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07-20-2007, 10:13 AM   #1
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Some concern about image quality.

Hi,

I'm new at digital photography so I'm not quit sure as what to expect to get at 100% view.
I recently acquired a prime to be used as my standard lens. I'm used to working with a 50mm on my previous camera (SP500) - yes, I'm that old.
Mostly, I shoot landscapes.
I made some comparison shots with the new prime and with the kit 18-55 set to the same focal length.
This made me wonder if I got a bad copy of the prime or a very good copy of the kit lens. Perhaps I was expecting too much?

Could somebody with more experience have a look at the shots and advise? I removed the exif (for now) to keep it more objective.
I shot Raw at f9 for the first set and at f10 for the two others - all with AV.
I linked to full sized files because I thought that would give the most information.

So, my questions are:
- can you identify the pictures taken with the prime?
- is there "enough" difference between the two to qualify the prime as 'ok'?

Set 1:




http://users.telenet.be/D_Young/2007%20Auvergne-2007-07-11_10-57-29_0044.jpg



http://users.telenet.be/D_Young/2007%20Auvergne-2007-07-11_10-59-24_0045.jpg

Set 2:


http://users.telenet.be/D_Young/2007%20Auvergne-2007-07-11_15-18-30_0111.jpg



http://users.telenet.be/D_Young/2007%20Auvergne-2007-07-11_15-20-32_0112.jpg

Set 3:


http://users.telenet.be/D_Young/2007%20Auvergne-2007-07-11_15-21-17_0113.jpg



http://users.telenet.be/D_Young/2007%20Auvergne-2007-07-11_15-22-49_0114.jpg


I was a lot more pleased with the results of my shots of objects from a closer distance up to cottages/streets. Hence my worries if the prime is realy oké at infinity.


Thanks for any input.


Last edited by Bart; 07-21-2007 at 04:45 AM. Reason: replaced embedded images with smaller versions (800x600)
07-20-2007, 03:59 PM   #2
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Hi Bart,
May I suggest that you re-size your photos to 800 by 600 pixels...I have a relatively quick connection but this is taking forever to down load.
cheers
Grant
07-20-2007, 08:41 PM   #3
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Hi, Bart!
I think the shots with the prime lens are
- 1st set = the second
- 2nd set = the first
- 3rd set = the first (it was a little windy during this test!)
If so, you have a nice prime.
Cheers!
07-20-2007, 11:35 PM   #4
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I suggest not to compare at center of pics but more near the edges where usually the difference is largest between a very good prime and a good zoom. I think in all three sets the 1st ones were taken with the prime. Tell me I'm completely wrong

07-21-2007, 05:19 AM   #5
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As suggested, I replaced the embedded images with smaller versions. The links still point to the full sized files. I thought the instruction "[imgwide]" worked differently - sorry.

As for which is which, allow me to wait a little longer to reveal this.

On the other hand, what I really would like to know is whether my prime shows acceptable image quality at infinity. When I view my pictures at screen size or even at 50%, I'm quite pleased with the result - image wise.
At 100% however, I have my doubts. But then again, perhaps I was expecting too much.

I'll just show you some crops from pictures with the prime at 100%, taken from a part of the picture at infinity. These are all at f5 with AV.







Comments, please?
07-21-2007, 06:38 AM   #6
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2, 1, 2, are the best looking shots, I'd say they are the 18x55 lens.
07-21-2007, 07:22 AM   #7
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I would say basically they're all OK at 100%, it's just that at f9 or so the lenses will likely have similar performance, the prime will do much better comparatively at wider apertures. The other factor is that all digital cameras have to use an antialias filter in front of the sensor to get rid of the staircase effect, so a bit of blur at 100% is normal. Sharpening is used to compensate, and Pentax images tend not to be adequately sharpened IMHO for 100% viewing, which is much better than being oversharpened as most other makes seem to do, and if you apply just a bit of sharpening they will come alive. Sharpening is a big subject in itself and as a digital newcomer it's well worth researching the topic if you want to get the best out of digital.
07-21-2007, 03:08 PM   #8
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Hi Bart,
Thanks for that.
I am not a pixel peeper, so my comments are entirely subjective...no science here mate!
Looking at the first two sets of shots, one is definatley softer than the other, to my eye/monitor the 2nd shot in the first set & the 1st shot in the second shot are taken with the Pentax 18-55. I say that purely because of the intensity of the colours, which was the first thing I noticed when my wife bought a DL with this lens, when compared to my DS & sigma 18-125 lens. The difference is exacerbated in low/poor light situations.
I am really not sure with the third set, not even prepared to make a guess there....the 'control' set perhaps?
Look forward to seeing your 'expose`'
Cheers
Grant

07-21-2007, 11:34 PM   #9
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Hi,

Thanks for your input everyone!

These were the lenses used:
Set 1
- Photo 1: FA 31mm
- Photo 2: DA 18-55mm @ 31 mm

Set 2
- Photo 1: FA 31mm
- Photo 2: DA 18-55mm @ 31 mm

Set 3
- Photo 1: DA 18-55mm @ 31 mm
- Photo 2: FA 31mm

The hits and mishits seem to confirm my own findings that there is not that much difference between the two as far as this kind of pictures is concerned - and at f9. When viewed in detail, there is a very significant difference in sharpness at the corners and I personally found the colours of the 31 to be more realistic but then again, that's hard to judge if you didn't see the scene in real life.
My main concern was that I feared something was wrong with the 31 due to the "lack" of difference with the "humble" kit lens. I didn't find that many examples of landscapes with the 31 on the web, mostly in 'small' format and not compared to another lens. Even the test sites, like Photozone.de, didn't have landscapes in their examples.

On the other hand, as I noted before, I'm quite pleased with the result of detail shots with this lens.
Some examples (crops @ 100%):

http://users.telenet.be/D_Young/Crop100/2007%20Auvergne-2007-07-13_11-51-57_0261_crop100.jpg (792 Kb)

http://users.telenet.be/D_Young/Crop100/2007%20Auvergne-2007-07-17_14-31-54_0832_crop100.jpg (1 Mb)


Bart
07-22-2007, 12:45 AM   #10
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I have looked through all the pictures and I must say they are both very good.

In fact, my guess is that if you have not revealed to us which photo is taken by which lens, no one would be able to tell which is using the prime lens in the first place!

Perhaps one can deduce that prime lens is of better quality than the kit lens..but the extra quality is not by a big margin and the results is almost indistinguishable. Hence, in terms of more bangs for the buck, I would say go for the kit lens, instead of the prime lenses, unless money is no objection.

What do others think?
07-22-2007, 02:13 AM   #11
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Bart, I've made a terrible mistake. Shame on me!
So, you have a nice kit lens (me too). I totally agree with Raider, although I never tested/have FA31. Maybe in marginal conditions (very rare in the practice of an amateur), FA is better and deserves money.
Regards!
07-22-2007, 02:37 AM   #12
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And to think that the 18-55mm costs about $75, the 31mm $750.
Ten times as much -- it's a Pentax con
07-22-2007, 04:30 AM   #13
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QuoteOriginally posted by raider Quote
I have looked through all the pictures and I must say they are both very good.

In fact, my guess is that if you have not revealed to us which photo is taken by which lens, no one would be able to tell which is using the prime lens in the first place!

Perhaps one can deduce that prime lens is of better quality than the kit lens..but the extra quality is not by a big margin and the results is almost indistinguishable. Hence, in terms of more bangs for the buck, I would say go for the kit lens, instead of the prime lenses, unless money is no objection.

What do others think?
This thread seems to answer some of the questions I raised in another thread, https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/9809-silk-purse-out-sows-ear.html
The extra money for the better lens pays off in corner sharpness, bokeh, CA, and contrast. Some of these things can be corrected in PP.

The limiteds and some of the better primes can give the image a "feel" that cannot be defined, at least not by me. Up to this point I have been a "Pentax primes only" snob and am now rethinking that position. The difference between these shots is so minimal it is amazing. I don't think it's a bad copy issue. I think this is an accurate display of the subtle differences in the two lenses.

Regards,
07-22-2007, 09:21 AM   #14
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I do not want to contradict myself but I have to say that so far the pictures taken were all on a sunny day (or with sufficient light) and Bart has not taken night pictures or fast action pictures to justify that kit lenses are in fact equal/similar to prime lenses.

While their performance is hardly indistinguisable in good light, I doubt the kit lenses can do as well in dim lighting or in action sports. Neither can the kit lens do portrait bokeh in an easy way. That being said, if one's primary interest is in landscape, I suppose prime lenses are not necessary.

This is also the primary reason I justify to my other half to buy a 50/f1.4 prime lens because i need to shoot good portrait with good bokeh.

Just my opinions. Not sure if others would agree. More feedbacks would be great.
07-22-2007, 12:07 PM   #15
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People,

I may have made a (slight) mistake. It was regkens remark about being able to 'augment' the results in PP that made me realise something: as I said in the original post, I shot RAW. The RAW files were converted however with DxO and DXO has a 'module' for the 18-55 but not for the 31. This means that the pictures with the 18-55 are far more 'corrected' than those with a lens where no 'module' is available for. This got me thinking. So, I used PPL to convert the pictures also.

Here we go:
Set 1
- FA 31
https://www.pentaxforums.com/gallery/index.php?n=2814
- Kit
https://www.pentaxforums.com/gallery/index.php?n=2815

Set 2
- FA 31
https://www.pentaxforums.com/gallery/index.php?n=2816
- Kit
https://www.pentaxforums.com/gallery/index.php?n=2817

Set 2
- Kit
https://www.pentaxforums.com/gallery/index.php?n=2818
- FA 31
https://www.pentaxforums.com/gallery/index.php?n=2819

I've uploaded these examples to the gallery (sorry about mis-using it in this way) and I added links here since this tread is allready slow in loading.
The size is limited to the restrictions of the gallery but I think a more significant difference is allready visible.
I've added some crops @ 100% to allow a detailed view. The fact that the same fragments for 2 of the 31 pictures were bigger than the allowed 1000 b where those of the kit were not, indicates - I think - more detail is present with the 31. I took a smaller fragment for those, in case you are wondering.

Crops:
Set 1
- FA 31
https://www.pentaxforums.com/gallery/index.php?n=2821
- Kit
https://www.pentaxforums.com/gallery/index.php?n=2822

Set 2
- FA 31
https://www.pentaxforums.com/gallery/index.php?n=2823
- Kit
https://www.pentaxforums.com/gallery/index.php?n=2824

Set 3
- Kit
https://www.pentaxforums.com/gallery/index.php?n=2825
- FA 31
https://www.pentaxforums.com/gallery/index.php?n=2827

PS I know that a FA 31 may seem 'over the top' for an amateur but I'm quite moderate regarding my spendings on this hobby/passion: not counting the K10D, my last serious purchase was a tele zoom lens (Vivitar 70-260) in the second half of the 70's.

I did use the 31 quite a lot in low light situations as well - inside buildings & churches - but I didn't compare those with the kit, simply because these pictures would have been next to impossible to achieve with the kit lens unless you are prepared to go beyond ISO 400 or use a tripod - neither of which I'm inclined to do.
FA 31 at f1.8 for 1/8s @ ISO 400:
https://www.pentaxforums.com/gallery/index.php?n=2828
https://www.pentaxforums.com/gallery/index.php?n=2829

I have to admit that I didn't compare any close-up shots either, simply because I was convinced there would be no match - perhaps my next 'assignment' & surprise?

My main lens up till now was the takumar 50mm 1.4. So, I got hooked on wide apertures. This, of course, gives the nice shallow dof and with some lenses, the unbeatable bokeh.

Action shots, on the other hand, are not my cup of tea - I guess I'm way to slow myself.
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