EQ-5 What Can I Expect

[JohnSadlerAstro]

Hi,

I've just purchased these as a replacement for my fast-fading EQ-2, what sort of tracking/mount stability can I expect without autoguiding or a pillar? I'm guessing it will be far better than what I'm using ATM, but I'm not sure by how much.

EQ-5 Mount

Motor Drive 

John

[jambouk]

Depends on many factors:

- the fitting of the kit

- your polar alignment

- the quality control when your specific mount was manufactured and assesmbled

- your polar alignment

- the weight of your kit

- how well balanced the kit is

- the focal lengt of your scope

 

i suspect with a shortish focal length you'd get 30-60 second unguided subs reliably. 

 

Good luck.

james

[JohnSadlerAstro]

Thanks! I will be mostly using my camera with a 200mm les for the 1st few months, then ramp up to the telescope's 900mm if that works ok.

[jambouk]

With that kind of focal length you should be able to get much longer; unless you live under a very dark sky or are using filters, I suspect sky glow will be your limiting factor, not sub length. Prime lenses tend to give better results than telephoto lenses if you don't have the lens yet; stop it down a few stops so it's not fully wide open to reduce the amount of aberration you get at the edges. Once it's all set up I'd do test runs to see what exposure duration you can reproducibly get; do 5 subs at 60 seconds, 5 at 3 minutes, 5 at 5 minutes, 5 at 7 minutes, 5 at 10 minutes... this will take up a whole evening, but looking at these subs you'll be able to see where you either get too much sky glow or non-round stars. Pick the time point where all of the subs are perfect, or at least 4 80% of them, no point always having to throw away 50% of your subs. I suspect small periodic errors won't cause too much trouble at that focal length, but large ones might. You won't know what it's like until you try it out.

James

 

[JohnSadlerAstro]

Sounds good. Come to mention it, I was having trouble with blurring and distortion toward the edge of my photos--probably because I was using the lowest f-number as I could. With the lens at 200mm and f/5.6, I could get exposures of around 30 seconds--and nothing worthwhile with the scope. Hopefully, this new mount will open up lots of new possibilities, with some careful setup and research.

Thanks for the advice!

[Dave Lloyd]

I've found with the eq5 that polar alignment is the most critical aspect. Even with short subs and 300 mm f/l I get trailing if it's even fractionally off.

 

[JohnSadlerAstro]

56 minutes ago, Dave Lloyd said:

I've found with the eq5 that polar alignment is the most critical aspect. Even with short subs and 300 mm f/l I get trailing if it's even fractionally off.

 

Is the Polar Scope good? Like, is it easy to use?

[jambouk]

You'll need to align the polar scope with the RA axis of the mount; plenty of info about how to do that on here and on google

[jambouk]

Polar scopes are polar scopes. You need to set them up well with your mount and you need to know how to use them properly. Your polar alignment with a well set up polar scope will still be some way off a perfect alignment, but will be good enough with your short focal length lens for subs of 1-10 mins (as I say sky glow is likely to be the limiting factor). You could do a test for sky glow now with just a static tripod poiting the camera and lens at a high altitude and taking shots of 1, 2, 3, 5, 7,10 mins and seeing when sky glow kicks in  badly - the stars will trail on these test shots but you're just interested in the sky glow. You also need to hink about dew control if you are planning inaging sessions of more than 30-60 minsas your lens wil dew up otherwise.

[JohnSadlerAstro]

7 minutes ago, jambouk said:

 You also need to think about dew control if you are planning inaging sessions of more than 30-60 minsas your lens wil dew up otherwise.

I'm currently using a hair dryer to heat the lenses every 15 mins. Is there any risk of damage or cracking of the lens when I do this?

[jambouk]

The trouble with that method is three fold:

- time consuming

- runs the risk of drying crud onto the front of the lens (i'd always have a uv cut glass filter on the front of any lens anyway to protect the actual lens, £10-15 but worth it)

- changing thermal properties of the lens which could introduce artefact.

 

there are ways of making your own diy dew controllers if you are that way inclined.

[StarryEyed]

Mass produced mounts are put togeather as quickly as possible. So for astrophotography expect problems until you invest the time to tune it. Even after that you might find it doesn't perform so then you strip it down refine it and rebuild it. All things being good you might get some worthy behaviour. So for astrophotography expect the worst and anything better is a bonus. However you might get lucky and that's just the way it is with these mounts.

As for stability its good as long as you keep the legs short or replace them.

I should add that they are tuff reliable and great value for money. Mine is twelve years old and now my only mount others have come and gone. I often wondered if I should have bought a Vixen GP rather than a Skywatcher EQ5.

[JohnSadlerAstro]

It sounds like a good mount. Let's hope mine will perform well. It should be coming in a couple of days....