Equitorial mount question

Hi All,

Hope this is the place to ask questions as this is my first post.
I have been using an SLT102 (4" Goto refractor) for the last few year and have tried a bit of astro photography with it. Must say for a cheap scope I was able to get some nice (to me) DSO's with a 450d Cannon.
I can get about 15/20 secs at most and have decided to consider going for an Equitorial mount - HEQ5.
It takes a lot of patience to image on an SLT but I rely on Starry Night software to match what is in the FOV with what I expect to image. I was suprised to see that only after an exposure of some seconds can I actually see what it was I was aiming for(if you follow). So this matching up is important ..so to my question:

I don't know if these GEMS are all thay are cracked to to be for tracking/astro stuff but they contort themselves at weird angles (only ever see them on Youtube) so if I image will the camera (fitted to the back of the scope) be at odd angles and not 'straight'? If so how can one match up your image with planeterium software? ...as otherwise I'll get very conffused and curse the day I went for a GEM.

Hope this question makes sense! Appreciate any reply.
(attached ring nebula from SLT102)

I'm not sure that I've got your question right.

Generally GEM's are better at astrophotography because if they are correctly polar aligned then they only need to track along the right ascension (RA) axis (thats left and right along the equatorial equator). As no tracking is needed on the DEC axis (up and down with respect to the equatorial equator - ie along a local meridian). This avoids any drive tracking error in one axis by not using it.

Another advantage is that tracking follows the target in a natural way so that orientation in the field of view does not rotate over time.

With an alt/az you get field rotation. Picture Orion as it moves across the sky - its orientation will appear to rotate clockwise as it descends towards the horizion - with respect to the horizion (and any alt/az mount or to the human eye).

So long as you stick to multiple shortish exposures you can still get by with an alt/az as many stacking software packages can compensate for the field rotation.

Alt/az mounts aer less complicated than GEMS and I believe easier to handle, they are intuitive, and quicker to setup.

GEM's are less intuitive and sometimes you have to do a meridian flip whereby you need to slew the scope to the other side of the mount (and hence North-South swaps in the FOV as the scope is now "upside down" ).


Does that help any?

Mark

Thanks Mark for that fullsome reply.
I played around with Starry Night and I see the point you make on rotation. Your point on tracking that 'follows the target in a natural way' - I now understand.What was throwing me off were videos I had seen on equitorials and it looked to me that cameras they had attached where twisting and turning this way & that depending on the target and I could not see how one could match up the orientation of the image to what planeterium software was showing.I can see now that is not a problem.
I will carry on with my research on GEMS. Whilst I think I could manage a polar allignment ok but being a lazy type of amateur I fear I will skimp on it or worse still not take out the scope at all as I don't want the hassle! I have ruled out a CGEM - too expensive, CG5 -too noisy, EQ6- too heavy and might go for a HEQ5 pro (with Goto) which might future proof me should I get deeper in Astro photos.
Thanks again, Brendan.

Hi Brendan.
I have just made the leap from Altazimuth to equatorial.
And your question makes perfect sense tome (probably watched the same youtube clips:))
I was using a wedge with my scope before and got some extra long exposures for what its worth.
Will let you know how I get on with my new toy...

Declan.

Actually - I've gone into reverse! Got a DOB! having had a Goto.
The DOB has tracking I needed my techy fix.
I will be going GEM soon but I realised I was taking nice astro photos with my little Nexstar , but laptop, wires, ccd etc I needed a lot of time to set up. More often than not I did not take the brief opportunities we get to look at the sky - 'too tired to set up stuff', 'going to bed in an hour -not worth my while" - you know what I mean! (LazyAstronomer)
I found too that I only had a vague idea of the sky do I went DOB.
It's the Skywatcher Flexi 200P Auto tracking (8").
I will just wheel it out for casual viewing - sit on a chair and learn the Sky. When I want a full night, high tech experience then I go for the EQ6/Laptop/dSlR/Eqmod/Ascom Starry Night/ Landesk from inside the warm house etc.

I will go that last route later in the year. Good to hear from you.

Brendan.

I understand your situation indeed.
Go through that whole routine myself. I even bought an auto guider that works WITHOUT a laptop just to cut down on
set up time. May be one day I will build my own obs..
I do find it frustrating at times.
Why couldn't my hobby have been knitting or something less fussy...
Good luck with the Dob!