5" Refractor VS 11" SCT

[Rodd]

C11Edge vs TOA 130.  Initially, this one is easy to decide.  11" vs 5"--no comparison.  But, larger refractors with exquisite optics can punch way above their weight.  Add to that the fact that the SCT has a 25%-30% obstruction, and 11" is far more affected by seeing.   A Vendor once told me "That TOA will compare with hold up to the C11Edge".   This comparison is complicated a bit by the fact that different cameras were used.  The C11 image was captured with a CMOS camera with a pixel scale of 0.4 arcsec/pix (I used the .7x reducer), while the TOA image was captured using a CCD with a pixel scale of 1.1 arcsec/pix.  However, there is no way that seeing was 0.4" on the C11 night.  Heck, even 1.1' was probably oversampled.  Seeing was good on the night of the C11Edge--I do not remember what seeing was like on the night of the TOA image.  I do know that the C11 stack has a FWHM of 1.85 and the TOA image has a FWHM of 2.95 prior to rescaling.  The TOA image was scaled and aligned to the C11 image.  No processing was done to the images other than crop, DBE and histogram stretch.  The stretch was manual for each image, but the C11 image was linear fit to the TOA image--so the images are directly comparable as far as signal strength, which the TOA wins hands down do to 11.5 hours vs 5.25 hours of exposure.  Even if the C11 image is no sharper than the TOA image--since both systems shoot at F7, the C11 system is much faster- -a huge consideration.  However, as what is plainly visible in my opinion, the C11 image is noticeably sharper then the TOA image.  Finally, the TOA image consists of 21 1800 sec subs (10.5 hours) while the C11 image consists of 63 300 sec subs (5.25 hours).  Both images were guided with an OAG.

TOA 130 10.5 hours

 

C11Edge  5.25 hours

[rl]

Interesting comparison. To my eyes both are good shots but the C11 wins...the stars look a bit tighter and the nebula has better detail.

[Stu]

Both nice shots obviously, but I would agree with @rl, the C11 wins.l in this comparison. Quite close though, perhaps repeating with more equal conditions/setup would be fairer?

 

[Chris]

The C11 Edge looks sharper to me. Did you nail the focus for the TOA Rodd? 

[tomato]

They are both great results, but the C11 wins both on sharpness and massively on capture time. With my pitiful number of clear nights, that would be a massive consideration for me also.

[Mr Spock]

I'd expect the C11 images to have more detail. However, it will need more exposure time to reduce the noise - very noticeable on the latter.

[RobertI]

Interesting comparison. I'm not an expert on imaging but could the longer duration exposures with the TOA (six times longer than with the C11) also be a factor, the longer exposure giving more opportunity for atmospheric disturbance and tiny guiding errors?

[Rodd]

5 hours ago, rl said:

Interesting comparison. To my eyes both are good shots but the C11 wins...the stars look a bit tighter and the nebula has better detail.

I agree. Needs a bit more time

[Rodd]

5 hours ago, Stu said:

Both nice shots obviously, but I would agree with @rl, the C11 wins.l in this comparison. Quite close though, perhaps repeating with more equal conditions/setup would be fairer?

 

conditions may have been the same, I don’t know. But maybe they weren’t too.  I think using the same camera would be better.  When I use the toa again it will be with the asi 1600 so it is definitely posdible

[Rodd]

1 hour ago, Mr Spock said:

I'd expect the C11 images to have more detail. However, it will need more exposure time to reduce the noise - very noticeable on the latter.

Yes. 

[Rodd]

1 hour ago, RobertI said:

Interesting comparison. I'm not an expert on imaging but could the longer duration exposures with the TOA (six times longer than with the C11) also be a factor, the longer exposure giving more opportunity for atmospheric disturbance and tiny guiding errors?

That could be. So many variables to consider 

[Rodd]

3 hours ago, Chris said:

The C11 Edge looks sharper to me. Did you nail the focus for the TOA Rodd? 

I focus the same way. I dont remember the night.  Focus is definitely a critical variable though.