Serene Life

by garik

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93,920 reputation
3196344
bio website mattgrum.com
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visits member for 4 years, 1 month
seen 15 mins ago

1h
comment Does simply opening and closing a JPEG file decrease image quality?
-1 Just done a quick experiment with Photoshop CC and repeatedly opening and saving an image with exactly the same settings does result in a different file each time, when compared to the original using a "difference" blending mode. Apparently Photoshop is not an "worth its salt". I can't speak for other editors but I'd bet money they are the same. You could write a program very carefully to avoid rounding errors when continually decompressing and recompressing an image, but there would be no point - JPEGs are not a good intermediate format, full stop.
2h
comment How can I give an assitant rights to edit without having the possibility to download the image?
This question appears to be off-topic because it is about computer security and not photography.
3h
comment Why is there no image noise in my webcam dark frame photographs?
It's probably nothing more complicated than clipping the blacks to a level greater than the noise. I highly doubt the manufacturers of the webcam developed a processor that would recognize a frame that contained only noise and process it differently.
2d
comment Why Isn't This Photograph Pin Sharp?
@IliahBorg I don't use DOF calculators either, I use live view at maximum magnification centred on the most distant detail I want to capture and starting at infinity bring the focus forwards as far as possible until it just starts to degrade.
Oct
27
comment Why Isn't This Photograph Pin Sharp?
@IliahBorg See my response to Pedr, above. When using a more appropriate value for the CoC such as 0.007mm (a bit pessimistic, but good for illustration) the DOF only extends from 26m to 54m, a good deal short of infinity. So you can indeed get the background to be noticeably blurred when examining the image close up, and in fact that can be seen in the RAW file. Even if you want a pin sharp background focusing at infinity is rarely a good idea, focusing slightly in of infinity will give you a huge increase in DOF.
Oct
27
comment Why Isn't This Photograph Pin Sharp?
@Pedr beware of DOF calculators, they assume a very old standard for what is "sharp" based on viewing a small print from a certain distance. Most DOF calculators assume a blur of 0.025mm wont be detecable, but the pixels in a 5D mkIII are only 0.00625mm apart, so a 0.025mm blur will cover about 10 pixels! Sometimes you can enter your own value for the acceptable circle of confusion (blur radius), I suggest you use something like 0.007mm to be on the safe side.
Oct
27
comment What is the benefit of a wide-aperture lens if you stop it down?
You stop seeing an improvement in viewfinder brightness at about f/2.5 (depending on the particular focusing screen used), so there is a benefit to using an f/2.8 rather than f/4 lens.
Oct
26
comment What's the dynamic range of the iPhone 6 Plus?
Dynamic range is a concept with a simple definition - it is the difference between the saturation point and the point at which noise overcomes any image detail. The different numbers are the result of using different value for the maximum noise level. DxO use a signal to noise ration of 1 (noise is equal in magnitude to the signal), I'm not sure what DPR use as I don't think they've published it.
Oct
20
comment Is there a viable way to touch up the paint on an old camera body?
I've heard of people using lead-based touch-up pens designed for firearms, depending on what country you live in they could be easy or difficult to get hold of...
Oct
14
comment Do I use the crop factor in calculating aperture size and area?
@BBking it is right, you do obtain the real focal length by dividing the 35mm equivalent length by the crop factor compared to 35mm (e.g. Nikon 1 kit lens is a 27-80 equivalent, divide by the crop factor (2.7) and you get 10-30mm which is what's printed on the lens barrel). I could change the answer but the question specifically asked how to calculate the aperture size when you have an equivalent focal length for real f-number.
Oct
14
comment Do I use the crop factor in calculating aperture size and area?
@BBking read the question again, the lens has a 50mm FF equivalent field of view on a 1.5x crop sensor, hence it's really a 33mm lens, hence the entrance pupil diameter (on all formats) is 11.9mm
Oct
10
comment Viewfinder coverage: is it area or angle of view?
@laurencemadill that's right, but I think the question is asking whether you 95% of the image area, or 95% of the image width.
Oct
9
comment Infinity focus problem
@user1207217 If the lens is indeed fully manual then what you see in live view should be pretty much what you get. In any case the final resulting image should be sharper than the live view image. I cannot think of any reason for it to be the other way round, unless shutter speed was a factor (the image you posted shows no signs of motion blur). How was the second image obtained? Was it a cell phone picture of the camera's LCD screen or did you download the image from the camera's memory card?
Oct
2
comment Auto focus vs Single Continuous/Point focus
Practice makes perfect :)
Sep
26
comment What settings should I use to take a burst at the highest possible FPS?
In short, noise reduction, card write speed and particularly autofocus have been shown to have a measurable impact on continuous shooting speed. Metering has not.
Sep
26
comment What settings should I use to take a burst at the highest possible FPS?
@MichaelClark The 1DX has a 100,000 pixel metering sensor which has it's own dedicated DIGIC4 processor (which can crunch through (demosaic, apply filters and reencode) the 5DII's 22,000,000 pixels with ease). Reading 100,000 pixels (no need to do any demosaicing) and performing a lookup is a breeze for an application specific chip designed to do nothing other than process pixels. Even if it takes as long as a microsecond then that's going to be well within the accuracy to which most people can measure the shooting speed!
Sep
26
comment Approximating a wide XPan shot
Shoot wide with a rectilinear lens and crop is bay far the simplest solution. It's worth noting that you don't have to spend a lot to get a wide prime these days (the Sam/Rock/Bow/Yang 14 f/2.8 is a steal), nor do you need a full frame camera, there are 10mm options (prime and zoom) available for APS-C!
Sep
26
comment What settings should I use to take a burst at the highest possible FPS?
I'd be amazed if metering calculations slowed down the shooting speed given that's it's done using an ASIC where 1/10th of a second is an eternity.
Sep
25
comment Is it assured that every type of lens will be made for a given interchangeable lens camera?
I wouldn't say it's extremely remote, look at what Sony is doing to the A-mount, (and of course what Canon did to the FD mount). What's going to happen when EVFs and CDAF advance past OVFs and PDAF? What about when curved sensors become cheap enough to have on in every lens? There are many reasons to abandon a mount, when it makes commercial sense Canon will do it.
Sep
25
comment Is it assured that every type of lens will be made for a given interchangeable lens camera?
@PhilipKendall I disagree, there's no need to speculate in order to answer the question: no, it is absolutely not guaranteed that there will be one of each lens type available in the future! It is indeed possible for manufacturers to stop making a certain type of lens.