Tube lens question

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mawyatt
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Joined: Thu Aug 22, 2013 6:54 pm
Location: Clearwater

Tube lens question

Post by mawyatt »

Hello,

Has anyone had issues with internal reflections within the makeshift lens tube which is made up of low cost 42mm screw sections?

I am referring to the technique of using an objective with an adapter to a reversed Raynox as a "tube lens", then an adapter to a 42mm threaded screw section that is repeated multiple times to get the proper extension for the Raynox "tube lens" from the camera body sensor.

I don't know if internal reflections within this setup might cause lack of image contrast.

I think others are using this same setup and wonder if they have any advise.

Thanks in advance,

Mike

Chris S.
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Post by Chris S. »

Mike,

I don't have that setup, but since nobody else has jumped in, I'll have go. My tube lens uses completely different parts, but is similar in concept. When I first built it, I took a few test shots before and after placing flocking material on the inside surfaces. Comparing the before and after pictures, the difference in contrast was substantial. I'd expected this, for a couple of reasons: Without flocking, when I aimed the lens at a bright light and looked through from the back, I could see reflected light on the inside of the tube. Also, other macro assemblies I've made have routinely displayed the same sort of internal reflection, and likewise benefited from flocking.

So I'd actually be surprised if the setup you describe does not require flocking. (BTW, one good flocking material is Protostar hi-tack flocked light trap. I'd recommend buying more than you need, as this is handy to have among one's studio supplies.

--Chris

mawyatt
Posts: 2479
Joined: Thu Aug 22, 2013 6:54 pm
Location: Clearwater

Post by mawyatt »

Chris,

Thanks. I'll order some hi-tack flocking today. The other day I stopped by Michael's Art supplies and picked up some black thick drawing paper, suspecting that lens assemble internal reflections might be a problem. I might try this until the proper material arrives.

Did you need to need to shield the objective to tube lens adapter, or just the tube lens to camera body extension?

Cheers,

Mike

rjlittlefield
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Post by rjlittlefield »

mawyatt wrote:Did you need to need to shield the objective to tube lens adapter, or just the tube lens to camera body extension?
It never hurts to flock everything. But as a matter of practice I find that the big problem is the stuff behind the tube lens.

It's also a good idea to make sure that you don't get reflections from inner surfaces of the tube lens itself. This can be done with a circular mask of black paper, with a hole slightly smaller than the lens diameter, placed just in front or behind the tube lens. With my Raynox's, a good place is inside the 49 mm female thread, where it gets trapped between the Raynox and a 49-52 adapter ring.

--Rik

mawyatt
Posts: 2479
Joined: Thu Aug 22, 2013 6:54 pm
Location: Clearwater

Post by mawyatt »

Rik,

With shielding the Raynox tube lens, do you see any vignetting effects on a full frame sensor? I already have some vignetting with my setup, (Mit objective to Raynox reversed with cone adapter, then from reversed Raynox 42mm extensions to D800 FX camera body.

Mike

rjlittlefield
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Post by rjlittlefield »

mawyatt wrote:With shielding the Raynox tube lens, do you see any vignetting effects on a full frame sensor? I already have some vignetting with my setup, (Mit objective to Raynox reversed with cone adapter, then from reversed Raynox 42mm extensions to D800 FX camera body.
Your vignetting problem is probably being caused by that cone adapter, which pushes the objective so far away from the tube lens that some of the off-axis rays can't get through the glass. I suggest to remove the cone adapter and replace it with a short 42 mm tube and a flat 26mm adapter.

--Rik

Chris S.
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Post by Chris S. »

mawyatt wrote:Did you need to need to shield the objective to tube lens adapter, or just the tube lens to camera body extension?
mawyatt wrote:. . .Mit objective to Raynox reversed with cone adapter. . .
Cone adapters are notorious for causing flare in finite setups, unless they are flocked. So even though I have no experience with one in an infinite setup, I’d flock it without a second thought. (This of course becomes moot, if you remove the cone to avoid vignetting on full frame.)

--Chris

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