TAL125R - First Impressions

[Marki]

Thanks all - just so frustrated by the weather now, as I'm desperate to get this baby out under the stars! But there is no prospect of any significant change from this changeable/cloudy/rainy weather for the rest of June, it seems !

[nightfisher]

Marki, i feel your pain, you must be so eager to get first light, im still waiting for first light on my ZS70 apo

[John]

Congratulations on the new TAL Marki - it looks in great shape

The packaging looks very similar to the TAL 125 Apolar's that I tried - that green polythene wrapping and the hand tied dust cover on the finder included !.

I'm curious to know what is under the black band at the junction of the tapered part of the tube on your scope ? - on the Apolar's it covered a welded join plus a couple of rivets.

Looking forward to your 1st light report as I'm sure you are - June has been a frustrating month weather-wise to get a new scope !

[Marki]

Mmmm - there are three equally spaced screws in that collar. Not undone them - didn't want the whole front end to fall off or anything !

[John]

Have you tested the collimation yourself yet ?

You can do it easily with a cheshire eyepiece following the guidance on this web page:

http://spacealberta.com/equipment/refractor/collimate.htm

[nightfisher]

Mmmm - there are three equally spaced screws in that collar. Not undone them - didn't want the whole front end to fall off or anything !

DONT TOUCH them, dont know what they do but i want to hear your first light report- not self destruct report, i was under the impression the fluted end screwed into the main tube, could be locking screws

[Marki]

Have you tested the collimation yourself yet ?

You can do it easily with a cheshire eyepiece following the guidance on this web page:

http://spacealberta....r/collimate.htm

Thanks John will get hold of a cheshire and do this - something to do whilst waiting for cloud to clear . And don't worry Jules, I ain't unscrewing anything or changing anything till Big Sister has had her first night under the stars

EDIT - re cloud and collimation; er, thats if I get a collimator with a light/laser.

[Marki]

Sorry if this is a newb question, but will a standard cheshire or laser collimator work? Just had a quick look at our Sponsor's website and the cheshire is equated with collimation for newts - does it matter or will these things work in anything?

[John]

You don't need a last collimator to check the collimation of the objective lens, the standard cheshire will do the job. I use a cheapo plastic one which works fine as per the link I posted earlier. A laser collimator is useful for checking that the focuser is square with the optical axis of the tube - assuming the laser is itself well collimated, it should exit the objective lens right in the centre if the focuser is properly squared on. My experience has been that F/8 and slower refractors are tolerant of a little mis-collimation and will still perform well.

[nicnac]

new TALs, great feeling int it

[nightfisher]

Any hint at a first light yet

[Marki]

Regretfully no.... so frustrated! Forecast looks pretty rubbish over the weekend - possible window of opportunity late Sunday/early Monday, and Monday night, but as I have early starts I may not be able to take advantage; still, fingers crossed! Bound to be a clear night along one of these days.... .

On the other hand my shiny red cheshire has arrived so I can look at the collimation when I get home later today.

[Marki]

I just checked the collimation with a cheshire, and if I understand what I'm seeing properly, its slightly out - I see a dot in a circle, but slightly "ghosted". So, in order to collitmate it I guess I need to get it so the image is not ghosted, and so need to access the objective cell with a suitable allen key. Anyone know how to get the plastic dewshield off from the front end of a TAL refractor?

[AndyH]

Unless they've changed it, it should simply pull off.

I wouldn't touch anything until you've had a first light and you can do a star test or are able to use an artificial star.

Andy.

[Marki]

Thanks Andy - guess I'm getting impatient again - the prospect of a first light seems as remote as ever given the weather atm. I guess I can count myself lucky its not actually flooded where I am.

[AndyH]

I would try messing about with the (collimatable) diagonal though. See if altering it's mirror, helps the view through the cheshire.

[AndyH]

I feel your 'no first light' pain. Shocking weather. I have zero doubt you're baning your head against a wall in frustration.

Try the diagonal mirror thing though. No harm in trying it. You can always 'square it off' afterwards with a laser etc. That's one of the great things about them. ie: if the optics are a tad off being aligned to the tube, altering the mirror should bring it central at the eye end. Especially handy for scopes that don't have push me/pull me alignment cells.

Andy.

[Marki]

Just done that now, thanks for the hint. The image was not centred, but is now much closer after adjusting the mirror. Didn't eliminate the ghosting though. Also tried the diagonal that came with the 100rs - this was in a much better state anyway (and the optics better collimated too). I'm awaiting a laser collimator so will check focusser alignment in due course, and I'll look into artificial stars too. Anyway, for now I will leave things as they are until I can get a star test done - the weather can't go on like this forever:).

[AndyH]

The house opposite me needs some it's concrete ridging re-done. I have a cunning plan that involves a stainless ball bearing being stuck in some concrete and talking to the roofers, should they ever come

[John]

I'd certainly star test the scope before playing with the collimation. It does not sound too far off to me. If you were seeing two separate distinct bright disks, not overlapping, the collimation would be reasonably out and would benefit from adjusting.

[Marki]

Thanks John, thats put my mind at ease a litlle more. Now, since star-testing relies on actually seeing stars, I guess I'll have to be patient... .

[nightfisher]

If the image is slightly ghosted, sounds like it is near perfect, from what i have seen if collimation is out, you would have 2 small dots, not sure if the 125r dew shield just pulls of, or screws of, on the 100rs it just pulls of. On the objective cell outer edge is 3 small allen bolts/ screws, but like andy says, leave it till you have done a star test, achro`s can tolerate a moderate amount of mis collimation with little ill effect

[Marki]

Well, after visiting some friends tonight, we got home late and the sky was still clear. Despite having had the odd drink, I chucked the eq5 into my front yard and set the 125 on top. No moon or planets visible from my location, so thought I'd just point at a bright star or two. Chose Vega first. Used a 20mm wideangle. Pulling over and under focus I could see the concentric rings I'd expect and they seemed quite close to circular. In focus the point of light seems ok. trying to look so close to the zenith wasn't great (had to kneel) so chose another target, Arcturus. Using higher power (a 6.3mm) on Arcturus it didn't seem so good - seemed like a smudged rainbow of light off to one side. Not sure what to make of this. Scope wasn't cooled, Arcturus lies over a nearby roof and was much lower and closer to a street light, so conditions maybe not ideal. Too tired to investigate this further now, but I noticed that the 6.3 had a finger print on it, and clearly needs a clean (I vaguely remember doing this when I nearly dropped it a while ago). I might also check again with the diagonal from my 100rs, and compare the mirror alignment to the new diagonal that came with the 125. I'll also do a side by side test with the 100rs, which I think is in good alignement. I need to think about this all, and find a night when I can put some time in (without a 6am start to follow!).

After using scopes with a 10:1 reduction on the focuser, I really think the 125 would benefit from this. Apologies for the rambling - off to bed :-).

[John]

Don't panic Mark - try the scope again when it's had time to properly cool. The star images in both my ED102 and ED120 improve noticeably when the scopes have been out for more than 30 minutes.

[F15Rules]

Hi Mark,

Firstly, many congratulations on getting a 125R, I admire your tenacity and determination to get hold of one! . And thanks too to John for pointing me to this thread, I've been on holiday away from home most of last week and part of this, and had limited internet connectivity, so didn't see this post..

It was great to see that the scope arrived in what seems like good condition, and I can completely understand your frustration at not getting an early proper first light.

As a previous owner of a 125R, I hope the following points might be helpful, but please forgive me if I've repeated something that's already been answered..

-Dewshield - it's a simple friction fit..it should be fairly tight, but will come off no problem if you pull and twist simulaneously.

- the black collar where the tube flares wider is I believe threaded, and the screws you mention will be locking/retaining screws. I believe the tube bottom end is a standard 100RS tube and is threaded to allow the wider, flared end to connect to the standard tube (probably a cost saving measure, but I personally really like the flared system.

- Collimation. If you're at all unsure about it, DON'T adjust the cell - especially before a proper first light. After all the effort you have taken to get one, it's not worth the risk of damage..

- Cool down...it's a much bigger lens than the 100RS, and if you keep it indoors, it will take around 45 minutes to cool properly

-Eyepieces..in my experience the supplied eps are "ok", not brilliant (just my own opinion, others will disagree)..except for the Tal 25mm plossl, which I believe is exceptional for the cost. The lens on your scope deserves top quality eps, so I would invest in higher end eps if/when you can. I am using a new Baader Zoom MKIII and am well chuffed with it..for around £185 you get effectively 5 eps of high quality.

- Diagonal. I always found Tal diagonals to be very good quality. However, I would again use a high quality diagonal in 2" size so you are using the central, best coated part of the mirror. In my view you can't beat the William optics one unless you can afford a TV everbrite, Lumicon etc..

Finally...manage your expectations. The Tal 125R is an achromat, and at F8.9 somewhat shorter FL than the 100RS, so arguably you will see very slightly more CA. But it goes deeper, resolves more and is just a great allround scope, so I am sure you will grow to love it..and it's as rare as Hen's Teeth, so don't make my mistake of selling it on a whim in search of more aperture! I think a good 5" achromat like this comes as close to an all-in-one scope as you are likely to get.

Congrats Mark, and I hope you get a proper first light very soon - with full report of course!! :grin:

best wishes

Dave