Considering upgrade to TAL100RS

[IDM]

Hi,

My main interest is in lunar and planetary observation and currently use a TAL100RS on an EQ5 go-to pro mount. I am just considering an upgrade. I have read good reviews of Celestron C8 XLT cassegrain scope. One endless online discussion was dismissive of the C8 saying their 6 inch Newtonian was better. So looking for any thoughts or advice. Essentially I would like a scope that is an decent improvement on the TAL.

 

Thanks in advance.

Ian

 

 

[johninderby]

Had a C8, then a Skymax180 and now settled on a Classical Cassegrain 8”. but may be a bit heavy for an EQ5.

The 6” Classical Cassegrain is very nice though and a great lunar / planetary scope. Big advantage over a mak or SCT is that it doesn’t have a corrector plate so cools down quickly and doesn’t  suffer from dewing. Also has a proper crayford focuser. 

https://www.firstlightoptics.com/telescopes-in-stock/stellalyra-6-f12-m-crf-classical-cassegrain-telescope-ota.html

https://www.firstlightoptics.com/telescopes-in-stock/stellalyra-8-f12-m-lrs-classical-cassegrain-telescope-ota.html

Edited April 1, 2021 by johninderby

[Cosmic Geoff]

I assume you want to keep the mount and change the TAL100RS for a bigger scope.

I dont know what aperture the 100RS is - I assume 100mm?

The C8 OTA would be a reasonable choice - it is a good scope, a substantial step up in aperture and not too heavy for the EQ5.  However now the Classical Cassegrain is an option worth considering instead of the SCT.   Is it for general purpose use, or what?

I would not choose a Newtonian - tried that on a EQ5 and hated it.

[wookie1965]

1 hour ago, Cosmic Geoff said:

I assume you want to keep the mount and change the TAL100RS for a bigger scope.

I dont know what aperture the 100RS is - I assume 100mm?

The C8 OTA would be a reasonable choice - it is a good scope, a substantial step up in aperture and not too heavy for the EQ5.  However now the Classical Cassegrain is an option worth considering instead of the SCT.   Is it for general purpose use, or what?

I would not choose a Newtonian - tried that on a EQ5 and hated it.

4"  I have one that's the aperture. 

[wookie1965]

Anything bigger heavier especially c8 you will need a bigger mount I.e HEQ5 or a EQ6 I use a Meade LXD55 127 emc (5") on my EQ5 and that is probably the maximum it can take. 

[Peter_D]

I wanted an upgrade in aperture last year. The classical cassegrain certainly had its plus points when I was researching. What ultimately put me off was I wasn't sure if I could manage its collimation - both primary and secondary mirrors are adjustable. Just something to be aware of, especially coming from owning a refractor.

In the end, I bought a used 8 inch Meade SCT (SCT you just adjust the secondary mirror) which I am happy using and collimating.

Edited April 2, 2021 by Peter_D

[johninderby]

The CCs hold collimation nearly as well as a mak unlike an SCT and both my 6” and 8”arrived perfectly collimated. Collimation of the CCs is easy BTW should it ever need doing. Not to be confused with an RC that can be tricky to collimate.

A CC has a parabolic primary and a hyperbolic secondary and have a long focal length whereas an RC has a hyoerbolic primary and a hyperbolic secondary and a shorter focal length which explains the differences in collimation.

So if buying a CC you can pretty well forget about collimation.

Edited April 2, 2021 by johninderby

[Peter_D]

30 minutes ago, johninderby said:

The CCs hold collimation nearly as well as a mak unlike an SCT and both my 6” and 8”arrived perfectly collimated. Collimation of the CCs is easy BTW should it ever need doing. Not to be confused with an RC that can be tricky to collimate.

Thanks John for the clarification. I was perhaps a little over cautious towards the CC. Maybe a design for me to re-examine.

[johninderby]

I ‘ve just added more info to my post about the differences in design between the CC and RC.

[dweller25]

Hello @IDM

If you are keeping the EQ5 then a C8 is the biggest aperture you can use on it.

I had a C8 some years ago and found it to be very good on the planets - however cooldown and dew can be an issue - but if you wrap the scope with two layers of reflectix from B&Q those issues are massively overcome.

The new Classical Cassegrains are nice too but are heavy for their size - the CC6 weighs almost the same as the C8 and I have read that they may not work at full aperture.....

https://www.cloudynights.com/articles/cat/user-reviews/telescopes/gso-8-inch-true-cassegrain-r3215

I owned a CC6 and it did not quite match the planetary views of my 4” refractor.

Alternatively I would suggest a 120mm ED refractor but you you would need a bigger mount.

Edited April 2, 2021 by dweller25

[IDM]

Hi Thanks,

 

For the helpful thoughts and comments. Clearly this is more difficult than I thought! The weight of the C8 does seem an advantage over the classical cassegrain. 

1 hour ago, dweller25 said:

I owned a CC6 and it did not quite match the planetary views of my 4” refractor.

This comment above, is what concerns me that I could go to all the expense and effort and be rewarded with little in the way of an improvement!

 

I am pretty unsure what to do, it feels like if I change the scope I should go for 8 inch in order to get the improvement I am looking for. But, unless I change the mount a classical Cassegrain maybe too heavy. The StellaLyra 8 appears to be 9.1kg, whereas the EQ5 is rated at 9kg, I am not sure if 100g is of consequence. I  also saw reference that it might actually weigh less than this. It would be good to have the weight confirmed. The other issue being that at 9.1kg, the combined weight of the scope and mount is getting pretty high for taking in and out of the house. Whereas the C8 is only slightly heavier than the TAL100 (100mm refractor). 

 

I am very grateful for the thoughts and feedback, and hope the discussion continues.

Ian

[dweller25]

The EQ5 is a clone of my Vixen GP which is rated at 7kgs which I have found in the real world at high powers to be correct. I would not put a 9kg scope on my Vixen GP.

The contrast transfer of the C8 (primary:203mm - secondary:68mm) is 135mm, so in terms of contrast and resolution it will outperform your TAL 100RS.

Here is a review of the latest model C8 .......

http://www.scopeviews.co.uk/CelestronC8XLT.htm

As I mentioned earlier reflectix wrapping really helps thermal management.

Hope that helps.

Edited April 2, 2021 by dweller25

[johninderby]

8.6kg without finder and diag but mine has a Baader Steeltrack and handle fitted that add a little bit of weight.

[IDM]

3 hours ago, dweller25 said:

The EQ5 is a clone of my Vixen GP which is rated at 7kgs which I have found in the real world at high powers to be correct. I would not put a 9kg scope on my Vixen GP.

That is interesting. Looking at the Rother Valley Optics website where I got my mount, they state approx 9kg Skywatcher EQ5 Pro GOTO Equatorial Mount & Tripod - Rother Valley Optics Ltd Certainly the Tal which from memory is about 5kg doesn't get close to its capacity, it only uses 1 of the 2 counterweights and the weight has to be put high up otherwise it's too much for the scope. Does anybody else have experience of the capacity of the EQ5?

Cheers

Ian

[Cosmic Geoff]

I had a 203mm f5 Newtonian (weighing around 9 to 10kg) on my EQ5, and the mount did not feel overloaded.  However this is as much as one would want to put on, even for visual use.