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1 minute ago, noone said:

Not sure I get that.

F stop is a ratio and a constant aperture zoom has a constant ratio (IE 2.8 at 24 and 2. at 60 for your Sigma).   

The physical size of the lens will be determined by the largest focal length if it is constant aperture.

I think what @Enjay is saying is that when you design a zoom it's maximum aperture will always be larger on the wide end, so in order to make a constant aperture zoom they just design it so that it closes down at the wide end to match the maximum aperture of the long end.

In this sense, if you had a variable aperture zoom, say an 18-55mm f3.5-5.6, then you could just set it to f5.6 and then zoom in and out and you'd have the benefits of a constant aperture, as well as being able to open up wider than f5.6 in the middle and at the wider end.

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Got myself some new glass for Christmas. I do prefer native lenses but the Sigma Speedbooster combo works really well! Screengrabs from GH5 + Speedbooxter XL + Sigma 35/1.4 + Black Pro Mist 1/4. 

Just got a Voigtlander 40mm 1.2. Haven't had a chance to test in video yet. But DAMN

A few stills from a shoot last night all on the Pocket 4K XL and CZ 35mm 2.8. 

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6 minutes ago, kye said:

I think what @Enjay is saying is that when you design a zoom it's maximum aperture will always be larger on the wide end, so in order to make a constant aperture zoom they just design it so that it closes down at the wide end to match the maximum aperture of the long end.

In this sense, if you had a variable aperture zoom, say an 18-55mm f3.5-5.6, then you could just set it to f5.6 and then zoom in and out and you'd have the benefits of a constant aperture, as well as being able to open up wider than f5.6 in the middle and at the wider end.

Maybe but it still does not make sense how he put it.

I used to use my Sony 28-70 FE kit lens AS a constant aperture 5.6 lens but I do not think it was less bright at 28mm than 70mm (when both at 5.6) and likewise, i do not think either of my two 2.8 zooms (Canon 20-35 2.8L and Tokina 60-120 2.8) are less bright at the long end.     The size of the hole internally changes but so does the focal length and the hole is smaller at 60mm than 120mm for instance with my 60-120 and they have the same ratio.

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6 minutes ago, noone said:

Maybe but it still does not make sense how he put it.

I used to use my Sony 28-70 FE kit lens AS a constant aperture 5.6 lens but I do not think it was less bright at 28mm than 70mm (when both at 5.6) and likewise, i do not think either of my two 2.8 zooms (Canon 20-35 2.8L and Tokina 60-120 2.8) are less bright at the long end.     The size of the hole internally changes but so does the focal length and the hole is smaller at 60mm than 120mm for instance with my 60-120 and they have the same ratio.

Aperture is literally the ratio of the diameter of the hole to the focal length.

At a constant aperture it should approximate a constant exposure.  I say "approximate" because exposure takes into account other things like the transparency of the glass and internal reflections etc, but it should be pretty darn close to exact.

I suggest you do a test - put the camera into full manual, find a large blank surface, and zoom in and out at constant aperture as well as at maximum aperture and see if the brightness of that surface changes.

You should see an increase in exposure (of that reference surface) when you open the aperture when zooming out.

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2 minutes ago, kye said:

Aperture is literally the ratio of the diameter of the hole to the focal length.

At a constant aperture it should approximate a constant exposure.  I say "approximate" because exposure takes into account other things like the transparency of the glass and internal reflections etc, but it should be pretty darn close to exact.

I suggest you do a test - put the camera into full manual, find a large blank surface, and zoom in and out at constant aperture as well as at maximum aperture and see if the brightness of that surface changes.

You should see an increase in exposure (of that reference surface) when you open the aperture when zooming out.

Put it this way.     If you look through a 2.8 zoom from the camera end (using my 60-120 2.8 for example) at both 60mm and 120mm, there will not be a difference but if you look through it from the front, at 120mm  the hole will be twice the size it is at 60mm. 

I agree it should be close to constant (and my experience is that it is) but that is not what he said.

 

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I just shot my bedroom blinds (vertical blinds) with my 60-120 2.8 at both 60mm and 120 both at 2.8 and both at 1/100.

I used auto ISO and both shots are at ISO 500.

There is a very slight difference in the histograms (same pattern but slightly higher peaks) but that is because at 120mm the thin gaps in the blind are a bit different at the different focal lengths....There is NO difference in brightness.

This is exactly as I expected.

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13 minutes ago, noone said:

I just shot my bedroom blinds (vertical blinds) with my 60-120 2.8 at both 60mm and 120 both at 2.8 and both at 1/100.

I used auto ISO and both shots are at ISO 500.

There is a very slight difference in the histograms (same pattern but slightly higher peaks) but that is because at 120mm the thin gaps in the blind are a bit different at the different focal lengths....There is NO difference in brightness.

This is exactly as I expected.

I think we're getting our wires crossed here.

Your above test is what I would expect.

If you have an 18-55mm f2.8-4 zoom then you would expect for it to be brighter at f2.8 than at f4.  If the manufacturer decides to offer a constant aperture 18-44 zoom then it might take that design and just make it 18-55/4, which it can do by taking the 2.8-4 design and changing it so that the 2.8 isn't available at the wide end.  ie, crippling the lens.

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7 minutes ago, kye said:

I think we're getting our wires crossed here.

Your above test is what I would expect.

If you have an 18-55mm f2.8-4 zoom then you would expect for it to be brighter at f2.8 than at f4.  If the manufacturer decides to offer a constant aperture 18-44 zoom then it might take that design and just make it 18-55/4, which it can do by taking the 2.8-4 design and changing it so that the 2.8 isn't available at the wide end.  ie, crippling the lens.

Indeed but he was saying a constant aperture zoom is crippled and brighter at one end than the other by  about a stop and that is wrong (and his examples are a constant f4 zoom and a constant 2.8 zoom)     Any variable aperture zoom is of course going to be different and the long end is going to be dimmer regardless of if it was made that way from scratch or using another lens as its base.

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4 hours ago, noone said:

Indeed but he was saying a constant aperture zoom is crippled and brighter at one end than the other by  about a stop and that is wrong (and his examples are a constant f4 zoom and a constant 2.8 zoom)     Any variable aperture zoom is of course going to be different and the long end is going to be dimmer regardless of if it was made that way from scratch or using another lens as its base.

Yeah, that wouldn't make sense.

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Media Division released another video, I bet many of you already watched it. This time they are examining the Canon FDs and their similarity to the legendary Canon K35s. It's one hour and 24 minutes long, and holds the same quality as their video on the C/Y Carl Zeiss video. 

By the way, there's a segment on removing yellow tint on thorium coated lenses with a cheap Ikea lamp @ 1h15m. I thought you might be interested @mercer

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5 hours ago, meudig said:

Media Division released another video, I bet many of you already watched it. This time they are examining the Canon FDs and their similarity to the legendary Canon K35s. It's one hour and 24 minutes long, and holds the same quality as their video on the C/Y Carl Zeiss video. 

By the way, there's a segment on removing yellow tint on thorium coated lenses with a cheap Ikea lamp @ 1h15m. I thought you might be interested @mercer

That was great!

I do wish they had done an FD aspherical VS FD L comparison though since the FDLs are going to be the ones more people use since the Aspericals are much much rarer and a lot of the few there are are in collectors display cabinets.

I always thought the FD Ls had hand ground aspheric elements too but it seems only the earlier asphericals do.

If buying the FD Ls ALWAYS ask or check the focus as they can have dissolving bearings (like my 85 1.2 L) where focus gets very loose.

They did make one tiny error when they said all FDs are manual as Canon did make a few AF FDs towards the end (I have an AF 50 FD).

Posting while gently stroking my 24 1.4 FD L!

 

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14 hours ago, noone said:

Indeed but he was saying a constant aperture zoom is crippled and brighter at one end than the other by  about a stop and that is wrong

The brightness is equal, but only because there is a special aperture that closes down at the short end because otherwise the physical aperture size does not change while the focal length varies. With a 4x zoom, the same physical aperture is (relatively) 4x wider at the short end than the long end.

Some of this is for technical reasons. A 4x zoom with let's say 1.4-5.6 would be very soft at the short end, and I'm not sure modern zoom designs have the same effective aperture at all focal lengths (the "aperture image" is magnified depending on the focal length). But the f-number definitely does not stay constant unless the manufacturer artifically creates this effect. It's marketing because people associate high-end lenses with constant f-number. Decades ago, when cameras could not easily compensate for changing f-number, pros really did need the constant aperture value, which I guess is the source of all this.

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24 minutes ago, Enjay said:

The brightness is equal, but only because there is a special aperture that closes down at the short end because otherwise the physical aperture size does not change while the focal length varies. With a 4x zoom, the same physical aperture is (relatively) 4x wider at the short end than the long end.

Some of this is for technical reasons. A 4x zoom with let's say 1.4-5.6 would be very soft at the short end, and I'm not sure modern zoom designs have the same effective aperture at all focal lengths (the "aperture image" is magnified depending on the focal length). But the f-number definitely does not stay constant unless the manufacturer artifically creates this effect. It's marketing because people associate high-end lenses with constant f-number. Decades ago, when cameras could not easily compensate for changing f-number, pros really did need the constant aperture value, which I guess is the source of all this.

Huh?    If the physical size of the aperture does not change with focal length it can not be a constant aperture lens (that is why I said maybe it should be called a constant f stop lens instead).     Aperture is NOT the fixed size of the rear end of the lens and the thing that remains constant is the ratio and that is why there is not change in brightness.

My 300mm 2.8 lens is a hell of a lot bigger than my 60-120 2.8 lens but if I somehow merged them into a 60-300 2.8 zoom it would be more or less the same size as my 300mm in the size of the hole from the front but the lens would be no different in brightness at 60mm to my existing lens.

Just do what Kye suggested and shoot you either of your lenses at each end against a target.

 

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Wow am I out of touch!

Just looked up some FD lenses on Ebay (worldwide available to Australia).

There are plenty of FD 85 1.2 L lenses though the prices are mostly still fairly high though maybe about what i would expect.

When it comes to the 24mm lenses though, the FD 24 1.4 asphericals are all (five of them) over $6000 Australian (I know our dollar is a bit in the toilet but that is ridiculous!).      The FD 24 1.4 Ls are all over $3000 (but only three of them) and even an f2 non aspherical is over $1000 Australian though most are a bit lower. 

There is a mint set of EF converted lenses for over 30 grand.

I would have thought that now that there are many more different 24 1.4 lenses available the prices would havecome down a lot rather than gone up.

Makes me glad i got no bidders when i put my 24 1.4 L on Ebay a couple of years ago with a starting bid of around $400 Australian and would have taken not much more (it looks a bit ratty externally but the glass is fine).

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1 hour ago, noone said:

I do wish they had done an FD aspherical VS FD L comparison though since the FDLs are going to be the ones more people use since the Aspericals are much much rarer and a lot of the few there are are in collectors display cabinets.

Yes! I was interested in this same thing as well.

28 minutes ago, noone said:

Just looked up some FD lenses on Ebay (worldwide available to Australia).

There are plenty of FD 85 1.2 L lenses though the prices are mostly still fairly high though maybe about what i would expect.

I've recently started looking at the FDs again after not owning any for a few years, and I am surprised by the price. Seems like even the FDn 50 f/1.4 or the wider f/2.8 lenses are more expensive now than when I bought and sold them. Weird!

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I was excited for the Media Devision video and watched it in full the other day. A few months ago I finally put together a new FD lens set that I converted to EF mount and de-clicked: 20mm 2.8, 24mm 2.8, 35mm 2, 50mm 1.4, and 85mm 1.8. I also have the 35-105mm 3.5 and 80-200mm 4 zooms but I haven't converted them. And I have a really shitty copy of the 24mm 2 that maybe I'll get repaired if it's not crazy expensive. The nFD lenses have been my favorite lenses for a long time, so I'm satisfied with the little kit I have, even if it is the "budget" option vs "Luxury" option. They're still sharp yet subtle and pretty. 

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5 hours ago, Enjay said:

The brightness is equal, but only because there is a special aperture that closes down at the short end because otherwise the physical aperture size does not change while the focal length varies. With a 4x zoom, the same physical aperture is (relatively) 4x wider at the short end than the long end.

Some of this is for technical reasons. A 4x zoom with let's say 1.4-5.6 would be very soft at the short end, and I'm not sure modern zoom designs have the same effective aperture at all focal lengths (the "aperture image" is magnified depending on the focal length). But the f-number definitely does not stay constant unless the manufacturer artifically creates this effect. It's marketing because people associate high-end lenses with constant f-number. Decades ago, when cameras could not easily compensate for changing f-number, pros really did need the constant aperture value, which I guess is the source of all this.

Last I will say on this because it should not be so difficult.

A prime lens that is exactly 100mm and f2 will have an aperture of 50mm and a prime lens of exactly 50mm and f2 will have an aperture of 25mm.  

A zoom lens that is exactly 50-100 f2 will have an aperture that is 25mm at 50mm and 50mm at 100mm focal length.

It is more difficult to make a zoom than a prime and I am guessing it would be more difficult to make a zoom that straddles wide and tele (like your two do) so maybe what you are seeing is something to do with the construction of your lenses.

My two are a wide only (20-35) and a tele only (60-120) and the 60-120 especially is easy to see how the aperture changes as you zoom.

Dunno if i am getting any of the terminology wrong but the end result is there is no difference in brightness with a constant 2.8 or whatever zoom at the long and short ends.

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9 hours ago, noone said:

A zoom lens that is exactly 50-100 f2 will have an aperture that is 25mm at 50mm and 50mm at 100mm focal length.

Yes, but the aperture does not change its size by itself when you change focal length! Such a lens would be 50/50=f/1 at 50mm and 100/50=f/2 at 100mm.

To keep that lens at f/2 so that it can be marketed as 50-100/2, the aperture has to close down to 25mm at the short end. This is done with a special double aperture mechanism that 1. closes down as you zoom out and 2. closes down more depending on what you set in the camera, firmware controlled.

The first part is purely mechanical. You can see this on some strip-downs lensrentals.com have done. Detach the lens from the camera, zoom out, and watch the aperture close, without any power supplied to the lens.

Constant f-stop is a complete marketing fabrication and not a "natural" property of any lens. As focal length decreases, the aperture gets larger in relation. Zooms are always brighter at the short end than the long end, unless the manufacturer actively prevents it.

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This is oversimplified of course - the effective entrance pupil, depending on the exact construction of the zoom (elements in front and back of the aperture), does change as you change focal length. That is what I called "magnification" of the aperture, as seen through the front lens.

But not that much, which is why all these zooms have values like 3.5-5.6.

A standard pro 24-70/2.8 zoom would definitely be something like a 2-2.8 if it wasn't for the said mechanism or additional light baffle, depending on the exact model. The f/2 would be soft and have strong vignetting, but it would at least be available.

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7 hours ago, Enjay said:

This is oversimplified of course - the effective entrance pupil, depending on the exact construction of the zoom (elements in front and back of the aperture), does change as you change focal length. That is what I called "magnification" of the aperture, as seen through the front lens.

But not that much, which is why all these zooms have values like 3.5-5.6.

A standard pro 24-70/2.8 zoom would definitely be something like a 2-2.8 if it wasn't for the said mechanism or additional light baffle, depending on the exact model. The f/2 would be soft and have strong vignetting, but it would at least be available.

Against my better judgement FFS  If they made it so it did not change the size of the aperture to the same constant f stop it is no longer a constant aperture lens ...how difficult is THAT.....It is simple physics/maths, focal length divided by f stop gives aperture diameter.     They build them like that for lots of reasons and of course a lens COULD be brighter at the short end if they chose but a constant f2 lens for example is just as bright at the short end than it is at the long end and NOT brighter at one end as you claimed  

Other properties will depend on the lens.    I have owned a lens that was just like that (2.8-4) and it was just as complex as any other and while i liked it it was nothing special  and the constant zooms i have had have generally been better.

The change looking through the front and seeing the aperture changing is exactly what the maths says it will be with any zoom    On a short slow lens you will not see much but even your 24-105 f4 zoom would be very visible if you can see through it wide open  I forgot I have a third constant aperture zoom but i do not use it and it has an aperture of around 17mm diameter at the short end and about 77mm at the long end so there is a very noticeable and large change (there will still be no difference though if I shot a target).

Not sure what you are trying to say now ( it seems you are now saying they can build lenses that are not constant or they can build them that are and the constant ones have a mechanical way of keeping the aperture constant)....well gee, of course but that does NOT mean a constant zoom is a stop or so slower at the short end than it is at the long end and that is what you said.

NOW I am done.

 

 

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6 minutes ago, noone said:

Against my better judgement FFS  If they made it so it did not change the size of the aperture to the same constant f stop it is no longer a constant aperture lens ...how difficult is THAT.....It is simple physics/maths, focal length divided by f stop gives aperture diameter.     They build them like that for lots of reasons and of course a lens COULD be brighter at the short end if they chose but a constant f2 lens for example is just as bright at the short end than it is at the long end and NOT brighter at one end as you claimed  

Other properties will depend on the lens.    I have owned a lens that was just like that (2.8-4) and it was just as complex as any other and while i liked it it was nothing special  and the constant zooms i have had have generally been better.

The change looking through the front and seeing the aperture changing is exactly what the maths says it will be with any zoom    On a short slow lens you will not see much but even your 24-105 f4 zoom would be very visible if you can see through it wide open  I forgot I have a third constant aperture zoom but i do not use it and it has an aperture of around 17mm diameter at the short end and about 77mm at the long end so there is a very noticeable and large change (there will still be no difference though if I shot a target).

Not sure what you are trying to say now ( it seems you are now saying they can build lenses that are not constant or they can build them that are and the constant ones have a mechanical way of keeping the aperture constant)....well gee, of course but that does NOT mean a constant zoom is a stop or so slower at the short end than it is at the long end and that is what you said.

NOW I am done.

 

 

Tried to delete, ran out of time.

If you like, Yes, they are "crippling" zooms by making them constant...happy now?   They make the constant for many reasons and I am glad they do (not crippling).     You want faster?   Add a speed booster (which is how some faster zooms are made- by adding a focal reducer group in the lens).

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