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Canon microfilm lens test

 
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gremlin



Joined: 15 Mar 2017
Posts: 13
Location: UK

PostPosted: Fri Mar 30, 2018 3:39 pm    Post subject: Canon microfilm lens test Reply with quote

I've been wanting to try a Canon microfilm lens but they are usually quite expensive. I managed to buy a C09 (what ever that means) for £25 on ebay.
This is 40 frames on an old 4mm long weevil, lens reversed on 150mm extension. I have no idea what the distance to sensor should be with microfilm lenses.
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Lou Jost



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PostPosted: Fri Mar 30, 2018 4:23 pm    Post subject: Reply with quote

The internet says that your lens is for 35.5x magnification. From that you can work out the best distance from lens to sensor and lens to subject.
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rjlittlefield
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PostPosted: Fri Mar 30, 2018 5:20 pm    Post subject: Reply with quote

The lens appears to be working well, at least at this reduced size for posting. What does it look like at "actual pixels"?

Quote:
I have no idea what the distance to sensor should be with microfilm

In general there is no clear answer to that question.

Normally microfilm lenses are used to to fill a large screen, while looking at the film through a thick piece of glass. Presumably the designers optimized them for that configuration. But then we macro photographers re-purpose the lenses, by using them to fill only a small sensor at lower magnification, while looking at a subject not through a thick piece of glass. Both of these changes drag the lens away from its design point, and unfortunately both drags are in the same direction.

Ultimately you just have to try several configurations and see what works the best.

Theory says that to compensate for the lack of glass on the subject side, you should have a longer distance behind the lens than it was originally designed for. But that distance is already too long if you think of using the microfilm lens by itself.

One attack on that aspect is to use a "stacked" configuration, with the microfilm lens in front of another lens that is focused much closer than infinity. That should provide a correction that is at least in the right direction.

Of course you should also test the lens in both orientations, forward versus reversed.

Whichever configuration works the best is by definition the "right" one.

--Rik
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gremlin



Joined: 15 Mar 2017
Posts: 13
Location: UK

PostPosted: Sat Mar 31, 2018 3:50 am    Post subject: Reply with quote

Lou Jost wrote:
The internet says that your lens is for 35.5x magnification. From that you can work out the best distance from lens to sensor and lens to subject.


that sounds like a lot more extension to achieve that Confused
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gremlin



Joined: 15 Mar 2017
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Location: UK

PostPosted: Sat Mar 31, 2018 4:01 am    Post subject: Rik Reply with quote

Thanks Rik, some good info there. I have some 50 & 80mm enlarger lenses, i could try a stack on those or a 100m macro. It's all worth trying, it's quite nice to experiment and get some results.
It does zoom in quite well and hold up.
I have a few microfilm lenses that I have collected, mainly Olmpus a 20mm 2.8 rokkor and this canon. a few have already been discarded.

David
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gremlin



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Location: UK

PostPosted: Sat Mar 31, 2018 7:32 am    Post subject: more extension Reply with quote

Just for fun I tried more extension by attaching a bellows unit giving 350mm. stacked 50 shots in zerene and fiddled around in photoshop.
Excuse the dust as this is more of a lens test but although it looks ok to me, how do you more experienced guys feel about the lens?
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Lou Jost



Joined: 04 Sep 2015
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PostPosted: Sat Mar 31, 2018 11:08 am    Post subject: Reply with quote

Can you post a 100% crop? What size sensor are you using?
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Lou Jost



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PostPosted: Sat Mar 31, 2018 11:43 am    Post subject: Reply with quote

We are accustomed to put enlarger, duplication, and projection lenses on long extensions and small sensors. When we do this, it is important to realize that we are throwing away most of the information transmitted by the lens. Maybe that's acceptable since we need to do that to get the image magnification we want. But if we use this C09 lens at its intended magnification (35x) on an APS sensor, we are using only 24/(35X16) = 4% of the image width of the lens, or less than 2% of its area.

Edit:I am assuming the microfilm is 16mm horizontally. That may not be the case, and if not, the "16" in all these calculations should be changed to the correct number.

For a given lens arrangement, I think the information contained in an aerial image is a constant and cannot not increase if you enlarge the image. So to use all the information contained in the aerial image of your lens, we ought to reverse it and put it on a tube lens whose focal length is chosen so that the image of a 16mm wide object is spread completely across your camera's sensor. Alternatively this might be possible by just extending the reversed lens by the required amount; the results will vary depending on the lens design.

For an APS camera, that's 1.5x magnification. This result doesn't depend on the magnifying power of the microfilm lens (as long as it is high enough to behave more or less like an infinity-corrected lens), but only on the film size it is designed to image. If you want higher magnifications, you should look for lenses designed for 8mm film, such as some cine lenses. You can vary the focal length of the tube lens slightly, or vary the extension slightly, to give you slightly higher magnifications, but if you go too far you are going to see a sharp drop in image quality relative to a purpose-designed lens like a microscope lens.
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