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04-23-2010, 12:46 AM   #1
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Idiot asks Why??

I have been using a 70mm Ltd for months now and recently bought 2 old lenses M 135mm f3.5 and 35mm-105mmA. I immediately noticed, when using these lenses, that objects in the images appear to have more form than in my DA70 ltd photo's. I deliberately say objects have form instead of image looking 3d because this is mistaken for using perspective to give depth.

Why is this. It's not about sharpness because the 70 is probably sharper than the other two. Is it because of the greater focal length specifically the 135 which gives a narrower depth of field. Am I too close to subjects when I use the 70mm at f2.4. Would I be better to use a smaller f stop when close to a subject?

What am I doing wrong with the DA70mm.

04-23-2010, 01:01 AM   #2
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Can you post an example, where you can see the same object with and without this "more form".
I'm not quite sure what your'e referring to...do the subject look more realistic, have more sharp parts or is it something else?
04-23-2010, 01:27 AM   #3
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Usually, a longer focal length means a 'flatter' image. My guess is that the old lenses give a higher contrast, but that's my 0.02. Examples are indeed welcome.
04-23-2010, 05:20 PM   #4
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Told you it is idiotic to ask this question

QuoteOriginally posted by ytterbium Quote
Can you post an example, where you can see the same object with and without this "more form".
I'm not quite sure what your'e referring to...do the subject look more realistic, have more sharp parts or is it something else?
Thanks for the replies.

I mean that my images taken with the DA70 look flat regardless sharpness or bokeh in relation to the image taken with the lenses previously mentioned.

I think my question has been answered.

04-24-2010, 01:58 AM   #5
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Well, but the M135/3.5 is a longer focal length. Then the images taken with it should look even more flatter. As well as images taken with 35-105 zoomed in.

That's really interesting...
04-24-2010, 11:21 AM   #6
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This is by no means an idiotic question. The Pentax pancake lenses use specific lens formulas that allow them to be compact and relatively inexpensive while the older M-series lenses mentioned were anything but compact. Lens design addresses issues such as desired edge-to-edge sharpness, viewing plane flatness, and correction for distortion. While I'm sure the DA pancakes are nice lenses their designs include compromises which must show up somewhere in image quality.

In astronomy there are telescope eyepieces designed to provide nicely sharp and flat images and there are those that provide well corrected images. The super-duper expensive eyepieces are those that do a pretty good job of both.

The real question is which results you prefer.
04-24-2010, 07:04 PM   #7
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Actually, the defining feature of the M lenses *was* that they were more compact than their predecessors (as well as pretyt much all the competition). The M135/3.5 has got to be one of the smallest 135mm lenses ever made for that format.

But I'd say the chance that the Op is actually referring to any subtle differences attributable to lens design issues is pretty small. Toug to say without seeing pictures, but I'm guessing he's just seeing effects of different focal lengths and apertures and the implications this has for DOF, etc - just as he guessed.
04-26-2010, 03:03 PM   #8
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QuoteOriginally posted by kottier Quote
Usually, a longer focal length means a 'flatter' image. My guess is that the old lenses give a higher contrast, but that's my 0.02. Examples are indeed welcome.
I doubt it's merely an issue of focal length or higher contrast. I have an old tele-takumar 300mm lens that has what is sometimes refered to, rather vaguely and inadequately, as the "Pentax pop." It's a rather subtle, intangible quality difficult to put one's finger on and not always appreciated or even noticed. But it does seem to be a characteristic of many Pentax lenses, even those with longer focal lengths. (I've heard it's present even in the old 500mm f4.5)

This is not the first time I have come across a complaint about the DA pancake lenses producing "flatter" images than other Pentax glass. Probably it is due, as a previous poster mentioned, to the compromises necessary to make the lens so compact. It would be interesting to know whether the old M series 40mm pancake suffered from the same defect.

04-27-2010, 01:49 PM   #9
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Best if the OP posted photos so we all can see the difference he is, or is not, seeing.
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