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Posted: Thu Jul 25, 2019 12:53 pm
Hi all! I'm here again for the third time in a row! (I'm sorry for this, I've got a lot of questions and just want to be sure about my purchase)
The scope i'm planning to buy comes with a 4x, 10x, S40x and S100x oil immersion objectives. In addition I want to buy an extra objective to put in the quintuple revolver, but I'm debating whether to buy a 20x or 60x objective. I feel like 20x won't be enough to really get a better look at smaller protists and diatoms. On the other hand I've read some things about S60x objectives on this forum about the quality not being amazing.
Which one should I pick? Thanks in advance!
Posted: Thu Jul 25, 2019 1:28 pm
I find a 20x objective very useful. Since you asked.
Posted: Thu Jul 25, 2019 1:41 pm
Ditto Ed' - my nosepiece holds a 4x, 10x, 20x (recently acquired), 40x and a 60x - the 100x I have is 'on the side' for those 1.20n.a. moments!
Posted: Thu Jul 25, 2019 2:24 pm
I'd MUCH rather have a good 20x than a good 100x. Amateurs rarely need that much magnification. Good 60x objectives are nice, but more rare so more costly for good ones, and generally not necessary. I removed the 100x objectives from my seven BH-2 outreach scopes several years ago. They all have nice DPlan or SPan 20x objectives.
Posted: Thu Jul 25, 2019 3:12 pm
I think the gap between 10x and 40x is too steep. A 20x gives you a smoother slope!
I have a 6.3x, 16x, 25x, 40x and 63x in my 5 objective turret.
Agree with Tom Jones about the 100x. Keep it in a drawer until you need to use it.
Posted: Thu Jul 25, 2019 4:11 pm
One more vote for a 20x. Enough magnification for many plant cells and protists. Reasonable depth of field. And for whatever reason, many of them (American Optical, Nikon, Olympus) are just great objectives. 10x - not enough. 40x - surprisingly sometimes not as good an image despite the higher magnification. Even the 20x plan achro imports, both finite and infinite, are often very good. It's a shame, IMO, that the 20x objective is not included with most basic microscopes.
I've not been super impressed by various 60x dry objectives I've tried. And while 60x oil objectives can be spectacular (with NA's around 1.4 and $$$ prices), you'll need careful specimen prep (thin, thin) to avoid depth of field problems.
To echo Tom Jones' comment about use with younger users, the combination of sharp eyes and a wider field of view makes a 20x great for many things. The shallow depth of field from 60x to 100x almost assures objectives will be run into cover slips (or worse) in a casual viewing.
Posted: Thu Jul 25, 2019 4:21 pm
It all depends on what you are looking at and to some degree , who made the objectives.
A 20X is very useful to bridge the rather large gap between the ubiquitous 10X and the ubiquitous 40X, so for numerous larger specimens you have a reasonably smooth flow , from 4-40X.
If you need to see some finer details of some very small things, 100X with as high an N.A. as is possible is indispensable. I do a lot of work with cultures, water.....a lot with bacteria. The meek will inherit the earth after all. These days , I have a 6 hole nosepiece, so my flexibility is very high but way back I worked with a 3 hole, then for some time with a 4 hole and then a 5 hole. I made good use of 15X eyepieces but only those that performed on the same level as good 10X W.F. eyepieces do. You don't have to get into empty magnification, if you use them properly and choose good ones. That means within a shade of the real field that the 10X shows and with the same eye relief and planarity.
In a 4 hole : 4X 10X 40X and 100X objectives gives useful wide field magnifications of 40X, 60X, 100X ,150X, 400X, 600X and 100X, even with average N.A. achromats of .10, .25, .65 and 1.25.
In a 5 hole , screwing in a 20X would add 200X and 300X into that nice array. So, a 60X really isn't needed at all, with this caveat. If you could get a higher N.A. version for your scope, it might be a consideration, .90 or higher if you were interested in some kinds of finer details. Y If you want that , with the 15X eyepieces and a high N.A. 60X, you can do acceptable 900X without oil.......but you will need light.
There are 2 other considerations.
1) Just who's objectives are we talking about? Just because two objectives are both 60X .80, it in no way means that they deliver the same quality of image. N.A. is an arbiter of resolution but it isn't the only arbiter of resolution. Then there is contrast, colour correction and the precision of manufacture and assembly. So , from one mfg. a 60X .80 objective might be a good idea and from another, definitely not.
2) The magnification/ N.A. ratio is also important. The closer a poorly made objective gets to a figure of 100 when you divide the magnification by the N.A., the higher is the chance that it will fail some critical quality tests. Cheaper objectives with high ratios are on the cusp. A 20X .40 objective has a ratio of 50, so if two objectives from the same mfg. are being considered the likelihood of a 20X .40 performing within spec. when compared to a 60X .80, is higher.
Case in point to illustrate 1) above. Two objectives below.
A) made in 1983 63X .80
B) made around 2015 60x .80.
All variables in the image captures were equal, except they were manually focused and likely exposed at very slightly different shutter speeds, since an aperture preferred setting was used. They were also photographed using different 10X relay lenses, both of them chosen because of their excellent corrective compatibility to the objective.
Posted: Thu Jul 25, 2019 4:42 pm
I have just been lucky to observe some slides with 4X-10X-40X-60X on an Olympus BH2. The 60X is a dry objective, a prestigious Olympus 60X0.9 DPlanApo. Resolution is OK, but not importantly better than that of the Zeiss 40X0.75. The working distance is shallow and brightness is quite low. This is not the case with the Zeiss 63X1.4 Planapo or 63X1.25 Neofluar: they are immersion lenses, and yield amazing images (albeit the WD and brightness are low).
Note: The Zeiss are used on a Zeiss stand, the Olympus on an Olympus stand.
So I would prefer a 20X over 60X dry objective.
Posted: Thu Jul 25, 2019 4:55 pm
I think i'm going to go for the 20x, I'll always be able to upgrade with a 60x objective in the near future (if I can find one with oil immersion that is!). All the extra information sure helped a lot, thank you all!