Scope help

[T A WOW]

Hello all.

Since my car passed its MOT with minimum fuss and my loan on it finishes soon I thought I may treat myself to a new scope. I'm after a large achromatic refractor. It will be mainly used for viewing solar system stuff and a bit of normal gazing (double cluster, Pleiades etc) and possibly for trying a spot of photograpy. I have seen on this scope http://www.telescopehouse.com/acatalog/Bresser_Refractor_152_1200_EXOS_2.html

And quite like the look of it. Does any one know of any good reviews on it as I can't seem to find one. Also would I be better of getting just the OTA and a different mount. (I would ideally like a goto)

Thanks for any input. Maybe recommend an alternative scope if you know a good one.

[Daz Type-R]

Hi.

I have no clue what so ever about achromatic refractors but I did not want to leave your post unanswered.

A lot of the people who will be able to help are away at the Kelling star party, which is on for another week or so.

Hopefully somebody is still around who could advise, if not, I'm sure somebody will answer your question when they are back.

On the face of it, it looks okay but I would wait for advice off the people in the know.

[Doc]

I've had one of these Bresser 152R for a few years, they are very good scopes, but are really heavy. They suffer alot with CA around brighter objects, some people hate this, others don't seem to care. They excell on deep space stuff and give wonderful widefield views.

They only have a single speed focuser which I found adequate.

As I said they are really heavy and need a pretty good mount, I had mine on a HEQ5 and that just managed it.

[Guest JohnC]

As Mick has said, achros are ok but do suffer with CA.

I had a Meade AR6 which was a great scope and did quite well on planets, however it required an EQ6 to carry it.

Colour was there but i found it ok. They are big scopes and the mount is everything.

With your stated aims i would advise going for a secondhand HEQ5 and maybe a secondhand ED100.

This combo is much better for planets especially if you are planning imaging them.

This would fit in the same budget as the scope you linked to.

I put a pic here of the AR6/EQ6 set up so you can judge the size.

[Daz Type-R]

Just jumping in here, I know Tobias is relatively new to this hobby (after meeting him at Belper the other week) so you guys may need to explain what CA is, I know it is Chromatic Abberation (I hope that's right or I'm going to look silly) but I don't feel I know enough about it to explain any further.

Tobias, if you do have a budget, like the guys have mentioned above, the mount it comes with may be no good for what you intend to do with it, so you will need to take into account a new mount, camera, power requirements for when in the field, extra eye prices etc etc.

Unfortunately, it all adds up!

Good luck.

[Doc]

That is true daz, I forgot that Tobias is new. So here is an explanation on CA.

Chromatic Aberration, also known as “color fringing†or “purple fringingâ€, is a common optical problem that occurs when a lens is either unable to bring all wavelengths of colour to the same focal plane, and/or when wavelengths of color are focused at different positions in the focal plane. Chromatic aberration is caused by lens dispersion, with different colours of light travelling at different speeds while passing through a lens. As a result, the image can look blurred or noticeable coloured edges (red, green, blue, yellow, purple, magenta) can appear around objects, especially in high-contrast situations.

Of course APO scopes and better corrected scopes don't usually suffer that much with CA, in the end the more money you spend the better colour correction you will get.

[Daz Type-R]

Good write up Mick, thanks a lot.

[T A WOW]

Thanks for the advice guys. I'll have to do some serious research before I make any purchase. I'm not in a hurry to buy, and I'm keeping an eye on eBay as I've seen a few really good (I think) scopes on there lately. Out of interest why is the mount so important?

[Guest JohnC]

Hi

The mount is the heart of any set up.

if it cannot carry the scope without shaking and vibrating it makes the scope almost useless.

As the magnification increases any knocks or shakes amplify as well.

In visual mode you can get away with bigger scopes on the mount.

when it comes to imaging most people half the payload to take into account the camera, filters etc.

Next time you are out at the darksite we will demonstrate some of this for you.

Look forward to seeing you again.

Best regards

john

[T A WOW]

I look forward to it.

Any idea when the next meet at belper will be?

[Guest JohnC]

As soon as we get a clear spell

[Daz Type-R]

Remember to check the forum regularly as meets can appear with less than 2 days notice, ideally we need clear skies and no or very little wind.

[cosmic dave]

As a refractor man myself I found the you get used to the false colour and it doesn't really bother you (well that's me anyway) like mick says its the mount you need to take into account, I sometimes can't use my frac when the winds up because of this, they say a telescope is only as good as its mount and they are not wrong,

As for the CA you can always get a fringe killer filter to help with this ?

David

[T A WOW]

Does anybody have any photos of what CA would typically look like through a scope like the one linked to. I've seen a couple of images on Google for CA but not sure if they're a true representation as they seem excessively discoloured.

[Doc]

On the moon you will see the outer edges have a blue/purple colour to them, on stars like Vega stars will appear blue/purple in colour.

[T A WOW]

Would it just be like a thin line around the outside of the image or quite a big err.... Blur sort of thing

[Doc]

It should be a thin ring, some people don't even notice it. You can buy filters like the fringe killer to mask it.

[T A WOW]

Ok great thanks. Hopefully someone with a refractor will be at the next meet so I can see what they're like.

[Guest JohnC]

I will bring the 150mm F5 to the next meet.

You are welcome to view through it at your leisure.

I laso have a smaller one to show you the colour differences.

Best regards

John

[cosmic dave]

I will have my 120mm frac at EMS1 if your there.

[T A WOW]

Can't make it to EMS1 unfortunately. Moving house that week.

[Brantuk]

If you have a cheap pair of binocs (around £50's worth) have a look at the moon in them - you'll see CA as a yellow tinge around the edge of it.

[T A WOW]

Just been looking through my finder scope. A Meade 8 x 50. I assume it's not achromatic or apochromatic and I can see a faint green line around what I was looking at. Not nearly as bad as the interweb was making out.

[Brantuk]

Yup - it's usually pretty minimal as far as observing goes - most folks can ignore it easily - or a fringe killer helps reduce it. However you don't want that if you're imaging. Far as I know most finders are achromatic.