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Archive 2013 · From DX to FX, dealing with DOF......help.
  
 
dougfatheruk
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p.1 #1 · From DX to FX, dealing with DOF......help.


Hi folks,

I have always been a crop sensor photographer and finally made the jump to FX.

Originally using the 17-55mm 2.8 and 35mm 1.8 on DX.

Now switched to a 24-70mm and a 50mm on FX.

Under low light i am struggling to work out the best approach, for example on DX i could use f2.8 and even f1.8 up close with natural light and get a somewhat acceptable DOF on faces, kids etc. Now under FX with the newer lenses i can't, so i need to know how best to approach this.

Do i just stop down and raise the ISO, this seems the logical way but obviously raising ISO feels like a hit on image quality and somewhat counterproductive.

I only seem to be finding this an issue at wide apertures, for all of my other needs the images are great and FX is doing what i wanted.

Thanks in advance
Mike



Edited on Feb 23, 2013 at 11:01 AM · View previous versions



Feb 23, 2013 at 10:12 AM
lou f
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p.1 #2 · From DX to FX, dealing with DOF......help.


just close it down a stop or so...


Feb 23, 2013 at 10:46 AM
DavidWEGS
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p.1 #3 · From DX to FX, dealing with DOF......help.


For a similar reason, I have both FX and DX. I was familiar with FX long before digital FX from using film, but DX offers something that just works well compared.

When you shoot, you simply have to stop down: DX (eq. FL) at 24mm and F2.8 = FX 24mm @f4.5 (approx.). As you get closer to F8 on DX, FX is more like two stops down IMO.

So, you can either stop down and stick with FX, or adjust to the shallower DOF. Alternately, a DX body backup for those situations where you feel it needed, might be a good option.



Feb 23, 2013 at 12:19 PM
dougfatheruk
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p.1 #4 · From DX to FX, dealing with DOF......help.


Thanks David.

I'm swaying towards the DX/FX combo.

It appears full frame isn't the one stop shop I anticipated.

Cheers



Feb 23, 2013 at 02:11 PM
Bernie
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p.1 #5 · From DX to FX, dealing with DOF......help.


Another reason for the DX line -- at least for those of us who like to get things in focus or at least within the DOF capabilities of the sensor and lens.

Too many still shoot a 1.4 lens wide open and then wonder why they can't get a sharp image. Between a live subject and body sway on the part of the photographer, the DOF is so razor thin it can be very difficult. And it's even more difficult with an FX sensor.



Feb 23, 2013 at 03:35 PM
Two23
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p.1 #6 · From DX to FX, dealing with DOF......help.


dougfatheruk wrote:
Thanks David.

I'm swaying towards the DX/FX combo.

It appears full frame isn't the one stop shop I anticipated.

Cheers



This is one of the reasons I just stayed with DX. (The other being I dislike tying up big $$ into digital camera bodies.) You could just crop your images back to DX size to achieve the same effect. But then, you spent thousands of dollars for basically the same result you were already getting before. Stopping down is the obvious answer.


Kent in SD



Feb 23, 2013 at 05:33 PM
curious80
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p.1 #7 · From DX to FX, dealing with DOF......help.


To get the aperture for equivalent DOF you need to multiply by 1.5 (the "crop factor")

So f2.8 on DX has the same DOF as f4.2 on FX. SImilarly f1.8 on DX has same DOF as f2.7 on FX, etc. For all practical purposes you can consider it a one stop difference.

That does not mean that you need a DX/FX combo. Sure you might need to raise the ISO by one stop but FX sensor has a one stop noise advantage over DX so at the end of the day you get the same quality as you would get with DX (with the added benefit that you no longer use your lens at close to wide open where it is the weakest).

Of course if most of your shooting is DOF limited like that then you may need to evaluate if you are really getting any major advantage from using the FX camera.



Feb 23, 2013 at 06:24 PM
Elan II
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p.1 #8 · From DX to FX, dealing with DOF......help.


I'm going to add a technical note and a summery for future reference.

At a given focal-length/focus-distance/aperture-setting, the DOF of FX and DX sensors is identical. The problem is that you have to either shorten the focus distance, or increase the focal length to fill the FX frame with the same view of a DX frame. Either one thins out your DOF.

As you already know, your choices are to crop the image, or to close the aperture. In scenarios where shutter speed is an issue, you have to raise the ISO setting to compensate, thus giving up much of the FX low light advantage. This is one shortcoming of the FX system. The significantly higher cost of comparable lenses to DX is another. For many photographers these are outweighed by other advantages of FX, or are not an issue at all. For me they were deal breakers.






Feb 23, 2013 at 09:32 PM
dougfatheruk
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p.1 #9 · From DX to FX, dealing with DOF......help.


Hi Elan,

Thanks for the info.

In restrospect i'm kind of feeling like my FX bubble has burst a little.

I spend a lot of time photographing in natural light where possible close up, and as you stated i will now need to stop down and raise ISO where I would have previously used f1.8 or f2.8.

It really does beg the question of whether i have made the right decision for my needs?

Had Nikon announced the D7100 sooner i'm confident I wouldn't have made the jump, i waited many months for the D7000/D300s successor and typically it came just weeks after my upgrade.

@Curious80, you raise some interesting points, vignetting is now an issue so staying clear of wide open is advantageous.




Feb 24, 2013 at 01:19 AM
michaelwatkins
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p.1 #10 · From DX to FX, dealing with DOF......help.


Embrace Auto ISO?

In theory your FX sensor has a noise advantage, so let the camera do its thing with sensitivity when light is less than ideal, and you pick the aperture that suits the subject.



Feb 24, 2013 at 04:52 AM
 

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JimFox
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p.1 #11 · From DX to FX, dealing with DOF......help.


Hey Doug,

Also, don't be afraid to raise your ISO. You mentioned that raising your ISO was counter productive. That in a real world sense is not true anymore. I am not sure which new FX camera you got, which would be helpful to know as remember a D800 is much harder to handhold than a D600 because of the increased resolution, better technique is required for sharp shots.

But don't be afraid to shoot at higher ISO's. If you expose properly, you will have hard time shooting. You also didn't mention what ISO you are currently shooting at, but use them... you will be surprised that if you expose properly your ISO 800 shots can look just as good unless you are using a microscope as your ISO 100 shots. The difference is very small. Same as shooting at ISO 1600 or more... if you search through this forum you will find plenty of postings by people shooting at ISO 3200 of people and the shots look great... again... the key is proper exposure.

Jim



Feb 24, 2013 at 05:28 AM
zacheryjensen
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p.1 #12 · From DX to FX, dealing with DOF......help.


Err, counterproductive to increase the ISO? My D800's 6400 ISO images look 2-3 stops better than even the best performing 16mp DX sensors at the same framing and final reproduction size.

You have a huge advantage of high ISO capabilities in FX, almost always beyond just one stop that it takes to get the same DOF at the same angle of view, and even at the same noise level, other factors of improved image quality (lower magnification of glass-induced image flaws like CA and contrast-defeating diffraction) carry the result well beyond what DX can do.

I'm saying this as someone who has shot extensively with 12, 14, 16 (multiple generations) and 24mp DX sensors as well as the D3s's physics-defying 12mp full frame sensor and currently shooting the D800.

The D800 produces better looking results than all of them. The D3s obviously beats it at pixel level noise, but loses so much character from being so low resolution.

Assuming you have a current generation FF camera, it will produce better looking images at the same angle of view, depth of field, and sensitivity levels as any DX camera. Don't hesitate. Just make your images.



Feb 24, 2013 at 07:42 AM
form
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p.1 #13 · From DX to FX, dealing with DOF......help.


On average, most full fre cameras have about 1 stop or better iso noise performance than aps-c cameras in the same brand/similar range. Think of full frame as giving you the option to gather more light and have a narrower dof if you want it.


Feb 24, 2013 at 09:40 AM
dougfatheruk
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p.1 #14 · From DX to FX, dealing with DOF......help.


Hi folks,

Thanks for all the incite, I appreciate it.

I've got a D700, I got a good price used under 2K clicks and couldn't resist.

ISO typically as low as I can get it but 1600 was previously my usable ceiling and that was at a push.

I think I'm definitely hypothesising too much and as stated, need to put it to real word use.

Another issue is in DX you can turn the zoom ring to 55mm and generally not have too much of an issue, doing that on a 70mm on FX typically gets the nose out of focus, so definitely a case of changing my shooting style.

Thanks again.



Feb 24, 2013 at 12:41 PM
ja_joyce
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p.1 #15 · From DX to FX, dealing with DOF......help.


The way the math works out is you need to stop down about 1 more stop to get the same DoF with the 50% longer lens you use on FX vs DX. Check an online DoF calculator (or get an app for your phone) for the specific combination of focal length, f-stop and distance you are interested in.




Feb 24, 2013 at 04:31 PM
mfletch
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p.1 #16 · From DX to FX, dealing with DOF......help.


dougfatheruk wrote:
Hi folks,

Another issue is in DX you can turn the zoom ring to 55mm and generally not have too much of an issue, doing that on a 70mm on FX typically gets the nose out of focus, so definitely a case of changing my shooting style.

Thanks again.


Yes, there will be a bit of a learning curve with the differences in DOF, but put in the time and see if you can adjust. If not, DX will still be around for the foreseeable future, and it shouldn't be hard to trade your way back if DX better meets your needs.

I had a similar but opposite issue. I shot 35mm film for 19 years prior to moving to digital in 2006. I was so familiar with the 35mm format, that I could compose my shot and have a mental picture of how the DOF and final image would look, and this important with no LCD to chimp with. When I got my first DSLR, a 1.6x crop Canon, I struggled to get my chosen settings to "look" like i felt they should look. I always carried a film body for backup and would shoot the most important shots(the ones I needed to nail) on film, because I could still predict its output better, even with the ability to chimp on the DSLR. About 2.5 years into my DSLR experience, the D700 was released, and I jumped for one. From day one with the FX format, I could fire the shutter and get the DOF and look that I was attempting to shoot. For me, the transition to digital was complete. Sadly I haven't shot more than 2-3 rolls of film in last 4 years, but I haven't needed it.

I don't believe there is much of an image quality capabilities between FX and higher end DX bodies. Shoot whatever feels best and fits your shooting style better.



Feb 24, 2013 at 04:44 PM
theSuede
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p.1 #17 · From DX to FX, dealing with DOF......help.


Actually, no need for DoF calculators or any other complicated stuff.

Just know that light, noise and DoF go together just like Ohm's law.
If you want a certain shutter speed and a certain DoF, noise will be very similar no matter what camera format you choose!

The main thing about larger sensors (FX) is that for the same shutter speed and DoF, the lenses are almost always sharper. The 24-70 @F4.0 is quite a lot sharper than the 17-55 @2.8.

What you're left with with FX is an option to get:
slightly shorter DoF and slightly less noise or:
same DoF, sharper image, same noise

There's no free lunch as they say. And it's certainly true in physics.



Feb 24, 2013 at 04:49 PM
Elan II
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p.1 #18 · From DX to FX, dealing with DOF......help.


theSuede wrote:
Actually, no need for DoF calculators or any other complicated stuff.

Just know that light, noise and DoF go together just like Ohm's law.
If you want a certain shutter speed and a certain DoF, noise will be very similar no matter what camera format you choose!

The main thing about larger sensors (FX) is that for the same shutter speed and DoF, the lenses are almost always sharper. The 24-70 @F4.0 is quite a lot sharper than the 17-55 @2.8.

What you're left with with FX is an option to get:
slightly shorter DoF and slightly less noise or:
same DoF, sharper image, same noise

There's
...Show more


That's a good point. Getting a sharper image with the same DOF and shutter speed is big plus. That's why reducing the DX vs. FX equation to a couple of issues doesn't work. There are additional layers.

A couple more considerations.

Many of us shoot FX lenses with DX bodies, especially primes. Corner performance of the same lanes takes a major nosedive with FX. You can see that more clearly now that all the testing sites are using both formats with the test lenses.

Increasing the focal length with FX to end up with the same field of view effect camera shake. This point becomes somewhat murky when pixel density is taken into account.

If you like to go long, you have to add a 1.4x TC to FX to end up with the same field of view as DX. This has the same effect as stopping down, except the TC makes the image less sharp instead of sharper.

What you shoot can help you decide which format is best for you. I shoot wildlife, macro, architectural and landscape. Wildlife and macro work better with DX. Architectural and landscape are better with high resolution FX right now. With my mix, DX does better with most and well enough with the rest. If I was shooting mostly people and portraits, I would go with FX.






Feb 24, 2013 at 06:03 PM
roland hale
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p.1 #19 · From DX to FX, dealing with DOF......help.


What kind of FX camera are you using that you can't close down a stop or two and bump up the ISO, or drop your shutter speed?


Feb 24, 2013 at 10:25 PM
theSuede
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p.1 #20 · From DX to FX, dealing with DOF......help.


Elan II wrote:
That's a good point. Getting a sharper image with the same DOF and shutter speed is big plus. That's why reducing the DX vs. FX equation to a couple of issues doesn't work. There are additional layers.

A couple more considerations.

Many of us shoot FX lenses with DX bodies, especially primes. Corner performance of the same lanes takes a major nosedive with FX. You can see that more clearly now that all the testing sites are using both formats with the test lenses.

Increasing the focal length with FX to end up with the same field of view effect camera shake.
...Show more

A couple of counters:
Nah, corners on FX aren't usually worse, when you compare at the 1 stop higher aperture value.
Longer lenses though are certainly a point - especially considering that Nikon has a weak spot in their lens lineup in cheap(ish) long lenses for use on FX. Oh 400/5.6 where art thou?
Medium "reach" lenses are firmly and securely in the FX stronghold though. DX isn't even close.

As always, chose the tool that works for you. But before deciding on pure gut feeling, do an actual reality-based comparison. And preferably, mark the results blindly. Have a friend rename the crops before you mark them. You'll be surprised about how many of your preconceptions that turn out be iffy in practical use.



Feb 24, 2013 at 10:46 PM





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