September 01, 2014, 11:09:29 AM

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Messages - epsiloneri

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1
Lenses / Re: 50mm Coma Sigma Art vs Regular Sigma F1.4
« on: August 01, 2014, 01:33:34 PM »
Thanks for the comparison, great work. From various reviews it seems that even the great Otus shows significant coma at 1.4, have you made any comparisons yourself? A bit disappointing, I hope the rumoured future Sigma 24/1.4 Art fares better, with a coma similar to the Samyang 24/1.4 (or even better).

2
Canon General / Re: Dragonfly, Powered by Canon Lenses
« on: July 13, 2014, 04:26:33 AM »
Thanks Pieter! I read your paper with interest. Dragonfly is a very cool project from an astronomical perspective, but there are also several points that could be of interest for the more general Canon shooter / astrophotographer:

  • The optics are found to be essentially diffraction limited, at least <1 degr of the center, which is quite amazing. This means that the image sensor will give increasingly sharp images all the way to a pixel pitch of about 0.63 ┬Ám before out resolving the lens. This is 6.8 times smaller than the effective pixel size of a 7D and would imply a 839 MP APS-C or 2.18 GP FF sensor! The lens resolution is likely decreasing from diffraction limited away from the central regions, but this sets the upper usable limit for sensor resolution. In practice, there will be other things limiting the resolution, like turbulence in the atmosphere (for anything shot at a distance).
  • Strehl ratios between 0.2-0.8 (where 1.0 is 'perfect') indicates that the lens provides a very high contrast (which we knew). I wonder if the Canon designers have deliberately tried to keep the effective point-spread function constant with wavelength (reducing colour mis-matches in images), deacreasing the Strehl at short wavelengths.
  • The precise focus of the lens is strongly temperature dependent: a temperature difference as small as 1C gives a significant shift in focus. This is mostly relevant for exposing an extended period, like in astrophotographical applications.
  • The foot of the 400/2.8L IS II provided by Canon shows significant flexure so that care must be taken during tracked exposures.
  • For those wanting more images, I found two papers accepted by ApJL providing such for M101:

    http://arxiv.org/abs/1401.5467
    http://arxiv.org/abs/1406.2315

The project seems to have left the start-up phase only recently (they are apparently still extending the array), so I'm sure we can expect more results soon. Note, however, that they are targeting the faint structures around galaxies, and with only two broad-band filters ('r' and 'g'), meaning the images will probably not be as spectacular aesthetically as narrow-band imaging of more photogenic nebulae. But when they're done with the galaxies perhaps they can put in some nebular filters instead, and give us the most surface-brightness sensitive images of nearby nebulae :P

Actually, surveying for nearby supernova remnants in H-alpha might be a pretty interesting project scientifically in itself for this Dragonfly.

And then we have the transiting exoplanets, of course, but that has probably been covered pretty well by the already mentioned super-WASP projects and the upcoming NASA TESS mission.

3
I can confirm that DPP 4.0.0 does not support 7D CR2 :( But it can be installed in parallel with DPP 3.14.15 that still supports it.

4
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.

5
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.

6
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?

7
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.

8
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.

9
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

10
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)

11
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.



12
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

13
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

14
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)

15
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...

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