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06-15-2011, 02:46 AM   #1
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Lens for low light/indoor

Hi

I am presuming fast lenses like f1.4, 1.8, 1.9 etc., are more for this job but also my theoretical understanding of portraits from learning and reading from this forum I putforth a few questions:

At the above mentioned f stops, I presume the DOF to be too shallow that (if I take a close up portrait for example) part of the face will get focus or in other words not all will come into focus for portraits unless I need to stop down the aperture to something around 2.4 or 2.8 (please tell me if I am right this far!!?) to get a decent portrait with background blur, again all this I am talking in terms of shooting without flash and low light conditions.

Now, if I were to stop down to those levels as indicated isn't it better to go straight away to lenses that are f2.4 and f2.8?

Or, in the case of those lenses listed above with f 1.X stops, are these still effective in low light and are still termed faster for my ideal no flash/low light portraiture than the f 2.X lenses?

I hope I managed to convey what I wanted to ask - this will help me filter down my lens choices.

As a backdrop: I looking for a decent above 70mm to 100mm prime lens for indoor and low light shooting.

06-15-2011, 02:54 AM   #2
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The depth of field increases as the distance from film plane to subject increases - so if you take a picture of a person a few feet away at f1.8, not all of them will be in focus. If you take a picture of a building a few hundred yards away at f1.8 most, if not all of it will be in focus.

Generally lenses are at their softest wide open, so I guess (and it is a guess, I don't have nice enough lenses to check or care) that an f1.8 lens at f2.8 will look marginally better than an f2.8 lens at f2.8.

For an idea of dof, this is f1.7 (25 year old Chinon 50mm k-mount) from no more than 2 feet. The eyes are about the only thing that is sharp.

06-15-2011, 03:51 AM   #3
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...or you can stand further away - the depth of field also depends on distance to the subject, given a fixed focal length.

Also worth considering is whether the lens auto focuses well (or at all) in low light. I find the 18-55 focuses very accurately and fast in poor light where the FA50, which should do better given it's 1.4, hunts or completely gives up. For really low light, you will want a lens with quick shift focus so you can take over and manual focus.
06-15-2011, 04:11 AM   #4
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QuoteOriginally posted by Northern Soul Quote
The depth of field increases as the distance from film plane to subject increases - so if you take a picture of a person a few feet away at f1.8, not all of them will be in focus. If you take a picture of a building a few hundred yards away at f1.8 most, if not all of it will be in focus....
QuoteOriginally posted by calsan Quote
...or you can stand further away - the depth of field also depends on distance to the subject, given a fixed focal length.
There's an echo of sorts in here

06-15-2011, 04:36 AM   #5
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QuoteOriginally posted by sany Quote
As a backdrop: I looking for a decent above 70mm to 100mm prime lens for indoor and low light shooting.
Indoor shooting is quite a challenge with a long lens...You will need large spaces. Unless you have control of the space like a studio etc. Otherwise if you are at a gathering you will be backing up onto people and things!

Try the DA 70mm f2.4 lens. Takes great pics. Bit long for indoors for me.
06-15-2011, 04:48 AM   #6
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QuoteOriginally posted by psychdoc Quote
Try the DA 70mm f2.4 lens. Takes great pics. Bit long for indoors for me.
Absolutely - in the average house in the UK, 70mm is too long on 35mm, let alone on APS-C where it becomes effectively 105mm.

Give the DA 35mm f2.4 a whirl - it's effectively an old 'standard' lens.

Received wisdom states you need something around 90mm (FF) or 60mm (APS-C) for the most flattering portraits, but as psyhdoc says, unless you have a studio or big rooms, you might struggle to get far enough away to use them.
06-15-2011, 05:16 AM   #7
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I don't know about homes elsewhere, but ~70mm is my ideal portrait FL, whether on film or DSLR. I find the perspective just about perfect. On a DSLR, I also find I am using the DA 17-70 at or near that FL when I take portraits.
06-15-2011, 05:24 AM   #8
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QuoteOriginally posted by GeneV Quote
I don't know about homes elsewhere, but ~70mm is my ideal portrait FL, whether on film or DSLR. I find the perspective just about perfect. On a DSLR, I also find I am using the DA 17-70 at or near that FL when I take portraits.
Population density of New Mexico - c. 16 people per square mile.

Population density of the UK - c 670 people per square mile.

Or, to put it another way, the UK is three quarters the size of New Mexico, and has 31 times as many people in it.

I guess your houses are probably a bit bigger than ours!

06-15-2011, 05:51 AM   #9
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One thing to consider, aside from focal length, is that the softer focus wide open on some lenses actually makes them more desirable as portrait lenses. You do not always want to see every pore and blemish in a portrait.
06-15-2011, 06:07 AM   #10
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QuoteOriginally posted by sany Quote

Now, if I were to stop down to those levels as indicated isn't it better to go straight away to lenses that are f2.4 and f2.8?

Or, in the case of those lenses listed above with f 1.X stops, are these still effective in low light and are still termed faster for my ideal no flash/low light portraiture than the f 2.X lenses?

As a backdrop: I looking for a decent above 70mm to 100mm prime lens for indoor and low light shooting.
As you can see from the baby photo posted above closeup portraits are possible at f:1.4 but focusing is not as easy as at higher f-numbers. But sometimes you'll want only the eyes in focus or sometimes the light will be so low you'll need the extra light gathering ability of the f:1.4.

A lens at f:1.4 needs 1/2 the light as the same lens at f:2 (light gathering power varies with the square of f-number). Sometimes you'll need the extra lens speed even with your K-x but often f:2 or slower will be sufficient.

Depth of field for a lens varies in direct proportion to the f-number so while the f:2 lens needs twice as much light as a f:1.4 lens it has a 40% greater depth of field.

I sounds to me like you might like one of the fast 85mm lenses. Here's an example of what the relatively inexpensive Rokinon (Samyang) 85mm f1.4 will do with low light - this is a jpeg with no post processing:

The bottom image is a 100% crop to show detail; the camera was a k100D.

Usually one can get by with a slower lens - but not always. I've never heard anyone complain about having a lens that's too fast

Last edited by newarts; 06-15-2011 at 06:23 AM.
06-15-2011, 06:12 AM   #11
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QuoteOriginally posted by Docrwm Quote
One thing to consider, aside from focal length, is that the softer focus wide open on some lenses actually makes them more desirable as portrait lenses. You do not always want to see every pore and blemish in a portrait.
True - hence the 85mm f2.2 soft lens

That said, if you start with a sharp image you can always soften in in PP. You can't do much to sharpen a soft image though, so I'd lean towards getting the sharpest starting image.
06-15-2011, 06:26 AM   #12
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QuoteOriginally posted by Northern Soul Quote
Population density of New Mexico - c. 16 people per square mile.

Population density of the UK - c 670 people per square mile.

Or, to put it another way, the UK is three quarters the size of New Mexico, and has 31 times as many people in it.

I guess your houses are probably a bit bigger than ours!
I've lived in Germany, 609 people per square mile, so I have some perspective. Most of New Mexico is not populated at all, so most of the population is in cities. The density of Albuquerque is 3,000 per sq. mile. I wonder if or how much the North of England is denser than the City of Albuquerque.

The fact is that we take portraits where people are, and indoors is indoors. A room here might (or might not) be a couple of feet longer or wider, and we might have more total rooms or bigger yards, but that really that is not the determining factor for a portrait focal length. Most of my portraits with ~70mm are at distances which are well within the size of a city apartment anywhere in the industrialized world.

It is really just a question of personal preference, to which we are all 100% entitled.

Last edited by GeneV; 06-15-2011 at 06:51 AM.
06-15-2011, 06:37 AM   #13
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QuoteOriginally posted by GeneV Quote
I've lived in Germany, 609 people per square mile, so I have some perspective. Most of New Mexico is not populated at all, so most of the population is in cities, which are not that different from other cities.

The fact is that indoors is indoors. A room here might (or might not) be a couple of feet longer or wider, and we might have more total rooms or bigger yards, but that really that is not the determining factor for a portrait focal length. Most of my portraits with ~70mm are at distances which are well within the size of a city apartment anywhere in the industrialized world.

It is really just a question of personal preference, to which we are all 100% entitled.
Ok - I wasn't having a go! I know where my wife's uncle lives in Canada, the houses are massive by my standards.

I find my 18-55 kit too long at 55mm in my house unless it's just head and shoulders, but as you say, your mileage may vary.
06-15-2011, 06:46 AM   #14
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Thanks All!
My original intention for starting the thread was to find out stopping the f1.x lens to f2.x readings will it still retain its title as a fast lens and for low light if not can the same job be done by lens with max aperture at f2.x.

Having said that, when i said indoor - i didnt just mean for homes but also some big gathering in bigger halls for functions where sometimes part of the halls will not be properly lit etc., I was trying to equip for all these. Where as for home use i already have the 35mm.

So I was planning my next investment on something that could be fast for the above use as well i can take it out for shots as well that is the reason why i was looking at that FLs(70-100).
06-15-2011, 06:57 AM   #15
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QuoteOriginally posted by Northern Soul Quote
That said, if you start with a sharp image you can always soften in in PP. You can't do much to sharpen a soft image though, so I'd lean towards getting the sharpest starting image.
Couldn't agree more. The sharper the better, and on those occasions when you don't want an uber-sharp image, just make adjustments in PP, or stick vasoline on a filter or whatever.
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