ZWO 120 Chip too Small? (Focal Reducer)

[Macavity]

Having "solved" Newton's Rings re. my ZWO 120MM / Lunt50 combo,
the immediate problem I found with my ED66 / 400mm setup was: 



This is cropped *square* at 960 x 960 pixels, but you get the idea? 

HAPPILY there is a solution! Get a "C-type" Focal Reducer (+ rings):
http://www.365astronomy.com/365Astronomy-0.5x-Focal-Reducer-with-C-mount-for-Video-Astronomy.html

You can use the Focal reducer on it's own (below) -- Or add one / more rings:

The adapter also has a useful filter thread too! The RESULT:

From Left: NO Reducer; Reducer; Reducer + 1 ring; Reducer + 2 rings!
(The approximate Scaling Factors:  1.0x;  0.85x;  0.78x;  0.72x resp.)

The In-Focus is *negligible* with just a focal reducer close to the chip!
If you add *rings*, it might become an issue. Idem "Aberrations", etc.

But, on the face of it, the images look "much the same" to me... 
Clearly the PIXEL size doesn't change  -- No "free lunch"!
But Hey, it works for me (and may help you)? 

P.S. No "rocket science" involved here! But (you guessed?) I quite LIKE
doing stuff like this. I am making a Website for "personal consumption".
No pathologies (Hopefully!) but my memory ain't what it used to be! 

[xtreemchaos]

been using on for a while , thay work very well with the Quark. well done nice report. charl.

[michael.h.f.wilkinson]

Neat solution. I got an ASI174MM and later an ASI178MM for WL and Ca-K exactly because the ASI120 wasn't big enough (I actually had a DMK21 before, now that has a really small chip)

[Macavity]

1 hour ago, michael.h.f.wilkinson said:

Neat solution. I got an ASI174MM and later an ASI178MM for WL and Ca-K exactly because the ASI120 wasn't big enough (I actually had a DMK21 before, now that has a really small chip)

It's *not* an easy choice - For Solar Imagers particularly? I am (now) 
more impressed by the humble ZWO120MM (Idem MC) than before! 

The CMOS chips *seem* more prone to Newtons Rings for H-Alpha?
I bought a (CCD Chip!) DMK41 to solve the NR problem - It did! But
these are rarer, "slower", quite expensive... and not totally perfect...

In *retrospect* I wonder about the Celestron (IS) SKYRIS series???
The "445" ticks a lot of boxes? USB3, CCD (for the H-Alpha) - Same
1280x960, 3.75 pixels (as a ZWO120). But £700(!) is a BIG chunk
of anyone's "household" budget! Anyone need a (human) kidney?

I won't be experimenting anytime soon. But one can still wonder... 

[Merlin66]

Interesting.

where did you find the spacer rings?

 

[Macavity]

2 hours ago, Merlin66 said:

...where did you find the spacer rings?

Good question! I got the THREE 5mm C-CS rings as a *package* with the
original version of the 0.5x reducer from Opticstar UK. But it seems they no
longer distribute them as the "set"? The do have single rings... in theory?

http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Imagers-Opticstar.asp?p=0_10_5_0_3_102

The reducer appears to be entirely generic? I know this because I "repaired" the
Opticstar one (where I put the plano-convex doublet LENS back in inverted!) and
it now looks & performs exactly the same optically as the one "365" one.  

If you put the lens back the wrong way, the aberrations are pretty awful! 

[Pete Presland]

Very nicely sorted!