Some information missing on objective - what to use

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Some information missing on objective - what to use

Post by kpassaur »

I am as new at this as you can get. Not photography, just using a microscope objective. I have read numerous articles and I was planning on saving for a Nikon 10X infinity objective. I figured that way I could get to 10X and skip testing and playing with everything else as many people say it is a good way to go. However, I found a super cheap Bosch and Lomb Microscope at a flea market and I figured why not try it. Worst case I use the stage on it. Anyway, it came with four objectives:

0.18 Cover Glass
0.09 N.A. Flat Field

0.18 Cover Glass
0.25 N.A. Flat Field

0.18 Cover Glass
0.65 N.A. Flat Field

100X OIL
0.18 Cover Glass
1.25 N.A. Flat Field

I'm sure these are not the best but they don't seem like trash either as they are well made.

However, none of them say anything more such as 160 nor do they have the infinity symbol . So, my question is, do I need to just put these on a bellows (or tubes) and at about what length? If not do these need to be mounted on the end of an existing lens and if so what mm? If neither of the above, should I just cut my losses, and resell it to try and get my money back.

Any help from someone who knows would be greatly appreciated.

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Post by gpmatthews »

Almost certainly 160mm finite tube length objectives

Though we lean upon the same balustrade, the colours of the mountain are different.

Alan Wood
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Post by Alan Wood »

Graham is almost certainly correct. Infinity-corrected objectives almost always include the infinity symbol (8 on its side). Older 160 mm objectives often do not have that number marked.

It should be fairly easy to try the 4x objective. If you have a digital SLR, it's body is probably around 40-45 mm deep, so use bellows to provide another 110 mm extension.

Cut a hole in a piece of card just big enough to hold the threaded end of the objective, and hold it in front of the bellows.

I guess the working distance between the subject and the front of the objective will be somewhere in the 10 to 20 mm range. Just experiment and see if you can get a sharp image.

Alan Wood

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Post by ChrisR »

Note that the 160mm or infinity distance, is the distance to be focused at, sensor side, for best performance.
They'll still give you an image if the distance is wrong, just not as good as the manufacturer intended.

The "error" goes up with NA. You may notice little at NA 0.25.
The same in principle is true of Chromatic Aberration, which is supposed to be corrected in the eyepiece.
Again, they're supposed to be used with a 0.17mm glass coverslip for Spherical Aberration correction, but you won't notice that either at NA 0.25.

So, at 4x and 10x, it's well worth a try.
Chris R

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Post by Lou Jost »

Just look at the microscope. If it consists of an empty tube with an eyepiece at one end and objectives at the other, its objectives (assuming they are appropriate to that microscope) are finite. The eyepieces still may be doing some of the correcting, so the objectives may not be ideal. MUCH better to spend a very small amount of money for a real known-good lens. (Of course you can also spend a fortune; that depends on your needs and your self-control and whether you have a spouse and children competing with your microscopy for resources!)

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Post by Ichthyophthirius »


I found different information on this. Hard to say anything without knowing (seeing) the product generation. The "Flat field" Achromats appear to have been used on microscopes like the Dynazoom. The manual is here:

One source (Pluta), says that the Dynazoom had infinity optics. But looking through the manual, there is no mention of it.

Assuming that it is 160 mm, then the manual states that the objectives require BOTH corrective tube body lenses and corrective eyepieces.

It's worth just trying out the 4x and 10x. They don't require a cover glass. Regular B&L 160 mm objectives have a distance to the intermediate image of 149 mm (instead of the more common 150 mm, but 1 mm makes no difference for image quality).

Regards, Ichty

P.S.: You might actually have a really nice microscope on your hands. Instead of reselling, you could try getting into microscopy :wink:

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I sort have got it to work

Post by kpassaur »

Thanks for the responses.

The microscope is as Ichty mentions a Dynazoom. When I opened up the link he sent it was exactly the same. The unit is old and from what I have seen a common model in universities. This one is pretty beat up but the stage is still worth while and the objectives seem ok. It's sort of hard to tell as the eye pieces are messed up on the microscope and I don't have any slides etc.

I have tried 160mm and 150mm with no success. Perhaps I am doing something wrong - it wouldn't be the first time. I have looked up the flange to sensor distance for canon and it says 44mm, so on my bellows I added 106 and 116 with no luck. Perhaps it was me so I checked with a ruler and it is close provided we are talking to the objective mount not the end of the lens.

I then just mounted the m42 reducing plate directly to the camera with an adapter and it sort of works. The down side is working distance is virtually non existent. I mean I am talking putting my finger nail on the end of the objective and the nail is close to being in focus at the end of the lens (brass portion) I think it would be nice to have at least a few mm of working distance.

Also, on a crop sensor Canon the 4X and the 10X only have a circle, on the 40X it fills the entire sensor. All of them seem to focus a little before the end of the actual lens when mounted directly on the camera (no tubes or bellows)

Any other ideas?

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Post by Ichthyophthirius »


On page 4-5 it says that the working distance is 8.6 mm for the 4x and 2.4 mm for the 10x.

For the 4x you can improvise a test slide by using a clear plastic ruler or writing something using a permanent marker. For incident light you can use a stamp.

One more thing that you could try is checking if it is an infinity objective (just in case). Just mount the 4x directly in front of a camera lens, something between 100 - 200 mm focal length, preferably a prime lens and focussed to infinity.

Regards, Ichty

phil m
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Post by phil m »

The B&L Dynazoom came in two variations. The earlier version was a 160mm tube microscope that was designed to use the B & L 35.7mm parfocal objectives, or any other 160mm objective for that matter.
Sometime into the production of the Dynazoom, B & L introduced the Flat Field objective series. These were a larger size, pretty close to DIN but not really, because they were in fact semi-objectives, with each one corrected to have it's intermediate image completed by a negative telescope lens located just above the nosepiece. This essentially serves as a rear lens for all of the objectives. From that point on the system is infinity but without that negative lens in the system B & L flat field objectives cannot be used on any other microscope. Dynazooms mfg'd. to utilize such objectives are clearly marked Flat Field on the viewing body. The objectives you have are the basic flat field achromats from the 60's. They also produced flat field fluorites, and flat field apochromats for the system.

Later, sometime into the Balplan era, they introduced planachromats and dropped most of the fluorites from their line, probably because the new planachromats( as of mid-70's) were as good as most fluorites. They did introduce at least one new planfluorite( 50x .80 oil) and continued with the flat field apochromats.

The flat field achromats are as good as any other objectives being made in the 60's. The planachromats were a significant improvement, primarily in the areas of colour correction and contrast where they mostly achieve fluorite performance, so any older Dynazoom or Balplan fitted with the flat field optics can be cheaply upgraded with a set of planachromats., or if you can find them, Flat Field Apochromats.

Magnifications of compatible objectives I know of are.
Flat Field Achromats 4x .09, 10x .25, 40x .65, 100x 1.25
Planachromats 2.5x .06, 4x .09, 10x .25, 10x L.W.D. .25 ,20x .50, 40x .65, 100x 1.25
Flat Field Fluorites 50x .85, 100x 1.30 oil ( probably others)
Planfluorites 50x .80 oil
Flat Field Apochromats 7.5x .20, 12.5x .30, 25x.65, 75x 1.2 oil, 125x 1.4 oil (probably

All of these objectives can be used on the Flat Field Dynazoom or the Balplan, as long as the negative lens has been installed.

The actual objectives themselves, because they are semi-objectives are not the magnification that is marked on them, rather , they are that magnification once multiplied by the negative rear lens. Based on patents, it seems that the factor is probably 5X, so the 20x objective is actually a 4x and so forth. I also suspect that there is some further compensation in the negative telescope lens. I can't see them working as a macro lens at all, unless one managed to incorporate the telescope lens into the system in the correct location to the semi-objective.

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