Prime Lens... Move away, focus closer... Move further... Zoooom! (?!)

[Khufu]

This is fun! I'm sure lots of you do (or don't) get the whole "lenses focus light" thing and are aware (or aren't) that if you hold a Canon* lens between a light bulb and a piece of paper you'll likely see an unfocused blob of light projected onto the paper, which with a bit of jiggling will turn into a projection of the lightbulb and its fittings... try this with the 400mm f/5.6L and you can get sharp projections of relatively close things with a foot or so between paper and lens - I was quite surprised to find that as you move the lens further from the paper and adjust the focus ring you can start to sharply focus a much larger projection and of closer subjects!
It's like this thing starts to become a closer focusing medium format lens!... oooor potentially a less-light, higher-magnification crop of a larger format image, or, er, a "teleconverted" set-up without the degradation of a moar-glass approach, right?!

Has anyone here played around with these kind of ideas much? It's a bit exciting but I'm getting way too sleepy to keep playing tonight... maybe.

My other thoughts, considering the actual (massive) distance between the sensor and back lens element of the 400mm f/5.6L prime is that this thing could probably be hacked down in length and have a focal reducer thrown inside and virtually turn an APS-C Canon camera into a 400mm FF equivalent mini-monster... with a bit of confidence and know how...

I've been playing with a wee 1.25" 0.5x focal reducer I grabbed off ebay - was thinking of engineering something for the EOS M... Could also get Medium Format lenses to play along with FF cameras, woo

Okay, time for bed - unless my next post says I came back soon...

*other brands are also available

 

[Tinky]

i think Canon rightly see EF / 135 as their holy grail and would rather adapt new camera systems to that than convert existing lens designs to different back focus registers such as EF-s and EF -m.

But I suppose there is some kind of precedent in the DO lenses which enable telephotos to be reduced in size somewhat... is it worth hacking a 400 5.6L to find out?

Also not keen on too many links, lens to fl reducer to ef-m mount?.. too many fine tolerances, too many e to e contacts for my tastes.

i just think canon want you to use big pixels with big lenses and that means bigger cameras.. the m is perfect with a pancake, anything else looks like an unwieldy chimera...

 

[BozillaNZ]

This is fun! I'm sure lots of you do (or don't) get the whole "lenses focus light" thing and are aware (or aren't) that if you hold a Canon* lens between a light bulb and a piece of paper you'll likely see an unfocused blob of light projected onto the paper, which with a bit of jiggling will turn into a projection of the lightbulb and its fittings... try this with the 400mm f/5.6L and you can get sharp projections of relatively close things with a foot or so between paper and lens - I was quite surprised to find that as you move the lens further from the paper and adjust the focus ring you can start to sharply focus a much larger projection and of closer subjects!

Even if you can get it to work at some degree, the peripheral of image circle will give pretty bad quality (aberrations, vignetting, etc), as the optical formula was not designed to deal with collecting wider angle of light .

 

[Khufu]

This is fun! I'm sure lots of you do (or don't) get the whole "lenses focus light" thing and are aware (or aren't) that if you hold a Canon* lens between a light bulb and a piece of paper you'll likely see an unfocused blob of light projected onto the paper, which with a bit of jiggling will turn into a projection of the lightbulb and its fittings... try this with the 400mm f/5.6L and you can get sharp projections of relatively close things with a foot or so between paper and lens - I was quite surprised to find that as you move the lens further from the paper and adjust the focus ring you can start to sharply focus a much larger projection and of closer subjects!

Even if you can get it to work at some degree, the peripheral of image circle will give pretty bad quality (aberrations, vignetting, etc), as the optical formula was not designed to deal with collecting wider angle of light .

That's... sort of the opposite of what I was trying to explain, heh!

The projected image gets physically larger, hence acting like a zoom if you were to collect the light projected on to a 24mm x 36mm selection at the centre of the projection - the entire image is enlarged, you'd be collecting much fewer photons but the image is optically "zoomed in" and very sharp, sort of like a variable aperture zoom

 

[BozillaNZ]

That's... sort of the opposite of what I was trying to explain, heh!

The projected image gets physically larger, hence acting like a zoom if you were to collect the light projected on to a 24mm x 36mm selection at the centre of the projection - the entire image is enlarged, you'd be collecting much fewer photons but the image is optically "zoomed in" and very sharp, sort of like a variable aperture zoom

Ok, then what's the different between your way vs say, extension tube? tele-converter? APS-c sensor? cropping in PP?

Either way you are cropping into the image circle, digitally or optically, which will inevitably reduce sharpness. If optically cropping does not reduce sharpness when a 2x TC won't give you any worse image quality compared to no TC, which is not true. You can't divide resolution without facing softness.

 

[Khufu]

That's... sort of the opposite of what I was trying to explain, heh!

The projected image gets physically larger, hence acting like a zoom if you were to collect the light projected on to a 24mm x 36mm selection at the centre of the projection - the entire image is enlarged, you'd be collecting much fewer photons but the image is optically "zoomed in" and very sharp, sort of like a variable aperture zoom

Ok, then what's the different between your way vs say, extension tube? tele-converter? APS-c sensor? cropping in PP?

1. No difference. It's going to be a looong tube...
2. Less glass, less manipulation.
3. Most of us who've compared FF and APS-C in the real world seem to agree that APS-C doesn't resolve so well with their <40% sized photosensors and shifted variables to compensate, ie. gain (pseudo-"ISO"), general physics...
4. the cropped image is then what has been captured by many times fewer pixels.

Either way you are cropping into the image circle, digitally or optically, which will inevitably reduce sharpness.

inevitably... if one chooses to keep zooming beyond the resolving capabilities of a lens, however I'm unsure at present of what those parameters are and I'm not convinced that this lens's pivotal point before declining in quality is precisely that of having it's light distributed across a 5D3's sensor - but that would be a mighty fine coincidence!

If optically cropping does not reduce sharpness when a 2x TC won't give you any worse image quality compared to no TC, which is not true.

I've gone over and over this trying to get it to read right but it's just occured to me that maybe "when" = "then" - sorry, I really have been struggling with this, is that what you meant?!

Well, I'm still not convinced that adding more glass is equal to having an image projected wider, with less glass - but your mind seems made up.

You can't divide resolution without facing softness.

oh, you absolutely can! Up to around 1000x before glass becomes impassable by visible light:

d = (λ/2) x And = (λ/2) x An

I can't imagine we've all been hallucinating what we see as that light at the end of the tunnel of microscopes all these years

 

[Khufu]

i think Canon rightly see EF / 135 as their holy grail and would rather adapt new camera systems to that than convert existing lens designs to different back focus registers such as EF-s and EF -m.

But I suppose there is some kind of precedent in the DO lenses which enable telephotos to be reduced in size somewhat... is it worth hacking a 400 5.6L to find out?

Also not keen on too many links, lens to fl reducer to ef-m mount?.. too many fine tolerances, too many e to e contacts for my tastes.

i just think canon want you to use big pixels with big lenses and that means bigger cameras.. the m is perfect with a pancake, anything else looks like an unwieldy chimera...

Heh, sorry, I wasn't actually thinking about the 400mm lens still by the point I got onto the focal reducer/EOS M idea (I was tired and following tangents) - but was just thinking in terms of how people have focal reducers to use FF lenses on Sony NEX models and other brands, but never anything for EOS M!

Also, this little focal reducer I've been playing with actually fits inside the 400mm lens with a few mm around it - I'm curious how this might work as a bit of an in-lens speed booster/focal reducer on, say, an SL1, or even a 7D II or ather APS-C camera... the connections are still all there! The image would need cropping though, 0.5x is quite a boost/reduction! (and beyond the lens design's parameters)


This is all just hypothetical btw, guys - I'm in no hurry to hack an inch off the body of my lens but it does seem like a workable idea to "speed boost" for aps-c... just thinking out loud and invite other curious minds to, and educated minds to set us straight and fill in the gaps, too