Prime focus with Tele vue powermates

[Mercona]

Ok, so recently I decided to step up and buy a Tele vue vue 4x powermate. I also bought the t adapter for it so I can connect my camera. I have an Astro tech 6" RC. Now for the life of me I cannot get this thing to focus. I can pull the eyepiece out and painfully hold it and work my way back to focus outside the holder. Because of that I've used many different hollow Barlows to get the distance. I can barely get a good view with the set up I have in the picture, but it's ridiculous looking. What the heck am I doing wrong. I'm at a loss right now. Hsha

[Mercona]

[Waldemar]

For camera use with PowerMates, special adapters are available. I use the 2" versions without problems, but maybe the attached file can help you out a little.
Maybe you concentrate on the wrong end of the PM. The focal distance between PM and camera or ep is not critical.
The distance that matters is the one between PM and telescope focal point.

Regards, Waldemar   

Powermates.docx

[PeterCPC]

Yep, Waldemar has got it. You need to use an adapter like this one http://www.telescopehouse.com/t-ring-adapter-pmt-4201.html

Peter

[John]

I don't know about imaging but for visual use the Powermates leave the focus position of the eyepiece pretty much exactly where it is - no movement required.

 

[Mercona]

Thanks for the replies guys, I have that adapter. I tried straight hook up with it. Telescope-televue powermate-adapter-camera. Still won't come into focus.

 

[Mercona]

I'm thinking maybe I need smaller telescope extension tubes. These Astro techs come with 2 -2" extension tubes rings and suppose to come with a 1" but I bought mine at an auction so it didn't come with a 1" tube ring. The focus only has 1.5" travel so maybe instead of 2- 2" rings I need one 2" ring and a 1" ring to get the PM to focus right. 

[Waldemar]

10 hours ago, Mercona said:

I'm thinking maybe I need smaller telescope extension tubes. These Astro techs come with 2 -2" extension tubes rings and suppose to come with a 1" but I bought mine at an auction so it didn't come with a 1" tube ring. The focus only has 1.5" travel so maybe instead of 2- 2" rings I need one 2" ring and a 1" ring to get the PM to focus right. 

That may very well be the problem. Maybe even shorter. Basically when you can get into focus with an ep, your camera should be no problem, because of the not critical focus distance of the PM to camera.

[Mercona]

Today I had two 2" rings on and held the tele vue out as far as it would go but still clamp down, and the focuser fully extended then  added a 25mm Meade EP. I had to hold the EP out of the holder about 1/2" and got perfect focus, so now I'm thinking I need another 2" ring  and I should be able at that point to use the focuser to draw it back into focus. Takes about a week to get here, so my patience will be tested. Haha. Thanks again guys. 

[Mercona]

I'm not sure what the actual focal will be with 6 extra inches. The telescope specs has the focal length at 1370mm so I'm guessing its that plus roughly 152mm of rings puts it at about 1522mm?

[John]

I have to admit that I'm a bit confused about this. When I've used Powermates with my scopes, eyepieces reach focus more or less exactly where they did with no Powermate used. No need for extension tubes etc, etc

[YKSE]

In theory, Powermate is a telecentric, i.e. magnification doesn't change whereever you place a powermate. But reality is not that perfect, looking at Televue's graph here about all the powermates, it looks like only the 2x powermate is almost telecentric, while 5x powermate is much more like a barlow, placing the 5x powermate in front of a diagonal (about 80-100mm light path), it'll more like a 8x magnification instead of 5x. and 4x powermate has mild magnification variation too.The barlow effect will most likely change focus position.