Microscope Objective 4x

[colinbm]

I have purchased a cheap Chinese 4x Microscope Objective Lens.

This covers 8mm x 6mm on a full frame camera & is a very simple set-up with a 160mm x M42 tube length & the camera on a focusing rail.

Soon I will try it out for UVA photography & UVIVF.

First some baby steps.

The first photo is of an 8mm section of a steel ruler.

The second photo is a 8mm section of a leaf with back lighting.

 

 

 

[nfoto]

It is likely designed for a coverslip thickness of 0.17mm. If this is dropped, you get spherical aberration and curvature of field. Which is quite obvious in the first image.

[nfoto]

Going the photomacrographic way, the Laowa 25mm f/2.8 provides 2.5-5X magnification with very good image quality. The Mitakon 20mm f/28 is much cheaper but only gives 4-4.5X.

 

A finite focus microscope objective relies upon the secondary optical system, the ocular, to give flat field correction.

[ulf]

Microscope objectives with a 4x magnification normally has a rather low NA in the range of 0.1-0.15.

Then the effects of a missing coverslip is not that big.

 

Field curvature is normally not that important either for our rather 3-dimensional motifs that need photo-stacking anyway.

Most finite Nikon Plan microscope lenses have most of their optical correction already in the objectives, making them more suited to be used as camera objectives.

Unfortunately they do not pass much UV-light and are mostly usable for VIS.

 

For our type of reflected light-photography it is important to find objectives with a long working distance.

 

Birna, do the Laowa 25mm f/2.8 have any useable UV-reach?

[ulf]

One of these, mounted in front of a camera lens could be fun, (for VIS only).

Nice price:

https://www.ebay.co.uk/itm/174550704396?hash=item28a408610c:g:pNYAAOSwQC1fzy4l

[nfoto]

Ulf, the Laowa 25 just barely dips into UV so unfortunately not the solution for low magnification UV work. A pity as the lens itself is highly useful and it has become my standard tool for the 2.5-5X range.

[colinbm]

Thanks Birna & Ulf.

If I am going to use cover slips I'll need a good supply of them.

[colinbm]

I picked a small flower from a running weed in my yard.

The flower is about 8mm across, so I did a shoot in the sun so I could see what I need to do in the set-up etc.

Some very poor images unfortunately as it was windy, but I wanted to see what to expect & particularly how the 4x microscope objective preforms in UVA, which I am pleased with.

 

First an overall of the plant in visible sunlight with a 28mm lens.

 

 

 

Second of the flower head in visible sunlight with a 300mm lens.

 

 

 

Third of the flower head in visible sunlight with 4x microscope objective lens.

 

 

 

Forth & last, sorry for the poor image but the wind did it. At least it proves the 4x microscope objective is UVA capable, as the camera is.

 

The flower head in UVA sunlight with a BaaderU & 4x microscope objective.

 

[Andy Perrin]

Can you add a coverslip in your setup like Birna suggested?

[colinbm]

This cover slip, can I add it like a filter glass in front of the lens ?

It is a bit hard to cover slip a flower ?

[colinbm]

Also next time I will do this inside with artificial lights & use Zerene Stacker.

[Andy Perrin]

I think yes? I do not know microscopes well though.

[dabateman]

I wouldn't worry about a coverslip.

Just have fun with it.

Make sure you have lots of light shinning down or through your subjects.

You can also push it to your liking with longer or shorter tubes.

Sure the images won't be like a Zeiss. But you said it was a cheap Chinese 4x.

I have a cheap Chinese 4x Plan that I paid too much for, around $50. Had I searched I could have gotten it for $10.

A great Nikon or Leitz or Zeiss objective will cost hundreds to thousands just for the objective. But my microscope science career is mostly over and its time for fun.

 

Just play with it and enjoy it. You first ruler shot is a great start. Just focus on learning how to focus it and give it more light than you think.

 

You can even try to work out its best light focal cone if you want, to maximize its aperture and sharpness.

[colinbm]

" light focal cone "....that is a new word for me...

I was wondering about putting smaller apertures behind the objective.

[dabateman]

Yes I am not using correct terminology. Trying to simplify something.

A microscope has a light source, a diaphragm (controls the shape and amount of light like a lens aperture), a condenser (a lens that focuses that light on to the subject at the peak focus point for your objective), then a sample holding stage and your objective.

The condenser is what I was referring to badly. You can optimized the light so that it focus in the peak plane for your specific objective and broaden after that point to just fill the exact diameter of your specific objective front glass opening. That would be highly customized to your objective lens and give you the best images.

 

[nfoto]

Have a look at Köhler illumination. That's the principle to aim for in microscopy.

[colinbm]

Thanks Birna, now I understand it.

I'll probably be doing mostly reflected light, but it is nice to know what is needed for light transmitted through the specimen.

[colinbm]

https://rsscience.com/kohler-illumination/

[ulf]

I think yes? I do not know microscopes well though.

Yes that makes sense, for eliminating the aberrations Birna was mentioning.

[ulf]

Have a look at Köhler illumination. That's the principle to aim for in microscopy.

Only if the object to examine is transparent.

There are other ways to illuminate to inspect non transparent samples.

Some of them needs a long working distance to avoid shading the illumination by the lens.

[colinbm]

A M42 aperture arrived today, so I placed it behind the 4x microscope objective, the smallest aperture is 2mm.

This makes an improvement & an increase in depth of field.