My first Schmidt Cassegrain, any tips?

[emadmoussa]

I have been eliminating reflectors from my life - 3 so far -, and jumping from one cherished refractor to another. Then I go hit by the aperture fever ...again...So since a reflector is out of the question and a more than 6" refractor will be a large beast - if exists any way - I took the path of a Schmidt Cassegrain for the purpose of high power and sort of portability. I'm expecting my Celestron C11 XLT in the coming few days...

Any tips for an SC newbie? Pros and Cons?

Thanks!

[DirkSteele]

Pros include compact tube for any given aperture and focal length, easy to collimate and maintain, and if it is a decent example, good optical quality. Things to be aware of include the longer cool down time due to the closed tube nature of the OTA, the front corrector is prone to dew, so a dew shield (which can be as cheap as cut up camping mat, or complex as a dew prevention system from a company like Kendrick) is a must, and the focusing mechanism. The telescope focuses by moving the primary mirror up and down the telescope OTA which results in image shift and mirror flop. I am a visual only astronomer a little image shift is not a complete disaster. The flop can be a pain if you are imaging a planet on a small chip though. You can reduce the mirror flop issue by ending your focus “uphill,” in other words by finishing focusing with an anti-clockwise movement which moves the mirror up the OTA against gravity reducing the risk the mirror is unbalanced. The alternative solution is to purchase a crayford type focuser (something like this http://www.firstlightoptics.com/starlight-instruments-feathertouch/feathertouch-2-inch-crayford-focuser-sct.html ) which eliminates that problem completely.

Perhaps other issues, if you are interested in deep sky astrophotography is the very long focal length. This makes guiding a real challenge and requires longer exposure times. You can of course purchase a f/6.3 focal reducer, or even use the Hyperstar system, which places the camera at the location of the secondary and turns the scope in to an ultra quick f/2.

[Zakalwe]

Bob's Knobs.

Worth every penny and he is a great retailer (you will have them in about 4 days).

[E621Keith]

I second the dew shield. They are a not optional, you will need it.

For visual observation, mirror flop of modern Celestron SCT is very small and not really an issue. Older SCT seems to have much bigger problem.

[Zakalwe]

Oh, and a decent focuser. The new Revelation rack and pinions are very nice and reasonably priced. I have a Moonlite on mine and a decent focuser makes using the scope a pleasure.

[emadmoussa]

Pros include compact tube for any given aperture and focal length, easy to collimate and maintain, and if it is a decent example, good optical quality. Things to be aware of include the longer cool down time due to the closed tube nature of the OTA, the front corrector is prone to dew, so a dew shield (which can be as cheap as cut up camping mat, or complex as a dew prevention system from a company like Kendrick) is a must, and the focusing mechanism. The telescope focuses by moving the primary mirror up and down the telescope OTA which results in image shift and mirror flop. I am a visual only astronomer a little image shift is not a complete disaster. The flop can be a pain if you are imaging a planet on a small chip though. You can reduce the mirror flop issue by ending your focus “uphill,” in other words by finishing focusing with an anti-clockwise movement which moves the mirror up the OTA against gravity reducing the risk the mirror is unbalanced. The alternative solution is to purchase a crayford type focuser (something like this http://www.firstligh...ocuser-sct.html ) which eliminates that problem completely.

Perhaps other issues, if you are interested in deep sky astrophotography is the very long focal length. This makes guiding a real challenge and requires longer exposure times. You can of course purchase a f/6.3 focal reducer, or even use the Hyperstar system, which places the camera at the location of the secondary and turns the scope in to an ultra quick f/2.

Thanks for the tip. It'll be majorly for planetary and lunar. I've got other kit for deep sky.

[Zakalwe]

Thanks for the tip. It'll be majorly for planetary and lunar. I've got other kit for deep sky.

Then you will see a massive improvement if you opt for a decent Crayford focuser.

[emadmoussa]

Cheapest option out there?

[michael.h.f.wilkinson]

I am aiming to get a Revelation rack and pinion for my C8 at some time. Having said that, I have been content with the internal focusing system for nearly 18 years, so it is not that bad, even for planetary imaging.

A dew shield is very handy but not expensive. Storing the OTA in a cool location shortens cool down time greatly.

[emadmoussa]

One question though, due to lack of space. If I store the OTA vertically on its front, will that affect the mirror stability, say if it's left in this position for like a month or so -- considering the UK weather?

[emadmoussa]

I am aiming to get a Revelation rack and pinion for my C8 at some time. Having said that, I have been content with the internal focusing system for nearly 18 years, so it is not that bad, even for planetary imaging.

A dew shield is very handy but not expensive. Storing the OTA in a cool location shortens cool down time greatly.

Yeah, I had the same advice when I got my 200P long ago...but I thought the focuser was just fine. Nice image

[faulksy]

One question though, due to lack of space. If I store the OTA vertically on its front, will that affect the mirror stability, say if it's left in this position for like a month or so -- considering the UK weather?

no it wont harm it, but beaware of hot temperatures as the grease in the focuser mechanism has been none to melt and drop oil on your optics, not good

[MartinB]

no it wont harm it, but beaware of hot temperatures as the grease in the focuser mechanism has been none to melt and drop oil on your optics, not good

I have heard of this problem as well so would never store my SCT this way.

You're getting a great scope

[michael.h.f.wilkinson]

I always store my OTA flat for similar reasons.

[emadmoussa]

Will do as a drum or a little chair?

[Cath]

no it wont harm it, but beaware of hot temperatures as the grease in the focuser mechanism has been none to melt and drop oil on your optics, not good

I have always stored my SCT vertical on the front cover in a spare bedroom. I did look for any grease problems when I recent had it all apart to flock it, but it all looked perfectly OK, no grease was anywhere where it shouldn't have been, it was still very evenly spread just on the area where it should be, it hasn't gravitated away at all. So all's well with the C6 at least.

[cgarry]

I have always stored my C14 vertically on its front and never had a problem. However, I am getting a bit paranoid now!

Cheers,

Chris

[M4lcs67]

Some may say I am bonkers, but We had a bespoke unit built under our stairs a few months ago and one of the criteria was that one of the cupboards made was large enough to fit all my astro gear, including my C9.25 ota in its box (purchased from Ikea), CG5 mount and tripod. 2 plastic toolboxes from B&Q to hold all my little bits and bobs including eyepieces, hand controllers and counterweights etc. Also my 127 SLT and tripod. and lastly my 12v Maplin transformer in its plastic box. Everything fits in like a glove.

I'm happy as all my gear is nicely where I want it and the missus is happy because there isn't any clutter anywhere.

Deffo recommend a dew shield and also a tape and controller. You will need it.

[Cath]

Yea a dew shield is MUST, as I soon found out myself. Seems impossible to use an SCT without one, particularly if it has a corrector plate (big front lens).

[emadmoussa]

Yea a dew shield is MUST, as I soon found out myself. Seems impossible to use an SCT without one, particularly if it has a corrector plate (big front lens).

Well, I'm planning on making it myself...I already made 3 of these for my smaller scopes..

[M4lcs67]

I use the Astrozap heatertape and controller. They work nicely for me. The beauty of the Astrozap controller is that there are 2 separate controllers that work independently from each other, so if you needed to you could have one on the front of the scope and one on the eyepiece working at slightly different rate if it needed it. I did learn to my cost that without a heatertape you may as well forget it.

[cgarry]

Yea a dew shield is MUST, as I soon found out myself. Seems impossible to use an SCT without one, particularly if it has a corrector plate (big front lens).

If you have an SCT without a corrector plate then you have bigger problems than dew...

[Cath]

Well yes lol

Should have dropped the 'S'

[emadmoussa]

If you have an SCT without a corrector plate then you have bigger problems than dew...

:D -- I was thinking the same thing...

[michael.h.f.wilkinson]

I have a simple dew band with controller, but I rarely use that, as the dew shield seems sufficient on most nights. On really humid nights, I do hook out the dew strip