Focal Length and DOF Blurring

[Colin Southern]

It did in my case because the tube was small and the tissue at the end of the snoot was considerably bigger

You originally said:

I would simply tape a facial tissue or two over the flash head. I did it to soften the light

I replied:

Um, it won't soften the light because the effective size isn't changing significantly.

Now it's:

the tube was small and the tissue at the end of the snoot was considerably bigger

Well I'm sorry, but if you put a tissue over the end of a snoot (say a 3" snoot) you STILL end up with a 3" light source. It may be attenuated somewhat, but it won't be any softer. On the other hand, if you fire a snoot into a diffuser you can then vary the softness depending on where the diffuser is positioned (no change up against the snoot through to very soft if it's very close to the subject). If that's what you're meaning then fine, but that's different to "tape a facial tissue or two over the flash head"

... it may not work for your pro gear but it did with my home stuff ... sorry BUT.

Principles of light don't change according to the quality of equipment used.

Your second para is best ignored.

I wasn't sure what you meant at first, so I had a re-read of what I wrote:

The other problem is it also becomes an increasing portion of ambient, which means you need to black out the studio more -- and then AF doesn't work and you can't see unless you use modelling lights - but then they set fire to the tissue paper, and also become part of the exposure ...

My apologies -- I worded that badly. I'm not saying that "tissues on fire then become part of the exposure" - I'm saying that when you shoot wide apertures then ambient light becomes an issue (eg you can't shoot with overhead florescents on like I do normally). You need to cut out far more ambient light and than in turn means you end up with a very dark studio - so AF doesn't work. Only solution is to switch on modelling lights to be able to focus, but because they're continuous, they can put out a LOT of heat (mine are 300W halogens) - which in turn (a) would be a very definite fire hazard, and (b) the modelling lights then become part of the exposure (which personally I don't like)

Pity Cantab was misled.

???

[AB26]

cobble something together with PVC piping.

THANK YOU Manfred.

[jcuknz]

I am not going to argue with you becuase you know your field and are highly competant but I know what happened at my home and I don't have a 3" snoot .. I am afraid that mine was just a cardboard box tube taped to the flash unit, an early Sunpak.

As for AF not working in low light I can assure you that if you have contrast detection it is very hard to stop AF snapping into focus whatever the light level as I found to my suprise and delight when I went out to the street at 11pm one evening long after sunset assuming we had had one that day

But of course you want and achieve great IQ so have a full frame Canon and I assume are stuck with Phase Detection whereas I am happy with a GH2 MFT for what I do these days. Different needs ... different pros and cons.
I think the result of using tissue softened the result ... not as much as proper studio gear but for the DIYer at home reasonable.

[jcuknz]

Sorry double post CiC rather slow tonight.

[AB26]

Why all the quibble?

Dennis it is simple: get the Nikon 85 F1.8 (around $600).

[jcuknz]

In my workroom cum studio cum greenhouse [ tomato plant top right ] the lighting boom I made and used for this experiment to see what could be done with one light. A hole was cut in the side of the snoot to let light escape to light the background. Subsequently have bought some cheap lighting stands but I rarely use other than natural light. Used my Nikon bridge camera with flash hidden from subject but enough escaping to trigger the Sunpak.
The model will be told to wear better make-up next time he comes else I'll use my lady model.

[Colin Southern]

It's hard to compare the three because there are other more significant lighting differences than just the hardness/softness of the lighting, but looking at the harness of the of the shadow under the chin and to the camera left of the nose, if anything, I'd say that the double-tissue shot is even more defined.

I'll shoot a tennis racket against a white background using a snoot attached to a strobe with 0, 1, and 2 tissues attached to show what I mean (when I get a chance) (in the middle of moving at the moment).

[jcuknz]

Just to clear things up the purpose of the tissue is to reduce power and we have got hung up on softness which you obviously think differently to me in your intepretation of softness but that was incidental to my original comment where the flash was too powerful. I see no point in you shooting a tennis racket.
As for shooting length I have read of shooting through mirrors and standing out in the corridor to gain camera-subject distance.

[Colin Southern]

you obviously think differently to me in your intepretation of softness

Not sure what your definition is, but this one aligns perfectly with mine:

http://www.photomatters.org/hard-light-soft-light

The point I'm trying to make about lighting is that if strobes are two powerful, you only have a few choices:

- You can move them further away, but that makes the light harder, so may not be an option

- You can stop down, but that does have DoF implications

- You can attenuate the light source with ND film / tissues / baking paper etc, but this then effectively changes the ambient to flash lighting ratio - and normally in a studio, ambient light is a PITA.

Normally in the studio I'm shooting at around F11 and I can leave 8x fluorescent tubes (room lighting) on because it has absolutely ZERO impact on a shot (we actually tried this the other day by taking a shot at F11 / 1/125th / ISO 100 with the strobes off -- in ACR we maxed out the exposure, mid-tones, and shadows -- and all we could see was noise). In a situation where I wanted to shoot with fast glass to get me the best leverage in a cramped space with minimal subject to background ratios then it would be a different story - at something like F1.4 or F2 it just creates problems all around -- AF doesn't want to work if I turn the overheads off - but overheads start to muck up the lighting if I leave them on -- subjects pupils dilate so much it looks like they're smoking dope - DoF gets so thin it's hard to get tips of noses, ears, and eyes all in focus (and that's with a head-on shot -- heaven forbid that the eyes are at different distances to the camera).

Just my 10c worth. I just don't want people to do what I did and invest around $3000 on something like the venerable EF85/1.2L II and then never use it because in real-world shooting the EF70-200 F2.8L IS USM II kicks it's butt.

[jcuknz]

If ambient light is a problem then take out one of the ballasts, and if phase detection won't work then get a contrast detection camera .. I really think you are making a mountain out of a molehill. My f/1.4 lens came with a 135 f/2.8 and a body and cost me $50. and I have just bought an f/1.7 for $38. I think I have said we live in different worlds.

[Colin Southern]

I really think you are making a mountain out of a molehill.

Which I'm sure that the OP won't find particularly reassuring when he invests considerable $$$ in an F1.8 or faster lens to get creamy bokeh in a studio setup, only to find that he can't use it effectively at that aperture due to the reasons I've mentioned.

My f/1.4 lens came with a 135 f/2.8 and a body and cost me $50. and I have just bought an f/1.7 for $38. I think I have said we live in different worlds.

Yep - we sure do. Really looking forward to seeing the quality of your studio portraiture shot with them; with a bit of luck I'll be able to offload $100,000 worth of gear - upgrade to a $50 kit - and knock a hefty slice off my mortgage.

[jcuknz]

I am sure I can think of various ways to nullify your problems with electronics in todays world and I am sure you know more about that field than I do ... yes definitely a mountain

[Colin Southern]

I am sure I can think of various ways to nullify your problems with electronics in todays world and I am sure you know more about that field than I do ... yes definitely a mountain

I don't have any problems -- but then again, I'm not silly enough to try shooting at F1.8 or faster in my studio with strobes ...

/done

[William W]

. . . I guess I would also like to add some more capability to the lenses I already own and not duplicate any functionality that they already have. [to accomplish Portraiture Outside and especially Head shots in my home studio]

Then don’t buy any new lenses at the moment.
Research Flash Lighting.
Buy at least two more Flash heads.
Then spend time and effort learning how to use Flash Lighting for Portraiture.

WW

[DennisS]

Now I am a bit confused, Bill - as Colin pointed out earlier, opening up the aperture will make it difficult to reduce the flash output enough to be in sync range. At this time I have a mono-light and an external flash. The mono-light has about 20% more GN than the flash. I can understand how adding more flash will allow me to have more light control as back light, hair lights, etc, but how would this allow me to get a good bokeh/blurring in the space limitations I have in my studio. I can see that a 2 light system may not be the best but I plan to build on this later. From all the above posts, it would appear that I should consider a 9 blade diaphragm or better to improve bokeh and/or just increase the subject-background distance for more blurring and f/2.8 to avoid extreme DOF.

The Nikon 24-70mm f/2.8G ED AF-S Nikkor Wide Angle Zoom Lens (US $ 1900) appears to be a good candidate that meets most of my needs. I understand this is way beyond the budget estimate I stated earlier, but it seems to meet most of the required criteria I may need to have, based on earlier posts.

Of course, for that price, I can get a bunch of flash units but not sure I understand how that will get me good bokeh/blurring.

[Colin Southern]

Another option Dennis, is to simply use a background that gives the illusion of being out of focus to start with.

To be honest though, I think - that if space really is that limited - then you may end up being between "a rock and a hard place" in that if your camera to subject distance is less than ideal then you're going to need to stop-down the lens to get sufficient DoF to cover the model's face -- or you're going to need to use a wider-angle lens, which will introduce unflattering facial distortions.

Quality portraiture requires quality lighting; yes, the background is important, but great lighting, correct lens length, adequate aperture are more important (thinks like correct focus, sharpening, colour-correction etc are a given in this context).

If I were in your situation I'd be concentrating on my lighting - getting strobes firing into large softboxes on stands - key light - fill light - hair light - rim light - reflector under chin - background lighting etc. For some of my portraiture I'm working up to SEVEN zones of light. Backgrounds are rarely a problem.

If you REALLY want interesting backgrounds then set your lens to F2.8 - get some compatible lighting that'll allow you to sync at higher speeds (I use the Canon 600EX-RT system that allows me to sync up to 1/8000th) - and get outdoors.

Personally, any lens faster than F2.0 has always spelt trouble for me; I own the venerable EF85mm F1.2L USM II and the EF135mm F2.0L USM and neither of them see the light of day (or the strobe of night) -- in real-world terms, the EF70-200mm F2.8L IS USM II kicks their butt.

[William W]

Now I am a bit confused . . .

The Nikon 24-70mm f/2.8G ED AF-S Nikkor Wide Angle Zoom Lens (US $ 1900) appears to be a good candidate that meets most of my needs. I understand this is way beyond the budget estimate I stated earlier, but it seems to meet most of the required criteria I may need to have, based on earlier posts.

I didn’t post to confuse you. Sorry for your confusion.

Let me explain another way.

I understood that you have several goals.

What I saw is that you have made the error of assuming the (best) answer for the goals that you have, and you phrased your question in that terms.

i.e. you assumed that the best initial solution for you would be to buy a new lens – in fact a to buy a very fast prime lens.


To ensure that we are discussing the same thing, I read from your posts that your goals are:

Post #1 - You want headshots (I assumed outside) with nice creamy bokeh

Post #6 - You give a budget US$500~600

Post #8 – You want to make headshots in the home studio, which is very tight in space – in this post the HOME STUDIO is described as the main function, shooting outside is a secondary function.

Post #10 – Here you clarify and it seems you want to make portraits outside and in the studio with sort of equal frequency – in this post you state another goal to:

“add some more capability to the lenses I already own and not duplicate any functionality that they already have.”

It was this last goal that I picked up on and quoted and made comment to.


Expanding with some facts pursuant to this last goal:

1. Depth of Field:
DoF for a typical Head Shot (Portrait Orientation) using Nikon APS-C,
@ F/2.8 ≈ 5 inches
@F/4.0 ≈ 7 inches
@F/5.6 ≈ 9 inches
@F/8 ≈ 12 inches
@ F/11 ≈ 16 inches
Conclusion, in the Studio, for head shots, typically you will be at F/8 ish.

2. Shooting Distance:
Shooting at about 12ft (as you described) you’ll get an Head Shot in Portrait Orientation with an 105mm lens on your camera.
Conclusion – you will need a lens between about 50mm and 105mm to accommodate the size of your studio

3. Studio Lighting:
Options - Continuous Lights, Available Light or Flash.
Conclusion – flash is the most desirable for many reasons - if you want to follow a detailed discussion ask, suffice at this poiut we agree you will use Flash in the Studio.

4. Aperture required for Flash Sync with Studio Flash Heads
Conclusion – as per Colin’s description – you’ll be at about F/8 to F/11


Best solution to goal with budget allowed -
- get good backdrop curtain
- get a couple more flash units
- learn good studio lighting techniques including how to light the backdrop
- use the two zoom lenses that you have at about F/8~F/11


FOR OUTSIDE.

1. DoF
The DoF will not change

2. The Shooting Distance and the Background Distance
What can be controlled outside, are, both the Shooting Distance and also the Background Distance.

Given that the DoF remains the same you can use to your advantage the fact that you can control, the Background Distance and the lighting as in this shot made with a an APS-C

Canon camera and a 50mm lens set at F/5.


A very similar image could be made with your camera and one of the kit lenses, the predicate being that the BACKGROUND is a good distance away from the Subject, and also the LIGHTING ON THE BACKGROUND enhances the bokeh toward what you desire.

It is important understand that Bokek and DoF are related, but are not the same.

It is also important to understand that Bokeh is NOT just a function of the lens, but also other constituents are the Background, the Background Distance the Background’s Texture and the type and Direction of Lighting on the Background.

Also it is important to understand the lens’s bokeh (i.e. when wide open) is different to the iris + lens’s bokeh (i.e. when the lens is stopped down.

To enhance the OUTDOOR shot and or to create a different flavour to the Background (bokeh) one can use Flash as Fill which allows the Background to be slightly underexposed, relative to the Subject, which is very useful when the Background is relatively bright. In this case the extra Flash units will allow Subject Fill Lighting (outside) and in turn allow a variance and control of the Bokeh by way of EXPOSURE of the background.

Certainly the desire to acquire a fast Prime Lens and to learn how to use it is an admirable goal, but from what you have outlined doing so will be of very limited use for Studio Headshots and limited use for Outdoor Headshots, even considering the desire to affect nice creamy bokeh.

The point I made about differentiating between Lens Bokeh and Iris + Lens Bokeh is self-evident when one studies many of the exponents of Available Light Portrait Shooting – the use of the very wide apertures are more often employed as the shot gets wider (a “tight Portrait shot” is an Head Shot – a “Wider Portrait Shot is a Full Length Shot: this has nothing to do with the Focal length of the lens)

So for example – typically (for APS-C) (yes there will be exceptions) – for an Head Shot we would be at about F/8 ~F/11 – for very shallow DoF we might see some work made at F/5.6 . . . but as already mentioned F/2 .8 would be silly UNLESS the effect was to make the shot ONLY with 5 inches DoF – and that means only one eye in acceptable focus for an Head Shot with the Subject 15° off the axis of facing directly down the lens’s axis. . . . and when working at these apertures (F/5.6 to F/11) you will sometimes find that the (lens) Bokeh of the Kit Zoom will be as good as or even better than a fast prime which is stoped down 3 or 4 stops.


Have your goals changed?

You mention the 24 to 70/2.8.

Are we now discussing more than just Head Shots and will the outdoor wider Portrait Shots take precedence over all the Studio Work?

Has your Budget changed? - are we now 3 times the original?

For example if we now have a priority, or even a goal of making many ¾ Shots or a Full Length Shots, (outdoors), we open up an entirely different kettle of kippers.

Because, as one example, for a Full Length Shot of a 5’10’ Model (Your Nikon APS-C Camera shooting Portrait Orientation) – using F/2.8 we have a DoF of about 24 inches . . . which is very useful as it is just about the “thickness” of a model’s body in ½ Profile.

***

But - for your goals as you first described and how I understood them - the above is why I advised that you consider lighting and not lenses, as you first priority - and - if your goals and budget have NOT changed, then buying a 24 to 70/2.8 is a waste of money, IMO.

And indeed for OUTDOOR portraiture - ¾ Shots or Full Length Shots - a more elegant solution apropos Budget - would be to buy a second hand 85/1.8 Prime and use it at F/2.

WW

[DennisS]

Thank you Bill for your detailed explanation. That has certainly opened my eyes to the possibilities of working with light and controlling the bokeh by way of exposure - did not know that was a possibility. I will be working to master this before I go out and get another lens. What you say makes sense - your example shot more than proves your point...!!!

No, my goals have not changed but I did not see a Nikon DX lens with f/2.8 between 60 and 105mm so that FX lens would cover it. In any case, after reading your post, I can see that I need to hold off in getting a new lens and just work the light for now.

Thank you again for taking the time to give that in-depth explanation.

[William W]

You are welcome.

OK – I now better understand exactly what is the playing field: thank you for being specific in your reply.

In this case, I would advise that you BUY ABSOLUTELY NOTHING for time being (I think you might be thinking that anyway).

It often takes a lot of will power to NOT seek to make a change: but rather to look inward for find the right question to ask, first – I am not meaning to be philosophical about this, but I have seen the ‘correct’ answers to ‘incorrect’ questions only result in purchases that don’t supply the desired outcomes.

I think the very first thing you can do is get an hold of those two kit lenses and that fast 35 you have and make a lot of Portraits outside ensuring that you keep a good Distance between the Subject and the Background and see what you like - and also what you do not like.

***

And, please, when you are outside use your 35/1.8 some of the ¾ and Full Length Portrait Shots.
Make sure the camera is square to the subject.
The Camera at about the Subject’s CHEST height.
Use about F/2.2.
You will be about 10feet from the Subject, make sure the BACKGROUND is about 25 ~30ft from the Subject.
Also in this shooting scenario, try a dab of Flash as Fill.

***

For the Studio – as we have discussed and other have commented, you are not really going to get ‘creamy bokeh’ shooting at F/8 in the studio with a backdrop 7 ft behind the Subject.

There is a simple DYI method around to approximate the outcome you want – a big roll of white backdrop paper and lots of matt spray cans of paint. Make a mottled pattern. This is very effective for B&W, but, choosing the paint colours carefully (Autumn Hues) and making a variance and random spray pattern, Colour ‘Headshots’ can be very good also.
Lighting is One Flash (you already have) use a big umbrella bounce, single light staring position about 15° off camera axis and 2ft above Subject’s Head.

If you get really keen a small Flash can be added for a side kicker/hair-light to give depth and modelling. That small flash can be used in manual mode – you can keep it at the same distance for any particular F/stop . . . meaning you could pick one up for a few dollars.

***

PLAESE NOTE - with all that as my suggestion – I am NOT saying for you not to buy anything new next week or next month – I am just suggesting have a bit of a structured play with what gear you have first, before deciding on what path you want to pursue and what questions need to be addressed, to follow that path.

Good luck with it.

***

Post Script:

These are the best and most suitable to this thread “bokeh” and “DOF” and “Portrait” examples that I can find at short notice and quickly.

The detaills

• This is a typical ‘Head Shot’ framing using a Canon EOS 20D and the two “kit lenses” –just like you have.
• Background is about 12ft from Subject.
• Subject is exposed correctly.
• Subject is the size of a typical human head (depth and width)
• Background is underexposed and the light varies across the scene.
• These were shot in Available Light with a reflector bouncing in a bit more onto the Subject.
• These are the JPEGS, SOOC and the Student’s exercise was to show that the DoF does not change, provided that the: framing; Aperture and Camera Format stays the same – but the examples are useful for you, also:

Example 01 – using the 18 to 55F/3.5~5.6 “Kit Lens”


Model: Canon EOS 20D;
ExposureTime: 1/250 s;
FNumber: f/5;
ISOSpeedRatings: 400;
ExposureProgram: Manual;
ExposureBiasValue: 0;
MeteringMode: Average;
Flash: Flash did not fire, compulsory flash mode;
FocalLength: 37 mm;

***

Example 02 - this one using the “Kit – Zoom Telephoto Lens”


Model: Canon EOS 20D;
ExposureTime: 1/160 s;
FNumber: f/5;
ISOSpeedRatings: 400;
ExposureProgram: Manual;
ExposureBiasValue: 0;
MeteringMode: Average;
Flash: Flash did not fire, compulsory flash mode;
FocalLength: 91 mm;

You’ll also please note that F/5 is NOT enough to have the depth of the head in acceptably sharp focus.

WW

[DennisS]

You’ll also please note that F/5 is NOT enough to have the depth of the head in acceptably sharp focus.

This is great stuff - the F/5@91mm clearly shows the head is not all in focus and also that just 12ft between subject and background gives some decent blurring. I will go out and experiment with the 35mm prime as you suggested.

....you are not really going to get ‘creamy bokeh’ shooting at F/8 in the studio with a backdrop 7 ft behind the Subject

Yep - kind of figured that now and will use your tips on the backdrop and lighting to make the most of what I have as far as studio space is concerned.