About Lens Clones

[OlDoinyo]

Quick outline of a pinhole bandpass test:

 

1) Set up lens to be tested so that you have a clear line of sight through the optical train to a UV-white background.

 

2) Mount a pinhole aperture on your converted camera stacked with a Baader or other UV-pass filter (no lens.)

 

3) Shoot a pinhole image of the lens against the background.

 

4) In workup, set the background to white or near-white and swap red and blue channels.

 

5) If the view through the lens looks colorless or pale yellow, good; darker shades of orange, not so good.

[Cadmium]

Alex, I am sorry, it looks like you are upset with me, I didn't mean to upset you. You are an expert about lenses, I tell people that often, and I always appreciate your knowledge.

I was just pointing out that the aperture doesn't unscrew from the back of lens with the optics. That is not really about the 'front and back', it is more about the aperture.

Also, your pics of the two Kyoei lenses are labeled as Kuribayashi. I was pointing that out for anyone who might be looking for whichever one so they know.

These were two simple corrections, and both points are valid, and valuable, and not overly 'particular' of me to have made.

We are all here trying to help each other, share, and learn. The more accurate the information is the better for everyone.

It is a group effort, each of us contributes something, and it is not a waste of time.

[dabateman]

@OlDoinyo,

Ok so outside (hopefully some uv light), set up my block of PTFE on a table. Place the test lens in front of block, allow enough space for sun light to illuminate the block completely.

Then place my pinhole pro lens on the SD14 or Olympus E510 full spectrum camera. Add my Baader venus 2 filter to fron thread of pinhole pro lens. Capture a pinhole image of the full PTFE block and part with lens.

Look at image and see if there is blockage or color cast through the lens.

Does that sound correct?

[OlDoinyo]

Yes, that sounds correct. I find that the color swap helps me see it---somehow pale blue-grey tints are harder to spot than pale yellow. In my experience, the hue is more of a reliable guide than whether the center swatch is brighter or darker, as the latter attribute can be influenced by things such as beam divergence which have nothing to do with bandpass.

 

Do not use the SD14 for this test--it will tell you nothing. Use the Oly with appropriate custom WB.

[Cadmium]

Just as a quick rough UV lens transmission depth comparison between lenses, if you compare any two or more lenses,

the lenses that transmit UV deeper will tend to look more pink using the same camera white balance for all.

The lenses that don't transmit UV very deep will look more blue.

Here is an example, not the best example, because these were all individually white balanced out of the camera, but it still shows up.

[dabateman]

@Cadmium,

Is that a test of the lentar 400mm f6.3 and lentar 450mm f6.5 lenses? I have those same lenses with T mount. I was hoping they would transmit some uv as the design is simple. I got mine years ago for less than the cost the poor person spent mailing them to me.

 

[Cadmium]

Yes, Lentar 400mm f/6.3 lens.

[JCDowdy]

Sometimes I wonder why should I waste my time trying to help people here.

 

Oleksandr,

 

Speaking not only for myself, your contributions here are not wasted.