Differences in Amscope 100x iris objectives

[Scoper]

What are the differences between the Amscope 100x darkfield iris objectives other than cost?

PA100X-IRIS $366

PA100X-IRIS-G17 $298

Both are plan 100x and both have irises

Thks

[Scoper]

And they are both 160mm objectives

[Scarodactyl]

Can't really know without testing them. They're probably from different series, maybe different manufacturers. Amscope doesn't necessarily know much about them, just the nominal spec, what they cost and what margin they need.

[apochronaut]

Chinese microscope production took a big leap forward when Olynpus and Nikon reached out to various of the larger makers in order to economize on production costs. Thus, they have piggy backed on those two manufacturers optical specifications from then on. The The liklihood that those two objectives are not based on Nikon and Olympus corrections is very low, thus each would work best with the correct compatible eyepieces, despite them both being for a 160mm finite system. Bausch & Lomb was also there fairly early on and contracted a factory to produce their middle line Galen III microscope system. The Bausch & Lomb and also branded Cambridge plan 100X 1.25 with iris is suspiciously similar to the g17 model. Sometimes you will see one or the other of those sold on ebay quite cheaply. The optical quality is quite good.
Neither of those Amscope objectives is a new design, with both probably going back to the 80's. There wouldn't be any reason to improve them, since 160mm tube microscopes are slowly becoming obsolete, at least from an industry point of view. All new designs are infinity.
Amscope also previously sold a 100X 1.25 45mm parfocal iris objective made in India. They may still but I would purchase one from the distributor in India : Radical. This avoids Amscopes rather hefty markup. Just search microscopes india ebay and you will get Radical's store. You can buy an entire DF kit , oil DF condenser and iris 100X 1.25 objective for under 200.00 with free shipping. A dry condenser , so you can also go below 40X can be included for a little more. The condenser sleeve is 37mm but it isn't that difficult to convert one to a dovetail. While that Indian objective is not plan, you have to decide whether that is necessary or not. With samples thicker than a smear , it often isn't. Indian optics are good value. I have bought from Radical and they have generally been good, shipping is fast and free. They back up their products. The contact person I dealt with is Jai Deep, who is perhaps the sales boss.

[Scoper]

Mystery solved…

PA100X-IRIS $366…0.31-1.25 na

PA100X-IRIS-G17 $298…0.5-1.25 na

So what advantage does the lower n.a. offer in darkfield?

[apochronaut]

Mystery solved…

PA100X-IRIS $366…0.31-1.25 na

PA100X-IRIS-G17 $298…0.5-1.25 na

So what advantage does the lower n.a. offer in darkfield?

You cannot achieve DF if the objective N.A. is greater than the condenser N.A.

Since immersion DF condensers have a lower N.A. limit above 1 , otherwise rhey would be dry condensers, the objectives used with them must be lower or have some method of lowering the N.A. internally.
In practice most DF immersion condensers are 1.1 or more often 1.2 . There is a twilight area in DF where scattered light can illuminate the dark, so in order to get really good DF the differential between the objective and condenser needs to be around .20 N.A., sometimes more. Thus a condenser at 1.1 N.A. cannot work well with an objective above .90 or even lower with samples that have high scatter.

Funnel stops or iris diaphragms are the standard mechanisms used to lower an objectives N.A. for DF use.

[Scoper]

Mystery solved…

PA100X-IRIS $366…0.31-1.25 na

PA100X-IRIS-G17 $298…0.5-1.25 na

So what advantage does the lower n.a. offer in darkfield?

You cannot achieve DF if the objective N.A. is greater than the condenser N.A.

Since immersion DF condensers have a lower N.A. limit above 1 , otherwise rhey would be dry condensers, the objectives used with them must be lower or have some method of lowering the N.A. internally.
In practice most DF immersion condensers are 1.1 or more often 1.2 . There is a twilight area in DF where scattered light can illuminate the dark, so in order to get really good DF the differential between the objective and condenser needs to be around .20 N.A., sometimes more. Thus a condenser at 1.1 N.A. cannot work well with an objective above .90 or even lower with samples that have high scatter.

Funnel stops or iris diaphragms are the standard mechanisms used to lower an objectives N.A. for DF use.

Thks for the reply…

I was surprised the n.a. was 0.31…most objectives 100x with irises I see are about 0.5 - 0.6

[zzffnn]

I think 0.5 is more than enough. Going down to 0.3 doesn’t do anything. You can buy cheaper iris objective by searching “iris objective” on eBay; a new Amscope is not better than a good used branded objective.

[apochronaut]

At .31 everything would just be s fuzzy blob in the dark. I have a very old Spencer 20X with an iris. .20 to .50. Even with that, at .20 there is terrible detail. worthless. I cannot think of a reason at 100X, and with an oil DF condenser that you would need to go below .80, even if the sample was very dirty and full of scatter.