bobn2

bobn2

Lives in United Kingdom Worcestershire, United Kingdom
Joined on Aug 28, 2007

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On Olympus OM-D E-M5 rumored to be out of production article (211 comments in total)

Slow news day?

Direct link | Posted on Nov 15, 2014 at 11:46 UTC as 41st comment
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

photohounds: This discussion obsesses on the fact that you get more (but not excessive) depth of field. Yes it IS an obsession that neatly avoids some facts.
.
Using the 50mm/f2 vs 100mm/f4 example above ..
You ALSO get TWO STOPS BETTER shutter speed (4 times as fast).
(better sharpness)
You get QUADRUPLE the flash range (faster recycle or More range)
I once shot a Canon FF PRO user with the 50mm f2. She remarked: "I've never SEEN so much detail".
.
Further - you also get (mostly) MUCH smaller, lighter lenses and faster zooms.
.
You also get typically 1/2 to 1/3 the VIGNETTING that full Marketing Frame (FMF) lenses can manage. This is excellent if you like to shoot images with the main subject OUTSIDE the centre third of the image but still want it sharp. Generally (with few exceptions) APS-C lenses fall halfway between for good vignetting resistance.
.
Examples .. http://photohounds.smugmug.com/Performing-arts/Eurobeat-by-Supa/

Re: For example, if an mFT photographer shot a scene at 50mm f/2 1/200, there is no reason the FF photographer could not shoot the scene at 100mm f/4 1/100.

I assume you meant

if an mFT photographer shot a scene at 50mm f/2 1/200, there is no reason the FF photographer could not shoot the scene at 100mm f/4 1/200.

and I would add, for clarity, and end up with a very similar looking photograph, particularly with respect to noise and image quality.

Direct link | Posted on Sep 19, 2014 at 20:24 UTC
On Nikon D750 First-impressions review preview (1434 comments in total)

'But, while it may look a lot like a D610, the D750 feels rather different, thanks to its magnesium alloy shell. This allows it to be lighter than the 610, which uses a plastic composite body on a magnesium alloy chassis, '

Sorry, that's wrong. The D610 (and I'm guessing D750) don't have a 'magnesium chassis', they have a plastic chassis. The D610 has magnesium top and back covers. I'm thinking the D750 just has a magnesium top, since the back is probably moulded plastic, due to the arrangements for the flippy screen.

Direct link | Posted on Sep 12, 2014 at 07:40 UTC as 349th comment | 2 replies
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

(unknown member): Found a very good explanation on why the sample images in this article look that way. As I have mentioned in a previous post, I almost fell for it until I noticed that the different sensor sizes actually have the SAME resolution of 18Mp. This resulted in smaller sensels that contributed to the equivalent SNR for smaller sensors even though they had greater exposure. Had the article used the same sensor (same pixel density) then the full frame will show a much noisier result by virtue of underexposure.

Read about spatial resolution here:

http://www.clarkvision.com/articles/f-ratio_myth/

Possibly you're capable of seeing that your source is saying the opposite of what you are. You claim that the light decreases due to the inverse square law as the focal length gets bigger. He says that the light decreases as the focal length gets smaller, due to the reduction in size of the aperture.
If you'd bother to read around that source rather than quote mining, you'd realise that Clark is just as wrong as you but in the opposite direction.

Direct link | Posted on Aug 3, 2014 at 09:00 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

(unknown member): Very basic question:

Can this "equivalence" ever be achieved with film? Consider Kodak Ektar 100 in 35mm and 120 formats. If yes, then how?

If it can't be achieved then either:
1. film is exempted from basic photography
or
2. equivalence-fu is wrong.

@dtmateojr - "Grain is what you call noise in digital." - up to a point, they are both a reflection of haow many photons you've counted.
"Does the grain change when you expose 35mm and 8x10 Ektar exactly the same way?" - why this arbitrary restriction on using the same film in the two different formats?

Direct link | Posted on Aug 2, 2014 at 07:42 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

(unknown member): Very basic question:

Can this "equivalence" ever be achieved with film? Consider Kodak Ektar 100 in 35mm and 120 formats. If yes, then how?

If it can't be achieved then either:
1. film is exempted from basic photography
or
2. equivalence-fu is wrong.

@ dtmatejor
If you'd beother ed to look at the post Joe referred you to, rather than just dismissing it, you'd have seen that the equivalence for film was based on just the same idea as digital. The equivalence depends on the number of photons making up the image. A digital sensor counts those photons directly (more or less). Film cout's the resulting photoelectrons rather differently, a pair of photons renders a grain reducible. To render an image from the same number of photoelectrons for a larger frame needs bigger grains (in fact you could also do it perfectly satisfactorily for the smaller grain film, but you'd need to print on a higher contrast paper to compensate for the low maximum density that using the small grain would cause.

Direct link | Posted on Aug 1, 2014 at 12:03 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

mostlyboringphotog: Finally, I grok it so that now I see why mFT aficionados would care more about the "Total Light" equivalency more so than any other format owners.
BLUF: I have learned thing or two and agree that "Total Light" comparison is a fairer than same FOV, same brightness comparison.
The equivalence in the image (GB criteria) comes from the equivalent setting (Sven) but I say it's the combination of the settings that is giving you the equivalence. The individual parameters are not equivalent to each other without the others set as well. Therefore, it's misleading to say any one parameter is equivalent to another one.
A good lens should be a good lens and not a good lens equivalent.
No more animosity even to que and pete's as I have groked...

@Androole re:"Of course, in these examples the smaller sensors will actually tend to be slightly better in terms of real-world signal-to-noise ratio. 1" is not a full stop behind M4/3, M4/3 is not a full stop behind APS-C, and APS-C is not a full stop behind FF. An EM-5 is only about 1.5 stops behind a Sony A7 in terms of ISO performance, despite having a 4x smaller sensor, for instance."

There's a reason for that, the smaller sensors are where the real competition is, so they tend to be made with the newest processes and tricks such as BSI and light pipes, while the bigger sensor have been relegayed to old production lines which can't be used for small sensors any more. Thus small sensors tend to have higher efficiency than large ones. Maybe they are about four years ahead in sensor efficiency.

Direct link | Posted on Jul 17, 2014 at 17:04 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

Roland Karlsson: Nice try to clear up some misunderstandings. Unfortunately it does not always help, as this thread shows.

http://www.dpreview.com/forums/post/53973560

The main irritating thing (for me) is that I do not have any problems with this whatsoever - still all the confusions pops up now and then. This seems to be hard stuff for many people - for some strange reason.

When equivalence might be useful:
1. When someone who has developed their technique on one format is thinking of moving to another, it gives a guide as to which settings to use to achieve the results that they are used to.
2. When someone uses different cameras (maybe a smaller lighter system for travel) to know how to set the controls to get the results that they are used to.
3. When someone is trying to emulate an effect they have seen, taken using a different sensor size to theirs. They can see the settings used for that shot and know which settings to use on their camera to get the same effect.
re: "It is deliberately made more difficult to understand by introducing irrelevant concepts. "
I think the reverse is true. There is a small group trying to deliberately obfuscate because the message of equivalence conflicts with their own personal set of 'truths' which are often to do with the perceived superiority of their own equipment choices.

Direct link | Posted on Jul 17, 2014 at 09:27 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

Roland Karlsson: Nice try to clear up some misunderstandings. Unfortunately it does not always help, as this thread shows.

http://www.dpreview.com/forums/post/53973560

The main irritating thing (for me) is that I do not have any problems with this whatsoever - still all the confusions pops up now and then. This seems to be hard stuff for many people - for some strange reason.

@boggis the cat re: "almost nobody wants to reproduce a shot as closely as possible using two systems, so "equivalent photos" is a pointless confusing factor."
I don't think that's true. I don't believe that people differentiate so much what type of photo they take by sensor size. I think they buy a camera or cameras that they like and then use it to take the kind of photos that they like. And when they reach a level of adeptness, they start to use the camera controls to fine tune the type of photo they like, for instance taking control of DOF, motion blur, balancing between sharpness and noise and so on. From that point of view, I can see where 'equivalence' is valuable from three points of view, which I will explain below.

Direct link | Posted on Jul 17, 2014 at 09:23 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

mostlyboringphotog: @DPR/Richard,
May I make a modest proposal:
Instead of simply "Equivalent Aperture or F-stop" can we use "DOF Equivalent Aperture or F-Stop)".

After annoying Sven umpteen time, sorry that it took 141 post and 5 days to come up with this modest proposal but I'm not known to be swift.

To all those who would think but that's what is implied in the Equivalent F-stop, remember that F/2 is NOT equivalent F/4 for brightness in any format. No such corollary for Equivalent FL, which makes it less controversial.
This proposal is not for the forum posters who know all this already.

Thanks again all, particularly Sven, GB and Richard for engaging me.

@ Fygaren
"Theta is the range of half-angles of whitch the light can enter the lens."

Which is defined by?.....

"I dont see the contradiction.Both depends on aperture is what Ive been saying."
What you've sometimes been saying. If you agree with everyone that both depend on aperture, what are you arguing about.

"The sun (aperture) can converted in to electrisity(f-number) in a solar panel, the sun can make hot water(DOF) with a solar thermal collector. Knowing the electric current you can calculate the exact temperature of the water knowing both collectors efficiency. "
Yet another pointless example. Sorry, it illuminates nothing.
"Now my point: The electrisity has little to do with the hot water, but that is the connection made with f-number and DOF."
Wrong, it's a simple variable substitution. Happens all the time in science and engineering.

Direct link | Posted on Jul 16, 2014 at 14:38 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

Zdrasviti: pixel size is the most important thing in terms of image quality thats why 12 mp full frame ( d3-d700) sensor is still the lowest noise level on planet.

@ Zdrasviti, re: "pixel size is the most important thing in terms of image quality thats why 12 mp full frame ( d3-d700) sensor is still the lowest noise level on planet."
Wrong on both counts. Pixel size is a secondary factor. Having lower pixel counts gives some advantage in shadow noise, if the electronic part of the pixel stays the same. Your assessment of the performance of the D3/d700 is very optimistic. There are many modern ff sensors that have lower noise.

Direct link | Posted on Jul 16, 2014 at 14:28 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

rfsIII: There must be an professor of imaging science out there somewhere who can be hired by DPR to write a nice counterpoint article that will untangle this topic and bring sanity to what is essentially a holy war between two under-informed camps. I would start at http://www.rit.edu/cos/optics-rit and work westward from there.

@MichaelJP, re: "that is the sensor performance at different ISO,
that is how the sensor behaves with more amplification of the signal from each pixel".
The signal to noise ratio of a competently designed amplifier is maybe 40dB more than the SNR of a large pixel. In short, amplifying the signal from pixels doesn't increase the noise at all.

Direct link | Posted on Jul 16, 2014 at 14:23 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

mostlyboringphotog: @DPR/Richard,
May I make a modest proposal:
Instead of simply "Equivalent Aperture or F-stop" can we use "DOF Equivalent Aperture or F-Stop)".

After annoying Sven umpteen time, sorry that it took 141 post and 5 days to come up with this modest proposal but I'm not known to be swift.

To all those who would think but that's what is implied in the Equivalent F-stop, remember that F/2 is NOT equivalent F/4 for brightness in any format. No such corollary for Equivalent FL, which makes it less controversial.
This proposal is not for the forum posters who know all this already.

Thanks again all, particularly Sven, GB and Richard for engaging me.

@fygaren

Re: "Interesting. I found the following that supports it:
"f/number = 1 / [2sin(theta)]
For very small values of theta sin(theta) can be approximated simply by theta which then allows us to write the formula above in the familiar form f/number = f / D, with f the focal length and D the diameter of the incident light. But this last one is a simplification..I would say that light-gathering ability is fundamental to the luminous exposure as it directly affects the image-plane illuminance."

So that contradicts your previous view that DOF depends on aperture, but exposure depends on f- number. Now we find that both depend on aperture (what is theta) fundamentally. The next thing to work out is why luminous exposure should be sanctified. For all the semantic wrangling, that's the 64000 exposure question.

Direct link | Posted on Jul 14, 2014 at 23:10 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

mostlyboringphotog: @DPR/Richard,
May I make a modest proposal:
Instead of simply "Equivalent Aperture or F-stop" can we use "DOF Equivalent Aperture or F-Stop)".

After annoying Sven umpteen time, sorry that it took 141 post and 5 days to come up with this modest proposal but I'm not known to be swift.

To all those who would think but that's what is implied in the Equivalent F-stop, remember that F/2 is NOT equivalent F/4 for brightness in any format. No such corollary for Equivalent FL, which makes it less controversial.
This proposal is not for the forum posters who know all this already.

Thanks again all, particularly Sven, GB and Richard for engaging me.

In atomic physics, it's conventional to define masses in atomic units, the mass of a proton or neutron. However, mass is energy, so unfortunately the binding energy of atoms changes their mass, so one atomic unit is now exactly 1/12 the mass of a carbon atom. Using convenient units is common in physics. F- number is just such a unit, but as you point out, it isn't 'fundamental' to the DOF equations just as it isn't fundamental to the exposure equations.

Direct link | Posted on Jul 13, 2014 at 22:44 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

Erick L: Total light on sensor affecting noise doesn't make sense to me. Don't smaller sensors appear more noisy simply because the image needs to be enlarged more, noise included?

Seems to me that saying a FF sensor has less noise because it gathers more light is akin to saying a telephoto lens "compresses perspective".

The magnification changes the spatial distribution of the noise, which might render it more visible. The SNR is determined by the number of photons captured, so strictly cropping reduces the noise, but it reduces the signal more. The pixel grid makes things a little more complex, applying a low pass filter to the noise, but so long as the image isn't enlarged to the point where the grid is visible, that can be ignored.

Direct link | Posted on Jul 13, 2014 at 22:31 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

rfsIII: There must be an professor of imaging science out there somewhere who can be hired by DPR to write a nice counterpoint article that will untangle this topic and bring sanity to what is essentially a holy war between two under-informed camps. I would start at http://www.rit.edu/cos/optics-rit and work westward from there.

@rfsIii, re "There is nothing simple about optical science especially at the level we're discussing."
Sorry, this is an application of very simple 'optical science' - from the introductory text. Any of the introductory texts will do.
Re: "But I get the point. For whatever reason you're not going to reveal the name of anyone in your circle who has the academic or professional credentials to back up this theory of yours."
Suppose for the sake of argument that I was a professor writing regularly for a respected photographic publication - you'd respond by arguing about my 'professional credentials'. What this is, is actually the ad-hominem fallacy, rather than argue the case on its merit, you'd rather argue about who's making the case.

Direct link | Posted on Jul 13, 2014 at 18:22 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

mostlyboringphotog: @DPR/Richard,
May I make a modest proposal:
Instead of simply "Equivalent Aperture or F-stop" can we use "DOF Equivalent Aperture or F-Stop)".

After annoying Sven umpteen time, sorry that it took 141 post and 5 days to come up with this modest proposal but I'm not known to be swift.

To all those who would think but that's what is implied in the Equivalent F-stop, remember that F/2 is NOT equivalent F/4 for brightness in any format. No such corollary for Equivalent FL, which makes it less controversial.
This proposal is not for the forum posters who know all this already.

Thanks again all, particularly Sven, GB and Richard for engaging me.

@fygaren, re:"The hyperfocal formula you refer to is a simplified, easier to use in the field, version of Louis Derrs derived formula from 1906. His formula is considered to be the strictly correct one in modern times and only contains focal lenght, aperture diameter and circle of confusion diameter."
No, not a simplification, what you get when you substitute N=f/a into the equation. Actually the derivation of the exposure equation is exactly the same. You start off with consideration of the focal length and entrance pupil diameter and substitute in N=f/a when you've decided to work with relative rather than absolute aperture, and the reason that decision was made was manufacturer's convenience using the same emulsion over different plate sizes.
Re: "It has to be that way, or what Ive been saying would be wrong."
You're reversing your logic again.

Direct link | Posted on Jul 13, 2014 at 17:53 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

mostlyboringphotog: @DPR/Richard,
May I make a modest proposal:
Instead of simply "Equivalent Aperture or F-stop" can we use "DOF Equivalent Aperture or F-Stop)".

After annoying Sven umpteen time, sorry that it took 141 post and 5 days to come up with this modest proposal but I'm not known to be swift.

To all those who would think but that's what is implied in the Equivalent F-stop, remember that F/2 is NOT equivalent F/4 for brightness in any format. No such corollary for Equivalent FL, which makes it less controversial.
This proposal is not for the forum posters who know all this already.

Thanks again all, particularly Sven, GB and Richard for engaging me.

@fygaren re: "I have already explained how one is the result of the other and not the other way around, you can not "set" the result and think what makes the result follows, this is backwards."

This is precisely what you are doing. You are fetishising 'brightness' (more properly image plane illuminance) because you think that along with exposure time this determines a 'correct' exposure. In fact, the only thing that determines which exposure you call 'correct' is the ISO setting, which in turn determines the processing you'll use. There is nothing fundamental about exposure, what is fundamental is how many photons are captured to make the image, which is given by exposure only if the captured image size is fixed.

Direct link | Posted on Jul 13, 2014 at 10:24 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

mostlyboringphotog: @DPR/Richard,
May I make a modest proposal:
Instead of simply "Equivalent Aperture or F-stop" can we use "DOF Equivalent Aperture or F-Stop)".

After annoying Sven umpteen time, sorry that it took 141 post and 5 days to come up with this modest proposal but I'm not known to be swift.

To all those who would think but that's what is implied in the Equivalent F-stop, remember that F/2 is NOT equivalent F/4 for brightness in any format. No such corollary for Equivalent FL, which makes it less controversial.
This proposal is not for the forum posters who know all this already.

Thanks again all, particularly Sven, GB and Richard for engaging me.

@Fygaren
Re: the f-number show the quantitative measure of lens speed so that you can set the right shutterspeed (before we had auto metering). An example of use is the sunny 16 rule."
And so? You are in a completely circular argument, though you don't seem to understand that. The only reason a particular f- number with a certain shutter speed gives a 'correct' exposure is because you chose that exposure in the first place, when you chose your ISO (and you chose your ISO with film too, it was just a bit more cumbersome). As I said (and you failed to respond to, I suspect that you don't understand the point) brightness is pretty much irrelevant. Think, we can compensate lack of brightness simply by choosing a longer shutter time. Likewise, we can compensate lack of brightness by collecting over a larger area, so long as the number of photons that we collect is the same, we get the same result.

Direct link | Posted on Jul 13, 2014 at 09:43 UTC
On What is equivalence and why should I care? article (2071 comments in total)
In reply to:

nigelht: I have been contributing to the confusion because I didn't realize that folks on the opposite sides of this debate start from two very different perspectives.

One side believes that equivalence is from the perspective of magnification. Hence the arguments regarding total light, DoF, etc. When they see "100mm equivalent focal length from a 50mm lens on a crop sensor" their mental model is from the perspective using a 100mm lens (more magnification) on a FF camera.

The other side sees equivalence from the perspective of cropping. Hence total light doesn't matter, only intensity, because in our mental model the active sensor areas are identical. You CROP the larger sensor to the smaller size. All that extra "total light" falls outside the used sensor area. When we say 100mm equivalent focal length we mean cropped to 100mm using the same 50mm lens on a FF camera. Hence my earlier example of physically masking a FF sensor to crop size.

Swap mental models and see the other side.

@ nigelht, re: "There are still differences. Just like there is a difference between using a TC and cropping but it's close enough to get the idea of what cropped sensors do."
And if you put a 2x TC on a 35mm f/2.8 lens you end up with a 70mm f/5.6 lens. Go figure.

Direct link | Posted on Jul 13, 2014 at 08:29 UTC
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