View previous topic :: View next topic 
Author 
Message 
LordV
Joined: 22 Nov 2007 Posts: 1568 Location: UK

Posted: Tue Nov 25, 2014 8:38 am Post subject: MPE65 + Raynox MSN202 magnification 


Well it was raining so I decided to to see if I could get an image using a Raynox MSN202 +25 dioptre on the front of my MPE65. I didn't hold much hope but to my surprise I did get a useable image with the MPE at 5:1. The magnification though was more than I expected at near 9:1 instead of around 6.6:1.
See pics below of ruler mm scale and some focus stacks of a white fly taken at the max mags of the system.
Brian V.
mm ruler scale MPE65 at 5:1 on 5dmk2
As above plus Raynox MSN202 +25 diopter
_________________ www.flickr.com/photos/lordv
canon20D,350D,40D,5Dmk2, sigma 105mm EX, Tamron 90mm, canon MPE65 

Back to top 


rjlittlefield Site Admin
Joined: 01 Aug 2006 Posts: 19889 Location: Richland, Washington State, USA

Posted: Tue Nov 25, 2014 10:35 am Post subject: 


Brian, it's good to see you back here after a couple of months' absence.
The images look rather better than just "useable", but I'm accustomed to seeing that with your lens combos.
In this case the numbers make good sense. Cranked out to its 5:1 end, the MPE 65 acts something like a focal length 45 mm lens on 270 mm of total extension. The MSN202 at +25 dioptre will be 40 mm focal length. As a simple calculation, if the lenses were "thin" and with no separation, then the combo would be roughly 22 mm focal length and 11:1. The separation causes that to drop a bit, giving a convenient handwaving explanation for the 9:1 that you observe.
What calculation did you do, to get the 6.6:1 prediction?
Rik 

Back to top 


LordV
Joined: 22 Nov 2007 Posts: 1568 Location: UK

Posted: Tue Nov 25, 2014 11:01 am Post subject: 


rjlittlefield wrote:  Brian, it's good to see you back here after a couple of months' absence.
The images look rather better than just "useable", but I'm accustomed to seeing that with your lens combos.
In this case the numbers make good sense. Cranked out to its 5:1 end, the MPE 65 acts something like a focal length 45 mm lens on 270 mm of total extension. The MSN202 at +25 dioptre will be 40 mm focal length. As a simple calculation, if the lenses were "thin" and with no separation, then the combo would be roughly 22 mm focal length and 11:1. The separation causes that to drop a bit, giving a convenient handwaving explanation for the 9:1 that you observe.
What calculation did you do, to get the 6.6:1 prediction?
Rik 
Thanks for the info Rik.
Remember I'm just a simpleton so used Existing mag + (65/40)
Brian v. _________________ www.flickr.com/photos/lordv
canon20D,350D,40D,5Dmk2, sigma 105mm EX, Tamron 90mm, canon MPE65 

Back to top 


TheLostVertex
Joined: 22 Sep 2011 Posts: 298 Location: Florida

Posted: Tue Nov 25, 2014 8:55 pm Post subject: 


rjlittlefield wrote:  Brian, it's good to see you back here after a couple of months' absence.
The images look rather better than just "useable", but I'm accustomed to seeing that with your lens combos.
In this case the numbers make good sense. Cranked out to its 5:1 end, the MPE 65 acts something like a focal length 45 mm lens on 270 mm of total extension. The MSN202 at +25 dioptre will be 40 mm focal length. As a simple calculation, if the lenses were "thin" and with no separation, then the combo would be roughly 22 mm focal length and 11:1. The separation causes that to drop a bit, giving a convenient handwaving explanation for the 9:1 that you observe.
What calculation did you do, to get the 6.6:1 prediction?
Rik 
I think I calculated a different way, but arrive at a similar value as you.
(Lens FL/Diopter FL + 1)(Lens Magnification + 1) 1
(45mm/40mm + 1)(5 + 1)  1 = 11.75
Was your method different? _________________ Steven
Flickr Macro Rig Control Software 

Back to top 


rjlittlefield Site Admin
Joined: 01 Aug 2006 Posts: 19889 Location: Richland, Washington State, USA

Posted: Tue Nov 25, 2014 10:00 pm Post subject: 


Well, this is certainly a special OCCasion!
I refer of course to the Opaque Calculation Contests that we run from time to time.
Following the rules for Standard Opaque Representation, my calculation could be written this way:
270/(1000/(1000/45+25))  1
Taking that apart from the inside out:
1000/45 is the strength in diopters of the MPE 65,
25 is the strength in diopters of the MSN202, so
1000/45+25 is the strength in diopters of the combination (assuming the lenses are thin and not separated), so
1000/(1000/45+25) is the equivalent focal length (EFL) of the combination. Then
270/EFL  1 is the magnification of that equivalent focal length, on 270 mm extension.
Your calculation and mine give the same results no matter what values I plug in for focal lengths and magnification (extension), so I'm quite confident that they're algebraically equivalent.
But I have no idea how to reach your form from first principles.
Can you explain?
Rik 

Back to top 


TheLostVertex
Joined: 22 Sep 2011 Posts: 298 Location: Florida

Posted: Wed Nov 26, 2014 2:46 pm Post subject: 


rjlittlefield wrote: 
But I have no idea how to reach your form from first principles.
Can you explain?
Rik 
Id love to! But unfortunately I can't This is infact just how I read the correct way to calculate a diopter on a lens was, and I do not recall the source off hand.
I should have wrote it a little differently though:
((Lens Fl/Diopter Fl) + 1)(Lens Magnification + 1) 1
Since I know that the first part is the calculation for the magnification of the pair focused at infinite:
(Lens FL/Diopter FL)
So at the very least I know that it is:
(Pair Magnification @ infinity + 1)(Lens magnification + 1)  1
Beyond this, I think my calculations go completely opaque! Do I win a prize?
It does appear that both have the same information in them(or equivalency there of) and they both produce the same answer. I would guess there is a way to get from one to the other, but I do not think I am able to dedicate that much thought to it at this moment. _________________ Steven
Flickr Macro Rig Control Software 

Back to top 


rjlittlefield Site Admin
Joined: 01 Aug 2006 Posts: 19889 Location: Richland, Washington State, USA

Posted: Thu Nov 27, 2014 2:07 am Post subject: 


Quote:  I would guess there is a way to get from one to the other 
There is, and it's just a matter of straightforward algebra.
All you have to do is take the deeply nested formula that comes out of firstprinciples analysis, and start hacking at it to reduce the nesting.
By the time you get down to the minimum nesting of parentheses (one level) and a single division (divisions are terribly hard to do by hand!), what pops out is the formula that you've quoted.
That formula is concise, easy to look at, and easy to evaluate. It's exactly the sort of formula that we'd like to find in a handbook.
There's only one problem: by then the formula is almost completely divorced from its physical origins. If some malicious editor were to swap some +1's and 1's when we weren't looking, it would be pretty hard to spot the corruption. Likewise for figuring out what assumptions the formula is based on.
This bothers me. Maybe I'm the only person in the world that it does bother. I don't know. But I do know that my personal preference is to avoid mistakes and misapplications, and the best way I know to do that is to avoid formulas that I can't pick apart and make sense of. I much prefer a sequence of simple calculations that all make sense, over a single pluginthenumbers calculation that I have to take on faith.
Rik 

Back to top 


