[ziscwg]

I too have this lens and like it a lot. Shooting action shots further away, the DOF is better. Up close, it's inches like in the pic below (at f2.5). The dog is small, maybe 9 lbs soaking wet.



And this one shot further away f2.5.

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Last edited by ziscwg; 04-28-2014 at 12:48 PM.

[jaikumarr18]

Am still getting mixed results from the lens. Not sure if this would be good for wedding photography though.

-Jai-

[elpolodiablo]

Using large aperture lens got a learning curve that you can't avoid, I know what you mean about getting mix result with your DA 50 1.8 but with some practice I am sure you will get the hang of it, I have a K-30 myself and I've been using my FA50 f1.4 and FA 31 f1.8 in low light, Yes you can reach the camera's AF limitation in low light, but it can achieve a lot before giving up.

All these shots were taken with K-30

FA 50 f1.4 for head shot portrait in good light, @F4

[


FA 50 f1.4 again, this time against strong light. @f2.8




2 shots with FA 31 f1.8 in low light. both wide open @f1.8








If I am honest I have more trouble focusing in poor light with my K-5 than K-30.

Another thing I think I should mention is that I also have a DA 18-135WR, this lens is not designed for manual focus, especially with the lack of distance scale, manual focus with the stock focus screen is just no worth the trouble. On the other hand, K-30 have a neat feature called focus peaking that helps you manual focus, on your DA 18-135 you have quick shift focus so you can manual focus at any time, but for your DA 50 1.8 you have to turn the AF switch to MF or else you will damage your focus motor when turning the focus ring. I love Focus Peaking, it just makes all my fast lens so much more usable. Give it a go, maybe that will solve your low light focusing issue

[jaikumarr18]

Thanks elpolodiablo. Those are some great shots. I was planning to buy 50 F1.4 but got 50 f1.8 for a very good price (AU$150 including delivery) and hence took that one. Am still not used to the focus peeking and hence could not produce some good results.

[pjm1]

If it's any consolation, I thought my 50mm (the same version) was unsharp for a while. I actually preferred to use my DA* zoom for 50mm shots as it "felt" sharper. It wasn't, of course, but I was getting better results. There were a few reasons (some have been covered already):

1. I was using a very shallow DOF and just couldn't get all (or the right parts) of the subject in focus
2. My focusing technique (even with AF) wasn't great at that point
3. I was occasionally using it on too slow a shutter speed - the blurring I was getting was sometimes a result of motion rather than lack of focus
4. I was using it at a wide aperture (1.8) which is when the lens is at its softest, especially away from the very centre
5. In low light AF is just less reliable
6. It's a light, fast lens so mentally you're expecting it to be more of a point & shoot, whereas it's actually less of one... this is the reason I had better results from my DA* as I slowed down, had to brace against the weight of the lens more and basically just set a better shot

Well, they were the reasons my shooting suffered - you may well be different. However, I now love the lens. I almost always use it in its sweet spot of 2.8-8.0, mostly with a pretty low ISO but, critically, a decently fast shutter speed (especially for fast moving objects). I also use selective AF point focusing exclusively, rather than shutter press focusing or focus & recompose. I still get a fair few misses, especially with the kids but most shots are now solid, focus-wise.

The sharpness of the lens is excellent, within its sweet spot and pretty much across the frame, too. You can check for front or back focusing (I did out of paranoia and my lenses were all spot on).

Alternatively, you may just have a bad copy - but I'd expect that to be the least likely scenario, TBH.

Here is a quick snapshot I took this evening with the lens in poor indoor light at f4. ISO was 800 and I had to drop shutter speed to 1/45... far from ideal conditions. I focused on her left eye and lashes, which are in focus pretty well (but not perfectly). Look at her right eyelashes though (i.e. those on our left just to be clear!) and they're OOF. Which shows how narrow the DOF is even at f4...



The full-size original is here if you want to pixel peep: https://farm8.staticflickr.com/7371/14075443995_c69a4bdb53_o.jpg

[jaikumarr18]

@pjm1, thank you for your tips. It would really help me in improving my skills with the lens. I have sent my camera for service currently and would take another 3 to 4 weeks to get it back. Will keep you posted. Also, the picture was just amazing

[pjm1]

One other thought / recall I've just had: the difference in sharpness with this lens between using natural light and flash was night and day. The speed of the flash light does freeze action especially if it is providing the majority of the light... so this lends further support to the lack of sharpness being in part a slower shutter speed.

I realise you've sent your camera (edit: re-read!) away now but you might want to try some flash shots when you get it back - even using the pop up flash as you're looking to see whether it helps cure the problem at this stage.

IMO the photo I posted is technically not that good (slightly front-focused, I think and I won't start with the lighting) - it definitely falls into the "snapshot" category but it served a purpose of highlighting the shallow DOF even at F8, let along F1.8 (I'm also biased that my model is cute!) The other thing to remember is the further away from the subject you are (i.e. the further the focus point) the wider the DOF. If you're doing really tightly cropped portraits as in my example, the DOF will be a lot harder to handle than if you're shooting a contextual shot. This might be why your handbag shot was bang on?

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Last edited by pjm1; 05-01-2014 at 12:35 AM.

[jaikumarr18]

One other thought / recall I've just had: the difference in sharpness with this lens between using natural light and flash was night and day. The speed of the flash light does freeze action especially if it is providing the majority of the light... so this lends further support to the lack of sharpness being in part a slower shutter speed.

I realise you've sent your camera (edit: re-read!) away now but you might want to try some flash shots when you get it back - even using the pop up flash as you're looking to see whether it helps cure the problem at this stage.

IMO the photo I posted is technically not that good (slightly front-focused, I think and I won't start with the lighting) - it definitely falls into the "snapshot" category but it served a purpose of highlighting the shallow DOF even at F8, let along F1.8 (I'm also biased that my model is cute!) The other thing to remember is the further away from the subject you are (i.e. the further the focus point) the wider the DOF. If you're doing really tightly cropped portraits as in my example, the DOF will be a lot harder to handle than if you're shooting a contextual shot. This might be why your handbag shot was bang on?

Thanks pjm. That actually makes a lot of sense. Since when I tried with F8 on group shot and only one person comes into focus. I cannot go higher than that due to poor lighting and I always try to avoid built in flash since it takes out the colour. If that's the case, I might need a powerful external flash to compensate for higher F stops. As you said, your model is very cute

---------- Post added 05-01-14 at 05:37 PM ----------

Also I still don't get the exposure compensation purpose. As per my understanding, exposure is combination of ISO, Shutter, Aperture and the lighting condition at that given point of time. So if am adjusting exposure compensation, it actually adjusts those values automatically? Hope you can clear my doubt

[pjm1]

Thanks pjm. That actually makes a lot of sense. Since when I tried with F8 on group shot and only one person comes into focus. I cannot go higher than that due to poor lighting and I always try to avoid built in flash since it takes out the colour. If that's the case, I might need a powerful external flash to compensate for higher F stops. As you said, your model is very cute

---------- Post added 05-01-14 at 05:37 PM ----------

Also I still don't get the exposure compensation purpose. As per my understanding, exposure is combination of ISO, Shutter, Aperture and the lighting condition at that given point of time. So if am adjusting exposure compensation, it actually adjusts those values automatically? Hope you can clear my doubt

jaikumarr18, first of all I need to apologise as there was an important typo in my last reply which isn't going to help de-confuse! My snapshot was taken at F4, not F8. Not sure where the F8 came from when I typed it! At F8 (two stops higher) I would have been able to achieve a fair bit more DOF, although my ISO would have had to go up by a factor of four (x2 per stop), i.e. 3200 to achieve the same exposure. By the way, 3200 is fine to use if you need to - ISO noise is generally a lot easier to clean up than curing or covering up for focus/sharpness issues. Don't be afraid to pump up the ISO!

Re: your point on group shots - they're difficult for a host of reasons and I'm not best placed to advise on getting them right. One thing I will say is that another factor in depth of field is that it's relative in terms of the size of an object in your frame. If something fills your frame, it's going to be harder to get everything in focus (because the front-back distance will be proportionally bigger) than if it is smaller in your frame. It's hard to explain without delving into maths, but if you fill your frame with a three dimensional image, you'll need a very high f/stop to get it all in focus. If, however, you zoom out or step back and have the same object only filling half of your frame, you should be able to get it all into focus with a slightly wider aperture, i.e. a smaller f/stop. Sorry, I know I'm throwing more variables at you but in terms of sharpness, if you're filling your frames then it's always going to be harder to get it all into focus (unless they're very flat objects).

Exposure compensation is a big subject, but let's start with the "exposure triangle". The exposure of an image is basically the light level of that image or the amount of light which the camera allows into the frame*. This is measured in Exposure Value (EV) "stops". Confusingly, EV is a "power of two" scale for everything except f-number (aperture). This means your EV increases by 1 when you double the shutter duration. If you double your ISO, then your camera's sensitivity to light will be increased by one stop, which means there's a very simple trade off between shutter duration and ISO: double one, halve the other (keeping the aperture constant). Aperture is even more complicated because the aperture is a measure of the diameter (or radius or circumference) of the aperture of the lens (it's actually an inverse ratio, but the important thing is it's related to the diameter of the opening). Since light comes through the lens along two dimensions, the amount of light entering the camera is going to be (inversely) proportional to the SQUARE of the aperture (f-stop number). This means halving the "f-stop number", say from f/8 to f/4 (which doubles the physical diameter of the aperture) will increase the EV by four. I did warn you it is confusing! What this means is the relationship between ISO, shutter duration and f-stop is that doubling ISO has the same effect on the recorded image light level as keeping the shutter open for twice as long or by decreasing the f-stop by 1.4 (the square root of 2: decreasing f-stop by 1.4 will increase the area of the aperture "hole" by a factor of 1.4 x 1.4 = 2). In other words, to keep an image light level constant, if you double the ISO, you can either halve the shutter duration or increase the f-stop number by 1.4 (which makes the hole smaller). We generally refer to DIFFERENCES in exposure value between scenes, images etc. and normally take into account sensitivity, i.e. ISO. This means if we're saying the image is underexposed by -2 EV, we need to add any combination of reduced shutter duration, increased ISO or decreased f-stop totalling 2 stops. This could mean doubling the shutter duration AND doubling the ISO, or doubling the shutter duration AND increasing f-stop by 1.4, or simply increasing f-stop by 2 on its own. Note that I've tried to be careful referring to the aperture in terms of "f stop" rather than aperture size: because even more confusingly, as one goes up, the other actually goes down! I've also been careful about referring to shutter DURATION - 2secs duration is obviously double 1sec, but more importantly, 1/2 sec duration is double 1/4 sec duration. People will refer to shutter speed, where the inverse relationship is true, but I thought that would just be more confusing...

* it's also the camera's "response" to the light level since ISO is, in digital cameras, an adjustment to the camera's sensitivity to light. Higher ISO means higher sensitivity, so you get the same "image response" to lower levels of light as you up the ISO.

Re: compensation:

1. Your camera "meters" the light. It uses (normally) a clever zoning system to analyse the scene and work out what the "right" exposure should be. Part of this is attempting to make the average tone a mid grey (it's more complex than this, but for our purposes let's keep it simple). When you use your camera on any mode except manual, the meter will be making exposure decisions for you. Without any exposure compensation, you're basically saying to your camera - over to you.
2. Its metering isn't perfect. If you're taking a shot of something which is very white (such as snow), it will not understand that the scene *should* be white. Instead, it will try to make it mid grey. This means it will be pushing the exposure lower than it should and you'll end up with a classic problem in "out of camera" photography: grey snow.
3. Conversely, if you're snapping a scene which is very, very dark, such as a picture of a full moon on a black sky, it will attempt to push the exposure UP, to make the black sky grey (which it probably won't be able to achieve because of total light levels) but it will blow out the highlights in the moon.
4. In scenes of high dynamic range (where the lights are bright and the darks are very dark), the camera won't be able to capture the full range, so you'll end up with it making a compromise of some sort and probably blowing out highlights and losing detail in the darks.

In examples 2-4, you need exposure compensation for different reasons. In 2 you need to adjust for the camera's false assumption: that the average tone should be mid grey. You need to tell it to push the exposure higher because the average tone should be nearly white. This means your exposure comp should be + (perhaps +1 or even +2). In 3, you have the opposite problem compounded by the fact you have a blown highlight - two potential problems to correct: you want a black black sky (so reduce exposure) and you need to pull down the exposure anyway to avoid the blown highlight - this means a negative exposure comp of -1 or -2 (say). In 4, there isn't a perfect solution with a single exposure - you're going to need to decide what you want to lose (or take multiple exposures at different settings on a tripod and blend or HDR). In most cases, it is recommended that you "expose for highlights" which means dial down your exposure compensation to -1, -2 or whatever to make sure the lightest parts of the scene are captured without blowing out. You then have some work to do in post to rebalance the image without losing the highlights again!

Sorry that's perhaps a bit confusing, but exposure compensation can be confusing! The simplest way to think about it is a rule of thumb: for naturally bright scenes, set your compensation to a + number. For naturally dark scenes, set it to a - number. If you have high contrast in a scene, "chimp" by looking at the LCD review and ensuring you have highlight and shadow warnings switched on, adjust your compensation (usually down) and retake until the highlight warnings disappear.

I won't get in to manual mode as that's more confusing still (but very important especially if you're venturing into using flash). However, the camera still meters for you and reports the "exposure value" but you make all the decisions on what exposure to actually choose. I'll leave that there.

Hope this helps! I will need to re-read to check whether I've introduced more typos again!

[jaikumarr18]

Thanks a ton pjm1. Really appreciate your time for providing in-depth details on exposure. I now clearly understand the importance of the exposure compensation. I never used that setting before and I believe going forward I might use it extensively. My next target is to acquire a good flash gun and hence posted a separate thread regarding the same. Once again, thank you for helping me out.

[pjm1]

No worries, but don't necessarily rush to get the next bit of kit. (He says, having spent the last three months rushing around buying kit!)

There is a balance between improving and developing skills quickly (and maintaining your rate of learning by moving on from one thing to the next when you're proficient at it) and spreading your time too thinly and doing too many things too quickly. Exposure is really important and the technical bedrock of photography IMO. Spend time understanding that and developing your own understanding of DOF, acceptable shutter speeds, ISO noise etc.

I am still at the early stages of learning all this stuff, so speak first-hand. I've also bought too much gear too quickly. It does mean I have, to hand, kit should I want to take a quick flash photo or a range of lenses, but it also means I don't know as much about each of them as I could, had I spent longer with each item on its own.

Just my 2p... feel free to ignore!

[jaikumarr18]

Thanks pjm. I completely agree on not rushing to get lot of kits but again my heart pounds when ever I see any kit for good price . I currently own K30 with 18-135mm WR lens and 50mm F1.8 prime and I believe that would suit my purpose for now. The reason I wanted flash is, I suffered during my friends birthday party with lack of light and K30 really could not cope up. An external flash would have really helped. But again, I used 18-135mm lens since I did not have 50mm lens at that time. I bought these books and it really helps to understand different techniques in photography.
1) Tony Northrup's DSLR Book: How to Create Stunning Digital Photography
2) Bryan Peterson : Understanding Exposure

So taking time to improve and develop skills. Am really happy to be a fellow pentaxian since am getting lot of help through this forum

[richandfleur]

Hi,

Just thought I'd comment here as moving to the prime lenses can be a bit of a challenge and I thought I'd throw a few more thoughts in the mix...

First up is the desire to shoot everything with the aperture wide open because it can. In general any lens is sharper a few stops up from fully open.
Just because it can, doesn't mean your photo needs you to. If you have two subjects at different depths in your photo, you still have to pick an aperture that produces a depth of field wide enough to capture both people in focus.
The prime will be sharper than your kit lens at say f5.6 for example, so you still benefit from using the prime, even when used at apertures that both the prime and the kit lens can use.

Second is the focus on faces. Basically for a portrait to work you need the eyes in focus, but often the autofocus picks up on the forehead, which is further forward than the eyes.
So, whilst your lens is autofocus capable, you way want to override this in favour of manual focus for some shots.
Focus Peaking, or a bright pentaprism optical viewfinder can help with nailing this focus point.
Or pick an aperture that will get both in focus.

And as others have mentioned, too slow a shutter speed will create motion blur. Shake reduction can help, but don't be afraid to push up your ISO too achieve a faster shutter speed.
Noise can be worked on a bit, but blurred photos will always be just that.
Also take a step back to see if you can introduce more light yourself, by opening some curtains, turning on some lights, adding a flash etc.

Personally I'm sold on the flexibility of primes (normally a word people use with zooms).
You get sharp images, and you get the option of going down to low aperture values. And you can zoom with your feet also ;-)
I'm not sure how well the face detection works on Pentax's live view at such narrow depth of fields, as in I'm not sure where it tries to target the focus.

[jaikumarr18]

thanks richandfleur. Am not sure how capable is DA50F1.8 in terms of manual focusing. I need to try and check it out.

[pjm1]

thanks richandfleur. Am not sure how capable is DA50F1.8 in terms of manual focusing. I need to try and check it out.

For me, I'm the limiting factor in manual focusing rather than the lens... I'm seriously considering both a viewfinder magnifier and a Canon ee-S focus screen to help resolve this - but that's drifting off topic now.