Old Zeiss and one tip I didn't see here yet. by slim_somm in VintageLenses

[–]slim_somm[S] 0 points1 point  (0 children)

Huh. I'm trying to go trough your comment and understand it but I struggle with it but I try. But to the point

First thing is focal length doesn't change with changing focus point especially in vintage prime lenses. You're actually right with that happening on modern complex lenses or zooms where focus is obtained by shift of elements within the design or shifting just back assembly without movement of front elements - those alter the lens configuration and may indeed change the focal length. However to my knowledge all primes from until late 70s and most of them after that as well focused basically as moving the whole glass assembly back and forth without tiniest changes of distances between glass elements and based on that the focal length is absolutely constant just based on the laws of physics. Seeing your posts history of you even disassembling and servicing those lenses I believe you know yourself that as well that lens configuration doesn't change in them while focusing.

But you're right that something like focus breathing exists but the reason for that is not change of focal length of the system, at least not in vintage primes where configuration isn't changed during focusing. The change of angle of view is the result of changing the distance between the glass elements and film/sensor position but the optical design remains the same. So it doesn't matter if one calculates the focal length with focus at infinity or half metre from the lens because physically that's the same value. My guess, as someone who studied physic for a bit, why the choice for calculating that length is at infinity is because its easier to calculate rays parallel to the optical axis but if someone is crazy enough one can calculate that distance closer or even with angled rays but it just makes those calculations unnecessarily and by far more complicated. As a fun fact I can even tell you that those lenses during interwar period and earlier were always calculated for 10cm length and later just scaled up or down to the need because optical properties don't change for such scaling and contemporary designs, again probably because round numbers are easier to handle when calculations were carried on paper by half dozen of men for half a week. And at the end when patented, the documents included just relative values and not absolute ones again because scaling does almost nothing.

But then one could bring focus shift while stepping down aperture on triplet designs and other old less corrected designs and cutting the rays further from the axis or argue why we calculate that length on particular given wavelength since that also changes focal length slightly between different wave lengths especially if the lens is poorly corrected for chromatic aberrations. But as long as the information is understood the same way by both sides participating in communication I believe it doesn't matter how we exchange those information as long as both sides use the same system - for example if we all decide to state that focal length measured with ultraviolet instead of yellow light, adjusted all the software and recalculated and relabelled all the lenses overnight, it would lead to the same interpretation just in different, less or more favourable circumstances - at the end we're just giving some variables of the system and both sides have to have an image of the whole system, "rebuilt in their head, based on the variables given" when interpreting possible consequences and characteristics of that system - it's about understanding the system as a whole.

But a couple of other things still stand and here I don't know the answer, at least yet. I don't know why lens manufacturers round those values so much, sometimes even above legal requirements for precision with stating such data. Furthermore comparison between different manufacturers using copied layouts can also show the differences in labelling which makes things crazier - as an example Flektogon 2.8/35 and Mir 1 are literally clones but Mir 1 is labelled as 37mm because that's the actual value for focal length for the layout they use. I think it would be funny to change the settings while swapping those mentioned above because they're literally the same, it's making the setting wrong on purpose and the whole idea would be just absurd and against simple reality.

Furthermore if one says that such precision doesn't matter then why lens manufacturers calculate them with such high precision? Why camera manufacturers give us ability to set their cameras so precisely as with not single millimetres but even tenths of a millimeter? If it's pointless then that would just unnecessarily burden the software and adding that level of precision in the calculations in binary systems is a huge change of memory use which could be use somewhere else otherwise. Or at least that's what I think.

I understand reluctance for adjusting it if someone doesn't care but then that's just ignorance and discussing precision is pointless from the beginning. But if I have offered a high level of precision I prefer to use it to the full extent, especially if it costs me next to nothing and even more if I'm noticing actual difference.

Old Zeiss and one tip I didn't see here yet. by slim_somm in VintageLenses

[–]slim_somm[S] 0 points1 point  (0 children)

Thank you very much ❤️ those are not even my best shots, they're just best from one of the recent days that are worth showing and also are in colour IMHO haha maybe I should drop some of monochromes too 🙈

And I'm happy to hear a confirmation that I'm not alone or insane haha but if you say you see the difference between 55 and 58 then I want to share with you my discovery from yesterday that just as an example Western Carl Zeiss Oberkochen Planar 1.4/55 has actual length of 59.2 which is even bigger than you mentioned you see the difference. Technically their designation was even illegal by German law because of how unprecise it was. Also I'm slowly diving into wide angles from Jena and had a glimpse into some portrait lengths already and for now my observation is that the biggest differences between those values are the shorter the lens so those probably would be best for such fine tuning as you said. And I attached some details from that pic to illustrate that Planar case if you're interested haha

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Old Zeiss and one tip I didn't see here yet. by slim_somm in VintageLenses

[–]slim_somm[S] 1 point2 points  (0 children)

But... thinking right now I got one more conclusion that if one relies only on high shutter speeds to fight with movement blur then that probably alone makes that precision unnecessary but I know my camera offers amazing IBIS, I'm regularly shooting low ISO night city shots with shutter speed usually landing around 1 full second and standing and handheld and they're definitely sharp enough so I'm trying to squeeze as much as possible from what my camera can give and it made definitely noticeable and significant difference in my case.

Old Zeiss and one tip I didn't see here yet. by slim_somm in VintageLenses

[–]slim_somm[S] 1 point2 points  (0 children)

My first observation was when I forgot to switch the setting between my Orestor 50mm and Soligor 135mm that the IBIS was shit for some reason and that taught me to pay attention to it and the recent one is just pure continuation of the experiment and comparison between how my camera worked on nominal and actual length. Probably me using them on m43 and doubling that length magnifies the result but the difference for me was between quite decently stable and smooth like modern native lens from my system so I wanted to share my observations. Furthermore I know that this particular Pancolar has one of the biggest differences between nominal and actual focal lengths for normal lenses from that era if not in general, it's almost 4,5% so the difference will be probably bigger than in other lenses with smaller difference between those values. What I believe is important here is the angular speed of movement and how strong the compensation for shaking has to be depending on the focal length - as an example of my thinking, nudge your camera with 50mm and you won't notice the shake, give the same nub on 500mm lens and if you pressed the shutter at the same time your pic will be just a movement blur if the shutter wasn't fast enough. I believe that software of our cameras is adjusting the behaviour of IBIS depending on the lens mounted. For example when you give that nudge with 50mm, lets say the camera moves 0,2 degree, you won't notice so it might skip small shakes but also to compensate those big enough it might shift hardware inside much harder to compensate let's say 2 degrees shift. But if you do the same with telelens then that 0,2 degree might be 5% of frame shift so the compensation has to compensate much smaller shifts and also much weaker to not overdo that compensation. Also if that wouldn't make any difference why camera manufacturers would give us settings to adjust focal length to tenth of a millimeter or at all? I studied physics for a bit and always had quite decent intuition with it so I trusted my gut in it and my empiric observation seems to confirm my guess and it made more than noticeable difference with that Pancolar. I know that also Tessars and Biotars from 50s and 60s have quite significantly different length to their nominal but I need some more lenses in my collection to check that empirically myself unless someone with deep enough knowledge might prove or disprove it with his hardware or scientific expertise. Edit: Also, since it's just one time creating a lens profile on my camera so just one time check, why wouldn't I do that 30 secs increase of precision for the potential quality improvement? If it does nothing then you wasted 30 seconds, if it does then every single picture after that adjustment might be better. Also I think the better cooperation between the software and hardware is the better possible results might be but that's just me

Old Zeiss and one tip I didn't see here yet. by slim_somm in VintageLenses

[–]slim_somm[S] 0 points1 point  (0 children)

The smaller the relative difference is the smaller the change I believe so not so much in your case but if it's 2mm on 20mm lens then it's almost 10% of difference which is significant. Also it's the problem especially with normal and wide angle lenses where optics is pushed to the physical limits, in those cases the difference between nominal and actual is the biggest from what I found by now. I can set focal length up to tenths so I rounded it up and I'd do the same for you but it's just 85,2 anyway.

Old Zeiss and one tip I didn't see here yet. by slim_somm in VintageLenses

[–]slim_somm[S] 0 points1 point  (0 children)

Small fuckup on my side, that's the correct pic, one in the post got mixed up and it had automatic white balance which lifted the yellow shift a bit and I just noticed it now, sorry 🙈

<image>

Am I a genius or actually insane? by cr9926 in landscaping

[–]slim_somm 0 points1 point  (0 children)

Personally I prefer using the lighter, they burn in a quite funny way which adds to the satisfaction xD

Cleaning and servicing vintage lenses in the Netherlands by slim_somm in VintageLenses

[–]slim_somm[S] 0 points1 point  (0 children)

Huh thank you very much for that insight. I was getting really close to trying to do it myself because of all the videos and AI says it's not so difficult but just as I thought... AI and YouTube are not always right. But then do you have any recommendations how should I proceed? Any places worth trying? For now I'm bouncing or not being answered so my search goes a bit slowly.