bobm
Contributing Member
Posts: 36
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Post by bobm on Apr 1, 2007 4:13:47 GMT -5
It's fact, Peter - it's the reason why a lot of lenses appear to perform far better on DSLRs with crop sensors than FF, as the sensor only ever sees the lens' sweet spot.
That's why, with regard to digital, it's so important that any lens tests indicate the crop ratio of the camera used since a crop cam will never see the "dodgy" looking corners....
It's also why I considered using MF lenses on my FF 5D as the diameter would be naturally greater so I would in theory, be using my 5D's sensor as a crop type.
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Post by daveinpasadena on Jul 4, 2007 0:54:50 GMT -5
The difficulty of design and manufacture of refractive optical systems increases non-linearly as an inverse power of the f-ratio. The brightness on the focal plane goes as the square of the inverse f-ratio. This is why F2 is not really considered "fast" while F1.4, seemingly a minor numerical increment, is.
The lens speed (i.e. minimum f-ratio) effectively meters sensitivity to *extended* sources of light, while the effective aperture of the lens measures sensitivity to point sources of light. The effective aperture is the focal length divided by the focal ratio, so 50/1.2 lenses with differing filter sizes have the same light gathering power irrespective of the filter ring size. For ordinary photography it's the minimum f-ratio (speed) that is the key to efficiency, not the lens diameter. Lens diameter and speed are necessarily interrelated however since film size is fixed. This means that if the speed is increased (i.e. f-ratio decreased) yet the focal length kept the same, the only way to achieve this is to increase the lens effective diameter (real lens diameters increase similary). Raw optical glass costs are a function of diameter, also in a non-linear way, thus the "fast" requirement tends to beg larger diameter glass which contributes to cost. The "glass" in question may actually be rather exotic material like fluorite or ED glass to aid in aberration suppression, further impacting expense.
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Post by Peter S. on Jul 4, 2007 6:52:51 GMT -5
I heared the argument, that the cost of a lens is roughly proportional to the _area_ of its front element - which seems to some extent to be more or less proportional to the effective aperture (area). This does not seem to hold for retrofocus wide angles however...
And yes, there is a big phallus factor between a f/1.2 and a f/1.0 lens ;-)
Best regards Peter
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Post by Peter S. on Mar 9, 2008 13:06:47 GMT -5
Dear fellow camera collectors, I found an Italian website that got information on a few lenses, that are horrifying fast. First there is a 1.5/400(!). You read right: F/one-point-five for a 400mm telephoto!!! www.luciolepri.it/lc2/marcocavina/articoli_fotografici/Zeiss_UR_40cm_1,5_T/00_pag.htm And then there is a 0.7/50... www.luciolepri.it/lc2/marcocavina/omaggio_a_kubrick.htmMaybe somebody finds out how to pipe this through an automatic translation engine. Best regards Peter PS: please admins, I don't know how to get that comma in the first URL working. In an regex it would be a backslash - but I don't know how the forum S/W is working.
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SidW
Lifetime Member
Posts: 1,107
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Post by SidW on Mar 9, 2008 20:20:37 GMT -5
If I need to put a decimal into a filename I do it with "p", e.g. 1p5 (but you obviously can't do that in someone else's filename).
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Post by Just Plain Curt on Mar 10, 2008 5:07:10 GMT -5
I tried to modify it by changing the comma to a decimal, still wouldn't work, then I tried a p, no luck either sorry.
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Post by estudleon on May 11, 2008 14:07:54 GMT -5
In the 50 mm f/1,4 is fast now, in the early of 50's was super fast. But I want to know wich 50 mm f/1,4 is sharper at 1,4 and 2 than at middles 5,6 or 8. Is there a normal that do this?
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Post by towermax on Feb 1, 2009 2:12:19 GMT -5
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Feb 1, 2009 9:46:33 GMT -5
In modern digital photography "fast" lenses don't really mean that much IMO. When you can shoot with a DSLR at ISO 1600 or 3200 and get less "grain" than a filmcamera got at 800, an f2.8 lens pretty much becomes an f1.2 film equivalent.
I've never been a fan of lenses faster than f1.8 or f2. The f1.4 and faster lenses are big, heavy, and usually not particularly sharp. I think for a lot of photographers, owning an f1.2 lens is like owning the faster computer they can find or the largest TV screen.
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Post by John Parry on Feb 1, 2009 14:54:02 GMT -5
I agree with you Wayne - there's very little to be gained with that extra half an f-stop. A little more flexibility, but you would have to do a cost-benefit exercise to really justify the massive leap in price.
My M42 cameras generally end up with a Pentacon 1.8 on them, simply for the closer focus range (the digital macro settings knock me for six!), but other than that I've found nothing to chose between Pentacon and Asahi, Yashinon or Fujinon 1.7 or 1.8s. These were all the flagship lenses of their day. And I can't help wondering what you would need a faster lens for. Sport action, certainly - but a 50mm?
No - these were trophy lenses. Nice, but fairly inconsequential in the great scheme of things!
Regards - John
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PeterW
Lifetime Member
Member has Passed
Posts: 3,804
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Post by PeterW on Feb 1, 2009 19:18:46 GMT -5
Wayne:
Absolutely agree. Most of my pictures are taken between f/4.5 and f/8 with occasionally f/11 if I want huge DOF. I've used f/1.8, but only very rarely, usually to isolate something and throw the background out of focus. I find, though, that a close-focusing 200mm prime lens is generally better for this than a 50 or 58mm lens.
peterW
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schen
New Member
Posts: 5
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Post by schen on May 2, 2009 13:11:52 GMT -5
At the risk of sounding simplistic; I've always catagorized a "fast" lens as any that is significantly (1/2 stop or more) faster then the "norm" for the focal length. Some examples would be for 35mm format, 35mm lenses are typically f2.8 so I basically look at some of the lenses that are f2.0 or so as "fast", or 200mm lenses that are typically f4.0 or maybe f3.5, so anything such the f2.8s as "fast".
I know that pretty relatively and flexible, but isn't everything?
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Post by nikonbob on May 2, 2009 14:39:54 GMT -5
In modern digital photography "fast" lenses don't really mean that much IMO. When you can shoot with a DSLR at ISO 1600 or 3200 and get less "grain" than a filmcamera got at 800, an f2.8 lens pretty much becomes an f1.2 film equivalent. I've never been a fan of lenses faster than f1.8 or f2. The f1.4 and faster lenses are big, heavy, and usually not particularly sharp. I think for a lot of photographers, owning an f1.2 lens is like owning the faster computer they can find or the largest TV screen. I have to mostly agree with what you said especially concerning digital high iso negating the need for fast lenses. OTH if you are manually focusing on a DSLR the extra brightness afforded by a fast lens may be much prized if you are shooting in dim light. You have ask yourself how much of that type of shooting you do and does it justify the added expense and weight of a fast lens. Bob
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Post by estudleon on Jun 5, 2009 15:53:02 GMT -5
The leica literature recommend to use the fast lens that we can (if you see the price of the fast lens of leica, you will understand . . . .).
But the fastest, why?
Not for my taste and necessities . Rino.
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Post by dee on Oct 18, 2009 2:35:18 GMT -5
I love available light photography at max aperture - 50 f 1.4 Rokkor on 4/3rds Leica Dig 3 , but it all so depends on the period we are speaking of . Also my f2 Summitar on the M 8 . However , a 50 / f 3.5 is perfectly useable when the need to focus is eliminated by a rangefinder . My ' new ' Jupiter 3 [ Sonnar derivative ] born of the 30s was considered genuinely ' fast ' Even my 70s Rokkor 1.4 was fast in times of ASA 64 and ASA 25 . Unheard of today with ASA 100/200/400 being the norm . The factor to be taken into consideration is tha shallow depth of field of the 1.5 over a F2 Jupiter / Sonnar on my Kiev II .
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