112 replies to this topic

[Boom]

Since this thread has kind of become a 4" Meade SCT data repository, I just want to add that the Mirror-Lens version is officially known as the 107D.  I've always heard yucky things about that one, but there was at least one owner that was very happy with his.

 

[CHASLX200]

This maybe the perfect scope for my 7 year old granddaughter. I can mount it on an EQ3 I have laying around and put a battery powered RA drive, Clive. I guess you were right Dwight.

It just beats me how so many can be so bad and then a few are like APO's at high power looking at a star image.

[wfj]

Perhaps because some have the corrector hole large enough that the secondary decenters, so tested fine, but drifts off and performs badly off center?

[CHASLX200]

Perhaps because some have the corrector hole large enough that the secondary decenters, so tested fine, but drifts off and performs badly off center?

Could be.

[starman876]

I have to check the one I have again. Nice straight lines under DPAC, but not so good visually.  Never could figure that one out.  Could be the diagonal I was using now I think about it.  

[rolo]

I have to check the one I have again. Nice straight lines under DPAC, but not so good visually.  Never could figure that one out.  Could be the diagonal I was using now I think about it.  

I think the views with the Tak Prism diagonal are better than the WO mirror. Maybe its just me but it seems that way.

[tim53]

I have to check the one I have again. Nice straight lines under DPAC, but not so good visually.  Never could figure that one out.  Could be the diagonal I was using now I think about it.  

That's happened to me a bunch of times.

[Steve Allison]

I have to check the one I have again. Nice straight lines under DPAC, but not so good visually.  Never could figure that one out.  Could be the diagonal I was using now I think about it.  

The large central obstruction of the 2045, as you know, reduces contrast. For this reason, my 75mm achro gave a more detailed view of Jupiter. But on high-contrast objects like Saturn and the moon, the little Schmidt wows. Double stars are likewise wonderful.

 

Maybe you were looking mostly at very low-contrast objects? This could explain why your DPAC results were good, but your views not so good.

 

Just a surmise...

 

Steve

[wfj]

You could always DPAC with/without the diagonal and compare. Suggest that like with DPAC on a bad newt diagonal, you’ll see less distinct lines that will blur to 1/2 wave or more.

 

[starman876]

 

You could always DPAC with/without the diagonal and compare. Suggest that like with DPAC on a bad newt diagonal, you’ll see less distinct lines that will blur to 1/2 wave or more.

 

That is a good point.  Should give that a try.

 

Thanks

[Bomber Bob]

I'm gonna try the reverse:  My standard DPAC of the objective only; then, test each of the diagonals I use regularly... I'll probably get some surprises in the results...

[wfj]

Suggest that long f/ will test the diagonal independently the best. Stop down a good refractor to get f/50 or so (most aberration is on the edge anyway, so you’re only making the good better).

 

Since the angle of the light cone will be narrowed, the solid “mass” of optical path will be closer to parallel. You might see inhomogeneous patterns of the glass that way more defined instead of as a blur. Convexity/concavity/irregularlity in surfaces would then alter line width seperately.

[starman876]

Suggest that long f/ will test the diagonal independently the best. Stop down a good refractor to get f/50 or so (most aberration is on the edge anyway, so you’re only making the good better).

 

Since the angle of the light cone will be narrowed, the solid “mass” of optical path will be closer to parallel. You might see inhomogeneous patterns of the glass that way more defined instead of as a blur. Convexity/concavity/irregularlity in surfaces would then alter line width seperately.

it will be interesting to see the results