Starboosa Telescope T2-Extension Tube Kit for SLR Cameras and Eyepieces - Length 3mm 5mm 7mm 15mm 20mm 30mm 55mm - M42x0.75 on Both Sides (Upgraded)

I also have some Neewer extension tubes and those are just as well made as the Starboosa ones, but at a much better price point. Granted, this set has the smaller sizes, but I have another set with the smaller sizes and I rarely use any of them under 7mm, and I rarely use that one. They are handy to have when you need something that narrow, but you'll get much more use out of the larger sizes.A set like this is definitely a must have for serious astrophotographers, but the price makes this a 4 star product instead of a 5 star. Quality is good, it's just the price is a bit too high.

Almost perfect. The 3mm is actually 4mm though. Fully assembled the length should be 135mm however its a little over 136mm. This is due to a tolerance issue in the 3mm, which you can see in the photos.Overall though I'm not docking any stars because the threads are satisfactory, and this kit is a perfect combination to help you achieve the required 55mm backfocus for most imaging systems. 3mm and 7mm tubes are not common in these kits. With that in mind I would recommend this kit over others to save yourself headaches down the road trying to achieve proper back focus

great kit to achieve proper backfocus. I use the various parts with both of my telescope rigs. these are strong enough and work great.

I made the mistake of ordering these thinking that they would work as is on my digital SLR but they are not optimized for that. So I was not able to use them for their original purpose.I can tell you that the threading was clean and they fit together well and tightly. The will offer a varied distance for those who install them and can use them.