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11-18-2015, 07:03 AM   #61
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QuoteOriginally posted by Class A Quote
And which manufacturer could offer a 23/1 APS-C lens for a price that anyone could afford?
A used Sigma 35/1.4 plus a speedbooster clone together yield a 23/1 APSC lens which can be bought on today's used market for roundabout 600 EUR, netting excellent image quality. Quite affordable I would say. And obviously possible.

Some Canon kids spend 4 times as much on a lens which results in the exact same images on FF.

11-18-2015, 07:42 AM   #62
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QuoteOriginally posted by HavelockV Quote
A used Sigma 35/1.4 plus a speedbooster clone together yield a 23/1 APSC lens which can be bought on today's used market for roundabout 600 EUR, netting excellent image quality. Quite affordable I would say.
You are using a "used market" price whereas I was talking about a manufacturer to customer scenario.

More importantly, I have my doubts regarding "excellent" image quality. DPReview report vignetting, CA, and weaker large aperture corner performance when comparing the "speedboosted" lens to the unconverted original on FF. Using an adapter of any kind is also not ideal for optimal quality due to mount tolerances.

This is not to say that a "speedboosted" lens cannot be 100% fun. I'm just saying that producing a lens that performs exactly on APS-C as it performs on FF is more expensive than just adding on a speedbooster.
11-18-2015, 07:51 AM   #63
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Please re-read this:
QuoteOriginally posted by Class A Quote
However, knowing light-per-unit-area is not enough to know the resulting image quality. For the latter, you also need to know the area size with which you are collecting the light.
The text above doesn't merely imply that total light can give you one aspect of image quality. I know you're trying to make a point, but it's a misleading point.

And this:
QuoteOriginally posted by Class A Quote
It is not "irrelevant", as it can be helpful in many ways, one of which is to make informed gear buying decisions.
One can also make buying decisions based on a gut feeling or ill-conceived ideas, that's fine, but it does not make sense to ridicule people who make informed decisions.
The implication here is that people using "equivalence" are making "informed gear buying decision", while the others don't. It is once again up to interpretation, but I'm far from nitpicking here. Note that you started your response by attacking my "ability to understand" this "equivalence"; I continued to read your post in this light.

This takes care about the putting words into your mouth issue

To end it before it gets too long, IIUC Wired was talking about "light gathering" as exposure, not "total light" because the latter was less relevant to him. The good, old system works so well because it's universal and doesn't try to do things outside its responsibilities.
11-18-2015, 12:20 PM   #64
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I can poke the bear even more than f stop is not a true accurate representation of light transmitted for exposure or otherwise.... that would be a T stop. *hides*

11-18-2015, 12:41 PM   #65
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I look forward to the day when everyone on Pentaxforums has a full-frame digital Pentax, and we no longer have all these heated discussions about 'equivalence' littering the forum.
11-18-2015, 12:43 PM - 1 Like   #66
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QuoteOriginally posted by rawr Quote
I look forward to the day when everyone on Pentaxforums has a full-frame digital Pentax, and we no longer have all these heated discussions about 'equivalence' littering the forum.
What does Full-Frame mean?
Is that when the sensor is 1.5x times bigger and you have to divide your lens's focal length by 1.5 to get an equivalence of the focal length on Pentax current cameras?

11-18-2015, 01:48 PM   #67
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QuoteOriginally posted by rawr Quote
I look forward to the day when everyone on Pentaxforums has a full-frame digital Pentax, and we no longer have all these heated discussions about 'equivalence' littering the forum.
it wont end

because then people will be going on about the crop factor using the DA lenses on the new FF. Then the APSC people who will not upgrade for various reasons will be upset because the DA* lenses haven't been updated with new focus motors and optics.

don't worry. there will always be a fire pit to dance around in Pentax land.
11-18-2015, 02:05 PM - 1 Like   #68
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QuoteOriginally posted by Wired Quote
I can poke the bear even more than f stop is not a true accurate representation of light transmitted for exposure or otherwise.... that would be a T stop. *hides*
Sounds like a challenge. Then, I would vary the output medium, size and viewing conditions from a format to another (not an entirely unreasonable scenario) just to throw off DOF calculations

11-19-2015, 05:56 AM   #69
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QuoteOriginally posted by bdery Quote

SR and WR are two of the main perks of Pentax. Let's not dismiss them
And TAv, which is unique, and adds a level of image control between Av/Tv and Manual.


When shooting airshows, you'll often hear discussions about what ISO you have to put to guarantee a certain speed in Av.
We don't need to: Pentax uses what's at hand (CPU and metering) to give us control over aperture AND speed while maintaining exposure.
With current sensors' ISO capabilities, we basically have full manual (artistic?) control in changing lighting conditions without the hassle.


Anybody else does that?
11-19-2015, 06:07 AM - 3 Likes   #70
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Original Poster
this thread started with some information from a show. It somehow diverged on a flame bait about formats.

I have refrained from commenting a lot on this (even though I started the thread). I'll try to close this part of the discussion, and either let the thread die or bring it back to the original topic.

Equivalence in simple terms means trying to get the exact same image with two different formats. It is one way to make a parallel between formats, however it is abstract and complicated for many people because it mixes a lot of concepts together, some technical, some related to gear, some related to technique, some to composition and framing.

When I said a full frame did not always deliver better noise performances, I was talking about the sensor ONLY. Noise is driven (all other things being equal) by the pixel size. When we talk about equivalence, "all other things" are specifically NOT equal. But that was not the point I was interested in making.

A f2.8 lens remains a f2.8 lens whatever sensor you place behind it. The f-number is a property of the lens. When using a crop sensor (I use that expression on purpose) all you're doing is literally cropping a part of the image circle. But guess what? You're cropping to when you use a FF sensor. Otherwise you'd get a circular image.

Now if you want to recreate the exact same image (with the same bokeh, DOF, FOV, illumination) on two sensors, well. first, why on Earth would you want to do that? And second, you're never be able to do it perfectly. Because you won't be using the same lens. so what's the point?

Carry on folks, let's talk about upcoming equipment (or not) and leave the rest where it stands, please.
11-19-2015, 06:42 AM   #71
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QuoteOriginally posted by bdery Quote
I'll try to close this part of the discussion, and either let the thread die or bring it back to the original topic
A very fine summary explanation, thanks, but you don't really expect this to change anything, do you? If absolutely necessary "we" will simply go to another thread and fight over there
11-19-2015, 12:26 PM   #72
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QuoteOriginally posted by bdery Quote
Equivalence in simple terms means trying to get the exact same image with two different formats.
Not quite. Only from a geometrically point of view, plus about the same shot noise (same, if it's using t-stops). But that's actually strengthening your point.

The question "what does it take to get the same 1) image from two formats" is a lousy 2) one, IMHO. A much better one could be "what are the practical differences between these two formats, and how do I use them to my advantage".

1) except for some very important parameters
2) even for deciding which format is "the best". Because then the answer, necessarily and regardless of your needs, can be reduced to one word: FF.

P.S. Perhaps you already answered this, but...
From what I see you've been quite impressed with the 70-200. Do you intent to buy it?
11-19-2015, 12:31 PM   #73
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QuoteOriginally posted by bxf Quote
Yikes!
I need to go out and buy new light meters. One for each size I have from APS-C to 6 1/2 to 8 1/2 inches. My silly spot meters have no place to input format size.
11-19-2015, 11:16 PM - 1 Like   #74
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QuoteOriginally posted by redrockcoulee Quote
My silly spot meters have no place to input format size.
I already mentioned earlier that light meters do not need to distinguish between formats because they measure exposure.

Exposure is a relative measure of light-per-unit-area and hence independent of format size. Hence exposure, on its own, is unfit for predicting image noise. An image taken with a Q at f/1.9 will be much noisier than an FF image taken at f/1.9 (when viewed at the same size).

This is why the notion of "total light" is much more useful than "exposure". Only based on the latter one can suggest "f/2.8 = f/2.8.

N.B., obviously physical lens properties never change, but the meaning of parameter numbers change between formats. Almost everyone understands that focal length requires a "currency conversion" between formats to allow focal length numbers to be compared, but not too many understand that the same is required for f-ratio and ISO.

I had already given up on this thread, and only replied because the post I quoted was an attempt to ridicule my position. I will try to abstain from replying in the future, but please note that
  • I thought the thread was on course to steer away from an equivalence discussion, but several equivalence doubters kept on going back to that topic. I don't mind, but be careful about whom to blame when threads go off-topic.
  • I thank Kunzite for his measured response. I still disagree with a number of his views, but he did not use aggressive language anymore. I did not respond to the post because I don't think that resolving our communication differences is of public interest.
  • Bringing in t-stops complicates matters rather than simplifying them.
  • "Equivalence in simple terms means trying to get the exact same image with two different formats. is a complete misrepresentation. The notion of "equivalence" is about a correct understanding of the impact of format size on image quality (noise and detail). While such a correct understanding allows one to figure out when images will be equivalent even when produced on different formats, it is inappropriate to equate a notion with one of its applications or, worse, claim that this application is the goal of having the notion.
  • Noise is not driven by pixel size. The evidence exists on DxOMark. Here is a horse that won't stop dying, no matter how much one beats it. Yes, there are some highly technical second-order influences of pixel size on pixel noise, but the first-order effects and light shot-noise dominate and we are talking about image noise not pixel noise, hence one can forget about pixel size.

Last edited by Class A; 11-20-2015 at 12:03 PM.
11-19-2015, 11:47 PM   #75
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QuoteOriginally posted by Class A Quote
Noise is not driven by pixel size. The evidence exists on DxOMark. Here is a horse that won't stop dying, no matter how much one beats it. Yes, there are some highly technical second-order influences of pixel size on pixel noise, but the first-order effects and light shot-noise dominate and we are talking about image noise not pixel noise, hence one can forget about pixel size.
What drivel.
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