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02-17-2014, 09:06 AM   #1
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50mm film lens vs 50 mm for digital

I am looking at getting a 50mm lens to help with taking pictures in lower lighting areas. What I would like to know is if the old film lens f 1.4 is equal to the f 1.4 digital lens since a digital sensor is smaller footprint then 35mm film is? So would the film lens be darker than a newer digital lens on a digital camera?

02-17-2014, 09:11 AM   #2
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50mm is 50mm and F1.4 is F1.4.

A 'film' lens simply projects a larger image circle than a 'digital' lens. The Field of View is the same regardless. On APS-C the 50mm lens has the same Field of View as a 75mm lens on 35mm FF.
02-17-2014, 09:12 AM   #3
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QuoteOriginally posted by bergfire Quote
I am looking at getting a 50mm lens to help with taking pictures in lower lighting areas. What I would like to know is if the old film lens f 1.4 is equal to the f 1.4 digital lens since a digital sensor is smaller footprint then 35mm film is? So would the film lens be darker than a newer digital lens on a digital camera?
You get the same amount of light and the same focal length regardless of how big the sensor is on the other end APS-C digital cameras simply see less of the frame, that's all.

Adam
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02-17-2014, 09:16 AM   #4
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We had a bunch of threads exactly like this.
So, to state more clearly. 50mm focal length is a lens property, independent of the camera. The captured field of view however, is reduced because the sensor is smaller. So a 50mm lens for medium format, for film, or for crop sensor will all be the same on a crop sensor, but a bigger image circle will simply be wasted.
The only problem is going the other way - a 50mm made for crop sensor will have very dark edges (vignetting) on film/full frame. But even this is not necessarily true for all lenses - some "crop only" lenses actually produce an image circle big enough to cover full frame.
So a film 50mm f1.8 will give you the same brightness, the same DoF and the same FoV as the DA 50mm f1.8 (if you are testing them both on the same camera). There might be differences in construction and how it renders the photo, though (things like contrast, colours, sharpness, bokeh).

For example, DA 200mm and FA 200mm would give the same field of view on a crop sensor camera. You will not get any extra reach with the FA.

02-17-2014, 09:30 AM   #5
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QuoteOriginally posted by boriscleto Quote
A 'film' lens simply projects a larger image circle than a 'digital' lens.
That isnt exactly gospel. There are a number of members who have shown DA*55 1.4 will cover a 35mm frame. The fact is most of the primed lenses in the normal range cover a FF circle, but are marketed as crop because crop is all we have (digitally speaking).
02-17-2014, 09:54 AM   #6
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Thank you for your prompt answers. Your answers have made it easier (cheaper) for me to learn more about photography since I can get a used film lens to play with in ambient light.

Last edited by bergfire; 02-18-2014 at 04:11 AM.
02-17-2014, 10:00 AM   #7
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Just be careful. Once you own 5 50mm lenses you officially have LBA.
02-17-2014, 11:19 AM   #8
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If you are looking for a legacy 50mm I suggest something like the Pentax A 50mm f1.7, if you don't need autofocus. The A series lenses still have auto aperture and allow Av and other modes.
If you want to go even cheaper, with less automation, get the Pentax M 50mm f1.7. Great quality, low price, but no AF and no auto aperture (so you have to use M mode and meter with green button).

However, the DA 50mm f1.8 is also relatively cheap. Since it is optimized for digital, it is fully automated with fast AF, but it has no distance scales and no aperture ring. You can get it for under $200, which is a pretty good deal, considering it is new and comes with warranty

02-17-2014, 11:51 AM   #9
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QuoteOriginally posted by Na Horuk Quote
The A series lenses still have auto aperture and allow Av and other modes.
If you want to go even cheaper, with less automation, get the Pentax M 50mm f1.7. Great quality, low price, but no AF and no auto aperture (so you have to use M mode and meter with green button).
For the sake of accuracy, both the Pentax-A 50/1.7 and Pentax-M 50/1.7 are auto aperture lenses*, though only the Pentax-A version supports automatic aperture control** by the body. The key is the "A" position on the aperture ring. If you do start shopping for the Pentax-A 50/1.7, be aware that most have some sort of issue with using the aperture ring off the "A" position due to a flaw in the plastic materials used in manufacture. This is not a big deal if you never intend to use the aperture ring, but should influence sale price if not operational.


Steve

* "Auto" aperture refers to a lens providing a coupling mechanism to allow automatic stop-down and reopen of the iris diaphragm at exposure time. There are many K-mount lenses that are labeled "Auto", but which do not have the "A" position on the aperture ring and which do not support setting the aperture (f/stop) by the body.

** "Automatic Aperture Control" is the Pentax term for body-controlled aperture that was introduced in the early 1980s with the A-series cameras and lenses.
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