A O Spencer 25X eyepieces

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Grahame
Posts: 99
Joined: Fri Jun 29, 2018 7:42 am
Location: New Zealand

A O Spencer 25X eyepieces

#1 Post by Grahame » Mon Jun 24, 2019 10:15 am

Hi folks,
Does anyone have any experience with these eyepieces?
I can't find very much about them on the net.
Thanks
Last edited by Grahame on Mon Jun 24, 2019 11:59 am, edited 1 time in total.

apochronaut
Posts: 3569
Joined: Fri May 15, 2015 12:15 am

Re: A O Spenser 25X eyepieces

#2 Post by apochronaut » Mon Jun 24, 2019 11:33 am

Eyepieces such as those were made to fill a market requirement for a specific purpose, usually in some application where an occasional higher magnification of specific details is necessary, when using a scope that is normally set for a pretty low magnification. B & L had a 30X eyepiece.
When used in a zoom microscope at the base zoom level or with a fixed magnification model such as the #571 1X model, they give you an opportunity to bump your magnification to somewhere around 20-25X, without overstepping the boundaries of optical laws. AO must have felt that there would be a big enough demand for one, that they made a good one. For a 25X , they are exceptional , having a W.F. equivalent to that with the same magnification one would get using a 10X on a zoom scope, however high magnification eyepieces always have a smaller eye relief. This one is 13.2mm, so not too bad, while the 2 10X W.F.s available are 18.2 and 18.6 mm.

I don't have a 1X fixed model scope to compare with but I suspect that the resolution at 25X in a 1X scope might be slightly superior to the same magnification achieved in a zoom scope with 10X eyepieces. .....don't think there would be much advantage at anything higher , though. I have a set and I can count the number of times I have needed to use them on one hand. I recall that they were necessary to just barely reveal an important detail on some aquatic mite larva that I found on a water bug.

I hope I have the correct eyepieces here; cat.# 186. You have used the Spenser brand( actually, should be Spencer), which I don't think would have been marked on even the earliest of those eyepieces. There may have been a 25X compens, from the past. I can't recall seeing one and there was a 2.5X compens. The application of those two, would be entirely different.

Grahame
Posts: 99
Joined: Fri Jun 29, 2018 7:42 am
Location: New Zealand

Re: A O Spenser 25X eyepieces

#3 Post by Grahame » Mon Jun 24, 2019 11:58 am

Thanks apochronaut
Thats useful info.
Yes they are the 186
Good to know they are decent optically.
Like you I doubt they will be used often, but if I can pick them up at the right price they will be useful to have around.
I thought I had Spencer spelt wrong :(

wabutter
Posts: 55
Joined: Thu May 09, 2019 12:27 am

Re: A O Spencer 25X eyepieces

#4 Post by wabutter » Tue Jun 25, 2019 1:12 am

The other aspect of the 25X eyepiece came about when there was a need to maintain the 4 inch working distance of the StereoStar Zoom microscope and provide a higher mag. Instead of using a 2x aux lens. Also, remember that using the lower zoom or fixed mag on the stereo also provided a greater depth of field at a comparable total magnification as using the 10x eyepieces.

Wayne

apochronaut
Posts: 3569
Joined: Fri May 15, 2015 12:15 am

Re: A O Spencer 25X eyepieces

#5 Post by apochronaut » Tue Jun 25, 2019 12:18 pm

That's a good point. They are very useful for manipulating the subject. Good for basic dissecting, liberating small sections of a subject for further examination elsewhere.
It should be pointed out too that at an equivalent total magnification, 25X eyepieces will exhibit any out of collimation condition worse than a 15 or 10x eyepiece will. There are situations where a 10X pair in a slightly out of collimation microscope will still function well for most people but switching to 25X eyepieces will render the instrument unusable, even if the zoom ratio is reduced by 2 1/2 times.
The collimation needs to be spot on.

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