How do I do megapixel crop math?For example: If I have a 50mm prime, but I want to be able to crop in post to 75mm, a factor of 1.5 while retaining a resolution of say 20mp, all I'd need to do is multiply 20*(3/2) for a value of 30mp, since that is the ratio of 75mm/50mm, is that correct?I'm thinking about changing up the way I shoot and switching over from 2 zoom lenses, to 2 prime lenses and I want to make sure I can cover all of my usual focal lengths by crop in post. I am not entirely clear on how this effects compression. It seems like taking a 20mm and cropping to 40mm, you would still end up the compression aesthetic of the 20mm, but I've heard people say otherwise.
>>4379017Technically speaking you don't crop to a focal length, you crop to a field of view. You can look up online calculators to do the math for you.>all I'd need to do is multiply 20*(3/2) for a value of 30mp\Not entirely sure what you're on about here, as you can't crop something and retain/increase the MP count. You can upscale an image but that's a whole other thing and not a common one at that.>I'm thinking about changing up the way I shoot and switching over from 2 zoom lenses, to 2 prime lensesThis has the potential to make you a better photographer while delivering better IQ and wider apertures. But not if you're going to do what you planned to after it:>I can cover all of my usual focal lengths by crop in post.Do not do this. This is cropper's cope. You will never get any better if you rely on this. Not only will you defeat the point of using a prime, you'll be getting objectively worse quality out of your shots. Even if you upscaled everything flawlessly without artefacts (good luck), the tigher you crop the sharper your lens needs to be to keep up with the demands.>It seems like taking a 20mm and cropping to 40mm, you would still end up the compression aestheticWhere have you heard all these terms? It sounds like you've just come off a youtube spree. There's a half truth here:If you shoot a 20mm lens, no matter what you do in post, you will have the distortion and subject distance of a 20mm lens. You can't undo that. To understand what I mean, go look at some portraits taken at 100/85/50/35/28mm etc. You WILL see a big difference between 100mm and 28mm.[EXIF data available. Click here to show/hide.]Camera-Specific Properties:Equipment MakeCanonCamera ModelCanon EOS R50Camera SoftwaredigiKam-8.4.0Firmware VersionFirmware Version 1.1.0Image-Specific Properties:Image Width1400Image Height1400Image OrientationTop, Left-HandHorizontal Resolution350 dpiVertical Resolution350 dpiImage Created2024:09:23 01:28:00Exposure Time1/200 secF-Numberf/0.0Exposure ProgramManualISO Speed Rating100Lens Aperturef/infExposure Bias0 EVFlashNo FlashFocal Length0.00 mmImage Width1400Image Height1400RenderingNormalExposure ModeManualScene Capture TypeStandardExposure ModeManualFocus TypeAutoMetering ModeEvaluativeSharpnessUnknownSaturationHighContrastNormalShooting ModeManualImage SizeLargeFocus ModeManualDrive ModeSingleFlash ModeOffCompression SettingFineMacro ModeNormalWhite BalanceAutoExposure Compensation3Sensor ISO Speed160Color Matrix34
>>4379017Ask chatgpt. It will even do the math for you.
If you're cropping from ff to APS-C then to find your resultant resolution you need to divide your starting resolution by the crop factor squared, so 1.5x1.5 or 2.25. Thus to end up with a resolution of 20mp you'd need to start with 45.
