[Another dyemention]

So I recently aquired this lens and have taken about 200 pictures with it. Nothing controlled or scientific but I've not gotten a single sharp image from it. I started testing for front and back focus today and found the lens to be back focusing. I started running out of daylight so I just made some adjustments and started shooting my wife and kid. I got to +10 on the fine adjustment and my kids face was out of focus but his shirt was much better. However, it's still not sharp. Not as sharp as I would expect this lens to be at 4.5. Of all the reviews I've sen on this lens, I've not seen a single one saying it's not sharp. Supposedly this lens is even used as a basis for comparison at some photo review websites. So not sure if my lens is just a bad copy or how to even go about checking it further. In addition, even at ISO 100, the images still look hazy orgrainy or fuzzy. I've owned more than 10 different lenses over the past year and have not seen any results like this. I'm using a k50 btw. I'll post some pics when I get a sec and I appreciate any advice. Thanks

---------- Post added 06-20-15 at 07:43 PM ----------

I used a tripod and 5 energizer batteries set at 45 degrees to the line of site to check for back focus btw. At "0", "energizer" was out of focus but the writing on both sides of the battery was decently sharp.

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Last edited by Another dyemention; 06-20-2015 at 07:45 PM.

[Adam]

So I recently aquired this lens and have taken about 200 pictures with it. Nothing controlled or scientific but I've not gotten a single sharp image from it. I started testing for front and back focus today and found the lens to be back focusing. I started running out of daylight so I just made some adjustments and started shooting my wife and kid. I got to +10 on the fine adjustment and my kids face was out of focus but his shirt was much better. However, it's still not sharp. Not as sharp as I would expect this lens to be at 4.5. Of all the reviews I've sen on this lens, I've not seen a single one saying it's not sharp. Supposedly this lens is even used as a basis for comparison at some photo review websites. So not sure if my lens is just a bad copy or how to even go about checking it further. In addition, even at ISO 100, the images still look hazy orgrainy or fuzzy. I've owned more than 10 different lenses over the past year and have not seen any results like this. I'm using a k50 btw. I'll post some pics when I get a sec and I appreciate any advice. Thanks

---------- Post added 06-20-15 at 07:43 PM ----------

I used a tripod and 5 energizer batteries set at 45 degrees to the line of site to check for back focus btw. At "0", "energizer" was out of focus but the writing on both sides of the battery was decently sharp.

Have you tried focusing in live view, or focusing manually? If the lens still isn't sharp, I'd be inclined to believe that it's defective.

[vonBaloney]

Focus manually and see if you can get something sharp. That lens should be sharp as hell from wide-open (it does fringe a bit wide-open, but still sharp). I mean, really really sharp -- it should be obvious, it is the sharpest lens I've ever seen personally. If it is an AF problem, ask Sigma about it -- they may be able to calibrate it for you (which would mean sending them the lens and the camera I think). If you bought it new, you might just exchange it.

[Another dyemention]

I've focused manually on a few shots but nothing like "controlled" just messing around. The focus ring is pretty easy to turn so it doesn't seem very precise. I'm sure it'll just take some getting used to. I just sold my k135/2.5 which was like a dream focusing manually. So I'm kinda used to that. And I bought it used from KEH.

---------- Post added 06-20-15 at 08:02 PM ----------

Have you tried focusing in live view, or focusing manually? If the lens still isn't sharp, I'd be inclined to believe that it's defective.

I've tried in live view but didn't notice a difference. I'll try more stuff tomorrow but I've not had any problems with any lenses before so Ive got no experience with any of this.

[Class A]

I agree that the lens should be extremely sharp, even at f/2.8.

It looks like you need to send it in for AF calibration, preferably with your camera, however consult with KEH how to proceed.

BTW, don't shoot objects like batteries at a 45 degree angle. You'll never know what detail the camera picked out to focus on. It is a better idea to stage the batteries in the depth direction and focus on the middle one, straight on. This setup will only give you a very crude indication but it avoids the pitfalls of shooting at real life objects at an angle.

[Another dyemention]

I agree that the lens should be extremely sharp, even at f/2.8.

It looks like you need to send it in for AF calibration, preferably with your camera, however consult with KEH how to proceed.

BTW, don't shoot objects like batteries at a 45 degree angle. You'll never know what detail the camera picked out to focus on. It is a better idea to stage the batteries in the depth direction and focus on the middle one, straight on. This setup will only give you a very crude indication but it avoids the pitfalls of shooting at real life objects at an angle.

I had the batteries set up on a flat surface, on end, and about a half inch apart. they were straight up and down just going away from right to left at a 45 degree angle.

[Another dyemention]

This first picture was at 2.8. You can see his shirt is more in focus than his face. This is about as sharp of a picture ive gotten so far (his shirt) but really isn't any sharper than my 18-135.
the second pic was at 4.5 and actually looks as if it front focused.

---------- Post added 06-20-15 at 08:34 PM ----------

his eyes in the first pic are more in focus than the rest of his face but you can see how hazy or fuzzy it looks.

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Last edited by Another dyemention; 08-05-2017 at 12:47 PM.

[Class A]

I had the batteries set up on a flat surface, on end, and about a half inch apart. they were straight up and down just going away from right to left at a 45 degree angle.

OK, good.

BTW, what AF method are you using?

Do not let the camera select the focus point. Choose it yourself and stick to the centre point for tests. The other points may be misaligned on your camera.

You really need to start doing controlled shots, otherwise you won't make progress.

BTW, the Sigma lens is an AF lens and hence it is normal for it to not have such a damped MF feel like an old K lens. Almost all AF lens focus rings turn much more easily than old MF designs. That doesn't mean they are less precise.

[Another dyemention]

I was using AF.S and center point. I will do some controlled shots tomorrow. It's Father's Day so maybe I can have a few hours to myself lol.

[Class A]

I was using AF.S and center point. I will do some controlled shots tomorrow. It's Father's Day so maybe I can have a few hours to myself lol.

OK, sounds good.

You should not be getting both FF and BF at similar focus distances and focusing with LiveView must be spot on, otherwise you are dealing with a seriously defective lens.

[Kozlok]

My Sigma 70 is dead sharp at any aperture. Focuses nicely, too. Send it back to KEH, ask for a different one!

[Bruce Clark]

Apart from FF and BF, there are other possibilities to consider.

The camera does take some time to achieve focus and trigger the shutter, during this time both the subject and photographer can move slightly. SR if activated. will not compensate for subject movement or forward backward movements by the photographer. Increase shutter speed to 1/250th at least.
Depth of field. At f2.8 and at at distance of 24 inches you have a depth of field of a mere 0.3 inches. At f4.5 the DoF is still only 0.45 inches. f11 provides 1.2 inches. This is not much to play with. Spot focus on the eyes.
Increasing shutter speed and using a small aperture will require increasing ISO or you may consider using flash.

[jonby]

There are three entirely different possible issues here: 1) an optical issue - the lens may be optically defective and not capable of producing sharp images (or as sharp as it should), 2) AF inaccuracy issues, 3) camera/subject movement issues. Unless you eliminate the effects of two of these while testing, you will not be able to determine anything for sure.

I suggest testing for the optical issue first. In other words, find out whether the lens is actually capable of producing sharp images at its focused distance. If it is not, then any testing for other issues is a waste of time. There is no doubt that a good copy of this lens should be sharp even wide open, and very sharp from f4 onwards. If it isn't, then you should certainly return it.

In order to test for optical sharpness, you need to eliminate any possibility of camera/subject movement, and also ensure that at least part of the subject lies within the focal plane. For this, I would suggest a receding plane around 7-12 metres away. A patch of ground is usually the best thing, as long as it has detail across most parts of it. If you can get above ground level with your camera, that is better, for example from a 1st floor window in your house, looking down on the garden at around a 30 degree angle (but only if you can open a window - shooting through glass is no good). You then need to set the camera on a sturdy tripod, focus manually using magnified live view at the centre of the frame, and take a series of evenly exposed shots starting at f2.8 and working down through the apertures (f4, f5.6, f8, f11, f16). You need to engage two-second self timer with mirror lock to ensure no vibration, and also ensure that your own movements near to the tripod cannot cause camera movement. It would be a good idea to test another lens you are familiar with at the same focal length, using the same setup, so you have something to compare to. Perhaps you have a zoom which spans 70mm?

Using a receding plane like this means that you should be able to see the subject coming in and out of focus as it passes through the focal plane. Shooting at a middle distance rather than close up will mean that your depth of field is big enough to have enough areas in focus to evaluate properly. This will give you a good idea of what the lens is optically capable of. If it seems to be in line with what you should expect (ie. very sharp), then you know the issue lies elsewhere - most likely with AF. If the optics aren't sharp, then any further testing will be a waste of time.

[Na Horuk]

Yeah, make sure you are taking test photos in good natural light, with a shutter speed fast enough to prevent handshake blur. Better yet, use a tripod with 2sec timer (and if you have one, use a remote trigger), at ISO 100, and manually focused on something that is less than a metre far.

The lens should be sharp. The most common problem on this forum that we get is user mistakes (handshake, misfocused, shot in low light, wrong jpeg mode, and so on), next is AF problems (this is why you try manual focus, regular focus (AF.S, centre point) and Live view focus (its different) to see where the problem lies). Finally there are actual optical problems with the lens. First check the lens mount, make sure its clean and has no obvious marks of damage. Next look at the back lens element, and then the front element. Finally, try manually turning the focus ring and watch closely how the lens extends - if anything is decentered, bent.. This is what you do before sending it for repairs. Hopefully you diagnose the problem before sending it in, so you can tell them where to start looking, and later test the lens once you get it back to make sure it is really fixed.

Other than that, yes, the Sigma 70mm should be pretty sharp, with lots of detail and contrasts.

[Another dyemention]

here are two shots I did today. First is at 2.8 and second is at 4.0. The focus fine adjust is at +10 for both shots. I did have to use a flash because its been gloomy here lately. Both shots were from a tripod with 2 sec timer manually focused in LV. The second one is acceptable but the first is pretty out of focus on the "ePe". I was focusing on "P" btw and was about 5 feet away.

---------- Post added 06-22-15 at 05:36 PM ----------

There are three entirely different possible issues here: 1) an optical issue - the lens may be optically defective and not capable of producing sharp images (or as sharp as it should), 2) AF inaccuracy issues, 3) camera/subject movement issues. Unless you eliminate the effects of two of these while testing, you will not be able to determine anything for sure.

I suggest testing for the optical issue first. In other words, find out whether the lens is actually capable of producing sharp images at its focused distance. If it is not, then any testing for other issues is a waste of time. There is no doubt that a good copy of this lens should be sharp even wide open, and very sharp from f4 onwards. If it isn't, then you should certainly return it.

In order to test for optical sharpness, you need to eliminate any possibility of camera/subject movement, and also ensure that at least part of the subject lies within the focal plane. For this, I would suggest a receding plane around 7-12 metres away. A patch of ground is usually the best thing, as long as it has detail across most parts of it. If you can get above ground level with your camera, that is better, for example from a 1st floor window in your house, looking down on the garden at around a 30 degree angle (but only if you can open a window - shooting through glass is no good). You then need to set the camera on a sturdy tripod, focus manually using magnified live view at the centre of the frame, and take a series of evenly exposed shots starting at f2.8 and working down through the apertures (f4, f5.6, f8, f11, f16). You need to engage two-second self timer with mirror lock to ensure no vibration, and also ensure that your own movements near to the tripod cannot cause camera movement. It would be a good idea to test another lens you are familiar with at the same focal length, using the same setup, so you have something to compare to. Perhaps you have a zoom which spans 70mm?

Using a receding plane like this means that you should be able to see the subject coming in and out of focus as it passes through the focal plane. Shooting at a middle distance rather than close up will mean that your depth of field is big enough to have enough areas in focus to evaluate properly. This will give you a good idea of what the lens is optically capable of. If it seems to be in line with what you should expect (ie. very sharp), then you know the issue lies elsewhere - most likely with AF. If the optics aren't sharp, then any further testing will be a waste of time.

I haven't had a chance to try this yet as it was raining all afternoon. But ill give it a go when I get some time.