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04-04-2013, 03:38 PM   #1
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Trouble with Sigma 400mm f/5.6 AF/not APO

I recently picked up the AF, non-APO version of this lens on Ebay (at a cheap enough price to not worry too much).

I have never worked with it previously, but had heard good things, and it was relatively well rated here and elsewhere. I wasn't ready to spring for a new expensive telephoto, but needed something in the 400mm range for migration season.

I got it home, and the copy I have seems to be fairly immaculate. No obvious damage, glass is completely clear, not even any dust visible inside. AF works very well, surprisingly quick and accurate for being an older lens. Even in low light, it still does pretty decently. The color is pretty good, with the downside of some CA even stopped down (but I knew about this ahead of time).

However, I have been having a hell of a time getting anything sharp out of it. And I don't even mean, tack sharp from a magazine...I mean, just reasonably sharp at all. I thought it might be an issue with front/back focus, but when I looked at some test pics, the focus doesn't seem to be off...it just seems like what is in focus is just not very sharp. And these were tripod pictures, at high shutter speeds in good light, and even stopped down to f/8 and f/11. At this point, I'm fairly sure this is not user error...even in fairly ideal conditions (i,e, NOT what I expect to have in the field), this is just not performing.

Is this a perrenial issue with this lens? I know it's not supposed to be amazingly sharp, but it's just really really soft to the point of only getting usable photos if I'm almost at the minimum distance, and the subject completely fills the viewfinder, and even then you don't want to look too closely to the detail because it's still not sharp at all. I'm not talkign about "not as sharp as it could be" I'm talking really unsharp.

Recommendations to figure out what the issue is? I hate to go through the whole AF adjustment process if the issue is more likely just a bad lens/bad copy of the lens.

04-04-2013, 04:07 PM   #2
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Try it inside against something flat and use live view magnified manual focus, then you will see if it is the lens.
04-04-2013, 04:29 PM   #3
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You might compare if it is equally soft at all distances.
I am not familiar with this lens but other sigma long telephoto, the focus ring pulls in and out to go from manual to auto focus. pull and push it a few times to see if it is engaged.

Best of luck
04-04-2013, 04:31 PM   #4
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What shutter speed are you using, and in the exif what focal length is reported.

Maybe it is that the lens reports back the wrong focal length (sigma does not pay licensing fees to Pentax for the mount data) , or maybe you are shooting too slow, F8 to F11 means that if your ISO is at 100 or so, you won't get much in the ways of shutter speed

04-04-2013, 05:32 PM   #5
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I'll try to address these in order, thanks for your replies!

1) bob, thanks I will try the flat/liveview combo.

2) Bob from aus - I will look at that. From memory, I think it was sharper as one got closer to the minimum focusing distance, but I'm not sure. It is defintiely in autofocus though...it's very responsive AF, and seems to lock onto my target well, just doesn't seem to be getting sharp results. The focusing ring is somewhat inset...there is a small cover that can extend down over it, which I'd never seen before, but it just seems to be a cover...doesn't affect AF

3)Lowell - I shot at a range of shutter speeds, but was shooting stationary targets on a tripod at up to 1/1000 with similar results. I tried a lot of different combinations...I expected it to be less sharp at 5.6, but at f/11 with plenty of shutter speed and ISO 200, it was still performing really poorly. I tired it with and without the stabilizer engaged. Doesn't seem to be an issue related to shutter speed, which is why I was so confused. When I boot up the camera, it indicates 400mm. Since this lens is a FF lens, should it be indicating 600mm? All my other FF lenses report back the actual focal length, not the crop factor length. The exif says 400mm too.

For what it's worth it produces some really beautifully creamy bokeh even at the smaller apertures. If it wasn't for the sharpness issue I would be in love with this lens.
04-04-2013, 07:17 PM   #6
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Ok so one point. Of this is an AF lens, it should be giving FL back to the camera, the fact it does not, suggests it may not be communicating. That also means perhaps the focusing is not working properly either. Is any part of the image sharp or is it just the point you focus at not sharp?
04-08-2013, 06:05 PM   #7
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I'm a little confused, what makes you say it's not giving FL to the camera? When I turn the camera on after attaching the lens, tha camera indicates 400mm on the startup. Should it be doing something else?

As far as I can tell no part of the image is especially sharp. The thing I'm focused on is the most sharp, so the focusing seems to be working in that regard...I'll try this weekend some of the things suggested, but it doesn't seem to be obviously front or rear focusing. So, for instance, the exaggerated example of shooting at 5.6, I'll get nice creamy bokeh to the rear, with the subject in focus. There's not much doubt that the focus is where at should be, at least in general terms. However, the area that's in focus just isn't very sharp. Even stopped down to f/11, I'm not getting sharpness anywhere in the subject.

I appreciate all the suggestions...when I have some time this weekend, I'll try to post some sample images and go through the suggestions here. I was out birding with a colleague and his 60d with 400/5.6. IN the same light with the same settings, the results were very different. Obviously his is a better lens in general, but the difference in sharpness was dramatic, and we switched cameras to ensure it wasn't a matter of unsteadiness on my part...didn't seem to matter if shake reduction was on or off.
04-08-2013, 07:03 PM   #8
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Maybe a dumb question, but it doesn't have a filter on it, does it? When I first got my 55-300 I had a filter on it and the results were pitiful, I thought I had gotten a lemon. Turned out the lens was fine once I took that filter off, the filter had a flaw in it. I had an FA 28-105 power zoom lens that the sharpness decreased dramatically the farther away the subject was. It didn't seem to matter what the focal length was.

04-08-2013, 07:46 PM   #9
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QuoteOriginally posted by jmbower Quote
I'm a little confused, what makes you say it's not giving FL to the camera? When I turn the camera on after attaching the lens, tha camera indicates 400mm on the startup. Should it be doing something else?
You shouldn't see any focal length screen at all with an autofocus lens; it works without your input. You'd only see "400mm on startup" with a manual focus lens. The camera will come up with the last number it was set to, whenever it can't get the focal length from the lens. You can test this by setting it to 28mm or whatever, switching off them back on. It sounds like you'll still see 28mm. I don't know how you get autofocus with a lens that won't report focal length, though.
04-10-2013, 01:20 PM   #10
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Sorry...just went and rechecked it...it does not show 400mm when I start it up. It had when I was changing lenses to an old manual, and I must have misremembered. The camera is set at ISO 400, which shows up in the start screen, so it was a bit of not thinking on my part. Sorry for the confusion!

ramsey: it does have a UV filter. I will try it with and without when I test it this weekend. Doesn't seem to be any obvious issue with the filter, but we'll give it a shot!

Thanks all
04-10-2013, 02:26 PM   #11
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QuoteOriginally posted by jmbower Quote
these were tripod pictures, at high shutter speeds in good light, and even stopped down to f/8 and f/11.
Just a thought: did you turn SR off? If not, do so when using a tripod.
Also I've found that there's some sort of strange learning curve with "new" long lenses. Even when I think I'm doing everything perfectly, I still go through a crappy photo phase before I get the kind of results I'm expecting.
04-10-2013, 02:50 PM   #12
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QuoteOriginally posted by jmbower Quote
I must have misremembered
Welcome to my world, the consolation prize for you, is that your not alone.
04-10-2013, 03:26 PM   #13
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As was stated above, filters are a serious issue with long lenses. If they are not perfectly flat, it will show up as unsharpness. I put a cheap filter in front of my 400 Pentax and had to return it to the seller. Went with a B+W to solve that problem.
On occasion, during lens assembly, an element can be reversed. A loose element will also cause softness.
09-15-2013, 09:31 PM   #14
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QuoteOriginally posted by jmbower Quote
I recently picked up the AF, non-APO version of this lens on Ebay (at a cheap enough price to not worry too much).

I have never worked with it previously, but had heard good things, and it was relatively well rated here and elsewhere. I wasn't ready to spring for a new expensive telephoto, but needed something in the 400mm range for migration season.

I got it home, and the copy I have seems to be fairly immaculate. No obvious damage, glass is completely clear, not even any dust visible inside. AF works very well, surprisingly quick and accurate for being an older lens. Even in low light, it still does pretty decently. The color is pretty good, with the downside of some CA even stopped down (but I knew about this ahead of time).

However, I have been having a hell of a time getting anything sharp out of it. And I don't even mean, tack sharp from a magazine...I mean, just reasonably sharp at all. I thought it might be an issue with front/back focus, but when I looked at some test pics, the focus doesn't seem to be off...it just seems like what is in focus is just not very sharp. And these were tripod pictures, at high shutter speeds in good light, and even stopped down to f/8 and f/11. At this point, I'm fairly sure this is not user error...even in fairly ideal conditions (i,e, NOT what I expect to have in the field), this is just not performing.

Is this a perrenial issue with this lens? I know it's not supposed to be amazingly sharp, but it's just really really soft to the point of only getting usable photos if I'm almost at the minimum distance, and the subject completely fills the viewfinder, and even then you don't want to look too closely to the detail because it's still not sharp at all. I'm not talkign about "not as sharp as it could be" I'm talking really unsharp.

Recommendations to figure out what the issue is? I hate to go through the whole AF adjustment process if the issue is more likely just a bad lens/bad copy of the lens.
Hello how are you?, I have just buy one of this from ebay, I don have it with me yet.
I want to know, if you have solve this focus or sharp problem,
And if it was a chip problem or what?, Thanks regards , JuliÓn
09-16-2013, 01:24 PM   #15
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It could be haze on an inner element. I purchased an AF APO version of the Sigma 400mm f/5.6 few years ago, sold it a few months later at a loss (disclosing the problem in the sale). The non-APO versions might suffer from the same problem, I'm not sure. Here's a thread about the problem:

haze in Sigma 400/5.6 APO (MF white version) (Page 1) - Maintenance & Repairs - Manual Focus Forum

Here's someone's photographs of a teardown of a lens to clean some haze, with the positive effects it had on the clarity of pictures:

Sigma APO 400mm MF disassembly - a set on Flickr
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