Tasco vs Dobsonian

[Orionskies (Julian)]

As a novice astronomer I thought I'd share about my recent upgrade to Dobsonian Saxon 8" from a Tasco Luminova 60mm X 900mm and in doing so it may assist someone thinking of a similar move.

The Tasco sadly had lay dormant in the closet collecting dust for about a decade. A quick dust off and a bit of oil is all it took to get it back in action. A Xmas gift of Flossel eyepiece's sustained my interest with the Tasco, but left me wanting more so I took the good advice on the forums gave the Dobsonian a go.

I used the same Flossel 25 mm and 10mm in both scopes to compare. The first time I looked through a Dobsonian I was somewhat disappointed maybe I was expecting too much but of the three planets I observed (Mars,Venus and Jupiter ) so far only Venus was noticeably larger when compared with the Tasco. The Tasco is also light and easy to move and no need for collimination.

But from there that is about as close as the Tasco gets to the Dobsonian with a larger clearer field of view and easy to use mount for a beginner. While the Tasco was a struggle from the start grappling with equatorial mount and a small finder would often end up in total frustration.And with the steady and easy to use mount and adequate finder deep space was with in reach. That being a challenge on its own but the thrill of first time observation of a globular cluster (I think I found Tuc 47 )was a oh wow moment!

There is an issue with I think they call it 'Dobsonian hole' when observing close to the horizon. So not great if you have close fences or trees in your main observation area.

For me the change has definitely been worthwhile and it has really opened up the night sky. I think once my expectations we're brought to a more realistic position backyard astronomy became really enjoyable!

Cheers Julian

[raymo]

Hi Julian, the aperture of a scope has nothing to do with how large an
object will look; it is purely a function of the scope's focal length.
Your Tasco is 900mm, your Saxon will be either 1000mm or 1200mm
depending upon whether it is f/5 or f/6 respectively. If it is f/5 the image will only be about 11% larger than your Tasco gives. The huge advantage is
that the Saxon has enough light gathering power to allow you to use
higher power eyepieces that will produce significantly larger images.
You will also find faint objects much brighter through the Saxon.
You will also get better viewing with a couple of better quality
eyepieces than came with the Tasco.
raymo

[Orionskies (Julian)]

Originally Posted by raymo

Hi Julian, the aperture of a scope has nothing to do with how large an
object will look; it is purely a function of the scope's focal length.
Your Tasco is 900mm, your Saxon will be either 1000mm or 1200mm
depending upon whether it is f/5 or f/6 respectively. If it is f/5 the image will only be about 11% larger than your Tasco gives. The huge advantage is
that the Saxon has enough light gathering power to allow you to use
higher power eyepieces that will produce significantly larger images.
You will also find faint objects much brighter through the Saxon.
You will also get better viewing with a couple of better quality
eyepieces than came with the Tasco.
raymo

Thanks for this Raymo.

I have the 1200mm, I've as yet only used 10mm and 25mm eyepieces I've also used a Barlow as well with these.

So I guess it only a matter of time till I acquire something smaller, any suggestions would be appreciated.

Thanks Julian

[grimsay (Iain)]

Hey Julian,

I've got a similar scope a Skywatcher 8" which also came with a 10mm and 25mm.

Having experienced Jupiter previously I was a bit disappointed with the view through the 10mm so I kept my eyes on the classifieds and picked a half-decent 5mm for around $60. This took the magnificent from 120x in the 10mm to 240x and satisfied my appetite.

Just had the scope out at 5am to view Jupiter and the detail I could see was stunning. I could clearly pick out white marbling in the cloud bands.

I'm not sure how this would compare to a Barlow combined with your 10mm but I've heard mixed comments/reviews regarding Barlows.

Grab a decent second hand 5mm from the classifieds it'll make a massive difference.

Enjoy,
Iain

Originally Posted by Orionskies

Thanks for this Raymo.

I have the 1200mm, I've as yet only used 10mm and 25mm eyepieces I've also used a Barlow as well with these.

So I guess it only a matter of time till I acquire something smaller, any suggestions would be appreciated.

Thanks Julian

[AEAJR (Ed)]

If you look at something at 100X in the Tasco and 100X in the Saxon, the image will be the same size.

As noted earlier, because the Saxon has a longer focal length each eyepiece will produce a little higher magnification. This has nothing to do with the aperture.

Where aperture matters is when going to higher magnification on bright objects or in the ability to see dim objects.

Your 60mm scope probably runs out of light North of 100X and around 120 you are going about as high as that 60 mm can go even on bright objects. Where the Saxon will handle 300X if the atmospheric conditions, the seeing, is favorable.

I am a big fan of barlows. A 2X barlow will turn that 25mm and 10 mm into 25, 12.5, 10 and 5mm equivalents. If the barlow is doing its job you should not see a lot of difference between 5 mm Plossl and a 10 mm Plossl in a 2X barlow.

In fact the 10 mm plossl in the 2X barlow will have much greater and much more comfortable eye relief than a 5 mm plossl which has almost none.

I am a big fan of barlows. I use a 2X with my Orion XT8i and a 3X with my Meade ETX 80.

[BeanerSA (Paul)]

What a great read, it's good to hear that you are enjoying your scope. And Dobson's Hole, is when you are trying to find and track stuff near the zenith, not the horizon.

[Orionskies (Julian)]

Thanks Iain, AEAJR and BeanerSA for your replies.

Thanks about the advice about the barlow AEAJR I didn't even know that barlows came in 3X so something for me to consider down the track.

I probably will try a 5mm eyepiece Iain in the near future so thanks also. When I first viewed Jupiter thru the Tasco it was fantastic because I wasn't expecting to see much, so I guess I just expected alot more from the Dob. Even with the Barlow there doesn't seem to be much difference so far but I have only viewed Jupiter a couple of times so far and on both those occasions it had been very hot the day before.

Thanks for the compliments BeanerSA and about Dobson's hole.. I'm going to have to name it "Dobson's Sink Hole" when observing too close to the horizon.