Thanks all for your kind and helpful remarks !
I should have clarified that the WD of the objective is important in this case, because I am experimenting with top illumination, by means of a LED ring around and near the objective tip.
...You may want to buy the exact 4x Amscope objective from the exact seller to make sure it is the good one...
In fact, my starting point was Robert Otoole's report. Unfortunately, for some time Amscope has stopped listing that 4X objective, and instead, is listing another model (??), which differs in shape: the hood of the front lens is tapered. These two objectives did not perform the same in Otool's report. To add to my confusion, Otoole's report was about a macrophotography gear, not a microscope (maybe only subtle difference, I am not sure). Furthermore, other microscopists mention significant quality fluctuations within a set of the same identical objectives. And I am aware of Apochronaut's comments about the Chinese 4X objectives, and the lack of detailed information from the manufacturer of the unbranded objective (this is an attractive paradox by itself
). So, I rounded it all up and purchased a "generic" or "unbranded" objective of the same external shape. It represents all objectives that look like this.
... Also note that Robert OToole used it without eyepiece (direct projection onto sensor). ...
This is another reason for me to keep the 4X objective and, with time give it a chance in direct projection.
...LOMO 3.7x likely won't work for you either, as it has very long working distance and is not parfocal with other LOMOs. I would think its parfocal distance is a bit longer than 45mm as well, but am too busy to test it now. Do you want me to test it for you next Tuesday or so?
I am in no hurry, since I intend to keep the objective anyway. If you can, at leisure, test the LOMO 3.7X on a Zeiss standard system, and tell about its aberration compatibility and parfocality with DIN objectives, it will be very helpful and greatly appreciated.
... For the price, the import 4x seems OK; especially for sorting and scanning slides...
Hence I will keep it. It would be foolish of me to try and resell it - ordinary shipping costs alone are higher than the price of a new one of the kind.
I admire Olympus SPlans, sadly they produce too much CA with a Zeiss eyepiece.
Thanks for mentioning the Zeiss 4X Planapo, which I forgot, and the Zeiss 1.6-5X; their disadvantage, however, besides the cost, is the shallow WD. The zoom is said to have WD=1.5mm at 5X, so I am guessing that it will not be much over 3-4mm at 4X, too risky to buy.