Just as a FYI, Brian Stevens at Lunt did mention the issue of tube currents was one of the reasons their 30 cm scope uses a open truss design.
The other issue I want to highlight is that etalons are very sensitive to temperature changes. My Solar Scope DSF100 etalons suffered greatly from thermal instability - and they sat ahead of the objective in the 1 mW/mm^2 region of direct sunlight and had a RG630/dielectric ERF ahead of them. None of the materials an etalon is composed of have a zero CTE, and reducing thermal loading and cycling as much as possible should be of paramount importance for optimum performance. Therefore using good pre-filtering as I previously described would help ameliorate such thermal loading and cycling...
D-ERF in converging beam?
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Re: D-ERF in converging beam?
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Re: D-ERF in converging beam?
Thank you Bob.
I have seen changes in my own 6" 'scopes during my [usually] long image capture sessions. I would put it down to seeing conditions as the day warmed up. Though that doesn't account for better seeing later in the day. When the thermal load on the landscape must surely be at its highest. With convection from the heated ground rising into a cooling atmosphere.
Solar Spectrum uses an onboard cooler/heater at a price rather beyond most amateur's pockets. Though a simple cooling fan could easily be applied to our "toasty" etalons.Your argument for better filtration might well be more effective. Since the PST etalon is fully enclosed by its glass lenses. An external airflow may go completely unnoticed. Will we all end up with skeleton tubes? With a battery of cooling fans blasting away at each of the components?
I have seen changes in my own 6" 'scopes during my [usually] long image capture sessions. I would put it down to seeing conditions as the day warmed up. Though that doesn't account for better seeing later in the day. When the thermal load on the landscape must surely be at its highest. With convection from the heated ground rising into a cooling atmosphere.
Solar Spectrum uses an onboard cooler/heater at a price rather beyond most amateur's pockets. Though a simple cooling fan could easily be applied to our "toasty" etalons.Your argument for better filtration might well be more effective. Since the PST etalon is fully enclosed by its glass lenses. An external airflow may go completely unnoticed. Will we all end up with skeleton tubes? With a battery of cooling fans blasting away at each of the components?
http://fullerscopes.blogspot.dk/
H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.
H-alpha: Baader 160mm D-ERF, iStar 150/10 H-alpha objective, 2" Baader 35nm H-a, 2" Beloptik KG3,
Lunt 60MT etalon, Lunt B1200S2 BF, Assorted T-S GPCs or 2x "Shorty" Barlow, ZWO ASI174.