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Author Topic: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]  (Read 16283 times)

swrightgfx

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #60 on: October 23, 2012, 01:31:16 AM »
The answer is NO. Simply adding a TC does not change the number of megapixels your camera has. It only magnifies the subject. The output of Camera A will be a PART of the subject, in high detail. The output of Camera B will be THE WHOLE subject, in high detail.


One could always take multiple shots with the 2xTC and stitch together. :P See: http://www.shen-hao.com/PRODUCTSabout.aspx?i=1012&id=n3 and
DSC3212 on Vimeo Small | Large
.

EDIT: Video doesn't embed properly, so click the link at the bottom.

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #60 on: October 23, 2012, 01:31:16 AM »

KitsVancouver

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #61 on: October 23, 2012, 03:05:15 AM »
As always we have descended into "I-need-120MP-on-a tiny area-cuz-I-can-argue-it-will-work".

Prior to the 1DX and 5D-III release, the same crowd (you know who you are, you have spent hours typing pages on here selling the same old 3 day old fish) screamed for 40+ MP and were bitterly disappointed when Canon went the low MP route for both bodies.

Its not about what you "want"...its about what they can sell in a profitable way in a competitive market.
Most pros own a 1DX... not 7D... so much for the high MP whining. Every flagship that Nikon and Canon have released so far have been lower MP while they release high MP APC and consumer grade bodies for the "My-MP-is-Bigger-than-your-MP" crowd.

I guess learning comes a tad slow... but there is no harm in asking....please continue :)

Wasn't the 1Ds Mark III the flagship?  Didn't it have higher MP than the rest of the cameras at the time?

sanj

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #62 on: October 23, 2012, 04:44:38 AM »
Am happy that this is in the 1d style bodies. As I believe such hi mpx is for hi end use and pretty useless for general photographers.
what elitest hogwash!  ::) -100 for such an arrogant and ill concieved post
I for one dont want an overbulky 1D style body as many others do not want them either
there is no reason or need for them these days. infact the Smaller 5D style body is better for a high MP audience since its more compact and lighter its less bulk and weight to carry around hiking to get to that magic landscape shooting location to take advantage of the billions of pixels.
and in the studio with that many megapixels its going to be shot like a medium format. On a tripod and tethered capturing the whole area then cropping later as desired.

Ohh brotherrrrr!!!! Wow. THANK YOU so much for taking time to read my comment and clearly stating what you feel.
As much as I wish, Elite I am not, but I will expand on my arrogant hogwash.
I believe 1d size body is that size for many more reasons than just a large battery. It gives it more processing power for things that matter to many (and nice things to have anyways): fps, shutter lag, VF blackout, duel cards, overall responsiveness etc.

Now, it would be awesome to have a high MP camera which is not totally to its potential because is it in a smaller size body. That's my point.

Further, all landscape photographers generally need a tripod to create their masterpieces and as you mentioned it would be mounted on a tripod in the studio. So the size does not matter if a tripod is being used/carried anyways.

In any case Canon will not design this camera based on what you or I think, they will make it best for the high mp. Hoping they have a super camera in 1d size body.

Regards!

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #63 on: October 23, 2012, 04:59:14 AM »
Am happy that this is in the 1d style bodies. As I believe such hi mpx is for hi end use and pretty useless for general photographers.
what elitest hogwash!  ::) -100 for such an arrogant and ill concieved post
I for one dont want an overbulky 1D style body as many others do not want them either
there is no reason or need for them these days. infact the Smaller 5D style body is better for a high MP audience since its more compact and lighter its less bulk and weight to carry around hiking to get to that magic landscape shooting location to take advantage of the billions of pixels.
and in the studio with that many megapixels its going to be shot like a medium format. On a tripod and tethered capturing the whole area then cropping later as desired.

Ohh brotherrrrr!!!! Wow. THANK YOU so much for taking time to read my comment and clearly stating what you feel.
As much as I wish, Elite I am not, but I will expand on my arrogant hogwash.
I believe 1d size body is that size for many more reasons than just a large battery. It gives it more processing power for things that matter to many (and nice things to have anyways): fps, shutter lag, VF blackout, duel cards, overall responsiveness etc.

Now, it would be awesome to have a high MP camera which is not totally to its potential because is it in a smaller size body. That's my point.

Further, all landscape photographers generally need a tripod to create their masterpieces and as you mentioned it would be mounted on a tripod in the studio. So the size does not matter if a tripod is being used/carried anyways.

In any case Canon will not design this camera based on what you or I think, they will make it best for the high mp. Hoping they have a super camera in 1d size body.

Regards!

eh ok i might have read your previous post the wrong way but it did sound a bit like keep it a 1D to keep the rif raf out kind of thing. sorry for giving you such a spray.

the bulk has no bearing on any of the 1D benefits, processing power can easily fit into a 5d sized body
VF blackout i love this on the 1D bodies wish i was carried over to the 5D
AF linked metering, more customiation ability
1 button press to enable bracketing - awesome there are so many 1D features that make it a 1D
only really have a 1D do you realise how much stuff the other models miss out on, stuff
however the time of the massive brick of a camera being the badge of honour showing that someone is a proffessional are long gone, some people use grips for legitimate reasons big hands, more comfortable for them, actually prefering to use the portrait shooting buttons.
many more use grips to try and look more impressive...

I use my 1Dmk3 still because of the bombproof build and where i use it wont use another series camera because anything without the latest L weather sealing lenses or 1D build would have a very short lifespan.
however I would LOVE to have a small camera to use built to the same standard.
while I love my 5Dmk3 its not going to hold up to the punishment a 1D body can take

remember back in the day when there was a choice if your 1V had the extra bulk of the HS or if it was just a nice 1V if the 1DX was available sans grip i would buy one.

battery tech these days means they could easily have all the functionailty voltage processing power no mode dial wheel, the works in a gripless body

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #64 on: October 23, 2012, 05:12:59 AM »
As for the question posed by PerfectSage, there does appear to be a real and practical answer, or at least rule of thumb, which would guide one towards the goal of advantaging all of that 116 lp/mm resolving power of the 7D sensor, and that is to choose optics that will present an image to the sensor with enough inherent detail.   if the source image truly does not contain the detail, the sensor will not find any that isn't there.  Whether or not that goal is a good one or not can be debated of course

Technically speaking, there is an asymptotic relationship in terms of spatial resolution. You can never actually achieve the same spatial resolution as the highest resolving component in an optical system. As you approach it, you begin to experience diminishing returns. Lets say you have a lens capable of resolving 86lp/mm. Nothing you ever do can ever allow you to resolve 86.1lp/mm...your upper bound is the resolution of the lens itself. At best, you could reach 85.99999999999... lp/mm, assuming you had a sensor with literally infinite resolution. You would need something like an f/0.3 lens to resolve around 115lp/mm of resolution, and approach the 116lp/mm of the 7D. Total "system spatial resolution" is derived from the RMS of the "blur circle" of each component in an optical system. The size of the airy disc at a given aperture in the lens, blur introduced by any and all TC's, the size of a pixel in the sensor, and if you want to get really accurate, the size of the blur introduced by low-pass and IR cut filters. Taking the RMS of each of those will give the the size of the blurry disc of a single point light source resolved by the entire system. Taking the reciprocal of that divided by two will give you the spatial resolution of the system as a whole in lp/mm.

very nice explanation Jrista, and the first coherant technical epistle I've seen here regarding the effects of lens choice as regards the resolving power of the sensor, both the contribution of individual components and the asymptotic behavior of the function.   Essentially, the 1/(2  * RMS) method suggests that when one component in the system is replaced by one that is significantly worse than the previous aggregate, that the effects will probabaly be noticed.  Moreover, the effect of such a substitution will be more noticeable with there are fewer components in the system.  Accordingly, using the approximation of only two components (the sensor/lpf and the lens), one can easily see that the choice of lens will influence the overall resolving power of the system.  Captain obvious, to be sure, but one could model the equation and see the effects (on end-2-end resolving power) of choosing one lens over another, an excersize left "to the reader", lol. .  I suspect most would rather look at photos though :D

Panurus

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #65 on: October 23, 2012, 05:29:34 AM »
Thank you jrista. FTM50 is better that FTM 0%.

Why not to go a step further for the fun: FTM 100%?

Let's see what is a contrast of 100%.
A picture of black and white lines, with a perfect optic, can for a particular spatial distribution give a contrast of 100%. In this case, the distribution is sinusoidal with min = 0 and max = 1.
http://www.flickr.com/photos/jeanrouck/6240117829#

The contrast value is there : 100% =  ( 100 + 0 ) / ( 100 - 0 )
 black is 100 and white is 0.
http://www.flickr.com/photos/jeanrouck/6240565328/#


For a  FTM 50%,  the darkest is 75%of grey and the brightest is 25 % of grey.
contrast : 50% =  ( 75 - 25 ) / ( 75 + 25 )
So we are far away from the original black and white lines.

Remark : If Imax / Imin = 3 , the contrast is 50 %.
 (100-33) / ( 100 + 33) = 50%
(75 - 25 ) / (75 + 25) = 50%
(30 - 10 ) / (30 + 10) = 50%

Maybe , this pictures help to see (undestand) that the number of pixels will never change the grey pixels in white and black pixels.  But one day, tools like the Richardson–Lucy deconvolution could help a little to find the original values and than more information will give better pictures.


Zeiss do a good job about FTM:  to read before dreaming about High MPx body.

Here is a picture with a part of the original sample,  a 24Mpix pict of the sample and 12 Mpix pict of the sample..
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild13/$File/Bild_13.jpg
So you can see how a little black line is transformed, with a 12 MPx and a 24 MPx, in grey lines.


More informations about real lens:

http://www.zeiss.de/C12567A8003B8B6F/EmbedTitelIntern/CLN_30_MTF_en/$File/CLN_MTF_Kurven_EN.pdf

Measuring lenses objectively – Part 2
http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_31_MTF_en/$File/CLN_MTF_Kurven_2_en.pdf

Here are the pictures of the examples.
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild1/$File/Image_01.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_02.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_03.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_04.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_05.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_06.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_07.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_08.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_09.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_10.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_11.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_12.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild2/$File/Image_13.jpg
http://www.zeiss.com/C12567A8003B8B6F/GraphikTitelIntern/CLN31MTF-KurvenBild14/$File/Bild_14.jpg

http://www.zeiss.com/C12578620052CA69/0/4FAB9EF851C018C5C12578D200405960/$file/cln_35_bokeh_en.pdf

« Last Edit: October 23, 2012, 06:42:32 AM by Panurus »

symmar22

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #66 on: October 23, 2012, 07:16:44 AM »
IF two sensors (39 and 50 Mpx) are out there, it could be they are planning release two cameras, one 39Mpx in a 5D type body (5Ds ?) that would be a competition for the D800, and later a 50Mpx camera in a 1D type body (1Dxs ?) to counter a future D4x(s).

This way everyone would be happy.

However I'd like to add my two cents about high res. cameras, and the fact that a lot of people seem to dismiss them on the pretext no one needs them, and 20Mpx are good enough for everything.

I can understand people are happy with their cameras and 18Mpx suit their needs, but some folks have other requirements. It's like if you would have said 20 years ago no one needs 4x5 or 8x10 cameras, 35mm is good enough for everyone. People who need high resolution sensors usually don't make 1000 pictures per day, it's about studio work, or architecture, or industrial photo, where quality is more important than quantity. When you work in a studio, you can spend hours on a setting before you even press the shutter, then all you need is a few frames, but with as much quality as you can deliver.

Nobody shoots wildlife or sports with a 4x5 camera, that doesn't mean 4x5 cameras were (are) useless for other styles of photography.
« Last Edit: October 23, 2012, 08:11:06 AM by symmar22 »

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #66 on: October 23, 2012, 07:16:44 AM »

Lee Jay

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #67 on: October 23, 2012, 09:03:40 AM »
My good, you Jrista  have great difficulties to discuss one thing at a time,  you mixing apples with pears in a mess
What are we discussing? how high resolution a good lens can resolve?, how many pixels  we can have  a benefit from??

The answer to that last question is infinity, except for limitations on the technical side of sensor design and production.  Cell phone sensors are down to 1.25 micron pixels or so which would equate to 28,800x19,200 or 553 megapixels on a full-frame sensor, so the current limitation isn't on the technical side of sensor fabrication for large sensors.  Eric Fossum (the guy that invented the active pixel CMOS sensor) believes we'll have gigapixel sensors in our lifetimes.

Lee Jay

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #68 on: October 23, 2012, 09:15:46 AM »
You still have a very skewed idea, or simply bad terminology, in describing what you are actually experiencing with a TC, though, Lee Jay. Your previous argument in that other thread, that the virtual image of the sensor shrinks when it is observed by looking through the lens into the camera is not indicative of what is really occurring. A teleconverter does not change how many megapixels you have, nor does it change the resolution of the lens.


No, but it has the same effect as doing either one.


The effects are different.


They are the same.  Smaller pixels and longer focal length, both given the same aperture diameter, do the same thing.  See for yourself:

http://photos.imageevent.com/sipphoto/samplepictures/Pixel%20density%20versus%20teleconverters.jpg


You are only thinking pixel size, which I guess is one way to look at it.


Yes, that is the subject we are discussing - is there a point to smaller pixels given the lenses we have available, to which the answer is obviously "yes", as can be shown by simple math and by examples from TCs which show you what the center of the image would look like with smaller pixels.

Quote
If you are referring to optical system resolution, rather than spatial resolution, then I agree. However you keep applying the units "lp/mm" to system resolution, which feels like a major conflation to me. Assuming the optical spatial resolution of the entire lens setup (original lens + TC) remains the same (which is generally impossible when adding a TC, as it reduces your REALTIVE aperture, which implicitly means your optical spatial resolution of THE ENTIRE LENS SETUP is reduced), the final system spatial resolution will be lower than that of the lens or the sensor, as it is the root mean square of the blur each individual component.


I can't even believe you just said that.  So, adding a TC reduces optical spacial resolution?  Better throw them all out then.

A TC doesn't change optical resolution.
Quote

In the context of scientific astrophotography, the imaging devices used are orders of magnitude more expensive than a consumer-grade sensor.


Which is irrelevant since I was talking about using $50 Walmart webcams for astro imagining.  Or, if you want to go high-end, something like a Flea-3, which is a better version of the same thing.

Quote
Quote
The notion that a camera can usefully resolve anything at MTF 9% (Reighley) is also pretty ridiculous.


Except that we do so all the time, in astro stuff.


You need to back that up with some actual examples...

Better ask Damian (one of the best amateur planetary imagers in the world) why he shoots 5.6 micron pixels at f/30 instead of his scope's native f/11:

http://www.damianpeach.com/best.htm

Look, the facts are simple.  If you want to see how a particular lens would perform on a camera with four times as many pixels as your current camera, simply add a good quality 2x TC and see for yourself how the center of that hypothetical sensor would look with the bare lens.  Period.

K-amps

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #69 on: October 23, 2012, 09:45:07 AM »
Forget 50mp... just let me swap out my 5d3 sensor for something with NO AA filter... 

While Canon is at it... please play nice with Sony and Sigma and get us a 16DR with Foveon type non-bayerless 22mp sensor with 5d3 type high ISO performance. 


Wake up...   what a wet dream that was...


5D3 without AA filter would be pretty moire and aliased though no? it's only 20D photosite density

:-)  True, if I was into shooting fabrics.

what about ripples on a lake or fallen leaves on a forest floor or jagged rocks, etc.  :D

Good point: I doubt ripples will be that consistent to fool the demosaicing algo's...   Leaves probably not, they are too random, and jagged rocks too... not saying it is impossible, just saying it will be too far between to be an issue. OTOH I could gain some resolution without the AA filter in the way... rest will be PP'ed.   
I don't shoot video... so PP'ing stills is not a huge deal for me...
« Last Edit: October 23, 2012, 11:03:46 AM by K-amps »
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dlleno

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #70 on: October 23, 2012, 10:53:30 AM »
I can't even believe you just said that.  So, adding a TC reduces optical spacial resolution?  Better throw them all out then.

A TC doesn't change optical resolution.

Lee Jay -- are you really saying that the TC will not introduce diffraction artifacts due to the change in aperture, and that the additional glass elements will present or expose no further optical abberations in the image presented to the  sensor?  Please do explain the conditions under which modifying the optical system by adding a piece of glass cannot change it's optical resolution properties. 
« Last Edit: October 23, 2012, 11:00:28 AM by dlleno »

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #71 on: October 23, 2012, 12:19:25 PM »
I can't even believe you just said that.  So, adding a TC reduces optical spacial resolution?  Better throw them all out then.

A TC doesn't change optical resolution.


Lee Jay -- are you really saying that the TC will not introduce diffraction artifacts due to the change in aperture, and that the additional glass elements will present or expose no further optical abberations in the image presented to the  sensor?


First one yes, second one no.

Diffraction (angular resolving power of the optical system) goes with aperture, not f-stop.  That's why telescopes are sold by aperture and not by focal length and f-stop (well, light gathering does as well and that's the second reason telescopes are sold that way).  The only reason f-stop was in the formula I posted was because that wasn't angular resolution of the optical system (which is what we're really after), it was spatial resolution at the sensor.

sin theta = 1.22 * lambda / D where D is the diameter of the lens' aperture.  A teleconverter doesn't change D and so it doesn't change theta.

http://en.wikipedia.org/wiki/Angular_resolution

I already said TCs are actually slightly worse than small pixels because of aberrations.  Fortunately, TCs are close to optically perfect these days so the degradation is quite small.  Regardless, this works in favor of my argument - a TC will give a good simulation of how a lens would perform on smaller pixels.  In fact, the smaller pixels will perform better so this TC test is a worst-case.

« Last Edit: October 23, 2012, 12:27:13 PM by Lee Jay »

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #72 on: October 23, 2012, 12:42:24 PM »
You are only thinking pixel size, which I guess is one way to look at it.


Yes, that is the subject we are discussing - is there a point to smaller pixels given the lenses we have available, to which the answer is obviously "yes", as can be shown by simple math and by examples from TCs which show you what the center of the image would look like with smaller pixels.


No, the topic we were discussing is whether adding a TC is exactly the same and just as good as using a sensor with a higher pixel density by the same factor as the TC added. Its a bit more complex than simply stating "well we are just talking about pixel size".

Quote
If you are referring to optical system resolution, rather than spatial resolution, then I agree. However you keep applying the units "lp/mm" to system resolution, which feels like a major conflation to me. Assuming the optical spatial resolution of the entire lens setup (original lens + TC) remains the same (which is generally impossible when adding a TC, as it reduces your REALTIVE aperture, which implicitly means your optical spatial resolution of THE ENTIRE LENS SETUP is reduced), the final system spatial resolution will be lower than that of the lens or the sensor, as it is the root mean square of the blur each individual component.


I can't even believe you just said that.  So, adding a TC reduces optical spacial resolution?  Better throw them all out then.

A TC doesn't change optical resolution.


YES, adding a TC reduces optical spatial resolution, because it reduces the RELATIVE APERTURE. Diffraction is dependent on aperture. For a small table, so we all (you, me, and other readers) have the same reference information:

Diffraction-Limited ApertureMTF 50 (lp/mm)
f/1691
f/1.4494
f/2346
f/2.8247
f/4173
f/5.6123
f/886
f/1163
f/1643
f/2231

If you start out with an f/4 lens, without a TC your lens could achieve up to 173lp/mm, if it was diffraction limited. A non-diffraction limited lens, one which is aberration limited, would have LESS spatial resolution due to the blurring caused by aberrations. If you add a 2x TC to that f/4 lens, regardless of what the focal length ends up being, the aperture is now f/8. That explicitly limits you to 86lp/mm optical spatial resolution on the upper bound, assuming you are, again, diffraction limited, and not aberration limited.

So YES, adding a TC has the effect of REDUCING MAXIMUM POTENTIAL SPATIAL RESOLUTION. Its physics. There is no way around that fact.

What you are referring to is magnification. Adding a TC enlarges the subject, so the portion of the subject that is projected through the lens and onto your sensor is LARGER. It would be similar to moving 1.4x or 2x closer to your subject without the TC...except that if you move closer rather than adding a TC, your relative aperture remains larger, which means the upper bound on spatial resolution remains higher.

I don't know how else to explain it, but magnification and spatial resolution are disjoint. You can technically increase subject magnification without changing your spatial resolution. You could also increase your spatial resolution without magnifying your subject. The two are independently variable. Examples of achieving each optically:

1. Double magnification while maintaining spatial resolution:
  - Swap a 400mm f/4 lens for an 600mm f/4 lens.
  - Same relative aperture, 2.25x larger subject.
  - Subject size in-frame is relative to the square of the ratio of the focal lengths: (600/400)^2 = 1.5^2 = 2.25
2. Double spatial resolution while maintaining magnification:
  - Swap a 400mm f/8 lens for a 400mm f/4 lens
  - Same subject size, double the relative aperture
  - Diffraction-limited spatial resolution increases from 86 lp/mm to 173 lp/mm
3. Quadruple magnification while halving spatial resolution:
  - Add a 2x TC to a 400mm f/4 lens
  - Half the relative aperture, 4x larger subject
  - Diffraction-limited spatial resolution drops from 173lp/mm to 86lp/mm
  - Subject size in-frame is relative to square of the ratio of the focal lengths: (800/400)^2 = 2^2 = 4

As you can see, despite losing spatial resolution with a TC, adding a 2x TC QUADRUPLED the size of your subject relative to the same sensor frame. You doubled the amount of resolved detail, despite the loss in spatial resolution...thanks to magnification.

Quote
Quote
The notion that a camera can usefully resolve anything at MTF 9% (Reighley) is also pretty ridiculous.


Except that we do so all the time, in astro stuff.


You need to back that up with some actual examples...

Better ask Damian (one of the best amateur planetary imagers in the world) why he shoots 5.6 micron pixels at f/30 instead of his scope's native f/11:

http://www.damianpeach.com/best.htm

Look, the facts are simple.  If you want to see how a particular lens would perform on a camera with four times as many pixels as your current camera, simply add a good quality 2x TC and see for yourself how the center of that hypothetical sensor would look with the bare lens.  Period.


Sure...but you've just invoked cropping. Who buys a 500mp sensor to crop out the middle 18mp? Let's stop equivocating here. There is a huge difference between quadrupling pixel density in a FF sensor, and adding a TC. With the TC, you only get the center 25% crop. With a FF sensor with quadruple the density, you get the whole subject. Equivocating by saying something along the lines of "My 400mm lens with a 2x TC is the same as having a 369mp sensor" is a fallacy. The 369mp sensor is capable of resolving a 4x more area of your subject with the same amount of detail as the 2x TC. That is a HUGE difference. That is a full two orders of magnitude difference.

The terminology you use in your approach to explain what a TC is doing for you is misleading. You are not increasing spatial resolution, which is what it sounds like you are doing when you equate the effect of magnification offered by a TC to using a higher density sensor of the same physical dimensions. You are magnifying your subject at a lower spatial resolution. The math here isn't all that complex. Apertures, diffraction, spatial resolution, magnification. It's all pretty basic, and no amount of wordmincing and dancing around the heart of the debate will get you past the facts.

 * TC's magnify.
 * Higher density sensors resolve more.

Two very different things.
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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #72 on: October 23, 2012, 12:42:24 PM »

jrista

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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #73 on: October 23, 2012, 12:51:45 PM »
I can't even believe you just said that.  So, adding a TC reduces optical spacial resolution?  Better throw them all out then.

A TC doesn't change optical resolution.


Lee Jay -- are you really saying that the TC will not introduce diffraction artifacts due to the change in aperture, and that the additional glass elements will present or expose no further optical abberations in the image presented to the  sensor?


First one yes, second one no.

Diffraction (angular resolving power of the optical system) goes with aperture, not f-stop.  That's why telescopes are sold by aperture and not by focal length and f-stop (well, light gathering does as well and that's the second reason telescopes are sold that way).  The only reason f-stop was in the formula I posted was because that wasn't angular resolution of the optical system (which is what we're really after), it was spatial resolution at the sensor.

sin theta = 1.22 * lambda / D where D is the diameter of the lens' aperture.  A teleconverter doesn't change D and so it doesn't change theta.

http://en.wikipedia.org/wiki/Angular_resolution

I already said TCs are actually slightly worse than small pixels because of aberrations.  Fortunately, TCs are close to optically perfect these days so the degradation is quite small.  Regardless, this works in favor of my argument - a TC will give a good simulation of how a lens would perform on smaller pixels.  In fact, the smaller pixels will perform better so this TC test is a worst-case.


First, telescopes are marketed by their physical aperture dimensions because they only have a a fixed aperture. The aren't like a photography lens, where the aperture is adjustable. There is no need to market telescopes in any other way because any other way simply doesn't apply.

You are misunderstanding what a TC does. A teleconverter is a magnifying glass. It simply enlarges what the original lens projects. It magnifies everything....including diffraction. You cannot add a TC to a lens an not increase the effects of diffraction, despite the facts you just described above. Here is another formula, for the physical size of an airy disc:

Code: [Select]
D = 2.44 x λ x f#
Note the fact that the RELATIVE APERTURE, or FOCAL RATIO, is what matters here...not the size of the entrance pupil. The size of an airy disc is of intrinsic importance to diffraction's effects at the sensor. The size of an airy disc is dependent on F-Number, which means the addition of a TC most definitely has an impact on spatial resolution, since it will increase F-Number by the same factor as the TC used (f/4 * 1.4 = f/5.6; f/4 * 2 = f/8, f/5.6 * 1.4 = f/8, etc.)

BTW, my formula above...it comes from the same wiki page you linked. Just a little farther down below angular resolution is the description of spatial resolution:

Quote
A similar result holds for a small sensor imaging a subject at infinity: The angular resolution can be converted to a spatial resolution on the sensor by using f as the distance to the image sensor; this relates the spatial resolution of the image to the f-number, f/#:

Code: [Select]
dl = 1.220 * (f * λ) / D
   = 1.220 * λ * f#

Since this is the radius of the Airy disk, the resolution is better estimated by the diameter, 2.44λ * F#.
« Last Edit: October 23, 2012, 12:57:03 PM by jrista »
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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #74 on: October 23, 2012, 01:05:35 PM »
Jrista... I usually gloss over your techno rant...  :P But the last post (with the DLA MTF table) was well constructed and easy to follow for peeps like me.  Thanks!
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Re: Are there 39mp & 50mp+ Test Bodies in the Wild? [CR1]
« Reply #74 on: October 23, 2012, 01:05:35 PM »