29.06.2021 Effect of aperture stops on a 150/10 PST mod telescope.

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Tuesday 29th warm but a white and cloudy sky. 

First exercise is to compare 100mm with 150mm apertures without making any other changes. 

I now have a metal "hat" which slips onto the full aperture, 160mm, D-ERF cell. Into which I can insert aperture stops. For this test I cut out a cardboard stop for the 100mm. I simply lifted the "hat" off for full aperture.

Both images were captured within seconds of each other.

The 100mm aperture needed 120 Gain. The 150mm only 60 Gain. 2x GPC in both cases. No change to focuser or etalon tuning.

Identical processing in AS!314 and ImPPG. [Batch of two] 

Saved to PhotoFiltre 7 for conversion from .TIFF to JPEG. No other change except addition of text aperture labels.

The difference is night and day with regards to fine detail.

Unfortunately the telescope moved slightly while I removed the "hat". On tiptoe on a low stepladder! The sun is 51° high. The D-ERF cell is 2.43m off the observatory floor!

To be safe I really ought to repeat the test a number of times in clear, blue sky conditions. One cannot be certain that a thin veil of cloud did not cross, or  move away, between the two exposures.
 

 

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