Achromatic Scope Query

[bomberbaz]

Ok I am considering buying a frac for use in visual or video astronomy. I have had a look around and the variety is simply mind blowing.

However after many hours trolling the web I have got my eye on a couple of OTA's that have my interest, although I am not committed and also not in a rush either given the time of year. So open to other ideas and suggestions.

I looked at these two:

http://www.opticstar.com/Run/Astronomy/Astro-Telescopes-Opticstar.asp?p=0_10_1_1_235

http://www.bresser.com/telescopes/messier_ar127s.html

It appears the bresser is a 2 element OTA and the Opticstar is stated as a 4. 

So what are anyone's thoughts and /or experiences of the stated OTA's and brands. The opticstar seems to tick the boxes according to the sales blab but we all know that sales blab is sometimes just that.

I am not expecting perfect views, the bresser is available for 325 and the Opticstar 450, I am prepared to pay that but I really dont want to go much over that.

Aperture wise I was thinkng minimum 100mm but these two came up at 127 so seemed a better choice for light gathering.

TIA for any comments.

Steve

[estwing]

good luck mate ...no help from me here!

[bomberbaz]

Thanks Calv, its still only a consideration at this pint matey.

[John]

I reckon both scopes are made by the same manufacturer Steve.

The Opticstar is I think a petzval design so will have a doublet lens at the front end and another couple of smaller lenses at the other end in front of the focuser. A number of companies make such designs including Vixen. They are not apochromats though but to be fair are not claiming to be. I believe the design aims to deliver a flatter field and a little less false colour than a conventional achromat doublet of the same focal length.

Sounds like you are looking for a scope to show wide fields of view, is that correct ?

[damnut]

Hi Bomberbaz,

The opticstar is an achromatic doublet with additional corrector lens's in the optical path. This DOES NOT make it an apo.

There will be similar performance, the chromatic aberration will be greater with the shorter focal length. I have owned the Bresser in its longer length and it was an exceptional scope . Review here by earth titan  :-- http://stargazerslounge.com/topic/114507-bresser-messier-127mm-achromat/?hl=earth+titan#entry1135918

They are great widefield scopes so long as you accept the shortcoming of an amout of CA. The finder in the bresser is great, illuminated double reticle.

I liked it so much I bought its big Brother the 152mm. Just make sure you have a substantial mount to use these great scopes.

[damnut]

John's & my post crossed in the ether...

[bomberbaz]

Sounds like you are looking for a scope to show wide fields of view, is that correct ?

Yes you are spot on John, the FL makes a big difference to what I can see especially for the video aspect which is why I am looking into this. 

[bomberbaz]

Hi Bomberbaz,

The opticstar is an achromatic doublet with additional corrector lens's in the optical path. This DOES NOT make it an apo.

There will be similar performance, the chromatic aberration will be greater with the shorter focal length. I have owned the Bresser in its longer length and it was an exceptional scope . Review here by earth titan  :-- http://stargazerslounge.com/topic/114507-bresser-messier-127mm-achromat/?hl=earth+titan#entry1135918

They are great widefield scopes so long as you accept the shortcoming of an amout of CA. The finder in the bresser is great, illuminated double reticle.

I liked it so much I bought its big Brother the 152mm. Just make sure you have a substantial mount to use these great scopes.

I reckon both scopes are made by the same manufacturer Steve.

The Opticstar is I think a petzval design so will have a doublet lens at the front end and another couple of smaller lenses at the other end in front of the focuser. A number of companies make such designs including Vixen. They are not apochromats though but to be fair are not claiming to be. I believe the design aims to deliver a flatter field and a little less false colour than a conventional achromat doublet of the same focal length.

Sounds like you are looking for a scope to show wide fields of view, is that correct

Thanks for the replies chaps. The bresser is then the same as the opticstar without the extra lens I think. 

So what is the main advantage then of this 2nd set of lens. How well do you think it will  reduce CA, and is the image better corrected accross the FOV?

I hasten to add I am far from committed to this as a purchase but it is a consideration for my foray into VA.

Steve

[ronin]

Reading the Opticstar item it looks as if they have put a flattener in the region of the focuser - a few are doing this but usually on apo triplets WO, APM being the 2 that come to mind.

At what was f/5 this would be useful as there would be curvature and geiing the spacing right can be a bit of a pain.

Makes it an interesting scope, as there has to be a convenient location/fixing point and as it appears to be a Bresser 127 why have they not done the same - suppose Bresser could be leving it to Opticstar to try out.

[John]

I believe the design will produce a flatter field of view which imagers in particular look for. It does also reduce CA a bit but not to ED doublet levels. I know some folks who bought a Vixen 120 petzval refractor were a little dissapointed at the amount of CA that was still visible.

Here is some information on the current Vixen to use the petzval design, the NA140SS:

http://www.firstlightoptics.com/vixen/vixen-na-140-ss-flat-field-refractor.html

[Moonshane]

Bear in mind that Petzval design scopes cannot be used with a herschel wedge for solar if you are looking for a multi-use scope. 

[bomberbaz]

Thanks for the responses guys, more to ponder over.

steve