RF 100-500mm with RF Extender 2x

[JKT]

Any chance of getting those formulas? I'd love to compare them to mine. Yours seem to be a bit more aggressive than mine.

Here are some values with mine. These are approximations of what happens when TC:s are added to a base lens while keeping aperture value the same.
Obviously resolution increase at target means smaller resolution value ie. more details. Perfect values for the 1.4x would be "140 / 100" and for 2x "200 / 100" .



Admittedly my calculations were originally meant for super macro, so some parts are a bit complicated for this and others can be too simplified.

 

[AlanF]

Any chance of getting those formulas? I'd love to compare them to mine. Yours seem to be a bit more aggressive than mine.

Here are some values with mine. These are approximations of what happens when TC:s are added to a base lens while keeping aperture value the same.
Obviously resolution increase at target means smaller resolution value ie. more details. Perfect values for the 1.4x would be "140 / 100" and for 2x "200 / 100" .

View attachment 215534

Admittedly my calculations were originally meant for super macro, so some parts are a bit complicated for this and others can be too simplified.

Thanks for these very interesting data. They bear out nicely the higher the resolution of the sensor and the narrower the lens the less effective an extender. As you have the raw numbers, could you post the table with all the resolutions normalised to the R6 base of the 100-500mm of 100/100 at the top Left. (ie RF 100-500mm on the R7 would be approx 200/200).

 

[AlanF]

Any chance of getting those formulas? I'd love to compare them to mine. Yours seem to be a bit more aggressive than mine.

Here are some values with mine. These are approximations of what happens when TC:s are added to a base lens while keeping aperture value the same.
Obviously resolution increase at target means smaller resolution value ie. more details. Perfect values for the 1.4x would be "140 / 100" and for 2x "200 / 100" .

View attachment 215534

Admittedly my calculations were originally meant for super macro, so some parts are a bit complicated for this and others can be too simplified.

Also, how do you find the 200-800 @ 800mm vs 100-500mm + 1.4xTC @ 700mm on the R5? And, if you have the time, the 200-800 @ 500mm vs 100-500mm @ 500mm? Thanks.

 

[JKT]

In order to give those numbers some things need to be decided first. Between different focal lengths should I keep the fov same or the distance? In low magnification it is not that important, but changes the numbers a bit anyway. The previous table was described as it was just to avoid this.

Those mid-focal lengths introduce the problem of aperture. I guess I could look it up from photons to photos, if they have the 200-800. I used the nominal values for the two lenses previously.

 

[JKT]

Oh well - let's assume the same framing in all cases, so the distance varies as necessary. Done that way the R7 numbers are not what one would expect. That just goes to prove that it has advantage only if you can't get close enough.

There's just one value as done this way the two values were the same. The odd values for the TC:s are the values they give in measurement and the f/7.8 for 200-800 @500 is a ballpark approximation. 490mm and f/7.2 are from Photons to photos.

Please do remember that the formulas are approximations and that it is assumed that the lenses are diffraction limited.

 

[AlanF]

Oh well - let's assume the same framing in all cases, so the distance varies as necessary. Done that way the R7 numbers are not what one would expect. That just goes to prove that it has advantage only if you can't get close enough.
View attachment 215557
There's just one value as done this way the two values were the same. The odd values for the TC:s are the values they give in measurement and the f/7.8 for 200-800 @500 is a ballpark approximation. 490mm and f/7.2 are from Photons to photos.

Please do remember that the formulas are approximations and that it is assumed that the lenses are diffraction limited.

Thank you so much again - much appreciated. Am I right in thinking the data for the TCs have have been corrected for diffraction? If so, how did you do this?

 

[JKT]

It changes the effective aperture. The resulting value is not shown in the table.

 

[AlanF]

It changes the effective aperture. The resulting value is not shown in the table.

What I don't understand, then, is that when you add the 1.4xTC to the 100-500mm, you decrease the value for the R6 from 100 to 97 and the R5 from 143 to 132 while maintaining the same framing. This seems too small a change. Looking at the Canon MTF graphs, the MTF 30 lp/mm value drops from about 0.83 to 0.75.

 

[JKT]

As I mentioned it is an approximate formula and doesn't know anything about deficiencies in the respective lenses. It considers just diffraction on otherwise perfect lenses. If part of the drop in the graphs is due to something else. For the same reason the results for 200-800 may be overly optimistic - it is good, but not L.

In super macro (up to 50x or so), the diffraction is usually so dominant in resolution, that the other effects are minor if the lens is any good to begin with - or alternatively one can find the best aperture and use that in the calculations.

 

[AlanF]

As I mentioned it is an approximate formula and doesn't know anything about deficiencies in the respective lenses. It considers just diffraction on otherwise perfect lenses. If part of the drop in the graphs is due to something else. For the same reason the results for 200-800 may be overly optimistic - it is good, but not L.

In super macro (up to 50x or so), the diffraction is usually so dominant in resolution, that the other effects are minor if the lens is any good to begin with - or alternatively one can find the best aperture and use that in the calculations.

What is the formula?

 

[JKT]

The "Formula" has a few main parts. First is the calculation of the aperture values on the object side. Then there is the resolution calculation on that side. After that those are transformed to image side and finally the optical resolution is combined with the sensor resolution to get an approximation. This combination is the most approximate part. The accurate calculation for that is anything but smooth and beyond me. Finally that result is transformed to object side. Well that is the basic process. Some things can be done either on image or object side and I'm not sure, which side I used for which in the Excel. I could post that, but it needs some cleaning first and it may take more than a little time to decipher.

 

[AlanF]

The "Formula" has a few main parts. First is the calculation of the aperture values on the object side. Then there is the resolution calculation on that side. After that those are transformed to image side and finally the optical resolution is combined with the sensor resolution to get an approximation. This combination is the most approximate part. The accurate calculation for that is anything but smooth and beyond me. Finally that result is transformed to object side. Well that is the basic process. Some things can be done either on image or object side and I'm not sure, which side I used for which in the Excel. I could post that, but it needs some cleaning first and it may take more than a little time to decipher.

What is the principle for the combination of diffraction Airy disk and sensel size?

 

[JKT]

That is an approximation I picked up from ... somewhere.

that is with rr being short for "resolution ratio", which means objective resolution on sensor side divided by the pixel spacing. Variable "hp" is number of pixels horizontally. What is the best exponent is somewhat open as is whether it needs some correction constant instead of current "1" as divisor. That would handle Bayer effect and angled lines.