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I've been looking into guiding using an ST80 as that seems to be a reliable and popular choice.

With plans to get an HEQ5 and eventually upgrade the scope to an ED80, it sounded like a match made in heaven.

However, as I have been reading around the subject I am wondering whether the ST80 is the best option. My 70ED is probably going to be swamped by the ST80 and I wonder if it will confuse balance and tracking if a slightly bigger scope sits on the back of the imaging scope? Would flexure be more likely with something that was "top" heavy?

The other option is a finder-guider package, and some of the "ready-made" ones I've seen look like a fairly cheap alternative - better weighted and size-matched to the 70ED.

Would the ST80 be problematic on a small scope like the 70ED? Or would it be okay? It would make sense to go that way with plans to upgrade the scope eventually, but I don't want to make life harder for myself!

Cheers

Mark

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I don't see it as an issue at all if you are guiding with a lager scope. I've known of some folks who have a small refractor and an 8" scope dual mounted and just swap them over for guiding duties, depending on which one is imaging at the time. As long as everything is clamped down tight as well, you reduce your potential of flexure. 

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In my view, its not the choice of guide scope that is the only consideration... You have to consider the camera that you will use with it because that (pixel size) will effect your pixel / arcsec ratio and that is more of a potential problem if you are at too high a resolution.

Ray

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Cheers everyone!

Why not get an OAG to use on the 70ED then when you upgrade either continue with the OAG or use the 70ED as guide scope?


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I haven't really given OAGs much thought as I was reading that there could be problems with fitting and focusing for DSLRs, but maybe that is an alternative - more research!  :grin:

I don't see it as an issue at all if you are guiding with a lager scope. I've known of some folks who have a small refractor and an 8" scope dual mounted and just swap them over for guiding duties, depending on which one is imaging at the time. As long as everything is clamped down tight as well, you reduce your potential of flexure. 

Thanks Sara, so I might get away with it then!

In my view, its not the choice of guide scope that is the only consideration... You have to consider the camera that you will use with it because that (pixel size) will effect your pixel / arcsec ratio and that is more of a potential problem if you are at too high a resolution.


Ray

Hi Ray, I am not entirely sure what that means, so I guess I need to do a bit more research! I was planning on coupling it with something like the QHY5(l)-II camera or possibly a ZWO - although as it is only (mainly) for guiding, the older QHY5 might do the job just as well

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Just look at your focuser when your DSLR is at prime focus, if you have enough inward travel left to fit an OAG then you should be fine. I imagine this is more of a problem on Newtonians that have restricted inward focuser travel, they can't make the tube too long or it would hit the secondary ;)

Consider filter placement as well though, LRGB isn't too much of a problem but if you are doing NB the filters really need to go between the imaging camera and the OAG or you will block too much of the light getting to the guide camera.

I use a filter drawer between the OAG and camera to get around this.

It is only tricky if you are trying to keep a specific spacing to a CC or flattener.

I've been very happy with mine on my little frac :)

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It'll be a while before I go on to filters but I am still a little worried about whether it would work. I was reading another thread about focussing with an OAG if using a flattener/reducer. I have a flattener which requires 55m to the sensor, so adding the OVL OAG, for instance, would add 15mm to the distance which sounds like it would be a problem - presumably regardless of how much play you have in the focusser, the critical distance from the sensor to the flattener has increased.

I did see a link to an OAG that replaces the T-Ring to get around this but still requires a 1mm spacer to get back to the 55mm critical distance - not sure how critical they are, but certainly don't want to be buying something only to find it doesn't work!

Nothing in this hobby is simple!  :grin:

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DSLR is normally 35mm to the sensor, that leaves you 20mm to fit everything else. I know my OAG setup wouldn't fit into 20mm but there are some that will. For me it doesn't matter though as the flattener on my scope is inside the scope so as long as I am in focus my sensor is in the right place :)

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

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Cheers everyone

Hi Ray, I am not entirely sure what that means, so I guess I need to do a bit more research! I was planning on coupling it with something like the QHY5(l)-II camera or possibly a ZWO - although as it is only (mainly) for guiding, the older QHY5 might do the job just as well

Whilst the qhy5 l mono is a good camera it like the two has 3.75 micron pixels, with a 400mm fl st80 you are probably too close to the seeing...@ 1.9 pixels / arcsec

Whilst this is no absolute barrier you will have a graph like the Pyrenees. I used a similar set up and with poor seeing it was all over the place. I damped it down with 5 sec + exposures, I have shortened my guide scope focal length to better match the camera I use.

Camera and guidescope do need to be matched ideally though it is flexible to a degree.

Ray

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DSLR is normally 35mm to the sensor, that leaves you 20mm to fit everything else. I know my OAG setup wouldn't fit into 20mm but there are some that will. For me it doesn't matter though as the flattener on my scope is inside the scope so as long as I am in focus my sensor is in the right place :)

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

Sorry for all the questions! But, if 35 mm in the DSLR to the sensor, and the flattener is at a set distance - adding the extra distance with the OAG would push you outside of the limits with the flattener.....my head is starting to hurt a bit.....I need to go measure up. Really starting to like the look of the OAG though, I just need to convince myself I can get it to work!

Thanks for taking the time to humour me!

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Whilst the qhy5 l mono is a good camera it like the two has 3.75 micron pixels, with a 400mm fl st80 you are probably too close to the seeing...@ 1.9 pixels / arcsec

Whilst this is no absolute barrier you will have a graph like the Pyrenees. I used a similar set up and with poor seeing it was all over the place. I damped it down with 5 sec + exposures, I have shortened my guide scope focal length to better match the camera I use.

Camera and guidescope do need to be matched ideally though it is flexible to a degree.

Ray

Thanks Ray - I clearly need to do more research then as I wasn't even factoring that in. Maybe the QHY5 would be better going down the OAG route. Presumably the same issue would occur with the ST80 and other guidecams like the Lodestar then? I need to go away and research sensor size etc, but you are saying a shorter focal length would be better with the QHY5? So a finder/guider maybe?

Maybe something like THIS?

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I assume you have a flattener with a T2 thread and the 55mm spacing is measured from that.

The bayonet on the DSLR is normally 35mm from the sensor.

So you need a T-ring and OAG that take up 20mm of space.

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That's starting to make sense - although I think the OVL makes it slightly too long and the direct fit one I saw would be a bit short - obviously it is possible somehow, so I just need to keep reading, researching and checking out a variety of OAGs! Thanks again for your help!

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Yes the finder guider is a good match for the smaller pixel cameras, not so the loadstar....a very well regarded camera with much bigger pixels that are usually binned as well, much more suited to longer fl guide scopes or oag....

The finder guider option is also light and easier to clamp down.

However, also consider you future requirements it's often the case that we swap n change as we go forward in this black hole of a hobby!!!!

Ray

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To long is a problem but too short just requires a spacer.

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Yeah the thin one with the T-Adaptor incorporated seems to need a 1mm spacer! So that might work....there is always something else to buy!  :grin:

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Yes the finder guider is a good match for the smaller pixel cameras, not so the loadstar....a very well regarded camera with much bigger pixels that are usually binned as well, much more suited to longer fl guide scopes or oag....

The finder guider option is also light and easier to clamp down.

However, also consider you future requirements it's often the case that we swap n change as we go forward in this black hole of a hobby!!!!

Ray

Ray, I've changed my mind about guiding about 40 times just today - think I am moving away from the ST80 and more towards the finder/guider I linked to or the OAG. For me, as a beginner, I feel the finder/guider might be a better option, but I suspect I'll change my mind again by the time I post this message!  :grin:

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Yeah the thin one with the T-Adaptor incorporated seems to need a 1mm spacer! So that might work....there is always something else to buy! :grin:

1mm spacer AKA a 42mm washer.

Incredibly cheap :D

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Why take on extra weight with a whole second scope, its flimsy cast aluminium rings (potential for flexure problems) etc?

Finder guiders are proven to work quite well with ED80's.

There are some threads here to even convert the one you already (if) have and attach a camera to it!

its almost 1.5kg less strain to HEQ5. Just a thought :)

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Why take on extra weight with a whole second scope, its flimsy cast aluminium rings (potential for flexure problems) etc?

Finder guiders are proven to work quite well with ED80's.

There are some threads here to even convert the one you already (if) have and attach a camera to it!

its almost 1.5kg less strain to HEQ5. Just a thought :)

Did have a finder, but sold it with my other scope, so the Altair set-up would be attractive as an all in one solution that keeps the weight down.

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Blimey, this thread is a bit of a storm in a teacup! The OP started off with the excellent idea of guiding with an ST80 and, like Sara, I'd have thought that a perfectly good idea. OAGs are good things when you need them, but they are more fuss than a parallel guidescope and if you don't need them - and with small imaging refractors you don't need them - why put yourself through it? I've guided everything from 66 to 140mm refractors with the ST80 and have never had any issues whatever. I've used an OAG on the big stuff (14 inch ODK) because there you have cogent reasons for choosing an OAG. But honestly, the ST80 is cheap as chips, fast at F5 and has a focal length which will be optimal for guiding out to at least 1.5 metres and possibly more.

Olly

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Hi Olly, thanks for the comments.

So how would the ST80 fare with a QHY5L-II stuck in the end of it then? From what I have been reading that would also need an extension tube - but that's easy enough, even for me. I am getting tempted mainly between the Altair solution for simplicity/weight and the ST80 for the lower price (although there isn't a massive difference) and the added bonus of a grab and go scope for trips.

I appreciate any question about "how to" in relation to anything astronomy related is always going to generate lots of different opinions, so I appreciate everyone chipping in - regardless of what anyone might think, it is helping me make a decision. Even when you think you have figured it out, there is always something else to consider! And it's also made me do a lot of reading this weekend, which is always a good thing!  :grin:

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So how would the ST80 fare with a QHY5L-II stuck in the end of it then? From what I have been reading that would also need an extension tube - but that's easy enough, even for me. I am getting tempted mainly between the Altair solution for simplicity/weight and the ST80 for the lower price (although there isn't a massive difference) and the added bonus of a grab and go scope for trips.

It does need an extension to reach focus with the QHY5, but the ST80 comes with a free barlow: just unscrew the lens from the tube and bingo - extension tube.

I agree with Olly, btw. OAGs and finder guiders are great, but they are solutions to problems you probably don't have, and take a lot more work.

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It does need an extension to reach focus with the QHY5, but the ST80 comes with a free barlow: just unscrew the lens from the tube and bingo - extension tube.

I agree with Olly, btw. OAGs and finder guiders are great, but they are solutions to problems you probably don't have, and take a lot more work.

Cheers! When you say finder-guiders take more work, do you mean in relation to converting the finder scope or in term of actual use, when compared to the ST80 as an option?

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