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Canon comparisons between 100mm macro (non-l) and 17-85

 
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Joyful



Joined: 19 Feb 2015
Posts: 143
Location: Cape Town, South Africa

PostPosted: Mon Mar 02, 2015 7:53 am    Post subject: Canon comparisons between 100mm macro (non-l) and 17-85 Reply with quote

Good afternoon from a very hot 30 degree plus fire-ridden Cape Town.

Before I dive in and buy a Nikon CPI Objective, I decided to test out my 100mm Macro and my 17-85mm lenses using progressively as many extension tubes with my Vello Macrolink.

I concentrated on photographing a millimeter ruler to see exactly how much magnification I was getting with each setup.

With 100mm Macro (non-l) at closest focussing point the Field of View was 22mm giving me the 1:1 magnification as expected. When I used all my extensions possible (about 250mm), the field of view dropped to 5mm which gives me a not-too-shabby 4.4:1. Image quality was still reasonable to my inexperienced eye.

With my 17-85mm (non-l) at closest focussing point and at 17mm the Field of view with lens on a reversing ring only my field of view is a surprising 10mm giving me a magnification factor of 2.2:1 (which was also achieved on the Canon 100mm with the Canon 25mm ext tube and the Vello Macrofier link)

When I add extension tubes to the reversed 17-85mm two things happen - first, the magnification goes up quickly, and 2 - image quality drops off just as quickly - which is a great pity, as I get down to over 10:1 with only 3 x Photix no 3 tubes - and I can still add about another 4cm.

Now a question - I have improved my images dramatically by flocking the insides of all tubes. Is there anything I can do with my same lenses to improve image quality now? Or is it time to get some new glass ?

Looking forward to hearing if anyone has done something similar, and what I can do from here on

Joyful
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ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 8394
Location: Near London, UK

PostPosted: Mon Mar 02, 2015 8:34 am    Post subject: Reply with quote

Hi Joy
First - use flash, or vibration will always be a suspect for fuzziness.

Then, read a lot about diffraction, it's the ultimate limiter on what resolution you can get from a given lens however well made it is.
Diffraction blur goes up with Effective Aperture.
EA can be worked out, for a simple lens, by
EA = (Magnification +1) x the aperture marked on the lens.

So if you're using an enlarger lens set to f/4, with enough extension for 5x magnification, that's (5+1)x4 = EA f/24.

That EA is small enough (number big enough) for a significant blurring effect.
If you set f/11, then the EA would be F/66 , which would look decidedly poor.

That's probably the cause of what you're seeing. Reversing a lens like your 17-85 is more complicated because it's not symmetrical, so you get a smaller aperture when you reverse it.

Microscope objectives have the biggest apertures available. Almost nothing is in focus, which is where Stacking comes in Very Happy .
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pontop



Joined: 18 Dec 2013
Posts: 83
Location: Uppsala, Sweden

PostPosted: Mon Mar 02, 2015 8:56 am    Post subject: Reply with quote

Warning: Once you are bitten by the microscope objective bug there is no going back......

/Bo
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Joyful



Joined: 19 Feb 2015
Posts: 143
Location: Cape Town, South Africa

PostPosted: Mon Mar 02, 2015 8:56 am    Post subject: Reply with quote

Hi Chris -

You guys are teaching me well.

I now use flash all the time - Canon twinlight set to M with power at about 1/32. Aperture as wide as can go, but then down a stop or two.

Before my tests, I plonked a small flower pot down on a simple adjustable wood stand and tried to take pics - but the flower wobbled all the time - so now I realise I must nail it down as well. Better immediately, as focus is more accurate.

I have Zerene, and the little that I have played with it I must say I LOVE IT.

Joyful
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Joyful



Joined: 19 Feb 2015
Posts: 143
Location: Cape Town, South Africa

PostPosted: Mon Mar 02, 2015 9:00 am    Post subject: Reply with quote

Pontop - I am so ready to be infected.

Quality is what I am after (I am an ex-Hasselblad user) - but now that I am retired Cost is a big issue.

I am struggling to get a reply from IMP South Africa to get cost estimates. Can anyone help ?

Joyful
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pontop



Joined: 18 Dec 2013
Posts: 83
Location: Uppsala, Sweden

PostPosted: Mon Mar 02, 2015 9:55 am    Post subject: Reply with quote

Watching a stacked picture emerge in Zerene reminds me a bit of my childhood time in the darkroom with my grandfather watching pictures emerge on the paper.
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