andy_haugdahl

<p>Trying to imagine this "wideconverter" or compressor, I assume that in order for a "compressor" to work, the focal plane is shifted closer to the lens.<br>

To correct for the reduction in focal plane distance the converter optics need to first expand and change the angles the light paths before re-compressing it.<br>

With high speed lenses This expansion could exceed compressor dimensions and effectively crop out portions of the light stream prior to the compression stage.<br>

Within a given barrel diameter, I assume the trade-offs could be shifted towards IQ or bandwidth/speed?<br>

distortion pattern / complexity is introduced by various lenses all having different light angles prior to focus plane that leads to distortion with a one converter fits all setup?<br>

I apologize if my terminology is lacking, I'm no optical expert. Is that more or less how this would work?</p>

<p>As for JDM's comment: "WHY do you want to convert existing 35mm-sensor or film lenses so that they will retain the equivalent focal length on a "crop body"</p>

<p>You would think the answer to that would be rather clear by now...</p>

<p>JDM, why don't you go grab a computer monitor; say a 21" one, lets call this an "EF" monitor, well put a cardboard box midway between you and the screen as to reduce the viewable image from 20 inches down to 12.5 inches... Lets call this box a crop sensor...<br>

Which do you think would look better? Viewing a cropped portion of the screen (in this example 12.5 inches) or putting some glass in the open void of the "cardboard crop box" to bend the light in such a way that you can see the entire screen including any distortions the glass presents.<br>

With good glass, I'd like to think it would look better with the glass there wouldn't you!?</p>

<p>Joseph, Thank you for the wonderful explanation! In your experiences with such a converter, what was your overall opinion? Appears I have a lot of reading to do.</p>

<p>JMD, It's not something for nothing. Among other things, you lose resolution - however in the case of a crop sensor, the reduction needs to reach 0.625x before resolution is affected.</p>

<p>I don't really know enough about optics to offer any valuable opinions, only conjecture :)<br>

With a 0.625x in place, Would you at least be able to use this as a fast Macro? Wonder what the maximum focusing distance would become.<br>

With the .625x installed behind the lens, you have to wonder if a front "filter" element could be used to compensate? (seems to me this method may be specific to each lens and cost prohibitive however)</p>

<p>I completely agree Alan.<br>

The best answer I could find as to what the complication is was posted actually on this forum by Richard Oleson back in 2003.<br>

<a href="http://www.photo.net/filters-bags-tripods-accessories-forum/005vgV">http://www.photo.net/filters-bags-tripods-accessories-forum/005vgV</a></p>

<p>Wow, this is quite the old thread... One other benefit of compressing the light to a smaller sensor, is the speed... 0.625 would add more then 1 stop.<br>

0.5x would yield a full 2 stops. (of course even an ASP-C sensor is too large for this) but a slight crop in resolution for 2 stops may very well be worth it.<br>

Could Diffraction Optics or any other combination of lenses be used to achieve such a product?</p>

<p>OK, so this completely baffles me...<br>

They make teleconverters e.g. 1.4x / 2.0x etc.. to extend the reach of your Lens at the cost of speed.<br>

Why don't they make the opposite!?<br>

Focus your EF lens onto an EF-S Crop Sensor to gain speed and return a lens to it's range.<br>

e.g.<br>

28-135mm f/3.5-5.6 is exactly that on a Full frame<br>

and<br>

a 45-216mm f/3.5-5.6 on a an APS-C.<br>

--------<br>

add a 2.0x teleconverters and you get 56-270mm f/7-11 on that Full Frame<br>

and<br>

90-432mm f/3.5-5.6 on an APS-C<br>

--------<br>

Now if they made a 0.625x converter. That same EF lens would become 28-135mm ~f/2-4 on a crop sensor. How awesome would that be?<br>

Want more speed? focus it down even further at the cost of resolution.<br>

With a firmware update, the camera could even perform the crop automatically making lower resolution automatically go faster.<br>

--------<br>

Again why don't they!? Blows my mind... Wish I could manufacture this and make a mint.</p>

<p>I just placed my order for the 70-200 F4 IS. (I know you were comparing to the non IS)<br>

Like others have said, the image quality difference is huge! Look at the color fringe on the first posted (race car) photo, you can tell it was taken with the 70-300 without even asking.<br>

I found my cheap 28-135mm to offer higher IQ then the 70-300 I tried on my body.<br>

In any case, you might find this helpful:<br>

<a href="http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=404&Camera=9&Sample=0&FLIComp=4&APIComp=2&LensComp=358&CameraComp=9&SampleComp=0&FLI=4&API=2">http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=404&Camera=9&Sample=0&FLIComp=4&APIComp=2&LensComp=358&CameraComp=9&SampleComp=0&FLI=4&API=2</a></p>

While I don't fully understand the color space differences and their effects in printing completely either, let me at least offer a few cents on color space.

256x256x256 yields 16.7m different colors / shades.

Adobe RGB while having the same number (16.7m) of colors, the colors could be in a different gramut.

Example: Can your monitor display Florecent yellow? It can't? Well imagine the Adobe RGB as having that in its color-space. Your monitor cannot display it, but it's there if you had a device that WAS capable such as a printer.

I think that's how the colorspaces need to be inturpreted.

If you increased sRGB to more colors, its not increasing the graumet at all, but only the number of steps or shades within the same space.

e.g. mm v.s. inches on a 12" ruler. (you still have a foot to work with) mm would simply provide more percision within the "ruler space" :)

Hope that helps, and feel free to flame me if I'm completely off base here.