Look at how small the human figures are as part of the entire frame, and yet when you look at them 100% you can read the words on his cap, individual beard hairs, see the stitching on their shirts & jeans, see the buttons on her camera. It's insane.
sebboh wrote:
doesn't matter they all move together as one group. the easiest way to measure is simply to measure how much the lens barrel moves if the lens barrel moves with the front element (i think both those lenses do). second easiest to measure would be the rear element movement, but it doesn't matter which, you measure because they all move together. you could also compare the R 50 lux to your cron rigid btw.
you are, in fact, wrong on this. iris size for example, must be the same for a given focal length and aperture independent even of sensor size. the same is true for distance travelled to change from one focus point to another – it depends on focal length independent of sensor size for any lens design (assuming all lens elements move together). there is probably some subtle variation between lenses with different designs versus an idealized single element lens, but the differences are not big enough to make a difference that you would noticed if you switched helicoids on any two lenses.
This statement would be true for a fixed group lenses only. Once you introduce floating elements that trim focus to the rear element then everything changes. The primary focussing elements will move in concert with the floating element, and final focus is delivered by the last group that is fixed. This is why FLE lenses ere so dependent upon accurate distance to the sensor.
Simple rear focussing (fixed front group) lenses are generally more tolerant of errors introduced due to adapters. Single fixed group lenses show no real effect other than the distance scale being out.
Phillip Reeve wrote:
I once compared to adapters of different length using Minolta legacy Lenses with floating focusing and didn't notice any difference.
I added some 100% crops in post #2 as a bonus you get the Leica AA 90/2
I was. I am glad I am learning new thing to some fundamental concept I was missing. Andrew's link is also very helpful. I will spend a little more time on that
My instinct seems right at least about FLE lens.
It almost make me change my 'opinion' about tolerance is more picky with lens with short flange distance but why Leica 'Magic' is gone with adapter, and there are so many 'more 'problems report with M lens?
an idealized single element lens illustration is great, Obviously, Leica M designer can afford to put more elements behind this virtual single lens element than Canikon, is that put more penalty for this distance tolerance? A speculation but not conclusion.
Question: Is it universally true that lens group will move together without FLE during focus?
Look at how small the human figures are as part of the entire frame, and yet when you look at them 100% you can read the words on his cap, individual beard hairs, see the stitching on their shirts & jeans, see the buttons on her camera. It's insane.
The thing about that pic that excited me is no shadow noise. It sure ain't Canon!
zhangyue wrote:
Question: Is it universally true that lens group will move together without FLE during focus?
Not always in modern lenses. This was done to facilitate the fixed front element during focus. As mentioned in the link there are:
zooms (of course),
front, internal or rear focusing lenses,
lenses including close range correction systems (CRC)
An example of rear focusing is the ZM 18mm, the front element does not move, but the rear element group does. This lens would quite tolerant of adapters, and would show minor degradation in the corners that would be overcome as the lens is stopped down. This type of lens is a rear focusing group. Some lenses are less tolerant of adapter issues, this type of lens may have two groups that move together to achieve focus.
Not all FLE lenses have a fixed rear element either. The floating element is generally used to correct the lens for close focusing accuracy. When I look at my Summilux ASPH the rear element does move in and out with focusing. So it is both an internal focus and FLE lens, which is a common attribute of Leica FLE lenses. As you can see, the lines between two group focussing and FLE are somewhat blurred if you pardon the pun.
Some lenses appear to have a fixed front element, but the front element is actually just protective. FYI
This is about the extent of my understanding in this subject, and I am sure that there are hybrid and FLE lenses out there that are more tolerant than the lux.
I am hoping that the A7r on-sensor lenses are optimized so that we can talk about the merits of lenses on the sensor!
Andrew Gough wrote:
This statement would be true for a fixed group lenses only.
yes, that's what i said. the vast majority of modern lenses move all elements together to focus (though the need for fast AF is changing this), even most m lenses with a few notable exceptions. FLE lenses are much more complicated mechanically btw.
zhangyue wrote:
I was. I am glad I am learning new thing to some fundamental concept I was missing. Andrew's link is also very helpful. I will spend a little more time on that
My instinct seems right at least about FLE lens.
It almost make me change my 'opinion' about tolerance is more picky with lens with short flange distance but why Leica 'Magic' is gone with adapter, and there are so many 'more 'problems report with M lens?
an idealized single element lens illustration is great, Obviously, Leica M designer can afford to put more elements behind this virtual single lens element than Canikon, is that put more penalty for this distance tolerance? A speculation but not conclusion.
Question: Is it universally true that lens group will move together without FLE during focus? ...Show more →
that is what the FLE designation means – not all the lens groups move together. different brands specify it differently and some specify whether it is rear focusing or internal focusing or whatever. sometimes zeiss doesn't feel the need to mention it for some reason...
as far as the more problems with m lenses, it seems to me that that is most likely due to the issue of oblique ray angles. notice that voigtlander and zeiss m lenses typically are worse offenders than leica lenses.
it could be possible that leica has higher tolerances across the board allowing them to design lenses that depend on a higher level of precision to function properly (talk to an optical engineer to find out if this is really possible). this could theoretically lead them to being more sensitive to low adapter tolerances. maybe...
Guys, all this is very clear but, what are the real effects of using a non perfect adapter in a FLE lens ?. ( I don't mean a ring with uneven thickness but one which is slightly thinner than necessary .Let's say 1.40mm. instead of 1.50mm).
Are we talking about a visible degradation of the image or it's a purely academic reduction of 0.001% in sharpness ? I suppose it depends greatly on the specific lens but I don't recall seeing any minimally serious test on this matter.
p.9 #10 · Sony A7r some full resolution test shots
If the adapter is a bit too long, then you won't achieve "infinity focus"; 0.1mm would probably do that.
If the adapter is a bit too short, then you probably won't notice, except maybe that the image seems to be a bit less sharp at the "infinity stop", than slightly closer on the focus scale.
In both cases, with lenses that have an adjustment for the infinity focus stop, you can probably compensate for such a small difference in adapter thickness.
p.9 #11 · Sony A7r some full resolution test shots
This is what happens with a 'normal' lens. My question was related to what has been discussed above in this thread : the effects caused in a lens with floating elements, which should be exactly located in relation to the focal plane, no matter the focusing distance.
p.9 #12 · Sony A7r some full resolution test shots
turnstyle wrote:
fwiw, I have the Voightlander adapter, and I'm trying to figure out if my side mushiness (Lux 50 on NEX7) is due to the adapter -- or if it's just what I should expect from the lens.
Thanks!
I assume you're referring to the 50 Lux ASPH? It, along with many Leica lenses, has a drop in sharpness in the full frame mid zone area, which corresponds to the frame edges of APS-C. The mid zone drop becomes more pronounced as the lens is stopped down from wide open, until after f/5.6. It was something I first noticed with the 21 Lux on the GXR and also saw on the NEX-7. Its mid zone dip is also quite apparent in FF M9 images (the 50 Lux ASPH isn't as dramatic, but you can see it if a subject is placed in this zone at f/2.8, for example). It's visible in my a7 test images, but interestingly, the 21 Lux behaves rather nicely on the a7, whereas I didn't like it on APS-C.
The side mushiness you see therefore could be caused by this, but if it's uneven (one side/corner worse than the others), then it could be an adapter problem or a decentered lens, or combination...
p.9 #13 · Sony A7r some full resolution test shots
artur5 wrote:
This is what happens with a 'normal' lens. My question was related to what has been discussed above in this thread : the effects caused in a lens with floating elements, which should be exactly located in relation to the focal plane, no matter the focusing distance.
OK, missed that. As long as you're focusing through the finder or in LiveView, I expect you'll do OK, or it'll be obvious that something bad is going on, if the register discrepancy is large enough. I also expect that the same infinity focus behaviour would be there, as for a non-FLE lens.
p.9 #14 · Sony A7r some full resolution test shots
artur5 wrote:
Guys, all this is very clear but, what are the real effects of using a non perfect adapter in a FLE lens ?. ( I don't mean a ring with uneven thickness but one which is slightly thinner than necessary .Let's say 1.40mm. instead of 1.50mm).
Are we talking about a visible degradation of the image or it's a purely academic reduction of 0.001% in sharpness ? I suppose it depends greatly on the specific lens but I don't recall seeing any minimally serious test on this matter.
Just like Roger's article, I would expect it to be much more than just 0.001% (i.e. getting to the barely visible region). With the advent of mirrorless FF, we can answer a lot of these in a more practical manner (same lens on Leica vs. Sony, Canikon vs. Sony, etc.). Most of the time, user's error would mask any possible IQ degradation anyway. Personally, I would worry more about left/right asymmetry than a bit of softness across the frame.
p.9 #15 · Sony A7r some full resolution test shots
artur5 wrote:
I'm not saying that your statement isn't theoretically right, but I have yet to see a test where a lens with floating elements shows noticeable image degradation when used with an adapter ring slightly out of specifications ( not skewed, just a bit thinner or thicker than required )
Here's one way to test it: with a FLE M-Mount lens (75mm APO-SUMMICRON) and the Hawk's macro adaptor to E-mount I can achieve close focus in two ways, either my using the lens' intended focus mechanism or by sliding the adaptor forward and then refocussing to the same subject distance. The adaptor extends by 3mm or so which would wildly exceed any feared manufacturing tolerances, but it's interesting to see how big the effect can be (and why FLE is worthwhile).
I tried this on my VG900 with a map on the wall. If this is interesting I can repeat with the A7r, when it arrives.
p.9 #16 · Sony A7r some full resolution test shots
dakw23 wrote:
Here's one way to test it: with a FLE M-Mount lens (75mm APO-SUMMICRON) and the Hawk's macro adaptor to E-mount I can achieve close focus in two ways, either my using the lens' intended focus mechanism or by sliding the adaptor forward and then refocussing to the same subject distance. The adaptor extends by 3mm or so which would wildly exceed any feared manufacturing tolerances, but it's interesting to see how big the effect can be (and why FLE is worthwhile).
I tried this on my VG900 with a map on the wall. If this is interesting I can repeat with the A7r, when it arrives. ...Show more →
that's awesome! thanks!
if you have time could you do a sensitivity test where you try it at a few different smaller adapter offsets?
also, how does it effect other areas of the frame (i guess i can answer this myself by looking at the full samples).
p.9 #17 · Sony A7r some full resolution test shots
Thanks a lot dakw23. This is enlightening.
See what I meant when I said that you can only trust people here to do the useful testing and not the 'big names' out there ?..
Of course every FLE lens won't behave likewise the Cron 75. but all the same it seems to defeat the purpose of using FLE lenses with extension tubes or in cameras which AF moving the sensor back and forth -as the old Contax AX or the rumored 'possible' Sony hybrid mount ( whatever the name will be )
I concur with sebboh on asking you, if possible, to try the above test focusing roughly with the lens ring and then fine tuning the focus with the Hawks helicoid ( the last fraction of millimeter) to see the possible effect of an adapter slightly out of specs.
Thanks again.
p.9 #19 · Sony A7r some full resolution test shots
dakw23 wrote:
Here's one way to test it: with a FLE M-Mount lens (75mm APO-SUMMICRON) and the Hawk's macro adaptor to E-mount I can achieve close focus in two ways, either my using the lens' intended focus mechanism or by sliding the adaptor forward and then refocussing to the same subject distance. The adaptor extends by 3mm or so which would wildly exceed any feared manufacturing tolerances, but it's interesting to see how big the effect can be (and why FLE is worthwhile).
I tried this on my VG900 with a map on the wall. If this is interesting I can repeat with the A7r, when it arrives.
Thank you for the test. Just want to make sure, did you check the other corners as well? Extended adapter might cause a slight tilt, so this might be an asymmetry issue.
p.9 #20 · Sony A7r some full resolution test shots
hiepphotog wrote:
Thank you for the test. Just want to make sure, did you check the other corners as well? Extended adapter might cause a slight tilt, so this might be an asymmetry issue.
i checked the corners on the files dakw23 provided. they all show the same result. that just means things are centered though, they could still be tilting when the helicoid is extended, which would also throw all 4 corners out of alignment.
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