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Messages - epsiloneri

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Bah, we all know the quality of those slow mirror tele lenses, I'm waiting for the big white refractor version. f/15 is way too slow for AF. Good with IS though.

Meaning, I care more about me liking my photographs than what others think.
Probably you're not a pro photog, then :-p ...
You're quite correct!
... however one valid point is: If you don't like the shots yourself, at least at some level, can you produce good results? If you think "well, the framing/cropping is off, but who cares?", can you continue to do good postprocessing on it?
What you think and what others think is often very different things, "good" is subjective. If you're a pro and you fulfill your client's standards, your own may not be relevant.

Technical Support / Re: Dynamic Range questions..
« on: September 27, 2014, 02:18:31 AM »
   One think I don't understand is that how a camera can have more than 14 stops of DR when the camera only record in 14-bits...
What camera does that? Detectors sometimes become non-linear near the saturation limit, but the A/D conversion is usually linear, AFAIK.

Many people obsess over things that no-one else sees.
It's nice if others like my photographs, but first I want to like them myself. Meaning, I care more about me liking my photographs than what others think. Maybe a tad egocentric :) With a more positive spin it could be called artistic integrity.

Photography Technique / Re: Why 3:2 aspect ratio?
« on: September 27, 2014, 02:00:17 AM »
I often crop to 4:3, in particular for portrait. Landscapes generally get much wider crops.

Canon General / Re: Square or cross shaped sensors
« on: September 27, 2014, 01:56:36 AM »
The obvious answer would be to use a circular raw detector, and then crop to whatever format you like (either in camera or post). This would make ideal use of the optics, which inherently provide a circular image. I think we will eventually get sensors like this, once the sensors become significantly less expensive than the optics. The pixels may then be hexagonal as well, perfectly sampling an f/1.0 diffraction-limited image and interpolated to produce the desired orientation of square pixels.

Lenses / Re: Is there a need for a 50mm?
« on: September 07, 2014, 04:10:38 PM »
I love walking around with my 70-200 with the 40 in my pocket.
You really need big pockets to put in the 70-200 should you want to switch to the 40, though.

Pricewatch Deals / Re: Sigma 50mm f/1.4 Art in Stock at B&H Photo
« on: September 04, 2014, 05:05:21 PM »
I'm still on the fence since I have the 35 -- don't know if it can make that much difference.
Unfortunately the 50 Art is not very suitable for astrophotography (if that was an application you had in mind). I don't have a problem with the AF, but I don't like the coma either... here's a lower right quarter of an image, see how the stars close to the corner are cross like. Beautiful for daylight, not so much for night vistas.

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).

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:

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.

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.

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.

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