Barrelcactusaddict wrote: ↑Sat Oct 16, 2021 6:05 pm
If I end up getting a used Mitutoyo 5x objective, do you think I'd be safe in assuming it's been previously disassembled if it has noticeable CA when used with my 100mm and 200mm Pentax telephoto lenses? As a hobbyist, my budget is absolutely abysmal, so I can't possibly afford a new Mitutoyo, much less an additional used objective to compare it to; hopefully I'll find an honest seller.
It's very chancy to buy a used Mitutoyo objective unless you have a return period and the ability to test the objective within that period. A huge fraction of second-hand Mitutoyo objectives are bad, even if they have never been disassembled; perhaps they have only been bumped, which can ruin them forever. Further, CA is not the most common problem--more likely issues are more subtle and difficult to recognize without a strict comparison with a known-good specimen.
Also, one can't rely on an "honest" seller, as many apparently well-intentioned sellers don't seem to know when they have a bad specimen. Testing an objective takes time, equipment, and experience that sellers of inexpensive objectives rarely have. In fact, if a seller could provide such testing, his or her offerings would probably sell for higher prices. So what you need to find is some idiot who is willing and able to test a prospective lens for you. As you are in the US, that idiot is probably me. I have a set of known-good Mitutoyo objectives, and have tested them against many other specimens for forum members.
So when you find a used objective you are interested in buying, PM me to see if I have time to test it for you within the return window. (I may not have time just then, as I sometimes travel or may be busy just then.) If it works for both of us, consider having the objective shipped straight to me from the seller, which preserves more of the return window.
A few rules of thumb: My sense is that 5x objectives are less likely to be bad than higher-magnification objectives--though I'm not sure I have enough data points to assert this with confidence. As you are in the US, you should prefer objectives from US sellers; with sellers in China, South Korea and other nations in the Far East, the percentage of bad objectives has seemed higher, and shipping costs--to you, and especially
from you if you need to return a bad lens--can be prohibitively high. (Yes, I do see that most of the 5x Mitties on eBay at present are from sellers in just such nations.) Don't worry much about the cosmetic quality of the objective--perfect looking objectives can produce optical crap, and ugly objectives can be optically stellar; this said, be aware that cosmetic issues should lower the price.
Also, if you can stretch your budget to purchase a "new" 5x Mitutoyo objective from Lightglass Optics (currently $420 USD), we have several reports from forum members that these specimens do indeed perform as new. In this singular case, you might not need to have the optic tested. In my experience, Lightglass Optics is a perfectly honest dealer. If they say an objective is new, it likely is. On the other hand, I've tested used objectives sold by them, and returned one or two. I think Lightglass sold them in good faith, not finding the issues on their own that I found; they definitely accepted the returns and provided refunds with zero issues.
--Chris S.