2" diagonal in 127 mak?

[hms_furious]

Is it possible to put a 2" diagonal on a 127mak?

 

I thought it might be the case of a cheapo adaptor ring or something but it seems not so. 

If I can, what would I need? 

Thanks 

[philj]

I fitted one once using a 2" visual back that screwed on to the back of the scope  I had to get an adaptor ring I think to convert the thread on the 127 to accept the visual back. It worked well.

[Space Hopper]

It will work, but the extra lightpath the big 2" diagonal will swallow up may be problematic.

The focal length of the scope  will be longer, and you may even lose a touch of aperture, although this is more

an issue if adding other components as well, ie a binoviewer.

Edited August 17, 2020 by Space Hopper

[RT65CB-SWL]

I use a 2"/SCT star diagonal with my ETX105...

[hms_furious]

Is it a worthy updgrade? 

[Louis D]

The wider field allowed by using 2" eyepieces more than makes up for the focal length extension to somewhere around 1700mm to 1800mm.  I also didn't notice any increased spherical aberration at higher powers.  People who mount a focuser on the rear threads have the same focal length extension issue, and I haven't heard them complaining about it on here.

If your 127mm scope didn't come with SCT threads already, you'll need this adapter and a 2" visual back.  There is vignetting in the outer field, but it isn't very noticeable visually.  What is noticeable is when bright objects pass the edge of the rear baffle, you get an oval shape that grows larger the farther off axis that bright objects gets.  Just recenter it and it goes away.

You can judge from these images I took through my 127 Mak demonstrating the additional field gained by using a 2" eyepiece versus a 1.25" eyepiece and the vignetting.  I realize now I didn't use a 1.25" visual back for the first image, so it might be about 12% to 15% wider with one.  At 85% center to edge, I sampled the luminosity of the lower image to be 65% of the center luminosity.

[RT65CB-SWL]

For me personally... yes! ...as it screws directly to the backplate with an appropriate SCT adapter ring (shown below) and peace of mind.

<--- this is the Baader ETX-SCT adapter ring that I use with my ETX105.
<--- this is the SCT adapter ring for the 127 Mak's and available from FLO. 

Edited August 18, 2020 by Philip R