DX/FX Further Clarification

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kwiksand

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Hey Guys,

I've got a quick query about camera lenses and newer crop sensors on DSLR's.

I've got a Nikon D40 with 18-55 DX Lens. I understand this to be true 18-55mm, exactly as an 18-55 would look on a full frame camera (or there abouts). For example 50mm on this lens would give a similar point of view than a 50mm on a D700 (Maybe I have this wrong).

I've been wanting to get a nifty fifty for a while, but have heard a lot of people saying with the crop sensor they're a bit too restrictive (with a cropped focal length equivalent to 75-80mm).

I'm really confused now though, as you all know, there's new Nikon lens out (or soon to be out) thats a cropped 35mm lens for these cameras to give the equivalent focal length to a 50mm on a full frame camera (52.5mm). But the lens is a DX lens, so how can this be?

I've read many articles on how the cropping works and I understand it, just the different lens designation is getting me a little confused.
 
Basically the sizes indicated on the lenses 18-55, 50mm etc are the full frame (FX) focal lengths regardless of whether your camera is DX or FX, however DX cameras (such as your D40) produce an image that is the equivalent of the field of view that you would get if you used a lens that was 1.5 larger.

Confused? Let me explain. If you put a 50mm lens on a camera with an FX sensor it will be a "true" 50mm (to be pedantic it's not, as Nikon FX isn't really full-frame, but forget about that for the moment ;)) whereas if you put the same lens on your D40, whilst it is still a 50mm lens the field of view that you have will be roughly the same as what you would get from a 75mm lens on the FX camera.

If that's still clear as mud, then perhaps this might help. If we assume that this is a 50mm lens, when it's put onto a full frame (or FX) body what you'll see through the viewfinder is basically the full image, however on your D40 what you would see would roughly equate to the area within the yellow box.


full-frame-crop-factor.jpg


So, to return to your query about the new 35mm lens, even though it is a DX one the focal length is still measured in FX money, so the it will give you the equivalent field of view of a 52mm lens on an FX camera, like a D700 or D3.

I hope that clears thing up a bit for you. I'm going for a lie down now :lol:
 
kwiksand said:
I've got a Nikon D40 with 18-55 DX Lens. I understand this to be true 18-55mm, exactly as an 18-55 would look on a full frame camera (or there abouts).
Click to expand...

No

kwiksand said:
For example 50mm on this lens would give a similar point of view than a 50mm on a D700 (Maybe I have this wrong).
Click to expand...

You do have this wrong.

kwiksand said:
I've been wanting to get a nifty fifty for a while, but have heard a lot of people saying with the crop sensor they're a bit too restrictive (with a cropped focal length equivalent to 75-80mm).
Click to expand...

IMHO they are. Set your 18-55 to 50mm and see if you like the field of view. Do it again at 35mm. Which do you prefer? There is no right or wrong here.
 
Flash In The Pan said:
So, to return to your query about the new 35mm lens, even though it is a DX one the focal length is still measured in FX money, so the it will give you the equivalent field of view of a 52mm lens on an FX camera, like a D700 or D3.

I hope that clears thing up a bit for you. I'm going for a lie down now :lol:
Click to expand...

Ah, that makes sense, but my next question is why do they bother making the DX lens? Aren't they just restricting the amount of people who'll buy the lens?? Surely making an FX lens that D700 + users can use as well as useres with cropped sensor would be a better idea?

Or is it purely a cost thing?
 
kwiksand said:
I've been wanting to get a nifty fifty for a while, but have heard a lot of people saying with the crop sensor they're a bit too restrictive (with a cropped focal length equivalent to 75-80mm).
Click to expand...

puddleduck said:
IMHO they are. Set your 18-55 to 50mm and see if you like the field of view. Do it again at 35mm. Which do you prefer? There is no right or wrong here.
Click to expand...

:plusone:

kwiksand said:
...but my next question is why do they bother making the DX lens? Aren't they just restricting the amount of people who'll buy the lens?? Surely making an FX lens that D700 + users can use as well as users with cropped sensor would be a better idea?

Or is it purely a cost thing?
Click to expand...


Full frame has only been available with Nikon digital users since the release of the D3 and D700. Give or take a little, two years.
 
There are a number of small reasons why DX lenses were pushed for a long time.

Firstly, yes, they are cheaper to make, as on average, they take less glass to make; the number of elements may not change, but certain elements can be made smaller. Seeing as optical glass can cost up to £1k per KG, it can make a noticeable difference to cost.

A knock-on effect from this is that they can be slightly lighter as well.

However, as mentioned above, the DX lens focal lengths are still made in terms of FF money. Therefor, with the smaller sensor size, you are sampling the image it it's best once it has encountered the lens. In other words, theoretically, the image quality of a lens is best at the center, and degrades as you reach the edges of the lens, so having a smaller sensor acts to eliminate the areas of the image that are the most adversely effected by the lens.
 
DX was the biggest conjob going IMHO. "Uses the sweet spot of your lenses" - great spin

I said about 2 years ago on another forum (before Nikon went FF) that'd we'd all be shooting full frame in 5 years. I still believe it.

I think DX will essentially end up in the Coolpix line, and we'll see FF down to D40 level, by end 2011.
 
This is why I don't want to buy any DX lenses at all (from now that is)! I would have bought the new 35mm (when I can afford it) if it had been FF but will buy an equivalent FF frame lens instead.
 
Guys, just to emphasise, focal length is focal length.

It's an actual measurement of the characteristics of the lens. If you cut one in half and had a couple of lasers and a ruler you could measure it.

To work out angle of view you need to know the focal length and the sensor size. Don't think about angle of view in terms of focal length alone, it always needs to be qualified by a sensor size.
 
puddleduck said:
DX was the biggest conjob going IMHO. "Uses the sweet spot of your lenses" - great spin
Click to expand...

Granted, I think they should have gone with FF from the beginning. However you can't deny that the image quality towards the optical axis is better than that of the outer edges of the elements.
 
Woodsy said:
Granted, I think they should have gone with FF from the beginning.
Click to expand...

This would however have increased the cost dramatically. If you have a disc of silicon and place FF sensors on it you might get 50 and across the disc there may be 20 faults causing maybe 16 of them to be faulty (allowing for a few to have two faults). If you half the size of the sensor you might get 110 sensors on the disc and with 20 faults again you might get 92 good ones. So 34 versus 92 .... this is the reason they went with smaller ones to begin with. The reality is actually even worse apparently.
 
puddleduck said:
DX was the biggest conjob going IMHO. "Uses the sweet spot of your lenses" - great spin

I said about 2 years ago on another forum (before Nikon went FF) that'd we'd all be shooting full frame in 5 years. I still believe it.

I think DX will essentially end up in the Coolpix line, and we'll see FF down to D40 level, by end 2011.
Click to expand...


Iam still new to DSLR's and have a D60 and enjoy the extra length the crop sensor gives me for my budget.

Is it only nikon that makes the DX lenses for the DX range of bodies or do Sigma/ Tamron make special lenses for cropped sensors.:shrug:

I have upgraded kit dx 55-200 to 70-300VR which I Know is not a DX lens and have also just got a sigma 70-200 Hsm macro which I am guessing is a FF lens.:thumbs:
 
Sigma's DX lens are marked "DC".

The Sigma 70-200 f/2.8 is full frame.
 
foggy4ever said:
Iam still new to DSLR's and have a D60 and enjoy the extra length the crop sensor gives me for my budget.
Click to expand...

It doesn't actually give you extra length. That is exactly like getting a pair of glasses painting the lenses black but leaving a small hole in the middle and calling them zoom glasses!

You are not actually getting any more zoom you are just looking at the middle of the picture blown up. Just like loading a picture into photoshop and sliding the magnify bar. :)
 
Thanks that good to know :clap:

Interesting point on nikon going FF through out range.

One more quick question. How do AF-S lenses operate on bodies with built in focus motors, does the body focus and the lens motor become redundant?
Do AF lenses work better than AF-S?


Should have read the thread from the start:bang: still I learn somthing new every day.:thinking:
 
cowasaki said:
It doesn't actually give you extra length. That is exactly like getting a pair of glasses painting the lenses black but leaving a small hole in the middle and calling them zoom glasses!

You are not actually getting any more zoom you are just looking at the middle of the picture blown up. Just like loading a picture into photoshop and sliding the magnify bar. :)
Click to expand...
Correct.... but....

For sensors with the same number of pixels, say for example a 10MB sensor in each camera... you WILL effectively get closer to the subject on the cropped sensor camera because you have a narrower field of view than the FF, but you are taking the image with the same number of pixels.

For wide angle shots, FF and smaller crop cameras are the bees knees, but for telephoto shots on a somewhat limited budget, crop sensor cameras are better.

I fail to understand that whenever these type of threads are posted, there always seems to be the pro (i.e. meaning positive, not professional) argument for FF or smaller crop gear. What also needs to be considered when comparing images of camera with different crop factors (FF or crop) are the number of pixels used to make up the image. If you take an image on a 12MB 1.3x sensor camera, and then the same image on a 12MB 1.6x sensor camera, you will have more detail in the 1.6x sensor camera image because you have a narrower field of view, but the image captured contains the same number of pixels.

Hope that makes sense!
 
theMusicMan said:
Correct.... but....

For sensors with the same number of pixels, say for example a 10MB sensor in each camera... you WILL effectively get closer to the subject on the cropped sensor camera because you have a narrower field of view than the FF, but you are taking the image with the same number of pixels.

For wide angle shots, FF and smaller crop cameras are the bees knees, but for telephoto shots on a somewhat limited budget, crop sensor cameras are better.

I fail to understand that whenever these type of threads are posted, there always seems to be the pro (i.e. meaning positive, not professional) argument for FF or smaller crop gear. What also needs to be considered when comparing images of camera with different crop factors (FF or crop) are the number of pixels used to make up the image. If you take an image on a 12MB 1.3x sensor camera, and then the same image on a 12MB 1.6x sensor camera, you will have more detail in the 1.6x sensor camera image because you have a narrower field of view, but the image captured contains the same number of pixels.

Hope that makes sense!
Click to expand...

Thanks musicman thats a great explanation on how I understand my simple but but not totally wrong quote:thumbs:
 
:popcorn:
 
puddleduck said:
DX was the biggest conjob going IMHO. "Uses the sweet spot of your lenses" - great spin

I said about 2 years ago on another forum (before Nikon went FF) that'd we'd all be shooting full frame in 5 years. I still believe it.

I think DX will essentially end up in the Coolpix line, and we'll see FF down to D40 level, by end 2011.
Click to expand...

You read it here first! I'm off to the bookies!
 
Flash In The Pan said:
(to be pedantic it's not, as Nikon FX isn't really full-frame, but forget about that for the moment ;))
Click to expand...


In what way? It's as close to FF (35mm [135] film) as you can get, having a sensor that measures 36mm x 23.9mm compared to a 35mm frame which is a nominal 36mm x 24mm (just measured the actual exposing "window" in a 35mm compact [the SLRs are all loaded] and the actual measurement is 35.65mm x 23.65mm). I'll accept that there are larger formats than 35mm (in fact, is there any real upper limit?) but if we take 35mm film as being FF, the Nikon FX sensor is also FF.
 
welly said:
You read it here first! I'm off to the bookies!
Click to expand...

I'd be first in the queue for one - although who knows!

There is no technical reason we can't have a D40 type body with full frame - look at the 20 year old Nikon EM, tiny body, but with a HUGE viewfinder.

It's really just a matter of cost, not technology.

I'd personally pay 3x the cost of the current D40 with a big viewfinder and a variant of the D700 sensor. Give me "A" mode, a shutter release button and that would do me. It would be an amazing travel camera.
 
cowasaki said:
This would however have increased the cost dramatically. If you have a disc of silicon and place FF sensors on it you might get 50 and across the disc there may be 20 faults causing maybe 16 of them to be faulty (allowing for a few to have two faults). If you half the size of the sensor you might get 110 sensors on the disc and with 20 faults again you might get 92 good ones. So 34 versus 92 .... this is the reason they went with smaller ones to begin with. The reality is actually even worse apparently.
Click to expand...

You are assuming that making the quantum wells smaller (with the same manufacturing techniques) still has the same failure rate as those made on larger sensors. I suspect this is not correct.

Of course, I am now assuming that you mean for a comparison of two different sized, same res sensors... which would validate my point. But I assume this is also not correct, and I do actually see your point now. :D
 
Woodsy said:
You are assuming that making the quantum wells smaller (with the same manufacturing techniques) still has the same failure rate as those made on larger sensors. I suspect this is not correct.

Of course, I am now assuming that you mean for a comparison of two different sized, same res sensors... which would validate my point. But I assume this is also not correct, and I do actually see your point now. :D
Click to expand...

I was simply demonstrating that you will get dramatically more good smaller cells from each slice than you would get larger cells. This is the reason for the smaller cells ie lower cost/more profit.

I have no problem with cropped sensor cameras I only have them at this time. Both formats have their advantages. We could just do a for and against thread and never have to broach the subject again!
 
I asked a very similar question last week I bought a nifty fifty for my D40 anyway after some advice from puddleduck.

joe
 
It's a shame it won't AF on your body...... or did you go for the G?
 
That's the problem, It's either the elcheapo DX 35mm or the 50mm G

Hmm.
 
Beagletorque said:
It's a shame it won't AF on your body...... or did you go for the G?
Click to expand...

Got the 50mm 1.8 AF, I'm still new to DSLR photography so I thought that a manual focus can only help improve technique, the focus indicator is a godsend though :clap:

joe
 
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