Evostar 120 vs Tal 100 RS

[Leda]

Is it worth ditching the Evostar for the Tal?

Is the 100RS as good as the 100R optics? (RS is made in china right?)

If the tal has better optics, but slightly less aperture, is it a good trade off?

I really want a Tal Russian scope but at the same time I don't want to lose aperture if its a large decrease in viewing/imaging.

I also see the Tal is a slower scope too than the Evostar.

I use my scope for anything really, solar, lunar, planetary and deep space.

[Caldwell 14]

The TAL 100RS is Russian and has excellent well corrected optics with little in the way of CA. The coatings on the objective lens on scope is perfect and with imperfections, thats more than I can say for two Celestrons I have owned and and Evostar I had look at a few months back. The Crayford is a big step up to from the Skywatcher/Celestron R&P focuser too. Anyway I chose the the TAL and I certainly don't regret it. Do you really want to own a soul-less Chinese clone? Tals ooze personality.

I'm sure you will get lots of Evostar fans out there too, I'm totally biased me

[John]

All the TAL's are Russian made - I reckon the 100R has exactly the same optics as the 100RS in it. The Evostar is made by Synta in China.

On deep sky objects the extra aperture of the 120 will show a bit more. On lunar / planetary the additional CA that the 120 produces will equalise things somewhat.

The differences won't be huge either way - I've owned both scopes and enjoyed them both. The TAL's have more "character" whatever that means !

The finish of the Skywatcher scopes is actually a little better than the TAL's for what it's worth.

The focal length of the scopes is the same (1000mm) so the field of view you can get with low power eyepieces would also be the same.

[Leda]

I know but my evostar is pretty new and hardly used

Shame to sell it at a large loss though. Cant afford both or I would get the Tal right now lol.

I also got a motor on my RnP focuser for imaging and a Red dot finder on it.

I also read on cloudy nights that they have a yellow hue to the Tal optics images.

I was hoping the Tal would have "sharper" images and being a slower scope, not as glaring on Jupiter or the moon , and less CA.

[nightfisher]

I did just this, sold my old evostar 120mm and bought the Tal100rs(russian made)

The Tal shows slightly less false colour, and more importantly near zero spherical abberation, my old evostar showed poor stars out to the edge of field.

The Tal is easier to mount, and has a far better focuser, i dont regret making the change, but its your money and the evostar will perform better on dso`s

[Peter Drew]

They are both good refractors, but for the small differences in any direction I would advise you to stick with what you've got.

[Caldwell 14]

They are both good refractors, but for the small differences in any direction I would advise you to stick with what you've got.

As much as I like TAL's I would tend to agree, if you just bought the scope that is, I wouldn't change it so soon.

[Apostate]

What if you had neither and were after a refractor to attach either a webcam or a DSLR in HD video mode so that you could image some planets? I'm not having much joy with my 6" newt, you see..

[nightfisher]

What if you had neither and were after a refractor to attach either a webcam or a DSLR in HD video mode so that you could image some planets? I'm not having much joy with my 6" newt, you see..

In this case its a massive yes for the TAL lighter, better focuser and better optics

[Stardust]

I've got both at the moment, the TAL will be staying. It was one of the very few things I bought from new. It has more charm and very sharp optics. The celestron is better on dso's, but I have a replacement for that.

[Apostate]

I've been tempted by the Tal more than once, but not had a mount man enough for the job.. I do now though..

Am i correct in thinking we are choosing reduced chromatic aberration over better resolution?

Woild the use ot filters (rgb etc for the imaging) tip the b_alance the other way?

[John]

I've been tempted by the Tal more than once, but not had a mount man enough for the job.. I do now though..

Am i correct in thinking we are choosing reduced chromatic aberration over better resolution?

Woild the use ot filters (rgb etc for the imaging) tip the b_alance the other way?

They are both achromats so both show some CA. 100mm F/10 will show less CA than 120mm F/8.3. You can filter out some of the CA although with some filters the side effect can be to introduce a yellowish tinge.

There are exotic devices that will remove virtually all the CA from an F/8-ish achromat but they cost a fortune and are as rare as hens teeth.

I'm not an imager but I believe CA can be removed during processing.

Another possibility would be a mak-cassegrain. They take longer to cool than refractors but are easier to mount (short tube) and have long focal lengths which lend themselves to planetary imaging. They have no CA as well !

I just have a feeling that you might regret the drop in aperture if you change to the TAL100, nice scope though it is.

[Apostate]

Yup - therein lies the rub.. I really like the Tal - it appeals to me for a number of reasons.. low cost being one of them. I've thought about a mak.. Hovered over the C8 on a CG5 GT for ages.. But I really don't think I know enough about this subject to make the most of it.

I picked up a HEQ5 (mount only) with Synscan for £250.00.. I've added a pier (£200.00) and I think adding a good achromat alongside my F5 newt will give me a good broad range to my observing and imaging for half the price of the C8. I'm trying to maximise the value of the set up - price vs skill.. I don't want to fall into the "all the gear - no idea" trap..

The question is - which refractor? Aperture vs CA.. Does 20mm actually make that much difference?

[John]

.....The question is - which refractor? Aperture vs CA.. Does 20mm actually make that much difference?....

Well I'm just into visual observing and my ED120 definitely shows more of everything than my ED102 does, with the exception of a wide field of view and that's because the 102 is a faster scope.

A 20% aperture gain is quite a lot with smaller aperture, unobstructed scopes.

[Apostate]

I would be using the scope on the planets, mainly so there is not too much of a problem with magnitude.. So if the aperture and focal length of the scopes offset one another in terms of magnification for a given eyepiece I should expect better detail from the bigger scope? Is that right?

[cs1cjc]

Hi,

I can see no published measurements of the Synta 120mm, but there are measurements for the 150mm listed below and also one for the Tal.

http://translate.goo...CGxe43y6ZMQGedQ

http://www.airylab.f... 2010-44001.pdf

http://translate.goo...Cs4yQ#post27322

F/8 and F/10 achromats are bound to show colour, the former more than the latter. In either case removal of red and blue should sharpen the image. I use the Baader Finge Killer (and do not its pale straw tint distracting) but I know others would recommend the Baader Semi Apo.

[Marki]

Well I'm just into visual observing and my ED120 definitely shows more of everything than my ED102 does, with the exception of a wide field of view and that's because the 102 is a faster scope.

A 20% aperture gain is quite a lot with smaller aperture, unobstructed scopes.

I agree with this, also as a mainly visual user. I have the 100rs and it is a great scope indeed - lovely sharp images and this is pretty much right across the field of view. However, my 5" refractor resolves much more - a 20% increase in aperture gives a LOT more light, hence you'll see loads more detail/brighter images etc.

The Tal 100R and 100RS are essentially the same, however, the RS has different coatings on the objective (well, at least a different colour ) and better internal baffling (at least comprared to the early 100r models) and a crayford focusser.

There is some colour-fringing apparent on the very brightest objects with my 100rs, but I really don't find it that noticeable, to be honest. Not tried with a Baader semi-apo though - might put one of those on my Christmas wish list... .

[Apostate]

Thanks Chris - I can't pretend I understand the test being performed but is does seem evident that the Tal has more than just marginally better optics. The star tests on the skywatcher looked bad. It does appear to have been a poor example of that scope, and an older model to boot - but what has swung me back toward the Tal are the implications for quality control. I have a Skywatcher and I know it's a good scope - but I'm expecting to adjust the optics in a newt and provision is made.. I'm not sure it'd be so easy in a misaligned refractor.

Next question is whether my better half will tolerate a scope over a meter long in the sitting room...

[KaStern_Former_Member]

Hello to All,

my Friend Kurt did have a 120/1000mm Skywatcher achromat.

That one was a good sample (very straight lines in the ronchi test),

but he sold it fast after having it compared to his home-made 8"f/5 Newt.

It was the colour aberration that bothered Kurt.

Apostathe,

you could stop down a 120/1000mm achromat to 100mm Aperture and get (nearly)

the same performance as with a 100/1000mm achromat.

With full aperture you have better resolution (at green light),

but you have more colour aberration.

Please note that in a conventional achromat longitudinal colour aberration is allways 1/2000 of the focal length.

So why is ca more severe in the 120/1000mm than in the 100/1000mm when fl is the same?

Colour abeeration between green focus and the foci for blue and red will be 0,5mm in both.

But in the 120mm aperture Achromat two things differ:

1) the airy disc for green light is smaller.

You need 120x in the 120mm achromat to see the airy disc

in the same angalar size like i the 100mm achromat with 100x.

2) the depth of focus is smaller in the 120mm achromat.

So the same 0,5mm of defocus of blue and red light will

lead to more severe ca in the bigger achromat.

Concerning the quality of manufacturing I cannot help you.

But there are some reports of good optics observers tell of their Tal achromats.

An alternative may be a used 100/900mm ED from Synta.

If you can get a good one it will be superior since ca is low in such an ED scope

compared to a conventional achromat.

Cheers, Karsten