LWW Loc: Banana Republic of America

“ Because extension tubes do not have optics, they don't affect the optical quality of a lens. Because of their function, there are other effects: decrease of light; shallower depth of field; and loss of ability to focus at infinity. The longer the extension tube, the closer the lens can focus. The amount of light and depth of field will be equally reduced.”

https://en.m.wikipedia.org/wiki/Extension_tube

cactuspic Loc: Dallas, TX

The tube is probably poorly flocked and you are probably getting light bouncing off the side of the tubes into the image. That would explain the loss of contrast. Variable length tubes may be difficult to effectively flock. a good source for flocking is https://www.fpi-protostar.com/flock.htm.

cactuspic Loc: Dallas, TX

The tube is probably poorly flocked and you are probably getting light bouncing off the side of the tubes into the image. That would explain the loss of contrast. Variable length tubes may be difficult to effectively flock. a good source for focking is https://www.fpi-protostar.com/flock.htm. The flocking thould not shed, but i recommend capturing any loose fibers by touching the surface of the flocking with blue painters tape.

Red6

As others have suggested it appears to be either light leakage connected to the extension tube(s) or how light is being affected as it through the tubes.

I think I would try another set of extension tubes. If you can order a set of extension tubes from another vendor, I think I would try that as a first attempt. I have used Vello extension tubes with success and while they are not dirt cheap, they are not expensive.

srt101fan

Thanks!

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

That would be the Effective Fstop. The F number is a simple ratio - the focal length divided by the diameter of the aperture (entrance pupil size) and distance is never considered. When you move the entrance pupil away from the sensor plane, the magnification increases, which diminishes the brightness of the image being projected from the entrance pupil. The amount can be calculated by using the inverse square formula. The "effective Fstop" is reduced as magnification increased. The rules apply best at a normal lens focal length (50mm for full frame camera). It's a subtle but by no means minor distinction.

If you were to put a 50mm extension on a "normal" lens and focus the lens to its infinity mark (with the extension it cannot focus on something that is at infinity), the entrance pupil is at its closest point, so there will be little light loss. Using the same setup and focusing at the lens' minimum focus places the entrance pupil at its furthest point from the sensor, and there will be considerable brightness loss.

My 45mm F2.8 PC-E becomes an F3.8 when focused to its minimum focus distance - 1:2 magnification - without an extension tube. The lens is a simple external focus design, which physically extends the lens (and the entrance pupil) as it focuses towards its minimum focus distance. It is still an F2.8 lens - which doesn't ever change.

https://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

http://www.hasselbladhistorical.eu/HT/HTComp.aspx

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

Tubes do get you closer and therefore the DOF decreases significantly. Critical focusing is essential when using tubes.

fjwallace

I don't think this is an issue in this case, but as you increase magnification, you also increase diffraction effects. I remember when I started, I thought the higher the f-stop, the better but when you calculate the f-stops you can end up way over 22 which is a number I try never to go over - this is where I notice diffraction effects. Just something to keep in mind as you continue to experiment...

imagemeister Loc: mid east Florida

YES, light is being reflected off the walls of the tube - the longer the tube or the more tubes, the worse this gets. Larger tubes or flocking the interior can help to mitigate this - so can using bellows instead of tubes !

Most serious shooters use bellows.
.

Don, the 2nd son Loc: Crowded Florida

Don, the 2nd son Loc: Crowded Florida

SteveG Loc: Norh Carolina

Can you PM me?

MrPhotog

Using a white background adds to your problem if the interior of the tubes is not properly darkened.

The lens projects a cone of light into the camera. With a predominately bright background there is a lot of stray, bright, light bouncing around in that tube.

At the very least, get a can of flat-black spray paint and (after masking the outside) put a couple of light coats on the inside.

Some of the better tubes have ridges or internal baffles to reduce this flare. These tend to have a larger outside diameter so the internal ridges do not intrude on the light path to the film or sensor. Some use a textured flat enamel finish. Some (rarely) use velvet or flocking.

The construction of bellows naturally forms a series of baffles along the length until the bellows are stretched out.

Try your pictures with a dark background and see if the flare is reduced or eliminated.

Using any extension with a lens requires an increase in exposure. You are moving the aperture further from the film or sensor, creating a larger cone of light, and covering a larger area with the same beam of light, so there is less light on any given area. Use the meter behind the lens and you’ll see that it directs you to use a slower shutter speed or larger aperture setting than you might need without the extension. Estimating exposure can be a problem with flash, so some people meter off of the modelling light and make adjustments from that.

JBGLADSTONE Loc: Oregon

I have not read each reply, that being said.

Maybe the optical view finder could be allowing in light?

Ken Owen Loc: mid-Michigan

I just recently purchased similar "Chinese" extension tubes and noticed that the instructions cautioned that you need to fasten the extension tube to the camera body BEFORE mounting the lens. Apparently the data connection may not work if you mount the tube(s) to the lens before the body.