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Here's what I want, now what do I need?


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Ok, so i have been all over the forum asking questions and collecting info. All this has brought me to this topic.

My aim is to take photo's of the sky using only my DSLR cameras and lenses. I have lenses from 12mm up to 400mm. With extenders I can shoot up to 1120mm.

I want a GEQ mount with a goto system to help a novice find stuff, and with decent tracking ability so that I can do long exposures without star trails. I want to be able to attach the camera directly to the mount without using an OTA. I am looking for portability and ease of use.

I already have; fantastic cameras and lenses and (so I have just discovered) a very old Tasco GEM mount with no motors. I have found a way to rig my cam to this mount without the OTA so I can use this like a normal tripod, but with better control.

As suggested by Psychobilly, it seems that the Skywatcher EQ3 will fit the bill. So it seems, I can mount the camera direcly to the mount with a dovetail plate of some description.

What else do I need and do you see any probs with this setup.

Incidentaly, I have found a way to attach a finder to the hotshoe of the camera to help in locating targets. It actually works quite well and hope this will help with polar alignment.

Your thoughts gentlemen and ladies please.

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You do not polar align the camera, you polar align the mount, so a finder on the camera will not aid this. Think about it you do not need the camera/scope on the mount to polar align it.

Unguided you can expect 30-60 second exposures before trailing, with the EQ 3 expect the lower end.

Can the 5D be set to exposures of more then 30 sec? My Canon and Sony cannot without the electronics to override the camera.

Focal length of 1120mm will require better tracking then the EQ3 will provide.

Do not mix up goto that locates an object and guiding that tracks an object, if goto tracked accurately imagers would not buy £1000 worth of guide camera and scope.

The unfortunate thing about camera lens is they are specified for say 120-400, but they are soft at the 400 end, which I find strange as that is what they are bought for, you do not by a 400mm lens to use at 120mm Wish that people like Sigma would get that in their head.

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Do not mix up goto that locates an object and guiding that tracks an object, if goto tracked accurately imagers would not buy £1000 worth of guide camera and scope.

Are goto mounts not able to track an object once located in the sky? I know it wouldn't be as good as a dedicated guiding system, but they must do simple tracking with the RA motor...

I've not got a goto mount (just eq1 + ra motor) and I assumed that GoTo's would at least do that once the object was found.

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As suggested by Psychobilly, it seems that the Skywatcher EQ3 will fit the bill. So it seems, I can mount the camera direcly to the mount with a dovetail plate of some description.

What else do I need and do you see any probs with this setup.

Ok, my forst observation is that this rig will (probably) be OK for short focal lengths, say up to 50-80mm and for reasonably short exposure times - maybe a minute or two.

However, it seems that you're wanting to image at focal lengths of 1000mm or so, with perfect (for 1000mm) star shapes, without any form of guider and to have GOTO on your mount. Personally I can't think of a solution that would do all that, that will cost less than several £-thousand.

To address Biggz question, mounts can track by themselves, more or less. They're OK for visual observing where the only criterion is that the object under scrutiny doesn't drift off the eyepiece view - which is not too hard to achieve. However for photography, you're looking for an absolute accuracy of about 1 part in a million (there are 360 degrees in a circle and 3600 arc-seconds in a degree - so the number of arcseconds in a full circle is something over a million) - all from a purely mechanical arrangement. It can be done, just about, but it's expensive. That's why most amateurs opt for a guidance system that locks onto a star.

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You do not polar align the camera, you polar align the mount, so a finder on the camera will not aid this. Think about it you do not need the camera/scope on the mount to polar align it.

If the camera is aligned with the mount then you should be able to use it to polar align. I use the finder on my scope to polar align my mount. There are markings on the mount when you lock off the scope and it's all aligned up. Of course any error in this alignment will add error to the polar alignment.

Can the 5D be set to exposures of more then 30 sec? My Canon and Sony cannot without the electronics to override the camera.

Not true. Virtually every dslr can set the exposure to as long as you want. You just need to use the 'bulb' setting. It's standard for 30 seconds to be the limit on 'the dial' though. On my Nikon I use a cheap IR remote to control the bulb to avoid vibrations. But if you use the old cardboard in front of the lens trick you can press the shutter to start and stop the exposure while blocking the light.

Also I don't think you need the most accurate tracking for taking exposures with a camera unless you goto extreme focal lengths. For example you need at least 2500mm before the moon even fills the viewfinder on a full size dslr. In practice you'll be shooting a lot wider than that. I can exposure for 5 minutes at 300mm without nticebale star trails. If you're doing subs you don't really need to exposure for much longer anyway.

If you're on a budget look at 'barn door' trackers. You can even make your own!

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You do not polar align the camera, you polar align the mount, so a finder on the camera will not aid this. Think about it you do not need the camera/scope on the mount to polar align it.

How do you polar align the mount without a scope on it?

The unfortunate thing about camera lens is they are specified for say 120-400, but they are soft at the 400 end, which I find strange as that is what they are bought for, you do not by a 400mm lens to use at 120mm Wish that people like Sigma would get that in their head.

No probs with the quality of my lenses. I use 'L' primes. You could cut yourself on my 400mm its so sharp. :grin: I generally photograph weddings, so my cameras and lenses are always top notch. If I could spend now as much on AP as I have done on photography, I could have an observatory. Unfortunately I don't have that sort of money now, so I am kind of doing AP on a shoe string using just dslr's.

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Ok, I have decided to get the Celestron CG-5 GT. Everything I have read about it indicates that it can find and track celestial objects with reasonable accuracy. At least well enough to do 5min subs if I align it accurately. I can polar align it without a scope or camera mounted. ( I never knew you could do this.)

It is reasonably portable and does not take too long to set up. I have a Maplin type battery jumpstarter pack and 12v 7ah batteries for power. I have a couple of home made dewbusters and dimmers to control them.

I have the book 'Making Every Photon Count' coz I need all the help I can get.

20x50 bino's

I have lots of patience and a ton of enthusiasm.

Anything I have forgotten? or anything else I need?

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