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 Replies: 10 / Views: 2,451 |
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Pillar of the Community
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4038 Posts |
I just picked up this objective and it seems to work pretty well. It seems to be optimized for around 2x-3x magnification. It was very inexpensive, as they don't seem to be have much respect. Well, here is the image it took of a 56-D Cent I've been using for lens testing. This is a stack of 6 images.  |
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Pillar of the Community
United States
4132 Posts |
Funny coincidence. I was just finishing up a test stack with a new version of my Lego focus stacking rig, and my subject was a '56-D.  1956-D Focus Stack Test by CaptainFwiffo, on Flickr That's with my 75ARD1 at f/5.6. IMO, it doesn't seem like microscope objectives perform better than regular bellows lenses at this level of magnification. Edited by CaptainFwiffo
01/08/2013 09:46 am
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Pillar of the Community
 United States
4038 Posts |
Well, this is an older, very inexpensive objective and while it doesn't blow away the 75ARD1 it certainly points out its limitations at this level. In reality there are few decent low power objectives, which is why I was pleased to find something that could do this well. For some reason most low power objectives have extremely short working distances so are tough to apply for any kind of macro work. I owned a Nikon PlanApo2 and was unable to use it due to the working distance of <<1cm. I actually thought the objective had been improperly assembled it had such ridiculously short working distance.
BTW, this lens has an infinity aperture of f4 ala the 75ARD1. Why did you close down your 75ARD1 to f5.6 for your stack?
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Pillar of the Community
United States
4132 Posts |
At 3x I get a lot of aberrations at f/4 and f/4.8 that end up making the final stack a lot less sharp. I thought stacking would hide it, but it didn't work out. I guess it has spherical aberration (or something?) when pushed too far past it's optimized range, but closing it down a stop minimizes it. Maybe it's just my copy, but f/5.6 still looks so good, I'm not going to fuss.
I'll give it another try later and post both results for an apples-to-apples comparison.
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Pillar of the Community
United States
4132 Posts |
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Pillar of the Community
United States
4038 Posts |
The f5.6 crop looks very good. Here is the B&L 48mm 100% crop:  |
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Pillar of the Community
United States
4132 Posts |
The resolution toward the center of the field on the B&L is pretty decent, and that's where it counts, though it has that star-trail effect further away.
It seems a lot of detail is lost to JPEG artifacts though, is that Photobucket over-compressing your images?
I've been looking through old photomacrography.net threads researching microscope objectives, and there are a couple Nikon CFI 10x/0.25 objectives that people have been using at 5x on 100mm tube lenses and getting really sharp results. They surprisingly have big enough image circles to cover APS-C. Working distance might be an issue though.
Have you used any of the cnscope objectives?
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Pillar of the Community
United States
4038 Posts |
I think I'm using the 48mm at the lower limit of its magnification capability, so coverage is not quite as good as it would be at higher mags. I have no idea what it's rated at, it's not marked on the barrel and I can't find any docs on it. The barrel just says "48mm 0.08", so I assume it's intended for multiple systems and somewhat variable magnification. NA of 0.08 puts it in competition with the lower-cost objectives up to 5x or so. Going down the Infinite path might be interesting for coin imaging. I have done some work in that area but have not even tested a Mitutoyo 5x that I bought years ago. I saw decent results from a Nikon 5x BD on a 150mm EL-Nikkor on bellows. But that's as far as I've taken my work with Infinites. I have indeed tried some of the 4x Chinese cnscope/amscope objectives and found some of them to be extremely good, comparable or better than a Nikon P4/0.1, which is a very decent objective for coin photos. I did a shootout (published on another forum) of four 4x objectives I had at the time and it turns out one of the Chinese objectives was the winner by a small margin over the Nikon. Here is the link: http://www.lincolncentresource.net/....php?t=19718I believe the winner was the only one not intended for a .17 cover slip, so it makes sense. |
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Pillar of the Community
United States
4132 Posts |
What's the working distance on the cnscope objectives? They are so cheap, I might pick some up, just for playing with, but they have a lot of options! Of the finite objectives they're currently selling on ebay I see: Achromatic 4x/0.10 160/0.17 Plan Achromatic 4x/0.10 160/0.17 (two versions, different prices, seem identical?) Semi-Plan Achromatic 4x/0.10 160/0.17 (two versions) LPL Plan Achromatic 4x/0.10 160/- (not sure what LPL means, but optimized for no cover slip) Metallurgical Plan Achromatic 4x/0.10 160/- Infinity metallurgical Plan Achromatic 4x/0.10 ∞/- The ones optimized for no cover slip should theoretically be the best, but they're more expensive (still relatively cheap in the broad scheme of things). It's not supposed to make a significant difference until higher NA values though. Not sure what the difference between the LPL and metallurgical ones is. I think it might have something to do with long working distance, but I'm not sure. Apparently some metallurgical objectives have a longer working distance to accommodate lighting of opaque subjects (in addition to having no cover slip). |
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Pillar of the Community
United States
4038 Posts |
IIRC, the WD was about 20-25mm.
Looking again at the objective that won my "shootout" I see it's actually a 160/0.17 so it seems that is not a huge limitation at this magnification. It's likely the Achromat you list first is the one I found worked best. I think LPL is cnscope's proprietary nomenclature indicating longer working distance, ie "Long PLan" or something like that. The M objectives are optimized for use without coverslip.
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Pillar of the Community
United States
4132 Posts |
It's funny, because that's the cheapest of the lot, and theoretically the least corrected. But focus stacking should more-or-less eliminate the need for a flat field, and maybe field flatness leads to other compromises. I've asked the seller if they can provide any additional information.
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Replies: 10 / Views: 2,451 |
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Posted 01/08/2013 12:23 am
