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promacjoe · 01-17-2015, 12:06 AM - **1 Like**

The only benefits you get from using a 645 lens on a K-3 or any 35mm camera, is flatness of field.

The focal length remains the same Regardless of what type lens you use. Only the image circle changes.

The usable portion of that image circle will be determined by the size of the film/sensor. Limiting your field of view.

Think of it like looking through a paper tube. a short paper tube, will give you one view. Double the length of the paper tube, And you will see less of the image. Magnification does not change only the field-of-view. However when printing, the relative image size will become apparent, and an increase magnification will be simulated. but only when printing on the same size paper. If you print them on paper relative to their sensor size, The subject would be the same size, but the larger sensor size will give you a larger field of view. you can achieve the same effect by cropping the larger sensor down to represent the aspect ratio of the smaller sensor. but you cannot go the other way.

It is a perceived magnification when printed on the same size paper.

mee · 01-17-2015, 09:40 AM

Ohh. My hangup was example 1 as I already understood example 2's concept.. but I think I understand now. The issue is the way I am looking at the chart and generally thinking about the concepts -- I only see data for Example 2 (different sensor size, same focal length[w/ lenses designed for different format) and not Example1 (same sensor size, same focal length [again w/ lenses designed for different format]) and I was attempting to understand 1 based mostly on the chart (as well as in general) and thought both examples were explained by the chart.

Thanks to everyone who took time to respond! A lot of information here.. the key is in focusing it into proper lanes and not mixing it together (as there are different concepts described)!

**DonV** · 06-09-2021, 10:19 AM

It is easier for me to just "know/remember" that the image size is the same for a given focal length; BUT the field of view varies- as is well illustrated in post # 9.

A part of the image is eliminated on the smaller sensor, but the objects in the image are the same size.

angerdan · 06-09-2021, 01:19 PM

Originally posted by mee

The chart on the webpage here explaining this shows different FoV's for those lenses.

This is the source:
The Crop Factor Unmasked - Articles and Tips | PentaxForums.com

Here i'd post other tables:
Best super telephoto prime or zoom - PentaxForums.com

Originally posted by angerdan

If someone needs to understand the angle of view of a larger image circle lens on a smaller diameter sensor, you can read this comprehension:
Crop Factor from a 645 to a K3 APS-C - PentaxForums.com

This table created and posted by Ole (founder of pentaxforums) shows the angle of view related to sensor size and focal length.
Field of View Tables, APS-C, 24x36, 645D, 645, 6x7 - PentaxForums.com

Originally posted by angerdan

Crop-Table by Ole:
Medium Format 6 x 7 on K20 Sensor - PentaxForums.com

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01-17-2015, 12:06 AM - 1 Like	#31
promacjoe Veteran Member Join Date: Jun 2014 Posts: 340	The only benefits you get from using a 645 lens on a K-3 or any 35mm camera, is flatness of field. The focal length remains the same Regardless of what type lens you use. Only the image circle changes. The usable portion of that image circle will be determined by the size of the film/sensor. Limiting your field of view. Think of it like looking through a paper tube. a short paper tube, will give you one view. Double the length of the paper tube, And you will see less of the image. Magnification does not change only the field-of-view. However when printing, the relative image size will become apparent, and an increase magnification will be simulated. but only when printing on the same size paper. If you print them on paper relative to their sensor size, The subject would be the same size, but the larger sensor size will give you a larger field of view. you can achieve the same effect by cropping the larger sensor down to represent the aspect ratio of the smaller sensor. but you cannot go the other way. It is a perceived magnification when printed on the same size paper.

01-17-2015, 09:40 AM	#32
mee Veteran Member Join Date: May 2010 Posts: 7,403	Ohh. My hangup was example 1 as I already understood example 2's concept.. but I think I understand now. The issue is the way I am looking at the chart and generally thinking about the concepts -- I only see data for Example 2 (different sensor size, same focal length[w/ lenses designed for different format) and not Example1 (same sensor size, same focal length [again w/ lenses designed for different format]) and I was attempting to understand 1 based mostly on the chart (as well as in general) and thought both examples were explained by the chart. Thanks to everyone who took time to respond! A lot of information here.. the key is in focusing it into proper lanes and not mixing it together (as there are different concepts described)!

06-09-2021, 10:19 AM	#33
DonV Site Supporter Join Date: Jan 2017 Location: Near Charlotte NC Photos: Albums Posts: 695	It is easier for me to just "know/remember" that the image size is the same for a given focal length; BUT the field of view varies- as is well illustrated in post # 9. A part of the image is eliminated on the smaller sensor, but the objects in the image are the same size.

06-09-2021, 01:19 PM	#34
angerdan Pentaxian Join Date: Feb 2015 Photos: Gallery \| Albums Posts: 2,643	Originally posted by mee The chart on the webpage here explaining this shows different FoV's for those lenses. This is the source: The Crop Factor Unmasked - Articles and Tips \| PentaxForums.com Here i'd post other tables: Best super telephoto prime or zoom - PentaxForums.com Originally posted by angerdan If someone needs to understand the angle of view of a larger image circle lens on a smaller diameter sensor, you can read this comprehension: Crop Factor from a 645 to a K3 APS-C - PentaxForums.com This table created and posted by Ole (founder of pentaxforums) shows the angle of view related to sensor size and focal length. Field of View Tables, APS-C, 24x36, 645D, 645, 6x7 - PentaxForums.com Originally posted by angerdan Crop-Table by Ole: Medium Format 6 x 7 on K20 Sensor - PentaxForums.com