first light

[stephend]

I finally got time to point the new 10" Dobsonian at the afternoon sky.

Spent 15 minutes trying to latch onto the crescent moon. Couldn't see a darned thing except fuzzy blue, even when I pointed it at my feet. Figured there was something wrong in the setup but suddenly there it was, by accident, the little crescent moon with all it three dimensional craters. It was just amazing. The little mountains in the middle of the craters are the best thing.

Then tried Mars. Mars was very, very disappointing - with a 10" aperture you should be able to see a lot of detail, right? ... and all I was getting was a single point of light through all three lenses ... but then I realised it was Aldebaran.

Real Mars was also disappointing. A fairly large obvious planetary disk glaring at me, but no detail at all. The last time I saw Mars through a telescope was at the you-beaut observatory at Faulconbridge, Blue Mountains. You could clearly see the polar ice cap and other surface detail. All I got was a red rubber ball that appeared to be burning, with glare and various streaky lines shooting off to the left. Still looked great and I guess I fiddled with various eyepieces and focussing for an hour or so, very happily.

Last I looked at the Pleiades. This used to attract me when I was a kid, when in virtually zero artificial light conditions that prevailed then and there I could see 14 stars in the "Seven Sisters". I think they used to say that if you were really good you could see 16 stars. Nowadays in Mayfield with permanent orange night skies due to Onesteel and other co-creators of the modern situation, I can see about four sisters, with averted eyes. With the telescope I could see about 500. I am absolutely gobsmacked and think I might just become a Pleiades observer. There is one little string of same-brightness stars that drops down and finally curls around in a bit of a hook, that is unbelievably neat and pretty.

Technical problems I need to investigate include:

The Meade 10" Dobsonian focal length is 1270mm and the smallest focal length eye-piece that came with the deal was 15mm. This should have given a magnification of 84x.
The 20mm should have given a magnification of 63.5x.
And the 2" deluxe 26mm eyepiece should have given a magnification of 48x.
Basically they all looked the same and though Mars stood there like a not so small moon, only red, there was no surface detail.

The telescope came with a very clever finder device which shows a red circle (or cross or whatever option you choose) superimposed on the sky. You would think this would be severely compromised by the position of your eye but in fact if you plant your face too far up or down or left or right you see nothing. If the red image is visible, it's always close to exactly dead centre. However, I found it didn't respond to adjustments. I could unloosen the up-down screw as much as I liked, but the red image would never close on the target. The left-right adjustment seemed to work better. Never mind, I got used to planting the red image about 3 degrees above the target and a fraction to the left, and it was all so easy.

What a buzz. The last big buzz I got from the sky was in 1977 when I witnessed a bright greenish meteor shoot across from south to north; about mid way it split in two; the main object continued in about the same path, the offshoot veered off at about 15 degrees and quickly burnt up. That was great.

Any comments on my magnification/detail probs greatly appreciated (!) . I know you can't expect too much when the seeing is dismal. We have industrial yellow smokey skies most nights, plus a lot of sea haze.

[roccodm]

Greetings i assume you have the scope colliminated properly= if you just took it right out of the box this may be the problem in light of some of the focusing problems you are experiencing- as far as the seeing conditions i would suggest that you pick up an Orion sky glow filter which attaches to your eyepieces they really work quite well clear skies Rocco WB9QPU

[stephend]

thanks roccodm, i will make a note of that. i carried out collimation according to instructions. i guess you can't expect much near sundown with everything cooling.

[erick (Eric)]

Originally Posted by stephend

I....Then tried Mars. Mars was very, very disappointing - with a 10" aperture you should be able to see a lot of detail, right? ... and all I was getting was a single point of light through all three lenses ... but then I realised it was Aldebaran........

Been there - done that! Or otherwise, it's - "What's Aldebaran doing up already??? Huhh??"

[edwardsdj (Doug)]

Glad to hear you're enjoying the new scope. It takes time to come to know your telescope. The more you use it, the more you will see

Collimation will be critical with this scope. What tools are you using? The collimation springs on the primary mirror are also often too soft and the collimation changes with the altitude at which you point the telescope.

The various streaky lines pointing off to the left on Mars could well be a collimation issue.

Your range of available magnifications seems a bit low to see much detail on Mars to me. 150x to 200x works well for me. Planets require high magnification.

My red dot finder has some locking screws (hex screws from memory) that must be losened before the finder can be aligned. Did you get instructions for the red dot finder that describe locking screws? You really have to get this aligned to have much success.

Unfortunately, Mars is getting smaller every night at the moment. The polar caps on Mars are not easily visible right now as neither of them is tilted towards us. The features on Mars are subtle. Experience and a red filter helps heaps. The easiest feature to see (Syrtis Major) is not facing us in the early evening at the moment either.

Saturn is returning to the evening sky though You need to stay up a little later for this at the moment.

Hope this helps a bit and enjoy your new scope

Have fun,
Doug

[stephend]

Thanks Doug.

The body, call it A, of the red dot finder has a small wedge shaped projection designed to fit into a matching recess in the part, call it B, that's screwed onto the scope (it came with B screwed on). This is presumably to reduce the chance of A slipping out and crashing onto the primary mirror.

When I assembled the telescope with the projection fitted into the recess, the finder was back to front. This was very funny, as I didn't know what a red dot finder was ... after much tinkering and head scratching I finally glimpsed the red dot while looking DOWN the scope.

So, then I reversed A and found it failing to respond properly to adjustments, as noted. What I will do is unscrew B, turn it around, then A will fit in as intended, and I may get better results. Also I will look for lock screws.

Trouble is there have been permanent grey skies since that first experiment

Re magnification, the manual recommends max. 500x for 10" aperture, so with focal length 1270mm this would mean a 2.74mm eyepiece. Your suggestion, 200x max., would require a 6.35mm eyepiece. This sounds more like it.

This will have to be when comet Santa returns.

Cheers

[Gargoyle_Steve (Steve)]

I think you'll find that 500x is not "Recommended magnification" but rather "Maximum recommended magnification", sometimes refered to as maximum usable magnification. This is often calculated at 50x per inch of aperture, or 2x per mm - 250mm or 10" scope - 500x.

I've had a 10" dob (GSO brand), basically same focal length, never went beyond 200x with it, and in fact even with the 12" now it's rare I go beyond that. High magnifications require very clear, still air - not just at ground level where we are but up as high as there is atmosphere. We're not talking air pollution here, we're talking moisture, dust, smoke, winds, high altitude jet stream - all contribute. Often times the scope is capable of much better mag/resolution than the atmosphere will allow.

My most used eyepiece in my 10" was a 13mm - just under 100x. I had an 8mm ep, rarely used it to be honest unless I was at a nice dark site on a night with good "seeing". I always thought a 10mm would have been good.

Cheers!

[edwardsdj (Doug)]

The part you call B is the dovetail bracket for the finder. This is just to allow the finder to be easily removed and replaced. It also allows you to easily swap in other finders.

The finder will be adjusted with screws on the part you call A. As I say, mine has both locking and adjustment screws. This was all described on a piece of paper that came with the finder.

Daylight is the ideal time to experiment with the finder. In this way you can easily see what you are doing. Aim the telescope at a distant object (like a mountain) and align the finder. You have to be familiar with your equipment by the time you get it under a dark sky.

500x is way too high a magnification. I wouldn't get an eyepiece that goes beyond 200x until you are really familiar with your setup. You will only be able to exceed 200x on rare nights of exceptional seeing.

My workhorse planetary eyepiece is a 15mm that provides 133x on my scope. This is great for general viewing of Jupiter and Saturn. I only go to 200x if the seeing can support it. As I said, Mars is getting smaller at the moment and you need to go a little higher (150x to 200x) to see much on it.

I'm sure you will be able to get pleasing views of Jupiter and Saturn with the eyepieces you have. Mars is a more challenging target.

Hope you are enjoying the new scope

Have fun,
Doug

[stephend]

Well I reversed the dovetail bracket; simple factory assembly mistake. This finder doesn't have lock nuts/screws, it relies on friction. I've managed to line it up. And a neat invention they are. Have also spent some more time on collimation.

Consensus seems to be that my 15mm ep giving magnification of 85x is not too bad. A 12mm giving 106x, and/or a 10mm giving 127x, might be good to get later on.

When clear skies return I'll look for Jupiter and Saturn.

Thanks.