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10-13-2012, 01:51 PM   #1
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SMC Pentax-DA 35 mm f2.4 AL vs SMC Pentax-FA 35 mm f2 AL angle of view

On the K-r would I see approximately the same image through the optical viewfinder - with the same angle of view (about 46 deg. "normal") - in both these lenses on the K-r ? Or does the full frame FA lens become the "normal" prime (about 52 mm focal length in 135 format) for the APS-C sensor in the K-r ONLY IN THE FINAL IMAGE ON THE SENSOR ? The actual image on the sensor will be a cropped central region of the image I see in the viewfinder ? Thus I would not see the same image in the K-r viewfinder with this FA as I would see with this FA lens on a full frame Pentax film SLR (e.g. MZ-S) say or the DA 35 mm lens on the K-r right ? I am a little puzzled by this. Any help will be appreciated. Thanks.

10-13-2012, 02:22 PM   #2
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Many have been puzzled by the crop topic, so at least you aren't alone
Any and all 35mm lenses will look the same through the viewfinder and on the sensor, whether that lens is 'made for digital' (aps-c) or full frame. The image comes out looking the same on whatever sensor you use. The 18x24mm sensor isn't large enough to capture the edges/corners of the image that a 24x36 sensor would capture, and that's referred to as the 'crop'. So the slightly-wide image of a 35mm focal-length lens is caught on a slightly-small aps-c sensor, making the result similar to a 50mm focal-length lens projecting onto a full sensor.

Hope that helps, but no promises!
10-13-2012, 02:23 PM   #3
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They'll provide the same viewing angle, both in images, and in your viewfinder. I might suggest getting the DA variant if you wish to use it solely on digital though, as it is much, much cheaper, and provides about the same level of IQ(And less fringing, if I remember correctly)
10-13-2012, 02:59 PM   #4
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35mm is 35mm. Focal lengths of the lenses are properties of the lens and have nothing to do with the camera/sensor/film. So a 35mm lens will look the same, through the viewfinder and in the finished image whether the lens was made for film or digital, APS-C or Full frame.

Now if you use the same lens on an APS-C camera and then on a Full Frame camera (film or mythical digital one) there will be a difference. And if the APS-C lens does not cover the full frame image circle it will vignette. The difference in FOV is caused by the size of the sensor (or film) not the focal length of the lens.

10-13-2012, 04:10 PM   #5
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The focal length number has been standardized for full frame sensors (or film). All 35mm (DA, FA, even the macro) will project the same angle of view, but here are the differences:
-When using a crop sensor camera they will all have the edges cropped/cut off, which makes it look like its a bigger focal length.
-When using a crop only lens on a full frame (or on film), its image quality in those edges will be poor, because the lens is optimized for a sensor that isn't as big. It will probably vignette on full frame (the edges will be very dark). FA lenses will work just fine on full frame, though. Also, some DA lenses have been tested on film, and they appear to be okay, as well.

The viewfinder tries to show you the final result, so the viewfinder in the K-r is also.. cropped.

The macro 35mm also has the same angle of view, but it allows you to focus much closer, which means it has a bigger maximum magnification. All of these three lenses are pretty good, the main differences are maximum f-stop (aperture), build (the FA has more metal parts than the DA), distance scales, aperture ring, and how close it can focus. The DA 35 is often called the plastic wonder, because it is made of plastic and relatively cheap, but still delivers great quality.
10-13-2012, 05:12 PM   #6
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Actually, there is one difference you might notice in the viewfinder with two lenses, the FA 35 would be a little bit brighter (half a stop to be exact) and a bit easier to manually focus than it's DA cousin. To extend this comparison, if you put a Samyang 35mm 1.4 on your K-r, it would be a stop brighter than the FA 35 and easier to focus still, at least if you shot all three lenses at the same aperture, let's say f/4. This brightness also helps the autofocus system to do it's job, though sadly not with the Samyang as it's MF only.

Otherwise all three lenses would look the same, a 35mm lens is a 35mm lens, it's the size of the sensor that determines what gets captured coming out of the other end. If you put a 35mm lens on the Pentax Q, it would give you roughly the same field of view that a 200mm would give you on a full frame, or a 135mm would give you on an APS-C like your K-r.

Last edited by maxfield_photo; 10-13-2012 at 05:19 PM.
10-14-2012, 08:27 AM   #7
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SMC Pentax-DA 35 mm f2.4 AL vs SMC Pentax-FA 35 mm f2 AL angle of view

Thanks but I am still puzzled.

@Na Horuk - "The viewfinder tries to show you the final result, so the viewfinder in the K-r is also.. cropped"

So the scene presented to me in the K-r VIEWFINDER with the FA 35 mm will be approximately what I would see
on a FULL FRAME SLR viewfinder with a FA 50 mm lens ? True ? If this true then how can the FA 35 mm show me
show me approximately the same scene in both a K-r and full frame MZ-S ?

On a FULL FRAME SLR (e.g. MZ-S) the FA 35 mm will give me a moderate "wide angle" view in the viewfinder.

Anyway thanks for all your help everyone.
10-14-2012, 08:57 AM   #8
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QuoteOriginally posted by psur45 Quote
So the scene presented to me in the K-r VIEWFINDER with the FA 35 mm will be approximately what I would see
on a FULL FRAME SLR viewfinder with a FA 50 mm lens ? True ?
Very true

QuoteOriginally posted by psur45 Quote
If this true then how can the FA 35 mm show me
show me approximately the same scene in both a K-r and full frame MZ-S ?
It does not. Check again. the angle of view on the MZ-S sould be comparable to a 24mm lens on your K-r

QuoteOriginally posted by psur45 Quote
On a FULL FRAME SLR (e.g. MZ-S) the FA 35 mm will give me a moderate "wide angle" view in the viewfinder.
That is correct

10-17-2012, 03:17 PM   #9
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Pentax DSLRs don't do any cropping based on which lens you use. They use the whole sensor all the time, and the viewfinder image is going to be pretty much the same as the end result.

Crop factor is just an easy way to figure out equivalent angle of view between different format size. The 135 frame is 1.53x bigger than the Pentax APS-C frame.

A 35mm lens on 135 is a moderate wide angle. Multiply 35 x 1.53 and you get an angle of view roughly similar to a 53mm lens on 135. This applies to ALL 35mm lenses. I've had both the DA 35/2.4 and FA 35/2 and they have the same angle of view on my K-r.

Now, if you had a Nikon full frame camera, then they do in fact have a crop mode that gets activated if you use an APS-C format lens. But you don't have to worry about that.
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