talteleoptics

John,

I completely understand the desire to have an idea on what will and may not work with that scope from aftermarket accessories prospective. My take on why this scope is more sensitive to non Tal eyepieces and diagonals is that optical design has a 3rd group of lenses at very end of the OTA tube where white body ends and Black Focuser housing begins. That means that drawtube can not travel deeper into the OTA as it done on extended travel focusers TAL100RS, TAL200K and typical TRIPLET APOs. They don't have lenses there. Therefore TAL125-5APO drawtube has max Length of the black focuser part. Moved all the way in, it bottoms out at the lens cell (where white body meets black focuser housing). That makes design more restrictive for over and under focus conditions that other telescopes don't have, allowing for more aftermarket accessories to work properly. Undestandably TAL made sure their accessories work with it as it was designed. Since I worked with TAL for some time, (not worked for TAL to be clear) my guess is that they will not be testing aftermarket sets to provide compatibility charts. May be Andy is our only hope? 

Regards

Roman

Just wanted to address the issue of 2” eyepieces on TAL125-5APO before we all get confused about it from posts above. John’s result with trying Teleview 2” diagonal and lack of infocus is not all that surprising because it is a combination of 2 things: diagonal and eyepiece design, in addition to focuser design. It is not a secret that different manufacturers have very wide varying focal distance of their start diagonals, not just 2” ones. It’s a well-known fact. There is no standard to meet on that aspect. Therefore people do run into total focal distance issues with using scopes and a accessories from different manufacturers. Speaking of short focal distance star diagonals, it is also well known that 2 companies make very short focal distance star diagonals. You guessed it one is TAL and second one is Baader.

Now regarding TAL specific use of 2” eyepieces. TAL does make a 2” stardiagonal part number is ZP-90-2 see pictures . I used it many times with TAL 125-5APO and TAL UWA24mm, UWA20mm 2” eyepieces. And using them you will have of about 1 Inch of infocus travel left. So there is plenty of room to use other manufacturer’s eyepieces if you have short distance mirror design. You simply can not make focusing system that works with all possible combinations of aftermarket accessories and keep price and telescope size reasonable. TAL 125-5APO works very well with TAL accessories and I would argue many aftermarket ones. You just need to be aware of limitations for some combinations of them.