Double stack etalon -is it worth it ?

[Merlin66]

Hmmm, an older thread..........

Just a comment about "dimmer views through a double stack"

This is NOT due to having an ERF in both etalons - the transmission of an ERF at H alpha is around 90%, so a second ERF would only give an addition loss of 10% of the light.

The impact of the double stack is to reduce the bandwidth of the "effective" etalon, from around 0.8A to 0.5A. This significantly reduces the light throughput. A reduction of around 40%.

All things being equal, a single etalon with a bandwidth of 0.5A would give similar views to a DS with a 0.5A bandwidth.

 

[richard ashbee]

On 20/05/2018 at 12:34, Mark at Beaufort said:

I bought a PST in 2005 initially to view an Annular eclipse followed by a Total eclipse a year later. I was very happy with my PST which I felt covered my needs. About 15 months ago I borrowed a Double Stack, at a star party, which screwed into the front of the PST. The difference it made was amazing IMHO.

Several months later a S/H DS came up on the SGL classifieds (£400) - I bought it and over the last year I have had some very enjoyable views of the solar surface. I do compare the standard PST with the DS in place from time to time and it confirms that I am glad that I bought the DS.

I agree that it does dim the view but I put a cover over my head which works brilliantly.

where did you get the black cover from? - thanks

[Mark at Beaufort]

Richard the black cover came from Telescope House many years ago. However, since then I bought a Hood from this company which is better - 

https://r-sky.org/en/products/observing-hood

In my case I bought the dark hood for DSO observing but they do make a solar hood - see bottom of page.

Several members on the forum have bought from them in Russia and I never had a problem.

[Peter Drew]

I double stacked a PST years ago, there was a marked change in the contrast of surface detail so quite impressed initially.  After the WOW factor wore off a bit there was something about the image that didn't quite suit me.  I think it was as though the image was frozen rather than live,  whatever it was, that and the cost put me off.  Instead, I put the money towards building a PST "mod", now that really made a difference!    🙂 

[BGazing]

22 hours ago, Mark at Beaufort said:

Richard the black cover came from Telescope House many years ago. However, since then I bought a Hood from this company which is better - 

https://r-sky.org/en/products/observing-hood

In my case I bought the dark hood for DSO observing but they do make a solar hood - see bottom of page.

Several members on the forum have bought from them in Russia and I never had a problem.

R-Sky is great, never a problem with them, fast and cheap shipping and good products. Solar hood is a godsend.