Tal 100RS...So, come on. Just how good are they?

[John]

Just stuck the TAL 100 out again tonight. No cool down at all from room temp but Epsilon Lyrae and Delta Cygni split very nicely straight off at 155x. Thats very handy

[F15Rules]

What a superb discussion .

I'll pin my colours to the mast as a paid up Tal 100 fan. Think I'm on my 7th now  , and I always feel a bit "undressed" if I don't have one.

That said, they are what they are - a superb value for money, good quality achromat of medium focal length. I tried to read each post here (there are so many) so that I wouldn't just repeat what has already been said, but in case anyone hasn't covered off a few points I'd offer these:

Plus points of the Tal 100 RS/R:

Optics (for their focal length, see below)

Value for money

Accessories bundled when new: the 25mm ep is a peach, right up their with Tele Vue, and the 6.3mm is actually also a nice eyepiece, the only downside being the short eye relief (common to all plossls). .but if you can live with that it's almost as sharp as a Circle T ortho.

Aperture - I think a 4"/100mm aperture is a really nice size for general viewing and is significantly brighter than an 80mm/3".

Simplicity of use

Negatives:

Variable quality of mechanics and cosmetics - although optics are in my experience universally good

Tube is easy to scratch and rings felt of poor quality

Baffling on early 100Rs wasn't great - much improved on later scopes though

Focuser is variable  - I've had superb ones (Astrobaby bought one of mine and I think that was the best one I had, my current one is "ok"  - a little lump in the middle of travel.

In terms of where Tals sit in the achromat league...well, at F10 you WILL see some CA, like it or not. I think the earlier purple lens versions controlled this better, maybe the coatings or maybe a better figuring of the lens, or a combination of both? I would say that the 3 best F10/F11 achromats I've looked through were (best first): Lyra Optic 102, Vixen SP102m, Tal 100RS - but no more than a few % points separating them. I loved the SP102M due to it's oversize tube (looks a lot bigger than a Tal) and great focuser (R&P). I loved the Lyra with it's superb build quality, very good lens contrast and overlength dewshield - really looks like a "proper" refractor. And I love the Tal because it delivers such great bang per buck value.

Also, I find that the use of filters can all but eliminate CA when viewing planets: Jupiter in particular I find responds well to blue and red filters, with the bands becoming more detailed and sharper.

Having said all that, the original poster asked what is the point of achromats? To answer that you have to go long...F13 to F15 long. At that focal length CA all but disappears visually, and the mag 3-4 threshold mentioned ref F10s drops to more like Mag 1.5 to 2.0.

On Vega, only the merest hint of violet is seen in my 80mm F15 and 127mm F15, and it's actually rather attractive. But the real difference you notice is in stellar/planetary definition, sharpness and contrast. Last night I had out my Kenko lensed Moonraker 80mm and Tal 100RS for a side by side comparison on Saturn - a very low, challenging target this year. The Tal 100 showed a definitely brighter image, but in ALL other respects the 80mm F15 caned the Tal. Light scatter, contrast, sharpness and depth of focus were all very clearly better in the 80mm. The sheer porcelain effect of the Saturnian globe at x 120 or so in the Kenko was just so...."satisfying"..pin sharp, NO CA at all, and the Cassini Division knife edge sharp in moments of good seeing, with the main band clearly visible.It's no coincidence that all the major telescopes of the 19th century which made major observing discoveries were long refractors of F15-F20 (or more).

If only Tal had made an F13 RS100, that would have been some planetary and double star scope.

Another point I think Shane made (Moonshane), regarding best images on double stars. I know Shane has superb newtonians at very unusually high focal lengths, and these would take some beating by any refractor. In comparison with "normal" length newts, however, I'd expect any decent refractor to deliver a better stellar point image, just because there is no central obstruction: same for Maks (and I'm a fan of good Maks). Just my opinion .

And finally, the humble achromat will deliver great images with very low cost eyepieces - no need for Ethos/Naglers etc here (although the do of course perform superbly). My Meade 5000 26mm plossl delivers delightful low power edge to edge sharp images in both my long fracs  - it cost me £35 posted second hand. The long focal length is very forgiving indeed on eyepieces.

I know many younger astronomers can't get their heads around why anyone would want a long tube which can seem unwieldy or a bit awkward to use, and so they gravitate to short stubbier apos. But for visual, and for oldies like me, I can't imagine anything more satisfying than the view through a traditional long (F12 or slower) achromat..well I can, but it's called a Takahashi FS128 and I value both my kidneys too much to even go there...

Long live the achromat and thanks to ALL for a great debate on this!  

Dave

[John]

And thats a super addition to this thread Dave

I was comparing my new-to-me-but-older TAL 100RT to my Vixen ED102SS ED doublet last night. I still have slightly offset diffraction rings in the TAL wheras the Vixen ones are completely concentric. Given the season and the need not to have a late night, my targets were limited to Jupiter, Venus and Saturn (later) plus some tightish double stars. The TAL was using the standard TAL diagonal (no choice really !) and the TAL 6.3mm plossl for 159x and the Vixen had a TV Everbright diagonal and a 4mm Radian for 166x.

I had both scopes on the same mount so I could literally just switch between them when comparing the views of a particular target. It's a great way to spot differences I find, almost like "blink comparison" in some ways.

The Vixen shows no noticable CA, at focus, on anything other than the brightest stars and Venus and then it's just a tiny splash. The TAL shows more CA around Jupiter, Venus (of course !) and the brighter stars but I could not see any around Saturn ???. When I get to view the Moon I'm going to try and find a way to quantify the CA difference between these two scopes, perhaps in terms of an estimate of the breadth of the visible CA halo in arc seconds ?.

In terms of contrast and resolution the TAL resolved the same double stars at the same magnification as the Vixen. The airey disk and 1st diffraction ring were more crisply defined with the Vixen and on some pairs the slightly offset diffraction rings of the TAL (still needs a minor collimation adjustment) made the secondary star harder to find, depending on the position angle. Both scopes resolved Marfik ( Lambda Ophiuchi) which is a 1.6 arc seconds split at the moment and pretty credible for 4" scopes.

Detail on Saturn and Jupiter were similar but the Vixen did show a slightly tighter and brighter image with features such as the Cassini Division slightly more sharply defined. Becuase of it's faster focal ratio F/6.5 v's F/10, the Vixen has a "snap" to it's focusing that is, currently at any rate, missing from the TAL. The TAL gets there though, with a little more perserverence, and you don't have doubts when you are at sharp focus with it.

One thing I did notice is that the Vixen / Everbright / Radian optical system had slightly higher light throughput than the TAL / TAL / TAL combination. The fainter moons of Saturn and fainter background stars "popped" into view that bit easier with the former and there were one or two faint stars that were visible through the Vixen that I really struggled to see with the TAL.

Overall though everything that I could see with the Vixen could be seen with the TAL, I just had to work just a little harder to pick out the faintest / most subtle targets with the Russian scope.

It was not a completely level playing field of course because the TAL is just slightly off collimation and it did not have the benefit of the premium Diagonal and eyepiece that the Vixen did. I still found the views through the TAL satisfying and it was only when I directly compared the same view at the same with with that of the Vixen that I noticed the slight deficit in it's peformance.

Cost-wise, the TAL, complete with it's original tall wooden tripod, equatorial mount (neither used for this comparison) and a couple of plossl eyepieces was bought used for around the same as the Radian eyepiece that I was using in the Vixen. On the value front the TAL eases comfortably into the lead of course

[Chris]

Great post Dave

All I can say is I must be getting older because my fracs are getting longer. Plus I finally got round to getting an observing chair

[Chris]

Very enjoyable read John I bet these two scopes aren't often compared, it does show the Tal in a great light against such a premium scope and the rest of its premium optical train.

As you say, the whole scope, mount and EP's for the price of the premium EP. 

I meant to add - Any plans to compare both OTA's with them both well collimated, and with the same/similar diagonal and eyepieces? I think that would also be interesting

[F15Rules]

Some great  points there John . Do you know yet if the diagonal might be the cause of any miscollimation? I've never had any Tal myself where the lens was out of true to any noticeable extent, with great, symmetrical diffraction rings on either side of focus. I know the Tal diagonals are collimatable and if yours was not part of the original equipment, maybe it was tampered with at some stage? Generally I have found Tal diagonals to be very good when collimated, with a good mirror quality.

It does sound as if your 100R was able to give your Vixen a good run for it's money collimation notwithstanding..and as you say, a whole observing kit for the price of a Radian is pretty stunning value really!  .

I totally agree with you regarding having the 2 scopes side by side: that's what I did and I was only able to be out for 25 minutes due to work today, so I concentrated on Saturn only. I could actually see a little CA on Saturn at higher power, but none at all with the F15 80mm. Your idea of measuring the visible CA halo while "blinking" between each scope is a good one and I'll be interested to see your findings.

Dave

[nightfisher]

@ John,

Interesting point regards CA and Saturn with the TAL. i have never noticed ANY CA when viewing Saturn with my 100RS but i do see a little with Venus and Jupiter

[Marki]

@ John,

Interesting point regards CA and Saturn with the TAL. i have never noticed ANY CA when viewing Saturn with my 100RS but i do see a little with Venus and Jupiter

Thats pretty much the same as my experience, Jules.Some (not much) colour on the edge of the moon, Venus and Jupiter. Nothing I noticed on Saturn.

Refering back to one of Shane's earlier posts, I do not notice any loss of detail on the moon with the 100rs, even when some CA is apparent (allowing for the limited resolution afforded by the aperture).

Regarding diagonal's, the one with my TAL125 was well out of true (which contributed somewhat to the poor visual expereience I had with it). The one that came with my 100rs was spot on out og the box.

I recently had the pleasure of using my 100rs under some very clean skies in rural France, and it once again endeared itself to me. It impressed me again with its clarity across the field, and excellent focusser. And for a small scope, it gave a fair account of itself on a range of objects. Even the edges of M13 gave tantalising hints of wanting to resolve (thought that may be a tribute to the sky quaity...).

[F15Rules]

Sounds very impressive John, high praise indeed! I've often wanted to have a go with a TAL, maybe one day I will.

Is there any consensus as to which versions are better? There seem to be various different coatings around....

Hi Stu,

I've had both lens types and can't honestly say I could see much difference optically. However, there is no doubt in my mind that the earlier deep purple (great band! ) version looks much nicer to my eyes. I know Neil English preferred the earlier glass to the point that he was going to switch a purple lens into a more modern RS tube - as I recall, I think the cells had changed though, and he wasn't able to do the switch..

Dave

[John]

.... I know Neil English preferred the earlier glass to the point that he was going to switch a purple lens into a more modern RS tube - as I recall, I think the cells had changed though, and he wasn't able to do the switch..

Dave

I think that would be the ideal combination. The original short travel 1.25" focuser is "characterful" perhaps but does have quite a lot of limitations. It works OK with orthos and plossls though.

I seem to vaguely recall that one of the focuser wheels could be tightened independantly of the other on the early R&P's allowing the tension of the movement to be adjusted or is my memory playing tricks on me ?

The white paint on the tube of this TAL 100 has quite a few chips and small scratches so some touching up is in order I think. The mount, tripod and other bits are in great order though

I have the original 25 mm TAL plossl too but there are a couple of issues with it:

- it's barrel has been machined a little oversized so it's a very tight fit indeed in the TAL diagonal (and other diagonals / 1.25" adaptors I've tried it in).

- a previous owner has cleaned it with something that has had the effect of polishing the coatings to an unnatural metallic sheen

The purple coated objective and the diagonal mirror are in very nice shape though. The diagonal is the collimatable type and I've had a play with my laser in the drawtube. I may be able to improve further on the centering by making a paper mask for the objective with an accurately placed central spot.

The tube rings will need replacing as well - the ones fitted are non-standard, robustly functional but rather crude.

The tube mounting plate on the TAL EQ mount has been replaced at some point in the past with a longer, wider flat steel plate which tube rings bolt right onto. That is a somewhat better job and makes it easy to stick other scopes on the mount.

Overall I'm very pleased to have a TAL 100 back in the fleet. I'll take some pics of the scope complete with it's original mount a tripod and post them up in due course

[Roy Challen]

I think that would be the ideal combination. The original short travel 1.25" focuser is "characterful" perhaps but does have quite a lot of limitations. It works OK with orthos and plossls though.

I seem to vaguely recall that one of the focuser wheels could be tightened independantly of the other on the early R&P's allowing the tension of the movement to be adjusted or is my memory playing tricks on me ?

quote]

Your memory is working fine, John:) just turn the focus wheels in opposite directions to adjust tension.

[nightfisher]

John, regards the focuser, you probably already know this but you are kind of stuck with the original, as the TAL OTA is a peculiar size sothe only was to change this is with another TAL one, (hard to get) or something like a skywatcher crayford and getting an adapter made for it, but with a little fettle they can perform rather well 

[happy-kat]

Overall though everything that I could see with the Vixen could be seen with the TAL, I just had to work just a little harder to pick out the faintest / most subtle targets with the Russian scope.

How much of that was also because the vixen had 2mm more aperture over the Tal? (assuming that it is 2mm bigger given the name)

[John]

How much of that was also because the vixen had 2mm more aperture over the Tal? (assuming that it is 2mm bigger given the name)

I don't imagine 2mm of aperture would make much of a difference but I could be wrong. The quality of glass and coatings of the Vixen, TV Radian and TV Everbright diagonal might. The latter almost certainly will be transmitting a few % more light than the TAL diagonal. I'll try the Vixen with the TAL diagonal sometime and see if I can reverse the effect. I can't do it the other way around because the TAL is 1.25" only but I can put a better quality 6mm eyepiece in the TAL and see what effect that has.

It's all good fun

[antares2063]

The only planet i have seen some minute CA with is on Jupiter, Saturn and the Moon throws up great views . I cant see Venus as yet as i have an obstructed West facing view from home.

Regards,

Junwei

 

[spaceboy]

Sorry if this is straying a little off topic but would not the degree of visible CA be very similar in any modern scope of similar focal lengths, be it a Russian or Chinese ?

My guess is any doublet of say 4" at a focal length of 1000mm is going to have a similar manufacturing process resulting in near identical spec on the optical elements. Anyone manufacturing telescopes for a living is going to want to slap on the best coatings they can for the intended price bracket so as to encourage future sales and reputation.

I'm sure when it comes to Apochromatic refractors more attention has to be paid to the process and differences are going to be more apparent depending on which exotic glass is chosen but is there really going to be all that much in it when your talking about budget achromats ?

Maybe I have become used to CA or I just don't allow it to become an issue and just enjoy the DSO rather than looking to pick faults with the scope but either way I can't say CA is all that noticeable in my 4" f/5 despite it often being said that CA is worse in faster achromats. My main priority with any scope I own is that the collimation is spot on. Once I know it is I can live with the other short comings each design throws in to the mix be it CA, SA or coma. I want to get the best views from the night sky like everyone else but LP and poor seeing has a bigger impact on the hobby for me than the kit I use.

[Chris]

Spaceboy

Do you use your 4" f/5 achro purely for DSO's? I would be a bit surprised if it didn't bother you when pointing your scope at Jupiter or Venus. I can't cope with the CA that 4" f/10 Synta achros show on the planets myself, wish I could!

[John]

Sorry if this is straying a little off topic but would not the degree of visible CA be very similar in any modern scope of similar focal lengths, be it a Russian or Chinese ?

My guess is any doublet of say 4" at a focal length of 1000mm is going to have a similar manufacturing process resulting in near identical spec on the optical elements. Anyone manufacturing telescopes for a living is going to want to slap on the best coatings they can for the intended price bracket so as to encourage future sales and reputation.

I'm sure when it comes to Apochromatic refractors more attention has to be paid to the process and differences are going to be more apparent depending on which exotic glass is chosen but is there really going to be all that much in it when your talking about budget achromats ?

Maybe I have become used to CA or I just don't allow it to become an issue and just enjoy the DSO rather than looking to pick faults with the scope but either way I can't say CA is all that noticeable in my 4" f/5 despite it often being said that CA is worse in faster achromats. My main priority with any scope I own is that the collimation is spot on. Once I know it is I can live with the other short comings each design throws in to the mix be it CA, SA or coma. I want to get the best views from the night sky like everyone else but LP and poor seeing has a bigger impact on the hobby for me than the kit I use.

In general I agree. There is some variation in CA levels between achromats with similar specfications and glass prescriptions but the levels of CA are broadly predictable as the table below illustrates. CA is generally not an issue when viewing deep space objects I feel. On other objects it can be objectionable but the extent to which this is the case seems to vary person to person. The other abberation that is present in most chinese achromats is spherical, either over or under correction. This robs the image of sharpness and reduces the scopes abaility to support high magnifications well.

[Moonshane]

"Another point I think Shane made (Moonshane), regarding best images on double stars. I know Shane has superb newtonians at very unusually high focal lengths, and these would take some beating by any refractor. In comparison with "normal" length newts, however, I'd expect any decent refractor to deliver a better stellar point image, just because there is no central obstruction: same for Maks (and I'm a fan of good Maks). Just my opinion ."

I agree with this Dave. In fact, other than my 6" f11 newt, I generally tend to use an aperture mask (usually 110mm f12 for my 12" dob and 170mm f11 for my 16" dob) for double star observation as the lack of central obstruction and the slower effective focal ratio really tightens up the stars. I've never used a Mak or SCT.

[spaceboy]

Spaceboy

Do you use your 4" f/5 achro purely for DSO's? I would be a bit surprised if it didn't bother you when pointing your scope at Jupiter or Venus. I can't cope with the CA that 4" f/10 Synta achros show on the planets myself, wish I could!

I use it as a quick one handed grab and go so point it at what ever is in the sky. I find the views of Jupiter and the moon fine with very little CA and filter this out even further with an 81A filter. If I stare at Jupiter I find that the CA can disappear altogether. Venus is colourful but then I wouldn't expect it to be any different as the bright glare of Venus in a Newtonian can be just as distracting unless stopped down. The ST102 on the moon is just as good a performer with only a piping of violet fringe along contrasted edges. I can't say I have too much trouble with reaching a sharp focus either and it performs just as well if not better than a well cooled Newtonian of the same focal length.

As I said previously it may just be that I accept CA in the same way I do coma ?? I certainly do not find what CA is visible as distracting in any way. If I had to nit pick I guess the only time it has caught my eye in a negative way was when I was observing a DSO that was near to a bright star. The fringing became more apparent to me as the star sat in my peripheral vision towards the edge of view. This was easily dealt with as I upped the mag so the star no longer was in the FOV.

[happy-kat]

With my limited use of my ST80 the quality of the eye piece has a massive impact on the visibility of CA. The cheap 10mm had horrific CA but my WO SPL6mm had little to moments of none when viewing Jupiter.

[Chris]

Yeah, those 10mm modified achromat eyepieces that are included with Synta scopes have really bad lateral chromatic aberration I find. The 25mm is ok though probably because it's a lower power and not as noticeable.

I guess these EP's are just to get you up and running, but I do wonder how many people new to the hobby know about upgrading eyepieces even? I guess this was more of a problem pre internet. 

It sounds like the EP's that come with the Tal are better  

[John]

Yeah, those 10mm modified achromat eyepieces that are included with Synta scopes have really bad lateral chromatic aberration I find. The 25mm is ok though probably because it's a lower power and not as noticeable.

I guess these EP's are just to get you up and running, but I do wonder how many people new to the hobby know about upgrading eyepieces even? I guess this was more of a problem pre internet. 

It sounds like the EP's that come with the Tal are better

I guess most folks starting out get a bit of a shock when they find that 3 half decent eyepieces will cost as much as the scope has !

[nightfisher]

I guess most folks starting out get a bit of a shock when they find that 3 half decent eyepieces will cost as much as the scope has !

Some of us still get a shock to see the one eyepiece can cost the same as 3 scopes 

[Chris]

4 x Tal 100RS = 1 x ES120 9mm