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10-14-2018, 08:41 AM   #1
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DA 35 Significantly Overexposes Shots

Hi.

Short: Is there a defect with my new DA 35/f2.4 if it consistently overexposes?

I received a new DA 35/f2.4 for my K-r yesterday to supplement my kit lens after reading this thread. The problem is the DA 35 leans greatly towards over exposing my shots. I've attached some test shots on manual (iso 800, f5.6, 1/60, center-weighted metering). The bright ones are from the DA35 and the darker ones from my DA18-55. I tried to focus on the same object and the shots were taken right after another as fast as I could swap the lenses so there wasn't significant lighting changes in the room. Leaving aside the question of whether these are the right settings for the best picture (the DA 18-55 shots do look closer to what I saw, but was itself a bit brighter in the corner of the room shot), I'd expect similar results (for good or bad).

The only way I can get acceptable shots with the DA 35 are to really up the shutter speed and/or lower the ISO. Av mode is practically unusable without significant underexposing via -2 to -3 EV. I know the pros among you will probably say "go full manual" and yeah that's always a thing, but my DAL 18-55 and DA 55-300 both respond very similarly to any given setting. This DA 35 is bonkers relative to the settings I expect to use and have learned over about 8 years of using this camera.

I've never used a prime lens. It could be me. I expected some differences, but this seems very drastic from my zooms. Defect or do I need to approach this with a completely new mental model of aperture, shutter, ISO for this one lens?

Attached Images
View Picture EXIF
PENTAX K-r  Photo 
View Picture EXIF
PENTAX K-r  Photo 
View Picture EXIF
PENTAX K-r  Photo 
View Picture EXIF
PENTAX K-r  Photo 

Last edited by dieselpunk; 10-14-2018 at 08:44 AM. Reason: Added context to shots taken.
10-14-2018, 09:32 AM - 1 Like   #2
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Take the lens off camera. Operate the aperture level manually does it open and close rapidly or is it really sluggish. Does it look stopped down to a small hole when off camera or is it a larger opening?
10-14-2018, 09:35 AM   #3
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Two things...

1) When you say 'do I need to approach this with a completely new mental model of aperture, shutter, ISO for this one lens' - does this mean you are using manual mode and doing things by the seat of your pants? Not a problem exactly, but if so that rules out Auto Exposure being involved.

2) Does the aperture lever move easily and smoothly on the lens?
10-14-2018, 09:50 AM   #4
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I suspect the aperture is not closing down swiftly enough.

btw the exif shows you were using Matrix metering

10-14-2018, 10:02 AM   #5
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QuoteOriginally posted by UncleVanya Quote
Take the lens off camera. Operate the aperture level manually does it open and close rapidly or is it really sluggish. Does it look stopped down to a small hole when off camera or is it a larger opening?
The lever moves easily and smoothly (no more/less smooth than my other lenses). I'd say at the largest f (22?) it's about 1mm open.

One thing though: on my DA 18-55 and DA 55-300 the lever wants to return the aperture to the size before I touched it (i.e. the lever springs back to the position before I moved it). On the DA 35 it just stays where I leave it. Is this a problem or the difference between zoom and prime?

QuoteOriginally posted by victormeldrew Quote
Two things...

1) When you say 'do I need to approach this with a completely new mental model of aperture, shutter, ISO for this one lens' - does this mean you are using manual mode and doing things by the seat of your pants? Not a problem exactly, but if so that rules out Auto Exposure being involved.
I usually haven't use manual mode with my other lenses. For these test shots I was using manual to control all settings between the two lenses.

More generally, I meant I've been used to looking at a certain scene and thinking, "I'll need 1600 ISO to get close to 1/50 for a proper exposure" if I'm using TV. Or if using Av I'll set something like f5.6 and ISO 800 and expect that the shutter will get me to a proper exposure. Right now Av always ends up over exposing - sometimes drastically so.

QuoteOriginally posted by pschlute Quote
I suspect the aperture is not closing down swiftly enough.
btw the exif shows you were using Matrix metering
Is matrix a bad thing?

I'll admit that I haven't had to think about metering much in the past. I did try many other shots with different metering programs with varying levels of differentiation. Should I have to make radical adjustments to my metering strategy (or non-strategy ) to use this prime? I also took the end table picture because the lighting wasn't challenging (unlike the window shot). All things being equal there's a lot more light coming in.

Right now I'm wondering if I should RMA this to get a replacement or if this is considered normal. Thanks!

Last edited by dieselpunk; 10-14-2018 at 10:06 AM. Reason: Clarified aperture lever response
10-14-2018, 10:25 AM - 2 Likes   #6
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In the table photos, the second one looks much better to me, the first is significantly underexposed. And while the last one is overexposed, the first one looks quite a bit underexposed to me. But it's a dark corner with sunny windows in the background, the contrast is very high to expect even nice exposure straight out of camera.

Here are two tests you could perform. For both, mount the camera on a tripod, or if you don't have one, set it on a table. Just make sure that the scene stays as much the same as possible. The lighting in your first shot is roughly stable since it's artificial, but the framing changed. Sunlight is only reliable if the cloud cover doesn't change during your tests. Also make sure the ISO/shutter are within the range of obtaining a good exposure (nothing red/flashing).

To test for aperture movement issues (aside from looking at it as you take photos):
1) switch to Av, take a photo at f2.4 (the widest); this won't require the aperture to move at all, and should be exposed correctly
2) stop down to f8, and check that the two histograms look similar

If the aperture lever is moving fine, I'd try:
1) Mount the kit lens (18-55), set the camera to P
2) Take a photo, write down the exposure parameters (shutter, aperture, iso)
3) Mount the DA 35, switch to M mode, and set the same exposure parameters; the photo with the prime may look slightly brighter because it's a lens with fewer elements, so it loses less light with internal reflections assuming the coatings are similar. But the difference should be barely noticeable, nothing dramatic.

About metering:
Matrix metering is usually better balanced overall unless you need something very specific with spot metering. Center metering may be more familiar to users of old cameras, and it's the only choice with manual lenses, but it's less accurate than matrix in difficult light (your second example). Manual exposure for the sake of it is certainly not a "pro" thing, whatever that means. M has its purposes but also drawbacks, if you're going to use it, guessing exposure is not that easy, and it's better to pay close attention to what the meter says.

---------- Post added 10-14-18 at 01:36 PM ----------

QuoteOriginally posted by dieselpunk Quote
On the DA 35 it just stays where I leave it. Is this a problem or the difference between zoom and prime?
Yes, that is a problem, they should be operating the same. The whole aperture mechanism relies on the fact that the lever has a spring to close it as far as the camera will let it go. I only noticed this point you made after typing my long response above

Last edited by aaacb; 10-14-2018 at 10:37 AM.
10-14-2018, 10:53 AM   #7
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I have a DA 35mm 2.4. Works fine on Pentax K50, Pentax K3 and Pentax K1 in both full frame and crop modes. You may have a defect.
10-14-2018, 11:03 AM   #8
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QuoteOriginally posted by dieselpunk Quote
One thing though: on my DA 18-55 and DA 55-300 the lever wants to return the aperture to the size before I touched it (i.e. the lever springs back to the position before I moved it). On the DA 35 it just stays where I leave it. Is this a problem or the difference between zoom and prime?
This is called a broken lens. Return it for a replacement

10-14-2018, 11:16 AM   #9
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QuoteOriginally posted by dieselpunk Quote
One thing though: on my DA 18-55 and DA 55-300 the lever wants to return the aperture to the size before I touched it (i.e. the lever springs back to the position before I moved it). On the DA 35 it just stays where I leave it. Is this a problem or the difference between zoom and prime?
This is most certainly not a desirable feature. This calls for an RMA asap.
10-14-2018, 11:17 AM - 1 Like   #10
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Agree that my DA 18-55 has always been on the dark side with rather mediocre contrast outside of brighter lighting.
Thanks for the set up and testing tips. Although it looks like my problem is mechanical, that's good insight about the histogram. Learning so many interesting things here.

QuoteOriginally posted by aaacb Quote
In the table photos, the second one looks much better to me, the first is significantly underexposed. And while the last one is overexposed, the first one looks quite a bit underexposed to me. But it's a dark corner with sunny windows in the background, the contrast is very high to expect even nice exposure straight out of camera.



---------- Post added 10-14-18 at 01:36 PM ----------

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Yes, that is a problem, they should be operating the same. The whole aperture mechanism relies on the fact that the lever has a spring to close it as far as the camera will let it go. I only noticed this point you made after typing my long response above
And I only thought to test the lever on my existing lenses on a hunch otherwise I would have scratched my head for another few days I'm sure. I'm surprised with a defect this large it worked at all.

Ok, mailing this one back then.
Thanks for the help folks!
10-14-2018, 11:40 AM - 1 Like   #11
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The aperture blades have to snap closed when the lever is released. When the lens is mounted, the lever keeps the lens wide open for a bright viewfinder and focusing. To take the shot, the camera moves its aperture arm to the f stop you choose to shoot at, before opening the shutter. The spring-loaded lever in the lens is supposed to follow along, so the blades can move into the correct position. All that should happen as quickly as possible - anything longer than a tenth of a second is too long.

QuoteOriginally posted by dieselpunk Quote
Is matrix a bad thing?
No. Metering is sort of like a companion's advice. You have three companions, matrix, center-weighted and spot. No one is right all the time. Each has different biases. The K-r is I think the last camera with 16-segment metering, so there's room for it to be better. Matrix is also trying to guess what kind of picture you want and tip its results to that type of photo. You have to listen to the advice and then decide if it's good enough. You seem to already know how matrix will advise you, so more advice won't really help. We'd all like perfect advice, but it's not quite there yet.

Spot is weird, because he only cares about one point in the center, and the advice is just for that spot.
10-14-2018, 11:48 AM   #12
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Spring is likely disconnected. Return is the right option.
10-14-2018, 05:37 PM   #13
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Doesn't matter whether the photo is over-exposed or under- they should be the same from each lens since the ISO, aperture setting, and shutter speeds are the same. I agree, the lens is defective, and as others have said, send it back for replacement.
10-17-2018, 07:16 PM   #14
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Got my replacement DA35 and things make so much more sense now! haha

Did some quick test shots this evening and I can already see that it's got superior image sharpness to the kit lens.
Looking forward to shooting with it this weekend. Thanks again for the help.
10-17-2018, 09:00 PM - 1 Like   #15
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Glad to see the problem is resolved. Happy shooting- it is a fine lens, capable of delivering excellent images, and a great value!
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