Aldi £20 spotters! and "chromatism" (i think) issues

[spitfire12]

HI all

Just thought i would et you all know that aldi is currently selling optus spotting scopes 20-60x mag 60mm AP.

i just got one of these and they ain't half bad, it comes with a tripod and bag and easily fits under your car seat so i bought it to live in my car!

the quality is good and it has a nice wide view EP! my only gripe is that when im looking at bright objects such as Saturn im getting what i think is chromatism, what im seeing is "lines" of light coming from the planet in my FOV. (sorry for the poor explanation its hard to put into words)

Ive read a review here: Society for Popular Astronomy :: View topic - Tweaking an ALDI spottingscope ..

and apparently the way to eliminate this is to use sandpaper (see first post in the above).

Does this sound right? or are there other ways to combat this?

Thanks!

[dph1nm]

Hmm - I wonder if this would be any use as a guide scope?

NigelM

[jayjt29]

Dont have them in my local Aldi..

Jay

[russ]

Can't see them listed on the website in the specials page?

[tonyh66]

Hmm - I wonder if this would be any use as a guide scope?

NigelM

I got one of these months ago, im considering trying it as a findscope/guidescope.

[leenewtoastro]

was a promo last year but as said no sign on the site at a quick look!

[spitfire12]

Theyre not advertised on the website, they are in those see through plastic things at the tills, you have to ask a member of staff to get one out for you.

Does anyone know why im getting a glare type effect when i look at brighter objects such as planets? and is there any solution?

cheers

[John]

The glare could be coming from a number of issues:

- low quality prisms

- mis-aligned prisms

- poor light baffling within the scope

- mis-aligned objective and / or eyepiece (the latter will be a low quality zoom)

- Chromatic abberation within the optical system cause by any / all of the above

The above factors would probably have a minimal effect on daytime observing but are much more critical for astronomical use, as you have found out.

I tried a mid-priced 70mm spotting scope recently and while it was fine for nature viewing the only astro object that looked half decent was the moon and even then only at lowest power and in the central portion of the field of view.

Low cost spotters are just not really suited to astro viewing, in my opinion.

But for £20 you can have some fun with it anyway !.

[Horus]

I don;t think I'd waste £20 , they have probabaly been thrown about by warehouse people etc

[spitfire12]

I believe it is Chromatic abberation and apparently this is caused by the gloss black surface inside the main tube and the O.G cell (im not sure what O.G stands for as im basing this on an external source and im not really sure how spotters work).

Apparently scouring these areas with sandpaper to create a matt black surface will resolve this, would that make logical sense?

Cheers

[Wobbly Bob]

Apparently scouring these areas with sandpaper to create a matt black surface will resolve this, would that make logical sense?

Cheers

It most certainly does. Some high end Refractors have knife edge baffles to eliminate internal glare. By roughing up the internal glossy suface one can reduce the amount of internal reflections. Another example is Flocking the inside of newtonians, this not only cuts down the reflections but also increases contrast.

[spitfire12]

Thanks for the confirmation there wobbly bob! i didnt really want to attack the innards of the scope with sandpaper without knowing it was the right thing to do.

Would a coarser or finer sandpaper be best? fortunately ive got access to air guns so ill be able to clear the dust out with no issues.

cheers

[Craigfunkulus]

Would you recommend this as something to get to tide me over until I save up enough pennies to get a "proper" telescope?

[John]

Would you recommend this as something to get to tide me over until I save up enough pennies to get a "proper" telescope?

In a word - no. I don't think any amount of sandpaper is going to turn this into a reasonable astro scope. 10x50 Binoculars would be a better bet in my opinion.

[John]

I believe it is Chromatic abberation and apparently this is caused by the gloss black surface inside the main tube and the O.G cell (im not sure what O.G stands for as im basing this on an external source and im not really sure how spotters work).

Apparently scouring these areas with sandpaper to create a matt black surface will resolve this, would that make logical sense?

Cheers

O. G. = Object Glass - the main lens of the scope.

Chromatic Abberation (CA) or false colour is caused by the optical system, ie: the lenses and prisms that bring the light to focus.

Roughing up (hence the sandpaper) then blackening the internal surfaces of the scope will reduce scattered light a bit which does cause problems with a reduction in contrast so it might help a bit I suppose

[Craigfunkulus]

Cool. I have been using my dad's binoculars for the past few weeks, I'll just stick with them. =)

Thanks.

[spitfire12]

for the sake of £20 im going to give the sandpaper a try, hopefuly tonight, but not if the skies are clear

ill do a write up when ive done it!

[Snarks]

They had a big pile of them a few weeks back at my local store :

ALDI - Thursday Special Buys 3rd February 2011

Only 3 left when I went last week.

[spitfire12]

thats the one!

I did rough the inanrds of the scope with sandpaper last night, just hoping for clear skies tonight so i can test it and report back!

looking at the current weather round here im not going to hold my breath!

[Big Jim Slade]

I grabbed one of these a month or so back before I got my scope, but found the eye refief to be dreadful (I do wear specs tho').

[ollieholt]

bought one of these.... doesn't even show anything, wont even focus on day light terrestrial objects.... unfocusable. truly terrible. the moon was nothing but a white Vaseline induced smudge. dont know whats wrong with it, had it to bits to see if something has moved nothing wrong.... really dissapointed but only 20£ down the hole.

[spitfire12]

That sounds nothing like mine...maybe there was something wrong with yours?

i was getting loads of glare (still able to focus though) but after sanding the gloss surface inside the scope that has been reduced by about 60-70%. I managed to get it focused on Saturn at 60x last night and the image quality wasn't far off that of my newt at similar mags, i could easily make out the rings and the colour of the planet.

so overall i would say after tweaking it, it was £20 well spent especially considering i can strap it to my back and take it wherever i wish.

[ollieholt]

Ahhh success!!!! I ripped it to bits and pieced it back together checking the parts were fitted correctly, put it all back together and yey it is working and I must say well worth 20 that I spent, orions nebula showed up well (for a cheapy) great first buy. I will have to check out Saturn! That sounds good, also roughing the inner surface I have seen alot of blue colouring around bright objects