Macro Setup For Measuring A 6mm Diameter Part

[jhinkey]

OK macro gurus, I have a small cylindrical part that has some interesting features on one end that we need to reverse engineer.  Physical measurements are tough due to the diameter being just over 6mm.  So I want to image the part with a macro setup using the macro gear I have on end.  I know or can measure some of the features with great accuracy, so I was going to use these as benchmarks to get the un-measureable features.

Since I want to take measurements from the image I want:
 - the 6mm diameter to fill the D800 frame (or my A7RII) as much as possible
 - little pincushion or barrel distortion as possible
 - low perspective distortion as the part does have some depth to it, thus being farther away is a good thing and I can focus stack if necessary

What I have is:
PB6 Bellows unit (and rail)
Worm geared macro stage
LED Ring Light
55/3.5 AIS Macro
200/4 AF-D Macro
PK11, PK12, PK13 extension tubes
62mm Agfa macro filter set that fits the 200/4D (not sure how good these are)

So, am I better off with massive extension (PB6 + PK set) applied to the 200/4AF-D Macro or should I use the add-on lenses to achieve my goals?

Thanks for any help!  I will start playing around with what I have to see how far I can get.

John

[Bjørn Rørslett]

You should aim for a minimum of 3X, preferably 5X.

Use the 55 reversed on the  bellows and add all the extension you can get.

[jhinkey]

You should aim for a minimum of 3X, preferably 5X.

Use the 55 reversed on the  bellows and add all the extension you can get.

Thanks Bjorn - how close will the 55 have to be?  I'd like to avoid shadows from the ring light if it's too close and will this produce perspective distortion?

- John

[Bjørn Rørslett]

You will get fairly close. Probably less than 5 cm. Do remember the lens has to be reversed and you probably should put a makeshift "hood" on it to prevent flare. A small hole slightly bigger than the subject,drilled in a rear lens cap, will work just fine as hood.

You have to choose between two evils: either a shorter focal length and getting close, or use a longer one that needs massive amounts of extension and only gets you a little less close. The proneness to vibrations increases by a longer bellows draw. Either way you should use a focusing light, use mirror lock up, and electronic flash for final exposure.

[null]

http://www.ebay.com/itm/3-5X-90X-LED-Boom-Stand-Stereo-Zoom-Microscope-USB-Camera-/400428152098?hash=item5d3b60b522:g:8NEAAOSwv0tVaNr7

http://www.ebay.com/itm/USB-2-0-5-1-MP-CMOS-Microscope-Digital-Color-Camera-Eyepiece-Video-System-/251780425559?hash=item3a9f486757:g:39IAAOSwc3ZUqjP1

Do you have a budget for this project? Amazing how cheap that stereo microscopes and digital cameras cost these days. 20+ years ago I set up an optics lab, this stuff cost a lot of money back then. My wife had one of the first 1MPixel microscope cameras in her lab.

I bought a Swift Stereo Microscope for use on my camera projects for $50, like new. Also bought a Tektronix 2465 for $150- those used to cost $15K.

[Erik Lund]

Wow I didn't see them that cheap, amazing how some products has evolved!

[jhinkey]

You will get fairly close. Probably less than 5 cm. Do remember the lens has to be reversed and you probably should put a makeshift "hood" on it to prevent flare. A small hole slightly bigger than the subject,drilled in a rear lens cap, will work just fine as hood.

You have to choose between two evils: either a shorter focal length and getting close, or use a longer one that needs massive amounts of extension and only gets you a little less close. The proneness to vibrations increases by a longer bellows draw. Either way you should use a focusing light, use mirror lock up, and electronic flash for final exposure.

Thanks Bjorn - I'll see if I can find a reversing ring very soon as I need to make these measurements by early next week to get them to the machinist.

My macro ring light doesn't do flash as it's an cheap LED model, but I can always use the electronic shutter on my A7RII if I really have vibration problems.  Prior to reversing the 55/3.5 I'll see what I can do with the 200/4D and my PB6 bellows.

The 200/4D + Agfa +1 diopter close-up lens almost gets me there (I have a set that goes to +4 diopters I think), but I have no idea what distortion I'm getting.  Perhaps for all of these I should print a small test target with a grid to characterize what distortion I'm getting with any of the methods.

Thanks for your help -

John

PS - For my engineering consulting work I get to use my photo gear every once in a while. 
Currently I'm using the 200/4D macro to image droplets from a diesel fuel injector using short duration pulsed collimated light from a 100Watt LED since my SB700 gives too broad a light pulse at 1/128 power setting (though it's plenty powerful enough).    Amazing what you can see when you use a crisp 10 microsecond light pulse.

[jhinkey]

You will get fairly close. Probably less than 5 cm. Do remember the lens has to be reversed and you probably should put a makeshift "hood" on it to prevent flare. A small hole slightly bigger than the subject,drilled in a rear lens cap, will work just fine as hood.

You have to choose between two evils: either a shorter focal length and getting close, or use a longer one that needs massive amounts of extension and only gets you a little less close. The proneness to vibrations increases by a longer bellows draw. Either way you should use a focusing light, use mirror lock up, and electronic flash for final exposure.

Any particular reversing ring that I should use?

[jhinkey]

Any particular reversing ring that I should use?

The local pro shop couldn't find their one in-stock BR-2 (they were shocked when I walked in and asked - they said "we hardly run into anyone that even knows what those are" - , so a cheap knock-off is arriving today via Amazon.  I'll try to take a picture of the setups and the images from them sometime this weekend.

[richardHaw]

PB6 + a reversed 28mm lens + off camera flashes

and focus stacking

[Bjørn Rørslett]

He mentioned 55/3.5 and 200/4 as available candidate lenses ...

[jhinkey]

PB6 + a reversed 28mm lens + off camera flashes

and focus stacking

Yes, I will likely have to do focus stacking, so I picked up my macro stage from my lab today plus a stiff aluminum rail (T-slot system) to mount everything to.

- J

[null]

The suggestion for using a retro-focus wide-angle lens in reversed position is a good one for these applications as it allows much more working room. If you don't own one, they are cheap. This is one of those situations where the correct tools make the job much easier to accomplish. I always figured that buying the proper equipment was much cheaper than paying my engineers to spend more time working the problem. But I always had a great time bringing in equipment from home to solve a problem. The last one- ended up giving the lens to the person running the project. Turns out that modern Nano-coated optics have horrible transmission in the 1.5micron band: the Meade 97 outperformed the $4K lens. Was also cool to see a Canon 50/0.95 mounted on a $25K Sensors Unlimited IR sensor and use it at 1.5uM, I loaned it.

[jhinkey]

Here's what's working for me:
D800 + 200/4D AF + PB-6 Bellows (200mm extension)



and this gives a full frame image like:


which is more than good enough.

This is a single image at f/22 so diffraction is taking its toll, but I'll back off to f/8 or so and do some image stacking - any recommendations for a basic image stacker that can use manual images?

[jhinkey]

Oh, I have not tried this with my 55/3.5 reversed as I don't yet have the adapter to go from the F-mount on the lens to 52mm so I can attach my ring light.  I thing the 200/4D is giving me pretty good results and I suspect is minimizing the perspective distortion.  I have the part coming tomorrow, so I may give it a try if I have the time.