April 20, 2014, 10:04:29 AM

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - dougkerr

Pages: 1 ... 3 4 [5] 6
61
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 23, 2011, 01:31:42 PM »
Hi, Jonathan,

Thus EF-S lenses + adapter would work on a cropped mode. . .
Always nice to see "cropped" used correctly (not to mean "smaller than something else we often think about").

Thanks.

Best regards,

Doug

62
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 23, 2011, 01:03:03 PM »
Hi, Jonathan,

Interesting observations.

I'm not sure how matters of sensor area fit into the thought process.

It is interesting to note that, among all the existing SLR-based still camera systems (that I have data for), the flange back distance is never less than 0.94 times the diagonal of the maximum system frame size (typically 43.26 mm, based on full-frame 35-mm as the "mother" size), and (if we exclude the "T-mount", not actually a camera system) is never greater than 1.09 times the mother frame diagonal.

If we think of the New Canon Thing having a "mother" frame size of 28 x 18.5 mm ("1.29x"), as some have speculated, then for the 30.0 mm flange back speculated upon here, that ratio would be 0.89.

That would not necessarily rule out a bona fide SLR version of the system, but it might be iffy.

Best regards,

Doug

63
United States / Re: 7d
« on: March 23, 2011, 12:50:48 PM »
Given the same focusing distance, depth-of-field will not change.
That's not necessarily true. The reckoning of depth of field is based, among other things, on an arbitrary criterion we choose, the circle of confusion diameter limit (COCDL). This is the largest diameter of the blur circle resulting from imperfect focus of objects not at the ideal focus distance that we, based on some outlook, are willing to consider "acceptable".

We may use many premises to choose a value of that. One traditional premise is as a certain fraction of the frame diagonal size. The concept behind this a fixed angular size of the "blur circle" when the image itself is viewed with a consistent angular size, for example, printed to a certain size and viewed from a certain distance.

If we follow that premise, then for a camera with a "smaller format", with a certain focal length lens, a certain f-number, and a certain distance to the subject, the calculated DoF will be smaller than for the larger-format camera - not because anything has changed in the optical physics but rather because our criterion of acceptable blur is changed for the new format size.

Quote
Given the same framing, depth-of-field will be greater on the 7D because your focusing distance will be greater (due to the crop factor, you'll have to back up)
Indeed.

But it is interesting to see how that happens. Two factors are at work.

Firstly, if we indeed hold to the choice of a COCDL that is a fixed fraction of the fame size, then, for a "smaller" frame size, that factor of itself will decrease the calculated DoF.

However, as you point out, to maintain the original framing, the needed distance to the subject will increase. This increases the calculated DoF, and by a greater ratio than it is diminished by the adoption of a smaller COCDL. Thus, the net effect is indeed an increase in the DoF.

Best regards,

Doug

64
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 22, 2011, 10:42:48 PM »
This diagram?

No dimensions, and no requirement to draw it to any particular scale.

True, but the "front" face exactly matches in proportions every feature of an EOS mount. Thus, if it the rest of it is drawn to the same scale, we can determine that scale to a high precision.

Quote
From this, you can determine the sensor coverage?  I see no information about the lenses, they are what determines coverage, nothing else.

Yes but there is an interaction with the mount throat diameter.

If in fact the lens design places the exit pupil at the mount throat (hard to do and not necessarily desirable from several standpoints), then the throat does not constrain the image circle. For an exit pupil forward of that, the mount throat does constrain the image circle.

Best regards,

Doug

65
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 22, 2011, 05:14:41 PM »
My apologies. I was in fact in error regarding the APS-C frame size (I picked the numbers up from an old table that I had somehow screwed up, without looking at it).

Here is the correct info:

The APS taken frame size is 30.2 mm x 16.7 mm.

There are three "delivery crop" frames standardized:

APS-H:  30.2 mm x 16.7 mm  (1.808:1)  (16:9 would be 1.778:1) [this is in fact the taken frame size - it is "full frame"]
APS-C:  25.1 mm x 16.7 mm  (1.503:1)  (3:2 would be 1.500:1)
APS-P   30.2 mm x 9.5 mm   (3.179:1)

Sorry for the error.

Using the "full-frame 35-mm equivalent focal length factor" convention, an actual APS-C frame size (not found, within 5%, in any digital cameras I know of) would be considered "1.44x".

So it's probably not a bad metaphor for such frame sizes as 22.3 x 14.9 mm ("1.61x" - EOS 60D) and 27.9 x 18.6 mm ("1.29x" - EOS 1D Mark IV).

Oh, wait - they call the latter of those sizes "APS-H". Well, that's actually 30.2 x 16.7 mm. So it would better to call the 1D4 size "APS-C".

Glad I don't have to decide that.

Who does get to decide that?

As for me, I use "APS-C" to mean "APS-C".

Best regards,

Doug

66
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 22, 2011, 04:19:36 PM »

Doug, I think you have a Typo in there, 1.3X crop APS-H is about 27.9 X 18.6 (1D MK IV) while 1.6X crop APS-C runs about 22.3 X 14.9.
No, I was speaking of the actual APS-C frame size, not the various digital camera frame sizes that are somewhere in that neighborhood and are often spoken of as "APS-C".

The APS taken frame size is 30.2 mm x 16.7 mm.

There are three "delivery crop" frames standardized:

APS-H:  30.2 mm x 16.7 mm  (1.808:1) (this is in fact the taken frame size).
APS-C:  23.4 mm x 16.7 mm  (1.401:1)
APS-P   30.2 mm x 9.5 mm   (3.179:1)

Best regards,

Doug

67
Canon General / Re: Canon falling behind in sensor performance
« on: March 22, 2011, 03:32:22 PM »
Sony has developed and implemented complex algorithms into their latest Exmor sensor.

I'm not sure what kind of algorithms there are in sensors. Sensor systems, maybe.

Best regards,

Doug

68
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 22, 2011, 01:19:14 PM »
Hello,
I've found an interesting rumor from June.

http://photorumors.com/2010/06/09/canon-aps-h-1-3x-mirrorless/

Now, it seems pretty plausible after that mirrorless patent came out.

Might make sense.

The EOS line has to date had three nominal frame sizes. It might be that the New Canon Thing (NCT) would also embrace bodies of differing format size, with something like 27 x 18 mm (32.44 mm image circle requirement) being the largest (0.75 of full-frame 35-mm format).

Then the "smaller" bodies might in fact have the rumored 18 x 12 mm format (0.50 of full-frame 35-mm format).

That would be a 3:2 ratio between the format sizes in the family, probably a sensible spread.

I have made no attempt to ascertain the design limits relating image circle to to such things as mount throat and back flange distance, so I'm in no position to opine on the design credibility.

You earlier suggested that you believe the mount implied by the patent would not support a frame size larger than what you call "APS-C" (by which I assume you don't actually mean the APS-C frame size but rather the Canon "1.3x" frame size often spoken of as "APS-C", perhaps nominally 22.3 x 14.9 mm). (The APS-C frame is 23.4 mm x 16.7 mm.)

Best regards,

Doug

69
EOS Bodies / Re: Canon Doesn't Need a Compact Camera System
« on: March 21, 2011, 09:00:03 PM »

Some sort of kerr cell shutter. The mirror only becomes semi-transparent with an electrical impulse.
Oh, interesting thought.

Not invented by me, by the way - by a cousin, we assume.

Best regards,

Doug

70
EOS Bodies / Re: Canon Doesn't Need a Compact Camera System
« on: March 21, 2011, 08:26:40 PM »
Id love to see a mirrorless canon FD mount system, . . .
[/quote]
You mean no autofocus, mechanical aperture control?

Quote
. . . adapter for new lenses.
What kind of new lenses? They would have to have a back flange distance of at least 50mm or so (could not even be EF lenses).

Best regards,

Doug

71
EOS Bodies / Re: Canon Doesn't Need a Compact Camera System
« on: March 21, 2011, 08:05:09 PM »
Is it possible to make a pellix mirror that "somehow" doesn't dim the viewfinder while framing?
Pellix is the tradename of a Canon camera. It uses a fixed, semi-reflective pellicle mirror (a mirror whose substrate is a stretched thin film - the term itself does not imply anything else about the mirror) in a single-lens reflex configuration.

A single-lens reflex camera using a fixed semi-reflective mirror can have a mirror box that is a bit shorter than the mirror box for a moving mirror system.

A fixed semi-reflective mirror in a single-lens reflex camera (pellicle or otherwise) inevitably results in some light loss in both the taking and viewing paths.

What kind of arrangement do you have in mind?

Best regards,

Doug

72
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 20, 2011, 03:54:29 PM »
Not that it matters much, but I have spoken of the flange back for the Micro Four Thirds system as "20 mm", whereas I see it often described as "about 20 mm" (no definitive value being cited).

There is a report from a fellow who, from a a T mount-to-Lumix DMC-G1 adapter, concludes that the Micro Four Thirds flange back is likely about 19.2 mm (recognizing that the adapter might have an offset for "safe infinity focus" built in, so perhaps the actual nominal flange back is a little larger than that).

Thus it might be that the nominal flange back for the Micro Four Thirds system is exactly half that for the Four Thirds system (which has been stated as 38.67 mm), or 19.33 mm.

Best regards,

Doug

73
Lenses / Re: List of rumored lenses
« on: March 20, 2011, 12:47:13 AM »

The EF 24-70mm has a front element large enough to be f/0.95, which makes me wonder - is the lens really as small as it can be ?
The  entrance pupil (whose diameter determines the f-number) rarely falls at the front element, but usually behind it.

As a result the front element may well need to have a greater diameter to avert vignetting.

Best regards,

Doug

74
EOS Bodies / Re: Canon Doesn't Need a Compact Camera System
« on: March 19, 2011, 09:24:28 AM »
Canon already makes quite a few "compact" cameras (my "rank" in this forum honors one), so I assume that what is being discussed here is an interchangeable lens camera system whose controlling dimensions are smaller than for the EOS family.

I am not personally interested in the availability of a reflex form in such a supposed new line, but if in fact Canon feels the need to be able to offer such, we might see indications of that in the choice of a larger back flange distance for the new system than we would otherwise expect (just as the Four Thirds system has a larger back flange distance than the Micro Four Thirds system, which is not considered to reasonably support a reflex configuration, as the Four Thirds system does).

Best regards,

Doug

75
EOS Bodies / Re: First Canon Mirrorless Related Patent?
« on: March 19, 2011, 08:42:32 AM »
Jonathan,

For further reference, in US Patent application 2011/0052185 (in which the figures seem to be identical to that shown for the Japanese application), the text discusses that the difference between the flange back of the "new" body and the flange back of the "current" [EOS] body is equal to the "thickness" of the adapter, "C", of which they then say (with respect to Figure 2):

Quote
The thickness is a
distance in the direction of the optical axis from the camera
body side installation surface 31a to the lens side installation
surface 33a

Best regards,

Doug

Pages: 1 ... 3 4 [5] 6