4x Objective Recommendations.

[SteveGreen1953]

Hello all,

First, I would like to thank everybody for the tremendous amount of knowledge that I have gleamed by lurking here. I didn’t realize that the techniques commonly practiced by the members were even possible until I stumbled onto this site.

I had hoped to be able to contribute something to the forums before asking any questions, but so far my ignorance has precluded any opportunity for that. I have a couple of macro lenses and Kenko tubes that have provided many hours of entertainment over the years. But, after seeing the incredible photos posted here I decided that I would really enjoy shooting smaller. To that end I started buying various pieces/parts as I was able to find them in my price range. So far I have acquired a Canon FD bellows, a Nikon 50mm f2.8N enlarger lens (I’m still waiting for one last piece to reverse mount the Nikon on the bellows), the adaptors to mount a microscope objective, and just today purchased a small X-Y micrometer stage.

My question concerns the last piece of the puzzle, the lens.

A friend loaned me a very inexpensive (the entire microscope with 3 objectives was less than $150) no-name 4x objective. About 90 degrees of the lens refused to focus, but the other 270 degrees gave me a taste of what was possible, and proved that this is the range of magnification that I would be happy with for the immediate future. The $20-$25 shipping cost of the Nikons on ebay are out of my price range, the recommended conjugate objective from Edmund Optics is out-of-stock until late June, and the AmScope 4X PLAN Achromatic had doubled in price when I went to purchase it (it has since come back down to the original $25 price, but their opportunistic behavior rubs me the wrong way.)

Anyway, I ran across this Chinese objective and was wondering if anybody had any experience with it: http://www.ebay.com/itm/320873640047?ss ... 1438.l2649.

I’m looking to shoot anesthetized/dead bugs and am seeking something similar to the El-Nikkor enlarger lens--not necessarily the best, but very good. I’d rather spend enough to accomplish that goal the first time rather than needing to spend the money twice. If it’s realistic, I’d prefer to spend no more than $150 USD, but all suggestions will be considered.

Any guidance in this matter would be very much appreciated.

Cheers! Steve



My friend's objective extended about 120mm with the worst part turned to the lower right and the image cropped to exclude stacking artifacts.



A shout-out to Mr. Ramos from the old Photobucket forums.

[canonian]

Hello Steve,

You probable want to read an excellent post on this matter: Lenses for use at 4-5X on an APS-sized sensor
I bought and very much like the Cnscope Plan Achromatic, both in price and performance.
Here are some of my examples, the first two 'NoName 4X Plan' images.

[SteveGreen1953]

Thank you Fred,

I very much appreciate you taking the time to answer.

I have read Rik's thread time and again while trying to make this decision.

Your photos are very nicely done. It's good to know that that little lens will perform. I noticed it when searching the Cnscope store, but was attracted to the one I listed for two reasons. First it's a metallurgical and consequently the second reason, it doesn't need a cover slip.

Perhaps I'm over thinking this.

Thanks again, Steve

[Pau]

..., but was attracted to the one I listed for two reasons. First it's a metallurgical and consequently the second reason, it doesn't need a cover slip

For this magnification (NA under 0.30) coverslip correcton doesn't matter at all. Both marked /0, /0.17 or /- are equally adequate.

[ChrisR]

Steve the Cnscope lens comes out well enough vs others of similar NA, certainly for the money.
It'll beat an enlarger lens at 4x and higher, without having to scrutinise pixel-level detail, because the effective aperture of those is against you.
It may start beating them at lower magnifications, I haven't tried!
If it's a "160" objective it's designed for 150mm between rear flange and sensor. If you go off that you'd expect some measure of degradation, but more of a problem going short would be a diminishing image circle, an issue which obviously depends on your sensor size.
That's not a problem with enlarger lenses!

[rjlittlefield]

For this magnification (NA under 0.30) coverslip correcton doesn't matter at all. Both marked /0, /0.17 or /- are equally adequate.

Just to hammer this point home...

A good measure of how much effect the cover slip has is to look at the wave error that is introduced by having it versus not having it. A lens is generally considered excellent if it has less than 1/4 wave error (0.25). With a lens of NA 0.10, adding or removing the cover slip changes the wave error by about 0.0014 -- roughly a factor of 100 smaller than would matter.

The effect rises steeply with increasing NA, so that at NA 0.30 the added wave error is about 0.10 and at NA 0.40 it goes to 0.30. That last value is definitely enough to see if you look closely, but it won't immediately grab your attention.

--Rik

[SteveGreen1953]

Thank you Pau, ChrisR, and rjlittlefield. I very much appreciate your responses.

I’m afraid that I was a bit clumsy when I mentioned the El-Nikkor 50 f2.8N. I only meant that while there are better, much more expensive enlarger lenses available, the little El-Nikkor does a credible job for a very reasonable price. I didn’t intend to compare it to a microscope objective in any way other than its image/cost ratio.

Apparently, I suffered a serious brain fade while working my way through the wealth of information on the equipment threads. This evening while once again researching metallurgical vs biological lenses I came across several references to the cover slip being unimportant at NAs below .3. I apologize for wasting time rehashing this issue.

Thanks again! Steve