If you're happy with the results you're getting then all is good Andrew

Some nice images there Stu. I'd consider stopping that big scope down this time of year, should sharpen things up a bit.

You did well to get these Pedro

You're getting some nice results there Martin!

A nice record of the event Pedro

I enjoyed the video JOhn

f50 with air spaced etalons needs rather perfect seeing to say the least.

Nice set of disks Phil!

Nice shots Alfred!

Hi At F28 you can remove the collimating lens from the front of the PST as its near enough to F-Infinity, or F40 for a air spaced etalon. The re-focusing lens will just about preserve the back focus from the PST. On a 127mm F7.5 with 2x ED Barlow element before PST with Collimating lens at the fron...

You haven't got -200mm of back focus needed. Without using a larger ERF I would just use the setup on the 152 frac assuming it is f10.

How do you rate the etalons Valery?

Incredibly unlikely...

That's great disk Robert! Glad the sun was shining in Skye for you!

Love all these old bits of kit you have Pedro!

Nice disks Eric, especially with the volcano...

Came out well and nice setup Franco!

Those bunnies are on the chip Jack

Nice images Martin! Good capture of the active regions. That extra etalon is working well.

SHG is that's possible John?

These turned out really well Eric.

They're a great set of images there Phil, you're getting some cracking shots with the Lunt80.

Excellent addition. Do you have a Mg version John?

Sorry, it won't work. It will also cut transmission at the wavelength being observed. That's why erf's are needed for narrow band. Stripping the mirror only works for wide band observing in white light.

It's not as straight forward as you think, a fraunhofer achro can often have better SA correction than a triplet, certainly so at shorter wavelengths. However, a triplet will have much higher Strehl at 540nm than an achro. Not all scopes are created equal either; a £8k TEC140 is going to be opticall...