Relationship between lens sharpness & sensor size.


Pikaholic

Link Posted 25/01/2012 - 21:05
I have recently bought the Pentax DA 35mm 2.4 AL lens that John Riley reviewed. I am wondering if the 6 megapixel sensor of my camera can do full justice to the sharpness of this lens. The few shots that I have taken do not appear much sharper than the kit lens but I haven't been able to test it in bright conditions. I don't how the high resolution of the lens is recorded in terms of pixels. Any comments please.
Old hand, slow fingers.

Pentaxophile

Link Posted 25/01/2012 - 21:21
The problem is, the kit lens is respectably sharp stopped down, and 35mm is its sweet spot! You're probably right that any difference would be more pronounced on a higher resolution sensor. However I don't buy primes primarily for extra sharpness - wider *usable* maximum apertures, small size and nice rendering / bokeh are the things I am looking for.
[link=https://500px.com/will_brealey/[/link]

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Opethian

Link Posted 25/01/2012 - 22:27
I've found the DA 35 2.4 AL to focus faster, and to have sharper corners (surreal even) than the kit lens. I also like how small it is, and very light. Certainly a good walk-around lens that makes you think for the shots you want to take, in the process coming up with something creative.

Twitter | Someone said time-lapse?
Pentax K5 | Samsung N9005 | DA 18-55 WR | DA 35 2.4 | DA 50 1.8
Tamron 10-24 SP | Tamron 90 2.8 Macro | Tamron 70-300 Macro
Samyang 85 1.4 ...and a few other manual lenses older than me.

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TheVicar

Link Posted 26/01/2012 - 20:18
Pentaxophile wrote:
The problem is, the kit lens is respectably sharp stopped down, and 35mm is its sweet spot! You're probably right that any difference would be more pronounced on a higher resolution sensor. However I don't buy primes primarily for extra sharpness - wider *usable* maximum apertures, small size and nice rendering / bokeh are the things I am looking for.

Pikaholic

I agree with everything Pentaxophile says, and if you are comparing shots stopped down at say f8, you are not going to see much improvement with the prime lens. Best to compare them at f4.5 which is wide open for the zoom, any superior sharpness of the DAL 35 will be maximised in this comparison. some people suggest a picture of a brick wall to try this test.

As you go wider than f4.5 with your new lens, it will be less sharp (bear in mind it is something you can't do at all with the kit zoom), but reduced depth of field gives you the opportunity for nice bokeh

Sadly, I found that both my DAL 35s were slightly less sharp than my kit lens and Tamron 18-200 at f8, with the lack of sharpness increasing at f4.5, and they were unusable at f2.4 so they went back

I hope when you compare at f4.5 you see a bigger improvement than you have seen so far, and get years of pleasure from your new lens

Peter
ist*DL2, 18-55Mk1, DFA 100 f2.8 Macro, Samsung GX-10, 10-17,18-55,50-200, Sigma 10-20,100-300, 150-500 Tamron 18-200, Jessops 360AFDP
ME Super, MX, 2No. 50mm f1.7, MZ-10, 28-70 f4, 28mm f2.8, Samyang 500 & 800 f8 mirrors, Vivitar 2x TC, K-01, K-30

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Algernon

Link Posted 26/01/2012 - 20:57
Your results are probably reaching the limit for the 6M sensor.

Both lenses are top notch anyway and my copy of the 35mm f/2.4
is slighty softer wide open, but pin sharp from f2.8 upwards
on a K-5 at 100ISO.

I would expect the kit lens to be slightly softer than the 35mm
in the corners and hardly anything between the two in the centres,
but I suspect that these lenses are probably sharper than the
K-5 sensor.
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi

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Pikaholic

Link Posted 26/01/2012 - 21:16
Thank you each for your helpful comments. I have also been reading the thread "NOT Happy with my DA 35 f2.4 lens" and the problems that people have experienced. I think if I had known all this I would not have bought the lens but I must take some more shots following your advice and post some for you to comment on, if that's ok. I bought mine from Jessops so it should not be duff, I hope.

Thanks again, Bob
Old hand, slow fingers.

Pentaxophile

Link Posted 26/01/2012 - 21:27
If your lens is genuinely 'duff' you should be able to take it back to Jessops, no bother. Stick at it for a bit though. Try it for some wide aperture portraits for example. If it's missing focus, try manual or live view focusing... If that gets you a better result (neither are affected by front or back focus issues), it may be that the lens is back or front focusing in AF.
[link=https://500px.com/will_brealey/[/link]

Pikaholic

Link Posted 27/01/2012 - 16:43
I've been out today taking some test shots that I will now include. The images ..916 and 926 are from the 35 f2.4 lens and ..917 and 931 from the kit lens. The full image first & then the 100% crops.
Help! I can't work out how to add the image to this place marker. Sorry.
Old hand, slow fingers.

JAK

Link Posted 27/01/2012 - 16:53
Pikaholic wrote:
I can't work out how to add the image to this place marker. Sorry.

Some instructions here: link
John K

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Pikaholic

Link Posted 27/01/2012 - 20:15
Thanks Jak, I have found the site difficult to use for lack of instructions.
I don't have access to a web depository and the Gallery isn't intended for this purpose so I shall not be able to show you the test images.
The new 35mm lens is sharper in the corners and does show better bokeh but for my requirements the differences are too small for me to justify keeping this lens. I can understand that for you 'Pro's' its important to have the best lens for the job but my photography is not that critical. The various 'work-arounds', such as live view and focus adjustment, you mention, are not available on the humble K100D.
It seems that modern Pentax lenses are designed for more recent models so I will look for a secondhand 'A' lens.
It's been an interesting learning curve and I thank you all for your helpful comments.
Kind regards, Bob
Old hand, slow fingers.
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