DSLR and EQ3

[g3az66]

Hi all,

first post from myself and looking for a few answers to some queries I have.

I own a dslr and have taken some night sky images with it and been very happy with them. These were with a conventional tripod and a 300mm lens. Shutter times were 30secs and star trailing was very evident.

Anyhow, I have acquired a Skywatcher EQ3 mount and need some advice on setting it up with my camera.

• How do I mount my camera to the mount?
• With no telescope how do I know it's pointing in the right direction? The mount has Synscan
• I understand polar alignment so if I line up Polaris in the centre of my viewfinder will this be enough to track without star trailing?

Thanks in advance

Gary

[Uplooker]

Hi Gary,

Without a tracking mount you will get star trailing, even with lower exposure times. This will be accentuated  depending on what length of lens you are using. To answer you're other questions:-

1. Get a short dovetail and an 1/4" UNC bolt. The dovetail will have a hole to suit same. Utilise the mounting hole on the bottom surface of your camera.http://www.modernastronomy.com/shop/accessories/dovetails/vixen-style-photo-dovetail/
2. You will have to align the camera with the mount. You could do this by having the mount / polar scope centered on Polaris. Then adjust the camera so that Polaris is centered in the view finder. Fine tune by taking a couple of 5-10sec exposures and re-centering.
3. No. to achieve this you would have needed to performed step 2. This could be improved by using the polar scope to polar align the mount. I am assuming that the mount came with a polar scope. You will need to align the polar scope reticule to the mount. There are instructions in EQ3-2 manual on how to do this or see post #7 here:- http://stargazerslounge.com/topic/227124-polarscope-reticule-alignment-hell-please-help/?hl=reticule#entry2446592

[wxsatuser]

As Ian pointed out, fix camera to a dovetail.

I bought some long camera thread stainless bolts off ebay and cut then to length.

I don't trust the usual undercut photo bolts to hold two grands worth of camera and lens

at precarious angles.

You can just see the dovetail in this pic

[malc-c]

Hi Gary,

Ian has given you some good advice there.  Polar alignment for a camera with a wide angle lens isn't that critical as the discrepancy will not be that noticeable.  Increase the focal lengths of the lenses and then errors in the alignment and precision of the mount become more noticeable.  You can get (or your mount may have one fitted) a polar scope which fits inside the RA axis of the mount.  Polar alignment is well documented so I won't repeat the procedure here, but this will give you better alignment, and trailing would be less noticeable on subjects that are near the celestial equator.  

The mount doesn't really have the precision of it's bigger brothers the HEQ5  EQ6 and EQ8 in the stepping motors and gearing, so again, with long exposures, and with targets that are not near the pole, trailing will be noticeable.  The way to overcome this to a degree is to take lots of short exposures (you will have to experiment with the times to get the max length without any trailing detected) and then stack them in software.

The only true way to get very good images with long focal length lenses on your mount would be to use guiding.  This doesn't need to be expensive.  You can purchase a secondhand 8 x 50 finder scope, and with some inexpensive adaptors connect a webcam to it.  Using a laptop with free software such as PHD / PHD2 and EQMOD you can then have the laptop take over the guiding as the software tracks a target star.  If you invest in a dedicated guide camera with an ST4 port, you can connect this direct to the synscan controller and let that take care of the guiding, thus doing away with the need for a laptop.  Having better tracking / guiding will give you better results as your exposure times will be a lot longer and stars will be more circular.

[g3az66]

Cheers guys for the advice...

Looks like I will have to get lots of trial and error shots in.

Thanks Malc for the guiding info. I have 600mm lens and it looks like that will have to be the way to go. Need to walk before I can run tho

[Darkstar_1]

Hi Gary,

Ian has given you some good advice there.  Polar alignment for a camera with a wide angle lens isn't that critical as the discrepancy will not be that noticeable.  Increase the focal lengths of the lenses and then errors in the alignment and precision of the mount become more noticeable.  You can get (or your mount may have one fitted) a polar scope which fits inside the RA axis of the mount.  Polar alignment is well documented so I won't repeat the procedure here, but this will give you better alignment, and trailing would be less noticeable on subjects that are near the celestial equator.  

The mount doesn't really have the precision of it's bigger brothers the HEQ5  EQ6 and EQ8 in the stepping motors and gearing, so again, with long exposures, and with targets that are not near the pole, trailing will be noticeable.  The way to overcome this to a degree is to take lots of short exposures (you will have to experiment with the times to get the max length without any trailing detected) and then stack them in software.

The only true way to get very good images with long focal length lenses on your mount would be to use guiding.  This doesn't need to be expensive.  You can purchase a secondhand 8 x 50 finder scope, and with some inexpensive adaptors connect a webcam to it.  Using a laptop with free software such as PHD / PHD2 and EQMOD you can then have the laptop take over the guiding as the software tracks a target star.  If you invest in a dedicated guide camera with an ST4 port, you can connect this direct to the synscan controller and let that take care of the guiding, thus doing away with the need for a laptop.  Having better tracking / guiding will give you better results as your exposure times will be a lot longer and stars will be more circular.

 Hi,

       would that be a particular webcam or would any suffice? I would have thought that a webcam would not have the resolution to follow a star for guiding. Also which adapter would fit the small  aperture of a finder scope, I ask because I am thinking of getting a star adventurer from FLO and thought guiding may be a good idea and a webcam/finder seems a good idea.

[malc-c]

 Hi,

       would that be a particular webcam or would any suffice? I would have thought that a webcam would not have the resolution to follow a star for guiding. Also which adapter would fit the small  aperture of a finder scope, I ask because I am thinking of getting a star adventurer from FLO and thought guiding may be a good idea and a webcam/finder seems a good idea.

The old Phillips SCP800 (converted) was always the preferred web camera for use with astronomy, but now they are like the proverbial hens teeth to find.  The MS life cam (HD720 and 1080P)  also works well, and I seem to recall a thread using a cheap (like under a fiver) webcam from Asda...  Most will need some modification to fit the finder.  The old Phillips web cam was that popular that companies even produced threaded adaptors that allowed the camera body to attach directly to the tube of a SW 9 x 50 finder.  

There are also stacks of finder guider thread, such as this one http://stargazerslounge.com/topic/133187-guiding-conversion-project-for-200p-and-eq5/page-17 which may help.

so long as you can get a bright star in the field of view of the finder the guide software should work just fine

[malc-c]

 I ask because I am thinking of getting a star adventurer from FLO and thought guiding may be a good idea and a webcam/finder seems a good idea.

Personally with that dedicated mount for DSLR camera, I don't think guiding will be an issue

[RichM63]

Cheers guys for the advice...

Looks like I will have to get lots of trial and error shots in.

Thanks Malc for the guiding info. I have 600mm lens and it looks like that will have to be the way to go. Need to walk before I can run tho

Hold up, you are going to use a 600mm lens and DSLR on an EQ3-2 and guide scope/camera? IMHO that will be simply too much weight for the mount. (unless it is a light mirror lens)

Static shots with you also holding the camera yes OK, but unsupported dynamic shots with a few grand's worth of lens hanging off it, no way.

I'm all for "I'll try this out because they said NO" but even I would not risk this one.

ATB,

Rich

[g3az66]

Hold up, you are going to use a 600mm lens and DSLR on an EQ3-2 and guide scope/camera? IMHO that will be simply too much weight for the mount. (unless it is a light mirror lens)

Static shots with you also holding the camera yes OK, but unsupported dynamic shots with a few grand's worth of lens hanging off it, no way.

I'm all for "I'll try this out because they said NO" but even I would not risk this one.

ATB,

Rich

Hi Rich,

My Nikon body weighs 760g and my Tamron lens comes in at 1950g. FLO quote the payload as 5kg for imaging and 7kg for visual. Are you telling me then that this is too much?

Also, should you include the weight of the counterweights in the payload?

BTW my mount is the EQ3 Pro

Thanks

Gary

[RichM63]

Counterweights are never included, as they serve to neutralize.

My misunderstanding was that you were going to use a 600mm Prime lens, costing £1000s + heavy and not a 150-600 Tamron zoom weighing 1950g as I don't know of a Prime 600mm Tamron.

Yes my EQ3-2 pro can handle the weight of this type of combo' during the day, and can cause quite a stir down by the river when shooting Egrets. Albeit with consternation when folk try to use RA/DEC to follow a bird.

But zoom lenses, any, are not best suited for AP and the longer the zoom the worse it gets. In terms of image issues.

I have the Tamron 200-500 see sig' and have yet to produce an AP image with it. It is just not designed for the job.

If you then add in guide scope+cam then EQ3-2 will not hack it.

I'd start with a cheapish fixed Prime and go from there. (50mm).

Best,

Rich

[g3az66]

I'd start with a cheapish fixed Prime and go from there. (50mm).

Best,

Rich

Cheers for the advice...

I have a 50mm prime and was gonna start with that anyway....

Just need some clear skies!

[Darkstar_1]

Personally with that dedicated mount for DSLR camera, I don't think guiding will be an issue

I asked because i noticed that the star adventurer comes with a guiding port, so presumably you could either guide or not. This begs the question, is the mount accurate enough as a stand alone platform?