October 22, 2014, 08:17:31 PM

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Messages - Mika

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16
Landscape / Re: Please share your snow/ Ice Photos with us in CR.
« on: February 16, 2014, 05:40:40 PM »
And then January (-25C mostly)

It's difficult to portray snow in so few photos, and given the limited time we have sunlight in January-February, it is hard to find good photography days. On the other hand when the light gets good, it remains so for the whole day. Think about staying in the golden moment for several hours and you get the idea...

I'll continue this tomorrow

17
Landscape / Re: Please share your snow/ Ice Photos with us in CR.
« on: February 16, 2014, 05:16:37 PM »
And here's for Decembers

About the last one, I wasn't particularly looking it from an artistic point of view. It's more of a documentation of reality of this Christmas here. In case you were wondering, yes, that is indeed a road. Unfortunately, overcast sky didn't allow me to try more refined artistic look.

Snow and darkness gives rather vivid colors.

18
Landscape / Re: Please share your snow/ Ice Photos with us in CR.
« on: February 16, 2014, 05:09:52 PM »
Thanks, this is a great topic!

Now I had a convenient excuse to rummage through seven years of winter photos, here's four from Novembers spanning over several years.

I do find winter photography with snow rather tricky. It's almost always a learning experience.  :D

19
EOS Bodies / Re: Patent: Canon 11-24mm f/4 Lens
« on: January 26, 2014, 06:50:42 AM »
I sort of concur with the people thinking F/4.0 would be perfect for this range. If it had to have a variable aperture ratio, then I'd actually like the shorter end to be slower one. But I sort of like that Canon designed it a static F/4.0, and that it is F/4.0 and not 2.8.

What it comes to bulbous front element, I was first thinking that principally, the aperture ratio should not affect it much (11 mm focal length F/4.0 equals 2.75 mm entrance pupil diameter, compare that to 4 mm of F/2.8 ). Then I realized that there is still a need for additional elements correcting the image edge, thus leading to a longer lens, which effectively enlarges the front element due to FOV. F/4.0 should ease things up a bit with respect to vulnerable front, but by looking at the lens diagram, I'd see it's still quite vulnerable.

What it comes to physical limits, it is not feasible to design a rectilinear lens with a FOV of 180 degrees. I think Theia Technologies has a 135 141 degree small-format rectilinear (sorta, it has some amount of barrel distortion but nothing close to fish-eye) with an aperture ratio of F/1.8. As a design exercise, I have once designed a 150 degree field of view rectilinear ultra-wide for a small format sensor. It was a sort of no-holds-barred thing; required several aspherical surfaces and special glass materials to get it function at least somehow, the total number of lens elements was over 15. I wouldn't like to try that again with a 35 mm sensor size.

So yes, rectilinear ultra-wides do become very expensive very quickly. I tip my hat to Sigma designers who could do a 12-24 with a relatively modest price. I tip my hat to Canon designers if they get the 11-24 on the markets.

EDIT: Moderators: why is this in EOS Bodies? I think I first wrote to a thread of the same patent under Lenses category.

20
Lenses / Re: Canon 11-24/4 patent
« on: January 25, 2014, 08:10:43 AM »
If I recall, Nikon had a 10 mm full-frame patent some time ago.

What I do like in Canon's approach is that it has a constant aperture ratio, and that this aperture ratio is F/4. From the usage point of view, I believe this is actually a better choice than F/2.8 for this focal length range. 16-35 is another case, though.

Let's see if they release it, though. Price may become an issue, but F/4.0 helps there a bit too.

21
Lenses / Re: I'm done - I have all the lenses I need
« on: November 01, 2013, 07:50:06 PM »
Congratulations!

Well, I'll have to say I'm gravitating to a certain set of objectives as well, though my job as optics designer sort of requires me that I have some knowledge of the common objectives and knowledge of using them too.

I admit I'm gravitating towards the shorter end of focal lengths, my most used objectives seem to be:
Sigma's 35/1.4
Canon's 50/1.0
Canon's 24-70/2.8 I (not looking to II, this one is better for me)
Canon's 70-200/4.0 L IS

These lenses I do have as well, but there's something I'd like to change in them:
Sigma's 12-24 I - If this was a constant 4.0... I run against 5.6 on cloudy days
Sigma's 120-400 - 20 - 30 % lighter version would be nice. Or 300/4 II, if it happens.
Canon's 50/1.4 - Quite a long to list on what I'd like to change here. Though the motivation for this is just outside photography in low light, where I would not like to take the 1 kg behemoth.

Though, I can live with Sigmas, but that 50 mm update Canon... I'd also be interested in trying out a fast wide angle (something like 24/1.4 or 20/1.8 ) when I can find one that I like. After that I think I'm pretty much set.

What did not work for me? Well, 85/1.8 and 28/1.8, I don't use neither of them that much. Though they make a good light weight set for holidays with a crop body. And since I travel quite a bit with bicycle, long and or fast teles are pretty much a no-go. For example 200/1.8 was far too heavy for me, and 70-200/2.8 IS II sounded intriguing until I realized its twice the weight of the 4.0.

22
Lenses / Re: Photos from 200-400. Also any comments...
« on: November 01, 2013, 07:05:09 PM »
Quote
If you're really interested, I would suggest Finland. There are some companies organizing photo safaris up north. Normally it is wolf and bear, but they also have a much larger population of lynx and wolverine, than we have here in Norway, so I would assume you could make them organize something that would suit you.
Check: http://www.insidenature.se/ostra-finland/ (you'll have to run it trough translation first though)

Thanks for pointing this out. Eastern Finland has a relatively large population of lynx and wolverine, and if you are serious, these guys could help you with wolverines and bears. There are several other people you could ask about, this one is famous for his book documenting his life with wolverines, but he does other stuff too.

23
Third Party Manufacturers / Re: Sony A7 or A7R pre-order list
« on: October 17, 2013, 03:22:01 PM »
I'm interested, but I don't do pre-orders, so I'll wait for reviews first - and possibly that the price will drop a bit before buying it.

Otherwise, it's pretty much what I've been looking for: a lightweight full-frame camera that is more portable for trips than the Canon's crop bodies. I will still use the Canon's larger bodies closer home for better handling, but on trips, this is about perfect.

Especially if they get a 35/2 and a 85/2 (or 1.8s) out soon the A7 will be darn good for holidays, able to tack about anything I can think of and still be lighter to carry around than an APS-C body with 28/1.8 and 85/1.8.

Actually, thinking about it, I may sell the 28/1.8 and 85/1.8 soon.

24
Lenses / Re: Best 35mm wide open????
« on: September 26, 2013, 07:15:28 PM »
Canon's 35L doesn't seem to fare much better according to Photozone, can't say for myself since I haven't used 35L.

When it comes to bokeh, I find PZ to be pretty useless. I do not find their sharpness charts much useful either.

I own the 35L. Tell me what you want me to prove to you - that it has great bokeh, or that it has poor one. I can prove both with examples.

Well, if I really wanted to characterize an objective, I'd put it in the MTF bench at work. Or start counting wavefront fringes in a double pass interferometer setup. Or check the actual lens performance from construction data. But online sites are far more convenient for referencing and save me from quite a bit of hassle.

So I don't have a great interest in finding out which one of the 35s has the best or worst bokeh in which situation. The point was that the difference between Sigma's and Canon's are comparatively small, and in some situations the other is better than the other and vice versa.

25
Lenses / Re: Best 35mm wide open????
« on: September 25, 2013, 08:06:24 PM »
About the bokeh picture Pi posted, I have seen many lenses (including Canon 50/1.2 and 24-70) produce equally bad background blur.

Examples (with the 50L)? I have pushed it to get bad bokeh but not nearly as bad.

I think Photozone has the worst 50/1.2 shot that I have seen and know for sure it is 50/1.2

Here you can find another example, but I'm not certain whether this is taken with 28-70/2.8 or 50/1.2. I'm leaning towards the zoom for some reason.

The first one is bad, the second one is OK. But they cannot beat this:

http://www.flickr.com/photos/zackhuggins/8483812543/#

Hehe, that's indeed pretty harsh. I'll have to try that myself some time. So far I've been pretty satisfied with Sigma 35/1.4. I think the other photo does have a pretty ugly background blur too. It distracts my eye from the subject (as does yours). Canon's 35L doesn't seem to fare much better according to Photozone, can't say for myself since I haven't used 35L.

26
Lenses / Re: Best 35mm wide open????
« on: September 24, 2013, 03:54:44 PM »
About the bokeh picture Pi posted, I have seen many lenses (including Canon 50/1.2 and 24-70) produce equally bad background blur.

Examples (with the 50L)? I have pushed it to get bad bokeh but not nearly as bad.

I think Photozone has the worst 50/1.2 shot that I have seen and know for sure it is 50/1.2

Here you can find another example, but I'm not certain whether this is taken with 28-70/2.8 or 50/1.2. I'm leaning towards the zoom for some reason.

But I reiterate that none of this is actually seriously detrimental for photography, you'll just need to know when this happens and avoid it.

ps. 50L can refer to another 50 too...

27
Lenses / Re: Best 35mm wide open????
« on: September 23, 2013, 05:12:31 PM »
About the bokeh picture Pi posted, I have seen many lenses (including Canon 50/1.2 and 24-70) produce equally bad background blur. In fact, most objectives do have this effect at some object and background distance and brightness combo.

Just learn when it happens and work around it; I can't think of an easy way (or better said, feasible way) to eliminate this effect in lens design.

28
Lenses / Re: Dxo tests canon/nikon/sony 500mm's
« on: August 08, 2013, 08:46:18 AM »
Sorry again about the delay, I was on a vacation trip.

I have not said that the MTF computed using the slanted edge method isn't useful. However, I have said that the MTF calculated with this method isn't scientifically accurate if you want absolute accuracy. The problem with the averaging is that it tends to lose information of the spot itself, while the average along two orthogonal directions is computed with sufficient sampling, pretty much nothing is said about what happens between the orthogonal directions.

For this reason, I don't believe it would be possible to reconstruct an accurate PSF with the slanted edge method and thus the measured MTF must be slightly invalid as well. You can think of this from the dimensional reduction point of view; it is generally not possible to recreate a 3D function from two 2D functions. Higher order aberrations do give rise for all sorts of interesting spot shapes and orientations with element decentering.

But as I said, slanted edge method allows comparable MTF measurements and is very good at that, but it does not allow absolute measurements where you have to guarantee the results.

It is relatively easy to think that there isn't differences between the behavior of rays when shifting from a wavelength range to another. I hear this argument quite often, and this may sound like blasphemy for some, but I disagree with that. For example, there is a considerable difference between the ray propagation physics between a visual wavelength range camera (typically not diffraction limited) and a THz system and you have to take them into account when designing them.

29
Lenses / Re: Dxo tests canon/nikon/sony 500mm's
« on: July 29, 2013, 06:34:48 AM »
I checked through some of the late night photos I have taken with 28/1.8 and 40D to see how large the star points actually are on the sensor. With 8-15 second exposure, I'm seeing that the star spots are within 4x3 pixels or 5x4 (the extension along the other dimension is the most dominant here, and is due to exposure time and Earth's rotation).

This is measured from a straight out of camera JPEG, with F/3.5 and with a lens that had slight amount of frost on the front element. And even then the spots are quite limited. I do think that had the conditions been better (no frost and better lens with equal aperture and better ISO than 40D has) and had I taken RAWs, most of the star images would fall within 3x3 region (as I said earlier) - spread is mainly because of the AA filter, otherwise stars should fall within a single pixel assuming any kind of reasonable performance of the objective and with F-numbers less than 5.6. With a PSF of size 3x3 pixels, it is hard for me to see how this could be used to compute the MTF even with sub-pixel sampling without averaging over larger area.

For example, 100 pixels with a 5 ┬Ám pitch respresents about 0.5 mm, which is significant. If we are talking about smaller averaging distance, for example 30 pixels, the uncertainty of the slant angle itself would be about 2 degrees. I haven't seen many error estimations to the slanted edge method, but I'm afraid I'll have to do that myself in the near future in a publication.

It is great to hear about your background in the tomography, it helps me understand how you think about these issues. But I have to remind you that we are talking about optical systems within visual wavelength range, where things are quite bit different from radio waves (MRI) or THz region or ultrasound. From my hazy memory, MRI actually measures time differences on different detectors, but it's 11 years since I have needed to think anything related to NMR? These medical wavelengths are used mainly because of the requirement of non-invasiveness and that's why you need to deal a lot with image processing techniques.

I think a better equivalent would be to compare image processing techniques in astronomical telescopes to get the state-of-the-art results in the visible wavelength range. Adaptive optics correction to the PSFs allows ground based telescopes just to match them with Hubble over a smaller field of view on good nights.

30
Lenses / Re: Dxo tests canon/nikon/sony 500mm's
« on: July 27, 2013, 11:57:47 AM »
Sorry about the delay in replying, the weather has been (almost too) good in this week.

What it comes to slanted edge testing, this is where I disagree (partially). If we consider a slanted edge test with a body+lens setup, there are several issues in that what I'd think as a deal breaker for recovering the real point spread function as I know it.

First, the pixel pitch typically does not actually support sufficient sampling. Second, the slanted edge is considerably larger and thus the average of the line spread functions is taken over a comparatively large image block where PSF has probably changed by some amount - this is typical for wide angle constructs where there are several aspherical surfaces. And if the length of the slanted edge isn't long enough, there will be uncertainty in the slant angle and the sub-pixel sampling is then affected. Third, given the slant angle is small, this test methodology cannot differentiate between imaging quality of tangential and sagittal axes and can miss changes in the averaging direction completely.

For an extreme example, it would report the MTF of a cylinder lens system equal to a spherical lens system if it was aligned along the imaging axis. This mistake of course, is hard to imagine happening in real life, but extending the thought for a bit, it is easier to understand that decentered elements along one axis could be missed with this. For this reason, lens would need to be turned 90 degrees to determine both directions.

The bar chart quality assurance benches that I have seen are used as OK/NOK step in quality control. The actual MTF measurement benches magnify the known spot with a high quality microscope objective, and thus this measurement of the MTF is much more local, and for that reason I accept it as a representative PSF. The only people who I do know to have sampled the PSF directly are astronomers.

What I'm saying here is not that the slanted edge method in lens+body setup isn't useful in determining MTF (with certain error bounds), it is. It is also very useful in relative comparisons if all systems are measured in the same bench. But what it does not do is provide scientifically accurate MTF values, and additionally, the online reviews are usually about resolving power of a body+lens combination, but the macro-contrast level is not that often reported.

So I suppose it all boils down on what is accepted as a PSF.

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