Short first light for the Long perng 90mm F/5.5 doublet

[ONIKKINEN]

Clouds cleared suddenly and i put my new grab and go kit to work. The frac and eyepieces is in a backpack and a Skywatcher AZ5 + steel tripod is somewhat easy to carry out in one hand. I dont really have a backyard in my apartment complex, but a short hop across a road to a (fully lit 24/7 🙄) parking lot frees up the horizon down to 10 degrees - so barely enough to see the Moon and Saturn sweeping across rooftops.

And Saturn was the true first look through the scope, i mean it would be rude to look at something else! Pentax XW10 and a 2.5x barlow in a TS- 1.25'' dielectric diagonal for a comfortable power of 125x. Saturn snaps into focus very easily even though its very low on the horizon. The view isn't super stable, but it is actually not even close to the worse views i have seen of Saturn so i am very pleased at this point, but to test how well the scope holds collimation with the heavy chunk of glass that is the XW10, i cruised around Saturn keeping it close to the edges of the FOV and seeing if the image degrades. I am pleased to report that it does not and its sharp across the field of view so doesn't seem like there is any sagging in the focuser. There was something to the side of Saturn blinking in and out of view once i got a comfortable position and looked for a while, maybe a few widths of saturns rings away and im not sure it could be anything other than Titan which is surprising with the bright night skies. No hint of Chromatic aberration for Saturn at this power!

Jupiter was next, still with the same setup of 2.5x barlow and XW10. Here, i do notice the chromatic aberration as a quite bright purple edge around all of Jupiter. It does bother me a bit since purple is a very unnatural colour to see for me (newtonians only before). I let the view seep into my eyeball for a while and kinda just got used to it in no time, but i can still see it and i am thinking for Jupiter i would be better off with some kind of purple fringe eliminating filter. I saw 2 rather obvious dark bands and a varying number of other lines across the disk. I see some kind of "mush" at the edge of one of the bands that keeps coming and going with the seeing (which was pretty good actually). Occasionally i see some spiraly-swirly structure in place of the mushy something. Surprised to see that a 90mm aperture scope can give pretty nice views of planets too! Almost forgot to write that i started observing Jupiter with 3 visible Galilean moons, but during observing a 4th one appeared from behind Jupiter! Actually checking now it was Europa and it was in front of Jupiter and not behind, but this i did not spot before it had crossed the disk.

Gave Mars a brief look but at 125x its a very small reddish not quite round disk. Cant really say more on this one, needs more power and a few months for Mars to come a bit closer.

Looked at the Moon for a very short while. Its basically licking the rooftops and the views were awful really. But here too there is the purple fringe. Bothers me less since the Moon is enormous and i dont feel like the view is bathing in the light, but if i can see it it probably means there is some contrast and sharpness loss so another target to test later if/when i get some kind of filter.

Just as a passing thought before heading back inside i pointed the scope towards the double double in Lyra and was welcomed with a very obvious split of both doubles. Quite pleased with the optics at the moment! Clouds are coming and going and most of the sky is covered in what looks like haze, so pack up the stuff and head home.

I did get the feeling that for Jupiter and perhaps the Moon i would be benefiting from some CA filtering.

And more power. Could definitely have used more power.

Edited July 16, 2022 by ONIKKINEN
Forgot the moons

[Ags]

Nice! Sounds like an RFT that can "do planets". It should be a great "sweeper" if you can get it to some darker skies. Nice to hear it splits doubles well too.

Just wanted to add that the Long Perng comes in two flavors - one with regular glass + lanthanum, and one with FPL51 + lanthanum. I think you have first one?

I've read these are also excellent solar scopes in white light and Ha, as the lens in both flavors of the scope appears to be well figured.

Edited July 16, 2022 by Ags

[ONIKKINEN]

3 hours ago, Ags said:

Nice! Sounds like an RFT that can "do planets". It should be a great "sweeper" if you can get it to some darker skies. Nice to hear it splits doubles well too.

Just wanted to add that the Long Perng comes in two flavors - one with regular glass + lanthanum, and one with FPL51 + lanthanum. I think you have first one?

I've read these are also excellent solar scopes in white light and Ha, as the lens in both flavors of the scope appears to be well figured.

Yes, indeed mine is the more affordable one of the 2: https://www.teleskop-express.de/shop/product_info.php/info/p11438_Long-Perng-90-mm-f-5-5-Doublet-ED-Rich-Field-Refractor-with-2--Crayford-Focuser.html

Quoted from the description:

Quote

The adjustable 2-element objective has a similar color correction as a normal Fraunhofer achromat with f/7, but offers a significantly higher speed. This corrector is achieved by the lanthanum-containing special glass.

No mention of any specific glass type like FPL51, but just that "lanthanum glass". If it did have an FPL-something lens in it it would be marketed for sure so safe to say it does not. But i am pleased to see that CA on this one i can live with for the most part, but will try filtering that out anyway to see if Jupiter gives a bit more that way.

Edited July 16, 2022 by ONIKKINEN