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09-11-2010, 09:59 AM - 1 Like   #1
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Tech Question: Why are FF DSLRs so Large?

A few months ago, I played around with Nikon's D700 and quickly realized that it's much too large for my taste (particularly when my wife opined that we could use it as a "lunch hook" - a secondary anchor - when not shooting pictures).

Frankly, I'm ambivalent about FF, but it does beg the question: why must a FF DSLR be so large?

Any of you camera tech gurus know any reason there can't be a FF camera the size of - say - a K20D or K-7?

Thanks,

Jer

09-11-2010, 10:52 AM   #2
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They don't have to be large- in fact, the Pentax *ist D was originally meant for a full-frame sensor, and it has room for one (AND the mirror is full-frame sized). I guess the currently FF bodies just have a lot of stuff packed into them- Canon, for instance, likes including a non-removable grip.

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09-11-2010, 11:31 AM   #3
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as adam mentioned, they don’t have to be that large. the istD is a great example. the thing is though, that ‘FF’ is still considered a ‘pro’ feature, therefore its put into a camera body that is designed for specific uses. the size is more about what the people using the bodies want in their ‘pro’ cameras. beyond that though, both nikon and canon tend to design their bodies larger just in general. its really too bad that Pentax seems to have no current plans for a digital SLR with a 24x36mm sensor, because they would likely rock the industry for sure with a FF body thats no bigger than the current k-7/k-5.

the truth is that Pentax/Asahi Optical Co. have been designing their cameras (and lenses) to be smaller, lighter and more compact than everyone else from day one. its a Pentax trademark.
09-11-2010, 01:24 PM   #4
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So why is it deemed to be too complicated to just drop in a bigger sensor into a K20/K5-7 chassis?

09-11-2010, 01:34 PM   #5
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QuoteOriginally posted by Adam Quote
They don't have to be large- in fact, the Pentax *ist D was originally meant for a full-frame sensor, and it has room for one (AND the mirror is full-frame sized). I guess the currently FF bodies just have a lot of stuff packed into them- Canon, for instance, likes including a non-removable grip.
Last time this came up I looked into it and found zero evidence the *ist D has anything other than an APS-C size mirror. If you have anything to refute that, please share. Check this dpreview shot of the insides.

http://a.img-dpreview.com/reviews/pentaxistd/Images/mountccd01.jpg
09-11-2010, 02:15 PM   #6
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Simple camera's parameters scale in proportion to the sensor's linear dimension.

An important reason for this is "natural vignetting"* which is just tolerable when the sensor diagonal is equal to the sensor's distance from the lens.

Hence one might expect a 24x36mm frame camera to be about 50% bigger in all directions compared to a camera with a 18x24mm sensor.

Dave

*"Natural vignetting" is the natural fall-off in light intensity with angle from the optic axis (as about cos(angle)^4). When the sensor's diagonal equals the distance to the lens the light intensity at the frame corners is about 2/3 that in the frame center.

Last edited by newarts; 09-12-2010 at 03:49 PM.
09-11-2010, 03:32 PM   #7
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QuoteOriginally posted by Adam Quote
They don't have to be large- in fact, the Pentax *ist D was originally meant for a full-frame sensor . . . . . .
No kidding? Interesting - I assume cost dictated using a smaller sensor?

Jer

QuoteOriginally posted by séamuis Quote
. . . . . . . . its really too bad that Pentax seems to have no current plans for a digital SLR with a 24x36mm sensor, because they would likely rock the industry for sure with a FF body thats no bigger than the current k-7/k-5.

the truth is that Pentax/Asahi Optical Co. have been designing their cameras (and lenses) to be smaller, lighter and more compact than everyone else from day one. its a Pentax trademark.
Yeah, my ambivalence might recede if Pentax built a "small" FF. In fact, I got my MX all the way back in '78 precisely because I liked its size and ergonomics compared with the competition.

Jer

QuoteOriginally posted by lats Quote
So why is it deemed to be too complicated to just drop in a bigger sensor into a K20/K5-7 chassis?
Good question - perhaps it's the cost of regenerating a credible family of lenses to support FF . . . . . but, what do I know?

Jer

QuoteOriginally posted by newarts Quote
Simple camera's parameters scale in proportion to the sensor's linear dimension.

An important reason for this is "natural vignetting"* which is just tolerable when the sensor diagonal is equal to the sensor's distance from the lens.

Hence one might expect a 24x36mm frame camera to be about 50% bigger in all directions comparec to a camera with a 18x24mm sensor.

Dave

*"Natural vignetting" is the natural fall-off in light intensity with angle from the optic axis (as about cos(angle)^4). When the sensor's diagonal equals the distance to the lens the light intensity at the frame corners is about 2/3 that in the frame center.
Hey thanks, Dave. But isn't this simply an optical effect - unrelated to the senor's characteristics (electronic dodads or photoreactive organic molecules)? Wouldn't the same hold true for a film camera? What am I missing?

Jer

Last edited by Sailor; 09-11-2010 at 03:43 PM.
09-11-2010, 04:53 PM   #8
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Well, if they can get a full frame "sensor", film cassette and take-up space, pentaprism and a mirror box in an MX or MG sized body I'd look for digital differences such as electronics, flash and related battery capacity as one significant design factor.

H2

09-11-2010, 05:04 PM   #9
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QuoteOriginally posted by Sailor Quote
Hey thanks, Dave. But isn't this simply an optical effect - unrelated to the senor's characteristics (electronic dodads or photoreactive organic molecules)? Wouldn't the same hold true for a film camera? What am I missing?

Jer
Yes, it is a simple physical optical effect. The lens registry distance on a 6x6 (60mmx60mm sensor) camera is about its diagonal - Exacta 66 => 74mm - from the sensor plane, etc. This is an approximate relationship, but if the lens is too close to the sensor (film) plane, vignetting is a serious problem).

See: Camera Mounts Sorted by Register to get an idea of how lens registry distance correlates with sensor/film size..

You ask "what am I missing.." I think you are missing nothing... increasing the size of the sensor implies increasing the distance from the sensor to the lens independent of how the sensor operates (ie digital, film, silver plate, etc..)

Dave

Last edited by newarts; 09-11-2010 at 05:09 PM.
09-11-2010, 05:18 PM   #10
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QuoteOriginally posted by newarts Quote
Yes, it is a simple physical optical effect. The lens registry distance on a 6x6 (60mmx60mm sensor) camera is about its diagonal - Exacta 66 => 74mm - from the sensor plane, etc. This is an approximate relationship, but if the lens is too close to the sensor (film) plane, vignetting is a serious problem).

See: Camera Mounts Sorted by Register to get an idea of how lens registry distance correlates with sensor/film size..

You ask "what am I missing.." I think you are missing nothing... increasing the size of the sensor implies increasing the distance from the sensor to the lens independent of how the sensor operates (ie digital, film, silver plate, etc..)

Dave
how did leica pull it off with the M9?
09-11-2010, 05:28 PM   #11
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QuoteOriginally posted by pingflood Quote
Last time this came up I looked into it and found zero evidence the *ist D has anything other than an APS-C size mirror. If you have anything to refute that, please share. Check this dpreview shot of the insides.

http://a.img-dpreview.com/reviews/pentaxistd/Images/mountccd01.jpg
That image clearly shows a full frame mirror box. The mirror itself is APS-C sized but has a lot of space around it - enough room for a full frame mirror.
09-11-2010, 05:39 PM   #12
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QuoteOriginally posted by newarts Quote
Yes, it is a simple physical optical effect. The lens registry distance on a 6x6 (60mmx60mm sensor) camera is about its diagonal - Exacta 66 => 74mm - from the sensor plane, etc. This is an approximate relationship, but if the lens is too close to the sensor (film) plane, vignetting is a serious problem).

See: Camera Mounts Sorted by Register to get an idea of how lens registry distance correlates with sensor/film size..

You ask "what am I missing.." I think you are missing nothing... increasing the size of the sensor implies increasing the distance from the sensor to the lens independent of how the sensor operates (ie digital, film, silver plate, etc..)

Dave
The registry distance of a Pentax DSLR is that of 24x36 mm (full frame) Pentax film cameras. I bet that we sooner or later will see a Pentax full frame in a body only slightly larger than the size of the K-7 (the SR mechanism may require some additional space).

There is no technical hindrance for a full frame Pentax. It is a question only if the interest is high enough to warrant the development - and the development/re-issue of FF lenses.
09-12-2010, 07:23 AM   #13
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QuoteQuote:
QuoteQuote:
Originally posted by newarts
Yes, it is a simple physical optical effect. The lens registry distance on a 6x6 (60mmx60mm sensor) camera is about its diagonal - Exacta 66 => 74mm - from the sensor plane, etc. This is an approximate relationship, but if the lens is too close to the sensor (film) plane, vignetting is a serious problem).

See: Camera Mounts Sorted by Register to get an idea of how lens registry distance correlates with sensor/film size......

Dave
how did leica pull it off with the M9?
The Leica M series has one of the shortest sensor/film planes of any 24x36mm camera: 27.95mm , which is quite a bit less than the film plane diagonal. Natural vignetting would be very large if the lens' end is close to the camera mount so the lens designers had a job on their hands! It might be part of the reason why Leica lenses cost so much?

I've no Leica M lenses to look at but I'd guess their rear lens element would be recessed pretty far to make up for the short registry distance.

I hope that some one with Leica experience will comment on this.

Dave
09-12-2010, 07:24 AM   #14
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QuoteOriginally posted by Ole Quote
The registry distance of a Pentax DSLR is that of 24x36 mm (full frame) Pentax film cameras. I bet that we sooner or later will see a Pentax full frame in a body only slightly larger than the size of the K-7 (the SR mechanism may require some additional space).

There is no technical hindrance for a full frame Pentax. It is a question only if the interest is high enough to warrant the development - and the development/re-issue of FF lenses.
Great observation!
09-12-2010, 01:02 PM   #15
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QuoteOriginally posted by newarts Quote
Simple camera's parameters scale in proportion to the sensor's linear dimension.

An important reason for this is "natural vignetting"* which is just tolerable when the sensor diagonal is equal to the sensor's distance from the lens.

Hence one might expect a 24x36mm frame camera to be about 50% bigger in all directions comparec to a camera with a 18x24mm sensor.

Dave

*"Natural vignetting" is the natural fall-off in light intensity with angle from the optic axis (as about cos(angle)^4). When the sensor's diagonal equals the distance to the lens the light intensity at the frame corners is about 2/3 that in the frame center.

That's not really an issue in this case, because Pentax didn't change the registration distance when they moved to APS-C sensors.

Last edited by alohadave; 09-12-2010 at 02:32 PM. Reason: added a word for clarification
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