Which 40x and 4x objectives for Nikon Labophot?

[karhukainen]

I have a Labophot with the following 4x and 40x objectives, but I want to keep an eye out for better versions. The main purpose is photo and videography.

- CFN Plan 40x/0.7 160/0.17
- Fluor 40x/0.85 160/0.11-0.23
- E Plan 40x/0.65 Ph3 DL

- E Plan 4x/0.1 160/-
- CFN Plan 4x/0.13 160/-

The CFN Plan 40x produces an insane amount of chromatic aberration. The Fluor is better in that respect, but it is also damaged (correction collar doesn't work) and I can't seem to make it work with DF. Would the CFN Plan Fluor 40x/0.75 be a good option? How much should I pay for one? I don't think I want an oil version because of the hassle. The E Plan is decent for phase contrast, but I'm wondering if some other version would be notably better. It's not a priority though.

Both the 4x objectives are pretty terrible. Lots of chromatic aberration and the image circle is too small for my photography setup (full frame DSLR with Nikon's own photo tube, the PLI 2.5x photo eye piece, another 3d printed tube from Ebay and an extension tube). From what I've read it seems even the CFN Plan Apo 4x might not be much better. Should I try some Chinese cheap version instead or maybe something from the other big brands?

I'm also a bit unsure if it makes sense to keep updating this setup since buying single objectives can be really expensive compared to a full system. I was almost going to buy a Nikon Eclipse e400 from another forum member, but I ran into some unexpected unrelated expenses and missed the opportunity.

[PeteM]

Two of your problems may have more to do with your condenser than the objectives.

1) The 4x objectives, and particularly the 4x CFN .13 n.a. should easily fill a 20mm FN IF you have a suitable condenser - such as the Nikon flip top unit, with the top down. You can also try dropping your condenser if it is a plain Abbe and doesn't quite cover the field. That might help you cover your sensor, if your camera setup is otherwise OK. It sounds like it should be if your adapter is made to the correct distances. It won't help with any residual chromatic aberration, which may also be partly a condenser problem.

2) There's likely a similar problem in trying darkfield with a simple stop and a 40x objective. A .65na objective tends to perform poorly unless used with a dedicated darkfield condenser. It gets worse at .70 n.a. and above. Nikon makes a dry darkfield condenser that should work with a .65 to maybe .75 or so dry objective and an oiled darkfield condenser that should work with a 60 to 100x oil iris objective.

As for the "insane" chromatic aberration of the CFN 40x. .70 n.a. objective, perhaps you have a bad copy? Others have complained of some aberration, despite the "chrome-free" claim, though I've found these objectives to be pretty decent. I've also used their Fluors and Plan Fluors. Visually, to me, they're about the same as the CFN 40x .70 n.a.. in brightfield. The Fluors, of course, have advantages deeper into the UV range for fluorescence.

A Fluor, unless marked Plan Fluor also won't have as flat a field - an issue you might overcome with focus stacking if you find a good one. The next step up would be a fairly pricey Plan Apo - hopefully a good one without oil intrusion, as is currently being discussed in another thread.

You may also want to revisit your camera adapter to see if the 2.5x Nikon relay objective is good and sitting at the proper distances above the objectives and to the camera.

[karhukainen]

Two of your problems may have more to do with your condenser than the objectives.

Thanks, Pete. I have two condensers, the Nikon 1.25 phase condenser and Nikon Abbe 1.25. The field of view seems same with both. I'm pretty happy with my other objectives which include a Nikon Plan Apo 20x and a Fluor 10x. I also have an CFN Plan 20x and it produces a lot of chromatic aberration as well. On the other hand, I have no idea what kind of performance I should expect from this scope and each of the objectives, especially compared to a Nikon infinity system.

1) The 4x objectives, and particularly the 4x CFN .13 n.a. should easily fill a 20mm FN IF you have a suitable condenser - such as the Nikon flip top unit, with the top down. You can also try dropping your condenser if it is a plain Abbe and doesn't quite cover the field. That might help you cover your sensor, if your camera setup is otherwise OK. It sounds like it should be if your adapter is made to the correct distances. It won't help with any residual chromatic aberration, which may also be partly a condenser problem.

I would say the bigger problem with the 4x is still overall bad performance.

2) There's likely a similar problem in trying darkfield with a simple stop and a 40x objective. A .65na objective tends to perform poorly unless used with a dedicated darkfield condenser. It gets worse at .70 n.a. and above. Nikon makes a dry darkfield condenser that should work with a .65 to maybe .75 or so dry objective and an oiled darkfield condenser that should work with a 60 to 100x oil iris objective.

As for the "insane" chromatic aberration of the CFN 40x. .70 n.a. objective, perhaps you have a bad copy? Others have complained of some aberration, despite the "chrome-free" claim, though I've found these objectives to be pretty decent. I've also used their Fluors and Plan Fluors. Visually, to me, they're about the same as the CFN 40x .70 n.a.. in brightfield. The Fluors, of course, have advantages deeper into the UV range for fluorescence.

The phase contrast condenser has a DF stop. Maybe the copy is bad, but then again all my CFN Plan objectives would probably be bad copies. I think they are likely decent enough for viewing through the eyepieces, but I always use a camera. I also have two photo eyepieces (the PLI 2.5x and if I remember correctly, a CF-PL 2.5x) which both seem fine and perform almost similarly.

[Phill Brown]

Something is out of alignment.
Wrong bulb or LED "upgrade".
Unlikely to be the objectives.

[viktor j nilsson]

The CFN 4x in particular should give an really clean image when used properly. It does seem like something is off.

[karhukainen]

Something is out of alignment.
Wrong bulb or LED "upgrade".
Unlikely to be the objectives.

The scope has been retrofitted with LED by the previous owner.

If anyone has photographs taken through these objectives, I would very much like to see how they look.

[PeteM]

Was it a DIY or commercial LED retrofit? I've had good luck with Saul's units and also the RetroDiode.

[karhukainen]

Was it a DIY or commercial LED retrofit? I've had good luck with Saul's units and also the RetroDiode.

I believe commercial, although it hasn't been installed very well (just seemed sloppy). There's some flickering on low power, but otherwise it appears to work fine as far as I can tell.

[Phill Brown]

If you like yellow and blue fringing LED is an upgrade.

[karhukainen]

If you like yellow and blue fringing LED is an upgrade.

The CFN objectives produce purple and green fringing, and the Fluor objectives some yellow and blue but it's not nearly as bad.

[PeteM]

My guesstimate is that the three likeliest problems are:

1) Inability to get both good Kohler illumination and a wide enough image circle. One would expect color fringing at the very edges of the illuminated field, but with that mostly outside the field of view with a proper illumination system, the field diaphragm closed just beyond the field of view, and a good quality condenser set up for Kohler. Your LED may not be right. The system may not be collimated and aligned, rendering the field and aperture irises ineffective. Those irises may not be properly adjusted. Finally, the entry-level Nikon Abbe condensers are more prone to color fringing and with a smaller illuminated field of view than some higher-end ones.

2) Your camera adapter may be slightly off. It should be parfocal with the eyepieces and provide a full field of view. A picture of your setup might help to see which versions of Nikon's photo tube, eBay tube, and 3D printed adapter you have. Could be that focus is slightly off, leading to aberrations and/or poor field coverage.

3) Lastly, problems with most of your objectives and particularly the CFN. It could also be that the 40x CFN is OK, but the stuck correction collar in the 40x Fluor is somehow set as somewhat of a stop that cuts of stray light - making it look a bit better??

[Phill Brown]

Close and focus on the Kohler iris.
There will be coloured edges.
LED is the cause not the objective.

[karhukainen]

Close and focus on the Kohler iris.
There will be coloured edges.
LED is the cause not the objective.

There are but the colours vary according to the objective. I can almost get rid of the edges when everything is properly aligned, especially with the Plan Apo and Fluor objectives.

[karhukainen]

My guesstimate is that the three likeliest problems are:

1) Inability to get both good Kohler illumination and a wide enough image circle. One would expect color fringing at the very edges of the illuminated field, but with that mostly outside the field of view with a proper illumination system, the field diaphragm closed just beyond the field of view, and a good quality condenser set up for Kohler. Your LED may not be right. The system may not be collimated and aligned, rendering the field and aperture irises ineffective. Those irises may not be properly adjusted. Finally, the entry-level Nikon Abbe condensers are more prone to color fringing and with a smaller illuminated field of view than some higher-end ones.

2) Your camera adapter may be slightly off. It should be parfocal with the eyepieces and provide a full field of view. A picture of your setup might help to see which versions of Nikon's photo tube, eBay tube, and 3D printed adapter you have. Could be that focus is slightly off, leading to aberrations and/or poor field coverage.

3) Lastly, problems with most of your objectives and particularly the CFN. It could also be that the 40x CFN is OK, but the stuck correction collar in the 40x Fluor is somehow set as somewhat of a stop that cuts of stray light - making it look a bit better??

I added a few setup photos.

The 3D printed tube from Ebay was bought from newhopper (or something like that). I just realised that the tube has two parts and the bottom one doesn't fully screw into the top part, which might explain why I need the 13 mm extension tube as well. Without it there are black corners below 10x. It doesn't affect the image quality, though. The system is parfocal. I never suspected that achieving proper koehler illumination would be a problem because everything seems to work fine in that sense. Dropping the condenser helps with vignetting when I'm using the 4x objective, but the green/purple fringe that I associate with CFN Plan Achromats still persists, and the image quality drops significantly towards the edges.

The correction collar on the 40x Fluor isn't stuck, but there's another problem that I described here: viewtopic.php?f=5&t=19057 Using it is a pain, and I haven't been able to use the objective for darkfield (I just get image that looks like brighfield).

[Phill Brown]

Close and focus on the Kohler iris.
There will be coloured edges.
LED is the cause not the objective.

There are but the colours vary according to the objective. I can almost get rid of the edges when everything is properly aligned, especially with the Plan Apo and Fluor objectives.

100% what I would expect from an LED with a frosted glass diffuser.

[karhukainen]

Close and focus on the Kohler iris.
There will be coloured edges.
LED is the cause not the objective.

There are but the colours vary according to the objective. I can almost get rid of the edges when everything is properly aligned, especially with the Plan Apo and Fluor objectives.

100% what I would expect from an LED with a frosted glass diffuser.

I'm not saying the LED isn't contributing to the issue, but I've used other microscopes and this doesn't look dissimilar.

[Phill Brown]

The light source is the cause.
LED systems with pretend Kohler will have similar aberrations.
It's just the way things are.
The objective can't fix the problem.
It could be cost effective to pick up a Labophot 2 with a dead PSU but working fine focus and add a variable 12v 5A DC supply.
There are 2 filters between the collimator and the iris that deal with the square filament 30w halogen.
The compound lens filter gives a sparkle effect in DF that is easier to live with than the fringing aberrations.
Good luck with whatever you choose to do.