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Szabolcs
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 Apr 26 comment What is the relationship between field of view and focal length for fisheye? @Brandon The inverse of what you mentioned: `2 arctan(r/f)`, where `r = 15 mm` is the half-diagonal of APS-C. Apr 26 comment What is the relationship between field of view and focal length for fisheye? @scottbb Well, yesterday I made an embarrassing mistake when I forgot that 1/2 factor from inside of the sine (see my comment on the other answer). If I had found that mistake earlier, I would have deleted the question ... I was worried about backlash. I don't care much about reputation score any more, so CW is okay. Apr 26 comment Prevent Lightroom from discarding lens model from EXIF @Linwood You are correct. It is that bug. The information is missing for all lenses, not just this Tokina, but I didn't realize this ... If you write it as an answer, I'll accept. Or maybe I should just delete the question? Apr 25 comment What is the relationship between field of view and focal length for fisheye? I found this page which claims that the distance `r` for a point from the image centre is `r = 2*f*sin(θ/2)`, where `f` is the focal length and `θ` is angle measures from the optical axis for that point. But it doesn't add up. Equal-area projection lenses that have a 180 degree diagonal FoV tend to have ~10 mm focal length (like this Tokina or the Nikon 10.5 mm). According to this formula they'd have a 20 mm radius 180 deg image circle. But the half-diagonal of APS-C is only 15 mm... Apr 25 comment What is the relationship between field of view and focal length for fisheye? What you wrote is valid for a rectilinear lens, i.e. for projection through a point. It also needs a factor of 2 in front of the arc-tangent. But this is not a rectilinear lens, far from it. Hence my question. Apr 25 comment Prevent Lightroom from discarding lens model from EXIF @inkista Yes, version 2015.5. Mar 31 comment Sum of pixel values more than incident photons @faf No, it's built in since version 10.1. What version do you have? Feb 24 comment What is this lever for on the lens mount? (F-mount, not aperture lever) Here's another photo I found. Feb 12 comment What is the shape of the focal plane? I understand your question, but it should be noted that you are completely misusing the terms focus point and focal plane. The focal plane is not the plane of objects in sharp focus, as shown in your sketches. You can google for what it actually is, e.g. en.wikipedia.org/wiki/Cardinal_point_(optics)#Focal_planes Feb 6 comment Does a full frame with a teleconverter perform better than an APS-C without a teleconverter? But I didn't actually sit down to do the calculations, so I might be wrong. My wave optics classes were a long time ago, I guess I should sit down, brush up on optics and derive the exact result ;-) But not until later today. Feb 6 comment Does a full frame with a teleconverter perform better than an APS-C without a teleconverter? @Michael Regarding diffraction: the frequency of light won't be changed by the optics of course. The wavelength will be different inside glass and air. What ultimately matters is the difference in optical path length from various points of the aperture plane to the same point of the projection plane. This led me to the conclusion that it is indeed the apparent size of the aperture (from the perspective of the projection plane, as seen through the TC) that matters. Feb 6 comment Does a full frame with a teleconverter perform better than an APS-C without a teleconverter? @Michael I don't see the point of your last comment, does it contradict with anything I said? I am merely trying to help the OP understand the issues involved so he can come to the answer himself without having to "just believe". Let's not make this about who is right, I am not arguing with you, I am chasing the right answer ;-) Feb 6 comment Does a full frame with a teleconverter perform better than an APS-C without a teleconverter? @Michael Now it is true that the same opening will correspond to a different "f-number" in the two cases. But that has no significance, does it? It's the physical opening that is the relevant quantity to compare: that's what has to be the same between the two to cases to have the same amount of light and the same depth of field, and that's what has the same maximum value between the two cases. (The maximum f-number will be smaller for the teleconverter case.) Feb 6 comment Does a full frame with a teleconverter perform better than an APS-C without a teleconverter? @Michael Thanks for the comments. Regarding noise levels: the point I was making is that for the same opening of the aperture blades the same amount of light (photons) will be "recorded" in both cases if the teleconverter has perfect transmission. Since it doesn't, in fact the FF gets less light in the end, and will have more noise. Regarding diffraction: it happens at the aperture blades (the smallest opening the light passes through). The magnification happens at a later stage along the optical path. Again, there will not be a difference given the same opening of the aperture blades. Feb 5 comment Does a full frame with a teleconverter perform better than an APS-C without a teleconverter? You say "in general when the best cameras are coupled with the best lenses the best teleconverters will usually give better image quality of static subjects shot from a tripod mounted camera than shooting without a TC and then cropping away.". But if you think about what a teleconverter actually does, all arguments point in the opposite direction. Please see my answer. If I made a mistake in my reasoning, what is it? Otherwise this is all just anecdotal. Jan 26 comment Is there a website which will help me crowdsource the decision between similar images? @igor Realistically, it is very unlikely that this proposal will go through (at least in its current form). It is not a good fit for the StackExchange format... That shouldn't stop you from trying, but you might at least want to think through the example questions and not make then A-or-B choices. What would be the purpose of voting on such a site? Which answer gets accepted? Why is this better as a Q/A site than as a discussion forum? It sounds like you are looking for something that has an interface for A/B choices instead. Jan 26 comment Is there a website which will help me crowdsource the decision between similar images? @igor Which photo gets stars on flickr has little to do with which one is better ... But flickr has several critique groups where you can ask for human feedback. flickr.com/search/groups/?q=critique Jan 25 comment How does software exposure compensation work in RAW files? To put it simply: a sensor pixel counts photons. The RAW file stores these counts for each pixel. When you tune the exposure with say, Lightroom, it just multiplies these counts by a factor. If a pixel collected 100 photons, you can multiply that by 2 to "make it look like" 200. Jan 21 comment Does the detail in an image affect how large the image file is? @supercat Here's an experiment showing the effect of noise on JPEG size (quality priority). Size is in bytes, written under each image. Of course the results should significantly depend on the encoder itself as lossy encoders have many choices to make about what details can be thrown away without humans noticing ... dropbox.com/s/gla3lmbe1d831od/lena.png?dl=0 Dec 29 comment Is autofocus important for ultra wide angle lenses? @PhilipKendall OK, done.