Reducing aperture

[C6rrules]

My Solarmax 60 ii has various quirks . Let’s no go to the plastic bolts holding the “good game “sliding focuser.

Amongst which is the comment that visually , the whole surface is not showing detail .

With the etalon set to prom and filament detail , turning off tracking allows a narrow band of “excellence “ to glide across . 
Hmm a bit challenging if you’re sketching !

I then experimented with aperture reduction . 

Firstly with a bit of card .

I then measured the diameter of the ota . The blue plastic top of Cadbury’s drinking chocolate is about right size . 
Three lids  later (!) just cutting around a thin line on the underneath , I found the exact fit .

About 2/3 circle was drawn on the lid and a careful cutting out ( old scalpel !) carried out . 

Pushing on the lid and observing:

Err wow ! One heck of a load of contrast and the whole disc detailed with tracking on . 

Have a go ! I’m a great believer in frac aperture !  Oh , many hot chocolates later !  
 

Clearer ( and blooming drier ) skies ! 
Nick.

Edited June 15 by C6rrules

[Paz]

I am not certain how translatable the situation with a Solarmax 2 is to a Daystar Quark but with my Quark I have to date been using a polarising filter to tune it, dimming to see surface features and brightening to see proms.

I've been reading up recently and apparently reducing the aperture (or rather, increasing the focal ratio by reducing the aperture) is good for surface details and the opposite is the case for proms.

I have a bit of card I have cut into a 40mm aperture mask for my 72mm refractor and will be testing to see if changing the aperture works better than a polarising filter for tuning the views. I just need some sunshine to be able to try it.

[Highburymark]

Focal ratio (and the angle of light entering the filter) is a critical factor in how etalons perform. For mica-based ‘eyepiece’ filters like Quarks, a minimum of F/30 is advised to bring out surface detail, and preferably F/40. Even up to F/60 can deliver improved contrast on filaments (as opposed to proms, which are normally clearly observed at all focal ratios). 
But air spaced filters also need slow focal ratios and as perpendicular light path as possible. I suspect what’s happening with the Coronado in the OP is the etalon has a very small sweet spot which is maximised by a narrower, more perpendicular light path. The Centre Wave Length obviously varies considerably across its aperture, which means with a faster system, much of the fov is off-band. Really great that you’ve found a way to make the most of the on-band area of the etalon.

[C6rrules]

Yep , I use a polarising filter and marked the sweet spot for those contrasting views. 
it certainly gets very addictive, for our health , I’d suggest a long peek every so often!

clear blue skies ! Nick