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01-20-2011, 12:22 PM   #1
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how to calculate the Raynox magnification rate?

I have in my hand

1) my kit lens, does 1:3 macro @ 55mm
2) my 70-210 does 1:4 macro @ 210
3) my 100mm macro does 1:2 macro.


I'm thinking of adding either the raynox 150 or 250, not sure which one yet... I want to find out the calculation for the magnification of the raynox on my lens before i figure out which one to get.

01-20-2011, 12:58 PM   #2
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While I can't answer your question. I can say that I have the 250, but I don't use it very often because I feel like it's overkill. Wish I had a 150. Just posted a shot with it last night if you're interested, over in the PP forum.
01-20-2011, 01:16 PM   #3
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With primary lens focused at infinity:
mag.closeup.lens = focal.length.primary.lens/focal.length.closeup.lens

With primary lens extended:
mag.total = (1+mag.primary.lens.extended)(1+mag.closeup.lens) - 1

Focal.length.Raynox.150 = 208 mm
Focal.length.Raynox.250 = 125 mm

for the 55mm lens:
55/208 <= mag.total <= (1.33)(1+55/208)-1 or 0.26 <= mag.total <= 0.68
55/125 <= mag.total <= (1.33)(1+55/125)-1 or 0.44 <= mag.total <= 0.92

Etc.

Dave

Last edited by newarts; 01-21-2011 at 08:40 AM. Reason: I changed a variable name for generality
01-20-2011, 01:22 PM   #4
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The 70-210 1:4 with raynox covers a big range. For the DCR 150:
Minimum = 70/208 ~ .33x
Max = (1.25)(1+210/208) -1 ~ 1.5x

Dave

01-20-2011, 01:53 PM   #5
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QuoteOriginally posted by clockwork247 Quote
I'm thinking of adding either the raynox 150 or 250, not sure which one yet... I want to find out the calculation for the magnification of the raynox on my lens before i figure out which one to get.
Those Raynox lenses are generally best with telephoto lenses. Your 70-210 will give approx. 1:1 (*) with the Raynox 150 and 1.7:1 (*) using the Raynox 250. The 250 gives greater magnification but that also means it's more difficult to get things in good focus.

What do you intend to photograph? Do you plan to try handheld or commit to a tripod?

I use the DA L 55-300 zoom and Raynox 150. Take a look in my album here to see an example of how large that makes a dime. Those are full photos, adjusted to meet filesize requirements but not cropped. If you require more magnification try the 250, otherwise go with the 150.

(*) UPDATE: I see newarts' calculations give different results than what I expected. I know I get 1.4:1 using my 55-300 with the DCR-150 because I measured, which matches the results of 300mm/208mm=1.44. When I have more time I'll look things over more carefully to see if I'm missing something.

Last edited by DeadJohn; 01-20-2011 at 02:04 PM.
01-20-2011, 03:09 PM   #6
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QuoteOriginally posted by DeadJohn Quote
(*) UPDATE: I see newarts' calculations give different results than what I expected. I know I get 1.4:1 using my 55-300 with the DCR-150 because I measured, which matches the results of 300mm/208mm=1.44. When I have more time I'll look things over more carefully to see if I'm missing something.
You'll get more magnification if you crank the zoom lens focus all the way out...that's the first term in the equation I posted earlier.
Mag.total = (1+original.lens.mag)(1+lens.focal.length/closeup.focal.length) - 1

Dave
01-20-2011, 03:57 PM   #7
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Hmm, cranking the zoom all the way out instead of focusing to infinity will also stop focus creep with the lens pointed down.

I assumed the maximum for my combo was 1.4 using the simple 300/208 calculation. By your formula I get (1+0.28)*(1+300/208)-1 = (1.28 * 2.44) - 1 = 2.12x magnification.

That's a 50% increase. I'll need to test that sometime soon. Thanks.

(I know I read the DCR-150 directions. Are they poorly translated or did I just fail to understand? Another thing to check...)
01-20-2011, 05:49 PM - 1 Like   #8
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QuoteOriginally posted by DeadJohn Quote
Hmm, cranking the zoom all the way out instead of focusing to infinity will also stop focus creep with the lens pointed down.

I assumed the maximum for my combo was 1.4 using the simple 300/208 calculation. By your formula I get (1+0.28)*(1+300/208)-1 = (1.28 * 2.44) - 1 = 2.12x magnification.

That's a 50% increase. I'll need to test that sometime soon. Thanks.

(I know I read the DCR-150 directions. Are they poorly translated or did I just fail to understand? Another thing to check...)
Don't be surprised if the magnification doesn't agree precisely with the equations. There are two main reasons to expect a difference:
1) The 300mm lens may not actually be 300mm & may also change focal length as you turn the focusing ring (ie. have internal focusing elements)
2) The equation I gave didn't take the distance* between the primary lens and the closeup lens. A better equation is:

Close.up.magnification = (Primary.lens.focal.length - distance.between.lenses)/closeup.lens.focal.length

Dave

*"distance" means you have to know the primary lens' actual optical location ("front principal plane") which doesn't necessarily coincide with the outer glass surface.


Last edited by newarts; 01-21-2011 at 04:02 AM.
01-20-2011, 07:48 PM   #9
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I tested with my 55-300 focus ring at maximum barrel extension rather than at infinity and, sure enough, I get even more magnification now. Thanks for that tip.

The directions are ambiguous regarding the best focus setting. One sentence suggests infinity and another suggests minimum focus distance, with no clear mention how it affects magnification.

The extra magnification I'm getting with the proper settings confirms I made the right choice with Raynox 150. The 250's extra magnification would become too tough to focus.

EDIT: I took a ruler photo and it looks like I get just over 2x magnification, closely aligning with the formula newarts provided above that gave 2.12x.

Last edited by DeadJohn; 01-20-2011 at 08:08 PM.
01-20-2011, 07:55 PM   #10
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QuoteOriginally posted by DeadJohn Quote
I tested with my 55-300 focus ring at maximum barrel extension rather than at infinity and, sure enough, I get even more magnification now. Thanks for that tip.

The directions are ambiguous regarding the best focus setting. One sentence suggests infinity and another suggests minimum focus distance, with no clear mention how it affects magnification.

The extra magnification I'm getting with the proper settings confirms I made the right choice with Raynox 150. The 250's extra magnification would become too tough to focus.

i'm probably getting the 150 then... i think it'll be enough for me.
01-21-2011, 04:18 AM   #11
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QuoteOriginally posted by clockwork247 Quote
i'm probably getting the 150 then... i think it'll be enough for me.
The DCR 150 is a good choice for the DA(L) 55-300 as you'll have adequate working distance (about 8"), at least up to 1:1 mag*.

Another important feature is the on-board camera flash will continue to work automatically, at least out to about 1:1 magnification. I think the lens gets in the way of the flash when the magnification goes much above 1:1 but that can be corrected by using a piece of white paper as a reflector.

Having the flash work is important as lighting is problematic for macro work due to the high f-stops needed for adequate depth of field. The 250's shorter working distance will put it in the DA 55-300's shadow at a lower magnification.

Dave

* A useful equation for working distance, w, at constant focal length is: w'/w = (1+1/m')/(1+1/m)
so going to m=2 from m=1 by extending a lens decreases working distance by a factor of (1+1/2)/(1+1/1) = 0.75
01-21-2011, 06:04 AM   #12
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This is the best resource I've seen for calculating macro magnifications:
www.peterforsell.com
01-21-2011, 06:23 AM   #13
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QuoteOriginally posted by audiobomber Quote
This is the best resource I've seen for calculating macro magnifications:
www.peterforsell.com
I agree that peterforsell's exposition is pretty good but think it is a little more complex than need be. There are many ways to write the appropriate equations, some more convenient than others, some more generally applicable than others.

However, I don't yet know a more succinct discussion to reference.

Dave

PS One detail he neglects to mention is the effect of close-up lens spacing on magnification, an easy correction (which is often omitted for simplicity's sake.)

Last edited by newarts; 01-21-2011 at 06:41 AM.
01-25-2011, 10:29 AM   #14
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QuoteOriginally posted by clockwork247 Quote
i'm probably getting the 150 then... i think it'll be enough for me.
Did you get that raynox 150? Think I'll get one too for my 55-300. Thx
01-25-2011, 11:14 AM   #15
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QuoteOriginally posted by tkossally Quote
Did you get that raynox 150? Think I'll get one too for my 55-300. Thx
Yes, the Raynox 150 is definitely the way to go.

The 250 is not a good match for the 55-300. The combo will do 1:2 macro and 2.4:1 macro and not much in between, due to serious vignetting. Working distance is also very tight. The Raynox 150 is an ideal mate for the 55-300mm.
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