On 4/23/2016 3:50 PM, Moose wrote:
Anyhow, I mounted the 75-300 onto both tubes together (10mm + 16mm)
and tried using the lens in the house at both 75 and 300. The tubes
give a very slight rotary motion which allows the assembly to rotate
perhaps 1/2mm on the mount circumference but that's all. There
doesn't seem to be any looseness that would produce a gap between lens
mount and camera. I think the mount flanges are some sort of hard
aluminum (certainly not stainless steel) but they seem reasonably sturdy.
The gap I mentioned is very small, and can only be seen from the side,
with light behind, at the top of the meeting of tube and camera body and
or meeting of lens and tube. It is a result of the weight of the lens,
esp. when extended, compressing the spring behind the top 'ear' inside
the female mounts on the body and/or adapter.
I mounted the 75-300 and both tubes back onto the camera. Took it
outside in moderately bright sun and examined the mounts junctions with
a 5X magnifier supplemented with my reading glasses. Didn't see any
daylight even pulling down on the lens.
So I'm also exploring the C-U lens approach. John Shaw writes that he
uses it with great success, many images sold.
I just took the 300 with both tubes out back and did some actual
shooting. I was having fun. I'd guess working distance at 300mm with
both tubes is about 1 meter. Since you've been singing the praises of
long working distances I'll remind you that your maximum working
distance with the 500D is 1/2 meter with the main lens at infinity. It
only gets closer from there.
Chuck Norcutt
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