[shaolin95]

Hi!
I was wondering if the 70mm limited is much sharper than my current A 50mm 1.7.
I do not know if 50mm is not what most people consider a portrait lens but in any case, do you guys think that getting a 70mm limited for the K20D is going to give me much sharper images than the 50mm 1.7 I have?
Thanks



PS sorry if it has been asked before, I would be glad to read any previous posts...just did not find much like this.

[ytterbium]

If you stop 50/1.7 to 2.2...2.8 it is already plenty of sharp.
Ltd70 Is a bit soft @ 2.4 and it's only 2.4.
It has further minimum focussing distance and it's not 1.7.
Ltd70 has fast AF.

Sample:

Make - PENTAX
Model - PENTAX K200D
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
Software - K200D Ver 1.00
DateTime - 2009:08:29 11:04:03
YCbCrPositioning - Co-Sited
ExifOffset - 598
ExposureTime - 1/125 seconds
FNumber - 2.40
ExposureProgram - Aperture priority
ISOSpeedRatings - 100
ExifVersion - 0221
DateTimeOriginal - 2009:08:29 11:04:03
DateTimeDigitized - 2009:08:29 11:04:03
ComponentsConfiguration - YCbCr
ExposureBiasValue - 0.30
MeteringMode - Spot
Flash - Flash not fired, compulsory flash mode
FocalLength - 70.00 mm
FlashPixVersion - 0100
ColorSpace - sRGB
ExifImageWidth - 3872
ExifImageHeight - 2592
InteroperabilityOffset - 54284
SensingMethod - One-chip color area sensor
FileSource - Other
SceneType - Other
CustomRendered - Normal process
ExposureMode - Manual
White Balance - Auto
FocalLengthIn35mmFilm - 105 mm
SceneCaptureType - Standard
Contrast - Hard
Saturation - High
Sharpness - Hard
SubjectDistanceRange - Macro

Maker Note (Vendor): -
Mode - Auto
Quality - Best
ISO - 100
White Balance - Auto
Lens Type - smc PENTAX-DA 70mm F2.4 Limited

Thumbnail: -
Compression - 6 (JPG)
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
JpegIFOffset - 54408
JpegIFByteCount - 6754

Excuse the boring subject. The fur is just very good sharpness indicator.
Is this sharper (full size - resize, auto contrast, sharpen; original 100% crop - bright jpeg from camera):

[shaolin95]

Nice pic and I do like cats so not boring for me.
As for your comments, it would seem the 50mm 1.7 I got is all I would need then but I see many users buying the much more expensive 70mm so I guess there is something to that lens that makes it so desirable... right?
Regards

[ytterbium]

Well, i got mine cheap - it came only with caps (only front one was original) and heavy weared body. Otherwise i could not justify the price it goes for new, especially if i had some AF 50.

Replaced the M50/1.7 just to have the AF, for twice the price i paid for M. With the shallow dof you just can't capture even slightly moving subjects unless you go F4 or darker.
The quality is comparable, 50 had somewhat colder colours and slight overexposure (it is was M so it could be), but the focal length seems a bit odd.
70LTD produces more real life looking images.
Sometimes i miss the F1.7, but not much. You could get better blur (subject isolation) with that.
50mm felt more natural, after that i feel like i need something longer than 70mm.. maybe 105 or even 135.

[legacyb4]

Well, the big changes are obviously the AF (along with quick shift focusing), longer focal length, and size of the DA 70. Not to knock the IQ of the 50mm, but the DA 70mm gives really nice results, doesn't exhibit as much fringing when shooting into the light (from what I've experienced), and is a real treat to work with.

Granted, it costs nearly 10x the cost of a used 50mm F1.7 so I'm not going to say it's an absolute must unless you've been bitten by the LBA bug...

[ivoire]

If autofocus is an upgrade consideration and you like your A50 f1.7, maybe the smcf 50mm f1.7 is an option. It would save you $2-300 as they can be had for around $150.

[Marc Sabatella]

Nice pic and I do like cats so not boring for me.
As for your comments, it would seem the 50mm 1.7 I got is all I would need then but I see many users buying the much more expensive 70mm so I guess there is something to that lens that makes it so desirable... right?
Regards

Sure - it's simply a better focal length for portraits, as it lets you get standard head & shoulders framing from a more flattering distance. Doesn't help to have the sharpest lens in the world if the focal length is too long or too short. Sure, you could shoot the 50 from that longer distance and then crop, but you lose enough sharpness in so doing that the 70 would outperform it more clearly.

Other reasons too, of course - really quick auto-focus (with quick shift), the build quality, etc. And other subjective IQ issues aside from sharpness - which is actually one of the *least* important attribute for a portrait lens (as is often related, you don't normally want portrait to show every pore in excruciating detail). Sure, you want a lens that's "sharp enough", but both the 50 and 70 are already way sharper than you usually need. Some people just like other qualities of the 70 better, in terms of color, contrast, bokeh, "rendering" (and yes that's a very vague term), etc.

[shaolin95]

I was expecting bokeh to be better with the 1.7 but I need to learn a lot indeed. :-)

[ytterbium]

What do you mean by better. With 1.7 you'd probably get "more" bokeh (more blurred out of focus areas and thinner focus area), but this dosnt guarantee that that the blurred shapes look nice, they may be blurry but still contrasty or edgy. Here is an example of one:
http://forum.manualfocus.org/viewtopic.php?id=13784#p111811
And here is another one showing similar amount of blur, but much "calmer" appearance:
http://forum.manualfocus.org/viewtopic.php?#p115180

At the same time 70mm is longer than 50 so the DOF is more shallow. At F2.4 it may be something like F1.8..2 on 50mm (when preserving the same subject size).
Here is a similar example, recent talks about manual Takumars inspired me to take:

Approx. the same relative subject size as in 70LTD shot, current settings: 55mm@f1.8.
You can see that less of the cat is in focus. Unfortunately this time the background is dark, so you can't see that it is much more blurry.
But keep in mind that this time i had to get very close to get the same framing and corresponding DOF. Most people would feel very uncomfortable at such distances.

[shaolin95]

So having a longer distance from the subject is indeed another of the advantages then I see.

[ytterbium]

That is not certain. You have a Tamron 70-300mm lens. Try for yourself, how the working distance feels to you. Shoot for a day exclusively at 70mm.

[shaolin95]

Good idea indeed. :-)
This forum is so different from the usual PC overclocking forums I hang around and not to mention AVSFORUM lol

[ytterbium]

Btw. Just sold my M50/1.4 and 70/2.4 for F50/1.7. Sometimes i just couldn't get the shot without the extra stop and M50/1.4 - hard time focussing.

[RolloR]

you'll definitely get more sharp photos from the autofocus lens than the manual focus lens