troubleshooting – Is there a focusing issue with the Sigma 17-50mm f/2.8 on a Canon 70D?

The first sample image in the question is focused well in front of the central pillar. The second is focused well behind the flowers.

You have told us that you are using single point AF but you haven’t told us which AF mode you are using: One Shot, AI Servo, or AI Focus? If you’re trying to focus and recompose using AI Servo the camera will refocus when you move the camera to point at a different spot. If you use AI Focus the camera will initially hold focus as it would in One Shot mode, but if you recompose and hold the camera too long in the new position the camera will sense that your selected AF point is no longer in focus and will switch over to AI Servo.

There appear to be other issues at work that might also be contributing to your results:

Diffraction The 70D is a Canon APS-C camera with 4.1µm pixel pitch. The Diffraction Limited Aperture (DLA) of the 70D is f/6.6. This is the point at which the effects of diffraction begin when viewed at the pixel level. As apertures are narrowed beyond the DLA the results get more and more noticeable at normal viewing sizes. The best way to avoid this is to shoot at around f/8 or wider and at f/6.3 or wider if possible.

Camera movement Not everyone can hold a camera steady enough to use the 1/focal length rule-of-thumb, even when viewing at the standard 8×10 sizes for which it applies. You may get useable results for viewing at smaller sizes, but nowhere near the equivalent viewing size of looking at part of an image at 100% on your monitor. If you have an HD (1920×1080 pixels) monitor that measures 23″ diagonally you are viewing images at 96 ppi. That means an 18MP image viewed at 100% is being magnified at the equivalent of 54×36 inches! That’s 5X the magnification of the standard 8×10 print.

The optical limits of your lens I’d like to know where you read excellent reviews of this lens. I’ve never seen any critical reviews from reputable reviewers written about it that impressed me very much. Before you can blame AF you need to be sure that something else isn’t causing your images to be blurred. To do that you need to eliminate as many of the other possible causes as you can.

  • Mount your camera on a stable tripod, turn off optical image stabilisation, and use a cable release or the self timer to release the shutter. This will help eliminate camera movement as the source of your problem.
  • Shoot under bright enough constant lighting that your shutter speed at ISO 100 can be 1/100 second or faster. Use the fullest spectrum lights available to you. This will further help to eliminate camera movement including vibrations caused by the movement of the camera’s mirror. Properly exposing using low ISO will also help eliminate poor image quality caused by a low signal-to-noise ratio and the resulting noise reduction.
  • Use a flat target that is lined up parallel with your camera’s image sensor and perpendicular to the optical axis of the lens. An easy way to do this is to aim your camera at a flat, stable mirror. Center the viewfinder on the center of reflection of the lens in the mirror. Then tape your focus target onto the mirror being careful not to move the mirror.
  • Use careful manual focus with magnified Live View. Take several samples while refocusing manually between each sample.
  • Repeat the test shots using One Shot AF mode with the single center focus point selected. Move the lens to infinity or minimum focus between each test shot. Use a half shutter press with your cable release to allow the AF to confirm focus before taking the photo.
  • Compare the best of the manually focused shots to the best of the AF shots.

If there is a significant difference then you have an AF issue. If there is not a significant difference then your problem lies elsewhere.

sigma – How do you add lens profiles to Adobe Lightroom?

There is a readme.txt at both



C:Program FilesAdobeAdobe Lightroom ClassicResourcesLensProfiles1.0ThirdParty

that reads

Install third-party (non-Adobe) lens profiles here.

By default, .lcp files are saved to C:UsersbensoAppDataRoamingAdobeCameraRawLensProfiles1.0

I left my original file in AppData and then copied that file to both these locations. I didn’t investigate which location Lightroom is dependant upon, but Adobe keeps identical lens profile directories on my computer; adding to their file clutter worked for me.

ct.category theory – In the category of sigma algebras, are all epimorphisms surjective?

Consider the category of abstract $sigma$-algebras ${mathcal B} = (0, 1, vee, wedge, bigvee_{n=1}^infty, bigwedge_{n=1}^infty, overline{cdot})$ (Boolean algebras in which all countable joins and meets exist), with the morphisms being the $sigma$-complete Boolean homomorphisms (homomorphisms of Boolean algebras which preserve countable joins and meets). If a morphism $phi: {mathcal A} to {mathcal B}$ between two $sigma$-algebras is surjective, then it is certainly an epimorphism: if $psi_1, psi_2: {mathcal B} to {mathcal C}$ are such that $psi_1 circ phi = psi_2 circ phi$, then $phi_1 = phi_2$. But is the converse true: is every epimorphism $phi: {mathcal A} to {mathcal B}$ surjective?

Setting ${mathcal B}_0 := phi({mathcal A})$, the question can be phrased as follows. If ${mathcal B}_0$ is a proper sub-$sigma$-algebra of ${mathcal B}$, does there exist two $sigma$-algebra homomorphisms $phi_1, phi_2: {mathcal B} to {mathcal C}$ into another $sigma$-algebra ${mathcal C}$ that agree on ${mathcal B}_0$ but are not identically equal on ${mathcal B}$?

In the case that ${mathcal B}$ is generated from ${mathcal B}_0$ and one additional element $E in {mathcal B} backslash {mathcal B}_0$, then all elements of ${mathcal B}$ are of the form $(A wedge E) vee (B wedge overline{E})$ for $A, B in {mathcal B}_0$, and I can construct such homomorphisms by hand, by setting ${mathcal C} := {mathcal B}_0/{mathcal I}$ where ${mathcal I}$ is the proper ideal
$$ {mathcal I} := { A in {mathcal B}_0: A wedge E, A wedgeoverline{E} in {mathcal B}_0 }$$
and $phi_1, phi_2: {mathcal B} to {mathcal C}$ are defined by setting
$$ phi_1( (A wedge E) vee (B wedge overline{E}) ) := (A)$$
$$ phi_2( (A wedge E) vee (B wedge overline{E}) ) := (B)$$
for $A,B in {mathcal B}_0$, where $(A)$ denotes the equivalence class of $A$ in ${mathcal C}$, noting that $phi_1(E) = 1 neq 0 = phi_2(E)$. However I was not able to then obtain the general case; the usual Zorn’s lemma type arguments don’t seem to be available in the $sigma$-algebra setting. I also played around with using the Loomis-Sikorski theorem but was not able to get enough control on the various null ideals to settle the question. (However, Stone duality seems to settle the corresponding question for Boolean algebras.)

Canon – EOS-M4 / 3 adapter stuck in Sigma lens?

So I just bought a new Canon camera and thought my Sigma 24mm 2.8 Superwide lens would be compatible with it as it is an EF mount. The lens itself was given to me second-hand and I'd been using it on M4 / 3rd cameras, so I never had to remove the adapter. I'm trying to do it now, but it won't even move at all. Am I being an idiot and it's all part of the lens? Also, this & # 39; adapter & # 39; It also acts as an opening as it has a caster wheel to help adjust. I have attached photos to see if anyone can help / give any advice.

P.s Is there a small hole where the adapter release button may have been?

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Finance – Unique partition of a sigma algebra in a finite state space test?

I know intuitively that for a certain $ sigma $-algebra in a finite state space that a partition exists and is unique. However, I am struggling to demonstrate this. I have tried working towards a contradiction assuming that there are two different partitions. However, I am struggling to execute this … any help would be appreciated

reference request – What is the distribution of the norm of the multivariate $ X sim mathcal {N} ( mu, Sigma) in mathbb {R} ^ d $

Leave $ X sim mathcal {N} ( mu, Sigma) in mathbb {R} ^ d $ follow a multivariate normal distribution. When $ mu = 0, Sigma = I_d, $ we know $ || X || sim chi (d), $ the distribution of chi, but I don't see why that would directly tell me something about the distribution of $ || X || $ in general cases of $ mu, Sigma? $

If necessary, you can assume that $ mu = 0 $ or $ Sigma $ is diagonal (not identity) or a combination of both.
At the moment, I am more particularly interested in $ mathbb {E} || X ||, var (|| X ||) $. References highly appreciated too!

Canon EOS 6D mark II with Sigma lens looks weird on LCD monitor

According to your comment, it has a Sigma 17-70mm f / 2.8-4 DC Macro OS HSM Lens, which is an APS-C lens, on a full-frame camera. An APS-C sensor is smaller than a full-frame sensor, so lenses designed for these cameras project a smaller image circle. APS-C specific lenses are not designed for use with full-frame cameras. (See this post for more details on sensor sizes.)

Canon's specific APS-C lenses (with EF-S in the model number instead of EF) have a different mounting flange to prevent you from mounting them on full-frame cameras like your 6D, but almost all APS lenses- Third-party C-mount EF will mount on Canon FF cameras.

Lens product descriptions generally (ideally always) Indicate fairly prominently if they are for full-frame or crop-sensor cameras, so you can use this information to help you determine if a lens is right for your camera. If the description of a lens indicates that it is for APS-C, crop-senor or digital, then this is a specific lens for APS-C and is not designed for your camera. If it indicates full frame, then it is (see note 1 below).

Here is information from Michael C's answer to this question and from a community wiki on decoding lens model numbers that should help you target the correct lens types in the future:

Look for this

  • Sigma Lenses: Model numbers containing the DG designator (no DC)
  • Canon lenses: model numbers starting with EF (no EF-S or EF-M)
  • Tamron Lenses: Model numbers containing the designator Di (no Di II or Di III)
  • Tokina Lenses – Model numbers containing the FX designator (no DX)
  • Samyang lenses: model numbers that Do not do contain the CS designator

When shopping at a site like B&H Photo, you can use the filter function to display only the lenses designed for your full-frame camera:

screenshot of B&H lens coverage filter checkboxes

Note 1: You may find a product description for a full-frame lens that talks about the effective focal length or equivalent of the lens on a camera with a crop sensor. This is because the reverse of your situation (using a full-frame lens on a crop sensor camera) is perfectly fine and quite common.

And now that?

Based on the fact that you linked to B&H in your comment, I will assume you purchased your B&H Photo lens. They have a pretty good return policy, so you can return this lens and use credit for a full-frame lens. If you bought your lens and camera from there, then hope you understand

If you can't return the lens for some reason, you might still be able to take advantage of it, as it seems to at least work properly on your camera.

  • You can take photos with it and then use software like Photoshop, GIMP, etc. to crop the unexposed parts of the photos. In fact, you would be making a crop sensor camera with your full-frame camera. You will lose some image size in this process, but it is not a total loss.
  • You could use this as an artistic effect and take photos where the circular view is part of the art.
  • Use it to take photos of crop circles. What a goal.

Large double onion ring in the middle of buds when using Sigma 35mm f1.4 DG HSM Art lens on my Canon 6D mark ii

I bought a Sigma 35mm f1.4 DG HSM Art lens, it works fine on my APS-C camera, but it doesn't work with my Canon 6D Mark ii (big double onion ring in the middle of buds), is this lens designed? work on both? Please let me know.

Thank you

Limit $ | Sigma ^ {- 1/2} (X- mu) | _2 ^ 3 $ for two-dimensional Bernoulli

Leave $ X in {0.1 } ^ 2 $ have average $ mu = left ( begin {smallmatrix} p_1 \ p_2 end {smallmatrix} right) $ and $ Pr (X_1 = X_2 = 1) = p $. Then we can calculate the covariance matrix $ Sigma = E ((X- mu) (X- mu) ^ T) = left ( begin {smallmatrix} p_1 (1-p_1) & p-p_1p_2 \ p-p_1p_2 & p_2 (1- p_2) end {smallmatrix} right) $.

I would like to use the Berry Essen limit, and for that we need an upper limit on the quantity $ gamma = | Sigma ^ {- 1/2} (X- mu) | _2 ^ 3 $.

I think one should be able to show
$$ gamma le C left ( tfrac1 { sqrt {p_1 (1-p_1)}} + tfrac1 { sqrt {p_2 (1-p_2)}} + tfrac1 { sqrt { min { p_1, p_2 } – p}} right)

by some universal constant $ C> 0 $.

The symbolic calculation of $ Sigma ^ {- 1/2} $ However, it's a bit difficult to handle, so I'm wondering if there are any tricks I can use to get to this result more clearly.

Or else, any proof would be appreciated.

probability: derive the probability ratio test to test $ H_0: mu = sigma ^ 2 $, $ H_1: mu not = sigma ^ 2 $.

Leave $ X_1 ,. . . , X_n $ Be independent $ N (µ, σ ^ 2) $ random variables. Derive the LRT to test $ H_0: mu = sigma ^ 2 $, $ H_1: mu not = sigma ^ 2 $.

As usual, I found MLE from $ theta in Theta $ and $ theta in Theta_0 $ calculate:

$$ Lambda = frac { sup _ { theta in Theta_0} L ( theta)} { sup _ { theta in Theta} L ( theta)} = frac {L (a , a)} {L ( bar {X}, S ^ 2)} $$
Where $ a = sqrt { bar {X ^ 2} +1/4} -1 / 2 $ and $ S ^ 2 = (1 / n) sum (X_i- bar {X}) ^ 2 $.

So i'm getting $$ Lambda = ( frac {eS ^ 2} {a}) ^ {n / 2} exp {{ frac {-1} {2 sqrt {a}} sum (X_i-a) ^ 2} } $$

And here I am stuck. Can I (can I even) simplify this further or can I just put this in the LRT and move on? In the examples they give me; they usually find the distribution of the statistic or find an expression in terms of some known distribution.

(1) Did I make a mistake?

(2) Can I simplify this further? In other words; How do I end the problem that is not alone? & # 39; & # 39; $ chi ( Lambda leq c) $& # 39; & # 39;