My first scope - need Eyepiece and general scope advise

[noeyedeer (Matt)]

hi Nige, Venus should look more like a cresent moon at the moment even at low power. I've found it easier to view as soon as I can spot it in the twilight. it's not as bright and I can see the crescent using a 40mm in my 10" ... I'll attach a pic.

another thing to do is to put your scope out to reach ambient temperature before you want to view. mirrors need to cool down and tube turbulence can affect viewing. ... but maybe not as much as you've experienced.

I'll find my phone pic of Venus .. and add some info to it in my next post
matt

[noeyedeer (Matt)]

these were taken around 1830aest using my phone held to the ep afocally?
I think I was using at the time a 40mm for the fist pic, and the second was a 15mm. iso100 exposure -2 ... actually I think I just zoomed in on the phone with the 40mm ep with the second pic

but you should see something like that not a star like image in the ep with Venus ...

matt

sorry Venus is the white object. the gray around it is the sky and my secondary mirror casting shadows on my phone's lense ...

maybe they were both through the 15mm ... was a while ago and I don't have a steady hand either way

[Pinwheel (Doug)]

Originally Posted by TAHAIC

I noticed a 55mm thread (approximately) on the focuser which I didn't notice when I posted the picture of the 40mm thread. Is this able to accept an adapter for 2" Ep's?

I have no motion tracker - is this readily available?

I might be expecting unrealistic image quality - I don't know what to expect.

The 2" thread is for a camera mount, But I'm sure a 2" EP adapter would fit, I don't know why you would bother when 1.25" are cheaper & plentiful.

You can buy a telescope clock ( motion tracker ) anywhere, Try Flebay etc.

Newtonian telescopes in my opinion are for Deep stargazing & Nebula's, Galileo never knew what laid beyond Jupiter. Down load a southern hemisphere star map & look at some of the jewels in our sky's. You will soon discover that the local planets are boring compared to what's up there. Enjoy

[TAHAIC (Nige)]

Thanks for the pics Matt, this helped me allot. Now that I know what it is supposed to look like I realise that I can see this but it is is being drowned out by large amounts of flaring which is even worse with my 6.5mm EP.

I posted on the general chat forum for some help in borrowing an EP to test my scope. I got some good help from the Brisbane Astronomical club on Friday night. They pointed me to Astro Petes at Mt gravatt. I meet up with them on Saturday night and we had a good look at my scope.

We collimated it with a laser collimator and tried some different EP's. To my disappointment the problem seems to be with the scope and not the EP's. My EP's worked ok in one of Peter's 8" Dobsonians and using his EP in my scope showed the same bad flaring out of focus image that my EP has. We were looking at Jupiter and we just couldn't get my scope to focus properly.

Just when its about to come into focus it just doesn't quite make it then it starts going out of focus again. there was four or five guys looking at my scope and no one could put their finger on what is wrong with it. I guess it really boils down to either the primary or secondary mirror's. My scope is a very fast f 3.7 - 8" FL 750mm like Pinwheel's and the secondary mirror is about 100mm x 70mm which is probably worth trying to replace before giving up on the scope. A primary mirror is probably not worth replacing since you can by a new Dob for about $500.

If any one has any suggestions I'm all ears.

Thanks for your help

TAHAIC

[Pinwheel (Doug)]

Originally Posted by TAHAIC

A primary mirror is probably not worth replacing since you can by a new Dob for about $500.

http://www.ebay.com.au/itm/111210013...84.m1438.l2649

[noeyedeer (Matt)]

I get a lot of flaring too looks like a big X shooting out from Venus. if I shot Venus with normal exposure with my phone it'd be too bright, so maybe it wasn't the best representation of what to expect. thou when I use the 6mm the glare is reduced quite alot.

I find Venus easiest to view as soon as it's visable as well. when the sky becomes darker Venus just gets brighter.

also it's a shame no one knows what's wrong with your scope. has the mirror been moved up the tube by any chance, for imaging?

matt

[mental4astro (Alexander)]

Hi Nige,

Mate, sorry to read about your scope. The up side though is you've made contact with some very good people.

I wouldn't recommend you chase a better set of optics for that scope. You would be better off going new or secondhand OTA. I got my 8" f/4 OTA for a good price new from a retailer - I had to make a new mirror cell for it though. No sweat really. I also made the dob mount for it too. If you are handy with tools, all you need is an OTA (optical tube assembly) and you'll be able to knock up a mount that will perform better than any mass production mount. The 8" dob I have doesn't have any springs or braking mechanism to control balance. Through just clever design, I can switch between a tiny 6mm plossl to a monster 800g 30mm 2" bruiser, and not have ANY balance issues - this just can't be done by mass production mounts.



Of cause, the other option is a commercially made scope. Optically nothing wrong with them, and the mounts will still work.

With respects to your existing scope, the mount is probably the best thing going for it. While is probably is a little light weight for an 8" scope, it would make for a fine mount for a smaller scope if you would like to do some basic imaging with it. An astronomy video camera would be a great pairing with that mount if you are able to get an RA drive for it.

Some food for thought.

Mental.

[Pinwheel (Doug)]

I was out last night with my Precision (same as yours) and watched Jupiter rise. What was interesting was while viewing low in the atmosphere there was the distortions you described, however as Jupiter rose & the night got cooler the image got sharper & sharper. I could make out Jupiter's bands & four moons just before pulling the plug and going to bed.
What I'm now thinking is when you were viewing venus while your scope was still warm & that atmospheric turbulence may have played a part here?

If you want to send me your complete mirror assembly, I'll test it on my scope to prove if the primary is at fault.

[Pinwheel (Doug)]

I took these tonight around 10 pm. The moon is bright and still low, but still sharp & no flair.

Photos taken on the Precession using the DSLR camera adapter screwed on the 2" thread at 500th of a second, single exposure.

[TAHAIC (Nige)]

Supplies/Bintel-Primary-Mirror-8--f/5/52/productview.aspx

Originally Posted by Pinwheel

If you want to send me your complete mirror assembly, I'll test it on my scope to prove if the primary is at fault.

I think this is a great idea providing you don't take my mirror and run off into the wilderness! PM me with your phone number and address - and I will send you my primary mirror assembly for testing! This way I will know if its the primary or the secondary mirror causing the problem.

Thanks mate.

Mental - if I need too I am keen to make a carbon fibre ATO and purchase a new mirror like - this. I can mount the focuser on the the new ATO utilising the same EQ mount. - hopefully!


TAHAIC

[TAHAIC (Nige)]

Originally Posted by Pinwheel

I took these tonight around 10 pm. The moon is bright and still low, but still sharp & no flair.

Photos taken on the Precession using the DSLR camera adapter screwed on the 2" thread at 500th of a second, single exposure.

no offense but these images look like crap - Please educate me in the exact details as to how you made these images!

TAHAIC

[noeyedeer (Matt)]

this was taken through the trampoline net thing (which I despise) and my phone with a 40mm ep. had to pack up before I could get a decent shot because of rain ... but it's clear now but i cbf lugging the scope back outside

matt

those other pics aren't so bad

[TAHAIC (Nige)]

Well in all honesty I shouldn't be making any comment on the quality of these images because I haven't got a clue! They are probably fine - maybe its just because it's a single exposure. The moon does look a little better through my scope's EP.

[noeyedeer (Matt)]

full moons just hard to image (for me anyways) because it's so bright and focusing on any area doesn't really bring out any details as say a half or crescent moon does. plus on the phone I can't do super short exposure times, like 1/500th or whatever which is needed (I shouldve used camera fv-5, instead of the stock but I didn't have time to play with it's settings). indeed through the ep it's not as crappy.

matt

ps added an older moon pic that wasn't through the trampoline safety net and was higher in the sky for a comparison. the details say it was 1/459th of a second and uncropped

[Pinwheel (Doug)]

I bet yous was taken in winter too! Mine was a hot night with Harvesting going on, Lots of dust & smoke in the air.

[noeyedeer (Matt)]

Originally Posted by pinwheel

i bet yous was taken in winter too! Mine was a hot night with harvesting going on, lots of dust & smoke in the air.

17/10

[Pinwheel (Doug)]

Originally Posted by noeyedeer

17/10

But was it a cold October night?

[noeyedeer (Matt)]

Originally Posted by Pinwheel

But was it a cold October night?

lol I can't remember ... according to bom max was 26.1 and min was 18.2 and I took the pic around 1930aest, so probably was warmish still at that time

matt

[Pinwheel (Doug)]

Originally Posted by noeyedeer

lol I can't remember ... according to bom max was 26.1 and min was 18.2 and I took the pic around 1930aest, so probably was warmish still at that time

matt

Well there goes that theory out the door...