Cropping and zoom/reach (1 Viewer)

I'm sure someone with a Physics degree will correct the flaws in my theory below, and tell me I've got it all wrong, but...

I'm trying to decide what lens (reach) I need on my DSLR(T) to compare to the 600mm + 1.7 TC of my bridge camera. Obviously there's other factors, like pixels on the subject and sensor size, but I'm pretty sure I've sorted it out, but it's early and I don't trust my brain yet.

A full resolution (20.1mp) image from my camera is 5456*3632 - if I take a 50% crop 2728*1816 from this image, it's the equivalent of zooming in 2X the 450mm. So if the image was taken at 450mm, the 50% crop would be equivalent to 900mm reach (close to the 600*1.7 from the bridge camera, and with a larger sensor). Have I got this right? As it seems too easy.

(Many cameras use this cropping method to increase reach (decrease field of view), they call it different things, but the method is the same)

That's about the summary of it. The bridge camera's 600mm equivalent reach is based on the very large crop factor applied due to the small sensor - the actual lens is probably something like a 6mm to 100mm or so. Adding the 1.7x teleextender pushes you to roughly 1,000mm equivalent.

On your DSLT, if you're shooting with a 300mm lens, you're getting an equivalent of 450mm due tot he 1.5x crop factor...so to get more, you have to crop that original photo roughly in half to double the equivalent focal reach.

However, you'd truly be better off if you can handle the weight getting a better, longer optical reach lens. The more pixels you can put on the target, especially with a nice, big APS-C sensor, the better - so if you can handle the long, heavy lens, putting something like a 400mm lens, or even 600mm lens on your camera would give you 600mm or 900mm equivalent reach without cropping - all 20MP would be available, so once you crop further, you end up with a much larger overall resolution photo, with nice big pixels on the target, cropped only slightly to match the reach equivalence you get from the bridge camera. And of course can crop even more if need be - generally the quality of the DSLR sensor together with a decent lens will yield far sharper, richer detail that can withstand much more cropping than a bridge camera's output - along with of course the greater high ISO ability, faster focusing capability, and so on.

I moved from a bridge to DSLRs years ago...and right from the outset, I had been spoiled with the equivalent 900mm reach from the bridge camera and extender - so I picked up a Tamron 200-500mm lens to go with my first DSLR - that gave me 750mm of reach, on a nice large APS-C sensor. As I moved up the DSLR chain, and got better sensors with more megapixels, I also upgraded the lens to a Tamron 150-600mm for even more optical reach. With my 16MP APS-C DSLR, I can get 900mm equivalent and it really makes the difference.

Thanks for replying, Justin.

Due to health issues, I can't carry much weight; well I can, but not for long, and it would mess me up for days. With a bit of experimenting, I worked out that I can manage a lens of about 500g for the hour I go to my local reservoirs, and after some research, I ended up with the Sigma 70-300mm F4-5.6 DG APO Macro.

I know it's only a cheap lens, but I'm actually quite pleased with it; the CA seems well controlled, and it seems sharp wide open throughout the zoom range (I wouldn't notice any corner softness with my APS-C sensor... might do with full frame though). If I get the light I'll see if stopping down gives me even sharper images, but up to now, I'm happy enough with the lens considering the low price.

I'll probably have to shoot 5mp images at 900mm for distant subjects, using the in-camera sensor cropping, or cropping from the 20mp image; it's not ideal, but I think it'll be fine for web images, and I'll mostly be using the 450mm at 20mp, as birds/mammals get quite close if you keep still and wait.

I can understand that. I am OK with carrying heavy weights physically/health-wise, but there are times I just don't want to - especially down here in Florida during the summers - temps will run right near 35-36 C and humidity over 80% most of the day...with chance of intermittent rain and lots of bugs in the wetlands, so the prospect of taking a 5 or 6 mile walk carrying 8-10Lbs of gear while covered in sweat and bugs just doesn't appeal. My DSLR and big lenses therefore tend to be fall through spring kit, and in summer I switch almost exclusively to my mirrorless camera and lens kit, which is as much as 4x lighter. I don't have the ultimate reach, but carrying 920 G total including camera, lens, and converter is so much more pleasant than toting 3,800 G plus! And the mirrorless cam with lens and teleconverter can be comfortably carried one-handed, yet still gives me an APS-C sensor with 24MP to put on target, with a 535mm equivalent reach...that leaves enough room for cropping and still get reasonably large prints from.

Then again, I do live in Florida - one of the few places on earth where you can go birding and shoot closeups of wild birds with a 35mm prime lens:
http://www.pbase.com/zackiedawg/image/140562657/original

Zackiedawg said:

I can understand that. I am OK with carrying heavy weights physically/health-wise, but there are times I just don't want to - especially down here in Florida during the summers - temps will run right near 35-36 C and humidity over 80% most of the day...with chance of intermittent rain and lots of bugs in the wetlands, so the prospect of taking a 5 or 6 mile walk carrying 8-10Lbs of gear while covered in sweat and bugs just doesn't appeal. My DSLR and big lenses therefore tend to be fall through spring kit, and in summer I switch almost exclusively to my mirrorless camera and lens kit, which is as much as 4x lighter. I don't have the ultimate reach, but carrying 920 G total including camera, lens, and converter is so much more pleasant than toting 3,800 G plus! And the mirrorless cam with lens and teleconverter can be comfortably carried one-handed, yet still gives me an APS-C sensor with 24MP to put on target, with a 535mm equivalent reach...that leaves enough room for cropping and still get reasonably large prints from.

Then again, I do live in Florida - one of the few places on earth where you can go birding and shoot closeups of wild birds with a 35mm prime lens:
http://www.pbase.com/zackiedawg/image/140562657/original

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That Cormorant looks like it poses for a living

I wouldn't mind some of that Florida light over here; the light is pretty bad at this time of year, but I still take pictures. There's often things happening in my garden that I want a reminder of in years to come, so my camera gets used whatever the light

Zackiedawg said:

And the mirrorless cam with lens and teleconverter can be comfortably carried one-handed, yet still gives me an APS-C sensor with 24MP to put on target, with a 535mm equivalent reach...that leaves enough room for cropping and still get reasonably large prints from.
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What mirrorless camera and lens are you using? I have the Oly EM5 with the panni 100-300 and have been told not to waste your money on a tele-converter. It just would not work very well on the 100-300 lens.

I'm shooting with a Sony A6000 and a 55-210mm lens. The teleextender I'm using is the Sony DH1758 1.7x, with 58mm threading. It's not going to match the overall IQ of a dedicated high-quality 500mm lens on a full frame, but it doesn't lose much compared to the native mirrorless lens you're using, while greatly extending the reach. I don't expect it to match my DSLR, but to give me a decent reach and about the same quality as I can get from the 55-210mm alone, and that it does. As far as teleextenders go, there seem to be 3 considered the better ones to look for: Sony DH1758, Olympus T-Con (B300), and Nikon E17ED.

ChrisKten, I presume what you are looking for is a way to calculate the plate scale of a particular camera lens combination. Basically to calculate the number of pixels which the camera sensor – lens combination will place on a particular target. A compressive explanation can be found at:

http://www.clarkvision.com/articles/cropfactor/index.html

Using the moon as a reference target, I can calculate that the Canon SX50 puts 1218 pixels on the moon's diameter. My Nikon D7100 will need 545mm of lens to accomplish the same. The Canon SX50 has a pixel pitch of 1.54 microns, and the Nikon D7100 has a pixel pitch of 3.90 microns.

The Canon 70D, with a pixel pitch of 4.10, would need 572mm of lens to match the magnification of the Canon SX50.

That aside, as the pixel pitch gets smaller and magnification factor goes up, the problem of diffraction becomes apparent at smaller apertures. The DSLR may be capable of producing acceptable images at f/16 however the bridge camera's 1/2.3” sensor becomes diffraction limited at f/5.6. So it's all in the trade offs you want to make.

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

BChiker said:

ChrisKten, I presume what you are looking for is a way to calculate the plate scale of a particular camera lens combination. Basically to calculate the number of pixels which the camera sensor – lens combination will place on a particular target. A compressive explanation can be found at:

http://www.clarkvision.com/articles/cropfactor/index.html

Using the moon as a reference target, I can calculate that the Canon SX50 puts 1218 pixels on the moon's diameter. My Nikon D7100 will need 545mm of lens to accomplish the same. The Canon SX50 has a pixel pitch of 1.54 microns, and the Nikon D7100 has a pixel pitch of 3.90 microns.

The Canon 70D, with a pixel pitch of 4.10, would need 572mm of lens to match the magnification of the Canon SX50.

That aside, as the pixel pitch gets smaller and magnification factor goes up, the problem of diffraction becomes apparent at smaller apertures. The DSLR may be capable of producing acceptable images at f/16 however the bridge camera's 1/2.3” sensor becomes diffraction limited at f/5.6. So it's all in the trade offs you want to make.

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

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Thanks for that; I'll read and digest it later

ChrisKten said:

A full resolution (20.1mp) image from my camera is 5456*3632 - if I take a 50% crop 2728*1816 from this image,.......

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This is not a 50% crop as you loose 75% of the pixels in your cropping (19.816.192 vs 4.954.048). You may want to check your logical conclusions again to see if this error changes the outcome for you.