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Zenith clearance? LX90 / LX200 without wedge


Chris

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I've been seriously considering an LX90 /LX200 for my mini obsy I'm putting together, but there is one question remaining that could make or brake the idea - Is there enough clearance between the back of the scope and the bottom of the fork mount for a small camera such as a lodestar or ASI at zenith?

 I'm mainly visual but definitely plan to do a bit of EAA, plus photometry and spectroscopy.

I've just got the dosh together for one, but if there isn't enough clearance for a small camera (no filter wheels or anything like that), I can't really risk it and would need to pick one of the alternatives options.

So calling all LX owners pretty please, final question, make or break :)

 

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You can fit a lodestar or ASI camera if you put directly on the back, into an SCT to 1.25" visual back,  or in the top of a diagonal, but not if you have a Crayford style focuser fitted, which many people do upgrade to.

if memory serves you can even get a DSLR on the back if fitted directly...

hope that helps

:)

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26 minutes ago, SkyBound said:

If you give me an hour I will measure the exact clearance and send you a pic...

That would be really great thanks :) The only worry is the T-adaptor for camera spacing you see, and doh! I did forgot to mention the reducer.

But if you can measure the clearance I can work it out! Which model do you have?

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Hi Chris,

If you are doing EAA/imaging I guess you will want to use a reducer. Typically a F6.3 reducer will require 110mm between the reducer and the sensor so this will make the whole thing quite a bit longer. You can use a diagonal, but not sure about whether this will allow the correct sensor to reducer distance, especially with the F3.3 reducer where the sensor to reducer distance is shorter (60mm I think). Sorry, not really helping am I? :confused3:

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7 minutes ago, RobertI said:

Hi Chris,

If you are doing EAA/imaging I guess you will want to use a reducer. Typically a F6.3 reducer will require 110mm between the reducer and the sensor so this will make the whole thing quite a bit longer. You can use a diagonal, but not sure about whether this will allow the correct sensor to reducer distance, especially with the F3.3 reducer where the sensor to reducer distance is shorter (60mm I think). Sorry, not really helping am I? :confused3:

lol thanks Rob, oh dear that's quite a bit of spacing, the idea is starting to look a bit doomed! I take it you need this spacing even with a smallish chip?

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Yes if you are using the Meade f6.3 reducer than that will require 105-110 mm of backspace...so that will be an issue.

i have the 8" LX90, well I say I have, I have borrowed it from a friend with the intention of buying..if I get on with it. But I have owned one in the past...a long long time ago, and had to sell to fullfill other financial commitments...you know the drill... :)

i will go an measure now, and get back to you...watch this space

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You can use the reducer with less or more spacing, it just gives different reduction ratio, they work well from about 70mm-130mm with an f ratio or approx f5 -f8, but outside of the f6.3 you do get a little deterioration of the image, and above F6.3 you get some vignetting also, but if you have a small chip that won't be an issue.

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1 minute ago, SkyBound said:

You can use the reducer with less or more spacing, it just gives different reduction ratio, they work well from about 70mm-130mm with an f ratio or approx f5 -f8, but outside of the f6.3 you do get a little deterioration of the image, and above F6.3 you get some vignetting also, but if you have a small chip that won't be an issue.

That's some useful knowledge thanks :) In that case I'll base my camera and reducer measurements on about 70-110mm spacing and see if there is any space left? 110mm would give better results by the sounds of it.

If this doesn't work I know you can get the basic non goto but clock drive SCT's which are fixed on a wedge, I've heard they are pretty bullet proof and cheap so that's an option also...otherwise it's back to an EQ mount with their sometimes awkward EP position, and counter weights to load and balance. Would be better for the EAA side of things though I guess.  

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I guess the other option is to go for a 'short and fat' camera. There was some debate about this on CN. Starlight Express has gone the 'long and thin' route for their cameras so that they were easy to move in and out to reach focus and also less of a cross section which is good for Hyperstar, but were not so good for fork mounted scopes. Atik on the other hand went for 'short and fat' cameras which was good for people with fork mounted scopes.  There are a lot of EAA folk with fork mounted scopes in the US so it must be possible! I know the Atik Infinity is very popular and used on fork mounted scopes with reducers. There are probably pictures of these kinds of setups on the EAA forum on CN if that helps?

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You could always use a diagonal, put the reducer on the back and then your camera in the diagonal...but you will have to work out the spacing.

and just for information, the backspace measurement for the reducer, is taken from the middle of the lens assembly, which is at the bottom of the rear threads on the reducer, and NOT taken from the rear glass, so that will save around 7mm.. :)

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12 minutes ago, RobertI said:

I guess the other option is to go for a 'short and fat' camera. There was some debate about this on CN. Starlight Express has gone the 'long and thin' route for their cameras so that they were easy to move in and out to reach focus and also less of a cross section which is good for Hyperstar, but were not so good for fork mounted scopes. Atik on the other hand went for 'short and fat' cameras which was good for people with fork mounted scopes.  There are a lot of EAA folk with fork mounted scopes in the US so it must be possible! I know the Atik Infinity is very popular and used on fork mounted scopes with reducers. There are probably pictures of these kinds of setups on the EAA forum on CN if that helps?

It would not make much difference as all the available space would be taken up with focal reducer backspace...unless the diagonal option would work...

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Thanks guys, in that case I'll google around for lx90/200 EAA setups and see how people do it...hopefully. not off the table just yet then, but it looks close even with very suboptimal spacing. I'll see if anyone is using a diagonal to image ??

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4 hours ago, RobertI said:

That's very true, you can't ignore the measurements! I guess a F3.3 reducer would release 50mm or so, but still probably too tight. Sounds like the diagonal is the way to go. Also looks like it's possible to put the reducer after the diagonal though not sure it's necessary? 

Thanks Rob :) I read the thread you linked cover to cover, putting the reducer after the diagonal was the only way the OP could achieve focus. I think he mentioned getting a couple of adaptors machined up at a local machine shop to help with this. His Meade 4000 3.3 reducer had a 2" nose piece as a result.

I'll find some more threads on the subject as it was one of those threads where you think you've understood it, then you realise you didn't, then you're not sureif you did or not?

The one thing that does strikes me is that it might not be the easiest or even the cheapest way of achieving what I would like. I have about 750 quid to play with after a big sell up. I have a Celestron Nexstar SE goto mount and a 200p remaining, so two non compatible bits of kit. Maybe I can also look at making the SE mount work for EAA and the 200p work for visual if I don't sell them?

 

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Another thought Chris, what about a short focal length lightweight refractor to go on the SE mount for EAA? I've seen some amazing EAA results with very modest fracs, in fact I got some remarkable shots with my little 50mm achro finder, especially with an Ha filter. And it was so easy to align and locate objects. That would also leave more of your budget for an ultra sensitive EAA camera like a Lodestar X2. I'm not helping am I? :) 

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Hi Rob, I fellow SGL'r actually came to my house to buy both the 4SE OTA and mount, but when I demonstrated the mount it started to behave a bit strangely and slewed upside down so the eyepiece was pointing at the ground! Needless to say he didn't buy the mount but still bought the OTA.

Therefore I need to buy a cheap OTA anyway just so I can check out the mount. I think it might have been something not set right on the controller or my power supply not behaving, it certainly worked fine at night a few weeks beforehand. 

I could kill two birds with one stone: i.e. get a cheap OTA that I can both use to fault find the mount, and if the mount is ok try the OTA with the mount for EAA and see how I get on. I could fund the OTA by selling my 200p and keep the 700 in the bank until I have more of a clear plan about a bigger setup in the 5x3 shed. It might be the case that I'm happy using the SE mount for the EAA side of things in which case I can just stick a big manual Dob in the shed, or I might find that I really do want one setup to cover both bases.

Fault finding the SE mount with an OTA that I can use for EAA sounds like a good place to start.....that's the plan! :)   

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