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11-17-2010, 10:45 PM   #16
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Here are the pics

1, 2, 3) All the test charts are at F1.4. Clearly front focused. Some significant
4) As sharp as F1.4 can get, 100% crop, indoors.
5) 100% crop. Outdoor, even F2.8 gives front focus. Had focused on the center of the flower, but leaves towards me are in focus.

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Last edited by icypepsi; 11-17-2010 at 10:55 PM.
11-17-2010, 10:53 PM   #17
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bokeh and sharpness

1) The bokeh can get jittery at times. if you do want it, then it does, but not too much
2, 3) Mostly the bokeh is smooth and even
4) Wall at F2.8 and -8 microfocus adj. Sharpest it can get.
5) 100%

All are with amazing color straight out of the cam (K7 on vibrant option). The CA is very less in my copy. Only 1 or 2 pics did I notice significant CA out of a lot that I tested.
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11-17-2010, 11:03 PM   #18
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QuoteOriginally posted by jeffshaddix Quote
Hey icypepsi, I'd recommend exchanging it for another copy with B&H; they do a good job with returns.

If you're not 100% satisfied with a product, then it's worth replacing while it's free and easy. I know CRIS (the repair shop for Sigma lenses) can make focus adjustments to lenses, but I'm not sure if they can fix the issue where the lens focuses differently based on distance to subject.

Pentax and Sigma alike have ever deteriorating quality control (cutting costs in the bad market no doubt). Hopefully the number of returns (especially to the world's biggest camera store) will give them a clue that quality control isn't worth skimping. I had to exchange my K-7 twice before I got an acceptable copy...and I still have a banding issue on the sensor. Do the photography community a favor and demand perfection when you buy expensive equipment like that lens.
Quite right. Gonna do that tomorrow, will pay the additional tax and check the lens at the store itself. Not that I can guarantee myself coz it will be low light and not ideal at the store. But at least I can get some idea. Besides, I need it for a vacation I'm leaving for on 24th. No point in waiting for the shipping to arrive.

I've read articles that talk about the tolerances to which these are manufactured and that it is quite difficult to get things perfect. I'd be ok if it were a fixed back/front focus throughout all apertures. But a BF/FF that shifts with subject distance and apertures.. hard to handle. Think of having a dial on the cam for adjusting it!! Insane!!!

Btw, what firmware is your K7? I believe the banding was fixed with the latest firmware.
11-18-2010, 12:37 AM   #19
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QuoteOriginally posted by icypepsi Quote
Dear Pentaxians,
Just a thought, but from your description it sounds like AF gets more inaccurate as you stop down. Have you considered this may be due to focus shift and it's just a property of the lens? If that's the case, exchanging it won't do you any good.

11-18-2010, 12:47 AM   #20
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I have never been to happy whit the Sigmalux (the velvet version) too.
The best one can pull out of this lens is at F 8 and perhaps F 11, that's all.
But at full open, what this lens was designed for I guess, it is nearly "the bottom of a coke bottle" than the magnificent optic gem as prized in the press, sorry to say.
I send this lens in, under warranty, to be repaired/adjusted, and was returned as being perfect now. But just a little was improved, not enough for me. It still needs an AF adjust of minus 9.
Nevertheless, I consider the Sigmalux as a good soft-focus lens. It reminds me, to a certain extend, the Rodenstock's Imagon. Perhaps that's why it renders such a wide tonality and soft bokeh.
So now this lens is sitting on the shelf till I need it, at F 8 for 'sharp' and open-to-F2.8 for soft…

From then on I never bought any third party lenses!
11-18-2010, 01:01 AM   #21
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Stick with the Sigma 50/1.4!

HEllo icypepsi!

I do have the Sigma too and have been using it for almost 1.5 years now.

It has a stellar performance with the K10D, even more with the K-7. I would not give it away anymore.

I do often Panoramashooting using this lens and I know why: The pics are just brilliant.

Right now there seems to be one inssue only, which does affect the live.view. I found this now with the new K-5. If you use the LV with face detection or Contarst AF it might be, that the focussing does not work.

But this seems to be a general problem of Sigma lenses with several newest DSLRs, as the manufacturers seem to have changed their Hardware-protocols.

But this should not be an issue, as with Phase difference and the optical viewfinder all works perfect!

So, stick with this lens, you are not going to regret it !


BEst from Germany
Georg
11-18-2010, 06:44 AM   #22
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Do you get the same focus error when using liveview?

I have a Sigma 30 1.4 and have focus problems in lowish light but liveview focuses much better.


Erik
11-18-2010, 09:10 AM   #23
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QuoteOriginally posted by Ubuntu_user Quote
Are you talking the Sigma 30mm f/1.4? If so, that is in PK mount... At least afaik.
Yes, you're right. I just wasn't clear. I was talking about getting the 30mm with HSM in our mount.

11-18-2010, 09:34 AM   #24
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Strange how opinions can be extremely different about this lens!
Some are very unhappy and others do love it, how comes?
11-18-2010, 10:00 AM   #25
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QuoteOriginally posted by Laurentiu Cristofor Quote
Just a thought, but from your description it sounds like AF gets more inaccurate as you stop down. Have you considered this may be due to focus shift and it's just a property of the lens? If that's the case, exchanging it won't do you any good.
Interesting (and scary, for the money we all spend on it!), but I think there is more to this. Like including the subject distance into consideration. He did, but needs elaboration and more study. So the article says my glass (tumbler) is half empty, instead of what I thought half full. Ok same thing. Even if I think that wide open is what my lens is built for and stopping down back focuses, getting the wideopen focus correct also needed clearly more then -10 microfocus. With that, again, my lens is out of the normal behavior. I was close to considering to try focusing a little behind, probably for the rest of my days with the lens. But humanly it was almost impossible for me, with the DOF being so thin If possible, could take time, but I don't want to buy that because again I would have to know exactly how much behind, which again varies on the subject distance. Now that compounds things. Would need tremendous practice. But with people out there that say it should not be the way my Sigma is behaving, I will certainly try to get a new copy.
11-18-2010, 10:06 AM   #26
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QuoteOriginally posted by philippe Quote
I have never been to happy whit the Sigmalux (the velvet version) too.
The best one can pull out of this lens is at F 8 and perhaps F 11, that's all.
But at full open, what this lens was designed for I guess, it is nearly "the bottom of a coke bottle" than the magnificent optic gem as prized in the press, sorry to say.
I send this lens in, under warranty, to be repaired/adjusted, and was returned as being perfect now. But just a little was improved, not enough for me. It still needs an AF adjust of minus 9.
Nevertheless, I consider the Sigmalux as a good soft-focus lens. It reminds me, to a certain extend, the Rodenstock's Imagon. Perhaps that's why it renders such a wide tonality and soft bokeh.
So now this lens is sitting on the shelf till I need it, at F 8 for 'sharp' and open-to-F2.8 for soft…

From then on I never bought any third party lenses!
so with all the mending, it is still something like my copy. I can feel your pain. In 2009 when I bought the K7, I looked at the 50D and was very particular about having the microfocus adj. I'm happy I chose one that has it too. But with the images I've seen, especially at F2.8 (posted by me above)/F4, don't you think it is pretty sharp? Well, maybe just a veenie bit less, compared to all of the pics I've ever seen online. Besides, online review graphs seem to tell that these tend to loose sharpness when stopped down more than F8/f11. I could not ask for anything more than this.. given my level of expectation (that I would maximum blow up the thing in to a 30" to 40" poster). Now if I were assigned to make a hoarding out of it.. maybe not

But out of curiocity, can you please post the pics of the canon lens (100% crop too). I want to see how sharp it can get.

Last edited by icypepsi; 11-18-2010 at 10:43 AM.
11-18-2010, 10:38 AM   #27
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QuoteOriginally posted by erikstarck Quote
Do you get the same focus error when using liveview?

I have a Sigma 30 1.4 and have focus problems in lowish light but liveview focuses much better.


Erik
Nope, LV and MF cut it just fine. At least for all my trials so far. On some instances MF did not hit it, but I attribute it to me not doing it well on the small K7 viewfinder.

Thanks, Georg. Looking forward. I have read about even the K7 not being able to contrast AF, on dpreview. But I can confirm that my K7 (firmware v 1.10) fantastically determins the correct focus. Too bad, I hardly use it But, with what I just found out, my Sigma copy could be out of the close-to-latest-batch (and looks like the last of the lot that have the velvet finish, posted above), maybe Sigma fixed it!?

Last edited by icypepsi; 11-18-2010 at 11:04 AM.
11-19-2010, 12:29 AM   #28
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Mysterious facts

[I did go to B&H and they were very helpful in getting me a replacement. But you can always make out that face of the gentleman who is doing it for you. He'll have an expression of helplessness!]

I discovered two very mysterious facts. Read on.

Mysterious fact 1. The gentleman was kind enough to let me try another Sigma in exchange, before I decide to take it home. By now I was an expert at seeing this flaw in the lens and I quickly tested and found that at 1.4 there is some BF, this time. I quickly set the microfocus to an appropriate value (must've been +3 or something, which is pretty acceptable) using an obj that was around approx 2-3ft away. And guess what, stopping down to F2.0, F2.8, F4, the lens (remember it is now at +3) started to FF progressively. I could not help but think of what what Laurentiu Cristofor had pointed out here https://www.pentaxforums.com/forums/showthread.php?p=1270746. Then, I shifted focusing to an object that was approx 6ft away. To my horror the plane of sharp focus had shifted again (same aperture and microfocus adj. value)!! So the microfocus adj. has to be done fresh for the changed subject distance!!!!

So, this lens is behaving exactly like my previous copy. Coming to think of it:
Copy 1:
sharp focus for F2.8 at -7 microfocus adj.
sharp focus for F1.4 beyond -10 (out of K7's reach)

Copy 2:
sharp focus for F2.8 at (approx.) -4
sharp focus for F1.4 at +3

Only, copy 2 was well within the reach of my individual K7 body. At this point, I began thinking that this is a general problem with all Sigma 50 1.4 HSMs and I did not take the exchange, further thinking that it may be something to do with my individual K7 too. But then again, why will the body be at fault to shift focus planes for different subject distances? Maybe not. So, I went straight up and tried a DA* 55mm F1.4. This thing was tiny compared to the Siggy! Pretty soon, as the expert that I am, I set my K7 to +X microfocus adj. value for sharp focus at F1.4. To my total surprise, this lens behaved exactly the same way as the Sigma 50mm F1.4!!! How shocking is that!!! Can I blame all 3 lenses? Not even a school kid will. But then, how could the K7 be at fault if the subject distance changes. It just seems unrelated. This is puzzling. Could some learned souls please solve this misery for me. Or, is it after all correct what Laurentiu Cristofor pointed us to? Quite possible (good I didn't shrug it off yesterday, or I'd be embarrassed today!!)

Now, I was so pissed that I even tried a DA* 50-135 F2.8. Quite surprisingly, set to a -4 microfocus adj, it appeared to be very consistent at anything I pointed it to. But let us not forget that my Copy 1 of Sigma too was fine beyond F2.8. Probably because there's not much to worry about given the heft of the DOF with 2.8 upwards.
[Btw, the 50-135 was an astronomically amazing lens!!! It was so damn sharp throughout it's zoom range that I felt like I was trying out just another prime!! I almost settled for it, when I told myself that I really wanted those 2 (or less) extra stops in indoor shooting. The difference I found between the Siggy HSM and the Pentax DA*s' SDM was that the HSM didn't give up easily in low light situations where SDM would give up too quickly, and the HSM does not seem to care about very minute focus adjustments when the subject changes position, but the SDM seems to have an intelligence to lock on to the changed position.. in other words tracks the subject beautifully! Maybe that is why the HSM's change in focal plane was noticeably more than that of the SDMs. I even like the perspective that I get out of shooting at, maybe 75mm. I really really liked this lens, but for not being able to go below F2.8. May I say it was way better than the Tamron 70-200 2.8 also in terms of sharpness and AF accuracy? And I also dread the scary SDM failure info. But frankly, there have been a lot of them out there buying it without a problem.]

Mysterious fact 2. Here's another horror that I discovered about the K7 (at least mine). It is running v1.10. If you remember I was mentioning in my OP that no matter how much microfocus adjustment I applied, it did not seem to matter, asif the cam had decided beforehand what to do. For some reason today, I swiched OFF and back ON everytime that I changed the microfocus adj. And OMG, the change is reflected even if there is a 1 notch change!!!! Now, that is the exact reason why in the outdoor testing of my Copy 1 of Sigma, no matter what I did, the FF was unshakable.

Here's what I did:
1. No microfocus adjustment change is registered by K7 when you get to the menu and change it, hit the "OK" button and immediately start shooting (I have a habit of half-pressing the shutter-focus button to spring the K7 system back into action for shooting). That is, without getting back using the "Menu" button. But, after hitting "OK", the damn thing confirms with a "SAVED" on the display. I believed it all these days!! What a waste of time!
2. microfocus adj. change is properly registered by K7 if you switch it OFF and back ON after the change. I don't know if it even does that if you "gracefully" come out of all the menu options to the status screen by hitting the "MENU" button repeatedly after it said "SAVED".

I swear, this is a real let down of all that precious night-time I spent without sleeping. I guess I'll start out another thread just to check if people have noticed this of if it's a v1.10 bug, or if it's just my cam. I strongly think it must be a bug.

So now, I came back with only the K7 body and no lens I am not sure if I must get a Sigma 50 1.4 or a Pentax DA* 55mm F1.4 and live with it, coz it could be that this is what lenses are meant to do below F2.8, or go for something else, like the Pentax DA* 50-135 F2.8. Please advise what is happening in this optical world. I'd really appreciate it. Hoping to have a lens to take with me on my vacation next week.

Last edited by icypepsi; 11-19-2010 at 01:10 AM.
11-20-2010, 01:15 AM   #29
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The article I quoted also mentions focusing distance as being a factor in focus shift, so it seems to fit with your observations.

I remember reading somewhere that some Zeiss lenses had the same behavior. Focus shift is also mentioned in this article from Zeiss.

Finally, looking at the photozone review, it also mentions this issue: "Upon closer observation you may notice that the focus shifts towards the back when stopping down ("Residual spherical aberrations") - especially from f/2 to f/2.8.".
11-20-2010, 09:53 PM   #30
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Another issue to consider

Here's one more thing I was rocking my head side to side on. We know that viewfinders show the image at the widest open aperture of the lens. But, I read that APS-C DSLRs can only show a preview in the viewfinder at the widest open aperture of F2.8. I can easily make this out with my K7. First, when I set the lens to F1.4 and use the "optical DOF preview" trigger on K7 and nothing happens. Technically, the lens is already at F1.4 and the K7 is not widening the aperture blades inside to bring the preview aperture of F1.4. Makes sense, so far that's normal. But you'd think that it's showing you a preview of F1.4. However, if I were to stop down to F2.0 (or anything else right up till F2.8), internally, the K7 has widened the lens to F1.4 for the viewfinder image. But, as I pull the optical preview trigger it makes a noise where the blades are brought back to F2.0 (or whatever your aperture is) to show the DOF preview, but the viewfinder was just the same. Intact. No decrease in brightness. You'd think it was at F1.4 and now it got to F2.0 with that sound and the viewfinder would go darker. It does it all, but the viewfinder does not get darker. Only when I stop down below F2.8, say F4, pull the optical DOF preview trigger, can I actually make out the difference in viewfinder brightness. This means, that wider than F2.8, and the viewfinder is not capable of seeing brighter, in this case at F1.4, showing the AF sensors the exact DOF.

Given this viewfinder limitation, assuming you are trying to focus at F1.4, and the depth of field that is a lot wider at F2.8, how in the world will the AF sensors make out what is happening? Obviously there will always be a +/- error on a focus fix that could be as wide as the depth of field at F2.8 (of course, depending on all the DOF parameters of that situation). Can someone please confirm this?

I don't know about FF, can someone also fill this gap please?
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