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90mm f2.8 lens bokeh- no such thing as a stupid question...but

dinneenp

Hi,
Would a Tamron SP AF 90mm 2.8 DI MACRO lens offer more blurred background/bokeh that a 17-50 f2.8 lens as it's focal point is further?

Or is it not dependent on the focal length at all?
Cheers,
Pa

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the_monkey

dinneenp wrote: »

Hi,
Would a Tamron SP AF 90mm 2.8 DI MACRO lens offer more blurred background/bokeh that a 17-50 f2.8 lens as it's focal point is further?

Or is it not dependent on the focal length at all?
Cheers,
Pa

It should yeah, focal length does affect it afaik, I get great bokeh with 400mm a f5.6 , while I wouldn't get the same at 50mm f5.6.

So 90f2.8 should give a little more bokeh then 50f2.8 ...

Prenderb

As I understand it (deep breath, stand back, wait for corrections :P )the bokeh is a function of the depth of field, so a lens configuration that gives you a narrow depth of field gives increased bokeh. As the monkey says, shorter focal lengths at the same aperture will give less bokeh, but I hope it's because of what I said.

Fajitas!

The 90mm should give you a softer, creamier bokeh. I've no experience with the lens, so I can't tell you what it's like.

Unless by bokeh, you mean depth of field, in which case, no, focal lenght doesn't dictate DOF, just the aperture and distance to subject will.

dinneenp

Thanks. I have the 17-50 lens and am looking at a 50mm f1.4 but now considering the 90mm. Two very different lenses, I know.

charybdis

You're not talking about bokeh.

It's a bit of a meaningless question to ask which would produce shallower depth-of-field, also. They're very different lenses, they're used differently, and will produce different results in different conditions.

That said; the shots you would take with the 90mm would probably have the appearance of shallower depth-of-field.

Also: the degree to which you think slightly shallower depth-of-field is as important in photography as your question suggests leads me to think you're going about this whole endeavour in a bad way.

Thecageyone

It's possible to get nice bokeh from th 17-50, and shallow DOF, if you wish. The 2.8 aperture does that, not the focal length.

The 90mm will most likely have better overall IQ, being a prime. But as for DOF ... already been answered really.

dinneenp

charybdis wrote: »

You're not talking about bokeh.

It's a bit of a meaningless question to ask which would produce shallower depth-of-field, also. They're very different lenses, they're used differently, and will produce different results in different conditions.

That said; the shots you would take with the 90mm would probably have the
appearance of shallower depth-of-field.

Also: the degree to which you think slightly shallower depth-of-field is as important in photography as your question suggests leads me to think you're going about this whole endeavour in a bad way.

Thanks for the reply.
I'm talking about taking pictures of (mainly) my young kids. And when asking which would give more blurred background I mean under the same conditions and in same setting (e.g. Garden, indoors etc) and not vert low light.

I know the 50mm should be quicker and is a lot smaller and that they're different lenses but I'm wondering hick would be better for this kind of shot.

Cheers
Pa.

charybdis

Thecageyone wrote: »

It's possible to get nice bokeh from th 17-50, and shallow DOF, if you wish. The 2.8 aperture does that, not the focal length.

The 90mm will most likely have better overall IQ, being a prime. But as for DOF ... already been answered really.

No. None of those things are anything to do with bokeh.

Otherwise, focal length is a factor when considering depth-of-field (which should be brutally obvious given that aperture is expressed in terms of focal length).

Thecageyone

What is it you don't like about the Tammy 17-50 Pa? I've seen you mention it wasn't up to your expectations a few times now. Personally I love it, sure, you can get sharper, but it's very versatile and the constant aperture is sweet. Maybe you got a bad copy?

I don't miss my 50mm 1.8 at all since I bought this, but I do miss just having a prime, I get that they can be a lot sharper. The nikkor 1.8 is a noisey little *&^$er though and I found it hunted a lot, even in good light! If I go for another 50mm it'll be either version of the 1.4, or the 85mm.

charbydis, are you saying aperture has nowt to do with DOF??

Iwannahurl

My tuppence worth, as an amateur photographer with a bunch of years' experience under my belt.

Firstly, my understanding of bokeh is that it is a more qualitative concept. Bokeh is background/foreground blur, sure, but I tend to regard the term as also referring to the quality of that blur. Therefore two different makes of lens of the same focal length and with the same maximum aperture will have similar depth of field and a similar degree of blur, but one may have a better quality of bokeh. My technical knowledge ends here, but I also believe the quality of bokeh relates to the design of the aperture iris (diaphragm). I have an old Minolta 85mm f1.4 that I use with my Sony A700, and that's a lens that's renowned for its bokeh. I'm sure I don't do it justice, but I like what I get all the same when the lighting is right.

There is a mathematical relationship between focal length, aperture (f-stop) and the distance the subject is from the camera. Don't forget also that in digital cameras there is a multiplication factor with sensors that are not full frame.

Here's a webpage that explains Depth of Field and also includes a DoF calculator. I learned all that stuff out of books and by trial and error when I first started tinkering with film cameras some time in the last millennium. I never think about the numbers now and I just go by the feel and look of things. No doubt I've forgotten the technical details, so I am open to correction and further education.

melekalikimaka

bokeh can mean alot of things to alot of people. you seem to be looking for depth of field over bokeh I 'think'.

Fajitas!

melekalikimaka wrote: »

bokeh can mean alot of things to alot of people. you seem to be looking for depth of field over bokeh I 'think'.

Bokeh:
In photography, bokeh is the blur, or the aesthetic quality of the blur in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."

Courtesy of Wikipedia.

From here on, that's all it means.

Thecageyone

Personally I prefer circular. So long as it's not teddy bears or love hearts it's no big deal.

Kintarō Hattori

Thecageyone wrote: »

Personally I prefer circular. So long as it's not teddy bears or love hearts it's no big deal.

Starts making one right away.....

melekalikimaka

Fajitas! wrote: »

Bokeh:
In photography, bokeh is the blur, or the aesthetic quality of the blur in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."

Courtesy of Wikipedia.

From here on, that's all it means.

thats three different things, is it either or?

charybdis

Fajitas! wrote: »

Bokeh:
In photography, bokeh is the blur, or the aesthetic quality of the blur in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."

Courtesy of Wikipedia.

From here on, that's all it means.

As much as I ♥ Wikipedia (they've sent me Christmas cards more than once (although I was a little upset as I thought the money I donated to them could've been put to better use)), it's not prescriptive.

The issue I have with the term "bokeh" being used to describe blur or "quality" of the blur as it is often talked about (in the sense of the shape of out-of-focus points of light or the size of the blur disc it forms) is that it's a pointless term. All lenses can generate circular blur discs. You can take photographs with a digital P&S with a wide angle lens that have bigger blur circles than other photographs taken with a telephoto lens on an 8x10 film camera.

In this sense, it's not a meaningful term.

Also, using "bokeh" as a literal replacement for the term "blur" strikes me as an American peculiarity of trying to sound all fancypants at the expense of clarity and accuracy; c.f.: "filet", "entree", "a la mode".

dinneenp wrote: »

Thanks for the reply.
I'm talking about taking pictures of (mainly) my young kids. And when asking which would give more blurred background I mean under the same conditions and in same setting (e.g. Garden, indoors etc) and not vert low light.

I know the 50mm should be quicker and is a lot smaller and that they're different lenses but I'm wondering hick would be better for this kind of shot.

Cheers
Pa.

The lens you're selecting for this will most likely depend most heavily on the working distances you think you'll be using.

Set your 17-50 to 50mm and try using it that way for a while. If you're happy with the focal length for your intended purposes: get the 50mm, if you'd rather something a little longer: get the 90mm.

Trying to decide on which lens of two different focal lengths to get on the basis of which one will produce shallower depth-of-field is pointless. If you really want to do that, get the lens with the longest focal length, largest aperture, and lowest minimum focusing distance you can then always take photographs at the minimum focus distance wide open.

Thecageyone

Did the term not originate in Japan?

It's all French to me anyway

All I know is, the wider the aperture, in my experience, the better "bokeh" [who actually likes that word/term?] I get. And often unintentionally.

I don't usually purposely compose a shot with it in mind. Sometimes it'll appear and I'll like what I see. The last time I did it on purpose, maybe besides that shot on the previous page, was doing one of those clichéd Christmas tree light bokeh jobs.

AnCatDubh

It may be helpful to stop thinking in terms of bokeh and more think about depth of field.

To do that you need to consider primarily - focal length, distance to subject and aperture (this being 100% accurate or not is nominally not relevant -- it works for me :cool:).

See worked examples below with constants of aperture and distance to subject and varying the focal length, which I think is what you are getting at in your question.

At 90mm and 20ft distance to subject @ f/2.8 you have 1.68ft of "in focus" depth of field.
At 50mm and 20ft distance to subject @ f/2.8 you have 5.58ft of "in focus" depth of field.
At 17mm and 20ft distance to subject @ f/2.8 you actually technically get infinite "in focus" depth of field from 9.13ft distance away from you.

Outside of your "in focus" areas starting at the near limit (see below) and running to the far limit you will be out of focus.

So, if I understand what you are asking, then yes at 90mm and assuming all other things being even, you will get more out of focus than at 50mm which in turn will be more than at 17mm.

But none of this says anything about the quality of the out of focus area - known as good or bad bokeh which will depend on attributes such as lens aberrations and the shape of the aperture (think quality of optics).

Worked examples calculated from DOF Master:

Assume Subject distance: 20 ft @ 90mm and f/2.8

Depth of field
Near limit 19.2 ft
Far limit 20.9 ft
Total 1.68 ft

In front of subject 0.81 ft (48%)
Behind subject 0.88 ft (52%)

Subject distance: 20 ft At 50mm f/2.8

Depth of field
Near limit 17.6 ft
Far limit 23.2 ft
Total 5.58 ft

In front of subject 2.41 ft (43%)
Behind subject 3.17 ft (57%)

Subject distance: 20 ft @ 17mm f/2.8

Depth of field
Near limit 9.13 ft
Far limit Infinity
Total Infinite

In front of subject 10.9 ft
Behind subject Infinite

As an exercise, stick your 50mm into it's lowest aperture and shoot from 20ft focussed on the subject, then 10ft focussed on the subject, then 5ft focussed on the subject, and just pay attention to what happens the background our out of focus area -- make sure you have elements in the scene that will allow you differentiate. This exercise will show the effect of distance to subject on the depth of field "in focus" and consequently the "out of focus" area. The quality of the out of focus area however should remain the same.

Oh, and by the way you will get far better bokey on 400iso neopan film than you will on your digital SLR sensor, and poleroids are better again.

(the last statement may not actually be true

)

Thecageyone

You know, that actually makes sense.

I wonder if Pa was at the wider end when not getting desirable results?

Fajitas!

charybdis wrote: »

As much as I ♥ Wikipedia (they've sent me Christmas cards more than once (although I was a little upset as I thought the money I donated to them could've been put to better use)), it's not prescriptive.

The issue I have with the term "bokeh" being used to describe blur or "quality" of the blur as it is often talked about (in the sense of the shape of out-of-focus points of light or the size of the blur disc it forms) is that it's a pointless term. All lenses can generate circular blur discs. You can take photographs with a digital P&S with a wide angle lens that have bigger blur circles than other photographs taken with a telephoto lens on an 8x10 film camera.

What!?

The word bokeh implies the quality of the "out of focus" area. Obviously you can take photos with a digital P&S with a wide angle lens that have bigger 'blur circles' than an 8x10 camera. That has nothing to do with the camera or the focal length of the lens. It's moreso concerned with the physical lens and physical aperture diameters.

Bokeh comes in different forms, on review, it's "good bokeh" and "bad bokeh" and in special circumstances "odd bokeh". Good is usually defined as being soft, naturally blurred and providing creamy colours that don't have a solid form. Bad bokeh is hard, angular, unnatural bokeh. It's nasty, you notice it straight away. Odd bokeh produces cirlces. Or lines. Or doughnuts. Or flying monkeys.

The word bokeh is describing the quality of what's being blurred. It is a meaningful term. In the same way as food can be good food, bad food and odd food.

Assume Subject distance: 20 ft @ 90mm and f/2.8

Depth of field
Near limit 19.2 ft
Far limit 20.9 ft
Total 1.68 ft

In front of subject 0.81 ft (48%)
Behind subject 0.88 ft (52%)

Subject distance: 20 ft At 50mm f/2.8

Depth of field
Near limit 17.6 ft
Far limit 23.2 ft
Total 5.58 ft

In front of subject 2.41 ft (43%)
Behind subject 3.17 ft (57%)

Subject distance: 20 ft @ 17mm f/2.8

Depth of field
Near limit 9.13 ft
Far limit Infinity
Total Infinite

In front of subject 10.9 ft
Behind subject Infinite

Correct me if I'm wrong but this should state 'apparent depth of field'. The depth of field should be the same if it's shot at 2.8, it's the magnification of the lens that will show more or less depth of field. If you're shooting at 90mm, you're going to need your focus to be a lot more accurate than you will at 17mm at 20ft from the subject - Try shooting the exact same composition with a wide angle and a telephoto, at the same aperture. Lens distortions and characteristics aside, you'll be getting the same image, with same depth of field.

Corrected by Daire!

Thecageyone

I always thought of bokeh as the circlular or pent/hexagonal sparkley bits you get in the backing, not the overall plain blur.

And it's 'Bok-eh'/[sounds a bit like]'bouquet' rather than 'bok-ah', as I've heard in some youtube clips. Right?

Fajitas!

No, the word 'bokeh' can be used to further describe the background blur. Good bokeh is considered to be smooth and unnoticable, the circles you're describing are nicknamed 'circles of confusion'. What I'd consider really nice bokeh from a lens would have no 'hard' circles or shapes, just a natural blur that won't take over or distract from the actual content of the image.

Thecageyone

Either works for me, so long as it fits with the overall image.

People get too hung up on terms and phrases. Let's just call it what we used to, blurred background.

smelltheglove

My tuppence worth;), I have the 17-50 tammy and had the 90mm which I just got rid of last week. I used it about 5 times max Id say, one being to take pictures to sell it, I didnt like the lens, the guy who took it off me loved it but as I explained to him it was of no use to me. Being a macro it was quite slow on focus and the noise of focus was quite loud, the actual noise not image quality. On the other hand I wouldnt change the 17-50 for the world and just got a tokina 50-135 2.8 which I am loving tbh.

Image from 90mm wont attach but pm me your email and Ill send one on to you. Image from the 50-135 below. Only a couple of hundred euro in the difference of price so on experience I would look around if I was you.

Thecageyone

STG, do you know anything about firmware updates for the tammy? I read somewhere that there was one that speeds up the AF. I never even knew lenses had their own firmware ... such a n00b ...

DaireQuinlan

Fajitas! wrote: »

Correct me if I'm wrong

Consider yourself corrected then

What ACD posted is correct. If you're shooting at the same position, with the subject at the same distance in every case, for a constant aperture, then of course the DOF will change as the focal length changes, there's nothing 'apparent' about it.

Try shooting the exact same composition with a wide angle and a telephoto, at the same aperture. Lens distortions and characteristics aside, you'll be getting the same image, with same depth of field.

Assuming by 'exact same composition' you mean trying to get the subject the same size in each case then this is correct. If you're shooting something at 10 feet with a 50mm, then shooting the same subject at 20 feet with a 100mm will give you the same subject size, and exactly the same DOF in both cases. General composition of course won't be the same because the FOV will be different but that's a whole different ballywhack.

charybdis

Fajitas! wrote: »

The word bokeh implies the quality of the "out of focus" area. Obviously you can take photos with a digital P&S with a wide angle lens that have bigger 'blur circles' than an 8x10 camera. That has nothing to do with the camera or the focal length of the lens. It's moreso concerned with the physical lens and physical aperture diameters.

Actually, as was pointed out earlier, it does have to do with the focal length of the lens, and if by "physical aperture diameter" you mean f-number you are also talking explicitly about focal length.

Fajitas! wrote: »

Bokeh comes in different forms, on review, it's "good bokeh" and "bad bokeh" and in special circumstances "odd bokeh". Good is usually defined as being soft, naturally blurred and providing creamy colours that don't have a solid form. Bad bokeh is hard, angular, unnatural bokeh. It's nasty, you notice it straight away. Odd bokeh produces cirlces. Or lines. Or doughnuts. Or flying monkeys.

Aside from ascribing good/bad properties to it, I'd broadly agree with this statement. Although, I will say that none of these factors directly depend upon a large aperture, shallow depth-of-field, or the shape of the aperture diaphragm.

I think it is illustrative to consider two lenses of sufficiently different optical design that are at the same focal length, aperture, and focus distance. Do they have the same bokeh?

Fajitas! wrote: »

The word bokeh is describing the quality of what's being blurred. It is a meaningful term. In the same way as food can be good food, bad food and odd food.

The issue is that "quality" is an overloaded term. To stretch your food metaphor, I think people are saying "this food is delicious" when they mean "this is a lot of food".

"Bokeh" is a meaningful (if esoteric) term, but it is not being applied correctly or consistently.

I think it would be useful to avoid terms like "quality", "good", and "bad" when attempting to describe things like this.

dinneenp

Thanks for all the replies.
Originally I mentioned "blurred background/bokeh", people have gotten side-tracked on the whole bokeh definition (it is a Japanese word).

I understand that the closer to your camera your subject the more background you'll get (with the widest aperture).

I got my question answered about 90mm f2.8 vs. 50mm f2.8- thanks.

It's not that I don't like my Tammy 17-50 lens, it 's just that my old 50mm f1.7 gave 'better portraits' (please dont' get into a long discussion about what constitutes a better portrait) and more blurred background (which is obvious- 1.7 vs 2.8). Maybe also liked that it's smaller and quicker, not 100% sure really.
Maybe I didn't appreciate it when I had it (couldn't understand why everyone praised/worshipped the 50mm prime so much) or maybe just cos it's gone I think I miss it....

I sold it to finance my Tammy and that I had to 'step back' a lot indoors so for that reason I could almost rule out the 90mm lens. But then I start thinking about summer outdoors and the length could go good. And you have macro thrown in. Maybe I should ask to borrow a macro lens from someone adn then will know if I like it or not (and save me buying a lens without knowing if it's what I want). In fact that's what I'll do.

I might like macro photography or find that it's a novelty for me and bored of it after a while. Currently I use my compact camera for 'macro' shots (not ture macro obviously but not bad).

Cheers,
Pa.

Thecageyone

17-50 for indoor, 90mm for outdoor, sorted

both nice lenses, giving you an overall solid range for your needs.

FoxT

dinneenp wrote: »

Hi,
Would a Tamron SP AF 90mm 2.8 DI MACRO lens offer more blurred background/bokeh that a 17-50 f2.8 lens as it's focal point is further?

Or is it not dependent on the focal length at all?
Cheers,
Pa

There are 2 aspects to Bokeh that I am aware of...
1- "Bokeh Quality" - ie are out-of-focus highlights blurred smoothly or jaggedly. This largely depends on the design of the iris of the lens. Cheaper lenses like the canon 50mm f/1.8 have a 5-blade iris, which can sometimes result in distracting pentagons in out-of-focus highlights. More expensive lenses have more blades in the iris, resulting in softer, rounder oof highlights. THIS ASPECT OF BOKEH IS NOT RELATED AT ALL TO LENS FOCAL LENGTH. ( see the-digital-picture.com for examples)

2 - "Bokeh Quantity" - ie how quickly things get blurred as you move nearer or further away from the plane of focus. Here is where it gets interesting.

The above shot was taken with a 70m lens at f/9. Subject distance was about 15cm from the front element of the lens. The figure is about 4cm high. As you can see, the feet are not in focus, I guess they are about 1.5cm behind the plane of focus here.

Now, If I had shot this with say a 180mm lens at the same f-stop, and, critically, with the figure occupying the full frame of the viewfinder ( pretty much as it is here) then the DOF/Bokeh would be identical. The difference is, I would be further away from the subject as using a longer focal length.

So, for a given aperture, bokeh will be about the same regardless of focal length provided the size of your subject in the frame is the same. ( ie for shorter focal lengths you move closer)

OR

For a given distance to your subject, your DOF will be shallower as your focal length increases, provided your aperture stays the same.

Summary:
- Wider aperture gives shallower DOF, regardless of focal length.
- Longer focal lengths give same DOF at any given aperture provided magnification is the same.
- Longer focal lengths give shallower DOF provided aperture & distance to subject remain the same.

Best way to grok all this is to experiment!

- FoxT