December 17, 2014, 09:54:05 PM

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Messages - epsiloneri

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Lenses / Re: Sigma 50mm Art 1.4 Focusing problems
« on: May 31, 2014, 02:03:18 AM »
This (open loop focusing) was true previously, but Roger Cicala have found that newer Canon cameras do closed loop focusing (ie the PDAF system confirms the focus after the lens has moved).
Yes, that's right.

Lenses / Re: Sigma 50mm Art 1.4 Focusing problems
« on: May 31, 2014, 12:47:39 AM »
Cameras are awesome devices, but they don't work by magic. Knowing a little bit about how the body and lens interact can be helpful in understanding and evaluating potential problems. The body detects how much out-of-focus an image is and sends a signal to the lens to adjust it, in one go in case of phase AF. The lens has to interpret this signal correctly and adjust properly; therein lies the software challenge for Sigma. The lens does not care how the body came to the conclusion that the particular adjustment was needed; ergo choosing focus point etc is entirely a body issue and has nothing to do with the lens (except in fringe cases such as the lens not illuminating the whole image plane - i.e. clearly a broken lens). As a corollary, the lenses' role for AF in low-light conditions is also questionable. Sure, faster lenses should give the body an easier time with more photons, but that's about it.

About AFMA, I would have expected the USB dock with AFMA to fix the relative AFMA of a lens, and the body to fix the absolute AFMA with respect to that particular body. You seem to say differently,Mt Spokane Photography. Why? Is this your expectation or actual experience? Once I get the dock and some time I could test multiple bodies with a single lens and FoCal to see how they correlate. Perhaps someone else has already tried that.

Lenses / Re: Review: Sigma 50mm f/1.4 DG HSM Art Lens
« on: May 18, 2014, 12:58:59 AM »
why did you set it up at 1.6m and not 1.5m I think this is quite a big varience you might experience problems with your calibration I measured the distance from the camera sensor plane to the target for each distance required on the sigma calibration
I don't have the USB dock (yet) so I'm not making distance-dependent MA calibrations. This was just to check the reliability of the AFMA at different distances. The variance of the AF is normal and comparable to the best Canon lenses. Or were you referring to the 1.5-1.6m difference?

Lenses / Re: Review: Sigma 50mm f/1.4 DG HSM Art Lens
« on: May 17, 2014, 06:29:48 PM »
To add another user experience, the AF of my copy of the Sigma 50/1.4 ART works just fine so far (I've had it a week), both in real-life shooting and from FoCal. This contrasts to the previous Sigma 50/1.4 EX, which has very problematic AF for me. Attached are the FoCal-produced contrast plots for 5D3 with

1) Sigma ART 50/1.4 @ 1.6m distance to target (AFMA=0)
2) Sigma ART 50/1.4 @ 2.6m distance to target (AFMA=+3)
3) Sigma EX 50/1.4 @ 1.6m distance to target (AFMA=+9)

As you see, the AF seems fairly consistent and a predictable function of AFMA for ART, but not so much for EX. There appears to be a small dependence on distance, although it could also be the accuracy of FoCal; I would have to make more tests with a larger distance range to find out. I've used AFMA=0 so far, and it has worked just fine in actual photography. Not more misses than expected for such a shallow DOF (similar to what I'm used to from e.g. the excellent 85/1.2L II). I also have had no problems with the Sigma 35/1.4 ART.

Lenses / Re: New Canon Tilt-Shift Lenses at Photokina [CR1]
« on: May 10, 2014, 12:55:10 AM »
Tilt+swing = tilt+rotation
Tilt or swing = tilt+rotation
Hm, let me put it like this then: if the tilt decides how forward you go, and swing how far to the left you go, then you can achieve the same result by first taking the bearing (rotating) and going only forward (tilt). It is the same thing, and not a matter of opinion.

Lenses / Re: New Canon Tilt-Shift Lenses at Photokina [CR1]
« on: May 09, 2014, 01:23:22 PM »
But the TS-E only tilt in one direction, no tilt and swing. While the rotating mount in nice it won't help in this situation IMO.
Tilt+swing = tilt+rotation

Now, for this lens o be useful even without being AF perfect it will have to be a superset of Samyang 24 1.4

1. NO Coma
2. No decentering issues.
3. Very good center wide open with good  corners.
Judging from the image quality tool at TDP, the Samyang 35/1.4 seems optically quite the match to the Sigma 35/1.4A, with both better than the EF 35/1.4L. The Samyang 24/1.4 though looks quite a bit worse than the EF 24/1.4L II wide open (though COMA is hard to infer since not explicitly tested). This hopefully means that there is room for improvement for a future Sigma 24/1.4A over the corresponding Samyang. (and yes, the EF 24/1.4L II unfortunately has terrible coma as I know from first-hand experience)

Me?  I'm just thinking I'd love to dig in on the at sample shoot and do some root cause analysis.  I guess that's the engineer and test geek in me, though.
Sounds like you'd do a good job testing the AF thoroughly if you got the chance. Please share your findings if you do.

Landscape / Re: Deep Sky Astrophotography
« on: February 27, 2014, 07:32:20 PM »
Nice image, and good to see that the 7D did not completely cut out the H-alpha. H-alpha regions must be some of the harder objects to image with a non-modified dSLR.

... I hate to feed your maniacal ego though...
You know, you've been taking little jabs at me like that for days.
Hehe... he actually gave you a compliment, although his German way of expressing it hides it pretty well ;D

Third Party Manufacturers / Re: Oh neat, a Nikon 300f2 (1981)
« on: February 14, 2014, 03:33:32 AM »
There are also many unique lenses used for medical/military/astronomy purposes, which you can't use in the regular SLR cameras. For example: [...]
Don't forget the 57600mm f24 lens in orbit, or the giant 14760mm f1.8 lenses on the ground. Of course, both will pale in comparison to the planned 420000mm f10 lens. All for non-DSLR cameras, of course :P

Lenses / Re: 100mm L not for portraits?
« on: January 29, 2014, 10:39:35 AM »
In the olden days ...
In the even older days you could tilt the focal plane and have both girls in focus. As long as they were still for the duration of setup and exposure....

(you can actually still do this with a TS lens, not the 100L, but it is a bit of a challenge with moving subjects)

EOS Bodies / Re: Patent: Microadjustment Automated
« on: January 15, 2014, 05:40:02 AM »
Hm, this sounds very much like what I suggested in this forum, 3 years ago:

1) AF focus on a target, say a properly aligned focus target. The camera registers what it thinks is the best focus.
2) Without moving the camera or the focus tagert, go to 10x live view and manually focus to what you think is the best focus, push a button or something for the camera to register what your preferred focus is.
3) The camera makes use of info from 1 and 2 to compute MA.
Alternatively, one could let the camera itself compare the AF between the AF sensors and the live view contrast AF, and compute MA under the assumption that live view AF is more accurate. That would be even simpler, and according to my experience, live view contrast AF is nearly always accurate (but slower). Contrast AF is not affected by front/back focus issues, since it uses the actual detected image for AF, so it would be perfect to correct for AF sensor MA. I can imagine setting up the camera on a tripod and align it to a focus target, select "calibrate AF" from a camera menu, and then let the camera automatically cycle through 10 AF measurement cycles (say), computing the best MA. Why not, Canon?

I'm glad Canon listened :D I hope this makes it into firmware at some point...

Canon General / Re: History: The Original Canon EOS 5D Camera
« on: December 28, 2013, 04:44:06 PM »
I'm throwing a flag on this statement.
I'm not sure what this idiomatic expression means, but I suspect it's not a compliment on my insightful post...

First off, anybody willing to accept the overall IQ of the 5D over later versions should have no problem adjusting color in ACR or other top-end editors. Secondly, since your statement is non-specific, it has no vlaue in a 5D vs "anything else" conversation.
In the text you quote I was responding to a specific question by privatebydesign (here rephrased): Why is the colour reproduction of different sensors discussed at all, when profiling ought to make them all identical? As I explained, the mapping of a full spectral distribution into three numbers (R, G, B) depends on the particular filter curves of the sensor. Profiling helps in making this mapping as close as possible to some standard, but it is in general not possible for sensors with different filter curves to give the same colours for arbitrary spectral distributions, no matter how careful the profiling. I can give a more detailed explanation with examples to help you see why this is so, if you are interested, but I suspect you are not.

In summary, that is why claims of "better colour fidelity" of a particular sensor (in this case that of 5D) cannot be simply discounted by arguing that you can always profile away any differences, since that is not generally true.

Picture Styles does have some limitations, like getting those settings applied to RAW files in third party software, but it is very powerful, with six HSL primary colour adjustments, there isn't much you can't correct for, certainly the differences between a 5D and a 5D MkIII are no issue.
I'm sure the colour reproductions you can get from 5D and 5D3 are similar enough to not be an issue, but I find the claims of 5D's higher colour fidelity interesting and wouldn't mind seeing some evidence for it.

Canon General / Re: History: The Original Canon EOS 5D Camera
« on: December 07, 2013, 03:54:05 AM »
I still preferred the colors out of my 5Dc than my MK3s. I skipped the mk2 series because it wasn't worth upgrading for me.
I never understand comments like this. It is digital, why not profile your camera to get whatever "look" you want from it?
There's more to colours than simply three numbers. E.g., the colour separation (amount of "cross-talk" between colours) might be different between different detectors (I'm not saying it is for 5D and 5D2, just that it could be). The Bayer detector has three filters: R, G, & B. By making the filters broader in wavelength, you gain some sensitivity, but you also run the risk of having the filters overlap in wavelength and counting the same light twice, e.g. for both R and G, and that will decrease the colour fidelity in your image compared to filters where there is less overlap.

So, not all detectors necessarily reproduce colours the same way, and it is no possible to correct in software (because it would be an ill-posed inverse process).

Landscape / Re: Milky Way near the moon?
« on: September 15, 2013, 02:35:53 PM »
This is the reason pictures of the moon taken by the Apollo astronauts do not show the stars... contrary to the beliefs of some conspiracy theorists  ::)

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