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08-13-2014, 05:52 AM   #676
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QuoteOriginally posted by Class A Quote
If the lens supports the larger format, it effectively collects more light (at the same f-stop).
True, ClassA, but now you are talking about the sensor.

The speed (f rating) is the ratio of how many mm wide a lens opens to its focal length.

There is no other consideration - same calculation for the Q as the 645Z.


Last edited by clackers; 08-13-2014 at 05:58 AM.
08-13-2014, 06:01 AM - 1 Like   #677
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QuoteOriginally posted by Class A Quote
If the lens supports the larger format, it effectively collects more light (at the same f-stop).

You can claim that the lens does not become "faster" because the exposure stays the same but I maintain that this is using unhelpful terminology. The relevant factor for IQ is the total amount of light, which increases with larger formats.

Are you really claiming that "f/4" on FF is the same as "f/4" on a Q? That both lenses are equally "fast"? They are in terms of exposure but what good is the exposure corresponding to "f/4" on a Q? About as good as "f/22" on FF, so very "slow" (as in "not bright") and noisy in low light and lots of depth of field.

Aperture and speed are strictly defined; it is not my claim or invention. It is also very useful definition that is not a moving target.
The relevant factor for IQ is another topic. This is about lens speed.
Sure F:4 is equally fast regardless of format as neither DOF or format are involved in the difinition of speed. Speed is tied to exposure by definition because it is a physical parametre based on the opening of the lens. This is THE most useful relation in photography cause I then know that regardless if I shoot with the Q or the 645z, I'll get the same shutterspeed at the same ISO. This is the fundament of the principle of reciprocity on which the theory of exposuer is based. I won't get the same image but this is not what this is about.

Last edited by Pål Jensen; 08-13-2014 at 06:06 AM.
08-13-2014, 06:04 AM - 1 Like   #678
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You won't finish this ever both of you, will you?
08-13-2014, 06:05 AM   #679
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QuoteOriginally posted by clackers Quote
True, ClassA, but now you are talking about the sensor.
I'm talking about the light that goes to waste on the smaller format.

QuoteOriginally posted by clackers Quote
The speed (f rating) is the ratio of how many mm wide a lens opens to its focal length.
Yes, an "f/4" lens remains an "f/4" lens on all formats. Just like it retains its focal length on all formats.

All I'm saying is that it is not helpful to regard an "f/4" lens on a Q to be as "fast" as an "f/4" lens on FF, with "fast" having the connotation of "being a very good light gatherer". The obtained exposure is the same, but "exposure" is not an indicator for image quality across format sizes (because total light matters, not candela/mm^2).

You probably wouldn't call an "8.5mm f/1.8" lens on a Q "wide" and I'm saying it shouldn't be called "fast" either.

QuoteOriginally posted by clackers Quote
There is no other consideration - same calculation for the Q as the 645Z.
Correct.

I'm not trying to redefine how the widest f-stop of a lens is calculated, I'm just trying to bring perspective to how different the meaning of the same numbers is for different formats.


Last edited by Class A; 08-13-2014 at 06:23 AM.
08-13-2014, 06:13 AM   #680
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I guess I'll chime in now...

The F stop (ratio of objective diameter to focal length) is a static ratio, not affected by format (which is the optical target where the inverted image is cast). A 200mm F4 is a 200mm F4 regardless of whether it is put on a POS sensor, 4/3, APSc, FF, MF, or view camera. It casts the same light circle, hence the Contax-Zeiss view in the late 90s (great idea but derailed by the digital sensor train hitting it). F stop ratio is an inverted measure of "lens speed" which is still the classic term used in many optical engineering shops that look at exposure times.

The light circle is diffused the wider it is cast, and the angle of it hitting sensors or film is made more acute at the extremes. The smaller sensor "crops" but gets a higher quality light source due to less surface diffraction. Most sensors are designed with this in mind.

There is an effect on the extremes of larger sensors, but it is more to the negative than the positive. The FF argument "Larger is better" or a 24mpFF is better than a 24mp APSc, is the most ridiculous argument I have seen on this site (not this thread or the respondents). Anyone that takes that position is demonstrating their total lack of knowledge and ignorance... Simple. At 36x24mm sensor one needs 51mp to match the IQ of a 24mp APSc. Whew...
08-13-2014, 06:20 AM   #681
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QuoteOriginally posted by GlassJunkie Quote
Simple. At 36x24mm sensor one needs 51mp to match the IQ of a 24mp APSc. Whew...
????

The picture you look at on a screen or print and put in a frame is the same size, though, and one would be rendered from 51mp, the other from only 24 ....
08-13-2014, 06:27 AM   #682
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QuoteOriginally posted by GlassJunkie Quote
Simple. At 36x24mm sensor one needs 51mp to match the IQ of a 24mp APSc.
Not simple. 24mp ff demands less resolving power from your lens. Each pixel will receive about a stop more light on ff 24mp. Aberrations will also be roughly half the size on FF on the same viewing size. Large pixel density is not a pro, it's a con.
DOF is preference bound so i won't talk about that.
08-13-2014, 06:32 AM   #683
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QuoteOriginally posted by clackers Quote
????

The picture you look at on a screen or print and put in a frame is the same size, though, and one would be rendered from 51mp, the other from only 24 ....
Yes, and the attendant lost of resolution occurs, unless the image is magnified by some type of fractal manipulation. You are spot on...

08-13-2014, 06:35 AM - 1 Like   #684
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Well, I have to say, after trying to keep up with this thread for a while, I just want Photokina to actually happen so we can at least reduce the flow of endless speculation and opinion by a notch or two...
08-13-2014, 06:36 AM   #685
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QuoteOriginally posted by GlassJunkie Quote
Yes, and the attendant lost of resolution occurs, unless the image is magnified by some type of fractal manipulation. You are spot on...
Disturbing answer, GJ.

You do realise that to get to that same size you're pushing the pixels apart twice as far in the APS-C image as the FF one, right?
08-13-2014, 06:37 AM - 1 Like   #686
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QuoteOriginally posted by Class A Quote
I'm talking about the light that goes to waste on the smaller format.
Unless the optics are also designed to project a smaller image circle.

That's relative.

QuoteOriginally posted by Class A Quote
All I'm saying is that it is not helpful to regard an "f/4" lens on a Q to be as "fast" as an "f/4" lens on FF
Again, relative.

QuoteOriginally posted by Class A Quote
You probably wouldn't call an "8.5mm f/1.8" lens on a Q "wide" and I'm saying it shouldn't be called "fast" either.
Relative. On the Q sensor that is, indeed, fast.

QuoteOriginally posted by Class A Quote
I'm not trying to redefine how the widest f-stop of a lens is calculated, I'm just trying to bring perspective to how different the meaning of the same numbers is for different formats.
The meaning is identical. If one number changes—sensor size—then it becomes relative.

QuoteOriginally posted by D1N0 Quote
Large pixel density is not a pro, it's a con.
Nope. It's a con for ISO relativity and a pro for cropping and editing. The quality of data points is proportionate to the quantity.

Relative.

Last edited by Aristophanes; 08-13-2014 at 07:57 AM. Reason: tpyo
08-13-2014, 06:42 AM   #687
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QuoteOriginally posted by D1N0 Quote
Not simple. 24mp ff demands less resolving power from your lens. Each pixel will receive about a stop more light on ff 24mp. Aberrations will also be roughly half the size on FF on the same viewing size. Large pixel density is not a pro, it's a con.
DOF is preference bound so i won't talk about that.
Agree with your comment on aberrations, although they will be re-magnified on re-expansion of the image to make up for resolution. Algorithms can deal with the CA issue since it is not scalar more effectively than fractally making up for lost resolution.

The extra light may be desired, but IMHO not with the related overheads (refection in the box, diffraction, weight of equipment required to support the sensor class (how many birders want to lug 800-900mm in the field to shoot flying birds?

100% agree with your DOF comment. Faster lens speed (For you Pal ) or larger apertures provide different bokeh.

---------- Post added 08-13-14 at 09:48 AM ----------

QuoteOriginally posted by clackers Quote
Disturbing answer, GJ.

You do realise that to get to that same size you're pushing the pixels apart twice as far in the APS-C image as the FF one, right?
I am not sure I am understanding "pushing the pixels twice as far"... Can you give me more color on it? THX
08-13-2014, 07:22 AM - 1 Like   #688
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I'll get back to reading this thread once discussion about Photokina starts again..
08-13-2014, 09:09 AM   #689
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QuoteOriginally posted by Pål Jensen Quote
This is not the same as equivalent speed. Equivalent speed gives equivalent exposure by definition. Equivalent DOF do not.
"Equivalency" compensate rigidly this reduction in light by boosting the ISO correspondingly. However, no photographer respond to light reduction by boosting ISO exclusively. Hence, it is no law but an option.
So, your argument is, because no law REQUIRES you to make the same image, that it provides no benefit to compare the capabilities of making the same image?
08-13-2014, 09:52 AM   #690
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QuoteOriginally posted by Alizarine Quote
I'll get back to reading this thread once discussion about Photokina starts again..
So sometime in mid-September?

I was thinking maybe we can make this thread about cheese sandwiches.
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