Wratten #29 deployed!

[Ags]

Jupiter 2019-07-30 21:15 UTC

If you take a look at my previous Jupiter pics (taken with a Wratten #8 filter) a couple of things stand out: the equatorial bands are broadened and the moons are stretched into vertical smudges. I suspected this was atmospheric dispersion the Wratten #8 was not correcting sufficiently. Today I picked up a Wratten #29 (dark red) for the princely sum of EUR 15 that I thought would improve matters.

Seeing was very bad tonight, and Jupiter is too close to a tall building, but I shot a 3 minute sequence. 2 minutes is the limit for Jupiter but I guess with just a low resolution 102mm scope I can get away with a bit more. As the Wratten #29 is very dark I increased the exposure from my usual 12ms to 33ms. Lookit the moons!

For comparison, here is a Wratten #8 image on a night of better seeing:

Edited July 30, 2019 by Ags

[Nigella Bryant]

Interesting that the wratten 29 filter image is sharper even though seeing was worse. I guess it's not affected so much by the seeing conditions and refraction of the light through the atmosphere. 

[Ags]

I found a mad new method to get the planet on the chip. After switching from eyepiece to camera I could not see the planet. I presumed it was simply out of focus so started dialing the focus knob. Eventually I was so far out of focus that the edge of a huge disk expanded into the field of view - the sensor was picking up Jupiter so defocused that the disk was probably 5 times bigger than the chip. The sensitivity of the ASI 178 is phenomenal! Anyway, once I saw the faint disk it was simple to improve the focus and move the scope incrementally to the center of the defocussed disk.

[astroman001]

Poor seeing affects shorter wavelengths more than long, so the red channel and IR always look the sharpest. Try an IR 742 filter for even sharper images.

Peter

[Ben the Ignorant]

I use a light red #23A to get the same effect in visual, wouldn't it or the middle-of-the-road #25 be dense enough for photography, but with shorter exposures than the dark red #29?

[Ags]

I thought about a #23A or #25, but even though they are a bit brighter they are really only adding atmospheric dispersion back in. I am looking to go the other direction to a full Near IR filter instead.

The other reason for the #29 is that I hope it will function as a low-tech H-alpha filter for DSOs. No it won't be perfect, but it will work better than the #25 for this. If I add an IR-block to the train, the #29 will be almost like a 70 nm H-alpha filter and as an added bonus will work at F2.0 when mounted behind my Nifty Fifty. In the old film photography days, the Wratten #29 was the filter used for H-alpha regions... I'm also hoping it will tighten up the stars in my ST80.