Stopping down is not a mistake, it is to maintain high image quality.
At close focus distances, you lose stops of light projecting the image circle larger than the sensor. Stopping down the aperture to f4 does not change your exposure by much. But stopping down does improves the lens' performance, so Zeiss chose to automatically close the aperture. The other options to keep image quality high are to make the lens larger or increase the MFD to where the light loss is minimal.
There are other examples of this. Leica also automatically stops down aperture on their Q, X 113, and 23/2 TL lenses. The Fuji X100 23/2 in comparison does not stop down, but shows this "glowiness" at close distances and looks pretty bad until you stop down the lens anyways. Zeiss could have allowed this, but takes the Leica approach.
All of that seems fine to me, but I think the mistake Zeiss made here is that the aperture blades don't curve, resulting in this nonagonal bokeh. I find it quite unappealing myself.
grahamgibson wrote:
Stopping down is not a mistake, it is to maintain high image quality.
At close focus distances, you lose stops of light projecting the image circle larger than the sensor. Stopping down the aperture to f4 does not change your exposure by much. But stopping down does improves the lens' performance, so Zeiss chose to automatically close the aperture. The other options to keep image quality high are to make the lens larger or increase the MFD to where the light loss is minimal.
There are other examples of this. Leica also automatically stops down aperture on their Q, X 113, and 23/2 TL lenses. The Fuji X100 23/2 in comparison does not stop down, but shows this "glowiness" at close distances and looks pretty bad until you stop down the lens anyways. Zeiss could have allowed this, but takes the Leica approach.
All of that seems fine to me, but I think the mistake Zeiss made here is that the aperture blades don't curve, resulting in this nonagonal bokeh. I find it quite unappealing myself....Show more →
I was hoping that such a big lens for a 40mm f/2 and a floating element design would yield great close-focus performance without resorting to stopping the lens down 2-stops!
The question remains - does this only occur at close focus?
I asked Lloyd to 'flip the switch' to the middle option 0.4m to infinity and see if the behavior persists.
If the bokeh is rendered as circles with the middle focus limit set, I'm fine with it and can accept the nonagonal bokeh balls if they only occur at close focus (something I do not foresee myself using regularly).
grahamgibson wrote:
Stopping down is not a mistake, it is to maintain high image quality.
At close focus distances, you lose stops of light projecting the image circle larger than the sensor. Stopping down the aperture to f4 does not change your exposure by much. But stopping down does improves the lens' performance, so Zeiss chose to automatically close the aperture. The other options to keep image quality high are to make the lens larger or increase the MFD to where the light loss is minimal.
There are other examples of this. Leica also automatically stops down aperture on their Q, X 113, and 23/2 TL lenses. The Fuji X100 23/2 in comparison does not stop down, but shows this "glowiness" at close distances and looks pretty bad until you stop down the lens anyways. Zeiss could have allowed this, but takes the Leica approach.
All of that seems fine to me, but I think the mistake Zeiss made here is that the aperture blades don't curve, resulting in this nonagonal bokeh. I find it quite unappealing myself....Show more →
If you can see blades in bokeh, it means that aperture is in light path and is affecting the amount of light.
Equally, improving quality by stopping down is only possible by geometrically removing "out-of-phase" rays that directly contribute to image brightness
Moreover, we are talking about measly 1:3.3 magnification which isn't even close to semi-macro. There's no way 1:3.3 results in 2 stops of light loss.
And lastly, Lloyd observed 2 stop difference in exposure, from which it was derived that it stops down to ~f4
eyal wrote:
I asked Lloyd to 'flip the switch' to the middle option 0.4m to infinity and see if the behavior persists.
This is true, I don't know the exact amount that stopping down actually reduces the exposure. It certainly is some amount, but the point is that the image quality is not up to Zeiss' standard at f2. Some people will be less discerning about IQ and wish that the behavior was not automatic. I'm just explaining the reasoning behind the decision which many people didn't seem to know or understand.
I thought he said it can be seen in all distances other than infinity. No?
maratus wrote:
If you can see blades in bokeh, it means that aperture is in light path and is affecting the amount of light.
Equally, improving quality by stopping down is only possible by geometrically removing "out-of-phase" rays that directly contribute to image brightness
Moreover, we are talking about measly 1:3.3 magnification which isn't even close to semi-macro. There's no way 1:3.3 results in 2 stops of light loss.
And lastly, Lloyd observed 2 stop difference in exposure, from which it was derived that it stops down to ~f4
Fred Miranda wrote:
I thought he said it can be seen in all distances other than infinity. No?
Yeah, right. I forgot that detail. It's still important to know how stopping down happens as you focus closer. It makes sense if it's very subtle in normal range from infinity to, let's say, 1-1.5m, and then starts to stop down significantly in 0.8m - 0.24m range.
If aperture is getting stopped down almost linearly, then it's much harder to explain why. A lens like that is capable of being excellent in 1m to inf range wide open without need to stop down at all.
And of course the switch possibly affecting aperture behaviour should be checked.
Lens size issue - Leica have said many of the SL lenses share barrel size, seems to be a developing trend. Making your largest (or near to it) lens the model for other potentially smaller lenses is not very smart, but might save them a few shekels. Uniformity at your ergonomic expense.
The joyful era of fine small lenses with crafted rings put in just the right position might be behind us, even as cameras are mostly getting smaller. Kudos to CV for bucking the industry-wide shift away from best practice. And doing it affordably.
I’ve never seen a lens that changes aperture and results 2 stops of light loss as your focus distance changes. Anyone know if this was with the close focus switch on or off?
Mr Chambers, although usually working very carefully, is jumping into conclusions a bit too early. He has reported the aperture change as 'a kind of design flaw' where is seems to be a normal behavior of lenses working close to macro range. Not exactly sure about this as I'm not an optical designer, but it's probably about lens extension and effective F-stop, which is neatly explained at http://www.cambridgeincolour.com/tutorials/macro-lenses.htm
See the paragraph 'Lens extension and effective F-stop' before the internet-panic attacks. There's probably a natural explanation for this, or the other possibility is that there is a major bug with the lens, which I find not credible since Zeiss usually knows the optical stuff they do.
Kalainen wrote:
Mr Chambers, although usually working very carefully, is jumping into conclusions a bit too early. He has reported the aperture change as 'a kind of design flaw' where is seems to be a normal behavior of lenses working close to macro range. Not exactly sure about this as I'm not an optical designer, but it's probably about lens extension and effective F-stop, which is neatly explained at http://www.cambridgeincolour.com/tutorials/macro-lenses.htm
See the paragraph 'Lens extension and effective F-stop' before the internet-panic attacks. There's probably a natural explanation for this, or the other possibility is that there is a major bug with the lens, which I find not credible since Zeiss usually knows the optical stuff they do. ...Show more →
I think you're confusing effective aperture change and physical blades moving. When macro lens is focusing up close, effective aperture reduces without stopping down. And 1:3.3 isn't exactly macro distance where such effect would be very noticeable anyway. So far Lloyd is correct in his observations and is reporting physical aperture blades contracting (and changing F-stop and the opening shape) as you focus closer.
maratus wrote:
I think you're confusing effective aperture change and physical blades moving. When macro lens is focusing up close, effective aperture reduces without stopping down. And 1:3.3 isn't exactly macro distance where such effect would be so noticeable anyway. So far Lloyd is correct in his observations.
Had to rethink this through again and you are correct (if I got it right ). If anything the aperture should actually increase to take into account the extended focal length (in order to remain at f/2) - hmmm... or is it so that aperture closes automatically so that the depth of field remains the same even with extended focal length. Because of extended focal length, the depth of field would be more shallow if the aperture would remain open, maybe it's a design practice to close it so that the depth of field (with the extended focal length) keeps about the same... Not sure really and I'm sure someone here knows better than me. At least in Oberkochen they probably know the answer.
Nevertheless, I would find this a very odd design flaw, like 'we got some of the elements backwards by mistake' as I know quality control is very important for Zeiss. I would wait and see how it turns out, as it seems (to me) that there's almost always some kind of hysteria nowadays going with the new products (pdaf-striping, one card slot, banding, etc. etc.). Most of them probably happen because expectations are so high (especially with Zeiss I presume) and even rather normal 'features' or limitations of technology are seen as dramatic design flaws. In time the expectations will settle to realistic levels. See the famous Roger’s Law of New Product Introduction: https://www.lensrentals.com/blog/2013/01/rogers-law-of-new-product-introduction/
Describes it perfectly!
As much as I respect Lloyd Chambers for his great work, I find that he is sometimes a bit too eager to write about flaws like it would be a some kind of mark of his objectivity. I would rather see him speak with Zeiss or whoever first, solve the puzzle and only after then report the conclusions. If it is 'a design flaw' or 'a product limitation' he should be clear about it when writing about it. The way he is doing now only adds confusion as everybody seems to lack real info and people get jump into conclusions too easily.
Stopping down close to MFD is pretty common behavior for macro lenses. A quick google search finds lots of people confused about their f2.8 macro lens stopping down automatically to f3.5, f4.5. The Leica examples (Q & X) stop the normally f1.7 lens down to f2.8 (1 1/3 stop). 2 stops does seem high though.
My EF-S 60mm macro stopped down about 2 stops at macro distance as well.
I think what needs to be figured out is at what distance to the subject the lens begins stopping down the aperture.
Jonathan Brady wrote:
My EF-S 60mm macro stopped down about 2 stops at macro distance as well.
I think what needs to be figured out is at what distance to the subject the lens begins stopping down the aperture.
RaMoFe wrote:
It is normal method with macro lens.
Tamron 90mm f/2.8 Di VC USD Macro F017 Lens stop down until f5.6.
"approximate formula" :
effective aperture = nominal * (1 + X)
X: actual magnification of lens
5.6 = 2.8 * (1 + 1) when X=1
But do those lenses actually stop down? Or is it effective aperture that changes, and diaphragm blades remain wide open?
I think if we applied this formula of effective f-stop to Batis 40/2 which has magnification of 1/3.3 at minimum focus distance, the formula would become: 2 x (1+(1/3.3)) = 2.6 if the blades were open at minimum focus distance, but if the aperture blades are closed to something like f4, the formula would become 4 x (1+(1/3.3)) = 5.2.
Effective F-Stop = F-Stop x (1 + Magnification)
When the blades are stopped down, I think the "F-Stop" in this formula would be affected accordingly...
Not sure what is the right answer here but I would also very much like to hear some official Zeiss explanation. Seems that many have raised questions on this to them already but there have been no answers yet (at least nothing shared). If no explanations, need to wait for really detailed reviews also covering this aperture blade behavior before making any buying decisions.
I like to take close-up shots using wide apertures (for nice bokeh effects) and it doesn't seem ideal if the lens is always effectively stopping down at such distances. I would also like to use it for e.g. food & drink shots in low light indoors conditions, not exactly at MFD but somewhere in the 0.3-0.5m range, and it's not good if the lens needs a lot of light in such scenarios due to closing down the aperture, also seriously limiting bokeh. I normally use wide apertures for such shots, e.g. f1.4 to f2 range works great on my Sony Zeiss 35/1.4 which can focus to 0.3m vs. 0.24 on the Batis.
Anyway, I think it will be very interesting to know how the aperture blades behave at different distances between MFD and infinity and whether there's any way to turn off this automatic aperture blade closure. I don't think the described behavior is a SW bug, seems too complex to implement to be happening by accident.
). If anything the aperture should actually increase to take into account the extended focal length (in order to remain at f/2) - hmmm... or is it so that aperture closes automatically so that the depth of field remains the same even with extended focal length. Because of extended focal length, the depth of field would be more shallow if the aperture would remain open, maybe it's a design practice to close it so that the depth of field (with the extended focal length) keeps about the same... Not sure really and I'm sure someone here knows better than me. At least in Oberkochen they probably know the answer.