Thoughts on doubling up

[rustigsmed]

Hi fellow IIS'ers,

Given the lack of imaging time available due to weather I've been giving some thought to either getting another mount and scope and more recently adding an additional scope to my EQ8. The advantage of two mounts is obviously shooting two targets at once but really the cost effectiveness is pointing me consider a side by side setup.

I had given thought to mounting a small refractor on top of the 12" newt but now i'm starting to think it would be more effective using a scope that captures data that can be more efficiently combined. otherwise I could end up with an undercooked widefield image and higher res image.

So the idea is putting a f6 8" newt on a saddle (or 10" f5) and capturing OSC/DSLR colour on the 8"f6 and going mono on the 12" for luminance and NB to maximise resolution and maintaining the same FL/FOV.

I have no experience with this and currently do have to set up each night (hoping to have an obsy by the end of next year). Tips on what gear is needed (including software) or potential issues people can see or tips would be appreciated.


edit:

apparently most side by side the mount head is rotated 90 degrees which I don't think is doable with the eq8 so i'm thinking I need
http://www.bintel.com.au/Accessories/Dovetail-Plates---Adapters/Losmandy-DVSBS-Plate/1083/productview.aspx

but mounted perpendicular on top of
http://www.bintel.com.au/Accessories/Dovetail-Plates---Adapters/Losmandy-D-Universal--br-Dovetail-Plate--DUP-/614/productview.aspx
(which I own already).

then its a matter of balance and hopefully matching enough holes up.


Clear skies

Russ

[Shiraz]

been thinking along the same lines Russ, but could not work out how to manage dither - really need two instances of the capture software running in parallel and talking to each other, so that both know not to image when dither is active. Looked a bit beyond my pay grade.

[gregbradley]

I am running 2 mounts at the same time at present (well I did one night and then needed some spare parts to continue!).

For me its the CDK17 on a PME and the AP RHA on an AP1600. The AP scope is quite widefield, the same as Mike Sionios. The CDK can either image at 3 metres or about 2 with a reducer. I am currently using the reducer as it matches my local seeing better and reduces imaging time.

So a Proline 16803 on the CDK with reducer is the same image scale as an 8300 sensor on the AP. The CDK can give more luminance detail and the RHA colour and or narrowband quickly. Both are fast scopes. 2 scopes and cameras is about matching the image scale.

If you have a dual mount wouldn't you be autoguiding with only one of them with an OAG and if you use dither they both dither at the same time?

I think also with that weight I can pretty much guarantee you your subs will not land on the same pixels one after the other.

Peter Reito is using a dual scope setup. I think he's spent a lot of time (and ongoing) resolving issues with this.

Obvious problems would be balance, alignment so they image the same thing and weight for the mount.

Thomas Davis images with 2 scopes, an FSQ and AP RHA. Not sure if its on 2 separate mounts or at the same time. He uses an STL11 colour for the FSQ and an STL11 mono on the RHA as I recall.

I used 2 different mounts as sometimes these setups will be in different locations but I built my observatory intending to have 2 setups at the same time so there is provision for a 2nd one. A 2nd one is a lot easier.
It was fun running 2 setups with 2 computers and setting up one and then adjusting the other whilst the other was doing something. I think it would end up being a whole lot easier than the flexure, mounting, aligning issues of scopes in tandem. Perhaps a smaller refractor on top would work. I have used an FSQ mounted on top of an FS152. One guider.

Too much weight and you will have tracking issues.

2 separate mounted systems can be framing the same image. You may need to allow for a small amount of cropping if they are not exactly the same. Perhaps it would be better if one was just slightly wider FV to give some tolerance.

Greg.

[rustigsmed]

Thanks Ray, I hadn't thought about the dithering, perhaps it wouldn't matter too much if doing L and RGB at the same time but if you were doing NB on one scope then its not shifting for a lot of subs. I had envisaged using SGP for the L/OAG and perhaps BYEOS with the smaller scope, you can pause and set delays on exposures quite easily. there would of course be even more mismatch on exposure length if it was the f6 v f4 scopes.

I also did some accurate line and circle work in ms paint which showed serious overlap of the tubes with the losmandy dvsbs in my mind's eye I thought the curve would 'create' some more useable space but it doesn't do it enough not even for the 8". I would say it is probably only suitable for 2x 8" at the most... and that I would need the saddle (middle to middle) atleast 310mm wide for the 12" and 8" option.

* however a 127 mak-cass with a 0.8 focal reducer would fit but would be slow.

so unless there are wider saddle options out there i'll just have to wait longer and go for a HEQ5 or NEQ6.



thanks for taking the time for commenting Greg, i'm a big fan of your setups and its interesting to hear what others do too. I wasn't too concerned with weight (maybe if I went the 10") but yes balance will be BIG issue and some overlap is probably a good idea. I might just throw a refractor on top for now, I was thinking of giving the side by side a go till I could afford an additional mount (and guiding solution) but now that I've measured the narrowness of the saddle its not looking worth it/possible. the idea was for me to go one of those cooled mono dslr's and regular cooled dslr so sensor size was the same.

[Shiraz]

hi Russ. I was not concerned so much about exposure length, but about imaging while dither is taking place.

Maybe going through the sequence will show what the concern is:
scope 1 and 2 are taking images that start at different times and with different sub lengths. Scope 1 finishes a sub and then instigates the dither, which moves the mount to point at a slightly different part of the sky and recommences guiding. When the mount has steadied, scope 1 starts the next sub. In the meantime, if scope 2 was in the middle of a sub while all this happened, that sub would be ruined by the dither offset. The only way around this is to synchronise the times at which the 2 scopes expose subs so that scope 2 doesn't try to image while dither is underway. I don't know how to synchronise the timing of two capture programs - do you know if it can be done?

Of course, this would not be an issue with two mounts....

[rustigsmed]

Hi Ray,

Thanks for the rundown, I don't know of any automatic ways of synchronising.
I was thinking if the second scope was a dslr you could use backyard eos (or Nikon), you are able to set delay times; which would mean if you could average out the time taken on say SGP, for the sub length, download time, auto refocus and dither you could possibly have the second camera in sync by entering the time to wait manually (eg 90 seconds), that of course would rely on how consistent dither and refocus takes. disadvantage is that byeos hasn't got its own auto focus function (but I have a feeling it eventually will in later versions).

Of course two mounts would be less of a problem; however I wonder if we had two mounts we would still be looking to maximise by utilising 4 scopes :lol:

[gregbradley]

How important is dithering? Data rejection in CCDstack works miracles and mounts are never perfect especially lower end ones.
median combine takes care of the rest.

Taking enough subs so the statistical averaging processes of various combine methods can do their magic is a good approach.
Its really a maths problem. To accurately identify an outlier you need to have accuarately established the bell curve of the data to see what is odd by sitting outside of it. That's pretty much how data rejection works and dither works. The odd value gets averaged out in the case of dither or some other method of determining odd values that should be taken out of the final stack.

Perhaps an example of a dithered stack of 10 versus a non dithered stack of 10 may be more conclusive but I would suggest the difference is negligible. Perhaps I am wrong and it makes a massive difference, in which case I'd love to see examples.

So worrying about something that isn't really an issue at all may prevent you from going ahead with a tandem setup and all its benefits not the least of which may be extra subs that can further increase the accuracy of your data rejection routines.

Greg.

[PRejto]

This thread is right up my alley. If the idea is to save time it must be balanced against the various problems that present that consume time! When it all works it's very sweet. Automating is another matter and needing to set up every time is not something I would want to do. It's enough trouble with a permanent setup.

Issues:

1. Getting reasonably matched FOVs and resolution through various scope/camera configurations. What you currently own may not work so this can get expensive.

2. Guiding and resultant flexure between the scopes. If two refractors this is doable. With mirrored scopes I think it would be rather difficult.

3. Aiming the scopes to the same FOV. NOT EASY!! I resorted to buying an Optec Libra, but then had to modify it to cure flexure issues.

4. Focusing two scopes. FocusMax V.4 will run a script called "Acquire Star Dual Focusers." However, you need two compatible imaging programs (TSX, CCDSoft, or Maxim). Running the routine, depending on cameras, can take 5-7 min to complete.

5. Dithering is possible. However, it requires a program that will sync exposures made in one program to the other. I had special software written for me that does this from TSX to CCDSoft. Thus, I can guide and dither in TSX and CCDSoft is a "slave." Thus, CCDSoft is not exposing during the dither move.

6. Automation. No automation program allows for dual imaging camera control currently. However, with the TSX sync software it is possible to control the camera in TSX via CCDAP5. CCDAP doesn't know about the camera in CCDSoft but it happily takes exposures every time TSX does. Also FousMax can now be configured so that commands to focus from CCDAP will run the dual focuser script. The current limitation is that CCDAP can only control one filter wheel. If I'm shooting luminance with one scope that is not a problem. I've yet to solve using both FWs automated. Probably currently cannot be done.

7. Weight/balance. First you need something like an ADM side x side solution and then on top of that a way to aim the scopes. It gets heavy pretty fast by the time you add dual electronic focusers (Optec's FocusLynx will control 2 focusers if you buy a second circuit board), dual filter wheels, and 2 cameras. That is a lot of gear to run on one mount! Balance is rather tricky to obtain and is never perfect. Also, loading and unloading the mount is quite hard as there is no way to avoid very unbalanced loads in the process of setting up or tearing down. This might be the main reason not to go down this path if not set up permanently (or at least semi-permanently).

8. I currently have 6 USB devices running into a powered hub up on the saddle and at the bottom of the mount an Icron Ranger 2204 USB/CAT5 for a long run into the house.

I'm probably sounding negative. I have found it a long and difficult journey to get where I am currently. I'm not sorry though but I was naive in my expectations initially. Let me know if you have any additional questions.

Peter

Pictures here: http://www.pbase.com/prejto/equipment&page=all

[rustigsmed]

thanks for the comments greg and peter.

good to hear from someone with first hand experience, so thanks for putting your experiences down Peter. your setup looks great, and interesting to hear about the fov issues and potential flexure issues with mirrored scopes.

I think for time effectiveness and difficulty i'll aim for a second mount esp considering I'm going mirrored and ... at best perhaps throw a small refractor on top of each one ... eventually :) if I ever get an obsy up and running. fingers crossed for end of 2016.

[PRejto]

Russell,

If you can run two mounts you will find life much less complicated. The expense is greater but I think it would be worth it!

Peter