Mega pixels vs film.

Grandpa Ron · Feb 21, 2019

I understand that the area of light sensor on a digital camera is not the same size as the surface area of the 35 mm film plane. Hence the need for various conversion factors for lenses etc. but two question still remain unclear.

1. How many Mega pixels does it take to equal the resolution of my old 35 mm Pentax K-1000 with its 50mm lens. That is to say image sharpness before cropping.

2. My camera is rated for 18 mega pixels, yet on a walk through the wood recently, my photos were between 5 and 10 megapixels. Even the same scene shot from the same position with more or less foreground or sky had up to 2 megapixels difference. Why do the number of pixel vary and won't it make a difference in my ability to crop?

Ysarex · Feb 21, 2019

Grandpa Ron said:
I understand that the area of light sensor on a digital camera is not the same size as the surface area of the 35 mm film plane. Hence the need for various conversion factors for lenses etc. but two question still remain unclear.

1. How many Mega pixels does it take to equal the resolution of my old 35 mm Pentax K-1000 with its 50mm lens. That is to say image sharpness before cropping.

2. My camera is rated for 18 mega pixels, yet on a walk through the wood recently, my photos were between 5 and 10 megapixels. Even the same scene shot from the same position with more or less foreground or sky had up to 2 megapixels difference. Why do the number of pixel vary and won't it make a difference in my ability to crop?

1. A Nikon Coolscan for years scanned 35mm film at a max resolution of 4000 PPI. The last model ran that up to 5000 PPI which was obviously overkill. The rule of thumb that we used was that you didn't want to scan much below 2400 PPI which was enough to capture all the film had to offer. Let's assume you're using very fine grain high-resolution film and go with the Coolscan original max of 4000 PPI. At that point you're scanning the grain in the film and that's 4000 X 2750 pixels = 11 megapixels. Fair to say then that resolution from a 35mm film camera using typical films is in the range of 10-12 megapixels.

2. The JPEGs that come from your 18mp camera are compressed. The JPEG file specification is a compression format designed to save space especially for transmission. Your 18mp camera probably saves files that are 5184 x 3456 pixels = 17915904 pixels. For storage without compression that would require 52 megabytes -- too big especially if you want a bunch of them on an SD card and copied to your phone and then later put on the Internet. JPEG compression then to the rescue and your files get shrunk. The compression basically reduces the data density of your image allowing for redundancy compression.

Joe

480sparky · Feb 21, 2019

Grandpa Ron said:
1. How many Mega pixels does it take to equal the resolution of my old 35 mm Pentax K-1000 with its 50mm lens. That is to say image sharpness before cropping.

Depends on the film and lens used.

Grandpa Ron said:
2. My camera is rated for 18 mega pixels, yet on a walk through the wood recently, my photos were between 5 and 10 megapixels. Even the same scene shot from the same position with more or less foreground or sky had up to 2 megapixels difference. Why do the number of pixel vary and won't it make a difference in my ability to crop?

I think you're confusing megapixels (total sum of pixels in an image) with megabytes (file size).

Dave442 · Feb 21, 2019

I felt that my D200 (10mp) was the point where I was better with digital over a 35mm film camera.

Grandpa Ron · Feb 21, 2019

Sparky, you are correct I was mixing mega-pixel with mega-bytes. The jpg compression answers the rest.

Thanks folks

ClickAddict · Feb 22, 2019

Just a note. As you are shooting JPG, if you switch to shooting RAW your 18MP camera should yield file sizes in the 22-25MB range or something like that as there is more data retained. The debate on JPG vs RAW is often a matter of your workflow needs and there are many posts about it already if you do a quick search.