Soft images at f8 and infinity focus

canteaus · 06-29-2015, 04:44 AM

Hi everyone,

I'm a long-time reader and first-time poster here on Pentax Forums

I'm having some focus issues with my Pentax lens. I own a film Pentax MX with a Pentax-M 50mm f1.4 lens.
Yesterday, I shot some landscape photos in super bright weather.
I set the aperture to f8 and my shutter speed was always above 1/500s of a second. I also manually-focused the lens to infinity because shooting far-away landscape.

When I saw my developed photos today, the images were soft. What's wrong here? Surely I didn't have camera shake.
My camera + lens has no problems taking sharp photos of closer subjects.

What's going on here? Is there something wrong with the lens at infinity focus?

Thanks

ChristianRock · 06-29-2015, 05:17 AM

I have two lenses where infinity focus is off. It basically means that your actual infinity is before the Infinity mark. What you are seeing, I think, is your lens actually focused past infinity.

Na Horuk · 06-29-2015, 05:40 AM

Originally posted by canteaus

I set the aperture to f8 and my shutter speed was always above 1/500s of a second. I also manually-focused the lens to infinity because shooting far-away landscape.

Are you sure the camera stopped down the lens correctly? Because a photo can look soft if its f1.4 focused at infinity. The other problem might be actual infinity focus - the lens' focus ring might be miscalibrated, or the lens mount might be a little off, thus preventing the lens from reaching infinity. One other possibility with a miscalibated focus ring is that the lens might focus past infinity.
The other thing is the film and developing itself, which might not be as "sharp" as you expect if you used modern DSLRs with digital sharpening. Especially if there was some atmospheric haze or something.

canteaus · 06-29-2015, 05:47 AM

I'm definitely shooting at f8 - there's no mistake about that.

Perhaps ChristianRock is right, maybe my infinity marking is past infinity.....

I guess the easiest way to test this is to find a digital Pentax SLR and test my lens?

Adam · 06-29-2015, 06:17 AM

Focusing at infinity can be tough with longer lenses. A magnifying eyepiece might help. But nothing beats live view with magnification

Na Horuk · 06-29-2015, 06:36 AM

Originally posted by Adam

But nothing beats live view with magnification

From the post I assumed OP used the lens on a Pentax MX film camera, but I may be wrong.
If OP used the lens on DSLR: Make sure you use M mode with a fixed ISO number, as the camera will shoot wide open at any other mode (they all default to Av, with no possibility of stopping down). LV with peaking and digital zoom can help a lot, since modern DSLR viewfinders are not designed for MF.

**jatrax** · 06-29-2015, 07:43 AM

Originally posted by canteaus

Yesterday, I shot some landscape photos in super bright weather. I set the aperture to f8 and my shutter speed was always above 1/500s of a second. I also manually-focused the lens to infinity because shooting far-away landscape.

As others have noted, just setting the lens to the infinity mark may not really be infinity. Many lenses actually focus beyond infinity.

Also, just because a landscape is 'far away' does not mean it is all at infinity. Is all of the image soft? Is any part of it sharp? It is possible the foreground is soft because you focused too far away and the background part is actually sharp. Focusing at infinity means the foreground will be soft.

Another thought is atmosphere. Long distance shots especially in the summer are often soft because of atmospheric haze.

stevebrot · 06-29-2015, 08:48 AM

Sharp and distance are two words that seldom occur in the same sentence in the world of photography and focus is generally not the reason. As jatrax noted, the reason is air...air full of junk and moisture and temperature-related refraction.

One other consideration is that of sorrow of the pixel peeper...

Steve

canteaus · 06-29-2015, 09:42 AM

Thanks for your help everyone.

I was shooting the 50mm lens on film, with my Pentax MX.

The subject was indeed, "far away" about 900 meters, so infinity should be right.

However, as many have mentioned, my lens might not be properly calibrated and I may be focusing beyond infinity. It was also a sunny day so maybe the weather had something to do with it.

I'm going to take some scientific shots with precise measurements and I'll report back with photos~ thanks again!

Na Horuk · 06-29-2015, 10:16 AM

Btw, were you using a lens hood? It won't improve sharpness itself, but it can help a lot with overall image quality. And on very sunny days, you might think about using a UV filter. UV filters are useless on DSLRs, but they have a use with film cameras, so you can read up about that

And no, 900m does not necessarily mean infinity. It might be just a hair before infinity, but still

BrianR · 06-29-2015, 12:03 PM

Have you ruled out a problem in the developing chain? Were there other photos on the roll that turned out sharp?

Originally posted by Na Horuk

And no, 900m does not necessarily mean infinity. It might be just a hair before infinity, but still

You'll be hard pressed to find an object actually "at infinity". The depth of field is also absurdly massive at long focus distances, there should be plenty of room for error here (especially at f/8).

stevebrot · 06-29-2015, 07:17 PM

Originally posted by canteaus

I was shooting the 50mm lens on film, with my Pentax MX.

The subject was indeed, "far away" about 900 meters, so infinity should be right.

A 50mm lens at infinity on film? Which 50mm and how are you assessing sharpness? If with anything other than a magnifying loup on the negative and something like Adox CMS 20 film, you are wasting your time and even then, the use case is sort of unusual.

FWIW, your best bet is to use the viewfinder focus aid to determine focus, not the focus scale on the lens. If the two do not compare, you can adjust the lens focus scale and infinity stop, though I would not do so against the focus screen. Instead, you collamate the lens and/or mount shims to the focal plane using a ground glass or focus screen*. Likewise, if you choose to collamate the focus screen, you do so against the focal plane.

Steve

* I know a tech who uses a split-image focus screen for this purpose.

**RKKS08** · 07-01-2015, 11:56 AM

At "really bright weather" (blue summer sky around noon) you should keep in mind that film IS sensitive for UV light, but the lens is not corrected for these frequencies. The effect is mostly making the picture looking very soft, like a slight haze .

I had to learn this back in the sixties and seventies, specially in high mountains, at the sea, and in winter in snowy landscape.
But you should use a SMC or similiar coated UV filter, and ONLY in connection with a lens hood. Otherwise you may worsen the problem.

Of course, with digital cameras you won't need that filter. UV frequencies are higher than the upper limit the sensors do accept.

ChristianRock · 07-02-2015, 01:16 PM

Originally posted by canteaus

I'm definitely shooting at f8 - there's no mistake about that.

Perhaps ChristianRock is right, maybe my infinity marking is past infinity.....

I guess the easiest way to test this is to find a digital Pentax SLR and test my lens?

Your MX should have a split screen that would allow you to see when the lens is in proper focus. That's how I found out that my 24mm lens was focusing past infinity.

canteaus · 07-02-2015, 10:27 PM

Originally posted by ChristianRock

Your MX should have a split screen that would allow you to see when the lens is in proper focus. That's how I found out that my 24mm lens was focusing past infinity.

Just one quick question then. Is there anyway that my split screen might not be properly calibrated to my lens?

Is my split screen seeing what my lens sees?

06-29-2015, 04:44 AM	#1
canteaus New Member Join Date: Jun 2015 Posts: 4	Soft images at f8 and infinity focus Hi everyone, I'm a long-time reader and first-time poster here on Pentax Forums I'm having some focus issues with my Pentax lens. I own a film Pentax MX with a Pentax-M 50mm f1.4 lens. Yesterday, I shot some landscape photos in super bright weather. I set the aperture to f8 and my shutter speed was always above 1/500s of a second. I also manually-focused the lens to infinity because shooting far-away landscape. When I saw my developed photos today, the images were soft. What's wrong here? Surely I didn't have camera shake. My camera + lens has no problems taking sharp photos of closer subjects. What's going on here? Is there something wrong with the lens at infinity focus? Thanks

06-29-2015, 05:17 AM	#2
ChristianRock Pentaxian Join Date: Jul 2013 Location: People's Republic of America Photos: Gallery \| Albums Posts: 9,910	I have two lenses where infinity focus is off. It basically means that your actual infinity is before the Infinity mark. What you are seeing, I think, is your lens actually focused past infinity. Last edited by ChristianRock; 06-29-2015 at 07:33 AM.

06-29-2015, 06:17 AM	#5
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Focusing at infinity can be tough with longer lenses. A magnifying eyepiece might help. But nothing beats live view with magnification Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

07-01-2015, 11:56 AM	#13
RKKS08 Site Supporter Join Date: Mar 2010 Location: Frankfurt am Main Posts: 1,241	At "really bright weather" (blue summer sky around noon) you should keep in mind that film IS sensitive for UV light, but the lens is not corrected for these frequencies. The effect is mostly making the picture looking very soft, like a slight haze . I had to learn this back in the sixties and seventies, specially in high mountains, at the sea, and in winter in snowy landscape. But you should use a SMC or similiar coated UV filter, and ONLY in connection with a lens hood. Otherwise you may worsen the problem. Of course, with digital cameras you won't need that filter. UV frequencies are higher than the upper limit the sensors do accept. Last edited by RKKS08; 07-01-2015 at 12:20 PM. Reason: typing

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06-29-2015, 05:40 AM	#3
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	Originally posted by canteaus I set the aperture to f8 and my shutter speed was always above 1/500s of a second. I also manually-focused the lens to infinity because shooting far-away landscape. Are you sure the camera stopped down the lens correctly? Because a photo can look soft if its f1.4 focused at infinity. The other problem might be actual infinity focus - the lens' focus ring might be miscalibrated, or the lens mount might be a little off, thus preventing the lens from reaching infinity. One other possibility with a miscalibated focus ring is that the lens might focus past infinity. The other thing is the film and developing itself, which might not be as "sharp" as you expect if you used modern DSLRs with digital sharpening. Especially if there was some atmospheric haze or something.

06-29-2015, 05:47 AM	#4
canteaus New Member Join Date: Jun 2015 Posts: 4 Original Poster	I'm definitely shooting at f8 - there's no mistake about that. Perhaps ChristianRock is right, maybe my infinity marking is past infinity..... I guess the easiest way to test this is to find a digital Pentax SLR and test my lens?

06-29-2015, 06:36 AM	#6
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	Originally posted by Adam But nothing beats live view with magnification From the post I assumed OP used the lens on a Pentax MX film camera, but I may be wrong. If OP used the lens on DSLR: Make sure you use M mode with a fixed ISO number, as the camera will shoot wide open at any other mode (they all default to Av, with no possibility of stopping down). LV with peaking and digital zoom can help a lot, since modern DSLR viewfinders are not designed for MF.

06-29-2015, 07:43 AM	#7
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Originally posted by canteaus Yesterday, I shot some landscape photos in super bright weather. I set the aperture to f8 and my shutter speed was always above 1/500s of a second. I also manually-focused the lens to infinity because shooting far-away landscape. As others have noted, just setting the lens to the infinity mark may not really be infinity. Many lenses actually focus beyond infinity. Also, just because a landscape is 'far away' does not mean it is all at infinity. Is all of the image soft? Is any part of it sharp? It is possible the foreground is soft because you focused too far away and the background part is actually sharp. Focusing at infinity means the foreground will be soft. Another thought is atmosphere. Long distance shots especially in the summer are often soft because of atmospheric haze.

06-29-2015, 08:48 AM	#8
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Sharp and distance are two words that seldom occur in the same sentence in the world of photography and focus is generally not the reason. As jatrax noted, the reason is air...air full of junk and moisture and temperature-related refraction. One other consideration is that of sorrow of the pixel peeper... Steve

06-29-2015, 09:42 AM	#9
canteaus New Member Join Date: Jun 2015 Posts: 4 Original Poster	Thanks for your help everyone. I was shooting the 50mm lens on film, with my Pentax MX. The subject was indeed, "far away" about 900 meters, so infinity should be right. However, as many have mentioned, my lens might not be properly calibrated and I may be focusing beyond infinity. It was also a sunny day so maybe the weather had something to do with it. I'm going to take some scientific shots with precise measurements and I'll report back with photos~ thanks again!

06-29-2015, 10:16 AM	#10
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	Btw, were you using a lens hood? It won't improve sharpness itself, but it can help a lot with overall image quality. And on very sunny days, you might think about using a UV filter. UV filters are useless on DSLRs, but they have a use with film cameras, so you can read up about that And no, 900m does not necessarily mean infinity. It might be just a hair before infinity, but still

06-29-2015, 12:03 PM	#11
BrianR Veteran Member Join Date: Dec 2010 Location: Ontario Photos: Gallery Posts: 3,332	Have you ruled out a problem in the developing chain? Were there other photos on the roll that turned out sharp? Originally posted by Na Horuk And no, 900m does not necessarily mean infinity. It might be just a hair before infinity, but still You'll be hard pressed to find an object actually "at infinity". The depth of field is also absurdly massive at long focus distances, there should be plenty of room for error here (especially at f/8).

06-29-2015, 07:17 PM	#12
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by canteaus I was shooting the 50mm lens on film, with my Pentax MX. The subject was indeed, "far away" about 900 meters, so infinity should be right. A 50mm lens at infinity on film? Which 50mm and how are you assessing sharpness? If with anything other than a magnifying loup on the negative and something like Adox CMS 20 film, you are wasting your time and even then, the use case is sort of unusual. FWIW, your best bet is to use the viewfinder focus aid to determine focus, not the focus scale on the lens. If the two do not compare, you can adjust the lens focus scale and infinity stop, though I would not do so against the focus screen. Instead, you collamate the lens and/or mount shims to the focal plane using a ground glass or focus screen. Likewise, if you choose to collamate the focus screen, you do so against the focal plane. Steve I know a tech who uses a split-image focus screen for this purpose.

07-02-2015, 01:16 PM	#14
ChristianRock Pentaxian Join Date: Jul 2013 Location: People's Republic of America Photos: Gallery \| Albums Posts: 9,910	Originally posted by canteaus I'm definitely shooting at f8 - there's no mistake about that. Perhaps ChristianRock is right, maybe my infinity marking is past infinity..... I guess the easiest way to test this is to find a digital Pentax SLR and test my lens? Your MX should have a split screen that would allow you to see when the lens is in proper focus. That's how I found out that my 24mm lens was focusing past infinity.

07-02-2015, 10:27 PM	#15
canteaus New Member Join Date: Jun 2015 Posts: 4 Original Poster	Originally posted by ChristianRock Your MX should have a split screen that would allow you to see when the lens is in proper focus. That's how I found out that my 24mm lens was focusing past infinity. Just one quick question then. Is there anyway that my split screen might not be properly calibrated to my lens? Is my split screen seeing what my lens sees?