Why do these dovetails look different?

[jnb]

Specifically these

I was thinking of getting a short dovetail to put on my current mount to hold just a DSLR and 250mm lens. That's not too much of a strain so the shortest of these would probably do. Originally my question was going to be is there enough space under the dovetail bar to accomodate a 1/4" screw head, if not then I'd get a slightly longer bar and position the camera just behind the telescope mount.

But now I look at those the question is why does the shorter bar look so different? The larger two are simple dovetails but the shorter appears to have a square section in the middle which would stop it fitting in a dovetail socket.

[Cornelius Varley]

This one might be a better option (Vixen style photo dovetail) http://www.modernastronomy.com/accessories.html#accDovetails

[jnb]

Ta that's a much better option. But I'm still curious as to why that short skywatcher dovetail is so different.

[Alien 13]

Ta that's a much better option. But I'm still curious as to why that short skywatcher dovetail is so different.

 

The cutouts on the small one is designed so that it can be locked in position better with the two screws on the mount, i have one but needed to drill the underside to remove the collar so i could fit a std camera screw.

Alan

[Bizibilder]

The small one is a casting (with the "locking slots" as mentioned above) whilst the longer ones are extrusions that have been cut to length and then drilled etc.

[RichM63]

+ the 2 longer ones possess '4 cone correcting' screws, which I doubt you would use on a Camera only rig. 

[Davey-T]

As Allen says above, have to drill it out to fit tripod screw, here's a few pic's of mine, apologies for the quality, done with wifes' point and click with broken auto focus. hope you can see enough to get the idea.

Araldited some big washers to the screw so it can be loosened  with out removing the dovetail.

Dave

    

[Alien 13]

As Allen says above, have to drill it out to fit tripod screw, here's a few pic's of mine, apologies for the quality, done with wifes' point and click with broken auto focus. hope you can see enough to get the idea.

Araldited some big washers to the screw so it can be loosened  with out removing the dovetail.

 

Dave

 

Dovetail1.JPG Dovetail2.JPG Dovetail3.JPG Dovetail4.JPG Dovetail5.JPG

 

That looks like mine, one thing i do like is that this dovetail cant slip even if the mount screws come loose.

Alan