Tracking time / sub length

[ThomasBR]

So, I am still considering which one to buy as my first scope. Two of the scopes I am considering are the SW 150p on EQ3-2 and SW 200p on EQ5 (both with dual axis motors). I have been wondering how long time these setups will track well enough to take long exposure photographs i.e. how much exposure time can I get for each sub? The plan is to have an unguided setup (until I can afford to expand my setup and a bigger rig). I hope I will be able to make a decent PA using a polar scope. If you can share any experinece with the above mentioned setups it will be nice

Th

[Brent]

I don't have any experience of the EQ5 but I do use a SW 150p on EQ3-2.

I would say that with very good polar alignment you could get possibly up to 40 or 50 second exposures, BUT, unfortunately the gearing on the EQ3-2 isn't good enough and you will get some tracking errors meaning losing quite a few subs due to star trails. Guiding really is the best way to go with the EQ3-2 but that involves soldering a guide port in on the controller.

[Bizibilder]

Probably around one minute maximum for either mount - but that would be pushing it. Probably better at 30secs.

If your interest is in astrophotography you really need to consider at least an HEQ5. I realise they are more expensive but in the long run they will work out to be a good investment!

I would also suggets the book "Making Every Photon Count" by Steve Richards (get it from FLO) as this gives you good advice and will prevent you from making expensive mistakes.

[ThomasBR]

So, I guess that since the 200p has larger apperature I'll get 77% more light collected during the one minute of tracking. As the 200p is only 43% more expensive it is good "return on investment" to go for the 200p?

[iamjulian]

I had the 150P on an EQ5. I found the sweet spot to be 30 seconds (most frames were good). By 45 seconds about half the frames started to show errors. I once got a perfect 60 second frame.

That is all unguided, polar aligned with a polar scope, and some quick and not very accurate drift aligning.

[iamjulian]

If you put a DSLR camera and guide scope on the 200P, I think you are pushing the weight limit of the EQ5. That seemed to be the advice I was reading a while back.

[Vega]

Your tracking time is also dependant on magnification. The shorter the focal length of the telescope your using, the longer tracking times you will get before you start to get 'streaking stars' in your images. Longest I ever got with my EQ3-2 With 1000mm focal length scope was 45 seconds. However with a standard SLR camera bolted to the mount with 18mm lens I could get 2 minutes ;-)

Cheers

Matt

[Bizibilder]

Don't worry about aparture for photography. Aparture rules for visual work but in photography you can simply increase the total exposure time and collect more photons!

[Black Knight]

I have used my 200p on an EQ5 pro mount to take images unguided. Once (and only once!), was my polar alignment good enough to take 2 minute subs. Most of the time I managed 60 seconds or less. When I imaged M42, the Orion Nebula last winter I used 30 second subs (out of choice), but they were still too long - I still got a burnt out core! Should have done 15 seconds .... oh well . So to some extent it may depend on your target.

In my own experience, very good polar alignment is a must, along with drift aligning. My own polar alignment was always a little bit suspect so drift aligning was a necessary additional step I had to go through every time.

The big thing with this particular setup I found was avoiding the wind. It doesn't need too much wind for the 200p on an EQ5 to start acting a bit like a sail. But if you are sheltered things will be better.

Adding a guide scope and camera to this setup would push it over the edge weight wise. I guess you could investigate using the finderscope with a guide camera. Many people have done this, and it was something I was going to try, but in the end I opted to upgrade my mount to an EQ6.

[Rustysplit]

I have the 200p/eq-5 set up. If you make sure that the polar scope is properly aligned in the mount and also polar aligned as well as you can, I can get around 90 secs on a still night. This is with a dslr attached. There is some error in the gears though. Balance is everything when you at the mounts limits!

[Black Knight]

Balance is everything when you at the mounts limits!

I second that!

[ThomasBR]

Thanks guys, it very nice to get advice from people ith hands on experience (guess that is why SGL is o good).

Sounds like a good idea to use the finder as guidescope. What kind of adaptor do you need to attach a guide camera to the finder?