How to measure magnification?


Status
Not open for further replies.

chooz

New Member
Aug 14, 2007
264
3
0
Singapore
#1
Hi All,

My lens has a magnification of 0.24x at maximum zoom (200mm). I added in a +2 close up filter. What is my magnification now?

Sorry if it sounded noob. I am really new to this end of the photography. Many thanks in advance.
 

sepia

New Member
Jan 4, 2009
67
0
0
Bedok
#2
Hi All,

My lens has a magnification of 0.24x at maximum zoom (200mm). I added in a +2 close up filter. What is my magnification now?

Sorry if it sounded noob. I am really new to this end of the photography. Many thanks in advance.
Not long ago, I was trying to figure out the magnifications of a set of extension tubes. This is the method I use.

I took a picture of a ruler taped to the wall, with the extension tube at minimum focusing distance...the ruler must fill the frame. The size of my sensor is 22.2 mm across (from camera manual). If it take 44.4 mm of the ruler to fill my frame, then the magnification must be 0.5 times, if it takes 22.2, then the magnification is 1.
 

chooz

New Member
Aug 14, 2007
264
3
0
Singapore
#5
I have done the measurement and calculation last night.

I am using a 200 mm lens on a Canon APS-C size sensor. The crop factor is 1.6, so this is equivalent to a 320 mm lens on a 35 mm film size.

APS-C sensor size = 14.9 x 22.3 mm
No close-up filter = 49 x 74 mm to fill up the image at min focusing distance
With +2 close-up filter = 38 x 58 mm to fill up the image at min focusing distance

Dividing the sensor size by the captured image:
Max magnification with no close-up filter = 0.31x (same as what is measured by dpreview)
Max magnification with +2 close-up filter = 0.38x

Dividing the image (with +2 filter) by the image (no close-up filter) = 1.3x


The common formula to measure magnification:
For a +2 close-up filter on the 320 mm lens = 320/(1000/2) = 0.64x

For a +2 close-up filter on the 200 mm lens (ignoring in the 1.6 crop factor)
= 200/(1000/2) = 0.4x (similar to what I measured at 0.38x)

So, my questions are:
1. Why is the magnification given by the formula (0.64x) different from what I measured (0.38x)?
2. Should I ignore the 1.6 crop factor when applying the formula (0.4x is close to what I measured)? Don’t think I should ignore the crop factor because the final effect on the sensor is equivalent to the 35 mm size.
3. Maybe my +2 close-up filter is not really +2, but only +1.25? :confused:
 

Harwin

New Member
Nov 5, 2009
1
0
0
#6
I want to start photography as a hobby but i have no idea where to start. Can someone please help me out here. I need to find out what kind of camera is suitable for starters and whether are there any workshops or tips i could get for starting up? Thanks everyone
 

sepia

New Member
Jan 4, 2009
67
0
0
Bedok
#7
I have done the measurement and calculation last night.

I am using a 200 mm lens on a Canon APS-C size sensor. The crop factor is 1.6, so this is equivalent to a 320 mm lens on a 35 mm film size.

APS-C sensor size = 14.9 x 22.3 mm
No close-up filter = 49 x 74 mm to fill up the image at min focusing distance
With +2 close-up filter = 38 x 58 mm to fill up the image at min focusing distance

Dividing the sensor size by the captured image:
Max magnification with no close-up filter = 0.31x (same as what is measured by dpreview)
Max magnification with +2 close-up filter = 0.38x

Dividing the image (with +2 filter) by the image (no close-up filter) = 1.3x


The common formula to measure magnification:
For a +2 close-up filter on the 320 mm lens = 320/(1000/2) = 0.64x

For a +2 close-up filter on the 200 mm lens (ignoring in the 1.6 crop factor)
= 200/(1000/2) = 0.4x (similar to what I measured at 0.38x)

So, my questions are:
1. Why is the magnification given by the formula (0.64x) different from what I measured (0.38x)?
2. Should I ignore the 1.6 crop factor when applying the formula (0.4x is close to what I measured)? Don’t think I should ignore the crop factor because the final effect on the sensor is equivalent to the 35 mm size.
3. Maybe my +2 close-up filter is not really +2, but only +1.25? :confused:


Hi. I am not an expert on this myself. Just wondering why you choose to applied the 1.6 multiplier on the lens but not the closeup filter. Shouldn't the crop sensor effect applied to both?
 

Rendell

New Member
Aug 2, 2009
569
0
0
Singapore
#8
What is the focusing distance? not 1000mm for both w filter and w/o filter right?

Correct me if I am wrong, the filter affects the focal distance and not the physical magnification of object.
 

Last edited:

chooz

New Member
Aug 14, 2007
264
3
0
Singapore
#9
Quote: "Hi. I am not an expert on this myself. Just wondering why you choose to applied the 1.6 multiplier on the lens but not the closeup filter. Shouldn't the crop sensor effect applied to both?"

yes, I applied the 1.6x crop factor in the calculation for the close-up filter. Just that in this case, the calculated results is closer to the real measurement if I don't include the 1.6 crop factor. Which I doubt is correct.

Quote: "Correct me if I am wrong, the filter affects the focal distance and not the physical magnification of object. "

The close-up filter reduce the minimum focusing distance and also magnify the subject. You can hold the filter and use it like a ordinary magnifying glass.

For this lens, my close-up filter only reduces the minimum focusing distance by 3 cm. Even at the same distance as without using a filter, the image is larger with the image.
 

ortega

Moderator
Staff member
Nov 2, 2004
23,694
10
38
Singapore, Singapore, Singapor
#10
does it matter?

to me only the resulting image matters
nice or not nice

so what if i have a 5:1 micro lens if i cannot take nice pictures with it
 

Shen siung

Senior Member
May 21, 2008
2,597
0
36
#11
does it matter?

to me only the resulting image matters
nice or not nice

so what if i have a 5:1 micro lens if i cannot take nice pictures with it
Partially agree with you.
IMO, it is like knowing what is hyperfocal distance, how to calculate it, how to apply it. If not knowing how, can still capture spectacular landscape; knowing how to calculate, it might not help in composition too. Vice versa.
 

chooz

New Member
Aug 14, 2007
264
3
0
Singapore
#12
I agree that it does not matter what the magnification is. However, I do not want to be short changed as well. I just want to make sure I have a +2 and not something less.
 

Rendell

New Member
Aug 2, 2009
569
0
0
Singapore
#13
I agree that it does not matter what the magnification is. However, I do not want to be short changed as well. I just want to make sure I have a +2 and not something less.
Honestly, I am confused.

The common formula to measure magnification:
For a +2 close-up filter on the 320 mm lens = 320/(1000/2) = 0.64x

For a +2 close-up filter on the 200 mm lens (ignoring in the 1.6 crop factor)
= 200/(1000/2) = 0.4x (similar to what I measured at 0.38x)
For different body, to get the same object, wouldn't your focusing distance (red) be different?
Eg. +2 close-up filter on the 320 mm lens = 320/(1000/2) = 0.64x
Eg. +2 close-up filter on the 200 mm lens = 200/(625/2) = 0.64x
Eg. +4 close-up filter on the 320 mm lens = 320/(1000/4) = 1.28x
Eg. +4 close-up filter on the 200 mm lens = 200/(625/4) = 1.28x

So +2 is the affecting the formula "blue" factor and not the final magnification 0.64x etc right?
 

Last edited:

chooz

New Member
Aug 14, 2007
264
3
0
Singapore
#16
By actual measurement, I get a 0.38x magnification.
By calculation using the formula given, I should get 0.64x.
So I am just wondering whether the filter is not really +2 or I made a mistake in my calculation.
 

sepia

New Member
Jan 4, 2009
67
0
0
Bedok
#17
yes, I applied the 1.6x crop factor in the calculation for the close-up filter. Just that in this case, the calculated results is closer to the real measurement if I don't include the 1.6 crop factor. Which I doubt is correct.
A 200mm lens mounted on a crop body has a equivalent of 1.6 x 200 i.e. 320mm on a full frame one.

A +2 filter is used on the same crop body, applying the same logic, shouldn't the formula became (1.6x1000)/2 i.e. 800mm?

So 320/800 gives 0.4 magnification.
 

Last edited:

Cutesperm

New Member
Apr 18, 2008
149
0
0
#18
Aiyo~ kid nows a day ah..
Just put on and shoot la. :sweat:
Y so many calculation. Theory is nice but practical is much useful in real life.
 

chooz

New Member
Aug 14, 2007
264
3
0
Singapore
#20
I am just asking a technical question which intrigue me.

Why degrade to name calling? Can answer, answer lah. Cannot answer, keep quiet lah.

To those with constructive suggestions above, my sincere appreciation.
 

Status
Not open for further replies.
Top Bottom