[NicoleAu]

lol @ all the stupid question threads this title brought up.

Anyway, I was curious. I have an M 50mm f1.7 lens and I'm buying another 50mm lens, but an FA f1.4 because I have an awful time trying to focus manually on children lol.

What I was wondering if anyone could tell me, is why they make f1.4 lens if they're virtually unusable wide open? Ie too soft for portraiture etc. Wouldn't it make more sense to start them at the aperture they start to perform well at?

Like I said, I hope this question isn't too stupid lol.

[Mike Cash]

For one thing, it helps gather more light, which I suspect helps the autofocus system in low-light situations even if you're shooting at a smaller aperture.

[NicoleAu]

Yeah I get that it helps to get more light which is good, but why are they so soft wide open?

[KxBlaze]

Faster the aperture = more $$$$$ to the manufacturer.

But seriously, I do not think it is unusable wide open. Definitely not as sharp as a few stops down but my M 50 1.7 is pretty good at 1.7. I have never shot anything faster than that on a Pentax camera and like Mike said when shooting indoors my 1.7 is great. I can normally get a shutter speed of about 1/80 and I shoot indoors a lot.

I have though, shot a 85mm 1.2 on a canon and even at 1.2 it was very sharp (but it was on a 5D MkII and the lens was well over $1000.

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Last edited by KxBlaze; 02-14-2011 at 04:25 PM.

[epqwerty]

They aren't soft wide open it really depends on the lens you have. The dof is shallow which is what you are getting confused with I think. So why make it lenses that are 1.4 or less is for ability to shoot at low light without having to use flash. But I think the best aspect of such a wide aperture is for the smooth creamy blur that you can get with such a lens. Mind you some of these lenses are made before the days or digital slr in which you can change your iso on the spot. Before you were restricted to the film that you placed in the camera at the time.

[JeffJS]

Yeah I get that it helps to get more light which is good, but why are they so soft wide open?

The long answer..

Circle of confusion - Wikipedia, the free encyclopedia

[Just1MoreDave]

Yeah I get that it helps to get more light which is good, but why are they so soft wide open?

Every lens is like that to a certain extent. You can see for yourself by setting up the camera on a tripod and taking a series of shots at each full stop aperture. Sharpness (particularily corner sharpness), contrast and color saturation all improve from wide open to maybe f8 or so, then start to decline slowly.

A few lenses have a limited maximum aperture for different reasons. Look at one of the 50mm macros which only open to f2.8. Macro lenses are well-corrected for abberations, and it would be very difficult and expensive to do that at f1.4. Also at shorter distances where you'd use it, f1.4 provides essentially no depth of field. Other lenses are limited for marketing reasons, such as the K55/2. The DA-L 35mm f2.4 is very close optically to the old FA 35mm f2, yet doesn't open to f2. I suspect that's a combination of marketing and optimization. I often use my FA 35mm f2 at f2.4 because it's better there.

Your first post had the phrase "virtually unusable" and I don't think that's true. You just have to be aware of the changing characteristics, depth of field, subject distance, and choose the best aperture for the situation. I have the K135/2.5, a great lens. At its minimum focus distance and maximum aperture, depth of field is not quite a half-inch - can't even get a whole nose in that. But I have taken nice portraits with it, just not at MFD/wide open.

[NicoleAu]

Blaze, that's kind of what I was asking, as in having to stop it down to get the best sharpness. I was wondering why not just have it start at that aperture anyway?

Ok that circle of confusion is confusing me lol.

Ok, it must be my copy of it that's soft wide open. But I have read a lot of reviews that the FA 1.4 is soft wide open?

Just saw Daves post and it explains a lot of what I was trying to find out. Thank you.

[blackcloudbrew]

These older MF lenses were made for older film cameras which generally had either larger viewfinders and / or a split image rangefinder which makes using these lenses a lot easier. You can get a different viewfinder from people like Katzeye. KatzEye™ Optics - Custom Focusing Screens I have on on my K-10 and it turned my 85mm f1.4 lens into a very usable lens at wide open.

[ragingtornado]

Definitely not "unusable" wide open, some of my best shots were taken at 1.4. You just have to be exact with the focusing, in which case i find the lens is actually quite sharp, considering the shallow DOF and price of the lens.

[sajah]

Every lens is like that to a certain extent. You can see for yourself by setting up the camera on a tripod and taking a series of shots at each full stop aperture. Sharpness (particularily corner sharpness), contrast and color saturation all improve from wide open to maybe f8 or so, then start to decline slowly.

To add a bit more perspective, a 50mm 1.4 at F2.8 will likely to be sharper than a 50mm 2.8 at F2.8 simply because with the first lens you close the aperture down and thus improve the sharpness while with the second lens it's wide open.

Of course this isn't always true, depends on the quality of the lenses in comparison but generally it's like this.

As Dave have said, having a 50mm 1.4 lens doesn't mean you have to always use it at F1.4. No one can stop you from using F2.8 for example, but when you really need F1.4 (for example in low light situation) you know you can have it.

[NicoleAu]

Thanks for all the responses, I also wonder why does the lens become sharper when you stop it down vs another one at the same aperture wide open, like in your example Sajah?

To add a bit more perspective, a 50mm 1.4 at F2.8 will likely to be sharper than a 50mm 2.8 at F2.8 simply because with the first lens you close the aperture down and thus improve the sharpness while with the second lens it's wide open.

[KxBlaze]

Blaze, that's kind of what I was asking, as in having to stop it down to get the best sharpness. I was wondering why not just have it start at that aperture anyway?

Ok that circle of confusion is confusing me lol.

Ok, it must be my copy of it that's soft wide open. But I have read a lot of reviews that the FA 1.4 is soft wide open?

Just saw Daves post and it explains a lot of what I was trying to find out. Thank you.

Because 1.7 or 1.4 is still usable (to some people) so it's nice to have that option instead of just being able to start at 3.5. Every single lens will be sharper stopped down a bit but again it's nice to be able to use 1.4 when you need it, like for indoor shots.

The FA is soft wide open but it's soft compared to stopped down. The FA at 1.4 will still be sharper than other lenses at 3.5.

[mccarvindh]

Many a times softness is desirable in portraits. I have definitely found f 1.4 shots usable. This link is a wide open shot with fa 50 1.4. It is not the best example of what this lens can do, but it is definitely usable IMGP3976 | Flickr - Photo Sharing!

[noblepa]

Thanks for all the responses, I also wonder why does the lens become sharper when you stop it down vs another one at the same aperture wide open, like in your example Sajah?

All lenses have a "sweet spot", or a particular aperture at which they are their sharpest. One lens may be sharpest at f/5.6, while another is at its best at f/8.

To some extent, what you refer to as "becoming sharper" may not be sharpness at all. It may be simply that the depth of field has increased and at the smaller aperture, more of the subject(s) in the picture are in focus.

A 50mm, f/1.4 lens, shot wide open, has one point of critical focus. Let's take a face. You may focus on the tip of the subject's nose. At f/1.4, there's a good chance that their ears are slightly out of focus. This is not a case of the lens being soft. Its merely obeying the laws of physics.

Without moving the camera, stop the lens down to f/5.6 or f/8. Now, the depth of field is more than enough to have the subject's nose, eyes and ears, all in sharp focus. The critical focus point hasn't changed. Only the depth of field has.

One reason for large apertures, such as f/1.4, is that, in some cases, for artistic reasons, the photographer WANTS extremely shallow depth of field. That is a problem for photographers shooting APS-C dslrs. A "normal" lens for aps-c is about 30mm, while it was 45-50mm for a 35mm or full-frame dslr. The shorter the focal length of a lens, the more depth of field it has. Couple that with the fact that many zoom lenses today, especially the kit lenses, have maximum apertures of f/3.5 or smaller. This combination can make it very difficult to achieve a shallow depth of field. Indeed, this is one of the primary arguments in favor of full-frame dslrs.