Lenstip reviewed the Laowa 7.5mm f/2

Matt Leppek

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Despite these drawbacks, I still love this lens. I use it for 80% of my landscape and star trail photography.

Glad you shared this article, it's nice to be aware of the flaws and limitations.
 

MRM

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Reading their review I wouldn’t get one, but owning one I feel differently. It is a amazing lens. I feel like the coma and astigmatism isn’t as bad as they tested and mine is amazingly sharp in the corners for a ultra wide, even wide open. Lens is well built except for the hood and the lens cap.
 

Matt Leppek

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Even for Astro photography I haven't noticed the agmitism (sp?) to be nearly as extreme as they found.

This lens is sharp enough to handle the Olympus high res mode pretty well. Generally 50 sharpening or lower is plenty for 64mp landscapes in my experience.

The lens cap is infuriating when you're in a rush. The biggest bummer is the insane vignette you get with a 46-77mm step up ring and filter, especially ND. I don't think this is avoidable with an ultra wide, but it sucks to buy more filters than you need to.
 

MRM

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Even for Astro photography I haven't noticed the agmitism (sp?) to be nearly as extreme as they found.

This lens is sharp enough to handle the Olympus high res mode pretty well. Generally 50 sharpening or lower is plenty for 64mp landscapes in my experience.

The lens cap is infuriating when you're in a rush. The biggest bummer is the insane vignette you get with a 46-77mm step up ring and filter, especially ND. I don't think this is avoidable with an ultra wide, but it sucks to buy more filters than you need to.
I agree. I find that on my copy it is actually really good with coma, spherical aberration and aberrations. Here is a pretty extreme corner crop of a recent Astro photo. Btw this was one of my first times every trying astrophotography and I didn’t even have a tripod with me. I set the camera propped on a jacket and used the timer. So if their is a loss of sharpness it shouldn’t all be on the lens I don’t know much about astrophotography but it takes a heavy crop to notice the imperfections which are minimal I think they got a bad copy to test which is an issue with this lens
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TonyVentourisPhotography

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For a nice compact ultra wide it is a really decent lens. Especially for the price compared to the other options out there. I found for most work it was great...but had some real flare issues in strong light that were present in the frame. It also has distortion when being critical in an architectural scenario. Otherwise I was surprised how decent it was. A +25 took care of vignette in Lightroom under that control. I love the size compared to the pro zooms.
 

archaeopteryx

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don't think this is avoidable with an ultra wide
Not entirely sure if you're referring to lens light falloff in the corners, increased effective optical density in dye based NDs, mechanical vignetting from filters obstructing the lens's line of sight, or some combination thereof. With a 46-77mm step up I'd expect at least one regular filter or a regular polarizer to be mechanically OK and probably two filters, albeit possibly with some dependence on how thick they are. But it'd be good to know what behaviour the lens actually exhibits.

Corner light falloff from natural and sensor vignetting is avoidable by minding exit pupil distance during lens design, which is commonly done for modern ultrawides, and certain other methods have occasionally been used historically. Light falloff from optical vignetting is avoided by reducing internal shading within the lens, which generally requires more glass and therefore larger and heavier optics. It would not surprise me if Venus compromised on all three of these properties in favour of reduced size and weight; accepting more vignetting because lens correction brightens up the pixels seems to be a bit of a trend in ultrawide design lately. If limiting raw vignetting is important (which it usually isn't), it happens both m43 7-14s are relatively conservative in this regard.

Optical density increases can be avoided by using coating based NDs rather than dye based ones.
 

martink111

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A quick question here: I just bought this lens and I’m noticing some very strange behavior as far as aperture goes. It has a noticeably poor transmission wide open (lagging typically about 2/3 of a stop from my other lenses at the same aperture), but each stop down corresponds to only about 2/3 of a stop in actual light loss. It is so extreme that when tested against my Olympus 12 F2 for reference, I can start both at F2 and 1/1000th and by the time I get to F22, the Olympus will read at 1/60th but the laowa will still be at 1/500th. The Laowa shot is somewhat dimmer, but not by 3 stops! Also, I don’t know if any of this is normal behavior for an ultra wide, but the lens shows very little defraction loss even at F22. I’ve included two shots at F22- one with the 12 and the other with the 7.5. I almost suspect that the aperture is miss reported or not properly functioning. Has anyone here encountered this before, or is this normal behavior for an ultra wide?
66F1A8C9-2E67-4A74-B9BC-AFDA04EB008D.jpeg
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Aside from that, the lens is incredibly sharp wide open at the center but as a number of reviewer’s had noted, it does take a while to sharpen up the edges. Contrast is almost too high in comparison with my other lenses and the color is exceptionally warm and hard to correct for with white balance cards. Overall, I really like it but I am concerned that there could be something wrong with it. Thanks in advance for your responses
 

archaeopteryx

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that's fairly normal for fast lenses, and wider probably makes it harder to be telecentric
Hmm. The post here largely duplicates @martink111's thread for the 7.5 with the thread and the post making somewhat different statements about the lens's behaviour. So I have some questions over the accuracy and repeatability of the test procedure.

Those aside, I've recently been testing effective apertures across a set of lenses from f/5.6 to f/1.7. The two f/1.7s in the test behave exactly as expected compared to the other lenses, including an f/2.8. I've also had at various other times an f/1.4, two f/1.8s, and an f/2. Based on this data set I would say a two thirds stop difference in central area brightness would be anomalous. The Lenstip review this thread includes a vignetting report so, if the effort here is to refer to vignetting/falloff/fourth power cosine, one can presumably expect any number from 0 to 3.3 stops just by looking at the review. Without a more precise statement of what the two thirds stop measurement in question is measuring I don't know that it's possible to disambiguate from well known behaviour of the lens.

It also depends what one means by telecentric. Formally, an image space telecentric lens has an exit pupil at infinity, a object space telecentric lens has an entrance pupil at infinity, and a bi-telecentric lens has both pupils at infinity. In any of these cases the lens's angle of view in the relevant space is therefore zero---meaning formally telecentric lenses are ultimate telephotos and cannot be wide angle by definition---and the field of view is no larger than the pupil. A corollary of the latter is field of view cannot exceed the size of the optics. The closest thing to a wide angle, object space telecentric lens is low magnification one, which is necessarily big, heavy, and expensive. See, for example, the Thorlabs 0.051x. Optical requirements are reduced for image space telecentricity but in most photographic circumstances there's limited need for it. The beam angle reaching sensor pixels is little different between an exit pupil at infinity and one at 100-200mm.

In the weak sense of telecentricity, where it's used to suggest an (ultra)wide is designed for digital sensors by having an enhanced exit pupil distance, I would suggest this is largely a marketing claim as retrofocal designs are associated already with long exit pupil distances (Cicala 2014b). Actual MTF increases are more likely to be associated with lens aberrations introduced to cancel aberrations created by the sensor stack, particularly for m43's comparatively thick stack (Cicala 2014a, Cicala 2014c), and increased use of aspheric elements in more recent designs. Potentially more relevant to this discussion, another shift in recent utlrawide design is to accept greater levels of falloff and correct them in software.

One can certainly also get substantial falloff with short exit pupil distance rangefinder/Biogon type lens designs but, from what I can tell the, m43 mount specification effectively requires rear elements be about 15+mm from the sensor. The Laowa 7.5 appears to conform to this, suggesting it's therefore necessarily a retrofocal design.
 
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martink111

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Hmm. The post here largely duplicates @martink111's thread for the 7.5 with the thread and the post making somewhat different statements about the lens's behaviour. So I have some questions over the accuracy and repeatability of the test procedure.

Those aside, I've recently been testing effective apertures across a set of lenses from f/5.6 to f/1.7. The two f/1.7s in the test behave exactly as expected compared to the other lenses, including an f/2.8. I've also had at various other times an f/1.4, two f/1.8s, and an f/2. Based on this data set I would say a two thirds stop difference in central area brightness would be anomalous. The Lenstip review this thread includes a vignetting report so, if the effort here is to refer to vignetting/falloff/fourth power cosine, one can presumably expect any number from 0 to 3.3 stops just by looking at the review. Without a more precise statement of what the two thirds stop measurement in question is measuring I don't know that it's possible to disambiguate from well known behaviour of the lens.

It also depends what one means by telecentric. Formally, an image space telecentric lens has an exit pupil at infinity, a object space telecentric lens has an entrance pupil at infinity, and a bi-telecentric lens has both pupils at infinity. In any of these cases the lens's angle of view in the relevant space is therefore zero---meaning formally telecentric lenses are ultimate telephotos and cannot be wide angle by definition---and the field of view is no larger than the pupil. A corollary of the latter is field of view cannot exceed the size of the optics. The closest thing to a wide angle, object space telecentric lens is low magnification one, which is necessarily big, heavy, and expensive. See, for example, the Thorlabs 0.051x. Optical requirements are reduced for image space telecentricity but in most photographic circumstances there's limited need for it. The beam angle reaching sensor pixels is little different between an exit pupil at infinity and one at 100-200mm.

In the weak sense of telecentricity, where it's used to suggest an (ultra)wide is designed for digital sensors by having an enhanced exit pupil distance, I would suggest this is largely a marketing claim as retrofocal designs are associated already with long exit pupil distances (Cicala 2014b). Actual MTF increases are more likely to be associated with lens aberrations introduced to cancel aberrations created by the sensor stack, particularly for m43's comparatively thick stack (Cicala 2014a, Cicala 2014c), and increased use of aspheric elements in more recent designs. Potentially more relevant to this discussion, another shift in recent utlrawide design is to accept greater levels of falloff and correct them in software.

One can certainly also get substantial falloff with short exit pupil distance rangefinder/Biogon type lens designs but, from what I can tell the, m43 mount specification effectively requires rear elements be about 15+mm from the sensor. The Laowa 7.5 appears to conform to this, suggesting it's therefore necessarily a retrofocal design.
Yeah sorry about the double-posting (I kind of thought this thread might be old and I didn’t want to flood it with pics anyways). Thank you for the very detailed analysis, it is a lot to digest but very helpful. What I meant by 2/3 of a stop is that against a plain background, if I increment the aperture settings on either my Olympus lenses or the new Venus by one full stop, I get completely different changes in shutter speed without obvious changes in overall exposure. Now that you mention the peripheral illumination, it does give me the idea that I should do a spot meter test to see if center brightness held constant gives the same result. I was kind of surprised given the reviews for the Venus that my vignetting seemed much better than anticipated… I imagine that the camera’s metering could have something to do with it. I guess if the vignetting continuously improves on stopping down, it would have the effect of improving the total T stop at each aperture setting. I’m not an optics guy so please bear with my lack of knowledge here. Again, not too concerned about the brightness wide-open; I’m just more concerned that the aperture is not working properly.
 

archaeopteryx

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I guess if the vignetting continuously improves on stopping down, it would have the effect of improving the total T stop at each aperture setting.
Correct. However, the total T stop is the integral over the entire frame and therefore dominated by the central area of little falloff. So it's a minor effect.

If I'm understanding your observations correctly, they suggest aperture area isn't incrementing as expected. For large discrepancies, such as those reported, and a manual lens like the 7.5 f/2 this is relatively easy to check by stopping the lens down off camera and looking at the aperture. For an ultrawide at small apertures you may need a magnified view, though.
 

martink111

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Correct. However, the total T stop is the integral over the entire frame and therefore dominated by the central area of little falloff. So it's a minor effect.

If I'm understanding your observations correctly, they suggest aperture area isn't incrementing as expected. For large discrepancies, such as those reported, and a manual lens like the 7.5 f/2 this is relatively easy to check by stopping the lens down off camera and looking at the aperture. For an ultrawide at small apertures you may need a magnified view, though.
That was kind of my thought too. I’ve run some additional tests and concluded that against my Olympus 12 F2, it is actually only a span of F2 to f11 for the entire lens range. What I mean by that is if I correct the exposures so that a shot at a plain wall and identical composition match as closely as possible between the two lenses then at an indicated F 22 on the Venus it matches F 11 on the Olympus. Also, it is pretty clear when compared against my friend’s Samyang F2 12 mm, his lens fully stopped down has a much smaller entrance pupil than mine does fully stopped down:

8CE12E19-6EBA-442E-B01E-4E6A942D7EC5.jpeg
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Now I realize that it is not apples and apples, but there definitely seems to be something off about this lens. I’m pretty conflicted about this. On the one hand, if the lens is misreporting aperture this badly I can’t imagine that nobody else had commented on this when testing or reviewing this lens if it were a design flaw. On the other hand, I can’t see how you can have a manufacturing defect do something like this unless maybe the aperture linkage is bent somehow. If it is a design flaw then any other replacement lens would have the same issue and so far otherwise I’m really liking this lens. The weird aperture does make it harder to properly expose but I’m getting the hang of it. On a sensor as small as micro 4/3 will it ever really be necessary to use smaller than F 11? Either way, I guess I have a few more days to play with it before I can return it if needed. Thanks again for your input on this
 

archaeopteryx

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his lens fully stopped down has a much smaller entrance pupil than mine does fully stopped down
Those are exit pupils so some control for difference in pupil magnification ratio as in addition to difference in focal length could be desirable. It won't change the result, though.

On a sensor as small as micro 4/3 will it ever really be necessary to use smaller than F 11?
Um, the depth of field in this focus stack collected with an effective aperture of f/13 is equivalent to f/256. ;) I've never used my Oly 9-18 narrower than f/5.6, but that's because I focus stack with it too and it's difficult to do an autofocus bracket with a manual lens. I'm not sure why you'd keep a returnable lens with a defective aperture, though from the available data it's not entirely clear if there's difficulty with the aperture itself.

I can’t see how you can have a manufacturing defect do something like this unless maybe the aperture linkage is bent somehow.
A more specific description of the behaviour would be needed to infer what might be going on mechanically. EDIT: For example, SiFu and TheEye's tables in the second link Reflector posted below suggest their lenses have an incorrect scale on the aperture markings but aren't having problems with the aperture blades' motion. It's unclear if a true f/22 could be obtained by rotating the aperture ring past the marked f/22 or if there's a mechanical stop which prevents that.
 
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Reflector

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I've heard that the Laowa 7.5mm f/2 has a miscaliberated aperture ring and it is about 2/3 stops (rather than the whole markings) or off an amount as such. I don't mind since I magnify to check DoF and I've learned (out of habit from adapting lenses in the past) to count down from the shutter speed displayed on the meter.

Edit:
Quick search to find where I remember reading this from I already found some posts over at DPR along those lines of aperture miscalibration:
https://www.dpreview.com/forums/thread/4421337
https://www.dpreview.com/forums/thread/4416002
 
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martink111

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Wow! My lens is off! I ended up doing the same thing yesterday using a 12 F2 and a 12 to 40 for reference. I attached my “corrected“ marker strip in the photo below:
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I noticed that the rear light baffle is a threaded on piece on this lens which was loose to the touch. I unscrewed it and tighten the aperture to its maximum. It definitely is not reaching the full travel:
60B14786-A634-4AC6-AD57-F9F665716ACF.jpeg
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If it is a design flaw which it certainly looks to be, I don’t think I’m going to find a better sample by returning it. Since it does what I want it to do and I really can’t fault it for image quality, looks like I’ll keep it. By the way, the DPReview links really show how much nicer the community is here – there is some serious nastiness in the forums over there! Thanks again and happy shooting!
 
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