# Do I need a fast lens if I have a flash?



## domu221 (Jul 4, 2012)

Title.

I have a 35mm f/1.8 and a speedlight. I'm planning to shoot under low light conditions (inside a house, at night). So since I already have a speedlight, do I still need to use my fast lens or can I use my standard 16-85mm f/3.5-f/5.6? Can you tell me the benefits of using a fast lens (f/1.8) or a standard one (f/3.5)?

My goal is to get the sharpest image possible.


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## manaheim (Jul 4, 2012)

A faster lens is also going to tend to be a higher quality lens.  A prime lense is also going to tend to be a higher quality lens.  Do you NEED the faster one?  No, probably not.  Will it behoove you to use it for the better quality images you will get?  Most certainly.

That said, you lose the flexibility of the zoom.

Welcome to photography.  The never-ending hell of compromises and trade-offs.


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## Big Mike (Jul 4, 2012)

Practically every lens has a 'sweet spot' where it will give you the best image quality that it can.  In terms of aperture, the sweet spot is usually around 1-2 stops from fully open, to about F8.  So a fast lens like your 35mm, probably has a large sweet spot.  Your other lens, on the other hand, probably has a rather small sweet spot, seeing as F8 is already 1-2 stops from wide open.

So as long as you flash can give you the lighting & exposure you need, while shooting at F8, you may not need your fast prime lens.  But that being said, even at their sweet spots, the 35mm lens might give superior image quality...that is something you'll have to figure out for yourself.  

Of course, another consideration is Depth of Field.  If you want a shallower DOF, you have that option with the 35mm lens and it's larger aperture.


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## cgipson1 (Jul 4, 2012)

Are you shooting people? A 35mm can cause obvious distortion in faces when you get close, even if you are careful. Usually 50mm and up is best if you are doing any type of close people shooting (half body, head and shoulders). Assuming Nikon, and probably a DX body. 

The 35 1.8G (if that is what you have) has serious CA issues, but is a pretty sharp lens (I had one, gave it to my girlfriend). The 16-85 is a decent lens (probably close to the 35mm in IQ) as long as you stop it down at least two stops from wide open (F5.6 to F8 or so). With a flash.. you should be able to get good exposures with either.

You didn't list which speedlight, or which body you have. It is always useful to give as much information as possible when asking questions like this.


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## davisphotos (Jul 4, 2012)

With a faster lens, you can get faster recycle times with your speedlight, bring in more ambient light so your flash will look more natural and have more control over your depth of field. Depending on what kind of event you are shooting, however, you may want or need the range of your zoom. I'm assuming you are shooting with a crop camera, in which case the 35mm will be closer to a 50mm, which is a good all around focal length, but if you are doing group shots inside it might be a bit tight.


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## o hey tyler (Jul 4, 2012)

manaheim said:
			
		

> Welcome to photography.  The never-ending hell of compromises and trade-offs.



This sums it up quite well.


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## cgipson1 (Jul 4, 2012)

davisphotos said:


> With a faster lens, you can get faster recycle times with your speedlight, bring in more ambient light so your flash will look more natural and have more control over your depth of field. Depending on what kind of event you are shooting, however, you may want or need the range of your zoom. I'm assuming you are shooting with a crop camera, in which case the 35mm will be closer to a 50mm, which is a good all around focal length, but if you are doing group shots inside it might be a bit tight.



It is still only a 35mm (just with a 1.5 crop view) and still has a 35mm's distortion...... focal length does not change, just the view / image crop!


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## Dao (Jul 4, 2012)

Whether you shoot at wide open or not, AF usually better with faster lens.


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## domu221 (Jul 4, 2012)

Thank you all for your replies. Yeah, I do have both a D3100 and a D7000 (but I might use the D3100 since its lighter) from Nikon. and an SB-700 Speedlight also from Nikon. And yes, il be shooting people.

So if I want more depth-of-field, I should just use the 16-85mm at around f/8 with the speedlight? or will the 35mm, at around f/2, give me the same depth-of-field?


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## chuasam (Jul 4, 2012)

Sharpness is overrated!


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## cgipson1 (Jul 4, 2012)

If you have a D7000, and decide to use a D3100 instead... you are making a mistake. The D7000 has far superior focusing (especially in low light), much better HIGH ISO / Low Noise ration... and superior TTL (as well as a host of other features!)


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## rokvi (Jul 4, 2012)

domu221 said:


> Thank you all for your replies. Yeah, I do have both a D3100 and a D7000 (but I might use the D3100 since its lighter) from Nikon. and an SB-700 Speedlight also from Nikon. And yes, il be shooting people.
> 
> So if I want more depth-of-field, I should just use the 16-85mm at around f/8 with the speedlight? or will the 35mm, at around f/2, give me the same depth-of-field?



F2 Will give you a shallower Dof. If you want more use a smaller aperture ( larger f/stop) eg: f/8. Try both if you have the time, so you can see the difference for yourself.


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