Zoom function in ACR or Elements Editor

[popcorn]

When I download an image from my Nikon D500 into Elements, the Zoom level is indicated as being 25%

25% of what?

Using my 200..50omm Nikon Zoom at maximum extension, I often take photographs of birds for identification purposes.  
I can't get enough detail through my binoculars.
When cropped to nearly fill the frame, the Zoom level on the cropped image is indicated as being 200%. 

Since the actual focal length equivalent on my D500 is 1,5 times, this is equivalent to a 750mm lens on a full frame camera.
Now since the zoom level on the cropped image is 8 times higher then the full sensor image, is the cropped image equivalent to a having used a 6000mm lens on my Camera. ( a 4000mm full frame lens )?
Is this correct?

The cropped image area is 1/64th of the area of the area of the uncropped image on my screen. 

These are nearly always taken with the camera hand held using shutter speeds in the region 1/500th of a sec and ISO 1600, and the results are good enough to get a reasonable image with enough detail to identify the bird.
I find this astonishing and feel that my math must be faulty.
  

[pontiac1940]

You might be overthinking the interaction of the sensor size and lens specs. 

Not sure if this will help. Just BTW, this was shot with a 600-mm lens on a full frame, 24-MP Sony A7III. 
 
When the crossbill photo is opened it shows at 17%. Because the actual photo is 6,000 pixels wide (and my monitor is 1920 pixels wide) PSE reduces the magnification so all can be seen so it can (say) be cropped to my liking. The top image is reduced in magnification for easy viewing of the whole photo. I cropped this photo for presentation online...see below.   
Click for full view 


By using <ctrl><+> or using <ctrl> and scroll  the image is made larger and larger. As shown below this is all that can be seen of the bird at 100% magnification. You can navigate around the photo using either "Navigator" window (From top menu: Window>>Navigator) or the little "hand" that is in the top of the tool bar on the right of the PSE window. For most PSE functions viewing at 100% is not useful. (For example, 100% might be useful for precise cloning.)   

<ctrl><+> and <ctrl><-> will increase and reduce magnification. If you crop and the result is (say) 1,500 pixels wide, and the resulting image is displayed at 200% it is still 1500 pixels wide..it is just magnified on screen. Hit <ctrl><-> to reduce magnification to 100%. 

The image below is still 6,000 pixels wide but you are merely seeing it at different magnification. (Click on these images to see full view.) 
Click for full view



While in about 17% view the photo was cropped. 

[popcorn]

Thanks pontiac,

Your explanation made the Zoom function clearer, I was however totally at a loss as to why the full image appeared in ACR as being at 25% zoom.
After reading your explanation and applying it to my gear, I did the math and came up with this:

FLATRON IPS235 LED SCREEN

Screen dimensions

20” x 11.25” 1600 x 900 pixels 80 ppi



NIKON D500

Camera sensor

0,925” x 0,618”’ ( 23,5mm x 15,7mm ) 5568 x 3712 pixels 6000 ppi



to accommodate the sensor image of 5568 pixels at the screen resolution of 80 ppi, the screen would have to be:



5568 pixels / 80 ppi = 69,7” wide and

3712 pixels / 80 ppi = 46,4” high



The image has to be reduced in size to fit on the screen:



The width from 69,7’’ to 20’’ which is 28,7% of its width

The height from 46,4’’ to 11,25’ 24,3% of its height



To display all of the picture, the image Has to be reduced to 25% of dimensional size.

My conclusion that by cropping to 200% I was obtaining an image equivalent to having used a 4000mm Tele Lens was incorrect.

Since by cropping I am reducing the number of pixels available, this is equivalent to using a very low resolution camera to get the same field of view as the cropped image, but from close enough to fill the frame.
A 4000mm lens, producing an image with the same field of view as the cropped image, would be using all the pixels available on the whole sensor to give a better image. 

Is this correct?

[pontiac1940]

Feb 23, 2021 12:37:12 GMT popcorn said:

Since by cropping I am reducing the number of pixels available, this is equivalent to using a very low resolution camera to get the same field of view as the cropped image, but from close enough to fill the frame.
A 4000mm lens, producing an image with the same field of view as the cropped image, would be using all the pixels available on the whole sensor to give a better image. 

Is this correct?

Not sure I understand ... my post might not clarify anything. 

"by cropping I am reducing the number of pixels available..." Yes, absolutely. If your original is 5568 by 3712 pixels and it is cropped so it is now (say) 1500 by 1500 pixels, then you lose ~90% of the pixels (from 20 MP to 2.2 MP) ...see graphic below.    

"this is equivalent to using a very low resolution camera to get the same field of view" ... yes, sort of, although a lower rez cam might or might not have the same sensor quality and probably not the same lens quality. Small sensors are notoriously noisy at high ISOs. I'd take a cropped image from a large sensor and high-end lens any day.   

"A 4000mm lens, producing an image with the same field of view as the cropped image, would be using all the pixels available on the whole sensor (yes) to give a better image. " Yes, but it is a moot point since 4,000 mm lenses don't exist for your 20MP camera .. it would have to be of incredible glass quality (and cost $50,000 )  Nikon Coolpix P1000 has a 3,000 mm lens but also has very small sensor, being a mere 6.2 by 4.2 mm. I've seen okay images off the Nikon P1000, but they lack outstanding image quality for large prints. They are also noisier under low light and high ISO...the sensor is so small. 

You use your gear for birding and bird IDs. (Excellent past time!) If you are not happy with image quality of your cropped images for your intended use, you might consider a more powerful lens and/or a camera with more pixels and full frame (vs APS-C sensor on the Nikon D500) so cropped images are better quality. 

Good luck! 

Clive 

This might be confusing ... probably nothing new for you. 

[popcorn]

My use of a 4000mm lens was hypothetical. I cant' afford a 600mm f=2,8.
That part of my post was really to express my wonder at how much clarity, maybe not detail, that I am able to get hand holding a 750mm lens at about 200m.
There is just about no camera shake, amazing stabilization.

[pontiac1940]

Thanks popcorn

I cant' afford a 600mm f=2,8. 
Agree!! The Sony f4 600 is $13,000 USD! Nope.   I am happy shooting a slower lens and using higher ISO with the full frame. 

That part of my post was really to express my wonder at how much clarity, maybe not detail, that I am able to get hand holding a 750mm lens at about 200m.

There is just about no camera shake, amazing stabilization.

Yes, image quality these days is amazing. We are very lucky today!! Image quality. Flexibility of digitals. Ability to edit. All good. I can't imagine being retired and having to buy slide film at $0.35 per image. HA! Some days I take 200 or 300 photos! 

Clive

 

[Chris]

Popcorn, I think what that is referring to is the relative zoom size of your image in the PS Elements window. It has nothing to do with the Zoom of your camera sensor or lens. For example, if your image is 6000 x 4000 pixels and your monitor has a resolution of 1920x1080 you need to shrink the image to about 20% to see the whole image on your screen. If you go to View/Actual pixels that will display part of your image as 100% actual size.

In Edit/Preferences/General I have checked to Zoom with scroll wheel which I find practical to zoom in and out when editing photos.

Kind regards
Chris

PS regarding the other point about using a lens on a crop frame sensor, photographers often factor in the equivalent zoom compared to a full frame sensor.  For example, using a 300mm lens on a 1.5 crop sensor will be "like" using a 300x1.5 = 450 mm on a full frame sensor body. However this calculation is only for convenience. Strictly speaking, the analogy has its limitations. There are some differences. A 300mm lens has greater depth of field than a 450mm lens. So using a 300mm lens on a crop frame body will give you the greater depth of field of a 300mm lens and not the narrower depth of field of a 450mm lens. A 450mm lens on a full frame body would throw the background more out of focus. If you used a 300mm lens on a full frame body and cropped it, then that is really what you are seeing when you use a crop frame sensor. 

[popcorn]

Hi Chris,
Thanks, I think that what you are saying re the Zoom factor is exactly what I calculated in my post yesterday, comparing the pixels in my sensor to the pixels on the monitor screen.
I have also always viewed my DX sensor as being a cropped FX. This is also not strictly true, it also depends on the relative pixel size of the two sensors.
I would have thought that you would need a 30Mp FX sensor to get the same resolution on the cropped image as that on an image with the same field of view obtained with a 20Mp DX sensor?
I am not too sure of my facts, but I would infer from this, that if you are going to use large focal lengths, it would be better to use a DX camera with say a 500mm lens rather than an FX with a 750mm lens?
But this is for another forum.