Should I really care about large aperture lens?

jito · Joined: 29 Nov 2011 Posts: 113

Lens with lower f number are more expensive than those with smaller apertures. I don't really know the reason, I can guess it has to do with large apertures being tricky/expensive to build.

I bought a couple manual focus of lenses with f smaller than 3 and start noticing many shots turned out to be out of focus. I googled this problem and it appears that most modern dSLRs have focusing screens calibrated to apertures with f greater or equal to 4.
Using the live view and its 5x or 10x magnification I am able to focus even at 1.8, but taking pictures using such method is a PITA.

Any decent autofocus lens (except for 50mm) will cost an amount of money which I am not really willing to spend. But I see more than only manual focus enthusiasts buying some manual focus lens with high apertures. For example, everybody is going crazy with the samyang 85mm f1.4 which is a recent manual focus lens. This makes me confused. How do they use such lenses? I see a lot of people claiming to be professional photographers using the samyang, how do they focus?
Or do high aperture lenses have other characteristics [besides the aperture] that make them better lenses?

I am tempted to get a vivitar 28-85 as a walkabout lens, the f2.8 is more expensive than the f3.5. Is the price difference solely based on the aperture or is the f2.8 better in other aspects too? I don't think would shoot much wide open with this lens, simply because my canon 1100d does not have a viewfinder with such precision.

adent · Joined: 06 Oct 2011 Posts: 304 Location: United States

The reason that you are having trouble getting in focus pictures is that the depth of field on a larger aperture lens is smaller. This means that if you are not spot on with your focusing it will be out of focus. Does your adapter have a focus confirmation chip? This will help a lot which is the method that I use. It gets me close, then it just comes down to knowing your equipment. On some lenses I have to go a little past the confirm point and some I have to back off a little. Just takes practice.

iangreenhalgh1 · Expire: 2014-01-07

Modern DSLRS suck for MF lenses, you can change the focussing screen to one with a focus aid like in old film SLRs, that should make a big difference. Focus confirmation works too, but with large apertures, it's still tricky as it's often literally a flash of the focus LED as you pass over the correct focus point.

For me, the solution is live view, I love it, I would never go back to using a camera without it, although I have just bought a dirt cheap secondhand a200 that doesn't have it, I am going to change the focussing screen and use a confirmation chip, just hope it works. I can probably manage without live view with MF lenses on the a200 as I will be doing 90% of the shooting at infinity and at small apertures for deep dof.

Some shots I took with a Hexanon 1.4/50 wide open on my NEX-3, for me, live view is essential to focus with a lens like this wide open as the dof is tiny:

On that Vivitar zoom, I say skip it, very few old zooms stand upto comparison with a prime lens and you will get much better IQ from old MF primes than you will from old MF zooms.

mfkita · Joined: 29 Jul 2007 Posts: 222

85mm F1.8 manual focus Nikkor on Canon 40D @ F2.8

As you can see, at full frame there seems to be a lot in focus...

Full frame...
http://img64.imageshack.us/img64/3366/85rlcuff12x13b.jpg

But....at near 100% crop you can see that there's not much more than a couple of centimeters in focus...

http://img156.imageshack.us/img156/4342/85rlccu43b.jpg
Manual focus is definitely not easier nor more accurate if you don't know how nor have the experience
...but the same is true for AUTO-focus, which is why so many people complain about out of focus shots taken with AF lenses...you have to understand the technology and how it works...

Nevertheless, when you consider that most people coming to dSLR photography now have no prior MF experience it is understandable that they are frustrated...especially using MF lenses on bodies NOT DESIGNED for MF lenses....

...but those of us with prior MF experience have something of ourselves, something of our aesthetic identity tied to manual focusing...it's the baggage we bring with us to digital photography...

Practice, patience, and persistence are the keys to expertise....and success....not to mention luck....so good luck....

Here's another less dramatic scene....50mm F1.4 @ 2.8-4 full frame and 100% crop...

visualopsins · Expire: 2025-04-11

Focus screen resolution is weak link here -- stock screens cannot resolve accurate DOF for lenses faster than f/3.5, thus focus seen could be anywhere within the f/3.5 DOF, even when lens is set to faster aperture. Look at DOF through viewfinder with lens at f/8, when opening aperture to watch DOF decrease until f/3.5, then hold size there even as aperture opens wider.

A focus confirm chip may help some, but since the Canon AF sensors are behind the focus screen, the confirm can be inaccurate. Noted focusing from infinity and then focusing from closer may yield two distinct focus ring positions, accurate focus being somewhere in-between. EDIT: This is wrong. In 5Dc White Paper on page 9, Canon says AF sensors operate at f/5.8. There are a few additional f/2.8 sensors used for faster lenses. If I interpret correct, AF confirm is limited to lenses f/2.8 and slower.

Canon makes focus screens for accurate manual focus of fast lenses. The part number is typically Ex-S where 'x' is a letter, specific to the camera model. For 5D classic the screen is Ee-S; for 5DII it is Eg-S.

People have cut Ee-S to fit in camera models without interchangeable focus screens. Lately Canon has had a brisk business selling Ee-S and Eg-S screens to Pentax camera owners(!), to grind to fit in their cameras.

mfkita · Joined: 29 Jul 2007 Posts: 222

I don't use them....too inaccurate and too distracting...but the ones I used were the 1st generation....I understand that subsequent versions are better....

buerokratiehasser · Joined: 12 Jun 2011 Posts: 470

Focus confirm is great, but has similar limitations. Sensors are often optimized for like f4 or f5. Unless micro-trimmed, sensors may be off by some tiny amount which shows when shooting at f2 because the DOF is so small. Sensor may not focus exactly where your center dot is, etc.

Also, many lenses are simply not so good wide open. If we don't count the lovely Sigma 2.8-4 (internet reports: "2.8 only at 28mm and extremly soft"), they show barrels of haze, CA, ghost images and general unsharpness. It wasn't that bad in film days since the crop factor was 1, people didn't look that close and film always had sort of an "analogue" look. Oh, and a slightly washy image was preferred to a shot with shake traces, I guess.

rbelyell · Expire: 2014-01-31

good question and many good answers given. to summarize:

1-unless you are shooting in low light or are looking for a very specific artistic effect there is no need for a lens faster than 2.8 and no reason to shoot wide open if your lens is faster than that. in fact lens manufacturers do not intend that their 'fast' lenses be shot wide open. most lenses are aharpest at about 2 stops over their wide open aperture. contrary to recent belief, you can still achieve a lovely blurred background (bokeh) with most 'normal' lenses at F2.8.

2-as lens FL increases, like from 28mm to 85mm, the DOF of the lens at any given aperture decreases as well. so a 28mm lens at 2.0 will probably get you a couple of feet in focus, while an 85mm lens at f2 will only get you a couple of inches in focus. here probably lies your difficulty with focus. some good rules of thumb that work for me is i take most single person portraits at 2.8, most multi person shots at 5.6, most street scenes at 5.6-8.0 and most landscapes at 8.0 or higher. bear in mind also that static scenes let you use higher aperture because you will not get blurred focus due to motion of your subject. people move, so you typically need shutter speed of at least 1/250 to stop most normal action. keep in mind also that your hand shakes too and this effects focus. as FL of lens increases so does the effect of 'camera shake' on focus. so as FL increases you have to increase shutter speed. good rule of thumb is the slowest SS you can use must at least equal FL of lens. so if you have to you can shoot a 28mm lens at 1/28 while an 85mm lens should not be shot below 1/85.

3-its good to have at least one 'fast' lens, 1.4-2.0, to enable low light photography. because of the DOF issues above, assuming cost is a consideration, you want a lens in the 35-50mm range, 35mm having better DOF so more will be in focus.

FluffPuppy · Joined: 11 Dec 2011 Posts: 365

ManualFocus-G · Expire: 2014-11-24

Being able to shoot in low light without flash is a massive reason to shoot wide open with a fast lens. Yes, focusing can be tricky, but practice makes perfect! I was shooting my fast moving niece at ISO1600 and f/1.4 with my Carl Zeiss Planar 85/1.4 yesterday...normally I would get 90% in focus, but she moves so fast these days I only managed a 30% keeper rate Laughing

It definitely helps to have a big viewfinder and MF focusing screen (5D and EE-S in this case):

Lloydy · Expire: 2022-01-01

Focus confirmation can be remarkably accurate. With my Pentax K10 and my crappy eyesight I use 'catch in focus' sometimes called 'focus trap' a lot with some manual lenses. And the results sometimes astonish me.

It does mean somehow shorting out all the pins on the camera mount, and with a cheap lens I scrape a bit of paint off the lens base, or use aluminium tape, and for some lenses I make a large washer thing, but whatever - it works.

I either do a test shot to get the aperture right and the focus very close, then set the camera to AF.S and either turn the focusing ring while pressing the shutter button until the subject is in focus according to the focus confirmation and the shutter fires automatically. This can be hand held but on a tripod is best - or I have the camera on a monopod, set the focus etc and then slowly rock the camera forward until it fires, this is very easy and effective.

But the point is, with relevance to this topic, that focus confirmation can be very accurate.

rbelyell · Expire: 2014-01-31

FluffPuppy · Joined: 11 Dec 2011 Posts: 365

luisalegria · Expire: 2018-01-18

It depends on the lens and the situation whether its should be shot wide open.

I would like to think that any decent manufacturer would honestly intend that its lenses are usable wide open. Not necessarily at their best, but more than adequate for the purpose, which in reality rarely requires pixel-peeping.

And as for long lenses (200mm+), they absolutely have to be good wide open because thats where they will mostly be used.

I recently got a very interesting book, Peter Buckley, "Bullfight", published in 1958. Most of the pictures are shot with a 300mm f/2.8 Sonnar wide open, on a Contax SLR. This was required, not only artistically, but to keep the shutter speed high with the Tri-X film of the day. There are some truly amazing shots in there. Many are grainy, some are imperfectly focused, but if they caught "the moment", thats all that counts.

abe in space · Joined: 24 Oct 2011 Posts: 40

Whoever said modern DSLRs screens are "calibrated" for f4 and up was...sugar coating the matter. That's a marketing gimmick. There's no "calibration." What it really means is, "modern DSLRs do not have focusing screens; to compensate for this, stop down." And it's not really surprising, though. Camera and lens innovations in the past 20 years have all been prioritizing totally different things: autofocus, image stabilization, and zooms. Even the lenses themselves contribute: the vast majority of AF lenses have dreadfully bad manual focus rings, especially smaller ones like the 50mm models.

But I digress. If you're doing still photography with a modern DSLR, I'd definitely want to get an aftermarket focusing screen. Seriously, there's just no comparison between shooting stills with MF on my old Canon AE-1 vs my T3i. However, as I'm not really a still photographer, and primarily shoot video, I'm in Live View almost all of the time, which allows me to zoom in, so that's how I focus. Eventually I'll likely get a larger off-cam monitor for even more precise focusing, but that's another matter, and not something a still photog would want to do. I'd order yourself a nice focusing screen and shoot in Live View in the meantime.

And of course, practice makes perfect.

luisalegria · Expire: 2018-01-18

For what its worth -

Its perfectly possible to shoot wide open without replacement screens on Pentax DSLR's at least.

It takes a bit of practice to get a high percentage of decently focused pictures. These DSLR's lack a proper groundglass, but with a good lens, wide open, you can still see the point of critical focus, once you are used to it. Make sure your diopter adjustment is accurate !
I get the focus confirm to get me in the general area, then I rock back and forth slightly until the part I want looks good. I don't think a microprism or split screen would improve much, and it may slow down the process.

Most of the problem really is deciding on the proper point of focus for the narrow depth of field, and catching it at the critical moment. An AF lens could just as easily decide to focus on the nose or ear rather than the eyes, just as an example, and look just as bad as a misfocused manual lens. In my case, I deal with a lot of birds at close range. I want to get the eye in focus on a constantly moving creature. Split image and etc. are just too slow and AF doesn't really know what I want.

rbelyell · Expire: 2014-01-31

yup youre right fluffpuppy (nice name btw), i meant to say 'most' but didnt. i also mispoke when i said 'not intended'. to be more clear, lenses are not 'optimized' for best performance wide open. fast lenses give one the option to 'grab' a shot at wide aperture that you may not be able to get at all with a slower lens. the best 'fast' lenses will even give you a 'decent' or 'good' shot within the severe wide-open-aperture DOF constraints, but they will not give you the 'optimal' shot the lens is capable of stopped down. all things being equal in good light, almost any lens i know will yield better IQ stopped down from the widest aperture. that is what most lens manufacturers intend.

so for the original question, 'should i care about fast aperture?', i would say 'no' unless you need low light performance, because most lenses are optimized for best performance stopped down.

and i totally agree with luis above that the real issue, both with focus and 'shooting fast' is understanding and negotiating DOF. at 1.4 with lenses 50-85mm you are dealing with DOF of less than a foot, with DOF decreasing as FL increases. thats why with these lenses it never made sense to me to make a practice of shooting wide open, as the in focus parameters are much too restrictive to the sharp look i personally want from my photos.

att 35mm at 2.0 your DOF goes from about one foot close up to maybe 5-6 feet at 10-20 feet, so things are a liitle easier, but still, most WA lenses work best around F8.

FluffPuppy · Joined: 11 Dec 2011 Posts: 365

rbelyell · Expire: 2014-01-31

well i'm always happy to learn something new! perhaps you could point out a few lenses that perform best wide open and deteriorate as you stop down. i'm sure many others are interested in this as well.

Orio · Expire: 2012-12-04

Leica's Apo-Telyt-R 3.4/180 is notorious to give the best performance wide open. It's a lens developed for naval sighting use.
Then I know some lenses that have wide open the same performance as stopped down, one of them is the Sonnar 3.5/100,
but I don't know any other whose performance degrades after wide open.

Esox lucius · Expire: 2011-11-18

I can divide my income in two areas: corporate assignments (print ads and product photography) and wedding photography. When I'm shooting commercial work, I'm mostly required to stop down for depth of field. When I shoot weddings, I shoot 98% of my frames at f/2.8 or wider, the 200/2 and 85/1.4 being my favorites and the 24-70/2.8 likely my most commonly used.

In photography, you aren't required to do anything as others do. Find your preferred lens and f-stop, and paint what you want to paint.

FluffPuppy · Joined: 11 Dec 2011 Posts: 365

jito · Joined: 29 Nov 2011 Posts: 113

I can't find the page now. But a while ago I red a rather comprehensive article explaining the limitations of modern dSLR focusing on high apertures. I'm not sure 'calibrated' was the exact word, it mentioned that the microlenses on the focusing screen are not accurate enough to show an image out of focus when the focus is off by just a little bit.

Personally I'd be happy with a split prism, Luís, why do you say it wouldn't improve much?

My m42 adapter came with a confirm chip, but after a few tries all I could get was a red warning saying 'lens error' or something like that, in any mode. I didn't bother and simply removed the chip. I don't regret it, it was cheaply glued not very accurately in place, in fact I kind of felt like I could potentially damage my camera by using some bogus electronics. I'm not sure I trust such cheap electronics to be plugged in such a sensitive part of my camera. But I am still curious.

Opinions seem to be divided, some say they help, some are frustrated that they are inaccurate. As a skeptical I ask: how does the focus confirm mechanism works? How does the camera senses a point is on focus? Also, where does the focus occur? I already heard two versions, some say its on the main sensor (hence the mirror should let some light pass), some say it's behind the focusing screen. If my camera (canon eos 1100d) has the latest, then I really don't understand how a confirm chip would help at all. Yet canon does sell a lot of AF lenses with high aperture, so I guess it should work somehow (how?).

I don't really intend to do this because of the risk of damaging my camera, but I have an old Olympus OM-10, with the right equipment, could the screen be cut to appropriate size and fit into my canon?

Another thing I'm not quite getting is all the references to experience and practice. As a newbie, I want to respect the experience of those that have been taking pictures for many years, but if I may, what exactly takes practice? Someone mentioned that if on knows his equipment he/she will know where the focus is for a given lens even without any sort of feedback, not even image sharpness. Is that what you guys mean by experience and practice? Sounds like a not so enjoyable way of taking pictures, even for those with practice.

I mean zero sarcasm in my questions, I'm genuinely curious.

rbelyell · Expire: 2014-01-31

i guess there is an exception to every rule, but given your reply fluffpuppy, i think i'll stand by my original statements that most lenses most of us will use or afford are both optimized and perform better stopped down than wide open. because of this, the advantage of shooting wide open is apparent to me only in low light and is thus overrated, and even counterproductive, in most other situations.

of course, as orio's post shows, when we speak of specialty lenses or lenses that are slow wide open (3.5-8.0), we would expect lens performance to degrade much less--or not at all--as you stop down from open. my points were addressing fast lenses of 2.0 and less.

FluffPuppy · Joined: 11 Dec 2011 Posts: 365