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mulder85

HEQ5 + SW 200P Dob OTA = Bad Idea?

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Hello,

I am sorry in advance if this specific subject has been discussed before, but couldn't find it. In any case, I need your wisdom :)

I am a proud owner of the best-seller Skywatcher 200P Dobsonian (8" 203mm aperture, 1200mm FL). Like many, I started relatively cheap because I wanted to know if I'd love the hobby or not. Turns out I did. Also like many, after the first few months of pure visual joy, I got incepted with the idea of AP. A couple years later, I am using a DSLR, a ZWO ASI 224MC and recently a TV Powermate 2.5x. These have all been incrementally improving the quality of my shots, which are planetary only for now.

The big elephant in the room is that this specific OTA is not ideal for AP, especially planetary. However I am thinking of moving on to the next step, and acquiring an HEQ5, to convert and put the Dob 8" OTA on it for visual and AP. Here is where I would like your opinion. Do you think that would be a waste? I have heard that this tube being so big, heavy and bulky, would push the HEQ5 at its limits for visual, and a NO NO for AP, especially with heavy powermates and the ZWO on it. Is that true?

And, assuming it is true, should I completely ditch the Dob, and focus on choosing a new better OTA? I was hoping to do that incrementally for practical and monetary reasons, for example this year doing the conversion, and 1-2 years from now getting a proper tube. However if it turns out to be a waste, I would like to avoid that path.

Honest opinions will be appreciated.

 

Thanks in advance,

Alex

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nothing is a waste of time mate, your HEQ5 should carry it ok for vis and with carefull balancing should be good for AP aslong as it isn't windy, I have 2kg over the recommended weight on my heq5 with no problems, of course a heq6 would carry it better but when need must. charl.

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Hi Aex,  It's not a bad idea at all... putting a 200p OTA on an EQ mount of some kind has been done lots of times by various people on here.

I used to use a 200p OTA on a celestron CG5 mount, with the 2" steel legged tripod.  This setup was ok for planetary imaging but not great, especially if there was any wind.

Mounting the 200p on a HEQ5 would be much better, as long as you're only thinking of doing planetary/lunar imaging with it.  If you want to do deep sky, long exposure imaging then you'd be much better off with a smaller OTA like the 130PDS (although saying that you would be able to get some half decent deep sky pics with the 200p on a HEQ5, you'd just be limited to relatively short exposures and you may end up being very frustrated trying to produce images).

To mount the 200p you will need the 235mm tube rings and a long, solid dovetail bar.

These pics of jupiter, mars and saturn were done by me using the 200p on the CG5 mount and an imaging source DFK something camera

572e5d2eba74a_Jupiter7thMay200pf13skytee.png.6b6610279c551c4f503788c641e94996.png578b7541a1782_200p_f13.5_160716jpeg.jpg.6f165fe28731fffac29e2743333d3d17.jpg578ce48ccc887_Marsedit.jpg.12ae4e6c8e2c625629408d9f4efdc1c7.jpg

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I use the shorter tube Skywatcher 200p explorer with my HEQ5 and the mount will take the scope but you may be making things hard for yourself. Focusing is difficult due to wobble when I touch the ota, and with a scope that size any slight winds will be a problem.

I use my set up for planetary imaging and short exposure lucky imaging of small DSO's that need the focal length and also EEA. If you do long exposure AP expect to lose a lot of subs. I also have a 130PDS and that is a much better match for the scope as far as AP is concerned.

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Been there, done that ...

It is doable with a few drawbacks. It is indeed pushing mount close to it's limit. For visual it was awkward to use because I did not want to remove dob mountings from scope (planed to continue using it as dob) - this limits how much you can rotate the ota in rings and leads to very strange eyepiece positions.

For planetary imaging it is indeed very good platform - good choice of ota, and mount will hold it OK and track well.

I even did some DSO AP with it with so so success. Here are a few pics done with that ota on heq5, and non cooled ASI185:

m13_v2.0.png

(pay attention to odd shaped stars - any wind will have great influence on guide precision).

M51.png

I've got a lot of LP and stray light and this ota is not very good at handling that - if you have any light sources near your imaging location - look into adding some sort of "dew" shield - extending tube as to prevent stray light.

At F/6 there is some coma starting to show even on ASI185 sensor size - anything larger than that and you will need coma corrector (not sure which one is going to work OK on F/6 - I did not try any). So you will be limited to bright objects and small fov.

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All,

Thank you very much for your thoughts, suggestions and examples. It seems that the consensus among you is that it is doable, quite challenging at times, and will not produce awesome results, but will do fine as an interim solution. In any case, a couple years from now, if this works well,  I plan to buy another OTA, more specialized for DSO, so at the moment, any DSO I might do will be short exposure only.

@vlaiv: Are the Dob mountings removable without further complications? I guess if they are glued to the tube you can't re-use it as a Dob later, right?

 

 

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39 minutes ago, mulder85 said:

All,

Thank you very much for your thoughts, suggestions and examples. It seems that the consensus among you is that it is doable, quite challenging at times, and will not produce awesome results, but will do fine as an interim solution. In any case, a couple years from now, if this works well,  I plan to buy another OTA, more specialized for DSO, so at the moment, any DSO I might do will be short exposure only.

@vlaiv: Are the Dob mountings removable without further complications? I guess if they are glued to the tube you can't re-use it as a Dob later, right?

 

 

I'm not sure, as far as I remember - there are couple of nuts and bolts holding those. One of the reasons I decided not to remove them is because you need to get the wrench in ota to hold nuts while you undo bolts from outside. This looked like very touchy job to me - either risk having nut fall down on main mirror, and there is no enough room to slide your hand past secondary to do it. Other option is to remove main mirror cell and then access bolts from other side. That is something that I would not do on regular basis (like switching between observing sessions on dob mount and AP on EQ). I can see myself doing that every couple of years if I judge that primary mirror needs cleaning (I have done so on my previous newtonian - 130mm F/7.9 and it was not easy task). Not sure if there is glue involved alongside nuts/bolts (it might be, but I don't think there is - I've seen 200p otas online with mounting support removed and only thing that has been visible are couple of holes in place where mounting support used to be).

Have a look:

P5170379.JPG

Btw this image is from another thread here on SGL (use cases of 200p dob, or something like that).

Here is another thread discussing remounting of 200p OTA (again some pics included with mount supports and without):

 

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Thanks again, that's a ton of material totally related to what I want to do. I'll use those as reference too.

Indeed it seems like if you don't remove the mountings,  you can't place the OTA at a convenient angle for eyepieces, and therefore visual stuff. But I suppose I could decide later on removing them or not.

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