Micro Photography set up

[TobyMac]

Hello all.

I am trying to set up a shoot for microscopic photography but am running into a few issues. I have a Nikon CFI Plan 10x objective and the adaptors to fit them onto both a 105mm macro lens and a 70-200. However I can't get the image sharp or if I do get the image sharp I have so much vignetting that the image becomes useless.
What am I missing or doing wrong.
The vignetting occured when I set the 70-200 at 200mm and f/22 and focused the lens to infinity.
The camera being used is a nikon d810.
Could it possibly be that I need to set the camera to mirror lock up because the unsharp image is a result of vibrations?

Any assistance would be much appreciated.

Thanks

[DanK]

I've never done that level of magnification (my macro tops out at 2:1 or 2.5:1) and therefore haven's used an objective like yours, but I wouldn't be surprised if the adapter eliminates infinity focus. Extension tubes do.

[Saorsa]

If this is the sort of setup you are working with I would expect some vignetting



You should definitely turn VR off and use mirror lockup after focus when shooting.

[Saorsa]

Here is an excellent article.

http://extreme-macro.co.uk/extreme-macro-tube-lenses/

it even points out vignetting with zoom lenses

Extreme macro photographers have obtained excellent results from lenses around the 200mm focal length, either fixed primes, or the long end of a zoom. However, if using a zoom lens beware, as a zoom at less than full focal length will usually (but not always) vignette. ... from http://extreme-macro.co.uk/extreme-macro-tube-lenses/

[JBW]

Hello all.

I am trying to set up a shoot for microscopic photography but am running into a few issues. I have a Nikon CFI Plan 10x objective and the adaptors to fit them onto both a 105mm macro lens and a 70-200. However I can't get the image sharp or if I do get the image sharp I have so much vignetting that the image becomes useless.
What am I missing or doing wrong.
The vignetting occured when I set the 70-200 at 200mm and f/22 and focused the lens to infinity.
The camera being used is a nikon d810.
Could it possibly be that I need to set the camera to mirror lock up because the unsharp image is a result of vibrations?

Any assistance would be much appreciated.

Thanks

Here's a link to all you ever wanted to know and maybe even a bit more on the subject.

[ajohnw]

You ideally need to use a 200mm lens with this objective. It's the nearest thing available to the tube lens in Nikon microscopes. However the version of the lens may matter as well, It will have an infinity sign on it followed by a /- or / some number. The dash ones are intended to be used without the usual cover slips on microscope slides. The number if present indicates the thickness of the cover slip that should be used. If you have one of those it may not be suitable.

There are various 10x objective types so plan cfi doesn't mean much on it's own. The NA should be on it as well somewhere. May be 0.25 or higher. On a microscope the depth of field on an NA 0.25 lens is about 8.5um, If the objective is in very good condition it should be possible to see a sharp plane of focus getting fuzzy either way from it. Used objectives are often faulty. There are also various working distances for the 10x objectives. What I would do is set something up according to that. Have the zoom set at 200mm and focused to infinity and play with the distance for best focus and maybe then the zoom setting. I don't think it would be a good idea to set F22. Maybe F8 or so to get decent performance from the lens. Microscope focusing mechanisms are designed to adjust the working distances to better than 1um. You need to bear that in mind when playing around. Even a low NA objective needs very find adjustment. You may find that the lens F setting does change the depth of field but only if it reduces the NA or F number of the objective. It probably wont and that wouldn't be a good idea anyway as F number / NA is what gives the resolution which is higher and higher as the NA goes up.

I have seen good quality images taken with this style of objective fitted to old 200mm prime lenses but people generally use plan apo's or fluor to get minimum chromatic aberration. These lenses are popular because all of that aspect is fixed in the objective. On normal microscope objectives some of the corrections are in the eyepiece.

John
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[Saorsa]

You ideally need to use a 200mm lens with this objective. It's the nearest thing available to the tube lens in Nikon microscopes.
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Here is a quote from another site on focus breathing.

So that's "focus breathing" in a nutshell. If it bothers you, at least you now know how to measure it, but in practice it's rarely going to pose any problems. Even some of the best lenses do it. The Nikkor 70-200 F/2.8 VR II is known to be a "heavy breather". At closest focus (1.4m) reports are that the focal length (measured by magnification/angle of view) is around 135mm and at 5m it's around 175mm. This bothers some users, other's don't really care.

In this application that could well be bothersome

[ajohnw]

It shouldn't be a problem Brian. This style of microscope objective is usually referred to as infinite tube. In practice there is no such thing in optics really but they can get pretty close so the focus of the dslr lens should be set close to infinity. How close would have to be via trial and error.

Vignetting was mentioned. Traditional microscopes have a tube bore of 23mm. On lower power objectives the actual image size used is probably about 20mm so with a 10x objective a 2mm object will fill the field. It may be possible to use a larger image size than that but I'd doubt if it can be much bigger. There are also larger bore tubes used on stereo microscopes and wide field microscopes. I doubt if stereo microscope objectives would be aberration free on their own. I'm not sure what the wide field objectives go up to but think it's 30mm but the objectives for these will probably have 25mm dia threads on them rather than the usual RMS 20.32mm dia ones. RMS types can go higher in some cases than the 20mm mentioned but I'm not sure how large the various Nikon CF types can go.

The other dimension that may be of interest is the parfocal distance of the objectives. The distance from the shoulder on the objective to the surface of the subject when it's correctly focused. If the objective has an RMS thread it's likely to be 45mm. On Nikon if it has an M25 thread it's likely to be 60mm.

It's usually possible to find details about any objective on the web. I can't bring myself to kill insects but might try it on gnats etc one day. People have used older objectives in the past that aren't full corrected like the Nikon ones. With these it's a case of putting the shoulder of the objective a certain distance from the sensor plane. There are different standards. RMS, JIS and Leitz. It's usually easy to find the mechanical tube length on the web but the optical tube length is what is needed as the eyepieces focus some way down the tubes. On RMS for instance the optical tube length is 150mm. Also on Zeiss objectives. The optical tube length can be adjusted to tune out certain aberrations. Very old monocular microscopes used to have this built in. If some one wants to try it I'd guess that bellows would be the best answer but a very fine focus adjustment is still needed. I understand some people adapt a microscope. Others buy things that are controlled via a stepping motor.

Nikon have made a number of styles of objectives that are colour corrected. They are all marked CF and some will have a 150mm optical tube length rather than the infinity types. Those will be marked 160/xx. If the xx ideally needs to be a -. Most lower mag objectives of any make are like that.

John
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