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DPChallenge Forums >> Photography Discussion >> 1-stop effect on DoF
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 10/30/2011 03:24:42 PM · #1
I'm kind of curious, I've been looking at lenses for a while now, and note that often there's two or more derivatives of the same lens, just with differing max apertures (e.g f/2.8 vs f/4.0, or f/4.0 vs f/5.6).

I'd just like to know, in terms of depth of focus is there really that much difference in 1-stop? I can understand the benefit of having twice as much light and thus requiring half as much shutter speed, but is there any real tangible benefit/difference in terms of the depth of focus with 1-stop (e.g. f/4.0 vs f/2.8)?
 10/30/2011 04:10:57 PM · #2
There is but it all depends on the application and focal length (as well as the actual lens and just what the difference in aperture is). At a standard focal length (e.g. 50mm) I personally find f/2.8 is about the starting aperture where you get a nice background blur on people shots on an APS-C sensor.
 10/30/2011 04:40:26 PM · #3
Focal length is certainly an important variable. But what I personally find more relevant is the focus distance. The closer the point you are focussing on, the shallower the depth of field. With my 50mm 1.7, the difference in DOF between f/2.8 (the largest aperture for which the lens starts being quite sharp) and let's say f/4 or even f3.2 is considerable with a subject around 2/3 meters away. With a subject significantly closer (let's say 50 cm~) the increase in depth of field is really in terms of a few centimeters, but for instance on portraits that can make the difference between having both eyes in focus on a side angle (or having one out of focus, if that's what you want). f/2.8 or less is in my experience mostly useful for portraits, as most lenses will not be quite that sharp at that aperture.

Message edited by author 2011-10-30 16:41:16.
 10/30/2011 04:47:21 PM · #4
I'm looking at around 200-300mm on an APS-C camera with a subject ~15-20 yards away. Main objective is to separate my subject (i.e. bird or animal in a zoo enclosure) from the background. Right now I have a 55-250mm/f4-5.6 lens that operates at f/5.6 at the maximum length. At 5.6, there's so little separation of the subject from the background which results in very disappointing images. Just interested to know how much difference switching to a constant f/4 aperture will make, or whether I'd have to make the jump to a 2.8 aperture lens.
 10/30/2011 05:06:05 PM · #5
rent or borrow a faster lens and see if it does what you want it to do.. I could give you an answer to your question, but if you want to see if any lens is what you want to use, then just use it and find out.
 10/30/2011 07:01:17 PM · #6
Originally posted by apercep:
rent or borrow a faster lens and see if it does what you want it to do.. I could give you an answer to your question, but if you want to see if any lens is what you want to use, then just use it and find out.

Neither is an option, unfortunately.
 10/30/2011 07:20:28 PM · #7
300 f4 rental
300 f2.8 rental

If you can't afford to rent one for a weekend, you can't afford to buy one either...
10/30/2011 07:38:48 PM · #8
Originally posted by apercep:
300 f4 rental
300 f2.8 rental

If you can't afford to rent one for a weekend, you can't afford to buy one either...


It costs $200 to rent the 2.8 for 4 days (minimum period)... what a ridiculous response.
 10/30/2011 07:41:51 PM · #9
Originally posted by HawkinsT:
Originally posted by apercep:

If you can't afford to rent one for a weekend, you can't afford to buy one either...

It costs $200 to rent the 2.8 for 4 days (minimum period)... what a ridiculous response.

Thank you Toby, I was biting my tongue. Spending $300 to rent the two lenses for 4 days makes no sense at all. Especially considering that is 1/3 of the price of purchasing a used 300/f4 IS.

Message edited by author 2011-10-30 19:51:52.
 10/30/2011 08:15:21 PM · #10
It might take a long time, but have you looked through challenges posted here? Sometimes people post all the stats that they use, sometimes they don't, but there are lots and lots of examples. Unfortunately, it might take you lots and lots of luck to find the pictures that show what you are looking for :)
 10/30/2011 08:20:31 PM · #11
Originally posted by dali_lama_2k:
It might take a long time, but have you looked through challenges posted here? Sometimes people post all the stats that they use, sometimes they don't, but there are lots and lots of examples. Unfortunately, it might take you lots and lots of luck to find the pictures that show what you are looking for :)


Look in the "Equipment" pages, using the link at the top of the DPC home page, and you can enter the lens model, and see images taken using that lens. That would narrow down the search for full aperture images quite a bit.
10/31/2011 03:22:29 AM · #12
I was bored tonight, so I shot some examples for you. It's cold and covered in snow outside and night, so I'll reshoot at the distances you specify during the day tomorrow sometime. For these, the setup is as follows:
Focal Length=200mm on APS-C sensor
Camera to subject distance=4m
Subject to background distance= 3 1/3m
You need to consider both of these distances and how they relate together. At a certain distance, the field will actually just be compressed and the background and foreground will be perfectly focused together. This is the longest fast lens I have. Remember the effect of aperture at the same distance will be magnified for focal length. I have illustrated this by shooting the same subject same distance using my Sigma 150 2.8. You'll have to ignore differences in contrast and IQ- the 80-200 is far better wide open. All images are straight from camera. I'll shoot some at 15-20m tomorrow for you.

10/31/2011 03:51:20 AM · #13
If i was going to buy a car, I wouldn't do it without driving it first. I wouldn't ask someone if I will like driving a corvette or a ferrari more, I would go drive them.. If i can't afford to rent the ferrari, I can't afford to buy it. Fast lenses are no different.. a 300mm f2.8 is $7299.00 so I think $200 is not ridiculous.It is $90to rent the 300 f4. To me ridiculous is buying a used 300mm f4, that may or may not be in A+ condition, and finding out that I need f2.8.. I'm not trying to start a fight, or tell someone that they are stupid, or run my mouth.. I'm expressing my opinion to someone who asked a question.
 10/31/2011 03:57:54 AM · #14
Go into a store and see if they'll let you play with them. Take your own card, take a ton of shots within the store then go home and look over them. It won't be ideal, but it will give you the chance to try them out before you actually go ahead and buy one.

This of course depends on you being able to find a place that will let you do that, but I would imagine any decent retailer should be ok.
 10/31/2011 08:10:47 AM · #15
The short answer comes in two parts:

1. At 300mm and shooting at a reasonable "subject isolation range" there's an appreciable increase in separation between f/2.8 and f/4, and nearly as much difference between f/4 and f/5.6. The difference starts dropping off as you climb the ladder, so f/5.6 to f/8 makes less of a difference, f/8 to f/11 even less, and so forth.

2. In many ways, the real advantage of the f/2.8 lens isn't that it is a stop wider and hence has shallower DOF when wide open; it's that it performs better at f/4 and f/5.6 then the f/4 version of the same lens will, since as a rule no lens, especially a telephoto, is likely to perform with its greatest optical clarity when shot wide open.

Renting a telephoto prime before buying is in fact an excellent idea; those things are a huge investment. With the less-expensive zooms, it's not as critical. It's a matter of what percentage of your outlay you can recover if you resell the lens. If you can sell a new, $7,500 lens for 80% of what you paid, you have dropped $1,500 -- for a $1,500 lens, that would be $300 lost. So apercep is not out of line with his response, and I'm surprised anyone would say it was "ridiculous" to do that.

R.

Message edited by author 2011-10-31 08:14:08.
 10/31/2011 08:15:47 AM · #16
And to make up the rental cost, you may be able to rent out the lens yourself.
 10/31/2011 06:15:51 PM · #17
So, I took some shots at 15m today, nothing fancy, just the front of my truck and the sidewalk in front of my house, which is covered in branches from our recent snowstorm.
Camera to subject is 15m, lens is 200mm
10/31/2011 06:23:58 PM · #18
Originally posted by gcoulson:
Originally posted by apercep:
rent or borrow a faster lens and see if it does what you want it to do.. I could give you an answer to your question, but if you want to see if any lens is what you want to use, then just use it and find out.

Neither is an option, unfortunately.


There has been a fall off of GTGs that I have seen posted lately, but in the past at GTGs I have lent and borrowed lenses for a few hours of shooting and looking through the after threads you have the chance to see what other people have done with varied equipment on similar shots. If you don't have the cash to rent a lens, put in the time to get some of your fellow DPCers in your neck of the woods together for a GTG and try out their toys.
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