DX Auto-Crop

Fortkentdad

Senior Member
I know my D610 can be put into DX mode but not sure that gives any more reach, it just auto-crops the image so that when shooting with a DX lens you avoid having to crop out the dark vignette or 'port-hole' circle around the photo. Sometimes it is OK to create a round image but usually not. Just not sure that you actually get a closer image when you put it into DX - only benefit is not having to crop pp to go from circle image to square image???

Have I got this wrong?
 

480sparky

Senior Member
DX mode is useful for other reasons. Even when using FX lenses, the '1.5x crop / extended reach' factor comes into play if using long lenses for sports or wildlife.

Using DX mode will also create smaller files, which are quicker to transfer to the memory card and thus clearing the buffer faster.
 

J-see

Senior Member
I tried it on my D750 with the DX lens but it'll probably be the same. If I don't use DX auto-crop it's not just vignetting that occurs but with the lens I used (10-24mm) massive distortion. If it's a zoom like mine, there's a range that works reasonable well without the DX auto-crop (besides vignetting) or when using the 1.2x crop.

I guess it depends upon what lens used how much the DX mode is needed. Vignetting however is always present and isn't always that easy to remove in post.

I don't get the same benefit of the higher Mpix DXs since when DX cropping, I lower my resolution too.
 

Eyelight

Senior Member
My thinking is the idea of reach only applies when bringing more sensor resolution to bear on the image created by the cropping. So, only applies when using a smaller sensor with higher pixel density.

Me thinks also the benefits of crop mode are using the best of the glass and smaller file sizes when it makes sense to lose pixels in the final image.
 

BackdoorArts

Senior Member
DX is a sensor size, not a type of zoom. Confused? Read this - http://nikonites.com/education/27205-crop-sensors-ultimate-primer.html#axzz3LEEVUa3W

"DX Mode" means that the camera only uses the part of the FX sensor of equivalent size to a DX sensor, or in other words, it crops 55% of the frame for you. So, instead of 24MP's you get about 11MP's.

Why would you do it?

1. You have DX glass that you want to use and it's easier than shooting in FX and then cropping away the circle from where the lens doesn't cast light on the sensor.

2. You have DX glass and you want to see just the portion of the frame that's going to be useful and not look through the viewfinder and see a tunnel (see #1 above).

3. You're shooting wildlife and even with FX glass the critter you want is only in a small part of the center of the frame, so if you shoot DX you'll get an effective pre-crop AND you'll save about 60% on image space allowing you to shoot more.
 

Marcel

Happily retired
Staff member
Super Mod
You get exactly the same image wether you are using DX mode except that the crop is already made for you in camera. You can gain a bit of width when you don't use the camera crop and do your own cropping, but on the pixel level, you get the same resolution.

DX in camera mode is just like "auto-crop" mode.
 

Eyelight

Senior Member
So, no, @Fortkentdad , you are not wrong. DX mode doesn't get closer or gain magnification.

Distance and focal length produce magnification and one of them needs to change to increase the real reach.
 

Fortkentdad

Senior Member
So this 'extra reach' of DX mode is just an illusion.

I've been tempted to use my DX 55-300 on my D610 because it has VR and I think that the Nikon is a better bit of glass than the other choice in my kit bag, an older Siggy 100-300 from my film days. It does not have VR. Both do auto-focus. The Siggy has the advantage because I get the full frame resolution - the Nikon's advantage is the VR and perhaps better glass. I think that the Nikon autofocus is better too. I get more bad shots with the Siggy than the Nikon did on my D5100.

These will have to do until I get a longer lens for my D610.

I did pick up a 70-210 old Nikon to bridge the gap while I wait until I break the piggy bank and get me something good and long.
 

Geoffc

Senior Member
I don't get the same benefit of the higher Mpix DXs since when DX cropping, I lower my resolution too.


Because in the case of a D7100 you end up with an image created by a DX sensor that is 24 mpix rather than the 11mpix off the cropped FX sensor. An older D300 gives 12mpix so the DX image is still better than the FX in crop mode.

The file size on a 24mpix DX is the same as a 24mpix FX as they both have the same number of pixels within.

So let's say you can fill the DX portion of a sensor with a subject using a given lens. The DX camera will provide much more detail as it's representing it with 24mpix not 11.

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J-see

Senior Member
I agree the DX has advantages detail wise and I assumed it would be better for any sort of shot I end up cropping. Like birding or macro. The reality is that even while my D3300 has more pixels/area, I ended up using the D750 all the time.

My better lenses perform better on it and I can take plenty a shot that is difficult to impossible with the DX. At least when desiring the same quality.

The sharpness in P-Mpix of my 200mm macro on the D3300 is 10/24 which is quite some loss. I don't have numbers for the D750 but on the D610 it is 19/24. So even while my D3300 has the 1.5x advantage, my D750 grabs almost double the detail when using the same lens. So even in DX mode, it doesn't do much worse. I guess here too 1.5x is partly the reason since that counts also for any imperfection.

The DX wide I used on the D750 sadly didn't work too well. Longer than 15mm it did take full shots in FX mode but when I checked the corners of the shot, I noticed it stretched the shot quite a bit. For some shots that doesn't matter much but for others it simply doesn't work. When shooting in both crop modes it solves most of those problems but quality wise it can't compete with the FX wide I'm using now.

But the DX was never intended to be used on FX and perform as well.
 
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J-see

Senior Member
I decided to test it.

I set my lens on a tripod and then attached both cams to it. Same aperture and ISO, focus on same spot. All shots are SOOC, auto WB and matrix metering. No post besides LR's lens correction and auto-sharpen/noise. What I noticed too is that I need twice the light with the D3300.

The D3300 shot suffered some very slight shake but nothing that hinders this comparison much. I can't put the mirror up and it likely picked up the trigger.

This is the D3300 in 24Mp DX mode.

012.jpg

Then the D750 In FX, 1.2x and 1.5x crop modes.

014-2.jpg

015-2.jpg

018.jpg

Now let's zoom in some:

012-2.jpg

014-2-2.jpg

015-2-2.jpg

018-2.jpg

My D3300 has more Mpix/area so logically it should translate into more detail/better shot.

I enlarged the FX mode until it had the same size as the D3300 shot. It's the worst pixel mode the D750 has compared to the D3300 sensor.

012-2.jpg
014-2-Edit.jpg

As you see it's not simply more Mpix/area = more detail or better quality. It depends entirely upon how good the lens/cam combination is. If the FX gets more out of the lens, there's no reason to shoot DX mode unless it's for practical reasons. There's also little reason to bird or macro with a DX if you have an FX. At least as long as that FX makes the lens better.

Btw, I always complained about the D3300 being too bright and here it shows clearly. In LR I need to lower the D3300's exposure by 1 full and 2/3ths of a stop to push the histogram until it equals the D750. The D750 shots also looks as I see them in front of me.
 
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Geoffc

Senior Member
I decided to test it.

I set my lens on a tripod and then attached both cams to it. Same aperture and ISO, focus on same spot. All shots are SOOC, auto WB and matrix metering. No post besides LR's lens correction and auto-sharpen/noise. What I noticed too is that I need twice the light with the D3300.

The D3300 shot suffered some very slight shake but nothing that hinders this comparison much. I can't put the mirror up and it likely picked up the trigger.

This is the D3300 in 24Mp DX mode.

View attachment 127737

Then the D750 In FX, 1.2x and 1.5x crop modes.

View attachment 127738

View attachment 127739

View attachment 127740

Now let's zoom in some:

View attachment 127741

View attachment 127742

View attachment 127743

View attachment 127744

My D3300 has more Mpix/area so logically it should translate into more detail/better shot.

I enlarged the FX mode until it had the same size as the D3300 shot. It's the worst pixel mode the D750 has compared to the D3300 sensor.

View attachment 127741
View attachment 127745

As you see it's not simply more Mpix/area = more detail or better quality. It depends entirely upon how good the lens/cam combination is. If the FX gets more out of the lens, there's no reason to shoot DX mode unless it's for practical reasons. There's also little reason to bird or macro with a DX if you have an FX. At least as long as that FX makes the lens better.

Btw, I always complained about the D3300 being too bright and here it shows clearly. In LR I need to lower the D3300's exposure by 1 full and 2/3ths of a stop to push the histogram until it equals the D750. The D750 shots also looks as I see them in front of me.
@J-see I'm intrigued by you findings as everything I've ever read and the controlled testing that I've performed myself is completely the opposite of what you are describing here. I had the chance to try a D700 and D300 a couple of years ago and I wanted to compare the crop factor. The "full" shots are the masters and shot at 200mm F4, with a 70-200 VRII 2.8 lens. The others are crops to make the image the same size. The really interesting one is the letter B. I thought they would be the same but the 700 is not cutting it on these as you can see what the lack of pixels does. The results of the test are here and quite clear to me. Here is a more recent test that I did between the D7100 and the D800.

I have a D800 and D7100 that I use for different things. If I want reach and detail when I can't fill the FX frame with the lenses I have the D7100 comes out and delivers more resolution. I use it for both wildlife and macro. Whereas the D800 is better for high ISO and landscapes type photography as reach doesn't tend to be an issue and I can use all 36mpix.

Lenses is also another interesting point. As a general rule, FX lenses are in their sweet spot on DX cameras because they only use the centre of the lens which tends to be sharpest. My 70-200 2.8 is great on DX for example.

I make a conscious decision whether to use the 7100 or the 800 based on what I'm trying to achieve. Neither is better, they are different. I know other people like @BackdoorHippie also choose their tools based on the job.

I am further intrigued that you need twice the light for DX. If I put the same lens on my FX and DX cameras and manually set shutter speed, F stop and ISO to the same values the exposure will be the same. I normally measure using a light meter to make sure it's correct. I suspect you have used the internal meter which will be looking at two different sized areas and there evaluating different criteria. Please confirm that everything was full manual, measured with a handheld meter and only non processed raw was used for the test or it all becomes a bit meaningless due to all the variables in measurement and processing. I recently tested our two D7100 bodies and the D800 and under that kind of control they are pretty much identical.
 
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J-see

Senior Member
I don't know what you read or controlled but the shots here are the shots taken with the exact same lens. The lens never left the tripod so the distance is identical. It shows what the numbers said at DxOmark; the lens + D3300 combo has a lot of loss compared to the better sensors. That shows.

The D3300 overexposes which is something I knew but it is irrelevant when it comes to detail here. I just didn't know how much it overexposed until comparing with the D750. Auto WB is also completely different but I never expected a 500$ cam to be perfect. The strange part is that the shutter doubled but the shot taken is overexposed even more. That's something strange the cam does.

I don't see why I would set all manual since this is about distance - detail. As such aperture and ISO counts. Shutter is irrelevant. Setting both identical manual would not give correct results anyways since the D3300's sensor is smaller than the D750 and needs more light. That's true here and that's true when I take it outside. I've never been able to shoot at the same settings I do with the D750. Maybe it's something with the D3300, I wouldn't know. I only know the limitations I constantly encountered. ISO evidently also has something to do with that.

That it can be different for other cam/lenses is entirely possible. It depends on their combination/loss. If the lens has little loss on the D7100, it could be the shot is better detail wise.

Still, if you like I'll reshoot some. Tell me what settings you prefer to see.
 
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J-see

Senior Member
Ha, I see why it overexposed that much. I forgot to check one little thing. ;)

I'll set them up again but I'll only shoot FF vs DX now.
 

J-see

Senior Member
Ok there we go.

All manual, standard lens correction and sharpening in LR, same distance on pod and same set-up light wise. I shot a flat surface this time to rule out front back focus differences. I took some seven shots with the DX and picked the best. It's still 1/3th of a stop more exposed than the D750.

DX vs FX full.

DX.jpg

FX.jpg

DX vs FX crop to 100%

DX-3.jpg

FX-3.jpg

DX vs FX scaled to the crop factor difference.

DX-Edit-2.jpg

FX-Edit-2.jpg

The quality difference here is very obvious. For me it evidently doesn't pay shooting crop instead of FX.
 
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wornish

Senior Member
The elephant in the room is the glass. An FX lens is bigger, heavier and more expensive therefore than a DX lens.

If you use a DX lens on a FX camera set in DX crop mode then the difference boils down to sensor pixel size, low light sensitivity and what auto focus technology is built in to the camera/sensor combination.

but for birding and macro DX wins.
 

J-see

Senior Member
The elephant in the room is the glass. An FX lens is bigger, heavier and more expensive therefore than a DX lens.

If you use a DX lens on a FX camera set in DX crop mode then the difference boils down to sensor pixel size, low light sensitivity and what auto focus technology is built in to the camera/sensor combination.

but for birding and macro DX wins.

That's not always true. Yes this is an FX lens but if for birding and macro DX would be better (sensor), it should show here. The popular idea is also that a good lens would perform better on a DX because it uses the better part of the lens. Not always it seems.

I did the test a third time, better safe than sorry.

029.jpg

048.jpg

100%

029-2.jpg

048-2.jpg

FX scaled to identical size:

029-Edit.jpg

048-Edit.jpg

The DX crop mode, even with its Mpix advantage is no competition for the FX even when cropped down in post. At least the D3300 vs D750. I'm not saying it is a phenomenal difference in the quality of the shot but when considering purely the quality/pixel, it is quite a lot.

I assumed it to be different until I compared pixel loss on paper and then shot these.

I just checked the optical sharpness for the D7100 with this lens and that is around 11 P-Mpix. The result should be fairly identical to this difference.

Anyone with a DX and FX is free to test this themselves. Maybe for them it is different.
 
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J-see

Senior Member
I checked it with another lens to see if there same is true there.

DX vs FX 100% crop

057.jpg

065.jpg

DX vs FX scaled to same magnification.

057-Edit.jpg

065-Edit.jpg

Until someone else tests the same and gets identical results, a possible explanation could be my D3300 being a qualitative worse cam than the standard or my D750 being qualitative better. Yet I never was disappointed by the shots it took.
 
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Geoffc

Senior Member
[MENTION=31330]J-see[/MENTION] I think we'll have to agree to disagree on this one. As you can see from my previous post I have done testing for this before and had many debates about it here on Nikonites. I never use DX mode in my FX body as it's not giving me anything, but I'm happy that the DX body gives me the extra detail for smaller subjects.

When you look at DXO scores are you factoring in the cropped FX image as those scores are based on pixels used in the test. Like for like the FX get higher scores than DX, but a D7100 beats a D4 because it has more pixels. The cropped D750 image is closer to a D700 in pixels.

All of this aside, perhaps the D3300 is just either not very good, back focussing or some other anomaly. I've never tried one so I can't say, however I know I would not be unhappy if the D7100 was my only camera.




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