Monday, February 25, 2008

Blog Admin: Posting comments

Just an announcement... Today I have activated comment filtering, because I'm starting to get comments here that have _nothing_ to do with astronomy hobby (i.e. spam). If you leave a comment, pls be patient to wait a while -> so I can check these comments before accepting them (I get email info when comment is posted). I do not have any intention to modify comment before allowing to publish it, only to check if it is someting related to spam.

Thanks, Timo

Antares 8*50 illuminated RACI finder

My Celestron C8 scope had only a plastic and flimsy red dot finder in original configuration. I needed a better magnifying finder, that will also help to spot dimmer objects on the night sky. There are no detailed measurement reports here, only a personal thoughs and ideas. Hope they will give you some idea about this Antares finder. The configuration looks like following:
Antares finder is attached the SCT frame with Baader finder bracket Rel4 -model. Maximum tube diameter that it can hold, is 72mm. I chose the larger model insteadt of Rel3, because of the larger "dewshield" tube in Antares finder. I was really amazed with the mechanical build and quality of this Baader product (with small cons, see comments). It is very sturdy and can hold bigger finderscopes also, maybe even small guiderscope (I have not tested this yet...). Supplied aluminum block between finder dovetail and finder bracket is removed to get finder more close to SCT.

Antares finder gives correct image in up/down and left/right directions because of 90 degree prism used. The image quality is good for the price, not perfect though. For higher optical quality the price would go very high, so I stay on this level now. Image quality is lower on the edge of field. Currently I did not had possibility to compare this Antares to other finders, so my comments are based on the actual (and short time) use. I've noticed that It takes some time to get familiar with the use of prism finder. I've noticed myself watching between the sky and finder EP, even when the finder is pointed to the right part of the sky :-) When scope position changes, there comes also an issue with finderscope viewing angle. In some directions it is facing sideways. It is possible to rotate finder in Baader bracket (by loosening setscrews a bit). Another method is to loose setscrew on Antares prism and rotate it (requires modification to allen screw). Finder eyepiece has double crosshairs with adjustable illumination (standard 1.25" size)

Antares finder - pros / cons
+ image quality decent/good for the price
+ correct / right angle image
- rear and front caps always dropping
- eyepiece focusing is jamming in low temparatures
- no separate focuser (eyepiece has to be moved)
- loose fit in lens hood tube (need to be attached again)

Baader finder bracket - pros / cons:
+ very good mechanical build and quality
+ feels sturdy
+ disconnected quickly from scope
- finder bracket screws are bit small and slippery
- plastic tips of adjustment screws need to be glued with superglue

Sunday, February 17, 2008

Saturn imaging at Nuuksio

After a long time waiting, finally skies cleared. Thanks to my work colleague for the car ride... Expectations were high, but I was disappointed with the results. Seeing was very bad, it caused lot of disturbance in the atmosphere. After stacking I also noticed some "stripes" in the image. Got to find out where they are coming from...

C8 image details:
Location: Nuuksio (Espoo, Finland)
Date: 15th February 2008
Time: 23:43 UTC
Telescope: C8 XLT (2032mm f/10)
Mount: Skywatcher HEQ-5
Barlow: TeleVue 3x
Webcam: Philips SPC900NC
Stacking: Registax v4, 952 frames

It was approximately one year (!) after my last Saturn imaging session (too long time to speak). I made a comparison image pair about Saturn rings. They look more and more narrow each time. Within one or two year, the rings should "disappear", since the plane is pointing towards earth.

Saturday, February 9, 2008

Thoughts about weather

What could I say... A lot. But it maybe would not be any "nice language". Raining wet and sleet. Sometimes snow falls on the ground, usually melts in couple of days. But always cloudy, cloudy etc... If correctly remember, during last 3 weeks my C8 hasn't had any night time usage.

While waiting for skies to clear, I am constructing leveling aid for HEQ-5 mount. It consists of aluminum plate and double spirit levels attached to it. You just drop the plate into tripod slot and start fine adjusting the tripod. When I've finished the project, I'll post an article.