8SE SCT Transformation Complete!

[cloudsweeper]

I recently got an Antares Focal Reducer (f/6.3) and a good Skywatcher 1.25" diagonal for this 'scope.  So now it has:

# (same) decent aperture and GoTo of course

# smaller, lighter diagonal

# similar max useable magnification

# flat field and sharper star images

# same best FOV, but greater FOV with all the 1.25" EPs

# slightly larger exit pupil (being faster)

And to complete the set-up, I have just got an Explore Scientific x2 Focal Extender to plug a couple of gaps at the high end of the magnification range (and other applications).  (See pic..)

I think this might just become my telescope of choice now!

Doug.

 

[Craney]

Is that a Lego Tyre for fine focus ???

 

[wookie1965]

Very nice great set up, love to have a look through it sometime. 

Edited May 22, 2022 by wookie1965

[Louis D]

For very low contrast planetary observing at high powers, you'll probably want to revert back to a 1.25" visual back (or 2" with 1.25" reducer) to eliminate about 8 extra lens elements in the optical path.  I do a similar thing by removing my GSO coma corrector in my Newtonian or TSFLAT2 in my refractors.

[cloudsweeper]

2 hours ago, Craney said:

Is that a Lego Tyre for fine focus ???

 

Yes, that's at the cheaper end of the transformations!  😉

 

18 minutes ago, Louis D said:

For very low contrast planetary observing at high powers, you'll probably want to revert back to a 1.25" visual back (or 2" with 1.25" reducer) to eliminate about 8 extra lens elements in the optical path.  I do a similar thing by removing my GSO coma corrector in my Newtonian or TSFLAT2 in my refractors.

Yes, there is a 1.25" Visual Back between the Reducer and the Diagonal.  I suppose however that using the Back without the Reducer/Extender would remove the advantage of sharper stars and increased FOV.

Edited May 22, 2022 by cloudsweeper

[RobertI]

I’ve been meaning to do a comparison of views with and without my 0.63 reducer for some time. Interesting that you find it gives sharper stars, sounds promising. 

[Louis D]

At high power, most correctors induce spherical aberration on axis.  They're mostly intended for use at low to mid powers.  The Tele Vue Paracorr 2 is supposedly an exception to this rule and can be used at high powers.  I can't say that SCT R/Cs aren't usable at high powers since I have no experience with them.  It might vary brand by brand how usable they are.

[cloudsweeper]

7 hours ago, RobertI said:

I’ve been meaning to do a comparison of views with and without my 0.63 reducer for some time. Interesting that you find it gives sharper stars, sounds promising. 

Yes, I reckon there is an improvement.  Without the Reducer, the (well collimated) SCT was less sharp than the fracs (of course).  And the Dob was better too.

In similar posts, other members have also remarked on noticing this.

Doug.

[Louis D]

9 hours ago, cloudsweeper said:

Yes, I reckon there is an improvement.  Without the Reducer, the (well collimated) SCT was less sharp than the fracs (of course).  And the Dob was better too.

In similar posts, other members have also remarked on noticing this.

Doug.

At low to mid powers across the field, the R/C will certainly improve star images just as Newtonian coma correctors and refractor field flatteners do.

My point was checking at high powers (let's say less than 1mm exit pupil for starters).  At equivalent powers with and without the R/C, do star images improve or degrade on axis?

I've found both the GSO CC and TSFLAT2 to degrade star images on axis at high powers due to spherical aberration manifested as star image bloat.  Splitting tight doubles would be a good test of this.

I leave my correctors in 99%+ of the time.  However, during the Mars opposition for example, I found the images to be sharper and contrastier without the correctors, so I left them out.

I'm just saying be aware that the R/C may not be a panacea for all observing.

[cloudsweeper]

1 hour ago, Louis D said:

 

I've found both the GSO CC and TSFLAT2 to degrade star images on axis at high powers due to spherical aberration manifested as star image bloat.  Splitting tight doubles would be a good test of this.

 

Thanks.  It's been good at x256 (0.79mm) and pretty good even at x320 (0.64mm).  Seeing is an issue then as well.  Reckon I'm satisfied that the config beats the straight 8SE!

Doug.