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Canon 100mm macro lens and Nikon CFI Plan achromat 10x lens

 
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Photosbykev



Joined: 06 Mar 2015
Posts: 14
Location: Gloucester, UK

PostPosted: Fri Mar 16, 2018 1:43 pm    Post subject: Canon 100mm macro lens and Nikon CFI Plan achromat 10x lens Reply with quote

The new Nikon objective turned up so I cobbled together something to stick it onto the front of a Canon 100mm macro lens with 65mm extension tube connecting it all to a Canon 5D4.

This is the result of 47 raw images shot at 1/2 seconds @f2.8 iso 400 with a small diffused LED light source off to the right. Stacking step was 10 microns using a WeMacro stage.

From my very very limited knowledge of using this type of hybrid lens setup i.e. it's the first time I've ever played with one, I'm impressed by the lack of vignetting, the sharpness appears to be good and there are no obvious optical artifacts reducing the image quality.

Clearly I need to improve the lighting which is on my to-do list but can I improved the image quality by using something else behind the Nikon objective?

The image is the letter E after the B in ELIZABETH on a 10p coin, and I estimate the magnification is around 10 as expected, this is the full uncropped image.

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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18908
Location: Richland, Washington State, USA

PostPosted: Fri Mar 16, 2018 3:05 pm    Post subject: Reply with quote

The Nikon objective is intended to be paired with a 200 mm focal length rear lens that is focused at infinity. In that configuration you get the nominal 10X magnification and no added aberrations.

When the objective is used with a rear lens that is 100 mm focal length, still focused at infinity, then you only get 5X with a correspondingly smaller image circle, and still no added aberrations.

Adding the 65 mm extension tube behind the FL 100 mm rear lens increases the magnification, but it also adds aberrations because it drags the objective away from its designed focus point. At only NA 0.25 the added aberrations are not so bad and maybe the combo makes a good compromise.

You could avoid the added aberrations and get very close to nominal magnification by swapping out the 100 mm macro lens and replacing it with a Raynox DCR-150 or Sigma Life Size Adapter, each of them mounted on roughly 180 mm of extension tube with suitable ring adapters, so as to make the rear lens focus at infinity when the objective is not in place.

A setup using the Raynox DCR-150 is detailed at https://www.photomacrography.net/forum/viewtopic.php?t=35350 . A similar setup using the Sigma Life Size Adapter would be simpler because the LSA has 52 mm threads. Some people have found that the LSA also gives less chromatic aberration than the Raynox.

Quote:
I estimate the magnification is around 10 as expected

Be cautious of "expectations" when the rear lens is not focused at infinity. Lens combos can behave very strangely in that situation. In any case, the only really safe method for determining magnification is to measure it. I strongly recommend shaking the piggy bank to purchase a "stage micrometer" slide, basically a 1 mm ruler with tick marks at 0.01 mm. Those used to be expensive, but they can now be purchased new from numerous eBay vendors for as ltttle as $5 (HERE).

--Rik
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Photosbykev



Joined: 06 Mar 2015
Posts: 14
Location: Gloucester, UK

PostPosted: Fri Mar 16, 2018 3:41 pm    Post subject: Reply with quote

rjlittlefield wrote:
The Nikon objective is intended to be paired with a 200 mm focal length rear lens that is focused at infinity. In that configuration you get the nominal 10X magnification and no added aberrations.

When the objective is used with a rear lens that is 100 mm focal length, still focused at infinity, then you only get 5X with a correspondingly smaller image circle, and still no added aberrations.

Adding the 65 mm extension tube behind the FL 100 mm rear lens increases the magnification, but it also adds aberrations because it drags the objective away from its designed focus point. At only NA 0.25 the added aberrations are not so bad and maybe the combo makes a good compromise.

You could avoid the added aberrations and get very close to nominal magnification by swapping out the 100 mm macro lens and replacing it with a Raynox DCR-150 or Sigma Life Size Adapter, each of them mounted on roughly 180 mm of extension tube with suitable ring adapters, so as to make the rear lens focus at infinity when the objective is not in place.

A setup using the Raynox DCR-150 is detailed at https://www.photomacrography.net/forum/viewtopic.php?t=35350 . A similar setup using the Sigma Life Size Adapter would be simpler because the LSA has 52 mm threads. Some people have found that the LSA also gives less chromatic aberration than the Raynox.

Quote:
I estimate the magnification is around 10 as expected

Be cautious of "expectations" when the rear lens is not focused at infinity. Lens combos can behave very strangely in that situation. In any case, the only really safe method for determining magnification is to measure it. I strongly recommend shaking the piggy bank to purchase a "stage micrometer" slide, basically a 1 mm ruler with tick marks at 0.01 mm. Those used to be expensive, but they can now be purchased new from numerous eBay vendors for as ltttle as $5 (HERE).

--Rik


Thank you for the information Rik, I've ordered the calibration scale Smile

I was using the Canon 100mm lens at minimum focus (not infinity) with the Nikon 10x mounted using a M58 to M25 step down ring. With the lens at infinity the image circle was too small and vignetting, at minimum focus the image circle covers the full frame sensor quite nicely.

The magnification estimate is based on the actual size of the letters on the coin (approx 2mm) against the sensor size of 24mm height giving a nominal 12x. The image posted above is uncropped from the Canon 5D4 full frame sensor.

I do have a Sigma life size adaptor which I've used on the Canon 100mm lens today with reasonable success by using a M58 to M52 step down ring (image below).



I'll start ordering 180mm of extension tubes to take me from the Canon EF mount to the back of the Sigma LSA (52mm) and I have the M52 to M25 stepdown to mount the Nikon on the front of the LSA.

Many thanks for all of the feedback Rik, baby steps but slowly getting there.

regards Kev
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Photosbykev



Joined: 06 Mar 2015
Posts: 14
Location: Gloucester, UK

PostPosted: Sat Mar 17, 2018 12:59 pm    Post subject: Reply with quote

A rough and ready test using a mixture of Canon extension tubes and a generic helical M42 to M52 focuser to give me the correct spacing for the Sigma LSA and Nikon 10x objective, the resolution is significantly better than my 1st attempt at the top of the thread.

The left hand side of the image is affected by flare but that is coming off the inside of the helical focuser which won't be in the final setup but the right hand side clearly shows an improvement.

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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18908
Location: Richland, Washington State, USA

PostPosted: Sat Mar 17, 2018 2:16 pm    Post subject: Reply with quote

Excellent -- thanks for the further information.

--Rik
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Photosbykev



Joined: 06 Mar 2015
Posts: 14
Location: Gloucester, UK

PostPosted: Sat Mar 17, 2018 2:57 pm    Post subject: Reply with quote

A quick play with a new lighting product from Adaptalux, flare is better but I know it's still there so some flocking paper needs to be applied inside the final setup to maximise the contrast and detail

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