Tal 1 year it changed to a 1.25" focuser

[Trevor PC]

Hi 

I am new to the lounge and looking to buy a Tal 1 as my first scope at the ripe old age of 64. I have read a great many pieces on the scope and feel it will be a good starting option, the thing is I want to get one with a 1.25" focuser, and hence the need to no when they stopped making the 32mm .

If I can find the 1.25" verity this will open up the eye pice options, as I know after looking that 32mm Tal eyepieces are very difficult to find.

I know others have moved the primary mirror up to enable focus on the 32mm verity, which I would prefer not to do.

 

Any help would be much appreciated.

Trevor

 

 

 

 

 

[markse68]

Hi Trevor, no idea what year they changed but you can tell by looking at the focuser itself- the 32mm were a push fit like this

and the 1.25” had a lock screw 

Also the ota length got a bit shorter but i would have to measure

Mark

Edited April 20, 2022 by markse68

[Trevor PC]

Hi 

Thank you for replying, is the second photo showing a screw retaining the cover a 1.25"?

 

 

 

 

[markse68]

yes- here’s a better pic

 

[Trevor PC]

Mark 

That's great what size eyepieces would you recommend for the planets, moon, and sun. 

Many thanks

 

 

[markse68]

I’m not really one for recommending eyepieces (it’s a very personal choice really)  but the 25mm standard tal plossl is a nice one. When i was using my Tal 1 a lot I used the 25mm plossl and I remember getting my first posh eyepiece- a Pentax 12mm XF which framed the whole moon nicely iirc. I also had the 2x Tal barlow which gave nice higher power views. 

Don’t look at the Sun through it whatever you do! They originally came with a sun filter for the eyepieces but modern advice is to throw that thing away as it’s very dangerous! They also came originally with a projection screen which is fine though i’ve heard it advised to only use uncemented eyepieces as the heat can affect the cemented types which rules out plossls and even the tal kellner that was standard supply, though i have no idea if that’s really true. Better bet might be baader solar film over the aperture, though do be careful- you only have 2 eyeballs and they can’t easily be replaced! I never observed the sun through mine though i did use the baader film with my Tal 100rs with some success.

The planets need quite high magnification really as they are small compared to the moon. A 10mm ortho makes a nice planetary ep and will barlow nicely. The baader bco is really a nice ep for not too much outlay esp second hand  and barlowed should do you well for Jupiter and Saturn, though the afov is a bit small- smaller than a plossl, so the scope will need more frequent position adjustment.

Mark

[Trevor PC]

Mark 

Many thanks, I was thinking of getting a white glass filter that fits over the front of the telescope to observe  the sun, have you any experience of these types of filter.

 

What would you say was the maximum useful magnification of the scope?

 

Many thanks

 

Trevor

[markse68]

I don’t have experience of glass filters but i read that unless you pay a fortune, and maybe not even then, the baader solar film is superior to glass. Seems crazy given how cheap it is but it’s to do with how thin the film is not causing any of the issues glass filters can and do I think.

I would think a 5mm ep (or barlowed 10mm) might be about the limit for the Tal-1. It doesn’t have a huge aperture and the mirror is spherical. But you’ll find the atmosphere is the real limiting factor for magnification

Mark

[Trevor PC]

Mark. 

Thanks again for the advice it is invaluable to some like me starting out on a journey that began about 50 years ago when a teacher at school was kind enough to share his love of astronomy with a couple of us.

Unfortunately life, family, and work derailed my love of space.

Will take your advice and look for the baader bco, and sun filter.

 

Will let you know how I get on.

 

Trevor

[Trevor PC]

Hi Mark 

Well the Tal 1 has arrived, it has a screw in mount, and came with a 3 x Barlow, 15mm Kellner, and a 25mm plossl,  and in the end it turned out to be 1.25", so all good.

I have a chance to buy a Baader 6mm bco, for about £20, would this be worth having.

I have bought a second hand Cheshire collimator, to have a go checking the mirror alignment, do you know if Tal centre marked the primary, or is this something I will need to do.

On reading about collimating, people state the Cheshire is good for centering the secondary, but a laser is better for aligning the primary, what are your thoughts on how best to do it.

 

Many thanks for any advice you can offer.

 

Regards

 

Trevor

 

 

[markse68]

Hi Trevor, I’d snap up the 6mm BCO for that price but it may be too much for the Tal- not much to lose though. Beware the eye relief is tight on that eyepiece.

Its the other way round with the laser- It’s quite convenient for aligning the secondary to the primary centre spot, but less useful for aligning the primary unless you use the barlowed laser method which doesn’t care about axial alignment accuracy of the laser. At least that’s how i use mine. A cheshire will work fine for both and is more useful for getting the secondary height right. You’ll need to centre spot the primary if it hasn’t already been done. I think i have a template from when i did mine i can send you as a pdf- you just have to print it to scale, ideally on acetate.

Great you found a 1.25” version- I hope you get on with it and have a great time! 

Mark

[Trevor PC]

Hi Mark 

Well the Tal 1 has arrived, it has a screw in mount, and came with a 3 x Barlow, 15mm Kellner, and a 25mm plossl,  and in the end it turned out to be 1.25", so all good.

I have a chance to buy a Baader 6mm bco, for about £20, would this be worth having.

I have bought a second hand Cheshire collimator, to have a go checking the mirror alignment, do you know if Tal centre marked the primary, or is this something I will need to do.

On reading about collimating, people state the Cheshire is good for centering the secondary, but a laser is better for aligning the primary, what are your thoughts on how best to do it.

 

Many thanks for any advice you can offer.

 

Regards

 

Trevor

 

 

[Trevor PC]

Mark 

Again thanks for the info, I found a website with a formula that basically said the theoretical maximum magnification of a scope was twice the size of the apperture, so 220 max minus some so around 200 might be OK.

Another formulae stated the minimum magnification was apperture/7, which works out at around 15, at which point you are not gathering any more light, have I understand this correctly, and if yes what does that mean for the 25mm plossl.

Regards

 

Trevor