My bird shots are just horrible! I need some help!

[480sparky]

I got ya. But if I were using an FX camera what I see in the viewfinder would look, to my eye, like a little wider view? Or not?

I understand the DX format crops the image of an FX lens, so an uncropped TTL view would look look different?

The only difference between an FX lens and a DX lens is the size of the image projected. DX lenses are designed to cover the smaller crop sensors. But the subjects they project are the same.

Here's a 50mm DX lens on a full-frame camera:

Here's a 50mm FX lens:

Notice everything is the same size? That's because they're both taken with a 50mm lens.

A DX-format lens only needs to project an image large enough to cover the smaller sensor. An FX-format lens needs a larger 'circle' to cover the full 24x36mm sensor. This is because a DX-format sensor is physically smaller than an FX one.

What will change, if you put that 70-300 on an FX body, is your field of view. Not the focal length. The FOV will be wider.

 

[Mike D90]

The only difference between an FX lens and a DX lens is the size of the image projected. DX lenses are designed to cover the smaller crop sensors. But the subjects they project are the same.

What will change, if you put that 70-300 on an FX body, is your field of view. Not the focal length. The FOV will be wider.

Aha. I understand a little better now. So the view I see with a DX lens on my D90 is exactly what I see if I use an FX lens on my D90? Something made me think it would actually change the FOV on a DX sensor but I see that now that makes no sense. Appreciate you clearing that up for me.

 

[480sparky]

Aha. I understand a little better now. So the view I see with a DX lens on my D90 is exactly what I see if I use an FX lens on my D90? Something made me think it would actually change the FOV on a DX sensor but I see that now that makes no sense. Appreciate you clearing that up for me.

A given lens will have a narrower FOV when used on a crop (DX) sensor simply because the sensor is smaller and thereby crops the image in-camera as opposed to doing the same with a computer.

 

[dramtastic]

Read this Mike from today, especially the last post.
http://nikonites.com/general-lenses/18652-dx-lenses.html

 

[mikew_RIP]

That must have cheered you up Mike,great start with your new lens

 

[Mike D90]

Trying to get this in my head.

Ok, so I now understand there is no difference in the angle or focal length between FX and DX lenses. The difference is in the sensor size of the camera. I also understand the crop factor of the smaller sensor and this happens in-camera.

What I need to absolutely understand is what happens through the lens or through the viewfinder. Is the image I am seeing, inside the viewfinder, the same image that is going onto my sensor (other than the fact that the D90 is a 96% view not 100%) when I am using an FX lens?? I might could ask this another way. Is the mirror and viewfinder of my D90 the same representation of the image that is on my CCD?

So what makes a DX lens different? What does it do to the light or image that is coming through the glass and onto the sensor that makes it a DX lens? I have read about the smaller "circle" projected onto the sensor but I do not understand exactly why there is a DX lens at all.

If I want a 10mm wide angle image capture of a tall building from 1/2 mile away, taken with my D90 camera, to look exactly like a 10mm wide angle image capture, from an FX camera at the same distance to building, what does it take to capture that same angle and perspective? Obviously there is something different going on with the DX lens that allows that to happen.

 

[Marcel]

Trying to get this in my head.

Ok, so I now understand there is no difference in the angle or focal length between FX and DX lenses. The difference is in the sensor size of the camera. I also understand the crop factor of the smaller sensor and this happens in-camera.

What I need to absolutely understand is what happens through the lens or through the viewfinder. Is the image I am seeing, inside the viewfinder, the same image that is going onto my sensor (other than the fact that the D90 is a 96% view not 100%) when I am using an FX lens?? I might could ask this another way. Is the mirror and viewfinder of my D90 the same representation of the image that is on my CCD?

So what makes a DX lens different? What does it do to the light or image that is coming through the glass and onto the sensor that makes it a DX lens? I have read about the smaller "circle" projected onto the sensor but I do not understand exactly why there is a DX lens at all.

If I want a 10mm wide angle image capture of a tall building from 1/2 mile away, taken with my D90 camera, to look exactly like a 10mm wide angle image capture, from an FX camera at the same distance to building, what does it take to capture that same angle and perspective? Obviously there is something different going on with the DX lens that allows that to happen.

The only thing that makes a DX different is that if you try to use a DX lens on an FX camera, you will get black corners just like Sparky showed in post #121.

For your last question, to get the same field of view of a 10mm FX lens on DX, it would take you a (10/1.5)=6.6666mm lens. It's the 1.5 factor that applies to all FX/DX conversion for focal length.

​I hope this helps.

 

[Mike D90]

I still do not really understand this.

If both lenses are the same, with respect to actual focal length and angle, what is different about the DX lens build that changes what it does for either camera? What I think the DX lens does is it just reduces the size of the light path that hits the sensor. Basically it crops the image down to the DX sensor size.

If this is the case then it makes no sense as to why they did that. Is that even necessary? If the camera sensor crops the image then why would the lens need to do this?

If I am even close to understanding this at all it would seem to me that, if I wanted the exact same photo from both camera types, I would have to move the DX camera farther away from the subject to get the same image as the FX camera.

Since the DX sensor crops the photo then moving back would be the only way to get the same exact frame fill as the FX camera would get. The only other way I can understand to do it would be to use a lens with a shorter focal length on the DX camera. But this should change the perspective on the DX image.

 

[480sparky]

I still do not really understand this.

If both lenses are the same, with respect to actual focal length and angle, what is different about the DX lens build that changes what it does for either camera? What I think the DX lens does is it just reduces the size of the light path that hits the sensor. Basically it crops the image down to the DX sensor size.

If this is the case then it makes no sense as to why they did that. Is that even necessary? If the camera sensor crops the image then why would the lens need to do this?

If I am even close to understanding this at all it would seem to me that, if I wanted the exact same photo from both camera types, I would have to move the DX camera farther away from the subject to get the same image as the FX camera.

Since the DX sensor crops the photo then moving back would be the only way to get the same exact frame fill as the FX camera would get. The only other way I can understand to do it would be to use a lens with a shorter focal length on the DX camera. But this should change the perspective on the DX image.

The focal length of a given lens does not change. When designing a DX lens, however, it only needs to cover the smaller area of a DX-format sensor (usually 16x24mm). A 50mm FX lens would need to cover a much larger area, 24x36mm.

What will change, when using focal lengths that are the same, between the two formats is the resulting field of view.

The lens doesn't crop anything. All it does is pass the light that hits the front element on through to the back end for the sensor to 'see'. The lens is ignorant of whether it's on a DX or FX camera. It doesn't need to know anyway.

The cameras do, on the other hand, may need to know whether the lens is FX or DX, but only the FX bodies. This is because every Nikon FX body ever made has a DX-mode funtion to allow it to shoot with DX lenses. In this scenario, the FX body can either manually or automatically detect a DX lens and shoot in DX mode, or be set to shoot in DX mode even with an FX lens (sports & wildlife shooters do this quite often).

 

[Mike D90]

So the DX lens is definitely a different design? Seems like I did read somewhere that they can be made smaller in overall size and lighter. Just seems like a waste to me in a way.

 

[480sparky]

Let me try this angle:

The actual, physical size of the FX and DX sensors are different:

This is readily apparent if you look at an FX body next to a DX body, and can see the actual sensors when both are set to "Mirror Up for Cleaning":

So how does this translate into anything meaningful out in the 'real world'? Well, lets' pretend we're out there taking photos. And we come across this peaceful scene:

Now, an FX lens on an FX body has to project a large enough image to cover the larger FX sensor, so it will project an image into the camera that looks like this:

(Yeah, I know.... it's right-side-up. In reality, the image would be upside-down, but let's ignore that for the purpose here.)

The lens needs to create a large enough image to cover a sensor measuring 24x36mm (represented by the white rectangle):

So an FX lens/body will record the final image as:

Now let's take the same focal length lens, but only it's a DX-format lens. It will project a smaller circle:

Because it only needs to cover a sensor that measures 18x24mm:

So the same focal length lens, on a DX body, will record a final image as this:

Now, if we put the two final images (FX and DX) side by side, we end up with this:

Notice how the subjects in both images are exactly the same size? It's just that the DX sensor recorded a smaller portion of the scene because the sensor is physically smaller! This results in a narrower field of view.

So if you compare the sensor size:

with the above two images, you should be able to understand the 'crop sensor' effect on field of view.

 

[Mike D90]

Let me try this angle:

The actual, physical size of the FX and DX sensors are different:

I sure appreciate you taking time to try to help me understand.

I am not having an issue understanding sensor size. I do definitely understand that. I also understand the the lenses focal lengths are the same between the lenses.

I also understand the image that is projected onto the sensor is cropped by the smaller sensor due to it physically being smaller.

What I cannot understand is why the need for a DX lens? If the sensor is going to crop an image then it wouldn't matter what size image circle is projected onto it. You have shown that in your images and explanations.

A DX lens projects a smaller image circle onto the DX sensor, but that image is no different in ratio than the FX lens. It is simply cropped to the size of the DX sensor. So my misunderstanding is in building the DX lens to begin with.

It makes no difference to the DX sensor which lens it gets its image from. It crops either one to the same size.

So unless it is simply to cut the overall size of the lens and its weight down I see no need for a DX lens.

 

[Mike D90]

Another and probably last shot of the Titmouse. I am going other places to look for birds.

 

[480sparky]

........What I cannot understand is why the need for a DX lens?. .........

The presence of DX sensors.

If the sensor is smaller, the lens can be made smaller. Lighter. And cheaper.

When digital first hit the market, sensers were very small. The first DSLRs were crop sensors simply due to the expense of the technology prevented making affordable full-frame sensors.

 

[Mike D90]

The presence of DX sensors.

If the sensor is smaller, the lens can be made smaller. Lighter. And cheaper.

When digital first hit the market, sensers were very small. The first DSLRs were crop sensors simply due to the expense of the technology prevented making affordable full-frame sensors.

So that is the real reason. Smaller lenses and I guess less cost to produce as you said.

 

[Bill16]

Why it was done was to cut costs and increase profits. Why it is still being done, cut costs, so a cheaper line DSLRs will appeal to the average Joe, and to require photographers to buy a whole new set of lenses when the switch to a full frame DSLR. Companies are glad to sell a cheaper smaller set of lenses for the DX line, even though the fx lenses work fine on the DX line of DSLRs. Why because it helps sell lenses. An average Joe will buy several lenses at a cheaper price, and only a couple if the price were at FX prices. And without thinking about it, the average Joe is paying more this way in total lens cost. Then if that average Joe decides to move on up to FX DSLRs he has to buy all new lenses, and the companies make even more money.

So I buy mostly FX lenses, and they will work fine on the DX and the FX DSLRs. Sure I lose AF on DX cameras that don't have the AF motor in camera. But it works even if it's less convienent, and work great on DX cameras like the D90 that have the AF motor.

But in the end, it's all about money, and increasing profits. Selling a Nikon camera to every person they can,making the cameras to appeal to every walk of life, and keeping the people buying all the cameras and extras they can.

 

[dramtastic]

Interesting then that Sigma produced a pro quality lens for DX bodies, the 18-35 1.8mm. Sure they can be used on FX Nikon bodies in crop mode, but it was specifically designed for DX. Not only that, it is the fastest zoom lens currently available and is considered a ground breaking product. This lens has one of the highest overall scores on DoXmark(even higher than their well regarded 35mm 1.4 Art) and has almost universally received rave reviews from both Pro blogger's and hobbyists alike.

 

[Mike D90]

Interesting then that Sigma produced a pro quality lens for DX bodies, the 18-35 1.8mm. Sure they can be used on FX Nikon bodies in crop mode, but it was specifically designed for DX. Not only that, it is the fastest zoom lens currently available and is considered a ground breaking product. This lens has one of the highest overall scores on DoXmark(even higher than their well regarded 35mm 1.4 Art) and has almost universally received rave reviews from both Pro blogger's and hobbyists alike.

Whats the retail price on that thing? 18-35mm is the focal length I am looking at right now for my next lens.

 

[Bill16]

I assume this was directed to me? But I didn't say anything about quality or lack of quality in either DX or FX lenses, just that it cost less to make the lens for DX than it does to make the same lens for FX.
Having two types of lenses allows the companies to make more profit is all. There can be awesome lenses in both DX and FX types. I'm thankful that they do have DX DSLRs myself, or I may never have gotten a chance to own a DSLR long enough to realize how great DSLR cameras are. Because I never would have been able to blow about 2k on a camera that I didn't even know if I liked that type of camera. Lol But now that I do know I love Nikon DSLR cameras, I may one day own a Nikon FX DSLR ! Lol

Interesting then that Sigma produced a pro quality lens for DX bodies, the 18-35 1.8mm. Sure they can be used on FX Nikon bodies in crop mode, but it was specifically designed for DX. Not only that, it is the fastest zoom lens currently available and is considered a ground breaking product. This lens has one of the highest overall scores on DoXmark(even higher than their well regarded 35mm 1.4 Art) and has almost universally received rave reviews from both Pro blogger's and hobbyists alike.

 

[dramtastic]

I didn't say you wrote anything about a lack of quality. All I was saying was that Sigma has put a lot of time in money on a pro lens specifically for a DX body. A ground breaking lens at that. I find that interesting and would be keen to understand why they went with that strategy.