Problem achieving focus on my 100X objective

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geo_man
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Joined: Mon Jan 21, 2019 4:54 pm

Problem achieving focus on my 100X objective

#1 Post by geo_man » Mon Jul 01, 2019 8:02 pm

Hi all, after reading Roldforf's recent post on 60X objectives, I decided to ask about an issue I'm having with my "new to me" Reichert Microstar 410. I can't seem to achieve focus on my 100x CAT 1759 1.25 NA objective (using prepared Amscope sides). Seems like I can't get close enough to the sample. I tried oiling the condenser and objective but still no luck. I was thinking the cover slip is too thick, but I'm skeptical of that. My 40x works fine. Any ideas? Thank you!

Hobbyst46
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Re: Problem achieving focus on my 100X objective

#2 Post by Hobbyst46 » Mon Jul 01, 2019 8:32 pm

Why not prepare your own test slide ? start with a slide of 1.05-1.1 mm thick. Place a small drop of glycerin (or water if you do not have glycerin) on the slide. Place the tiniest amount of dirt (brown/yellow soil, red road dust, not sand) - less than a pin's head - in the drop, and mix with a pin or toothpick to spread. Cover with a cover slip no 1.5 (thickness 0.17mm), press gently to form a very thin layer. The liquid need not reach the rims of the cover. Glue at least two opposing corners of the coverslip to the slide, with nail polish (fast dry type). Let dry (verify that it is dry !!). Try to focus on it with the 10X or 40X, then add immersion oil and try the 100X.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

geo_man
Posts: 119
Joined: Mon Jan 21, 2019 4:54 pm

Re: Problem achieving focus on my 100X objective

#3 Post by geo_man » Mon Jul 01, 2019 8:54 pm

Thanks Hobbyst46 for the good advice; I will do so and report back once done:)

Sauerkraut
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Re: Problem achieving focus on my 100X objective

#4 Post by Sauerkraut » Mon Jul 01, 2019 9:17 pm

I seem to recall in microbiology class, we used to fix stained bacteria on slides and view them at 100x oil without a cover slip. That might be something to try if the above doesn't help.

Personally, I've been disappointed with depth of field using 100x and exchanged the objective with a 20x, which is a very pleasing magnification imo.

Roldorf
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Location: Northern Germany

Re: Problem achieving focus on my 100X objective

#5 Post by Roldorf » Mon Jul 01, 2019 9:24 pm

I have never had a problem with focus on the 100x. Drop of immersion oil on the cover slip and 'bob's your uncle' as the saying goes, however the sample needs to be very thin otherwise you will have problems.
Alan
Bresser Science Infinity 4x 10x 40x 60x 100x oil. Canon EOS 4000d
Stereo Microscope Optika SFX 90

Hobbyst46
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Re: Problem achieving focus on my 100X objective

#6 Post by Hobbyst46 » Mon Jul 01, 2019 9:28 pm

Just a clarification : 1) it is not very important if the liquid reaches the coverslip rim or not. only important that the liquid layer is thin.
2) wait for it to dry - I meant the nail polish should dry ! lest it could adhere to the objective.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

Roldorf
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Location: Northern Germany

Re: Problem achieving focus on my 100X objective

#7 Post by Roldorf » Mon Jul 01, 2019 9:29 pm

Having said that when I first got the scope there was supposed to be immersion oil included and there was a 5ml bottle of oil in the package. I used it and couldn't get focus. It turns out that the oil was for the mechanical parts of the scope and was not immersion oil. I bought some and I have had no problems since. :lol:
Alan
Bresser Science Infinity 4x 10x 40x 60x 100x oil. Canon EOS 4000d
Stereo Microscope Optika SFX 90

geo_man
Posts: 119
Joined: Mon Jan 21, 2019 4:54 pm

Re: Problem achieving focus on my 100X objective

#8 Post by geo_man » Mon Jul 01, 2019 10:24 pm

Well I followed Hobbyst46's advice and it does seem to focus properly. I guess it's finicky but ok. Oil was needed on top and it might have been a bit better with the condenser oiled as well. Thanks to all!

apochronaut
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Re: Problem achieving focus on my 100X objective

#9 Post by apochronaut » Tue Jul 02, 2019 1:48 pm

The W.D. with that objective is .10. That means that if the sample/cover slip thickness is over .27, then your focus point will be right on top of the cover slip or not.

Budget priced slides are fairly sloppy when it comes to how thick they are. Most are designed for educational applications and for amateurs where a 40X objective is the maximum they will use. Thicknesses can be as great as .40 or more. Most are unsuitable for oil immersion use and most failures using an oil immersion objective are due an excessive sample/cover dimension.

The nominal cover glass thickness of typically .17, includes the sample thickness, so only with the thinnest smears should a .17 cover be used with objectives that have a slight w.d. . With something like a pond water sample, thinner slips of .12 or so are valuable.

geo_man
Posts: 119
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Re: Problem achieving focus on my 100X objective

#10 Post by geo_man » Tue Jul 02, 2019 4:18 pm

Thanks very much Phil, I will get some thinner cover slips and explore further!

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