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11-01-2010, 06:36 PM   #1
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Is this as sharp as it should be?

Hey all, I am still trying to get comfortable with my new Pentax setup, so doing most of my professional work with Nikon, since I am used to it. But I am trying to get a few shots each session with the K-7. Today I took this shot with the A series 50/1.7:



Sharpness looks fine in the web-sized version, but I just wanted to see if it's sharp enough in others' opinions. It wasn't quite as sharp as I expected, and additionally I had only a handful of keepers out of 30+ shots, because many were mis-focused. So I am wondering if this level of sharpness is what I can expect from this lens wide open, or if I might have missed the focus a little bit here as well. If the latter, I guess I just need to reconfirm I have my diopter set optimally (I think I do, though), and probably just get more practice with this viewfinder. Here is the 100% crop without any sharpening:



11-01-2010, 06:41 PM   #2
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looks slightly out of focus.... but anyways you should have stopped down to F/2-F/2.8 either way
11-01-2010, 06:45 PM   #3
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QuoteOriginally posted by yeatzee Quote
looks slightly out of focus.... but anyways you should have stopped down to F/2-F/2.8 either way
I understand stopping down for better sharpness, but I like to control my DOF, and I plan on using this lens wide open often, as I do with all of my fast lenses. So I'm just trying to determine if the less-than-expected sharpness here is me, or just the norm for this lens at 1.7.
11-01-2010, 06:46 PM   #4
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I have a lot of trouble focusing the A50 1.7. You might want to consider a split prism focusing screen like you had in the film days... because these digital ones make the DOF look larger than they actually are if you are shooting lower than 2.8 ish (in my experience).

Although, you likely shot have shot at f2-2.8, but I would still consider the focusing screen. The lens tends to be razor sharp at 2.8.

EDIT: This lens is sharper than it's peers at f1.7, but not as sharp as a 1.4 stopped down to 1.8. I don't care for my A50 wide open.


Last edited by paperbag846; 11-01-2010 at 06:53 PM.
11-01-2010, 06:53 PM   #5
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QuoteOriginally posted by paperbag846 Quote
I have a lot of trouble focusing the A50 1.7. You might want to consider a split prism focusing screen like you had in the film days... because these digital ones make the DOF look larger than they actually are!

Although, you likely shot have shot at f2-2.8, but I would still consider the focusing screen. The lens tends to be razor sharp at 2.8.

EDIT: This lens is sharper than it's peers at f1.7, but not as sharp as a 1.4 stopped down to 1.8. I don't care for my A50 wide open.
Thanks! I'll try some shots at 2.8 next time, just to judge sharpness and keeper rate. Since I am accustomed to shooting f/2 and wider on a FF body, the DOF I get from a crop sensor at 50mm and f/1.7 is somewhere in the ballpark, but ultimately this won't be my go-to portrait lens. I have a 77/1.8 coming at the end of the week, and that's what I plan to use most often for this kind of studio work.

I may try a KatzEye one day, but I reeally don't want to. Though I could probably get used to it, my limited experience with them has been no great pleasure.

I don't know what the functional "aperture" of the stock K-7 screen is, but watching things pop in an out of focus through the VF, it seems like it's better for manual focusing than the D3's VF, so I have high hopes for getting to the point where I can shoot MF lenses without changing screens.
11-01-2010, 06:55 PM   #6
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QuoteOriginally posted by Todd Adamson Quote
Thanks! I'll try some shots at 2.8 next time, just to judge sharpness and keeper rate. Since I am accustomed to shooting f/2 and wider on a FF body, the DOF I get from a crop sensor at 50mm and f/1.7 is somewhere in the ballpark, but ultimately this won't be my go-to portrait lens. I have a 77/1.8 coming at the end of the week, and that's what I plan to use most often for this kind of studio work.

I may try a KatzEye one day, but I reeally don't want to. Though I could probably get used to it, my limited experience with them has been no great pleasure.

I don't know what the functional "aperture" of the stock K-7 screen is, but watching things pop in an out of focus through the VF, it seems like it's better for manual focusing than the D3's VF, so I have high hopes for getting to the point where I can shoot MF lenses without changing screens.
Maybe try catch-in focus? It tens to have better eyes than I do.

However, I would think that keeping her whole face in focus at f 1.7 is going to be tricky.
11-01-2010, 06:56 PM   #7
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hi Todd, did you check the other areas of the image which looked sharp?
11-01-2010, 07:01 PM   #8
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QuoteOriginally posted by Pentaxor Quote
hi Todd, did you check the other areas of the image which looked sharp?
Yes, but I can't tell for sure.....if I was slightly backfocused it probably would have been obvious, but less so for front focus, since she has very smooth skin....if I were fornt-focused, it would be somewhere on the bridge of her nose, but I can't really differentiate sharpness between that and the eyes.

11-01-2010, 07:05 PM   #9
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QuoteOriginally posted by paperbag846 Quote
Maybe try catch-in focus? It tens to have better eyes than I do.
I haven't explored that feature yet.....but I plan to!

QuoteOriginally posted by paperbag846 Quote
However, I would think that keeping her whole face in focus at f 1.7 is going to be tricky.
Well, now that depends on what I consider acceptable focus. I tend to shoot portraits wider than most people. This should give me roughly the same DOF as my 100mm Zeiss at f/2 on the D3, and I routinely get what I want out of that setup: both eyes very sharp. Tip of the nose just becoming soft. Mouth as sharp as it needs to be for the kind of portrait I want to create. For example:

11-01-2010, 07:07 PM   #10
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I really like using this lens at f2 for the best sharpness/DOF combination for me, but focused accurately it is much better than your sample so it seems like you missed a little but it's still a great result.
it is actually really easy in this situations to see if you nailed the focus right since some other part of the face has to be in focus.

edit: I see this has already been brought up, so forget about it. and I love the 2nd photo!
11-01-2010, 07:07 PM   #11
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Try stopping down to f2.0, I find with my F50/1.7 it makes all the difference, even though it's just half a stop. You shouldn't gain too much DOF.
11-01-2010, 07:12 PM   #12
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The lens is a whole different animal at f2. A very deadly animal. That second shot is perfect, btw.
11-01-2010, 07:17 PM   #13
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Thanks a lot you guys. I was hoping it was just that I was missing by a bit, and I know I will get better with practice. I will definitely start to explore this lens at f/2 ASAP. Although if what I have been reading about Pentax glass is true, I am not gonna want to take the 77 off my camera once it goes on! LOL
11-01-2010, 07:18 PM   #14
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QuoteOriginally posted by Todd Adamson Quote
Yes, but I can't tell for sure.....if I was slightly backfocused it probably would have been obvious, but less so for front focus, since she has very smooth skin....if I were fornt-focused, it would be somewhere on the bridge of her nose, but I can't really differentiate sharpness between that and the eyes.
Yes, it kinda difficult to judge. but just in case you want to check for sharpness, you might want to use LV magnified mode just to see if indeed it's soft or just a result of being slightly out of focus. I usually do this setup with a tripod. it could be a bit of work though since it would require longer time to focus under LV.
11-01-2010, 07:20 PM   #15
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QuoteOriginally posted by Pentaxor Quote
Yes, it kinda difficult to judge. but just in case you want to check for sharpness, you might want to use LV magnified mode just to see if indeed it's soft or just a result of being slightly out of focus. I usually do this setup with a tripod. it could be a bit of work though since it would require longer time to focus under LV.
Yeah, that's the other problem, I was shooting hand-held because I still don't have my L-bracket. Should be here tomorrow.
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