Macro Filters

[Magicbenja]

Hey folks

I would like somebody a bit more seasoned with filters than I to clear up some confusion I have been having. I decided recently that a more a cost effective way to dabble with some macro photography and/or increase my focal length capabilities would be to purchase a macro filter or set of filters.

Then came the diopter rating attached to each individual filter. These came in plus +1 +2 +4 +7 +10 etc.

They confused me. I think I've managed to fathom what they are about and this is the conclusion I have drawn.

focal length of the macro filter = 1000 divided by the diopter rating

This would be for example:

1000/+4 = 250mm

which would then give me 305mm focal length? (my current lens is a 18-55mm kit).
which is a zoom from 3x increased 16x

Is that right?

Also, is it true that the lowest + numbers give the highest focal length or is that my imagination?

+10 would only give 100mm?

Sorry for the long post. Thanks

 

[Canon Bob]

Your first assumption that the focal length of the filter corresponds to 1000/diopter rating is correct....but things go wayward after that point.

The increase in "zoom" is really nothing to do with what you're trying to achieve nor the focal length overly relevent to the results.
The working distance of the combination will be equal to the focal length of the diopter when the main lens is focussed at infinity. When the main lens focus is set closer then the equations become quite complex as the internal extension of the lens becomes a greater and greater factor as minimum focus distance is approached.
It is also neccessary to know (or calculate) the front and rear principal focal points of the primary lens (nodal points) and their relationship to the rear focal point of the diopter lens.

The alternative is to stick the filter on and see how big an ant looks on your sensor.

Bob

 

[Magicbenja]

Ok. I didn't understand that entirely but I take your point.

Maybe if I simplify the question.

Which diopter macro filter will give me the most macro?

 

[grum]

+10 or all of them together if you can? Not an expert though so I may be wrong...

I use a Raynox DCR 250 - not sure what magnification it gives me but with a 45-200mm lens it can do this.

 

[Canon Bob]

Ok. I didn't understand that entirely but I take your point.

Maybe if I simplify the question.

Which diopter macro filter will give me the most macro?

Higher diopter numbers and greater primary lens focal length will give the highest magnification.....ie, the +10 diopter with your 18-55 set at 55mm will be as good as it gets.

Bob

 

[Magicbenja]

Thank you very much!

 

[jgs001]

As an idea, the Raynox DCR250 is reported as being a +8 diopter filter. On my camera, I get about 1:1 at about the 100mm mark. Take a picture of a ruler at your maximum magnification, and compare the the width of the camera sensor, if what shows on the pic is the same as the width of the camera sensor, you're getting 1:1.

 

[petersmart]

The cheap ebay set of close up lenses can give quite good results, but don't work very well on large filter sizes eg 72mm.

On the Canon 18-55mm kit lens they are a cheap intro to Macro photography.

That shot was taken with the 350D with the 18-55mm kit lens fitted with a close up lens (+2 I think)

+10 doptre is about the biggest you can get but you will find that the DOF is extremely small.

As a cheap intro to Macro these lenses are adequate but if you want to go further either a "proper" Macro lens like the Canon 100mm Macro or a set of extension tubes used with a "nifty fifty" also gives very good results - and with that combo you can also use the onboard flash.