Microscope objective vs MP-E 65mm

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DimitriKatsaros
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Location: Bellingham, WA, United States

Microscope objective vs MP-E 65mm

Post by DimitriKatsaros »

Hi all,

I have a Canon 6D on a stackshot and right now am using my MP-E 65mm lens but was wondering if I could do any better (sharper) with a Nikon (or any other make) microscope objective added to the front of my 180mm macro (also Canon).

Would I be wasting my time/money or could something be gained?

Thanks
Dimitri Katsaros

Pau
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Post by Pau »

Hi Dimitri, welcome aboard!

Providing it's an adequate objective, up to 4X you're well served with the MP-E.
At 5X you could get better resolution with a good objective, for higher magnification the objective clearly wins because it provides higher NA, but it also depends of the camera megapixel count (6D isn't the most demanding) and of the final image size you want.
Pau

rjlittlefield
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Post by rjlittlefield »

Dimitri, welcome aboard! :D

The 10X objective would be much sharper on subject.

See the reference images at http://www.photomacrography.net/forum/v ... hp?t=15876 ("Lenses for use at 4-5X on an APS-sized sensor"). Among a lot of other stuff, you will find these two images that directly apply to your question:
MP-E 65 at f/2.8 and 5X. For direct comparison with the CFI combo, next.

Nikon CFI 10X Plan Achromat on Canon 100 mm macro lens, giving 5X. This combo is much sharper than the MP-E 65, not surprising since the MP-E is running around f/16 effective while the combo is about f/10. What is surprising is that the combo holds up well clear to the corners, despite that this far exceeds the field size that the objective was designed to handle.
Note that the above pair is at matched magnification, 5X on sensor in both cases.

When you use the 10X objective on a 180 mm lens, it will be running at 9X. This will make the image on sensor appear to be less sharp than it is at 5X (fewer line pairs per image height at 9X than at 5X). But the sharpness on subject will be at least as high (equal or more line pairs per mm on subject). To the extent that sensor resolution is also limiting your sharpness (20.2 megapixels on full frame = 6.51 micron pixel size), the 9X setup will be even sharper on subject.

See http://www.photomacrography.net/forum/v ... hp?t=15922 for more discussion about how sensor resolution is a limiting factor at 5X with the objective, even with a higher resolution sensor than you have (using 15.1 megapixels on APS-C, 4.69 micron pixel size).

--Rik

DimitriKatsaros
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Joined: Wed Mar 19, 2014 10:13 am
Location: Bellingham, WA, United States

Post by DimitriKatsaros »

Right now I am using my MP-E at 3x and f/8 (I read somewhere that at 3x, this aperture was the sweet spot) as 5x in my setup is way too unsharp and dark. (I try to stick to ISO 100 or 125 and have a cross polarized and diffused lighting set up on my Canon MT-24EX.)

Could the 10x still provide an advantage and will I get enough light to be able to focus in live view?

Thanks
Dimitri

rjlittlefield
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Post by rjlittlefield »

DimitriKatsaros wrote:Right now I am using my MP-E at 3x and f/8 (I read somewhere that at 3x, this aperture was the sweet spot) as 5x in my setup is way too unsharp and dark. (I try to stick to ISO 100 or 125 and have a cross polarized and diffused lighting set up on my Canon MT-24EX.)

Could the 10x still provide an advantage and will I get enough light to be able to focus in live view?
This question strikes me as "apples and oranges". At 3X on full frame, you're shooting a subject field that is 14 mm across the diagonal. For practical purposes, there are no 10X objectives that will cover that large a field. A more typical value for the 10X objective would be around 5 mm diagonal (for example APS-C at 5X = 5.6 mm, or full frame at 10X = 4.3 mm diagonal).

If you want to shoot the smaller subject, then using the 10X would give a significantly sharper image. If you want to shoot the larger subject, then continuing to use the MP-E 65 is a good way to go. As shown at the link I gave earlier, the MP-E is sharper at low magnifications than most other lenses, specifically including inexpensive microscope objectives in the 4X range, some of which can cover a field of view in the 14 mm range.

As for whether the 10X will give enough light to be able to focus in live view, all I can say is that a lot of us do exactly that, with no problems. But your mileage may vary. At 9X, a typical 10X NA 0.25 objective will be working at an effective aperture of f/18, not much different from the MP-E at 5X and f/2.8, which is effective f/16.8 .

In all cases, note that the DOF of a 10X NA 0.25 objective is only around 0.009 mm. For anything except the flattest of subjects, you'll need to use focus stacking.
MP-E at 3x and f/8 (I read somewhere that at 3x, this aperture was the sweet spot)
You should always run your own tests to determine the sweet spot. It varies with different units of the same model lens, and with different cameras, and with different methods of post-processing, and with different people making the decision. The MP-E at 3X and f/8 is operating at an effective aperture of f/32 (=8*(3+1)). Many people would consider that setting to be firmly in diffraction territory and would use a larger aperture to get a sharper image, particularly if focus stacking is feasible for the application.

--Rik

DimitriKatsaros
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Location: Bellingham, WA, United States

Post by DimitriKatsaros »

The step size is no problem and field of view is not a problem either... I currently depth stack and then pano stitch everything together now as it is. :-) To give you an idea, I'm shooting tulip petals and need to do around 10 photos per field (give or take, depending on waviness) and then around 12 fields left to right for 120 shots. If I can go deeper and really capture the cell structure, that would be amazing. The cells are in my photos now, just not "tack sharp." I just hope it isn't because I'm looking through plant tissue. :-)

Thanks
Dimitri Katsaros

P.S. I definitely will try a larger aperture and see where I get... definitely will shorten the shutter time too! :-)

DimitriKatsaros
Posts: 5
Joined: Wed Mar 19, 2014 10:13 am
Location: Bellingham, WA, United States

Post by DimitriKatsaros »

HUGE difference with f2.8... thank you! :-)

The only problem I have now is battery power for the flash. At f2.8 on a bearded iris petal, the depth stack is about 128 images. The thing is, I shoot macro panoramas and need to get 6 images across and the poor four pack of AA Eneloops are not cutting it beyond a single stack. (Think "black" irises with a cross pol setup. :-) )

Are continuous lights plugged into AC the answer? If so, which ones?

Thanks Again
Dimitri Katsaros

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