John Sheehy

John Sheehy

Lives in Yonkers, NY, USA
Joined on Jul 9, 2003

John Sheehy's recent activity

  • Sorry; I must have had teleconverters on my mind. Everywhere I wrote "2x" in that post should have been "2b".
  • It won't give you much of a cardio workout, but you can do "negative" or "eccentric" exercise that builds type 2x fast-twitch muscle fiber, which you may find easier than traditional exercise. The ...
  • Good Job. What are the best ways to measure body fat, short of going to a doctor and getting in a tank? Are any of these electronic thingies fairly accurate? Or do you need to use calipers and do ...
  • I didn't mean that the histogram does not look Gaussian; I meant that you can't simulate real camera read noise with a simple Gaussian function. Here's a thought experiment for you. If you took a ...
  • Well, that depends on what you're shooting, and how big you're going to show it. People shooting small wildlife from a distance need to crop and magnify their captures. People who compose the ...
  • It is not. The Tamron at 600mm is superior to the 300/4L IS, cropped or with converters. The Canon may AF a little faster without a TC than the Tamron does at f/6.3 focal lengths, but that's about ...
  • When I was young, I was at a broad family gathering when I heard my first political thought that wasn't like what it was when I pledged allegiance to the US flag in school (I don't think anyone ...
  • Did you read about what Bill Randall wants to do with 3.9M of that?
  • I don't see what is poor about it. Yes, the lens is softer wide open at 600mm than at 300mm, but what else out there can get you a 90mm aperture with that amount of magnification for US$1069, or ...
  • I have a really hard time parsing people's comments about TC experience, because their standards and expectations are unstated. To me, a TC works when, using it from the same distance, with the ...
  • IMO, anyone who thinks that current pixel densities are excessive for any lens that isn't a toy hasn't the slightest idea what they're talking about. If I put my Pentax Q on my Tamron at 600mm ...
  • It is always a 150-600mm lens, IMO; you can say that it has the same range of FOVs as a 240-960 mm on a FF, but that can be a pretty hollow accomplishment with big numbers. I could say exactly the ...
  • There are filters that flatten the contrast in the scene, randomizing a small percentage of the light going through them to create a blanket of light over the image. They don't do anything you ...
  • CropQ and IQ are completely different things. A 1.5x crop from the D800E is like a full APS-c 1.5x crop camera with the same pixel size, like the D7000. A D7100 or any of the newer 24MP APS-C ...
  • Also, if it is linear, more confusion exists because your crop may have a different aspect ratio than the original, resulting in different percentages for horizontal, vertical, and diagonal!
  • ... and, of course, "20% crop" can also refer to a 100% crop as you use it here (crop made of 1:1 original:displayed pixels), after the image has been downsized to 20% (1/25 the original pixel ...
  • Assuming that both cameras use similar highlight headroom (the range tends to be 1/2 stop or less), then 2 stops more DR will show 1.5 - 2.5 stops difference with equal under-exposures. Of course, ...
  • The DR at the ISO with the highest DR should be the DR of the camera , IMO. DR at higher ISOs is somewhat meaningless to me, and is just a convoluted way of measuring read noise. Anyone who is ...
  • Do you mean high ISO performance? Low light shots can be taken at long shutter speeds at low-noise ISOs, and I have found myself shooting at ISO 25600 outdoors in the daytime. But yes, a monolithic ...
  • While I think that the overall score is stupid and only seemingly useful to people who don't feel that they would understand individual scores, I think that in terms of DR scores DxO has been very kind
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