• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Loose extension tubes? (1 Viewer)

Tord

Well-known member
Hi

Is anyone else experiencing slightly loose extension tubes, and misaligned setup?

I found out the other day that there is no way to tighten the screws in such a way that the tube is perfectly aligned with the focuser. For some reason there are two screws only on the focuser, positioned at about 120 degrees angle from each other. On purpose? The slight play that exists between the extension tube and the focuser allows the screws to excercise a radial pressure that will result in a slight angle, yet noticeable at close inspection.

Is this a defect, or could the tube or focuser be manufactured outside tolerances? Or is it "by design"?

What I did to workaround the issue was to wrap the extention tube in one layer of plastic adhesive tape, which pretty much provided a tight fit so now the misalignment is gone, at least it is not measurable with the naked eye.

Maybe I should also have added that the extension tube is manufactured with an "undercut", I suppose it is a measure of safety to prevent the extension tube from accidentally sliding out of the focuser.

/Tord
 
Last edited:
Yes, it is VERY aggravating. I solved it by filling the "safety gap" with very fine automotive polyester putty and gluing a layer of polycarbonate foil, about .006mm all the way around with super glue. Now it fits very snugly and the screws don't have to be turned so tight. It also makes it possible to pull out a centimeter or two for closer shots. Did the same to my T2 adapter too. The tape idea works fine too. I did that on my old Dobson reflector, but I wanted something better for the SW because it is being moved around and I don't want the sticky stuff getting in between.
 
What I did was to wrap the tape not to fill the "safety gap" but to increase the diameter of the male end of the extension tube for (almost) perfect fit to the focuser. One layer of tape was about right, two layers and the tube would not be possible to slide into the focuser. (I suppose I could have wrapped tape to fill the gap as well).

What I don't get is why there are two screws only on the focuser. Three screws with 120 angle between them would have made it possible to mitigate radial stress to a minimum. Any idea why?
 
I filled the gap only to make it easier to position where I want ti. The SW has placed the locking screws in such a way that they hit right on the edge of the gap, thus pushing the extension out as you tighten the screws. If you pull the extension tube out a bit, it no longer touches on the flange of the focusing tube, and that means more wobble. With the gap filled and the extension wrapped you have even contact all the time. Mine fits snugly enough now that I can move it when I want, it does not wobble, and the camera won't even fall off the scope if I forget to tighten down the screws. It would have been nice of SW to put a metal band inside the focusing tube the way I have one in ma extension tube. That would be better still, but as is, I have no more problems.
 
Does it matter too much? I often just snap away without doing the screws up at all. In one hand I have the camera plus extension tubes and just shove the whole lot into the scope to take photos. The only time I tighten the screws is when I will walk away and leave the scope for a while.

Paul.
 
Does it matter too much?
Paul.

Yes, when one is forgetful... :)

I loosened up the screw to the adapter nearest the camera, for taking portrait shots, and forgot about it. Down the camera went into solid granite rock - a fall of a meter. Thanks god the E-3 is robust, but it landed on the flash shoe breaking it somewhat. I manage to repair it though - although the popup flash pops up all the time now - black tape helps to hold it down.
 
Hi,

The thread title was perhaps a bit misleading. What I experienced was not loose extension tubes, it was rather misaligned setup (I thought the root cause was slight loose fit, but apparently it was the "undercut" causing this.

I tighten the screws all the time, I know from experience that cameras don't like a meter high fall.

/Tord
 
It looks like it will, and it costs $97. Tape is cheeper.;)
I felt that the misalignment and loose tube went hand in hand so I made everything fit nice and snugly and dead center.
 
Hi,

Will the click lock clamp add any extension length to the setup?

/Tord

Well you can see that from the images, can't you. It does have a physical length, so yes, it adds extension. How much exactly depends on which model your scope accepts, more specifically the adapter, if any. I have three of them, they are between 30 mm and 45 mm in length.
 
I believe I have solved the issue by making a third M4 thread to the ring that connects the extenson tube to focuser. With now three screws instead at two at 120 degrees angle in between I now get a rigid attachment. The play is gone and as far as I can see the alignment is perfect.

Cost for the tools: < 10€ (threading tool and 3.3 mm drill)

/Tord
 
Warning! This thread is more than 11 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Users who are viewing this thread

Back
Top