0.96 to 1.25 with a zoom.

[bomberbaz]

I have an novice acquaintance who has a decent tasco 115/900 reflector which is EQ mounted. The tripod is reasonably solid.

The mount head has a badly worn  gear in RA in one spot only. So I removed the counterweight and bar then set the mount to work in alt-az. Seems quite solid and functional in this mode plus is much easier to use for a complete novice. 

Anyway, happy enough with that part given it was a well meant gift from his swmbo. Suggesting a brand new setup wasn't really an option. 

The issue is It is fitted for older 0.95 eyepieces and after discussing options he doesn't want to go to the bother of the replacement focuser.

I am thinking a 1.25 adaptor with a zoom would work well. 

My understanding is that using a 8-24 zoom with the relatively narrow fov will minimise any vignetting,  thoughts?

Also is there anything else i am over looking. 

Cheers all

Steve

[DaveL59]

you'd need to consider if there's enough travel to reach focus as the 1.25 to 0.965 adapter will place the eyepiece and the nosepiece outside the end of the focuser drawtube. Quite possible that there won't be enough in-travel in which case you either need to swap the focuser or move the mirror up the tube (longer screws/springs maybe).

HTH

PS - it may work OK with a barlow in front but then you're pushing the mag a bit far for the scope?

Edited September 2, 2022 by DaveL59

[bomberbaz]

1 minute ago, DaveL59 said:

you'd need to consider if there's enough travel to reach focus as the 1.25 to 0.965 adapter will place the eyepiece and the nosepiece outside the end of the focuser drawtube. Quite possible that there won't be enough in-travel in which case you either need to swap the focuser or move the mirror up the tube (longer screws/springs maybe).

HTH

Thanks dave, didn’t actually take that fully into account. 

Given I have no idea about the focus point of a H20 0.965 vs a 1.25 zoom I will hold off.

I do know someone who can help in this matter though, cheers. 

[DaveL59]

1 minute ago, bomberbaz said:

Thanks dave, didn’t actually take that fully into account. 

Given I have no idea about the focus point of a H20 0.965 vs a 1.25 zoom I will hold off.

I do know someone who can help in this matter though, cheers. 

no prob, if you have a zoom you could give it a go and see just holding it just above the drawtube end. Might get lucky. I can't really offer to test as the old vintage scope is a frac and has a pretty long drawtube so I can hit focus with either size even with a diagonal in the train. With the TAL-1 and M with the older 32mm eyepieces you'd have to fit the barlow to use 1.25's as they couldn't focus without unless you shifted the mirror so could be similar with the older 0.956's vs 1.25

[bomberbaz]

 

23 minutes ago, DaveL59 said:

no prob, if you have a zoom you could give it a go and see just holding it just above the drawtube end. Might get lucky. I can't really offer to test as the old vintage scope is a frac and has a pretty long drawtube so I can hit focus with either size even with a diagonal in the train. With the TAL-1 and M with the older 32mm eyepieces you'd have to fit the barlow to use 1.25's as they couldn't focus without unless you shifted the mirror so could be similar with the older 0.956's vs 1.25

You could help Dave. Assuming the difference in focal position between 0.96 - 1 25 eyepieces is equally correlated in frac and reflector, could you simply fit a H20 then do like you said and hold a 8-24 zoom to advise your findings. It is only the difference in the drawtube travel between the 2 that I need to know. 

[DaveL59]

45 minutes ago, bomberbaz said:

 

You could help Dave. Assuming the difference in focal position between 0.96 - 1 25 eyepieces is equally correlated in frac and reflector, could you simply fit a H20 then do like you said and hold a 8-24 zoom to advise your findings. It is only the difference in the drawtube travel between the 2 that I need to know. 

could give it a go, or rather would except for total clouds here. Will try it in the day tho and see. My 8-24 is the huge SVbony one but I do also have their 7-21mm so will see what they give.

[bomberbaz]

6 minutes ago, DaveL59 said:

could give it a go, or rather would except for total clouds here. Will try it in the day tho and see. My 8-24 is the huge SVbony one but I do also have their 7-21mm so will see what they give.

Thanks Dave, a daytime result would yield near identical results I think, cheers. 

Steve

[Louis D]

There are cheap, retro style 0.965 sized eyepieces on ebay as a stop-gap measure.  They won't match up well with modern 1.25" eyepieces, but they'll at least produce an image.

Here's the view through a generic 0.965 6mm Huygens in an f/6 72ED refractor:

Here's the view through a generic 0.965 20mm Huygens in the same scope:

They're actually not too bad for what they are.  The AFOV is 39° for the H6 and 30° for the H20.  Usable eye relief is 3mm for the H6 and 13mm for the H20.

[DaveL59]

So a quick test on a tree top about 300m away using the vintage 3-inch scope. First up, with the H20 0.965 eyepiece and prism diagonal got me a drawtube extension of 115mm.

Next up the SVbony 8-24mm set to 24mm, sat in a 0.965 to 1.25 adaptor, drawtube reduced to 75mm

Finally the SVbony 7-21mm set to 21mm, again via the 0.965 to 1.25 adaptor, drawtube reduced to 72mm

Also tried a Vixen NPL 30mm which turns out to have been parfocal to the 7-21mm.

Hope that helps. It's quite a big reduction as you can see, 40-43mm inward travel in the case of these eyepieces tested. Somehow doubt that on a newt the focuser will give you that amount of extra in-focus travel so shifting the mirror may be in your future... 😉 

[bomberbaz]

Cheers buddy, no chance of it. He will have to make do withth h20 and a 2x barlow.

Thanks for trying

Edited September 3, 2022 by bomberbaz

[DaveL59]

4 minutes ago, bomberbaz said:

Cheers buddy, no chance of it. He will have to make do with the h20 and a 2x barlow.

Thanks for trying

no prob, you might post a wanted as the 0.965's have come up from time to time. I got lucky when I started a thread on that old vintage scope and got offered a set that was from a Prinz 660 IIRC. 

The h20 gives a nice clear image tbh and barlowed would be very usable. If you do find shorter FL ones try for Or types rather than Sr tho. I have an h12.5 that's also pretty good, the HM6 is harder to use but sharp and an Or4 in the set. Also obtained a Meade MA40 in 0.965 that's pretty good, so they are about just don't come up that often. Only thing I don't have is a barlow in that size but no real need for one for the old scope.