John Sheehy

Lives in NY, USA
Works as a Retired Communications Technician
Joined on Jul 9, 2003

John Sheehy's recent activity

  • 500mm/4 = 125mm 700mm/5.6 = 125mm 1000mm/8 = 125mm That's the same aperture for all; the same bundles of light coming off of the subject, entering the lens, and being projected onto the sensor.  ...
  • Sorry; I forgot I had this edit tab open. I didn't say anything about pixel size, there. I said something about pixel quantity , which is significant for image-normalized post-gain noise, which is ...
  • Replied in Diffraction...
    Without mentioning names or hinting at particular individuals, I'd say yes. It is said that you can tame the immoral behavior of dual-pixel sensors by dissolving the microlenses, which is a virtual ...
  • You have to stop those 600/6.3 zooms down a bit, though, because of the aberrations, and their IS is not as solid as Canon's IS tends to be these days. The zooms will clearly give the least noise ...
  • Who can Canon sell RF lenses to, and what are they looking for? Canon is clearly looking at the RF market as a market mainly with people who want light, compact gear, and it is not surprising that ...
  • That score itself, IMO, has very limited value. There may be errors in DxO's 1Dx3 measurements based on or related to known errors in the "measured ISO", but even in general, DxO's "low light ISO" ...
  • Every 90D RAW has an embedded JPEG in it, at full resolution (older Canons embedded reduced resolution JPEGs). There are lots of programs that will strip out the JPEG image and make a JPEG file for ...
  • Is "faster" the ultimate metric for light, independent of focal length? No, it isn't, in much of some types of photography. In genres of photography where you are usually cropping for your desired ...
  • It gives the same subject photon noise (assuming 100% transmission in the TC). The additive noise from reading out the photosites, on the other hand, can actually be lower, especially in the ...
  • Unfortunately, many people hear the term "diffraction limited" and think of something negative. I often think after posting a phrase like "an f/2.8 lens that is diffraction-limited at f/2.8", that ...
  • Clearly marketing hype to make things easy to misinterpret into something that is better than it really is. It is pretty clear that there are no actual 100MP images possible with this camera, ...
  • The open f-number mainly affect AF ability, which is unknown at this point. It has nothing to do with subject noise, directly. This results in no more subject noise in low light than a 400/5.6 with ...
  • "A" 50mm; yes. The nifty-50, or the 50/1.2L; no. A 50mm lens designed for a smaller sensor area can be diffraction-limited at very low f-numbers, but lets say it is 50/1.4 and sharpest wide-open; ...
  • Replied in Diffraction...
    Also, you may get much more visible sensor dirt if you stop down more than you really need to.
  • Some people see it as a substitute for what they personally want (a much faster RF 800mm), and something that seems to make the development of what they want less imminent. Therefore, it appears ...
  • Live view counts, when you use it, but I doubt that if it were still just DSLRs that Canon was releasing, that Canon would be creating live-view-oriented telephoto lenses, as telephoto is awkward ...
  • "Unusable" to one person is a gift from heaven to another. Large, heavy, and expensive define "unusable" to some people. I have heard aging wildlife photographers saying that they are pleased with ...
  • Canon seems to be targeting lightweight combos for native RF systems. That's what we're going to see first, and some people have been asking for this for a while, and I thought it was inevitable ...
  • The term "slower" exists for the purpose of choosing a shutter speed for a given film ASA/ISO. So, "slower" usually refers a higher f-ratio; not a smaller entrance pupil.
  • That's two stops. Each stop multiplies or divides the f-ratio by 1.4 (1.414... etc; the square root of two). Of course, open f-ratio is not necessarily a valuable independent lens quality. For ...
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