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ideal lens for close up filter
Posted By: mehulmandan, 01-28-2015, 09:51 AM

hello,
I have pentax 18-135mm and 55-300 mm lens with me. wanted to buy close up filter set. Which of the above lens should be given priority as both the lens have different diameter. Also step up ring is not available in my region.. which of the above lens will give better magnification?
Thanks in advance.

Last edited by mehulmandan; 01-28-2015 at 10:33 AM.
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01-28-2015, 09:59 AM   #2
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The magnification you can obtain by adding a supplementary close up lens depends on the native magnification of the lens you put it on. Supplementary close up lenses give greater magnification with longer focal lengths and extension tubes give better magnification with shorter focal lengths. Without knowing more about your lens, it is impossible to say exactly what magnification range you would obtain with a close up lens attached.

The only thing that can be said for definite, is that the maximum working distance(front of lens to subject distance) is totally dependent on the close up lens. The max working distance is the focal length of the close up lens.

The dioptre is defined as 1000/focal length. So a +4 dioptre lens has a focal length of 1000/4 or 250 mm (just shy of 10 inches in ancient US terms), and that would be your max working distance. You will not be able to focus beyond that.
01-28-2015, 10:10 AM   #3
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Macro Extension Tubes & Close-up Lenses

This site has a handy dandy calculator that will give different magnifications using extension tubes and also close up lenses.
Long story short. The longer the focal length the more magnification you get with a close up lens.
Inversely, the shorter the focal length, the more magnification you get with extension tubes.

This site also gives pros and cons of each. I have used both and I personally prefer a close up lens just because you eat a fair amount of light with extension tubes.

Edit: BLPP beat me to it
Gotta be fast with this bunch
01-28-2015, 01:04 PM   #4
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QuoteOriginally posted by cali92rs Quote
Macro Extension Tubes & Close-up Lenses This site has a handy dandy calculator that will give different magnifications using extension tubes and also close up lenses.
something is not right about this calculator.
Using their base numbers

Native Magnification 0.15 X
Lens Focal Length mm 50 mm
Total Extension Tube Amount 25 mm
New Magnification = 0.65X
New Closest Focusing Distance* = 209.4 mm.

If you enter a new extension tube number of 50mm you get,

New Magnification = 1.15X
New Closest Focusing Distance* = 201 mm.


If you enter a new extension tube number of 100mm you get,

New Magnification = 2.15X
New Closest Focusing Distance* = 230.8 mm.

The new close focus distance is getting larger not smaller. Which is backwards.

So I cannot trust this calculator.

01-28-2015, 03:27 PM   #5
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That calculator uses the same equations from the army book you've referenced before, (for others they're here FREE Army, Navy, Air force, Marine , Joint Forces, Canadian Armed Forces Manuals from Shopdawg.com and the relevant equations are in the photography-basic book, page 1-27) and is in agreement with this one:

Lens Magnification and Depth of Field Calculator

Though the one I've just linked to takes in the 'focusing distance' you've set the lens to instead of the 'Native Magnification' (one can be derived from the other).

Try the second calculator, note what's happening with the 'object distance' and 'image distance' outputs. The sum of these is the 'effective focusing distance':

(effective focusing distance) = (object distance) + (image distance)

and note how the 'image distance' is equal to the sum of the 'extension tube', the 'focal length', and the not mentioned 'built-in extension' of the lens (7.5mm for a 50mm lens set to 0.15x magnification, aka focused at 440mm). Also keep track with how these numbers satisfy the thin lens equation:

1/(focal length)=1/(object distance) + 1/(image distance)

as you add extension tubes the object distance goes down (this also known as working distance), but the image distance goes up and has no upper bound as long as your tubes are long enough. As you start adding extension tubes object distance is decreasing faster than image distance is increasing so your overall effective focusing distance is dropping, but eventually the the image distance starts to win ( the object distance starts to approach the focal length as the extension tubes get really long).

These calculators make the assumption of an inert lens (no internal moving elements) and use stuff derived from the thin lens equation. Accurate enough for most cases, especially if you're treating the lens as being locked at a specific focal length.
01-28-2015, 03:57 PM   #6
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the problem I have with the calculator is, The distance to the subject gets shorter when you increase the extension tube length up to the primary focal length, but the distance to the subject gets longer as you increase the extension tube length beyond the primary focal length. Basic physics tells us that as you increase the distance between the lens and film/sensor, you decreased the distance from the lens to the subject, it is an inverse ratio.

I only changed one variable, The extension tube length. That is why I do not trust this calculator.
01-28-2015, 04:14 PM   #7
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QuoteOriginally posted by promacjoe Quote
the problem I have with the calculator is, The distance to the subject gets shorter when you increase the extension tube length up to the primary focal length, but the distance to the subject gets longer as you increase the extension tube length beyond the primary focal length. Basic physics tells us that as you increase the distance between the lens and film/sensor, you decreased the distance from the lens to the subject, it is an inverse ratio.
It's agreeing with basic physics. See the second link, the 'object distance' is going down, this is the distance from the lens to the subject...it has a limiting value equal to the focal length. The first link is only reporting the 'effective focusing distance**' which is the distance from sensor to subject, and this will start to rise as you increase the total extension (counting tubes and built-in extension of the lens) past the focal length.


**edit- the Cambridge site is calling this 'New Closest Focusing Distance'
01-28-2015, 05:18 PM   #8
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HOW CLOSE DOES THE LENS FOCUS NOW ?


The 55-300 , how close does it focus ?
the 18-135 , how close does it focus ?


Which ever lens focuses the closest , is the lens I would buy close focus filters for . ( A +2 and a +4 would be a good place to start )

01-28-2015, 06:59 PM   #9
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If the .28 x magnification specified for the 55-300 includes the lens at 300mm (in the lens reviews) then that will easily give you the biggest magnification with any given dioptre of close up filter.
If you read the link that cali95rs supplied you will see that it says that the longer the focal length of the lens then the more it will react to the closeup filter.
So use your 55-300 at 300.
At 300 mm, focussed as close as possible with a x4 dioptre filter, the image on your sensor will be 1.8 times the size of the subject.
01-28-2015, 07:14 PM   #10
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If you want to buy a double element close focus thing, such as Raynox's, you can't use it on DA18-135, because of it's native internal focusing design! thus you are left with the other lens.
And other than this issue, I think a Raynox DCR-150 with DA55-300 is your best bet! you can have from 1:4 (@55mm) to 2:1(@300mm) macro ability in one setup, and the working distance will be around 20cm, which is pretty good.
And double element ones are much much much better than the single element ones. (I've tried them both)
02-01-2015, 12:08 PM   #11
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Thanks friends for valuable advice.
would love to see any sample photos with the above combination if any.
02-04-2015, 02:18 AM   #12
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QuoteOriginally posted by mehulmandan Quote
would love to see any sample photos with the above combination if any.
Here are two shots with DA55-300 and DCR-150, once time I tried using it.
Missed the focus on this one:



This was shot at highest magnification possible:



And here I made a comparison of using the Raynox on DA55-300 for a friend:

02-06-2015, 07:57 AM   #13
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QuoteOriginally posted by mtux Quote
If you want to buy a double element close focus thing, such as Raynox's, you can't use it on DA18-135, because of it's native internal focusing design! thus you are left with the other lens.
And other than this issue, I think a Raynox DCR-150 with DA55-300 is your best bet! you can have from 1:4 (@55mm) to 2:1(@300mm) macro ability in one setup, and the working distance will be around 20cm, which is pretty good.
And double element ones are much much much better than the single element ones. (I've tried them both)
I completely agree with mtux. Lots of Raynox samples in this thread:
https://www.pentaxforums.com/forums/122-lens-clubs/74221-raynox-macro-club.html
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