p.7 #2 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
darrellc wrote:
For those of you who understand MTF charts, what do you think of the published MTF charts (on the Tamron product page towards bottom)?
Did a quick comparison vs. Tamron 20 and 35/2.8 primes and looked a lot weaker on FF away from center. But maybe I’m misinterpreting…
The MTF looks similar to the 17-28, and I didn't have any issues with that lens. It's not a great chart, but I think it should be okay. I'm not a 1:1 pixel level peeper though, so who knows once they get into hands. Comparing a zoom to a prime is a also tough comparison.
p.7 #4 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
I think the 28-75 G2 was overshadowed by the 35-150 released at the same time which was new and exciting. The G2 is a much better lens than the G1, but there are also many standard zooms already on the market, and it was just an update. I think this one may have some more excitement behind it, so I am hoping to see it reviewed a bit.
I love my new 28-75 G2, so once this has some reviews and such, I will jump on it. I will probably wait to see when it pops up on Greentoe to get it a bit cheaper.
p.7 #5 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
darrellc wrote:
For those of you who understand MTF charts, what do you think of the published MTF charts (on the Tamron product page towards bottom)?
Did a quick comparison vs. Tamron 20 and 35/2.8 primes and looked a lot weaker on FF away from center. But maybe I’m misinterpreting…
Those Tamron primes are very good optically--the 20mm is a little better than the 17-28mm F2.8.
I just glanced at Sigma's published MTF of their old 20-40mm F2.8 EX DG. This Tamron is going to be a pretty good zoom. The size and weight are attractive.
p.7 #6 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
darrellc wrote:
For those of you who understand MTF charts, what do you think of the published MTF charts (on the Tamron product page towards bottom)?
Did a quick comparison vs. Tamron 20 and 35/2.8 primes and looked a lot weaker on FF away from center. But maybe I’m misinterpreting…
A perfect result is a straight line right at the top of the graph. Higher is better
You want the sagittal and meridional lines to be the same line (overlapping each other) any deviation indicates astigmatism
As usual the manufacturer only tests at 30 lp/mm which is not good enough
Cameras these days like the Riv will max out at 130lp/mm with a perfect lens.
The 7iv will do 100 lp/mm at most
We need to wait for reviewers to test at higher lp/mm counts. Tamron’s chart doesn’t look real, maybe it’s theoretical data or something. The test at 30lp/mm is also meaningless on a high resolution sensor
p.7 #7 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
MTF resolution (high value line pairs) drop-off toward the edges is typical of all wide lenses. This is usually a result of optical distortion making it impossible to get the entire focal plane in focus at a wide aperture. It normally doesn't mean the lens is "not sharp" at the edge per se. It just means you either need to focus at the corner to get a sharp corner or stop down to a smaller aperture to flatten the field.
p.7 #9 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
Always entertaining when these youtube "reviews" magically appear 30 seconds after a new product is officially announced. Are these "pre-production" hardware or firmware? How much confidence can anyone have in any of these early reviews?
p.7 #10 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
Interesting option given the weight + FL + aperture and lack of direct equivalent on the market. The optical performance looks great from MFT’s, and if the flare resistance is like that 17-28/2.8, that’s fantastic and a huge bonus.
I am personally more interested in the Sigma 16-28/2.8 or Tamron 17-28/2.8 as stand alones or with a kit—better for FL spacing and I love the wide end over the quite plentiful 30-40mm range.
Would love to see a 70-150/4 or limited FL range light weight tele.
p.7 #12 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
jeffbuzz wrote:
MTF resolution (high value line pairs) drop-off toward the edges is typical of all wide lenses. This is usually a result of optical distortion making it impossible to get the entire focal plane in focus at a wide aperture. It normally doesn't mean the lens is "not sharp" at the edge per se. It just means you either need to focus at the corner to get a sharp corner or stop down to a smaller aperture to flatten the field.
If this were true, would you then get edge to edge sharpness if you use a test chart that’s curved, following the focal plane?
p.7 #15 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
aCuria wrote:
I can understand the fisheye use case,
But for a rectilinear lens, this doesn’t make a whole lot of sense to me
Even with the 135GM there’s significant MTF drop off towards the edges, it’s not a situation unique to wide angles
we are this effect even on wide angles with little distortion
I agree. Field distortion and loss of corner sharpness is definitely not unique to wide angle lenses. Wide aperture lenses like the 135mm f/1.8 can suffer from it too. Whether or not it makes a difference depends entirely on how you want to use it. Wide angle lenses are often used stopped down which flattens out the distortion. So it often makes no difference if a wide angle lens is distorted at f/2.8 when it's being shot at f/8. Wide aperture lenses like the 135mm are used to separate the background so corner blurring can actually help.
That's all part of interpreting the MTF's. Strictly by the numbers a lens might not be optically perfect wide open. But if you're only going to use it at f/8 the wide open performance may not matter.
p.7 #17 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
tsdevine wrote:
I don't believe all lenses' edge/corner sharpness are a function of field curvature. There are other things that can cause sharpness to fall off.
Yes, there are certainly lots of factors impacting resolution. I never said "all" lenses were effected by field curvature. It is a common occurrence on wide angle lenses and it effects MTF where it occurs.
p.7 #18 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
No argument, but I'm not sure you can tell it's FC by looking at MTF. It *might* be....but I'm not sure how we would know until people start using the lens. And it could have some FC, but MTF and sharpness could be impacted by more than one cause as well.
Just wasn't sure it was coming through that it "could be" vs "is", at least to me. All good.
jeffbuzz wrote:
Yes, there are certainly lots of factors impacting resolution. I never said "all" lenses were effected by field curvature. It is a common occurrence on wide angle lenses and it effects MTF where it occurs.
p.7 #19 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
Another review:
Sharpness looks quite good and there is only minimal coma/astigmatism. LoCA seems to be very well controlled
What concerns me a bit is the outlining in the specular highlights at 40mm (over-correction of spherical aberration), which suggests that the lens might produce soap-bubble bokeh (same as we've seen on the first generation Tamron 28-75mm):
p.7 #20 · New Lens: Tamron 20-40mm F/2.8 Di III VXD, Thoughts?
keepcoding wrote:
Another review:
Sharpness looks quite good and there is only minimal coma/astigmatism. LoCA seems to be very well controlled
What concerns me a bit is the outlining in the specular highlights at 40mm (over-correction of spherical aberration), which suggests that the lens might produce soap-bubble bokeh (same as we've seen on the first generation Tamron 28-75mm):
The 17-28/2.8 is like that too. Usually a design tradeoff to improve sharpness, but the bokeh suffers a bit. Seems like a reasonable choice for wider lenses, and you won't always notice the effect--only with very strong/contrasty highlights. It definitely turned me off of the original Tamron 28-75 though, so something to watch for in samples on this lens, mainly at 40mm wide open.
