[DrMindbender]

So as the giftmas season starts to transition to the cold dark of winter, I'm starting to look at a supplement/replacement to my Pentax-K 50mm on my K5. The problem I have with it is that when shooting in low light conditions at F1.4, point light sources turn into horrendous blobs of light. As a result, I've been stuck at F2 or narrower. Now, my impression is that this was something that wasn't fixed with the M, A, F, & FA lenses and I'd prefer to avoid doing post work to fix it. As a result, and considering the cost of digital 50/55mm 1.4's, I'm looking at the DA 50mm F1.8.

The thing is though, I haven't seen a head-to-head comparison between the two lenses. So I'm not sure if the DA will be able to at least match my K at F2. So does anyone with experience with both lenses in low light conditions feel that the DA is an improvement over the K or should I hold out for a digital 50/55mm 1.4?

[aslyfox]

the closest I can find is this:

Pentax 50mm Prime Lens Shootout
Introduction

[ the SMC Pentax FA 50mm F1.4, D FA 50mm F2.8 Macro, and DA 50mm F1.8. ]

Read more at: Pentax 50mm Prime Lens Shootout Review - Introduction | PentaxForums.com Reviews

you could compare the

Pentax 50mm Prime Lens Shootout
Lens Specifications

Pentax 50mm Prime Lens Shootout Review - Lens Specifications | PentaxForums.com Reviews

with the lens specifications of the Pentax-K 50mm F1.4

https://www.pentaxforums.com/lensreviews/SMC-Pentax-K-50mm-F1.4-Lens.html

with those tested

[BigMackCam]

The DA50 f/1.8 is a great little lens, but it won't work miracles. It's sharp in the centre - even wide open - but quickly softens (very quickly wide open) away from the centre at wider apertures. It's a good little lens, and I happen to think it's a bargain for the price, but it will depend on your use case and subject positioning within the frame as to whether it will work well for you.

As an aside... Whilst I don't disagree that fast aperture lenses can be useful in low light, a fast aperture is only useful if it offers something close to the depth of field that we want creatively. What we ideally need is a lens that performs well at the aperture settings for our intended depth of field, and a camera that can record the resulting images without too much noise. The K-5 is an excellent camera (I still have mine), and it performs very well at mid-high ISO settings (especially considering its age)... but it has long since been overtaken in that department by the K-70 and, even more so, the KP. Either of those cameras - new or used - might be something to consider instead of (or in addition to) a new lens...

[pepperberry farm]

try either a Sigma 50/1.4 EX DG or a Pentax 55/1.4 SDM - I have the Sigma and it's impressive....

[dms]

Lenstip has a review of the DA 50mm f/1.8 and the comma is fairly pronounced, so likely not a good choice.
BTW they also tested the FA 50m f/1.4 so you can compare their comma results.

[DrMindbender]

The DA50 f/1.8 is a great little lens, but it won't work miracles. It's sharp in the centre - even wide open - but quickly softens (very quickly wide open) away from the centre at wider apertures. It's a good little lens, and I happen to think it's a bargain for the price, but it will depend on your use case and subject positioning within the frame as to whether it will work well for you.

As an aside... Whilst I don't disagree that fast aperture lenses can be useful in low light, a fast aperture is only useful if it offers something close to the depth of field that we want creatively. What we ideally need is a lens that performs well at the aperture settings for our intended depth of field, and a camera that can record the resulting images without too much noise. The K-5 is an excellent camera (I still have mine), and it performs very well at mid-high ISO settings (especially considering its age)... but it has long since been overtaken in that department by the K-70 and, even more so, the KP. Either of those cameras - new or used - might be something to consider instead of (or in addition to) a new lens...

In my case, it's for night shots taken beyond 10 meters (infinity). So depth of field is less of a concern.


Basically, I'm looking to improve the quality of images like this:



In a perfect world, the lens I'm looking for would improve sharpness and allow me to open the lens wide enough to drop the ISO to 1600 from 3200 to reduce the graininess.While I doubt that the difference between 1.8 and 2 would be enough to drop the ISO, I'm ultimately hoping that 30+ years of improvements in lens making technology would make a difference with sharpness even if I'm still shooting at F2. But, ultimately, I know that there is the possibility that I won't do any better no matter how much money I throw at fast 50's and I'll need to move on to my next Pentax body.


In the short term, I'm going to see what the A 1.7 can pull off.

[Merv-O]

The DA50 f/1.8 is a great little lens, but it won't work miracles. It's sharp in the centre - even wide open - but quickly softens (very quickly wide open) away from the centre at wider apertures. It's a good little lens, and I happen to think it's a bargain for the price, but it will depend on your use case and subject positioning within the frame as to whether it will work well for you.

As an aside... Whilst I don't disagree that fast aperture lenses can be useful in low light, a fast aperture is only useful if it offers something close to the depth of field that we want creatively. What we ideally need is a lens that performs well at the aperture settings for our intended depth of field, and a camera that can record the resulting images without too much noise. The K-5 is an excellent camera (I still have mine), and it performs very well at mid-high ISO settings (especially considering its age)... but it has long since been overtaken in that department by the K-70 and, even more so, the KP. Either of those cameras - new or used - might be something to consider instead of (or in addition to) a new lens...

I agree with Big Mac....The K-5 is more limited than the lens. Having sold my my K-50 and K-3 in favor of the K-S2 and KP, I notice new vitality in my (older) prime lenses. Pushing ISO comfortably to 12,500 and using noise reduction post production removes many of the obstacles (i.e., extreme edge softness) because I'm shooting at 5.6 to 8 with very decent results.
The KP in particular is most receptive to being pushed beyond what I have experienced in the past. Of course, for the purposes of this discussion, I omitted my (albeit similar) experiences with the
K-1ii because this thread focuses on APS-c products.

[Trickortreat]

Sigma 30mm f1.4 would be a better option for your needs if you dont mind a bit heavier lens.
The wider you go the easier to get sharp images handheld

[pres589]

I'm curious what you find with an M or A 50 1.7 vs. your existing K 50 1.4. I believe it will be an improvement. My M 50 1.7 handles highlights like what you're talking about pretty well and I believe better in these situations than my M 50 1.4. You could probably find an F 50 1.7 to get AF and slightly updated coatings for a decent price if that interests you.

I also have a DA 50 1.8 and on my K-5 it is a very nice portraits lens and general purpose prime. The coma wide-open may indeed limit its improvement over your existing 50.

I like pepperberry's suggestion of the Sigma 50 1.4 EX DG. Not that common in k-mount but performance wide-open is said to be very good.

[BigMackCam]

In my case, it's for night shots taken beyond 10 meters (infinity). So depth of field is less of a concern.

Understood. However, bear in mind that with your K-5 plus the DA50 f/1.8 wide open, if you focus at a point ten meters away then you'll only get just under three metres depth of field for "acceptable" sharpness. Less still if you use a 50mm or 55mm f/1.4 wide open.

My point being, relying on lens aperture alone to achieve an ISO setting with acceptable noise levels is limiting your creative control over the scenes you're capturing. Plus, few lenses perform at their best wide open. The DA50 is no exception. As such, a body with better high ISO performance - such as the KP - will allow you to use your lenses at better-performing apertures because noise is so much better controlled.

That said, it's worth trying the A50/1.7 to see what results you can achieve. It's an inexpensive experiment

[DrMindbender]

Understood. However, bear in mind that with your K-5 plus the DA50 f/1.8 wide open, if you focus at a point ten meters away then you'll only get just under three metres depth of field for "acceptable" sharpness. Less still if you use a 50mm or 55mm f/1.4 wide open.

My point being, relying on lens aperture alone to achieve an ISO setting with acceptable noise levels is limiting your creative control over the scenes you're capturing. Plus, few lenses perform at their best wide open. The DA50 is no exception. As such, a body with better high ISO performance - such as the KP - will allow you to use your lenses at better-performing apertures because noise is so much better controlled.

That said, it's worth trying the A50/1.7 to see what results you can achieve. It's an inexpensive experiment

Indeed it will be an interesting and inexpensive experiment. It looks like it's comparable to the K 50/1.4 at F2, which is why I started musing about the DA 50/1.8, and it came with all the toys to push it to the limits. At the very least, I'll be able to decide if the A 50/1.4 and 1.2 are worth it before I go with a new body.

The big headache with depth of field is that I'm trying to freeze motion with photos like the one above so that I can bring out the interiors. Simply put, light streaks are boring. Unfortunately, the minimum shutter speed I need for photos like that is 1/125s which means wide open and high ISO. Add to that the train in the photo is switching to a daylight schedule in four months which is well before I planned to get a replacement body which forces me to decide if this is the best I can do now with what I have and with what lenses are available. :S

[clackers]

I think using a tripod you should shoot a composite. One's your train at 1/125s and another is the rest of the scene at ISO 100, f11.

[leekil]

If you'e trying to freeze motion, underexpose it a stop or two with a faster shutter speed, and then boost the exposure in post. You might also be able to retain some of the highlight detail (if that's what you mean by blobs of light) as well.

[reh321]

Indeed it will be an interesting and inexpensive experiment. It looks like it's comparable to the K 50/1.4 at F2, which is why I started musing about the DA 50/1.8, and it came with all the toys to push it to the limits. At the very least, I'll be able to decide if the A 50/1.4 and 1.2 are worth it before I go with a new body.

The big headache with depth of field is that I'm trying to freeze motion with photos like the one above so that I can bring out the interiors. Simply put, light streaks are boring. Unfortunately, the minimum shutter speed I need for photos like that is 1/125s which means wide open and high ISO. Add to that the train in the photo is switching to a daylight schedule in four months which is well before I planned to get a replacement body which forces me to decide if this is the best I can do now with what I have and with what lenses are available. :S

I'm not clear on what you are trying to get. Right now, getting illuminated windows plus car body {with a view as clear as you'd get in daylight} would probably require using tripod as recommended by @clackers ..... if motion is involved, it isn't going to happen right now {maybe in another generation}. I have been immensely impressed by the low-light performance of my KP - using TAv mode, I select the shutter speed and aperture needed to capture the scene, and it finds an ISO setting to make it work. Even as high as ISO 12800 or 25600 it gives me good shots
First photo with KP - PentaxForums.com
Iso 25600! - PentaxForums.com
But Dynamic Range is tailing off by that point; you might get a good image of the rail car, but I doubt the windows would be anything other than pure light.

[DrMindbender]

I'm not clear on what you are trying to get. Right now, getting illuminated windows plus car body {with a view as clear as you'd get in daylight} would probably require using tripod as recommended by @clackers ..... if motion is involved, it isn't going to happen right now {maybe in another generation}. I have been immensely impressed by the low-light performance of my KP - using TAv mode, I select the shutter speed and aperture needed to capture the scene, and it finds an ISO setting to make it work. Even as high as ISO 12800 or 25600 it gives me good shots
First photo with KP - PentaxForums.com
Iso 25600! - PentaxForums.com
But Dynamic Range is tailing off by that point; you might get a good image of the rail car, but I doubt the windows would be anything other than pure light.

Well, daylight clear exteriors won't happen unless I would detonate nukes in orbit as the mother of all flashbulbs.

However, what I'm trying to do is to produce a sharper image. Eliminating the graininess is out of the question since I'm fairly certain now that I can't drop the ISO to 1600 with any lens and I won't have the funds for a new body in the time frame I have. However, considering the high contrast of the subject matter, I was considering the possibility that the glass in the DA might make a difference by itself especially since I won't be using it fully open. I believe the term of the problem with my K that I've been describing is called coma with some general CA and fringing thrown in which may have been improved with modern coatings. If I was wrong about improvements to lens coatings, or vastly overestimated the improvement they would provide, I'd go with a DA 1.4 and possibly reconsider the A & F & FA 1.4's to get F1.6 & F1.8 that I can't get with my K 50mm/F1.4.


And I've been using a heavy tripod from the start with this type of shots.