jpmtvcoop

2.8 on a 2.8 lens means shooting wide open. shooting 2.8 on a 1.4 lens is shooting at the same f stop but its relationship with the speed of the lens has changed. Are the characteristics of the DOF on a 2.8 the exact same on both lenses or does the Bokeh (background blur) change in texture/feel/look based on the latitude of the speed of the lens? Another way of looking at this is to compare the two shots shot at the same f stop but using two different speed lenses. The bottom line here is this... If the look one wants to obtain is the look of a 2.8 aperature, is it necessary to buy a lens faster than 2.8?

hangman45 Loc: Hueytown Alabama

The difference in look of the Bokeh has more to do with the type and number blades than it does with just aperture if both lens have the same shape and number of blades and shot at the same focal lenght at the same distance they should look the same on each lens at 2.8.
F4 on my macro looks different than my F4 on my 50mm and both look different than my 70-200.

Blurryeyed Loc: NC Mountains.

The 2.8 setting will be the same, here is a simple explanation of F-Stop.

"F-stop is the focal length divided by the diameter of the lens. For example, a 200mm f/4 lens will be 50mm wide. Get out your ruler and measure it. 200mm/50mm = f/4. That is why f-stop is typically written as F/4, meaning "focal-length over 4" or "focal-length divided by four".

hangman45 Loc: Hueytown Alabama

Yes 2.8 is 2.8 but OP was asking if Bokeh would be the same and that will be different on different lens.

Blurryeyed Loc: NC Mountains.

I think that your answer is correct in the quality of the bokeh, but DOF and other settings should not be effected as they are all dependent on mathematical equations relating to the focal length of the lens and the size of the aperture...

I was really just adding more info to what you had already stated.

jpmtvcoop

Ok so I get the idea that on different lenses with different number of blades a setting of f/2.8 the bokeh would look different but what about all things equal. Is a 2.8 a 2.8 as far as the amount of background blur or DOF? Lets say for example that I just love the look of 2.8 when shooting video with a background that is say 20 feet behind. Can I assume that 2.8 will always pretty much look the same give or take the brand of lens and the amount of blades? Making the equation a different one... say I like f/4. Would the DOF stay the same if the speed of the lens was and F/4 vs the speed of a lens was a F/1.4. Hope Im making sense here.

Blurryeyed Loc: NC Mountains.

If I correctly understand your question the answer is yes, but it is important to note that the DOF on a 300mm lens will be much different than DOF on a 50mm lens... but regardless of the lens widest aperture available, 2.8 on a 50mm f/2.8 should be the same as 2.8 on 50mm f/1.4

Bangee5 Loc: Louisiana

I think you are NOT talking about Bokeh but about backgrond blur in relation to DoF. Will the background be blured the same at f2.8 with a f1.4 len as it would be if the lens were a f2.8. I would think yes but also the focal lenght of the lens would affect the pictures you take.

altheman Loc: Christchurch, New Zealand

Gosh you learn (re-learn?) something new every day but bear in mind the d stands for the diameter of the aperture which when wide open will also be the diameter of the lens. I think I'm going to have dig out all my old photography theory notes for a bit of a brush up.

saichiez Loc: Beautiful Central Oregon

Roundness at all settings. The quality of the bokeh is increased by the roundness of the aperture opening. Therefore an increased number of aperture blades and the curvature at the tips of the blades complete the "opening roundness" at any given aperture. This is something that is designed more effectively in todays lenses to give that roundness through the whole range of opening. However, the OOF highlights become more obvious at larger apertures.

If you have a lens where the aperture wide open shows a definite geometric shape, like five distinct flats on a five blade aperture, the OOF highlights will appear in a five sided pentagon shape, which is considered not at all attractive.

So, while f2.8 is f2.8 on any lens, 1.4 will give more bokeh. In addition, the closer to a round circle each aperture becomes, the "quality" of the bokeh will be more attractive to many.

A 35mm film Canon Canonet GIII QL17 rangefinder has five blades and a wide aperture of f1.7. Great little camera. However, wide open, the aperture has five distinct sides, and the OOF points of highlights ALL have a very distinct soft pentagon focus. It's more of a circle at f2.8 and the bokeh creates more circular-like soft highlights.

So, the key points favoring "bokeh" quality, depending on your taste, are widest aperture and enough aperture blades, properly designed to create a very circular opening at any setting.

This is one of the reasons bokeh has been difficult to achieve in many digital cameras, and why so many people want to use older Manual Focus lenses originally designed for film. Lenses designed to achieve bokeh on smaller format sensors, particularly small sensor P&S cameras are simply not equipped with the circular openings because of the small number of blades in the aperture.

Part of the reason fast primes designed for crop sensors are so expensive. The smaller the format, the more "Bokeh" costs.

oldtool2 Loc: South Jersey

I would think there are too many variables to answer this question. Are you talking prime or zoom lenses? Do both lenses have the same number of blades? Do both have squared or rounded blades?

Give some specifics and you may get the answer you are looking for instead of a bunch of theory or assumptions.

Are you talking about a few lenses that you are thinking about purchasing?

Jim D

bvm Loc: Glendale, Arizona

If you really want to fool around and experiment, try this, I have a Nikon defocus lens. It takes a little time to see and know what your doing. BUT with digital now you can see it right away.If I remember correctly not even Nikon could really explain to you how it worked when I first got it.

PhotoArtsLA Loc: Boynton Beach

The trick is to find a lens which performs well at its maximum (widest) aperture, plus, you generally want an aperture which is quite low for the focal length, e.g. a 200mm f/2 or a 50mm f/1.2 or a 300mm f/2.8 and so on. Bokeh is a wily critter which appreciates, unfortunately, expensive lenses.

On the cheaper side, Defocus Control lenses, like the 105mm f/2 and 135mm f/2 from Nikon have unique methods, via a control ring, to play with the position of the depth of field, thus affecting bokeh. You can throw the depth of field to the front or rear of the subject up to f/5.6.

Messing with such lenses can create strange, dreamlike images.

Blurryeyed Loc: NC Mountains.

LOL seems like Photoshop could come up with a filter...

Nevada Chuck

2.8 is 2.8 is 2.8, regardless of what the fastest stop may be, so long as the focal length of the lenses are the same. But while the exposure will be the same, the bokeh will vary with focal length. Dial in 2.8 on a short lens like a 16mm or 20mm, and compare the bokeh with that of a 200mm also set to 2.8, and the difference will be seen.