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Coin Photography, Lens Testing
Coin Photography, Lens Testing

Coinimaging's posts

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I have completed the testing on the Schneider 40/4 enlarging lens. It is good but not spectacular, typical for a good enlarging lens. No real problems with it and it covers a reasonable magnification range of about 2:1 to about 5:1.

On another note, I do not directly import these posts to my website anymore. I now have my own PHP/mySQL system for news. It is easier for me to control posts and images this way, and it was a nice project for me. I would like to add comments to the posts sometime, but that will require some more work to do it right. 

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I have completed aperture testing on the Schneider 40/4 with the fingerprint removed. As you can see by the attached graphs, the performance is almost the same for all of the factors except for  the contrast. The contrast is visibly lower and measures about 2.5 with the smudge and about 6.2 with it cleaned. I don't normally report the measured contrast as it is not as consistent as other measurements and more susceptible to conditions of my test room and setup. But for this case it is useful as a guide to show how much the appearance changed.

Click on the images below to see them properly. I post Google's thumbnails and they are a little funny (appear the same on Google+).
3 Photos - View album

I went back and looked more closely at my 40/4 and found that there was a rather large fingerprint on the rear element (front for me since the lens is reversed). Since the rear element is fairly small, it takes up quite a bit of the available surface and most of the prime real estate in the center of the lens.  I cleaned it off and suddenly the contrast was back where I would expect it to be. I will redo the aperture testing to see what the measurement differences are. I will report those differences on the website.

Sometime later I will also do my comparison check between two of the same lens - one with bad fungus and one clean to see what the effects are. I suspect the changes will be similar, the most prominent being a drop in contrast.

I have been a little slow with the testing of the Schneider 40/4. I am almost done with the aperture testing. It has the best resolution at f/4 and it is sharpest at f/5.6. F/4.7 is a good compromise for most imaging. The main problem with it is its lack of image contrast. I had done some basic testing of this lens a couple years back and it seemed to have better contrast then. Not sure what is going on. I will have to look closely at the lens to see if there are any problems with it, like fungus. I don't normally think of this area as a fungus hot spot since I live in the high desert. The lens itself isn't the newest one out there, but it isn't the oldest either. It is one of the newer plastic housing ones, not the oldest metal housing. I will post any updates as they come available.

Sorry that I haven't been posting anything lately. Just too many things going on to do any lens testing. I want to start simple and plan on testing a Schneider 40/4 enlarging lens. I wanted to test a 50/4 of either Nikon or Schneider make and found that I didn't have the right adapter for either. They both have lens threads of around 32 or 33 mm and all I have is 30.5 or 34. I will have too look on eBay for step-up rings that I can use. So far the 40/4 seems to be relatively low contrast, but sharp wide open.

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I have finally finished my lens test page that puts all of my current data into a lens test form like my original tests, i.e. all the info on a single page instead of the multiple page format that I created a while back. It was an interesting challenge as it uses most of the same code, but in different format/order.

 I did add a feature that will allow you to move the graph legend on a couple of graphs. There are two graphs that have the problem where the graph line goes behind the legend for a few lenses.

 As with the other page it allows you to switch between effective aperture and aperture for those lenses that are shown as effective aperture on Nikon bodies.

For those of you that like the lens tests in the old format (single page), I am creating a page that will do that will all of my data, creating the page on the fly. It's still in process, but it isn't proving too difficult. I just have to reuse and rearrange the old code to make it work like I want it.

I haven't had a lot of time for lens testing lately, but will hopefully get back on that bandwagon sometime soon. It has been a busy month.

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I was looking at the Mitutoyo tube lens that I used for testing the Edmund Optics objective and noticed that the lens elements are fairly small on it. Is it limiting the effective aperture/NA of the objective? It certainly didn't perform as well as I would like with an NA that high. I have now also tested the lens with my 200AF micro as the tube lens. this is a popular way to use infinity-corrected objectives since tube lenses aren't all that common.

I found that it does perform a little better on resolution and sharpness with the 200AF. Otherwise, corners are slightly worse and CA is better with the 200AF.

I have fixed the ordering issues that my news section has had recently. The problem is that the info coming from Google is out of order and in some random order. I have adjusted my code to correct the order however it comes from Google. It runs slightly slower for it, but nothing too bad.

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I have added a small new article showing a good example of the lens aberration called field curvature. It isn't common to see it where you can actually identify it visually. The nice part about field curvature is that focus stacking will remove its effects.

My news area on my front page is kinda messed  up, but it appears to be a problem originating at Google+ and not one from my page. Hopefully it will be fixed soon.
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