objective abberations...

[René]

Here's a comparison between 2 high end lenses from the 160mm era. The DPlanApo UV 20x/0.8 (oil immersion) always gives a blueish tint to the specimen. In routine use it is ok, but certainly not for photography!! The dividing Microcystis cells are only 5 um across, so this is really pushing it to the edge, but the question remains whether this lens could be classified as apochromatic...


Olympus SPlanApo 20x NA0.70


Olympus DPlanApo 20x NA 0.80 oil

Camera: ImagingSource DFK72, 5Mp cmos via 2.5xNFK/0.3x relay. Raw crop from the middle part of the field. Inverted microscope, condenser NA 0.5, Luminus LED 4500K.

Best wishes, René

[René]

Just came across a message by Charlie on specifically this topic, he mentions: 'So I suppose it is just a characteristic of that objective, caused by the need to extend transmittance into the UV'

So I've added 2 more images, where I used a 550nm interference filter. I haven't used a monochrome camera, but kept all colour levels at 100 and postprocessed images by setting saturation to zero, increasing contrast heavily and gamma slightly (but with the same amount between these images). Can't distuinguish anymore between the lenses.


SPlanApo 20x/0.7


DPlanApo 20x/0.8 oil


BTW, The other of the DPlanApo UV series shows similar, but nowhere near this amount of abberation. No reason not to buy them. But not this 20x.

René

[discomorphella]

Hi Rene--

How well do you know the provenance of your DPlanApo 20? It doesn't take much to mess up an objective so that its no longer performing at the parts-per-thousand correction level that a planapo lens system is designed to. One good drop at some point in its life could do it...
If you can find a large diatom with some multiply-repeated structures to image it will be much easier to use imageJ or matlab or similar program to compare the respective resolving power of your objectives.

Regards,

David

[René]

Hi David,

No, it is inherent to the lens design. I have 5 dplanapo 20's and 9 splanapo 20's in the lab, they all behave the same. Imaging is on inverteds with sedimentation chambers with coverslip bottom, ie pretty much ideal. Charlie noticed the same effect. It isn't the normal chromatic abberation, it doesn't increase or decrease towards the edge of the field view.

Best wishes, René

[Pau]

...DPlanApo UV 20x/0.8 (oil immersion)...

Like Charles, I think that it may be related to the improved desing for UV transmission for epifluorescence.
Digital sensors are quite sensible to UV and it is usually rendered as blue
If you have a good UV cut filter you can test it in a color picture.

[Charles Krebs]

I've had two of them (DPlanApo UV 20x/0.8 oil immersion). Both looked new and both produced nearly identical results. I still have one and really love it for observation, but do cringe a little when I need to use it for a picture. (I keep it around for the times a slide has been oiled for 60X or 100X and I want to drop to a lower power objective). I was able to ask an Olympus microscope optics designer about this is a few weeks ago. I knew René had experienced something similar, so I sent him an email. So I don't need to type it all again here is the text:

I had a chance to discuss a few things with two Olympus microscope optical designers over the weekend. A bit of Japanese/English language barrier but not too bad. (These guys are pretty young... I doubt this one gentleman was more than about 6 years old when the BH2 objectives were designed around 1980 or so).

While he was not very familiar with this particular objective, I described the unusually strong, tight cyan/red color aberrations I have experienced (and as I recall you also have experienced). I mentioned that it is a wonderfully bright and sharp objective (I really do like observing through it) but when it comes to photography and color correction with "white" light it does not seem to compare well with the S Plan Apo 20X. I also specifically asked if, perhaps, there was a "special" immersion oil that was to be used with it.

As best I could understand, he said it was very difficult to offer and correct for UV transmission along with the "full spectrum" of white light. He said there were only two optical glasses they could use for this purpose, and that when the UV range is "added" they can't correct color aberrations as completely as when there is no need for UV transmittance. So if there is no specific reason that UV wavelengths are needed, you can have superior color correction in a "normal" Plan Apo. (Hopefully I understood his answer correctly).

I also have a D Apo 10X UV, and while I can see a hint of similar cyan/red on certain sharp edges, it is nowhere near as noticeable as on the 20x. And "Jacek" just posted a few shots taken with the 100X UV, and there again I can see only a slight hint compared to what I see with of the 20X (I've tried 2 different samples). No way of knowing if there was any post-processing to clean it up however.

So I suppose it is just a characteristic of that objective, caused by the need to extend transmittance into the UV.

Again, this was a casual conversation, and I hope I understood him accurately.