Pease 1/double stacking OIII filters

The early AM hours last Wednesday were unique in that my home was in deep blue seeing on the Clear Sky Clock for the first time in a long time. At about 3 AM M15 was well placed near the meridian. I decided to try to see Pease 1 in M15 with a 20 inch Starmaster. I have seen it previously with a 40 inch f5 Dob. My experience has been that it requires very steady seeing that will allow magnification of 400 to 500X to be used in order to have a chance. On Monday the atmosphere was so steady that it was no problem to use mags in the neighborhood of 500X. With the help of the excellent finder charts at the blackskies web site, I was able to see Pease 1. An OIII filter is necessary to see this 1 arc second planetary. I used a TeleVue 2X Big Barlow and later went back inside for my TeleVue 2X Powermate. I found that the image using the same 11 mm Nagler was brighter and had better contrast with the Powermate than with the Big Barlow. For the heck of it, I tried putting a 1.25 inch OIII filter in the Nagler while I had a 2 inch OIII filter in the Powermate. This "stupid pet trick" reduced the transmission so drastically that all I could see through the stacked filters was the very center of the dense core of M15 and the speck that was Pease 1. The guide stars used to find Pease 1 with a single filter were not visible through the stacked filters but Pease 1 was exactly where I had seen it with the use of the guide stars and a single filter. I'm not sure there is ever any good reason to double stack OIII filters but I was impressed that Pease 1 was still visible through two of them.

Stacking OIII filters. Wow. That's a testament to the light gathering power of a 20 inch mirror. I don't think I'll be trying that with my 6 inch newt anytime soon.

Really neat experience, thanks for sharing.