizzly day in London; good even, unchanging light for a test.  I took two photographs out of the window, focused on a traffic sign on the other side of the road, from exactly the same position in the shop.  First at f2 and second at f2.8 with the Summilux and then the same with the APO-Summicron.  The shutter speed on the 'Lux shot was 1/500th and on the APO shot was 1/360.  The shutter speed on the f2.8 shots were both 1/250th.  I took a further exposure at f5.6 on both lenses and the shutter speed was 1/60th.  (If relevant, no hood deployed on either lens.)

I talked with one of the staff and while talking tested the same f2 and f2.8 shots on an inside wall, which was evenly lit for one of the large black & white photos on display.  Same half stop difference in shutter speeds was observed at f2 between the two lenses and same shutter speed shown at f2.8.  The lady I was talking with suggested that this may be something to do with the firmware not recognising the new lens (which doesn't make sense given that the APO has been out for approx 10 years) and provided an M11 to test with.  That was interesting, because it defaults to multi-zone metering (I assume) and the shutter speeds were different, but the 50 'Lux required 1/640 and the 50 APO required 1/500.  

So, two cameras tested with the same lenses in two scenes and same half stop.  The accidental observation I had made a week and a bit ago and mistaken for odd reporting of the aperture in software, is harder to measure because I wasn't trying to keep the frame and exposures the same.  However, assuming there was some difference from the lenses, that was testing another 50mm APO against a regular shape 50mm Summilux, both secondhand.

I would speculate whether the vignetting observed on the APO at f2 could be causing this?  Seems too near the edges to be the cause.  The lady in the shop suggested the number of elements in the 50mm APO absorbed more light than the 50mm Summilux, which I think doesn't make sense.  My guess is that the lens is just shy of f2 fully open - a phenomenon seen with some f1.4 lenses I've had in the past, where there is not a full stop less in shutter speed when you open up.  (Not something I've tested on my 50mm Lux BC.)

Cheers

Chazphoto

[jaapv]

 

12 hours ago, Chazphoto said:

which I think doesn't make sense.

It does make sense, in fact it is the explanation. 

It is quite possible that both lenses have different t-stops.  
f-stop is a mathematical value which does not take the light transmission into consideration. t-stop is the actual light transmission of the lens. This is caused by differences in type and thickness of the optical glass.
The difference in exposure can be up to half an EV value. 
In movie use this can be quite visible, so cine lenses are usually measured in t-stops. 

https://www.dxomark.com/glossary/transmission-light-transmission/

Edit: found this simple video . Google for dozens of entries telling you the same. 

https://youtu.be/jI8uAzX0bBw

[jaeger]

On 7/17/2023 at 6:38 AM, frame-it said:

what do you mean by "reports an aperture" ?

there is no electrical connection between the lens and camera.

I think he means when both lenses are set to a same F-stop.  Summicron absorb less light and require higher ISO or slower shutter speed.

[Chazphoto]

Hi Jaap,

I'm with you on the difference between t-stops and f-stops, but didn't expect a half stop difference.  For some reason, I thought that the 50mm SPO had more elements than the 50mm Summilux, but they are both 8 in 5 groups.  Granted the lens types, thickness etc are different and therefore light transmissibility is different, but I do wonder if making the "tube" a fraction bigger wouldn't have overcome this.  I suppose that would have compromised the design goals in terms of overall size and probably complicated the optics even further.  The fact that this happens only at f2, suggested to me a mechanical rather than optical issue - but I know very little about the subject, so that is purely guesswork.

(PS: correcting the post immediately above, the Summicron absorbs more light and therefore requires a higher ISO or lower shutter speed.)  It's only half a stop however and only at max aperture.

All best

Chazphoto

[Jean-Michel]

As JAPP wrote, the f/number simply mean that the diameter of the aperture measures the focal length divided by that number; so, f/2 for a 50 mm lens just means that the diameter of the aperture is 25 mm, few if any lenses would not absorb some light. All the imprecision is adjusted in the development stage, film or digital. With slide film, you bought a few bricks of the same emulsion batch, did some clip test and, typically, would change the nominal ISO value to the “correct” one for the camera/lens combination you used.  Much the same with negative emulsions, I cannot think of a single type of film that I ever shot at the rated ISO. Same with digital, figure out what works and be done with it. 

[jaapv]

I have the impression that Leica did make the aperture slightly larger on the Summicron 35 APO, as the rated f stop is identical to the t-stop according to DXO

[Warton]

On 7/22/2023 at 4:40 PM, Chazphoto said:

Hi,

Having kicked this off, I thought I should record further observations.  In short, I think that the APO-Summicron 50mm requires half a stop more exposure at f2 than the 50mm Summilux ASPH, v1.  Here are my findings.

I popped into Leica Store Mayfair today with my M10-P and 50mm Summilux ASPH (BC version 1) and borrowed their 50mm APO-Summicron.  It has been an overcast, drizzly day in London; good even, unchanging light for a test.  I took two photographs out of the window, focused on a traffic sign on the other side of the road, from exactly the same position in the shop.  First at f2 and second at f2.8 with the Summilux and then the same with the APO-Summicron.  The shutter speed on the 'Lux shot was 1/500th and on the APO shot was 1/360.  The shutter speed on the f2.8 shots were both 1/250th.  I took a further exposure at f5.6 on both lenses and the shutter speed was 1/60th.  (If relevant, no hood deployed on either lens.)

I talked with one of the staff and while talking tested the same f2 and f2.8 shots on an inside wall, which was evenly lit for one of the large black & white photos on display.  Same half stop difference in shutter speeds was observed at f2 between the two lenses and same shutter speed shown at f2.8.  The lady I was talking with suggested that this may be something to do with the firmware not recognising the new lens (which doesn't make sense given that the APO has been out for approx 10 years) and provided an M11 to test with.  That was interesting, because it defaults to multi-zone metering (I assume) and the shutter speeds were different, but the 50 'Lux required 1/640 and the 50 APO required 1/500.  

So, two cameras tested with the same lenses in two scenes and same half stop.  The accidental observation I had made a week and a bit ago and mistaken for odd reporting of the aperture in software, is harder to measure because I wasn't trying to keep the frame and exposures the same.  However, assuming there was some difference from the lenses, that was testing another 50mm APO against a regular shape 50mm Summilux, both secondhand.

I would speculate whether the vignetting observed on the APO at f2 could be causing this?  Seems too near the edges to be the cause.  The lady in the shop suggested the number of elements in the 50mm APO absorbed more light than the 50mm Summilux, which I think doesn't make sense.  My guess is that the lens is just shy of f2 fully open - a phenomenon seen with some f1.4 lenses I've had in the past, where there is not a full stop less in shutter speed when you open up.  (Not something I've tested on my 50mm Lux BC.)

Cheers

Chazphoto

half stop?! You gonna be kidding me. If that were true, you would have noticed the aperture size difference just by looking at it. You don't even need to do any test to figure out a 1/2 stop difference in aperture. Even sloppiest lens maker in this world would not make this kind of mistake.

it's a 50mm lens, meaning at f/2 the diameter is 25mm; at f/2.8 the diameter is 17.9mm; half stop between is around f/2.4 which is almost 21mm.

You cannot tell the difference between 25mm and 21mm side by side? Sorry, I cannot believe this.

Edited July 23, 2023 by Warton

[Chazphoto]

Jaap, did you also see an F stop to T stop comparison on DXO for the 50mm APO?  Would be curious to see if my observations are borne out.

For those writing about the real-world significance or getting exercised about it, I'm not on the same page as Jean-Michel.  Useful to know, but once known you deal with it - and it is mostly not relevant.

Thanks

Chazphoto

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[hmzimelka]

10 hours ago, Warton said:

half stop?! You gonna be kidding me. If that were true, you would have noticed the aperture size difference just by looking at it. You don't even need to do any test to figure out a 1/2 stop difference in aperture. Even sloppiest lens maker in this world would not make this kind of mistake.

it's a 50mm lens, meaning at f/2 the diameter is 25mm; at f/2.8 the diameter is 17.9mm; half stop between is around f/2.4 which is almost 21mm.

You cannot tell the difference between 25mm and 21mm side by side? Sorry, I cannot believe this.

A lens with a designated f-stop of f/2 doesn't mean it has a t-stop of 2. 

A 50/1.4 at f/2 setting can have more light transmission than a 50mm f/2 at the centre of the frame, because the 50/2 lens may have a t-stop of 2.5 or worse.

My ZM Planar 50mm produces a brighter image centre at f/2 than my Summicron 50mm V at f/2. Probably around 1/3 stop difference. 

Edited July 24, 2023 by hmzimelka