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Author Topic: Telephoto "reach"  (Read 10452 times)
Ray
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« Reply #40 on: September 07, 2005, 08:05:15 AM »
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I repeat: a 200mm lens in DX format and a 300mm lens in 35mm format each take an image of about 40º angular field of view and record a portion of it with about 8º field of view, which measn that they use abot the same fractio of the image. Please explain how one format is cropping more than another.

Well, I'll answer this with a few other points from your previous posts.

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That leaves only your example of the 400/2.8: but Canon and Nikon do both have 400/2.8 lenses that are perfectly usable with EF-S and DX bodies! Surely you know that at such long focal lengths, nothing is gained by designing for a smaller than 35mm format image circle?

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Let me reapt anothe pont that yopu have ignored: longer telephoto focal lengths are almost always achieved essentialy but putting a teleconverter into a lens of shorter focal length, so that the resolution in lp/mm decreases in proportion to the increase in focal length, giving about the same resolution in lp per picture height. (Your low opinion of the effects of teleconverters on resolution has been noted already in these forums.)

My view has been for a long time that whatever the focal length, if a smaller image circle is the design criterion, then a higher resolution is possible. A 300mm lens designed for the 35mm format can produce significantly higher resolution (in terms of lp/mm) than a standard 300mm lens for an 8x10" field camera.

I don't understand precisely how this is possible, except in very layman's type jargon, ie. robbing the quality of the outer edges to provide greater resolution in the centre of the lens. According to basic principles, a 300mm lens throws an image circle 300mm in diameter. But modern lens design has changed that result considerably.

I've checked the Photodo results for the Canon 400/2.8 and 600/4 and it's clear the 400/2.8 has a higher MTF, is a better lens; but only marginally. At f8 we have a rating of 84 for the 400/2.8 and 82 for 600/4. This is the sort of difference between the Canon 50/1.8 and 50/1.4, but I have no doubt that a 600/4 on a 1Ds2 would deliver higher resolution than a 400/2.8 on a Nikon D2X.

Now, if you have some insights into lens design that can shatter some accepted fallacies, then I'm all ears. Please explain them clearly without hand waving, ambiguity and smokescreens  Cheesy .
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BJL
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« Reply #41 on: September 09, 2005, 04:10:55 PM »
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How many times have you read posts on this forum and others about the indecision of committing to the purchase of an EF-S lens which will be no use with FF 35mm?
Many times, in this forum and others. Meanwhile, Canon's EF-S mount cameras and EF-S lenses are selling very well.  What this tells me (yet again) is that the pattern of opinions and preferences expressed in internet forums is a very, very poor predictor of actual market trends.
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AJSJones
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« Reply #42 on: August 22, 2005, 07:05:47 PM »
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Thanks T

Very nice sentiment - and I, and others, do indeed enjoy my pictures, so I'm not anxious.

One thing you can't get from something written is the intonation of  a phrase such as  "ya, right"   Cheesy
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jdemott
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« Reply #43 on: August 23, 2005, 06:32:01 PM »
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Why? are there more megapixels at the edges or something?
A brief example (using round numbers for simplicity) may make it clear.  Image a full frame sensor with dimensions of 4500 by 3000 pixels, or 13.5 MP.  If you want to compare that camera to a camera that has a 1.5x multiplication factor, then you have to crop the field of view to 2/3 of its original dimensions, i.e., you crop both horizontally and vertically.  That would yield dimensions of 3000 by 2000 pixels or 6MP, the same result you would get if you divide 13.5 by the product of 1.5 times 1.5.  Put another way, if you have a 500mm lens and a 6MP camera with a 1.5 multiplication factor, then you would have to buy a full frame camera with at least 13.5 MP in order to provide an equivalent level of detail with the same lens.
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John DeMott
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« Reply #44 on: August 23, 2005, 07:18:58 PM »
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None of this math makes sense to me either. While you might be using a smaller area of the lens, depending on the size of the sensor being used, the image is still focussed on the entire surface area of the sensor providing you with all of the megapixels available. The image is not cropped in the same way that you crop an image in an image editor by literally throwing away pixels.

T
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lester_wareham
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« Reply #45 on: August 24, 2005, 09:39:31 AM »
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While 12.8 Mpx divided by 1.6 is 8 Mpx, that's not how it works.

If you use the crop factor correctly, you should divide by 1.6*1.6, or 2.56.

That yields 5 Mpx.
Exactly. A good reason for 20D owners to wait for the next version of the 5D, presumably 16-18Mp, presumably in 2007.
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Lin Evans
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« Reply #46 on: August 26, 2005, 12:30:11 AM »
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It's simpler to understand if you think of it this way:

A 1.6x crop factor means that you have approximately a 60 reduction in frame content. Since sampling sites (pixels) are distributed evenly, this means if you take a full frame sensor image and crop it to the dimensions of a 1.6x "crop factor" sensor you throw away 60 percent of the image, i.e., 60 percent of the pixels. That leaves 40 percent of the original pixels.

So whatever the original pixel count in megapixels is reduced by 60 percent which is the same as multiplying by .4.

11 megapixel 1DS cropped 60 percent = 11x.4= 4.4 megapixels
12 megapixel  5D cropped 60 percent = 12x.4= 4.8 megapixels
15.7 megapixel 1DS Mark II cropped 60 percent = 6.68 mp, etc.

The figures are not exact so substitute the actual effective megapixel rating and multiply by .4

For a 1.5x crop multiply by .5
For a 1.7x crop multiply by .3

Makes it a lot easier to quickly calculate...

Lin
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Lin
AJSJones
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« Reply #47 on: August 26, 2005, 11:08:08 AM »
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I'm still confused about the original subject.  

Isn't the extra "reach" on a 1.5x sensor one of their biggest advantages (in certain situations)?
Ya, right!!          
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duranash
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« Reply #48 on: August 31, 2005, 09:57:37 AM »
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Hummm - how do I delete a post?
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Ray
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« Reply #49 on: September 02, 2005, 11:53:15 AM »
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- larger chips/sensors waste more of a silicon wafer
 - larger chips/sensors have a higher probability of defects

I see this as an explanation for the price difference between the larger and smaller sensor, not a flaw in my argument. I've never suggested that the larger format would be the same price as the smaller format, everything else being equal, such as waterproofing, high frame rate, f8 focussing etc. That would not likely happen until the Chinese enter the market.

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Whether the price differential will become substantially lower is mostly guesswork.

Maybe I've confused the issue by using the term 'price differential'. The price differential can remain the same for all I care. Just lower the price  Cheesy .
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BJL
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« Reply #50 on: September 02, 2005, 01:22:46 PM »
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Those who are not photography enthusiasts are amply served with a plethora of P&S digicams. Those who are photography enthusiasts will gravitate towards the camera that produces the higher image quality. It's really quite simple.
I wil take your response one fallacy at a time.

Here you are using a false dichotomy, pretending that there is no middle ground of photographers between P&S digicam users and those who are willing to pay thousands of dollars for DSLR bodies and thousands of dollars more for the heavier lenses needed to get the much hope for high shutter speed advantage. The obvious reality is instead that this middle ground is now the most profitable sector of the digital camera market, serving the many photography enthusiasts who want a DLSR with interchangable lenses, greater speed that small digicam sensors can provide, and so on, and are looking for bodies at under $1000, or at most about $1,500 and use lenses not costing thousands of dollars, and so are far away from the 35mm format DLSR market sector.
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BJL
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« Reply #51 on: September 02, 2005, 02:10:41 PM »
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Is 12 mpxl's (give or take) enough?? Most will say so.

Volume production of FF chips will help to reduce the cost/price of the 1DsII and likely make it more competitive with the D2x so I can forsee price reductions/rebates of the 1DsII or more likely a 1DsIII as this is more canon's style.
I heartily agree that somewhere around 12MP (or even less) is the end of the MP race for the great majority of SLR users.

I also agree that the cost/price reductions seen with the 5D could at some stage flow through to the 1D/1Ds line. Not yet, because the 5D has to use a different, lower res., lower read-out speed sensor, but once the cost of higher read-out speeds comes down ("DIGIC III"?), Canon could perhaps use the same high resolution, high speed 35mm format sensor in a range of bodies, from "enthusiastic amateur" to top of the line "medium format eater", getting sensor costs down to about 5D levels.

Then maybe we will see a 1Ds model for under $5,000. The same technological progress would probably also lead to a 12MP plus "enthusiastic amateur" DX body for under $2,000. I wonder how close the much rumored D200 will come to this?
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Ray
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« Reply #52 on: September 04, 2005, 12:58:41 AM »
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of course sensor prices will come down a bit more, but what I seriously doubt is the dream of price reductions comparable to what is generally seen in electronics, because, as has been said many times, they depend to a large extent on reducing the size of electronic components: that size reduction is most of what drives "Moore's law", and is of course irrelevant when chip size is fixed at 24x36mm.

BJL,
This is not a good reason for the price of FF 35mm to remain high, but rather an aplogy for the insanely high prices. At best it's an explanation for prices not dropping as dramatically and quickly as other electronic components.

The sensor is a major component in a camera, but not the only component, and the fact that the 5D with its 24x36mm sensor will have a retail price somewhat lower than that of the Dx2 which has a sensor less than half the area, is testament to this fact.

There's an anlogy here with regard to CRT monitor prices. 11 years ago when I bought my first computer, I really wanted a 20" Sony monitor with a maximum resolution of 1280x1024 at 70Hz, but couldn't justify paying the A$3500 asking price. In terms of current dollars, allowing for inflation over the 11 year period, that's around $4500.

I find I can now buy a 20" monitor with a resolution of 2048x1536 at 70Hz for A$700 and a top of the range LaCie 22" with a res of 2048x1536 at 85Hz for around A$1600.

Now this is not as spectacular a drop in price that we are used to seeing with regard to hard drive capacity, RAM and processor speed, but nevertheless a very substantial price drop despite the obvious fact that a 20" CRT monitor cannot be miniaturised whilst still remaining a 20".
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Ray
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« Reply #53 on: August 26, 2005, 06:22:09 AM »
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BUT the pixel size on both sensors are not the same
We don't know the pixels size. That information is not generally released by the camera manufacturer. The figure we get is the pixel pitch, the distance between the centre of one pixel and the centre of the adjacent pixel. For example, I believe the size of the D30 pixel is around 5.25 microns, but the pixel pitch is (from memory) something like 9 microns. This figure of 9 microns is loosley bandied around as being the pixel size, which is incorrect.
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Ray
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« Reply #54 on: August 26, 2005, 08:43:59 PM »
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Apart from the obvious advantages of weight and cost, there are two clear advantages to the cropped format that affect image quality. (1) A usually greater pixel density which is able to resolve more detail provided the lens is capable of delivering it, (2) A usually superior edge performance to the image.

These advantages should be weighed against the advantages of the larger format, namely a usually greater number of pixels in total on the larger sensor.

The smaller format provides greater detail per square millimetre, or more line pairs per mm, whereas the larger format provides more detail and resolution per picture.

Can't make it any clearer than that  Cheesy .
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Ray
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« Reply #55 on: September 04, 2005, 03:26:13 AM »
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how do you conclude that the 5.4 microns pixel pitch of the D2X is anywhere close to the limit?

Just hearsay, BJL  Cheesy .

Wasn't this the 'raison d'etre' for the creation of the 4/3rds format; ie. 35mm lenses cannot resolve smaller than 5 microns.
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BJL
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« Reply #56 on: September 06, 2005, 08:04:42 PM »
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how do you conclude that the 5.4 microns pixel pitch of the D2X is anywhere close to the limit?

Just hearsay, BJL   .

Wasn't this the 'raison d'etre' for the creation of the 4/3rds format; ie. 35mm lenses cannot resolve smaller than 5 microns.
Firstly, why would DX format be limited by the resolution of 35m format lenses? It already uses new DX format lenses for the wider angles where resolution is most problematic, and Nikon is of course free to introduce as many new DX format lenses as are needed to keep up with future higher resolution sensors. Nikon has indicated a 2 micron resolution goal for DX lenses.

Secondly, the main reason for creation of both Four Thirds and DX format seem to be the cost and size advantages of smaller formats and shortrr focal lengths; the same ones that enabled 35mm film format to drive medium format out of the mainstream, and even out of the professional mainstream. A possible secondary reason is that digital sensors with microlenses work better with a ratio of back-focus distance to sensor size far greater than is the case for 35mm SLR formats. Nikon achieves that by keeping the same back-focus distance and reducing sensor size; Four Thirds reduces both dimensions, but the sensor size more than the back-focus distance.
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Ray
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« Reply #57 on: September 11, 2005, 11:23:52 AM »
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More and more people are buying dSLRs like the Rebel and d70, for them they get quality better than film with smaller, lighter lenses for cheap.  I have a feeling Canon sells a lot more Rebels than any of their pro/high end equipment.

For average joe, "cropped" sensors are nothing but advantage.
The squeeze is already happening. When the first of the 8MP P&S cameras appeared, such as the Sony F828 and Minolta A2, a lot of camera buyers who did not already own a stack of Canon or Nikon lenses but wanted the quality that a 6MP DSLR could deliver, opted to buy an 8MP P&S as a cheaper and more convenient alternative. A lot of those potential buyers were rather concerned about the noise and birefringence (purple edges). The resolution might have been equal to that of a 6MP DSLR, but noise was clearly greater and therefore no possibility of a high ISO option with such small sensor cameras.

There were good reasons for anyone concerned about image quality to reject these (relatively) noisy, small sensor cameras.

Those reasons are disappearing with the introduction of the 10MP Sony DSC-R1 which boasts a sensor size virtually as large as that of the 20D and a Carl Zeiss 15-75mm zoom with F2.8 maximum aperture. How does that compare with my Sigma 15-30/F3.5 zoom that costs more than half the price of the DSC-R1 including lens?

It wouldn't surprise me if this new Sony can produce sharper images than the 20D with nearest equivalent Canon zoom lens, and images with equally low noise at equivalent ISO settings.
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LesGirrior
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« Reply #58 on: September 07, 2005, 12:33:32 PM »
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My view has been for a long time that whatever the focal length, if a smaller image circle is the design criterion, then a higher resolution is possible.

I have no doubt that a 600/4 on a 1Ds2 would deliver higher resolution than a 400/2.8 on a Nikon D2X.
This has got to be a typo or something, if I have misquoted you I apologize.
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BryanHansel
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« Reply #59 on: September 09, 2005, 06:37:20 PM »
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After reading this thread, which is interesting, I find that although it has addressed both sides of the issue well, it has as BLJ said ignored market trends.  I wonder if two cameras were put on the market and the only difference between them being FF vs. DX.  Everything else, features and price were the same, which would sell better?

If the image quality up to 400 ISO was the same, I'd go for the DX over the FF everytime.  And if I could find a point and shoot with comparable quality in image to this hypothetical camera, I'd probably buy that too. To me the 12-24 DX delivers almost everything I need at the wide end and the extra reach at the long end seems to work for me.

So, my answer to the "Ya, right" is "Ya, all right."
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