Remove aperture ring to make super fast lens...

Discussion in 'Nikon' started by oliver_wilkins, Feb 23, 2010.

  1. Could I open up a manual nikon lens take out the aperture blades completely and reassemble to make a faster, albeit fixed aperture lens?
    What do aperture blades do apart from stopping down the light going through? Surely if narrow DOF and speed were my only objective I could just remove them and let the light flood through...
     
  2. You won't let in any more light than you do with the lens set to its fastest aperture, since that is already fully opened.
     
  3. Sorry, don't think so. Very rarely I've seen a lens where the diaphragm (aperture) was the limiting factor but not on a Nikkor.
    Wide aperture = high price so manufacturers aren't going to limit the aperture if they can help it. Buyers pay 3 times the price for an extra stop, even though picture quality suffers at the widest aperture.
    Bigger element = higher cost so elements don't have "spare capacity"
    I don't claim to have repaired every lens Nikon ever made; but if you've found one where the elements nearest to the diaphragm are bigger in diameter than the diaphragm I would suggest that the most likely explanation is that the diaphragm is stuck.
     
  4. If I remove the speedometer from my car, I'm sure that it will go faster than the top speed shown (140 mph)...
     
  5. Greg, if you remove or even swap the instrument cluster on some of the newer cars, they won't even start. :(
    On topic, the only prime lens I can ever remember seeing where removing the aperture blades would open it up a stop is the older 50mm f4 Schneider Componon enlarging lens, which dates from the 1960s.Most lenses have a fixed aperture which just happens to be the same as the number on the front ring.
    This idea might work on some constant aperture zooms where the aperture assembly constrains the optics at wider angles. Reassembling one without a manual and good tools is not a simple undertaking.
     
  6. Hey Greg,
    I got the same effect takin' off the bumpers and paintin' a pair of white stripes down the middle.
     
  7. On some of the zooms with the constant aperture opening throughout the range (whose aperture is stopped down as you zoom out), you could do that. I haven't seen or heard of any Nikon F mount prims whose aperture is somewhat stopped down even aperture ring is set wide open, except it is broken.
     
  8. What about variable aperture zoom lenses? Example the 18-55 3.5 to 5.6. Would using the OP's suggested technique result in a 18-55 constant 3.5 aperture lens albeit of lower quality?
     
  9. I always take all mine out! They just get in the way.
     
  10. "What about variable aperture zoom lenses? Example the 18-55 3.5 to 5.6. Would using the OP's suggested technique result in a 18-55 constant 3.5 aperture lens albeit of lower quality?"
    You would get an 18-55 lens with max. apertures from 3.5 to 5.6, but it couldn't be stopped down. A really bad idea.
    What suffices to give f/3.5 at 18 mm will be equivalen to f/5.6 on the long end of the zooming range. It's the same physical opening. You can't increase lens "speed" this way. The f-number is a ratio in which the focal length occurs.
     
  11. What does the iris do besides setting exposure? Aberration control. A big, big part of lens design. If the designer could have come up with a faster lens, you better believe the iris would have been bigger.
     
  12. Interesting responses, thanks.
    I did read that Kubrick had an F0.7 Zeiss NASA lens rebuilt with the apeture ring removed for his low light shooting on Barry Lyndon. Obviously those involved were super skilled, I wonder what their benefits were...
    On a more basic note, how is an F-stop measured? I used to think it was the ratio of the diameter between the front and rear lens, but that doesn't sound quite right...
     
  13. What suffices to give f/3.5 at 18 mm will be equivalen to f/5.6 on the long end of the zooming range. It's the same physical opening. You can't increase lens "speed" this way. The f-number is a ratio in which the focal length occurs.​
    Thanks Bjorn. Good to know that. That gives rise to another question. What about a constant aperture zoom, like the Nikon 17-55 2.8. Would it be possible to break the aperture ring to theoretically convert it to a 17-55 variable aperture lens (maybe 1/f to 2.8/f). because what suffices to give 2.8 at 55 mm should surely give a wider aperture at 17 mm. I hope I am making sense here.
     
  14. You measure the 1/f number of the aperture by measuring the apparent size of the aperture when viewed from the front of the lens and dividing it by the focal length. So for a 50mm f/2 lens, the iris will seem to have a diameter of 25mm.
     
  15. interesting thought, oliver, and sounds feasible. that would be fun. something that i myself would think of doing in my younger years :)
     
  16. A few lenses actually will be a tad faster without the diaphram; in rare cases.

    The modification is sort of like a CB radio power modification for a free-bander; it makes one thing slightly better and something else alot worse. In the CB radio case or 10 meter ham case; the power mod might add a tiny tad to the fundamental; and alot of crap all over the bands. Old Kilroy things it is better since his dumb averaging power meter reads higher; often his meter includes the crap ill stuff not wanted too.

    In the lens case removing the diaphram can with some lenses make the lens slightly faster on axis; ie dead nuts on axis ; and some times add some brightness to the corners too. BUT the mod trashes the corner sharpness alot; that is why the optical designer designed the diaphram's placement. He cut off the off axis rays abit purposely. He did a trade of dropping off axis illumination and gaining better off axis sharpness.

    Unless one has an exact lens/radio/carb to test and modify; there is no answer to these broad brush type of questions.

    Long ago I modified an Argus A2 so it was a tad faster; the 50mm F4.5 thus was about F4. I got a slightly faster central core and less sharp corners. This was eons ago.

    In movie usage there have been special cases where a lens is needed to be slightly faster in the central core and and the corners do not matter. Century Precision Optics did/does this in Hollywood; now a part of Schneider.

    If the diaphram was allowed to be opened up more on most designs where it could be done; average Joe would complain about poor corner performance
     
  17. As to the question of constant-aperture zoom lenses, they do the zooming by shifting a lot of the internal optics back and forth. Note that this also means the entrance pupil can move around, so while its virtual size (which enters the f-number definition) can be different as the focal length changes (thus giving the constant "speed"), the *physical* representation may not change at all.
    So the answer is NO, you can't make a zoom lens "faster" to any significant degree by removing the aperture blades.
     
  18. I did read that Kubrick had an F0.7 Zeiss NASA lens rebuilt with the apeture ring removed for his low light shooting on Barry Lyndon. Obviously those involved were super skilled, I wonder what their benefits were...​
    The lens in question didn't fit their movie camera, that might be the real reason for such modifications; they had to build a custom mount and might have lost infinity capability.

    On a more basic note, how is an F-stop measured? I used to think it was the ratio of the diameter between the front and rear lens, but that doesn't sound quite right...​
    Should be the relationship between the focal length and the aperture opening at infinity focus if I don't remember completely wrong...
     
  19. Actually, the ratio betwwen focal length and size of the entrance pupil when the lens is focused at infinty. The pupil is the virtual opening that collects light on behalf on the optics. We observe it as the appearance of the aperture stop when we look into the front of the lens. Being a virtual quantity, its size can be bigger than the diameter of the lens itself. For a wide angle lens, the entrance pupil typically is small even though the front lens can be impressive.

    There is also an exit pupil, similar to the entrance pupil, that illuminates the film plane.
     
  20. Thanks Bjørn. I'm aware of the pupillary magnification factor, but think about these things rarely so I forget the details...
     
  21. I suppose you could, however I can't imagine why you would ever want to destroy a good lens like that. Without your aperture blades in the barrel, the lens will be no faster than it is wide open.
     
  22. Thanks again Bjorn. That makes sense now.
     
  23. Scott; with some lenses one can leave the iris petals/bladess in place; one just changes a stop so the lens will open up more. After the mod the camera or even some lenses; like my old Argus A2 camera goes back together. After this mod the fstop opened up past F4.5 ; to about F4. *If* one was a collector type; a mode like this is destroying original nature of the item; so is doing a mod to a Non-AI lens. When one removes a stop the iris blades are still in place; and F8 is still F8. It is sort of like clipping a diode on a ham radio to make it transmit on MARS; it is not original; but it works over a wider range. With lenses opening up the iris more than the factory is rare done or even possible.
     
  24. Ok, to take it to a brutal level.
    What if I cracked open my nikon f 1.4 and I remounted the front and rear lenses in a toilet roll tube. If I basically juggled them back and forth for focus would i land an out of focus but somewhat faster lens?
     
  25. No, that still won't work. Bjorn has it. The maximum F-stop is a property of the optics. The aperture blades are installed in such a way that at the wide open position they will not impede the capabilites of the optics. (And why wouldn't they do that? If they could make an f/1.4 lens a much more valuable f/1.2 lens by redesigning the mounting parts for the diaphragm blades, they would.)
    Don't break your lens.
     
  26. Some of the smart a$$ responses on here show a deep lack of professionalism and respect. If you don't have anything to contribute to the poster then don't post a reply. You are not required to reply to every post you read and when you choose to be a child in doing so you serve as a nothing more than a deterrence to some who would otherwise post a question. Glad to see you had some honest and informative replies Oliver. Good luck getting it all figured out.
     
  27. Thanks Douglas. The question itself was somewhat theoretical as I wasn't particularly planning to break open a lens. I am just interested in the mechanics of lenses and how they trap light.
    I'm increasingly realizing the importance of technical understanding in terms of photography equipment and how that translates into how one uses the equipment to take photographs. The mechanics of shutters, apertures, lenses and light ratios surely remain as relevant in modern digital photography as they did 100 years ago.
     
  28. Hi Oliver. I don't have a definitive answer for you, but I have a 50/1.4 Nikkor. As far as I can tell, the lens barrel, not the iris blades, forms the aperture wide open (there is evidence of the blades in bokeh at f/2, but not at f/1.4). I guess you could have a theoretically faster (but not very practical) lens by removing the elements from the barrel completely and utilizing those edges of the elements encased the barrel, assuming that portion of glass is image-forming. I agree that optics is interesting. I learnt a lot from an old 1960s edition of the Ilford Manual of Photography, which covers the basic maths and mechanics, simple lens designs, aberrations, and other phenomena. This also seems like a good place to start.
     
  29. Andrew; you have it wrong.:)

    With *some* lenses; typically wide angle opens the iris is *purposely* hacking off the ill off axis rays. The iris *purposely* truncates the clear aperture.

    This is called optical design.

    It has been done 100 + years ago; thus it is ancient.

    As " to why would they not do it" ; it is a tradeoff; ie what a lens designer does.

    Before WW2 an optical guru would spend 5 years or even 10 to trace rays on a brand new design.
    The iris placement is fundamental to optical design. Where the iris is effects even a single element lens.

    They purposely sweat where the iris is placed in the optical design procedure. The max size of the iris; where it is placed are *all* part of optical design; even 150 years ago.

    With some lenses if one changes the stops one can get a slightly faster lens; but usually it ruins the corners.

    In lay sense the average Joe cannot modify any lens; tweak a carb; tweak a radio; understand the DlogE curve; redesign a kitchen because it involves understanding the tradeoffs involved.

    With lens the *purposely* designed in blockage can be the iris; PLUS the counterbore diameters that hold each element. All this is varied during the design of a lens; and with some lenses the clear aperture is *purposely* reduced to improve the corner performance. *If* one is only using the central core of a reused lens; in some cases the slightly faster mod works.

    For most all folks Andrew reply is valid; ie "Just do not do it".

    Here I did it 50 + years ago on a dumb Argus A2; and made the 50mm f4.5 be about F4 in the center; but the corners at F4 are worse. I did it for star photography with my first 35mm camera. The mod did not break the camera; or remove the diaphram either. It just allowed iris to open more; IF ie wanted it to. The mod also gave me a respect of optics and tradeoffs.

    Today learning and experimenting are not so much in vogue. There is this more helpless punting, scared dogma of not fiddling; which was once the norm. One can pick up a pre Ww2 photo magazine and it was all about how to build stuff by oneself; and experimenting.

    A multi element lens even like a simple 100 year old Tessar involves design with consideration of the iris. One uses the trial meridional plots with ray tracing. Purposely not letting the stop be as big as the front group allows one to improve the corners; with a typical lens as a normal lens. The exact same normal lens; maybe a 100mm F4.5 can be faster if it is a long for 16mm cine; since its angular coverage is less and one can thus open up the stop more.

    Alot of folks want simple answers to complex questions; thus a better answer to those is thus no. One cannot modify a lens; carb, car engine; it is too complex and the gurus have it perfect.

    For others; if they know that the gizmo is used in a subset of the original ways; a mod is sometimes possible; *if* one learns the tradeoffs; ie understanding.
     
  30. Typically if one removes (or moves out of place) all the stops *purposely* added to a lens design one might get a slightly faster lens *on axis* and poor corner performance. With the optical design on OSLO or CODE V one can play *what if* . The lens designer did this already; and purposely added the blockage/stops/features as part of the design.

    Now Kilroy wants a broad brush answer if it is ok to put a penny in the fuse holder; tweak a knob on 3 mile island control panel; change the carb jet on a mower; remove the governor on an engine; use 2 year old D76; use 30 year old tri-x; enlarge an ACME cameras image to be 30x42"; eat 3 year old fruit cake; drink 30 year old Coors; open up the diaphram on a lens.

    the answer is it depends

    With an actual piece of gear/fruitcake/old film one can see what happens and experiment.
     

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